Fans are effective for comfort cooling, and air circulation. However, fan applications depend highly on the design goals for desired air speed and distribution and any physical environment limitations. Understanding the elevated air movement design goals is the prerequisite in selecting an adequate fan type for a particular space.

Design goals

Figure T5 outlines the key considerations for defining the fan design goals, including personal control, targeted, variability, and uniformity. “Personal control” design emphasizes the goal of the fan system to provide thermal comfort for a single occupant, while the adjustment of fans is unlikely to affect the others. “Variability” has its advantage in multi-occupant spaces where occupants have the flexibility to adjust fan operation based on their desired thermal comfort needs, or they are free to move around and choose their preferable locations or thermal conditions. In spaces where there are variable or transient occupancies, non-uniform thermal conditions, or spaces with specific thermal requirements due to architectural features or activity levels, “Targeted” air movement may provide more comfort. Lastly, “Uniformity” (i.e., more regular control) emphasizes uniform air speeds and consistent thermal comfort experience applied in multi-occupant spaces where occupants do not have the flexibility to control fan or change their location, especially when occupants will be staying in those areas for extended periods.

Fan selection

Fan selection criteria mainly depend on the design goals of air speed and distribution, the purpose of elevated air movement (i.e., direct cooling across the human body or air circulation), and any limitations of fan usage in space (i.e., floor-to-ceiling height).

Ceiling fans are generally effective for comfort cooling and air circulation in nearly all scenarios and applications. Ceiling fans are recommended due to their effectiveness in air movement, provided that some limitations of implementation have been compromised, including insufficient height clearance for ceiling fan installation, presence of obstructions at the ceiling or on the floor that block airflow, an inadequate arrangement between lighting fixtures and ceiling fans that cause strobing or visual flickering effect, and high renovation cost for ceiling fans integrated design. Installation of ceiling fans is recommended if these limitations do not apply. Alternatively, other air movement devices shall be chosen if these limitations cannot be compromised. Figure T6 presents the fan selection examples (with/without ceiling fans) based on different design intent. In addition, different types of fans can be integrated to maximize occupants’ comfort and to achieve multiple design intent. For example, ceiling fans can provide a uniformly low-speed background air movement for all occupants in a large open space, while individual fans allow additional personal control to improve occupants’ local thermal comfort further whenever it is necessary (e.g., at transient conditions or near the window). An example of such a mixed design intent approach is presented at the bottom of Figure T6.

How air speed meets thermal comfort goals

ASHRAE Standard 55 – Thermal Environmental Conditions for Human Occupancy (2020) identifies six factors that affect thermal comfort, including clothing insulation, metabolic rate, air temperature, mean radiant temperature, relative humidity, and air speed. Increasing air speed enhances heat transfer via convection and evaporation, which provides a cooling sensation named “Cooling Effect”. It allows the body to maintain thermal comfort at higher air temperatures than what would be comfortable in still air. Figure T1 shows how the air speed is associated with cooling effect. More importantly, this cooling effect is instantaneous and beneficial during the transitional moments (i.e., stepping into the building from a hot and humid outdoor environment). The ASHRAE Standard 55 (2020) and the CBE Thermal Comfort Tool help design how much air movement is needed for thermal comfort and occupant satisfaction.

Thermal comfort calculation with elevated air speed

ASHRAE Standard 55 (2020) provides a method called The Elevated Air Speed Comfort to calculate thermal comfort in situations of elevated air speed. This method uses a combination of the Analytical Comfort Zone Method combined with the Standard Effective Temperature (SET) method. The SET output translates the six thermal comfort factors (from above) into a single temperature equivalent that can be compared across a variety of comfort conditions. In addition, the cooling effect initiated by increased air speed is also used to calculate the Cooling Fan Efficiency (CFE). CFE is defined in ASHRAE Standard 216 (2020) as the ratio of the cooling effect to the input power of the fan. CFE gives people a standardized way to compare how much cooling a fan provides when consuming the same energy.

Human response to air movement

Do the occupants prefer an environment with a cooler temperature or an increased air speed and slightly higher temperature? Research has shown that people prefer an environment where they can use fans with a slightly higher than usual temperature (i.e., 26 °C [79 °F]) compared with the typical air conditioning temperature setpoint (i.e., 23 °C [73 °F]) without fans (Schiavon et al., 2016). Studies conducted in office buildings showed that the results were aligned with the findings obtained from laboratory experiments (Lipczynska et al., 2018). In addition, using a human heat balance model, a study found that fans can be used to cool occupants even if the ambient temperature exceeds normal skin temperature (i.e., 35 °C [95 °F]) (Tartarini et al., 2021).

Fans can be added to an existing AC system to save energy and increase comfort. Besides the aspect related to the system's design, it is also important to consider how the new fans are introduced in the space and how the temperature setpoints are increased.

Implementation and adaptation

Occupants take time to adapt to the fan-integrated AC system at warmer temperatures and higher air speed environments. Depending on the site conditions and culture, a grace period for occupant adaptation may take up to 3 months. Any change in temperature cooling setpoint should be small, gradual, and follow occupants’ comfort feedback. Despite studies showing occupants can be comfortable at a higher temperature condition with increased air speed, in practice, they may perceive thermal dissatisfaction with a sharp change in room temperature setpoint (e.g., from 23 °C to 27 °C [73 °F to 81 °F]) without providing a grace period for adaptation. This is particularly important in building retrofits.

For a practical implementation of a fan-integrated system, building facility managers are suggested to go slow and have patience and perseverance with the progressive transformation process. For example, if the thermal comfort analyses indicate it is possible to increase the air temperature cooling setpoint from 25 to 27 °C [from 77 to 81 °F] at higher air speed conditions with fans, in practice, the temperature setpoint shall be first increased to 26 °C [79 °F] and maintained for at least two weeks for occupant adaptation before further increasing it to 27 °C [81 °F]. In addition, occupants’ feedback on the indoor environment shall be continuously monitored during the transformation period. If a lot of thermal dissatisfaction votes have been received, a slightly lower air temperature setpoint should be used. For example, the temperature should be brought down to 25.5 °C [78 °F] to be maintained for two weeks, then raised up to 26 °C [79 °F] again, and advice and training to the occupants about the use of fans should be provided.

Several studies have suggested that occupants can have a higher tolerance to thermal discomfort when provided with control of their micro-environment. Regardless of specific building functions or design intents, allowance for personal control of the fan systems is recommended.

User education

A key indicator of a successful fan-integrated system is ensuring occupants understand the purpose and use of the fans. Figure T13 shows an example of an information plaque informing the fan usage priority – Fan cooling first approach – when occupants feel too warm.

Using fans alone or in coordination with HVAC systems to cool people offers several significant enhancements compared to conventional HVAC systems, including improved thermal comfort, indoor air quality, air distribution, energy savings, and initial cost savings.

Despite the numerous benefits of fans and fan-integrated systems, comprehensive resources are unavailable to guide engineers and architects in designing and implementing such systems. The purpose of this guideline is to address this gap and provide practitioners with valuable materials and answers to common questions.

What are the available fan options?

Various fan types are available in the market, such as ceiling fans, desk fans, and pedestal fans. This guideline provides a comprehensive overview of the criteria for fan type selection. These criteria cover blade characteristics, fan size, airflow patterns, fan performance metrics, motors and drives, power and efficiency, and control strategies. Ceiling fans are generally preferred for their higher efficiency, control and effectiveness, but cost, flickering and fixed location are limitations. This guideline can assist users in selecting suitable fan types based on individual building characteristics and specific application needs.

How to integrate fans with my existing AC system?

Adequate fan choice mainly depends on design intents, space characteristics, and HVAC operation strategies. This guidebook discusses which HVAC systems can be integrated with fans. With well-defined design intent, the guidebook provides a step-by-step process for determining the number and size of fans and their layout, ensuring proper fan installation, and integrating the fans with the control of the HVAC system.

How do we implement and operate fans-integrated systems?

Designing a successful fans-integrated system involves more than adding fans to a building. This guidebook assists building designers and operators by helping them adjust appropriate settings in chillers, air handling units, environmental conditions, and operation strategies. This optimization maximizes energy savings while ensuring occupants' comfort within the building. Additionally, the guidelines explore HVAC systems design that can enhance air distribution effectiveness and minimize construction costs. Most importantly, the guidelines outline a transformation strategy for transitioning from conventional air conditioning to a fan-integrated system with minimal disruption to occupants. This comprehensive approach ensures a smooth and efficient integration of fans into the existing air-conditioning infrastructure.

Which design tools and case studies are available?

This guidebook recommends using the CBE Thermal Comfort Tool and the CBE Ceiling Fan Design Tool. These tools enable users to define the comfort zone with elevated air speed and determine the optimal arrangement of ceiling fans based on room conditions specified by the users. In addition, the guidebook highlights relevant codes and standards related to environmental conditions, fan testing procedures, fire safety, and seismic requirements (subject to variations in different countries' regulations). Furthermore, we presented several case studies of buildings successfully implementing the fan-integrated HVAC system.

We released two versions of our guidebook online: the Practitioner Summary and the Full Guide. These resources support selecting, designing, constructing, operating, and implementing fans and fans-integrated HVAC systems. The Practitioner Summary offers a concise overview (~15 pages) of key considerations for building practitioners, providing brief descriptions of the fan-integrated system. In contrast, the Full Guidebook provides a more comprehensive exploration (~70 pages) of the fan and fan-integrated system, including real building references, catering to users from diverse backgrounds. So we expect that many readers, after studying the Practitioner Summary, will move to sections of the Full Guidebook that are relevant to their work. Fans and fans-integrated HVAC systems will result in more sustainable and healthy buildings.

This technical guide does not cover all codes and standards related to fans and air movement published worldwide, and it highlights only several commonly used materials for references and examples. It is also noted that the usage of these materials could be subjected to variations by countries. Users are advised to implement these materials with caution.

Environmental conditions

(2020) identifies factors that may affect thermal comfort in an indoor environment. Proposed in ASHRAE 55, the standard effective temperature (SET) is a reliable index in estimating the heat loss effect for increased air speed conditions.

Green Mark is a green building certification scheme established in Singapore to raise energy performance standards and emphasize other sustainability outcomes. suggests the indoor temperature setpoint could maintain at 26 °C [79 °F] or above if the space is designed with elevated air speed.

Ceiling fans testing regulations

specifies the instrumentation, facilities, test installation methods, and procedures to determine ceiling fan application data for occupant thermal comfort in a space.

Performance testing on small-diameter ceiling fans (≤ 2.1 m [7 ft]) is recommended by the .

Performance testing on large-diameter ceiling fans (> 2.1 m [7 ft]) is standardized by the .

A modified testing method for large-diameter fans, the , is developed to enhance ceiling fan testing effectiveness. CFEI is derived from the fan energy index equation in with substitute coefficient for large-diameter ceiling fans.

Fire safety

The primary concern with ceiling fans about the fire code is the interaction with fire sprinklers. The National Fire Protection Association (NFPA) Standards, , summarizes the requirements of ceiling fan installation concerning fire sprinklers in buildings. It is noted that specific fire safety requirements may vary by country. Users should always consult local codes and requirements for a specific project.

Seismic requirements

Seismic considerations and requirements are especially relevant for installations of ceiling fans, especially for large-diameter fans, long suspension rods, or other requirements for seismic support. An example can be found in the . Users should always consult local codes and requirements for a specific project.

There are multiple fan types available in the market, but ceiling fans, in general are preferable compared to other fan types due to their air circulation effectiveness and low energy consumption, especially for serving multiple occupants within the same space. In addition, the installation and operation of ceiling fans are specific to the building design which is different from other portable fan options. This guide highlights a standalone section on ceiling fans, while other fan choices (i.e., other air movement devices) will be discussed in a separate section.

Ceiling fans

The US Department of Energy (DOE) defines various ceiling fan types in the "Uniform Test Method for Measuring the Energy Consumption of Ceiling Fans." Table T1 presents the criteria of ceiling fan blade thickness and tip speed adopted from DOE, and Table T2 summarizes the definition of several common ceiling fan types with supporting remarks.

Table T1. Ceiling Fan Blade and Tip Speed Criteria (adapted from DOE definitions).

Table T2. Common ceiling fan types (adapted from DOE definitions)

In general, a larger diameter fan (i.e., high volume low speed (HVLS) fan) blade can move a larger volume of air than a smaller diameter fan blade. As fan diameter increases, the rotational speed is typically limited to prevent excessive noise from the fan blades, especially near the blade tip. Additionally, where fans can be mounted at blade heights below 3 m [10 ft], the rotational speed must be limited to meet safety criteria for the maximum speed of the blade tips. HVLS fans require higher ceilings (typically at least 3.3 m [11 ft]) and larger spaces free from obstructions to accommodate their increased diameter, and these fans are most often found in non-residential stings, like commercial and industrial applications. Some large-diameter ceiling fans include “winglets” or blade tip fences to maximize airflow and minimize noise, which is a less common problem in standard fans as the blade tip speed is already constrained for safety reasons.

Fan blades

Blade shape, number of blades, and blade pitch are important factors in increasing energy efficiency while maximizing airflow through the fan blades. Generally, there are two main types of fan blades: flat blades and airfoil-style blades. The curvature of the airfoil blades helps increase airflow through the ceiling fan, minimizing air turbulence at the trailing edge, which it is more efficient and quieter when compared to flat blades. However, airfoil blades will not operate as efficiently (i.e., lower airflow) in reverse direction. Increasing the number of fan blades and blade’s angle will increase the airflow of a ceiling fan. Nevertheless, the increased weight and drag can cause energy efficiency loss. Standard ceiling fans typically have 3 to 5 blades with blade’s angle to be 8 – 15°.

Motors and drives

Typically, ceiling fans have three main types of motor (AC induction; permanent magnet DC (PMDC); and brushless direct current (DC) motors) and two types of drives (direct drive; and gear-driven). Table T3 highlights the characteristics of these motors and drives.

Table T3. Comparison between ceiling fan’s motors and drives

Diameter and rotational speed

Assuming all other factors being equal, a larger diameter fan will produce greater airflow, average air speed and uniformity of air speed in space than a smaller diameter fan at the same rotational speed. In general, the total airflow and the air speed from any measurement point are linear with rotational speed. This relationship begins to break down at very low air speed, very low rotational speeds, or where the fan blade height is unusually far from the floor.

Rated airflow

Air speed and uniformity

Ceiling fans' air speed is defined as the average air speed that passes through the fan blades sweeping area. It is calculated by dividing the rated airflow of the fan by its diameter. Fan air speed is a useful metric because it is more directly representative of the air speed that will occur in the space. Typically, the maximum air speed in the space is within 1.3 – 1.5 times of the fan air speed and will occur below the fan blade tip. Fans with higher maximum fan rotational speed will produce higher possible air speed in the room regardless of fan diameter. If the room design target is based on maximum air speed instead of rated airflow, the designer can directly compare fans with different sizes.

The variation of the air speeds in a space is an important design consideration. Figure T2 demonstrates an example of air speeds distribution from a 1.5 m [5 ft] diameter ceiling fan. The airflow ‘jet’ from the fan immediately narrows to a slightly smaller diameter than the fan blades. The jet then impinges on the floor, creating a stagnation point, and then spreads radially outwards along the floor. Away from the fan diameter and above the floor spreading zone, there is a still air zone where air speeds are almost unaffected. The depth of air spreading zone along the floor and its average air speed is dependent to the fan diameter: smaller fan (shallower) and larger fan (deeper). In general, larger diameter fans have lower air speeds directly under the fan center (i.e., near the stagnation point), but the air speeds distribution is more uniform than the smaller diameter fans.

Fan operates in reverse direction

Most of the ceiling fans in the market can operate in reverse direction (i.e., blowing air upwards). One application is destratifying spaces in the heating season, where downwards flow may cause a draft (overcooling) on the occupants even when the fan is operating at a minimum rotational speed. The air circulation pattern generated by reversely operated ceiling fans is similar to the normal operation condition, but the air speed is much lower and much more uniformly distributed in space. The upward blowing airflow is depended on the fan type and blade geometry. For the same diameter fans, fan with flat blades would generate higher upward airflow than airfoil-style blades. The average air speed for upwards blowing is approximately 60 – 70 % of the downwards case for flat blades fans. Furniture and ceiling obstructions are likely contributing to the drop of airflow.

Fans speed control

Most standard fans typically have several fixed fan speed levels. Standard AC motor fans typically have three levels, whereas DC motor fans tend to have more. Large-diameter fans usually have a variable speed regardless of motor type. Having a high minimum speed can be problematic in some applications. It may generate too much of a cooling effect for the occupants when temperatures are mild or cool. A reasonable approximation is that the minimum fan air speed should be below 0.4 m/s [80 fpm] or a 1.7 °C [3 °F] cooling effect at the minimum allowed blade height, depending on the specifics of the application.

Power and efficacy

Generally, the ability of a fan to operate efficiently at a lower speed improves as the diameter increases, but there is considerable variation in performance between models of fans with the same diameter. Fans with a lower turndown ratio (i.e., minimum fan speed divided by maximum fan speed) can be more flexible for different applications.

Other air movement devices

Places with lower floor-to-ceiling height or a ceiling with compacted fixtures could be limited for ceiling fan installation. Moreover, installing a ceiling fan may be challenging due to the presence of other equipment,fans like lights. These limitations can be mitigated by using other air movement devices. There are numerous kinds of fan available in the market, and this technical guide only illustrates six common types of air movement devices: desk fan, pedestal fan, tower fan, wall-mounted fan, bladeless ceiling fan, and air circulator. The selection criteria for these fan types are discussed as follows.

Typical functions and airflow patterns

The above-mentioned air movement devices basically have two major functions: (1) move air directly towards the human body and (2) room air circulation. Moving air towards the human body aims to cool the subject using convective heat loss, while air circulation aims to keep air in motion within the enclosed space to enhance air and temperature mixing. Nevertheless, most fan types can deliver both functions by adjusting the fan speed and operation distance between fans and occupants. Therefore, fan selection should be based on the intent, whether it is an individual adjustment for personal cooling (group 1) or producing a general air movement effect for multiple occupants’ usage simultaneously. Table T4 summarizes the typical function, application location, and approximate price range of different fan types for reference.

Table T4. Summary of other air movement device’s function, noise level and approximate price range.

Airflow patterns from different devices can be varied by fan size, blade types, and fan structure. There is no requirement or standard on typical air speed for the air movement devices described in Table T4. The air speed and airflow requirements are mainly dependent on the typical functions and locations of users.

For fans that intend for direct cooling towards the human body, customers tend to select a stronger fan that can produce more airflow and faster air speed. However, in some situations (e.g., operating the fan together with air-conditioning), the occupants do not require air movement that is too strong. Therefore, choosing a fan with a possible lower airflow turndown (minimum speed divided by maximum speed) capability could be the key to better comfort in terms of direct convective cooling. Meanwhile, if the function of a fan is used to circulate the air in a room, the fan selection approach should be either bigger in size (i.e., produce more airflow) or able to generate a high airflow jet with high speed to drive the in-room air. Figure T4 illustrates examples of airflow flow patterns for different fan types.

Noise levels

Noise from a fan can initiate dissatisfaction and unwillingness to its usage from occupants. The noise sources of a fan are mainly from the operating motor and the fast movements of the blades (i.e., turbulence ingestion). The sound level of domestic fans ranges from 30 to 70 dBA. Fans operating at higher speeds usually correspond to higher noise levels due to turbulence. Nevertheless, the noise cannot be characterized only by sound level. Its frequency is also an important aspect. Low-frequency noise has been identified to be annoying. It is not practical to conclude one fan type will always be quieter than another. Designers/users are encouraged to experience fan usage before purchasing.

Power and cooling fan efficiency

All the elevated air movement devices described in Table T4 consist of a motor and drive. The types of motor and drive used for these elevated air movement devices are similar to those that operate in a ceiling fan, which we have discussed in the former section. It is worth noting that a larger energy-saving potential can be achieved by using a DC motor instead of an AC motor, especially for small fans like desk fans or pedestal fans.

It is noted that the cooling effect depends on the effectiveness of convective cooling towards the subject’s body and is affected by air speed, airflow pattern, and fan operation distance. Eventually, the intent of fan usage (local cooling vs. air circulation) should have been considered when quantifying the fan's effectiveness.

Flexibility and other features

One major advantage of the above-listed elevated air movement devices over ceiling fans is the high flexibility of usage in terms of location, operation height and oscillating angle. Such flexibility enhances adjustment to occupant’s needs and comfort demands regarding elevated air speed under different circumstances.

In addition, some fans are also equipped with modern technologies that enable them with special features while being equally efficient. For example, fans equipped with filters for air purification, fans installed with UV-C light for air disinfection, and fans that emit water mist for air humidification and evaporative cooling.

This technical guide focuses on the integration of ceiling fans with air-conditioning systems in buildings, due to higher attention on design, installation, and operation. Besides, incorporating ceiling fans in the early system design stage can achieve additional savings in reduced construction costs and downsized HVAC system components.

Ceiling fan system design

Considerations of ceiling fan design in space are mainly two folds: fan size and installation.

Fan size and number determination

Determining the appropriate ceiling fan size (and number) within space is critical to air speed distribution and effective cooling. Table T5 lists the key features for fan size (and number) determination.

Table T5. Key features in determining fan size (and number) in space.

Figure T7 demonstrates an example of recommended ceiling fan size for single-fan applications. Provided that the room area aspect ratio (length : width) is within 1.5 : 1, one fan operation is applicable. The room area is 24 m² [258 ft²], and the characteristic width is 4.9 m [16 ft] (i.e., square root of the room area). The recommended ceiling fan diameters are between 0.2 – 0.4 times of the room characteristics width, equivalent to 1 m [3.3 ft] – 2 m [6.6 ft], assuming all other features in Table T5 have been fulfilled.

Figure T8 presents two examples of recommended ceiling fan sizes and layouts for multi-fan applications with the same site area (240 m² [2580 ft²]) but different room heights and room functions. Figure T8a shows a warehouse divided into two identical fan cells, and one larger-diameter ceiling fan (4.4 m [14 ft]) is centered in each fan cell. The design and installation are valid with sufficient room height (8 m [26 ft]). Figure T8b shows an office with the same area of the warehouse but a much lower room height (2.6 m [9 ft]). It also demonstrates two layout settings: fewer fan cells with larger fans (on the left) and more fan cells with smaller fans (on the right). Settings on the left have four 30 m² [322 ft²] fan cells and a 2.2 m [7 ft] diameter fan centered in each cell (calculated by 0.4 times of room characteristics width). A 2.2 m [7 ft] diameter fan is considered a larger-diameter ceiling fan, which requires at least 3 m [10 ft] mounting height above floor level (see Table T5), and it is not suitable to be installed in office space with relatively shorter room height. In addition, considering this is an office space, too large fan size would block the lighting fixture on the ceiling, initiating unwanted visual flicker. Using a smaller fan size may fulfill the installation requirement but result in a smaller airflow rate and reduced uniformity. The layout settings on the right, with more but smaller fan cells (13 m² [140 ft²]) and a 1.45 m [4.7 ft] diameter fan centered in each cell, can provide more uniform air speed within space, and it is a more suitable design for office settings.

Fan installation

In general, all ceiling fan installation procedures shall follow the manufacturer’s recommendations. The ceiling fan should be fixed on a structural surface (slab or beam) to guarantee sturdiness and stability. With the appropriate type of mounting bracket, ceiling fans can also be installed in sloped ceilings. There is no reinforcement requirement if the diameter of the fan is smaller than 2.1 m [7 ft].

The fans mounting heights from ceiling / floor and clearance from walls / obstructions are important regarding both safety and performance consideration (See Table T5 in details for both standard and large diameter ceiling fans). In rule of thumb, ceiling fans require a minimum distance from the ceiling of 0.2 times of the fan diameter to avoid “starving”.

Installation of ceiling fans should avoid conflicts with the lighting fixtures to minimize changes of visual flicker and strobing effect, as well visual discomfort. Figure T9 illustrates the potential problems when ceiling fans interact with lighting fixtures. It suggests that visual flicker effect is dependent to view angle of the occupants. Thus, the position of ceiling fans should not only be installed away from the recess lights, but also considering occupants’ position in space. Alternatively, designer may consider the possibility of using dropdown lightings (see Figure T9c) with minimum glare to the occupants. If the above limitations with respect to lightings cannot be resolved, designers may consider using other non-ceiling fan alternatives.

Air-conditioning system design

The conventional air-conditioning system requires diffusers and extended air ducts to distribute air evenly within the space. However, ceiling fans integrated with conventional air-conditioning systems can effectively mix and re-distribute the room air without the need for extra diffusers and extended supply air ducts. In principle, ceiling fans integrate well with most ventilation settings that require air mixing, including radiant cooling systems. However, they are unfavorable for systems that rely on stratification, such as displacement ventilation and underfloor air distribution system or systems utilizing active or passive chilled beams.

Figure T11 compares the design layouts between a conventional air-conditioning system and a recommended ceiling fan integrated air-conditioning system. The ceiling fan integrated air-conditioning system requires only the main supply air duct to throw cool air from a high-sidewall vent into the occupied space. Then the ceiling fan will mix and distribute the cool air in the space. The cool supply air would be best fed above the fan blades to enhance air mixing and avoid cold drafts. Immediate benefits of such design are reduced capital and maintenance costs for unnecessary ducting, diffusers, and variable air volume (VAV) boxes. In addition, the ceiling fans could work more efficiently with larger blades to ceiling height (assuming no false ceiling and without an extra supply air duct).

Ceiling fans integrated AC system

One major advantage of the integrated air movement design is the additional convective effects on occupants. This means additional energy saving from space cooling is possible due to the optimization of the air-conditioning system.

Design room conditions

The presence of space air movement allows higher dry bulb room temperature (2-3 °C [4-5 °F]) and dewpoint temperature (1-2 °C [2-4 °F]) when compared with conventional air-conditioning system design. Alternatively, if the originally designated air temperature is 23-25 °C [73-77 °F], it can be increased to 23-27 °C [73-81 °F] with elevated air movement to achieve similar or even better thermal comfort. The room operating air speed can be up to 0.8 m/s [160 fpm] without personal control, while there is no air speed limit if occupants have full control of the fans (i.e., just ceiling fan or ceiling fan + desk fan) within the space.

Components selection

Regarding the relaxation of designated cooling demand (i.e., lower sensible and latent load), the chiller and the air handling unit (AHU) from the original HVAC system can be downsized in the system design stage. The design supply air temperature setpoint (SAT) and chilled water temperature (ChWT) setpoint relaxation should be 50% to 100% of the zone cooling setpoint temperature adjustment. For example, if compared to a conventional HVAC design, the HVAC design with elevated air speed could have a 2 °C higher cooling setpoint temperature, and the SAT and ChWT setpoints should be increased by 1-2 °C. In addition, a smaller size fan in the AHU can be used for the ceiling fan integrated design because it returns smaller static pressure along the critical supply air path (only require the main supply air duct).

HVAC and fans system control

Figure T12 demonstrates the control schematic for the heating, ventilation, and air conditioning (HVAC) system with and without the integration of ceiling fans. It shows that when ceiling fans are integrated with the building automation system (BAS), it can react at the first stage cooling setpoint (say 23 °C [73 °F]) to cool down the zone before the HVAC system beings to operate for cooling. The ceiling fan speed shall increase with the room temperature, which is determined by the cooling effect or a representative point in space. The HVAC cooling starts when the indoor temperature increases to the second stage of the cooling setpoint (say 26 °C [79 °F]). Operating the HVAC system at this higher cooling setpoint has significant energy savings potential.

Some ceiling fans have onboard sensing and controls that allow fan speed and temperature automation without integration with the building automation systems (BAS). A lower-cost, simpler alternative to automatically control the ceiling fan based on temperature is to use a relay to turn fan(s) on and off. The fans then operate at a fixed pre-set speed. Fans' operation can also be tied to occupancy sensors in the zone, preventing unnecessary operation, energy use, and maintenance. In some cases, it may be beneficial to operate fans even when unoccupied, such as pre-cooling applications that benefit from increased convection from surfaces in the space due to the air movement generated by the fans.

Potential savings

Comparing the two designs in Figure T11, the ceiling fan integrated air-conditioning system could save up to 45% in capital construction cost compared to the conventional system. These savings are mainly obtained from reduced ductwork, diffusers, VAV boxes, sensors, and controls. Savings can also be obtained from the extra time and workmanship for additional ducting and fittings installation. More importantly, the majority of these ducting and fittings are not reusable and become construction waste when the building is demolished. The cost of purchasing and installing ceiling fans in the space is low compared to the above cost savings.

In addition, substantial energy for space cooling can be accrued when implementing the elevated air movement with a higher temperature cooling strategy. Approximately 17 % of cooling energy saving can be achieved by increasing the cooling temperature setpoint from 22 °C [72 °F] to 25 °C [77 °F]. In such room temperature setpoint adjustment, higher chilled water supply temperature (10 °C [50 °F]) can be used instead of the conventional temperature setpoint (7 °C [44.6 °F]), which it would account for approximately 12% of additional energy saving from the chiller. In a Singaporean zero-energy building, a 32% HVAC energy saving was obtained when the setpoint was increased from 24 [75 °F] to 26.5°C [80 °F]. These cooling energy savings are at least two orders of magnitude higher than the energy used for ceiling fans operation in space.

This guide enables engineers, architects, and facility managers to maximize the many benefits of fans and integrating fans (also known as elevated air movement devices) into HVAC systems. It introduces the advantages of using fans, describes how they work, explains how to select them, and provides guidance and resources for designing spaces with fans in buildings.

The key benefits of fans are as follows:

• Thermal comfort: Increased air movement across the skin remove heat from the body by convection and evaporation. Given the ability of some fans to provide more personalized thermal conditions, they can increase comfort.

• Improved air distribution: Operation of fans supports the HVAC system to increase air mixing, providing more uniform temperature and air quality distribution throughout a space in both heating and cooling conditions.

• Improved indoor air quality: Increased air speed may reduce an occupant’s exposure to indoor pollutants via dilution of the concentration of local sources, enhancement of the deposition rate of airborne particles onto indoor surfaces and increased ultraviolet germicidal irradiation system (UVGI) effectiveness for disinfection.

• Energy savings: Fans incur significant energy savings by reducing cooling demand of the HVAC system when the indoor temperature setpoints are increased. The HVAC savings potential is about two-orders of magnitude above the fan energy use.

• Cost savings: Beside the cost savings related to energy savings, using ceiling fans to distribute air more effectively throughout a space can reduce ductwork and diffusers required to serve a zone. Additionally, the higher temperature cooling setting allows HVAC system size reduction for chiller and air handling units, thus reducing the capital cost.

CBE Thermal Comfort Tool

The CBE Thermal Comfort Tool is an online tool developed by the Center for the Built Environment at the University of California, Berkeley, which helps users define comfort zones at elevated air speeds according to ASHRAE Standard-55 and EN-16798 methodologies. More details on how the tool functions can be found in the online User Guide.

CBE Ceiling Fan Design Tool

The Ceiling Fan Design Tool is an online tool developed by the Center for the Built Environment at the University of California, Berkeley, which helps users determine optimal ceiling fan arrangements from the user-defined parameters, such as room dimensions and design air speed ranges. The tool can inform users about the estimated air speed, cooling effect, and air speed uniformity when compared between different fan layouts. More details on how the tool functions can be found in the online User Guide.

Fans are more than just a basic amenity for residential applications. Increasingly, fans are found in applications varying from industrial to commercial buildings, from semi-outdoor spaces and high-end hospitality settings, and everything in between. The extensive use of fans in residential applications (over 80% of single-family homes in the United States have at least one ceiling fan), as demonstrated in Figure 1 below, indicates their effectiveness in supporting thermal comfort and occupant demand for controllable air movement.

This widespread applicability stems from the many benefits that fans can provide in interior environments. The key benefits of fans include thermal comfort, improved air distribution, improved air quality, energy savings, and first and operating cost reductions.

Thermal comfort

Simply stated, thermal comfort is an occupant’s satisfaction (“comfort”) with the thermal environment. Humans have been using air movement for centuries to help regulate thermal comfort. In warm conditions, there is generally less heat loss from the skin than in cooler conditions, so people are at risk of warming up as our body needs to lose the heat produced in the body core continually. Increased air movement across the skin carries away more heat from the body via two physical processes, convection and evaporation, thereby restoring comfort. Since the advent of mechanical air-conditioning systems, building designers have largely focused on air temperature and humidity. However, modifying other thermal comfort factors, such as air speed, changes how the air temperature is perceived. Occupants near a fan feel cooler than they would feel at the same temperature and humidity in still air, like the phenomenon of “wind chill”. Therefore, when the air temperature is warmer, occupants near a fan will be more comfortable than they would be in still air conditions. In addition, large-scale studies of occupant survey data indicate that occupants would prefer more air movement than they have, especially if they report feeling warm, as illustrated in Figure 2. These studies also show that increasing air speed can increase satisfaction under all comfort conditions. As Figure 2 shows, in these cases, 40% of occupants also prefer more air movement.

Improved air distribution

In addition to the thermal comfort benefits, increasing air speed by using fans in concert with the HVAC system can also improve air distribution and provide the desired thermal conditions more consistently throughout a space. When correctly designed and operated, fans support the HVAC system to minimize temperature gradients within a space, providing more consistent temperature and air quality conditions throughout a space. This improved air distribution can be effective for both heating and cooling scenarios. For example, ASHRAE Standard 62.1 – Ventilation for Acceptable Indoor Air Quality lists a ventilation effectiveness of 0.8 for ceiling-supplied warm air systems (due to stratification of the warm air near the ceiling), but adding ceiling fans in this scenario brings the ventilation effectiveness back to 1.0, or fully mixed condition, reducing the amount of outside air required. As described in “HVAC systems that are not favourable for ceiling fans”, fans do not work with HVAC systems based on stratification as displacement ventilation and underfloor air distribution.

Improved indoor air quality

Fans can also improve air quality by increasing air movement and improving air distribution in space. It changes the airflow pattern in the space, reducing an occupant’s exposure to indoor pollutants in several ways. In spaces with stagnant air or short-circuiting, sources of air pollutants accumulate in the room locally. Air movement redistributes the air, diluting the concentration of these local sources of pollutants in the room air. A study has demonstrated measurable air quality improvement from ceiling fans and desk fans by dissipating carbon dioxide (CO2) and other exhaled pollutants that would otherwise gather near occupants in still air conditions (Benabed et al., 2020). Another study shows that using the ceiling fan reduced the concentration at the exposed person’s breathing zone by more than 20%. The effectiveness of the upper-room ultraviolet germicidal irradiation system (UVGI) typically relies on natural air convection within the space to disinfect microorganisms brought from the breathing zone up to the irradiated zones near the ceiling. Using ceiling fans greatly improved UVGI effectiveness by mixing the microorganisms-laden air up to the irradiation zone, thus disinfecting them at a higher rate than cases without ceiling fans. Elevated air movement increases the deposition rate of airborne particles onto indoor surfaces such as fan blades and room furniture, floor, ceiling and walls, thus reducing the likelihood of occupants inhaling them. Increased air movement also prevents the sensation of stale or stuffy air and helps dissipate odors.

Energy savings

Perhaps most importantly, when implemented effectively as an integral component of a building’s thermal comfort strategy, fans can also result in significant energy savings by reducing the demand for the HVAC system. Although they consume energy, the potential HVAC savings outweigh fan energy use, typically by a factor ranging between 10 and 100 times. The primary energy saving derives from thermal comfort benefits, keeping occupants comfortable at higher temperatures and allowing for increased cooling setpoints. In cooling, a room with fans is thermally comfortable over a wider range of temperatures than a room without fans. This wider range of temperatures reduces the cooling and AHU fan energy. Lastly, when ceiling fans provide air distribution, reducing the extent of distribution ductwork and diffusers, they also help reduce HVAC fan energy by reducing the pressure drop in the air system.

Cost savings

Using ceiling fans to distribute air more effectively throughout a space can reduce the extent of distribution ductwork and diffusers required to serve a zone. Additionally, if the same zone is designed to a slightly higher cooling setpoint due to the comfort cooling effect provided by the fans, this can reduce the required latent and sensible cooling capacity of the HVAC system, providing first cost savings to the chiller, air handling unit, and ductwork. The cost of fans is low compared to the savings generated by reducing ducts and HVAC capacity. Moreover, as fans can help reduce energy consumption, they will reduce energy costs.

Ceiling fan requires the most attention regarding its design, installation, and operation when compared with the portable counterparts (e.g., desk fan, pedestal fan). On the other hand, it presents the biggest opportunities for integration with the HVAC system design and operation for cost and energy savings. Additionally, incorporating ceiling fans into the design for new construction projects can generate substantial net first cost savings. Therefore, this section discusses the installation requirements of ceiling fans in buildings and the design and operation approaches when integrating with the HVAC system.

Ceiling fan system

Selecting fan sizes and determining the layout

Determining appropriate fan size and layout is critical to effective cooling from ceiling fans. The highest air speeds - and therefore the greatest cooling effects - from a ceiling fan are felt directly beneath the fan blade tips and dissipate the farther an occupant is from the fan. For larger diameter fans, there is a substantial stagnation region directly under the fan center. Air movement and the associated cooling effect are also impacted by obstructions such as furniture, partitions, or equipment. Any permanent obstructions should be considered in determining fan layouts, but spaces that may change in layout over time should take this into account for any application.

Considerations should also include the overall design intent for the ceiling fan application, including the desired air speed uniformity, and overall coverage of the space. Spaces that are likely to benefit from more uniformity will require larger fans or more fans than the spaces that are likely to benefit from variability (see the Applications example from Table 4). Fan size and layout must also consider relevant code requirements (see Codes and Standards), and potential conflicts and spacing requirements from other building systems such as fire sprinklers and lighting equipment.

To maximize uniformity of air speeds in a space with standard ceiling fans, choose the largest possible fan that fits in the space while maintaining appropriate mounting height and clearances from walls and other obstructions (see Fan mounting height and clearances). For small and roughly square rooms such as residential spaces or private offices, where only one fan is required, a simple rule of thumb is that the fan diameter should be between 0.2 and 0.4 times the characteristic room width, as Figure 34 shows. For spaces with a single fan, as closely as possible given practical considerations, the fan should be centered in the room to maximize air speed uniformity. Generally, a single fan centered in a space can effectively serve a rectangular space with an aspect ratio (length : width) of up to 1.5 : 1. Rectangular spaces with higher aspect ratios, or other unconventional shapes, benefit from multiple fans to ensure relatively uniform air speeds throughout the space. For rectangular shape (and other unconventional shapes) room, the characteristic width of the room is the square root of the floor area. For example, in Figure 34, a 6 x 4 m [20 x 13 ft] rectangular room, the characteristic width is 4.9 m [16 ft] and using the simple rule of thumb above yields fan diameters between 1 to 2 m [3.3 to 6.6 ft].

For spaces requiring multiple fans the overall layout should be determined by subdividing the space into multiple equal roughly square “fan cells”, and then centering a ceiling fan in each cell. Fan cell size is determined largely by the overall dimensions of the space, and the preferred size of ceiling fans to be used. In many cases there may be a variety of options for fan cell and fan diameter. Fewer large fan cells will require larger diameter fans, while a larger number of smaller fan cells will require smaller diameter fans. When all fans operate at the same speed, the individual fan cells within larger spaces will behave much like smaller spaces with a single fan, and as such should target an aspect ratio of no more than 1.5:1. For Ratios above this value it is possible and beneficial to create split this cell into two fan smaller cells with smaller aspect ratios. As with smaller single-fan spaces, fan diameters should be at least in the range of 0.2 to 0.4 times the characteristic width of the fan cell. Higher values will increase the uniformity of air speeds throughout space. Fan-to-fan spacing should be determined based on centering the fan as much as possible within each fan cell and should take into consideration needs for air speed uniformity in the space. Spaces with high uniformity requirements may necessitate larger fans and closer fans spacing. Large spaces with high ceilings (at least 3.3 m [11 ft]) should also be considered using large-diameter ceiling fans to maximize airflow and uniformity of air speeds (both horizontally, and vertically). Figure 35 presents two examples of recommended ceiling fan size and layout for multi-fan applications with the same site area (240 m² [2580 ft²]) but different room heights and room functions: (a) warehouse and (b) office. In particular, Figure 35b demonstrates two layout settings: less fan cells with larger fans (on the left) and more fan cells with smaller fans (on the right). Despite the settings on the left, four fans with a diameter of 2.2 m [7.2 ft], fulfil the rule of thrum mentioned above, large-diameter fans (i.e., >2.1 m [7 ft]) requires at least 3 m [10 ft] safety mounting height above floor level. Therefore, these fans selection and arrangement are not suitable for office setup with 2.6 m [9 ft] room height. The settings with smaller size but a greater number of fans on the right are more suitable in this situation.

The CBE Ceiling Fan Design Tool automatically suggests fans dimensions and numbers based on the room dimensions, applying the describe considerations to determine an ideal layouts. Refer to section “CBE Ceiling Fan Design Tool” for more details.

Fans installation

Users are advised to install ceiling fans following the manufacturer’s recommendations. Nevertheless, they can be installed in all types of ceiling, and there is no reinforcement requirement if the diameter of fan is smaller than 2.1 m [7 ft]. To adjust the fan height, some products allow extending the length of the downrod. The ceiling fans should be fixed in a structural surface of the building to guarantee sturdiness and stability, which can be a slab or beam. For suspended ceiling, the downrod should be longer to ensure sufficient blade-to-suspended-ceiling-height. A canopy shall be positioned below the suspended ceiling to improve aesthetics (see Figure 36a). With the appropriate type of mounting bracket, ceiling fans can also be installed in sloped ceiling (see Figure 36b).

Fan mounting height and clearances

Another key consideration for ceiling fan effectiveness is mounting height and clearances. Mounting heights and clearances from walls and other obstructions are determined based on both safety and performance considerations.

Standard ceiling fans must be mounted at least 2.1 m [7 ft] above the floor to prevent any accidental contact with blades (see Figure 37). In addition, industry standards recommend fan blades be at least 20 cm [8 in] below the ceiling, though clearances of 31 cm [12 in] or more are more optimal at providing air circulation into the swept area of the blades and avoiding ‘starving’ the fan. The distance between blades and the ceiling at which ‘starvation’ occurs increases with fan diameter. An approximation for this has the distance between the blade and the ceiling should be at least 0.2 times the fan diameter. For spaces with relatively low ceilings, “hugger” ceiling fans are available without downrods to maintain adequate clearance, though these fans typically have poorer energy performance than standard fans mounted at an appropriate distance from the ceiling. In spaces with higher ceilings, standard ceiling fans should be suspended on downrods at 3 – 8 m [10 – 26 ft] above the floor to adequately cool occupants. In addition, standard ceiling fans must be located so that the sweep of the blades is at least 45 cm [18 in] from any vertical obstructions such as walls or columns, though clearances of 0.6 – 0.9 m [2 – 3 ft] are often recommended to enable proper air circulation.

Safety regulations require almost all large-diameter fans (above 2.1m [7 ft] in diameter) to be mounted such that the blades are at least 3m [10 ft] above the floor (see Figure 38). A small number of large-diameter ceiling fan models can be mounted below 3m [10 ft], but these fan models have limited rotational speeds to comply with safety regulations, and as such provide limited maximum airflows. As mentioned above, large-diameter ceiling fans typically require a minimum distance from the ceiling of 0.2 times the fan diameter, though manufacturer recommendations may vary. Similarly, large diameter fans typically require at least 1 m [3 ft] of clearance from any obstructions to the sides or below the fan blades for safety and the ensure proper airflow around the fan blades.

In addition to distances from ceilings, floors, and walls, fan placement must also consider any other obstructions in a space, including lighting, mechanical equipment and ducts, fire sprinkler systems, warehouse storage racks, as well as any relevant code requirements (see Codes and Standards section below). For example, when planning an installation of large-diameter ceiling fans in a warehouse, fans should be mounted at least 1 m [3 ft] above the highest level of any storage racks, stored items, and the tallest extent of any other equipment that may be used in the space such as forklifts. Fan placement and mounting height should also take into consideration any potential furniture placements, even though they may not be permanent. Cabinets or tall bookcases may interfere with fan operation, or cause safety hazards if located too close to ceiling fans.

Multiple ceiling fans operation

We learn in previous sections that the zone air speed and flow pattern from a ceiling fan can be determined by its fan size and rotational speed. However, in many circumstances, ceiling fan does not work individually but include multiple fans serving the same zone (e.g., open plan office). How does the zone air speed and flow pattern change with multiple fans interaction?

Detailed measurement of air speed induced by ceiling fans has been conducted in climatic chamber (Liu et al., 2018). It showed the speed difference and the distance between two ceiling fans will affect the airflow profiles within space. Figure 39 demonstrates the air circulation patterns interacting between two ceiling fans at both side view and top view for the conditions of (i) comparable air speed vs dominant air speed and (ii) fans set closer to each other vs further apart. The fans distances represented in Figure 39 are not recommended for design but aim at showing airflow pattern interaction with multiple fans.

If both fans are installed close to each other (i.e., 1.3 x D, center-to-center distance) and operated at medium or high speed, both air jets will skew towards each other, creating a high turbulence zone in the mid-layer between the fans. For the same close fan distance, if one fan is operating at a much higher speed than the others, the air circulation will be dominated by the stronger fan, while the weaker fan’s jet will be skewed towards the stronger one. A low air speed zone will be observed directly under the weaker fan, since the stronger fan has dominated the airflow (i.e., dragging air from the weaker fan and guiding the airflow along the floor level). For the same fan speed testing conditions but with two fans installed further apart (> 1.7 x D, center-to-center distance), the influence of airflow pattern by the other fan will be smaller, meaning that the air jet mainly follows the principle as a single fan condition. In other words, the airflow effectiveness by each fan has been maximized when compared with close fan installation case. From these experiments, the ceiling fans separation distance and their operation speed would impact a lot on the airflow pattern in space. These parameters must be verified early in the building design stage to maximize the system efficiency. Visualization tools that demonstrate the measured air speed and flow patten for a single ceiling fan and double ceiling fans operation at different distance and fan speed are available below:

single-fan case: https://cbe-berkeley.shinyapps.io/single-fan

double-fan case: https://cbe-berkeley.shinyapps.io/two-fans

Impact of infiltration rate

The outdoor flow rate, sometime measured in air changes per hour (ACH), is one important parameter that determine the indoor environment quality and building energy consumption through mass and energy exchanges between indoors and outdoors (Nazaroff, 2021). Figure 40 illustrates the outdoor air exchange dynamics instigated by a ceiling fan through two distinct opening configurations, namely, the normal window opening and the door-like opening.

In the normal window opening condition, the induced airflow caused by the ceiling fan traverses upwards along the sidewall. A fraction of the upward flows will be dragged out of the window while the remaining that is retained indoors will form a closed-loop circulation back to the ceiling fan. In such a case, little impact of the room ACH will be independently initiated by the ceiling fan. However, the ACH will be dependent on the outdoor wind direction with respect to the window facing. When the window is facing the leeward side of the building, the ACH will be relatively low and thus operating ceiling fan would increase the air-exchange rate. Conversely, if the window is on windward side, the use of ceiling fan could reduce the ventilation rate when compared with no fan condition.

The adoption of a door-like opening configuration is indicative of an enhanced ventilation rate during the operation of a ceiling fan. The momentum of the stimulated airflow generated by the fan results in an outward displacement of air in close proximity to the floor. Meanwhile, negative pressure gradients developed at the apex of the door promote the inward influx of outdoor air, effectively enhancing air circulation. The degree of improvement in air exchange, expressed as the air changes per hour (ACH), is largely dependent to the performance capacity of the ceiling fan, specifically, its air flow rate and rotational speed.

Ceiling fan interaction with lighting

While many ceiling fans are available with built-in lighting (i.e., light kits), typical ceiling fan lights may be insufficient for many lighting requirements and applications. Most applications will be best served by an independent lighting system with additional ceiling fan(s) installed alongside recess lighting that occupies the same ceiling space.

When the ceiling fan blade interacts with light distributed from a recess fixture (see Figure 41a), light flashing on surfaces (i.e., strobing) and at the light source itself (i.e., flicker) can occur. Some design recommendations have been proposed to overcome these problems, but these do not always resolve problems that are caused by the application of ceiling fans. To remove flicker, it is often suggested to move the ceiling fan away from recess lights (see Figure 41b). While this recommendation will likely prevent strobing, it does not stop flicker (Kent et al., 2020).

The visual line of sight from the occupant to a recess fixture can still be blocked by a ceiling fan since the ceiling fan blades are mounted below the electric light (see Figure 41b). Therefore, this design arrangement between the ceiling fan and recess lighting still creates flicker seen from multiple viewing positions inside the space. Another design option is to use dropdown lighting (i.e., light fixtures are suspended at the level of fan blades or below them, see Figure 41c), which bypasses issues of flicker completely, and prevents strobing on the floor surface. However, drawbacks to this configuration may occur in low floor-to-ceiling applications when reflections from adjacent surfaces are projected back onto the ceiling or onto wall surfaces, creating strobing. Meanwhile, glare from electric lights may also be produced when they are mounted closer to the occupants’ head.

Strobing and flicker can also occur when ceiling fans interact with daylight transmitted through skylights (see Figure 42). These problems will naturally arise when direct sunlight is admitted into the space, increasing both the temperature and the need to use ceiling fans. Unlike recessed lighting, maneuvering the ceiling fan may not remove strobing when the roof is fully glazed by the skylight. The size and number of blades are often larger to increase the effects of space cooling in these applications. This generally increases the area and frequency in which strobing, and flicker may occur inside the space.

There are many adverse effects that are caused by visual flicker. Increased visual discomfort was an overt consequence from a design layout that followed current recommendations in a recent study. Short-term exposure (i.e., about 10-minutes) to flicker from the configuration, shown in Figure 43, made it hard for people to concentrate, which lowered their mental performance (Kent et al., 2020). This could hinder learning in schools or reduce productivity in offices. Under a longer exposure time, like daily working conditions, and for populations highly sensitive to flicker (e.g., photosensitive people), the effects of flicker caused from ceiling fans may be exacerbated.

Not all buildings that use ceiling fans and recess lighting together will produce flicker. This mainly concerns smaller spaces, where the risk of the two technologies interacting with each other is higher. Designers should distribute ceiling fans and electric lights to achieve the desired air-movement and illuminance level while avoiding issues that lead to visual or thermal discomfort. When there are risks of strobing and flicker caused by ceiling fans, some alternatives solutions can be suggested.

Transparent ceiling fan blades: This allows light to be transmitted through the blade material, avoiding flickering even when the ceiling fan position would obstruct the electrical light. Nevertheless, it poses additional safety concerns when compared to opaque blade fans, especially for low floor-to-ceiling height applications.

Bladeless ceiling fan: Fan blades are covered by a casing material that prevents them from interacting with electrical lights.

Other fan types: Fans not mounted onto the ceiling pose no risk to the lighting design of the building.

Diffuser panel (skylight applications only): Diffusing the daylight entering though the skylight may alleviate, or even completely remove strobing and flicker from occurring.

Air-conditioning system

The intent of this section is to discuss some common HVAC system that integrates with ceiling fan. The discussion will be focused on how ceiling fan integrates with the system, instead of how to design the HVAC system itself, which is addressed in the Integrated ceiling fan and HVAC control section

Conventional HVAC system with diffusers

Ceiling fans can be directly implemented to existing air-conditioned buildings with installed ceiling diffusers, as long as that the requirements of mounting height and clearance are fulfilled as described in previous section (see Figure 44). The benefits of installing ceiling fans, i.e., increase building efficiency, improve thermal comfort, and enhance air speed and temperature uniformity, can be achieved. For the air-conditioned space that has shorter floor to (false-) ceiling height, the use of other air movement devices is encouraged due to safety consideration.

Side-wall supply jet

The function of diffusers and branch ducting in conventional HVAC system is to distribute conditioned air evenly through indoor space, especially for the areas that are away from the main supply air duct. The same purpose, however, can be achieved by operating ceiling fans, meaning that the diffusers and branch ducting could be reduced or completely removed.

Figure 45 demonstrates a new approach on how HVAC system integrates with ceiling fans. The cool air is supplied from a high-sidewall vent directly towards the center of the space. Then the ceiling fan mixes the supplied cool air with the room air and distributes it over the indoor space. The immediate benefit of such HVAC – ceiling fans integrated system is the reduction of unnecessary duct work on the ceiling, thereby saving significant amount of costs on the initial construction and continuous maintenance. Further discussion on cost saving with a case study will be demonstrated in the later section of this guide. Secondly, without a false ceiling and extra ducting on top, the ceiling fan is operated more safely and effectively due to maximized mounting height and sufficient clearances between the ceiling and fan blades, especially for a space with limited floor to ceiling distance.

In such a system, the cool supply air would best be fed through the fan (i.e., above the ceiling fan blade), rather than impinged into downward airflow initiated by the ceiling fan (i.e., below or level to the ceiling fan blade). Although the air velocity distribution pattern will be dominated by the ceiling fan airflow in both cool air supply conditions, the air temperature profiles delivered to the occupied zoom is different. Figure 46 shows the cool supply air merged with the ceiling fan downward airflow, which possibly initiating a cold draft into the occupied zone, when the cold air is supplied at fan blade height (Chen et al., 2020). In contrast, if cool air is supplied above the fan blade, the supply air is immediately mixed with the room air, it provides a uniform air temperature into the occupied zone.

This approach has been studied for cooling conditions. In heating, the fan may be used in reverse mode but there is no available knowledge about its performance, therefore caution should be used.

Radiant heating and cooling

Radiant heating and cooling systems can achieve significant energy savings, peak demand reduction, load shifting, and some thermal comfort improvement compared to conventional all-air systems. The pipes can be either embedded into to the slab (ceiling or floor) or installed inside a radiant panel. Ceiling fans are a good match with radiant heating and cooling systems as they can also increase heat transfer from the radiant system (requiring lower temperature differences between the room and the water, further improving efficiency), and provide the occupant with a means of instantly changing the comfort condition in the space. Figure 47 shows the integration of ceiling fan with radiant system with water pipe embedded into the slab and inside the radiant panel.

In terms of system efficiency, compared with a conventional radiant ceiling cooling system (without ceiling fan), the cooling capacity of a radiant system with ceiling fan can be increased by up to 22 % and 12 %, respectively, when the fan is blowing upward and downward (Karmann et al., 2017). Upward blowing fan moves the air directly towards the radiant cooling panel on the ceiling, thus resulting in higher cooling capacity. Likewise, a downward blowing ceiling fan, with higher air speeds along the floor, would maximize the cooling capacity of a radiant floor system. Another study on radiant floor systems found that downward blowing ceiling fans increased the radiant slab cooling capacity by 16 % at 24 °C [75 °F] operation temperature and increased by 26 % at 26 °C [79 °F] temperature (Pantelic et al., 2018). Experimental results suggest that elevated air speed in space enhances cooling capacity and system efficiency in radiant system by improving the convective heat transfer.

HVAC systems that are not favorable for ceiling fans

While we have introduced above the HVAC systems that are favorable integrating with ceiling fans, there are also some HVAC designs unfavorable for ceiling fan operation. These systems mainly aim at temperature and pollutant stratification instead of air mixing, such as displacement ventilation and underfloor air distribution system.

Figure 48 presents the airflow patterns of a typical displacement ventilation system. The conditioned cool air is supplied from an air handling unit through diffusers, either located against a wall or at the corner of a room. The cold air gets warmer by absorbing heat from the heat sources (e.g., occupants, equipment) and slowly rises to the top. Thermal plumes are formed due to the density difference between the cold and warm air. Finally, the warm air on the ceiling is removed by the return air outlet. One benefit of displacement ventilation is the improvement of air quality by removing fine particles in the room (light particle goes together with the thermal plumes and exhausts out). The presence of ceiling fan, in this case, will adversely mix the air and temperature inside the room causing the thermal plume dependent on the temperature gradient to no longer exist.

Similarly, the airflow pattern in the underfloor air distribution (UFAD) system (see Figure 49) also relies on the temperature difference within the space, by providing fresh and cool air from underfloor to the lower occupied zoom and exhausting the warm air in upper unoccupied zoon from the ceiling return. Again, the presence of ceiling fan in UFAD would break the ventilation path, resulting in negative system effectiveness.

Integrated ceiling fan and HVAC control

This section describes the control strategy for integrating ceiling fans and HVAC system.

HVAC system control with / without a fan

Figure 50 demonstrates the control schematic for the HVAC system with and without the integration of a ceiling fan. The HVAC signal for heating reduces when indoor temperature increases accordingly, and it stops when the indoor temperature goes beyond the heating setpoint say 21 °C [70 °F]. For a case without ceiling fans, the HVAC signal for cooling starts when the indoor air temperature goes higher than the first cooling setpoint temperature say 24 °C [75 °F]. Alternatively, for a case integrated with ceiling fan, the fan may respond to zone temperature, acting as the first stage of cooling for a zone before the HVAC system begins to operate in cooling mode. The ceiling fan will operate at the first cooling setpoint of 24 °C [75 °F] to provide convective cooling and maintain occupants’ thermal comfort without operating the HVAC. The fan speed increases with zone air temperature until reaching 25.5-26.5 °C [78-80 °F], at a point which the HVAC system begins to modulate and to maintain that setpoint, providing the second stage of cooling. Operating the HVAC system at this higher cooling setpoint has significant energy savings potential.

Ceiling fan speed control

Ceiling fans can be integrated with the building automation system (BAS) through several mechanisms. True integration requires speed control of the fans, and this is typically achieved using either a 0-10 V input or a BACnet interface. Using the same control case above, Figure 51 shows the control scheme for the ceiling fan speed when responding to zone temperature.

Within the dead band, especially when HVAC is in heating mode, the ceiling fan should be turned off or operated at lowest possible air speed (or even rotating in reverse for destratification or general air mixing). The fans will need to stay on if the HVAC system and its air distribution strategy was designed with less ducts and diffusers assuming the fans would have been in operation for air mixing. When the temperature reaches the fan cooling setpoint, e. g., 24 °C [75 °F], a signal from BAS will operate the ceiling fans in the space to provide the first stage of cooling. The ceiling fan speed increases with the room temperature, which is determined by cooling effect or predicted at a representative point in space. HVAC for cooling operates when the room is at the HVAC cooling setpoint, e.g., 25.5-26.5 °C [78-80 °F] and operates to maintain the room at that temperature. Ideally, the fan speed will increase with the room temperature till the maximum (i.e., 100 %). At all stages, the fan should be controllable by users, meaning that occupants can override fan speed and on/off status any time. The same applies for the HVAC cooling setpoint. However, there should be an automated system review (or regular manual review) of setpoints throughout the building to ensure they have not been adversely overridden by an occupant and left in place indefinitely.

Ceiling fan control alternatives

Some ceiling fans have onboard sensing and controls that allow fan speed and temperature automation without integration with the BAS. A lower cost, simpler alternative to automatically control the ceiling fan based on temperature is to use a relay to turn fan(s) on and off. The fans then operate at a fixed pre-set speed. This only provides on/off control, and as such can only be effective over a small range of temperatures without a ‘typical’ occupant in the space experiencing conditions that are either too warm (insufficient air movement) or too cool (excessive air movement). This approach is mostly applicable for:

• the use of ceiling fans predominantly to mix the air within the space and aim for relatively low air speeds (e.g., ≤ 0.25 m/s [50 fpm]) in the occupied zone. Example applications include: destratification in heating, or air mixing to reduce the need for distribution ductwork.

• for spaces where variability in air speeds is beneficial (e.g., the occupants can easily move within the space, such as a lobby, event space, or hallway).

Fans operation can also be tied to occupancy sensors in the zone, preventing unnecessary operation, energy use, and maintenance. In some cases, it may be beneficial to operate fans even when unoccupied, such as pre-cooling applications that benefit from increased convection from surfaces in the space due to the air movement generated by the fans.

Smart ceiling fan and HVAC control algorithm

Apart from controlling the ceiling fans based on temperature setpoint, smart fan control can also be achieved based on occupant’s characteristics, such as occupancy and user preference feedback. To do this, all ceiling fans are connected and controlled by a central controller, as part of the smart building management system, to acquire environmental data such as temperature, relative humidity (RH), and occupancy from a network of sensors in the space. From those inputs, the control algorithm calculates in real-time the optimal fan speed to maximize thermal satisfaction for occupants (Liu et al., 2018). The ceiling fan controller can also be integrated with the HVAC controller for cooperative operations by adjusting the zone temperature setpoints when necessary. There are two main control strategies, automatic mode that is based on ASHRAE 55 comfort model and cooperative mode, that is based on people feedback.

In automatic mode, the integrated PMV-SET (Predicted Mean Vote - Standard Effective Temperature model used in the ASHRAE 55 standard) is utilized to evaluate the thermal comfort in each zone in real-time to determine the optimal fan speed settings (Liu et al., 2018). The model inputs include real-time temperature and RH from the environmental sensors. Personal parameters, i.e., metabolic rate and clothing, are pre-defined within the algorithm. The cooling effect due to elevated air movement is obtained by iteratively solving the SET equation. The output of the PMV-SET model is the desired air velocity to achieve the pre-set targeted PMV range, which is the comfortable range between -0.5 to 0.5. Figure 52 illustrates the PMV-SET with Occupancy control algorithm at automatic mode.

In cooperative mode, the ceiling system operates based on the environmental data and real time occupants' preference feedback, such as preference for cooler or warmer thermal sensation and preference for more or less air movement. Occupants would give their feedback anytime via a software application receiving individual users’ feedback regarding their preference on fan speed and/or thermal sensation. In this way, the user sensation preference becomes an active input component as a “human-sensor” in the closed-loop ceiling fan control system (see Figure 53). For example, if most of the occupants in the space (i.e., 80 % - adjustable by setting) prefer a cooler environment, first a higher fan speed will be set to satisfy the occupants’ needs; if this is still insufficient, then a lower indoor temperature setpoint could be set. This strategy has been successfully applied to a Zero Energy Building in Singapore achieving high energy savings (~32%) and high thermal comfort (Kent et al. 2023).

While the benefits of elevated air movement by ceiling fans are acknowledged, places with lower floor-to-ceiling height or a ceiling with compacted fixtures could be limited for ceiling fan installation. This limitation can be mitigated by using other air movement devices.

Fan types

Various air movement devices are available in the market, but no standard classification protocol defines them. Based on the function and location of usage, this guide discusses five major types of air movement devices: desk fans (bladed and bladeless), pedestal/tower fans, wall-mounted fans, bladeless ceiling fans and air circulators.

Desk fans

The term ’desk fan’ generally describes a fan that is portable with a size small enough to place on the desk or table within reach of an occupant. It can be subdivided into bladed and bladeless fans. Desk fans with blades available in the market generally have a diameter between 7 to 35 cm [3 to 14 in], like the one shown in Figure 21a. Desk fans with a smaller diameter than this range would also be beneficial when working close to the user (< 0.5 m). Meanwhile, a larger fan would be too bulky to place on the desk. In addition, some desk fans are attached with a clip-on base, which allows users to clip the fan on the partition or the edge of their desk (see Figure 21b).

To ensure safety when the fan is in operation, the fan's blades are enclosed inside a resistant plastic or metal mesh. Usually, some small fans with low power (<5 W) do not need an enclosure as the risks are minimized. Further, there are fans with no blades in the market to enhance safety and an aesthetical outlook. Figure 21c shows an example of a bladeless fan. Although it looks and operates “bladeless,” these fans have blades operating inside the fan body. The inner blades with the motor draw air in at the bottom and push air up into the ring portion of the fan to create the air stream. The size of the ring portion varies by fan product and is not necessarily circular in shape. In general, bladeless fans operate at a louder noise and require more energy to move the same volume of air when compared to their axial counterparts.

Pedestal fans / Tower fan

Pedestal fans, also known as standing fans, are quite similar to desk fans but with the fan head mounted to a height-adjustable pedestal, elevating the fan to about 0.6 to 1.2 m [2-4 ft] from the ground. The fan operates on a tall stand to enhance air circulation (avoid obstacles on the floor) in larger rooms, and its ability to oscillate left and right delivers air to a broader area. Figure 21d shows an example of a pedestal fan. Although pedestal fans are meant to be portable, they usually come with a heavy base to maintain stability when operating, which is less portable when compared to desk fans. This heavy base allows larger fan size operates on top, i.e., provides more airflow, with market-available blade diameter ranging from 30 to 76 cm [12 to 30 in]. The number of blades for a pedestal fan usually ranges from 3 to 5, with some special models up to 9 blades.

Another common type of fan used on the floor is the tower fan. Unlike axial fans (draw and deliver air along the fan axis), a tower fan is a crossflow variety (draw and deliver air perpendicular to the impeller fan axis). A crossflow fan pulls air from the inlet into a cylindrical impeller vane housed inside the tall and slim fan structure by setting up a cylindrical vortex of spinning air. The vortex then swings the air to the opposite side of the impeller blades and pushes the air out alongside the rectification plate (i.e., the outlet duct). The enclosed impeller blade design maximizes safety for residential usage, especially with kids and pets around. The tower-like structure is fixed on a base and rotates horizontally to extend the air movement sweeping area. The tower fans are compact and lightweight and fit well for any indoor space, serving personal cooling and air circulation. The airflow produced by the tower fan is usually laminar and uniform along the tower. Figure 21e shows an example of a tower fan.

Wall-mounted fans

A wall-mounted fan is a pedestal fan without a base mounted on the wall. Sometimes these fans may also mount to the ceiling. Yet, different from conventional ceiling fans, these “ceiling mounted” fans can oscillate at 180 °. It is a good choice to provide a breeze over the human body and enhance room air circulation when the space and floor-to-ceiling height are limited. Figure 22 shows some examples of wall-mounted fans.

Bladeless ceiling fan

A bladeless ceiling fan operates as a centrifugal fan, unlike the conventional ceiling fan which uses an axial fan. In theory, a bladeless ceiling fan is not bladeless but a special design with many small blades installed at the fan’s circumference structure. The fan rotates the entire design structure, which draws air under the fan and hurls it out at the side from 360 °. These fans are intended to enhance air movement and air circulation within a small space, such as a living room or bedroom. Figure 23 demonstrates some examples of bladeless ceiling fans. They are less common than other fan types. The installation requirement is similar to a ceiling fan with blades, but the bladeless ceiling fans do not require a minimum mounting height to prevent “air choking”, which means they are suitable to be installed in a space with low floor-to-ceiling height.

Air circulator

Air circulators aim to provide a high-velocity air jet to circulate air and keep air moving continuously in the room. The strong air movement is not intended to be blown directly toward the human body but to initiate air circulation. Depending on the brand, the air circulator diameter range is between 23-40 cm [9-16 in]. Such fans are ideal for air circulation in small rooms, such as bedrooms and enclosed offices. An extra-large air circulator about 50 to 76 cm [20-30 in] in diameter, also known as the drum blower, with durable metal construction, can deliver extra high-velocity airflow. These heavy-duty air circulators are ideal for warehouses, industrial workshops and loading docks. Figure 24 illustrates some examples of air circulators.

Fan selection considerations

Typical functions

The above-mentioned air movement devices have two major functions: (1) move air directly towards the human body and (2) room air circulation. Moving air towards the human body aims to cool the subject using convective heat loss, while air circulation aims to keep air in motion within the enclosed space to enhance air and temperature mixing. Generally, a smaller fan that generates less airflow (i.e., desk fan) is more suitable for direct cooling towards the human body, while a larger fan and fan that generates stronger airflow (i.e., bladeless ceiling fan, air circulator) are designed for air circulation. Nevertheless, most of the fan types can deliver both functions by adjusting the fan speed. Therefore, fan selection should be based on the intent, whether it is an individual adjustment for personal cooling (group 1) or simultaneously producing a general air movement effect for multiple occupants’ usage. Table 2 summarizes the typical function, location of application, and approximate price range for different elevated air movement devices.

Table 2. Summary of other air movement device’s function and approximate price range.

Noise levels

Noise from a fan can initiate dissatisfaction and unwillingness of usage from occupants. The noise sources of a fan are mainly from the operating motor and the fast movements of the blades (i.e., turbulence). The sound level of domestic fans ranges from 30 to 70 dBA depending on the fan types (e.g., desk, pedestal, ceiling), fan models and speed. Table 3 suggests the noise level for some corresponding features for comparison. The noise level from an axial fan, initiated by turbulence, increases with the blades' rotational speed. Therefore, higher speeds usually correspond to higher noise levels. While for the cross-flow fan, the air output is generally laminar with lower air speed (i.e., lower blade rotational speed); thus, the noise being generated is also relatively lower.

Nevertheless, the noise cannot be characterized only by sound level; its frequency distribution is also important. Low-frequency noise is identified to be annoying in dwellings, and this kind of noise is associated with appliances such as fans. Sometimes, a louder noise with uniform frequencies might be less annoying than a lower sound level that peaks at specific frequencies. Furthermore, the fan design also plays an important part in defining a fan’s sound level and frequencies. Thus, concluding that one fan type will always be quieter than another is not practical. Users are encouraged to experience fan usage before purchasing.

Table 3. Noise level by comparison.

Power and efficiency

Most elevated air movement devices described above are powered by the electric grid. The electricity powers up the motor and spins the blades like the ceiling fan. Most of these air movement devices are not fixed in position, which can plug in any power socket outlet near the desired operation area. Some small fans can be powered by rechargeable lithium-ion batteries, meaning that the fan is cableless to enhance additional flexibility when operating. Some small desk fans with diameters between 7 -15 cm [3-7 in] can be powered by a USB plug linked to a computer.

In general, efficiency is the ratio of the output to the input. For fans, the Cooling fan efficiency (CFE) index (Schiavon & Melikov. 2008) used to evaluate the cooling performance is defined as the ratio between the cooling effect of the device and its power consumption. The following equation represents the calculation of the CFE index, where$P_f=$ the input power of the fan (in W) and$\Delta t_{eq}=$ the whole-body cooling effect (in °C or °F).

Due to different designs and usage, the performance of cooling fans (e.g., ceiling fan, desk fan, tower fan) with regards to their cooling effect and cooling efficiency can be varied. Figure 25 demonstrates the test results on some ceiling fans, desk fans, tower fans, and standing fans to depict their relationship between CFE and fan power. The desk fan tested in this study consumed the least power (16 – 20 W) and obtained the highest cooling fan efficiency (0.095-0.177 °C/W [0.17-0.31 °F/W]). The results are interpreted upon normal condition usage of fans, meaning that the desk fan is smaller in size (i.e., smaller motor) and the fan operation distance is closer to the human subject (maximize cooling effect) when compared with other fan types. Indeed, desk fans are designed to provide local cooling by generating airflow towards the human body instead of circulating air for the entire space (like the other fans do). Eventually, the intent of fan usage (local cooling vs. air circulation) should have been taken into consideration when quantifying the fan effectiveness. While the efficiency of the fan itself is somewhat important, any fan’s electricity consumption (even not the most efficient type) is always relatively low when compared to using just air-conditioning to provide thermally comfortable conditions to humans. More details are discussed in the section “Potential savings” in this guide.

Motor and drive

All the elevated air movement devices described above, with or without blades, consist of a rotary part driven by motor and drive. The types of motor and drive used for these elevated air movement devices are similar to those that operate in a ceiling fan, which we have discussed in the former section. It is worth noting that a larger energy-saving potential can be achieved using a DC motor instead of an AC motor, especially for small fans like desk fans or pedestal fans.

Air Speed / Airflow pattern

Performance of air speed from different devices can be varied by fan size, blade types, and fan structure. For axial fans, estimation of air speed is similar to ceiling fan (i.e., dividing the rated airflow of the fan by its diameter). However, such estimation is not applied to bladeless fans and tower fans which have a different airflow driven mechanism.

There is no existing requirement or standard on typical air speed for the air movement devices described above. Air speed and airflow requirement is more critical to the application than place of usage. We will discuss the air speed and airflow requirements based on the usage of (i) direct cooling towards human body, and (ii) room air circulation.

Direct cooling towards human body: When choosing an air movement device, customers tend to select a stronger fan which can produce more airflow and faster air speed. While it is true that bigger and stronger fans can provide better cooling effect, the question is do we really need that much air movement if the fan is intended to operate close to us? The fact is, sometimes we may experience too strong air movement from a nearby fan blowing toward our body, even though it is working at the lowest available fan speed. Figure 26a shows the environment is thermally comfortable if the surrounding air speed is 0.5 m/s [98 fpm]. A cooling effect of 2.8 °C [5 °F] means that, with current thermal condition, the subject is actually feeling 2.8 °C [5 °F] lower than the actual temperature (equivalent to 23.2 °C [73.8 °F]). If the fan is placed closer to the occupant, or the air speed is increased to 0.8 m/s [157 fpm]. Keeping other thermal parameters unchanged, Figure 26b suggests a cooling effect of 3.5 °C [6.3 °F], where the occupant became slightly cool and outside the thermal comfort zone. This example demonstrates that choosing a fan with possible lower airflow turndown (minimum speed divided by maximum speed) capability could be the key for better comfort in terms of direct convective cooling. Figure 27 illustrates the airflow examples for desk fan, pedestal fan, tower fan, and wall mounted. The oscillating function of these fans helps to deliver air movement at a wider coverage range and to minimize the risk of unwanted draft from long term spot cooling.

Room air circulation: An air movement device that aims to circulate the air within a room is either bigger in size (i.e., ceiling fan, bladeless ceiling fan) or able to generate high airflow jet with high speed (i.e., air circulator) to drive the air movement.

The airflow pattern of bladeless ceiling fan is quite similar to a reversely operated ceiling fan, but it applies the centrifugal technique to draw the air from the bottom to the center of the fan then throw it out perpendicularly at the side from 360°. Figure 28 shows a schematic on how air is driven by a bladeless ceiling fan. The goals for such air movement strategy are (i) to elevate the average air speed in the occupied zoon and (ii) to mix the air in the space minimizing stratification. It is worth noting that this system works best with close loop airflow within a small to medium size enclosed room (e.g., enclosed office, residential). Since there is no direct air jet blowing towards the occupants, the air speed in occupied zone will be too low if there is no air reflected from surrounding walls. To minimize this problem, some bladeless ceiling fans have modified the fan body design, which is able to guide the airflow slightly downward (i.e., less than 90° flow) towards the occupied zone.

An air circulator intends to produce a high-speed strong air jet to move air from one side of the room to the other. Figure 29 presents a schematic representation of the airflow pattern for an air circulator in an enclosed room. Similarly, this strategy aims to move the air to increase the average air speed and to enhance air mixing in space. Thus, the air circulation effectiveness also works better in small to medium size rooms. Different from the bladeless ceiling fan approach, however, air jet from the air circulator is freely adjustable within the occupied zone. Basically, the air circulator can reduce the fan speed, temporally act as a desk fan, or pedestal fan blowing air directly towards human body for immediate cooling. In addition, to enhance long distance air movement, some air circulator’s fan blades are modified to a propeller (or turbine) type. Instead of moving air parallel to the fan axial, it drives the air in form of a vortex which propagates along the fan axial. This feature helps to centralize the airflow across longer distance and to drag surrounding air towards the propagation of air stream to maximize the airflow rate. The air movement distance from an air circulator is much longer when compared with normal desk or pedestal fan with a flat blade.

Flexibility

One major advantage of the above listed elevated air movement devices over ceiling fan is the high flexibility of usage in terms of location, operation height, flow direction and oscillation. Such flexibility enhances adjustment to occupant’s needs and comfort demand regarding elevated air speed under different circumstances. Except the wall mounted fans and bladeless ceiling fans, all other fan types listed in Table 2 are flexible to be relocated based on the occupant’s needs: on the desk or floor, directed to or away from the occupants, and any places that can move air to the desire direction. Fan operation height of pedestal fans are adjustable, usually about 0.6-1.2 m [2-4 ft] from ground (depending on brand and type), while some other fan types, such as desk fan and air circulator, can adjust the air stream shooting height by tilting the fan head at certain vertical angles.

Most of the fan types listed in Table 2 can oscillate horizontally in a range of 60 ° to 160 °. Some modern fan types can also oscillate vertically. Horizontal or vertical oscillation of fan allows the air movement to cover wider area within the space and to serve multiple occupants at the same time. In addition, the fan oscillation function could minimize the stale air areas by moving the air from different directions, even behind some obstacles such as furniture or partitions, which enhances effectiveness of air mixing. It is one of the major benefits of ceiling fans usage in space. Portable fans can be operated in different rooms in the same space (i.e., one fan serves multiple rooms).

Other features

Some fans are equipped with technologies that enable them with special features. Some tower fans and bladeless fans are equipped with multiple filters, contributing to air purification. Particulate matter and sometimes gases in the air can be filtered out and cleaner air will be circulated within the space. Different types of filters can remove various kinds of contaminant. Some special fan models are installed with UV-C (i.e., germicidal UV) light inside the fan framework to disinfect the air during circulation process. UV-C is effective at deactivating viruses, bacteria, mold, and fungus. Some fan models can emit water mist that moves along with the air stream to reduce its temperature thanks to the adiabatic cooling (evaporative cooling) process. Figure 30 presents an example of a pedestal fan with evaporative cooling function.

Controls

Compared with ceiling fan, other fan types listed in Table 2 are mostly portable, except for wall mounted and bladeless ceiling fans, and manually operated.

Control panel on fan body: Most portable fans are equipped with a control panel on the fan body (See Figure 31a). It shows a simple On / Off plus fan speed control button, and a rotary switch connected with the watch spring to provide basic timer control (i.e., after how long the fan will be switched off automatically). Wireless IR remote control: Many modern fan types can be wirelessly controlled by an IR remote. Figure 31b shows an example of the remote control. Basically, it can adjust the on / off switch, fan speeds, vertical or horizontal oscillation, and set timer. Some remote controls may even be able to control other special functions if the corresponding fan has corresponding features, such as lighting switch. Wi-Fi or Bluetooth control via phone App or Internet: Wireless control via phone App or internet is very similar to the IR remote control approach but uses a smart phone instead of a remote control. Figure 31c presents an example of Wi-Fi connection via smart phone.

Design layout and components

This section discusses the difference in design and components needed between the conventional HVAC and ceiling fan integrated HVAC system using the same building layout plan (see Figure 54). In conventional HVAC system (see Figure 54a), diffusers are the prime fitting to distribute cool air over the space. They should be evenly installed and require detailed commissioning in balancing the air pressure over the supply air duct (i.e., maintain standard flowrate in each diffuser) to ensure air distribution effectiveness. Depending on the system requirements, variable air volume (VAV) boxes are installed for better zone temperature control.

Alternatively, shown in Figure 54b, the ceiling fan integrated air-conditioning design for the same layout requires only the main supply air duct throwing cool air directly from the sidewall towards the center of space. The ceiling fans can effectively mix the air and temperature within the space, without any diffusers nor extensive supply air ducts for uniform air distribution. The number of ceiling fan and corresponding installation location can be estimated using the CBE Ceiling Fan Design Tool.

System design, selection, and operation

One major advantage for air movement design is the additional convection effects on occupants and zone equipment, meaning that additional energy saving from space cooling is possible due to HVAC system optimization.

Design room conditions

The presence of space air movement allows higher dry bulb room temperature (2-3 °C [4-5 °F]) and dewpoint temperature (1-2 °C [2-4 °F) when compared with conventional HVAC design. Alternatively, if the original designated air temperature is 23-25 °C [73-77 °F], it can be increased to 23-27 °C [73-81 °F] with elevated air movement to achieve similar or even better thermal comfort. The room’s operating air speed can be up to 0.8 m/s [160 fpm] without personal control, while there is no air speed limit if occupants have full control of the fans (i.e., just ceiling fan or ceiling fan + desk fan) within the space.

Systems selection

Regarding the relaxation of designated cooling demand (i.e., lower sensible and latent load), the chiller and the air handling unit (AHU) from original HVAC system can be downsized in the system design stage. The design supply air temperature setpoint (SAT) and chilled water temperature (ChWT) setpoint relaxation should be 50% to 100% the zone cooling setpoint temperature adjustment. For example, if compared to a conventional HVAC design, the HVAC design with elevated air speed could have 2 °C higher cooling setpoint temperature, the SAT and ChWT setpoints should be increased by 1-2 °C. In addition, a smaller size fan in the AHU can be used for the ceiling fan integrated design, because it returns smaller static pressure along the critical supply air path (only require the main supply air duct).

Potential savings

Construction cost

Estimation from a consultant firm suggests that the ceiling fan integrated air-conditioning system in Figure 54 could save up to 45 % in capital construction cost when compared with the conventional HVAC system design. These savings are mainly obtained from reduced ductwork, diffusers, VAV boxes, sensors and controls. Savings can also be obtained from the extra time and workmanship for additional ducting and fittings installation. More importantly, the majority of these ducting and fittings are not reusable and become construction waste when the building is being demolished. The cost of purchasing and installing the ceiling fans in the space was very low when compared to the above cost savings.

Energy consumption

Substantial energy for space cooling can be accrued when implementing the elevated air movement with higher temperature cooling strategy. An energy simulation model of a standard office, in Figure 55, shows approximately 17 % of energy saving in the HVAC system by increasing the cooling temperature setpoint from 22 °C [72 °F] to 25 °C [77 °F]. In such room temperature setpoint adjustment, higher chilled water supply temperature (10 °C [50 °F]) can be used, instead of the conventional temperature setpoint (7 °C [44.6 °F]), which it would account for approximately 12% of additional energy saving from the chiller. Meanwhile, the consumption of cooling energy savings by increased room temperature setpoint tends to be much greater than the ceiling fans energy consumption. A study of 100 automated ceiling fan showed 36% of compressors energy savings when compared with air-conditioning only conditions, while the fans consumed only 2% of the total compressors consumption (Miller et al., 2021).

Continue testing and adjustment

Conventional air-conditioning design requires detailed testing and commissioning on the airflow through the diffusers and the air pressure drop within the supply air duct. However, there is no standard procedures available for system testing for ceiling fans integrated system. Two recommendations are proposed to test the system’s effectiveness in the post-occupancy stage. First, conduct physical measurement on indoor temperature, mean radiant temperature, relative humidity, and air speed at the occupied zone, and check the zone comfort range using the CBE Thermal Comfort Tool. The post-occupancy air speed and pattern could be different from that in the design stage because these parameters are sensitive to room furnishings (e.g., desk, partition, and shelf). Second, it is strongly recommended to conduct a post-occupancy evaluation to understand the actual feelings and needs of the occupants. It is the most direct way reflecting occupants’ satisfaction and to plan mitigating action for improvement. If there are areas where air movement from ceiling fans cannot be reached, providing occupants with personal fans (i.e., desk, pedestal, or tower fan) could be a solution.

Overview

In this section, we discuss the thermal comfort related effects of increased air movement using fans for cooling applications. We also discuss tools such as the CBE Thermal Comfort Tool to help determine the right air speed and other factors for optimal thermal comfort. Figure 3 shows the cooling effect – or how many degrees warmer the air temperature can be to provide the same level of thermal comfort – associated with increased air speeds. This figure also highlights that the design air speeds discussed in this guide are well below the air speeds that a person experiences every day. For example, a design speed of 0.5 m/s [100 fpm], equal to approximately 2 °C [4 °F] cooling effect, is approximately half the air speed that a person experiences just from the relative motion of walking slowly through still-air conditions.

Human body thermoregulation

Thermal comfort, here defined as the occupant’s satisfaction with the perceived thermal sensation, depends on how much heat is released or retained by the occupant’s body. Human thermoregulation, as depicted in Figure 4, is the heat transfer process to and from the body that occurs in four ways: radiation, convection, evaporation, and conduction.

Thermal comfort factors

ASHRAE Standard 55 – Thermal Environmental Conditions for Human Occupancy (2020) identifies six factors that affect thermal comfort. The metabolic rate is the rate of transformation of chemical energy into heat and mechanical work, based on the level of activity (e.g., walking presents a higher metabolic rate than seating). The clothing insulation is the insulating effect of clothing preventing heat loss from the body (e.g., shorts and a short-sleeve shirt have lower insulation levels than pants and a heavy sweater). The air temperature is the temperature of the air, usually measured by the thermostat. The mean radiant temperature is the average temperature of the surfaces surrounding a certain point, weighted by the view angle of each surface to that point. The air velocity or air speed at a certain point is the influential factor we explore when fans are used. And the last one is humidity, which indicates how much moisture the air contains.

How elevated air speed meets thermal comfort goals

Fans increase air speed and heat transfer via convection and evaporation, which provides a cooling sensation. It allows the body to maintain thermal comfort at higher air temperatures than what would be comfortable in still air. In addition to providing comfort at increased temperatures, fans are capable of providing instantaneous comfort effects that thermostat adjustments usually cannot because it controls a slower process. A thermostat and HVAC system that conditions the whole room generally takes 15 minutes or longer before the occupant can perceive a change in their thermal environment. However, when an occupant feels too warm, turning on or increasing the speed of a fan instantly provides a cooling sensation, also known as the cooling effect. Fans are also ideally suited to providing adaptive or transitional comfort for changing human comfort conditions. Adjusting fan speeds can help accommodate the natural fluctuations in body temperature and comfort preferences throughout the day. The adjustable nature of fans can provide enhanced thermal comfort during transitional moments, such as the changing comfort needs when transitioning from an active metabolic rate event (for example, after walking from a meeting in a different part of the building or arriving in to work from a morning commute) to a resting metabolic rate (such as sitting at a desk in an office), or simply due to different personal thermal comfort requirements of occupants in the same physical space. The ASHRAE Standard 55 (2020) and the CBE Thermal Comfort Tool both help to inform how much air movement is needed for thermal comfort and occupant satisfaction.

Thermal comfort calculation with elevated air speed

ASHRAE Standard 55 (2020) provides a method called The Elevated Air Speed Comfort (Section 5.3.3. of the standard) to calculate thermal comfort in situations of elevated air speed. This method uses a combination of the Analytical Comfort Zone Method with the Standard Effective Temperature (SET) method (Normative Appendix D of standard). Since increasing air speed has a cooling effect, the method calculates adjusted air and radiant temperatures according to how occupants are expected to feel under increased air speed conditions to calculate a new PMV value. The “Standard Effective Temperature” (SET) output translates the six thermal comfort factors (presented before) into a single temperature equivalent. The SET provides a single metric that can be compared across a variety of comfort conditions.

The cooling effect is also used to calculate the Cooling Fan Efficiency (CFE). CFE is defined in ASHRAE Standard 216 as the ratio of the cooling effect to the input power of the fan. CFE gives people a standardized way to compare how much cooling a fan provides when consuming the same amount of energy.

Elevated air speed for destratification in heating mode

In addition to directly cooling occupants, fans also effectively mix the air in a space, which has several applications. The most common of these applications is where the temperatures in space are unwantedly stratified, with warmer air close to the ceiling and cooler air near the floor (Figure 5). This typically occurs in spaces with high ceilings or where the heating equipment has a relatively high discharge temperature and low mixing momentum. In these conditions, ceiling fans can mix the air in the space such that the temperature at the floor (and near where the thermostat is located) is close to the average temperature in the space. This can save energy and improve occupant comfort. Ceiling fans are most effective in providing destratification, as they are located close to the ceiling and can run in either direction to achieve this mixing, although they will use more power to achieve the same mixing effect when operating in reverse (moving air upward) than forwards (moving air downward). Note that during destratification, the space is typically operating in heating mode and operating at the lower end of the range of temperatures that define the thermal comfort zone. As such, it is very important to maintain very low air speeds in the occupied zone to avoid the sensation of draft. Depending on the specific conditions, the occupant locations, and the minimum speed capabilities of the fan, running the fan forward or reverse may be better to achieve this goal.

Evidence of occupant’s preference for air movement

In theory, elevated air movement accelerates heat loss from occupants via convection and evaporation in a warm environment. The question is, do occupants appreciate elevated air movement? Or do the occupants prefer an environment with cooler temperatures than increased air speed? An experiment conducted in a climatic chamber in Singapore investigated occupants’ thermal acceptability under different temperature setpoints with and without fan operation. Figure 6 shows that occupants were thermally more acceptable at 26 °C [79 °F] with higher air movement from personally controlled fans when compared with the condition at 23 °C [73 °F] without a fan. Surprisingly, it also reported that the subjects found themselves thermally more acceptable with temperature at 29 °C [84 °F] with a fan than at 23 °C [73 °F] without a fan. These results revealed that the cooling strategy of only lowering the temperature setpoint might not sufficiently satisfy the occupants, while elevated air movement within the space can play a role in increasing thermal acceptability at higher temperature setpoints.

To validate the results from the experiment in a climatic chamber, a similar experiment has been conducted in a Singapore office building studying the occupants’ thermal acceptability and thermal preference responses under three conditions (23 °C [73 °F] without a fan, and 26/27 °C [79/81 °F] with fan). The study found similar higher thermal acceptability among the occupants for the environment at 26 and 27 °C [79 and 81 °F] with elevated air speed than the condition at 23 °C [73 °F] without fan operation. Besides, the occupants were overcooled and reported a preference for a warmer environment at 23 °C [73 °F]. These results from a real building aligned with the findings obtained in the climatic chamber experiment, where both studies suggested that occupants in tropical climate regions preferred a warmer temperature with elevated air speed over an environment with a cooler temperature without sufficient air movement.

Heat stress and air movement

Some health guidelines actively advise not to use a fan when indoor air temperatures exceed the skin temperature (~ 35 °C [95 °F]). Is it true that a fan shall not be used under heat-stress conditions? Using the human heat balance model, a study found that fans could potentially be used by a healthy young adult even if air temperature exceeds 35 °C [95 °F], because elevated air speed through the human body increases sweat evaporation from the skin (Tartarini et al., 2022). Figure 7 demonstrates under which conditions the fan use could be beneficial. The green zone shows the environmental conditions in which the fan operating at V = 0.8 m/s [160 fpm] is beneficial (i.e., providing additional cooling to the human body). The dark green zone represents the conditions where fan usage is still beneficial, but people are likely to suffer from heat strain. The red zone indicates the conditions under which fans are not beneficial and should not be used. The red line shows the temperature limit from WHO, which the usage of fans is not recommended. These findings indicate that fans could be used in some conditions to cool people even when the air temperature exceeds skin temperature. More human experiments and tests with non-healthy groups should be performed. If available and affordable, air conditioning would guarantee safer conditions than just fans.

Fans can be added to an existing AC system to save energy and increase comfort. Besides the aspect related to the system's design, it is also important to consider how the new fans are introduced in the space and how the temperature setpoints are increased.

Progressive transformation and user adaptations

The benefits of higher temperature cooling with elevated air speed, in terms of energy saving and higher occupant comfort level, have been verified in multiple studies (see "Benefit of Elevated Air Speed"). However, occupants are used to a conventional cooling strategy with only air-conditioning at lower setpoint temperatures.

Occupants take time to adapt to the fan-integrated AC system at warmer temperatures and higher air speed environments. Depending on the site conditions and culture, a grace period for occupant adaptation may take up to 3 months. Any change in temperature cooling setpoint should be small, gradual, and follow occupants’ comfort feedback. Despite studies showing subjects can be comfortable at a higher temperature condition with increased air speed, in practice, occupants may perceive thermal dissatisfaction with a sharp change in room temperature setpoint (e.g., from 23 °C to 27 °C [73 °F to 81 °F]) without providing a grace period for adaptation.

For a practical implementation of a fan-integrated system, building facility managers are suggested to go slow and have patience and perseverance with the progressive transformation process. For example, if the thermal comfort analyses indicate it is possible to increase the air temperature cooling setpoint from 25 to 27 °C [from 77 to 81 °F] at higher air speed conditions with fans, in practice, the temperature setpoint shall be first increased to 26 °C [79 °F] and maintained for at least two weeks for occupant adaptation before further increasing it to 27 °C [81 °F]. In addition, occupants’ feedback on the indoor environment shall be continuously monitored during the transformation period. If many thermal dissatisfaction votes have been received, a slightly lower air temperature setpoint should be used. For example, the temperature should be brought down to 25.5 °C [78 °F] to be maintained for two weeks, then raised up to 26 °C [79 °F] again.

Several studies have suggested that occupants can have a higher tolerance to thermal discomfort when provided with control of their micro-environment. Regardless of specific building functions or design intents, allowance for personal control of the fan systems is suggested.

User education

A key part of the success of any fan installation is ensuring that occupants understand the purpose and use of the fans given that, in some context is a novel solution. Presenting the changes clearly to the occupants is very important, so they can be informed on how to use the new equipment and why modifications are being proposed. In cases with regular occupants (as opposed to spaces with transient occupants such as lobbies or event spaces) who do not have direct control over the fan operation, occupants should be informed about the purpose and operation of the ceiling fans. Ideally, spaces where occupants do not have direct control over fan operation, should also allow for flexibility so that occupants may find a location within the space that best suits their comfort preferences. In applications where occupants have access to fan controls, it is also helpful to post information or instructions encouraging occupants to adjust ceiling fan settings when they are too warm rather than resorting to reducing thermostat setpoints. Figure 56 shows an example of an information plaque with basic recommendations for user control.

CBE Thermal Comfort Tool

A helpful tool to find comfort zones at elevated air speeds according to ASHRAE 55 methodology is the , an online tool.

The user enters temperature, air speed, humidity, metabolic rate and clothing level into the tool to calculate results including PMV, SET, and ASHRAE 55 compliance as well as generating the graph below in Figure 57. The blue shaded area represents the ASHRAE 55 compliance comfort zone while the red mark shows where the user inputs are relative to the comfort zone. The tool also supports compliance to the European thermal comfort standard EN 16798; however, this standard does not include the calculation adjustment for convection effect included on ASHRAE 55, being less favorable to estimate increased air speed effect.

The CBE Thermal Comfort Tool also takes into account elevated air speeds. As the air speeds increase, the range of acceptable temperatures increases, and the blue shaded area shifts to the right. Using higher air speeds allows the user to ASHRAE 55 compliance at higher cooling temperature setpoints. Note that Standard 55 has a maximum average air speed permitted in the case that occupants do not have control over the system (0.8 m/s [160 fpm]). This can be specified as an input in the Thermal Comfort Tool as well. To support this functionality, users can also select the “air speed vs. operative air temperature” mode from the drop-down menu above the chart to view the comfort range and results in terms of air speed and temperature (see Figure 58).

CBE Ceiling Fan Design Tool

Modelling, simulation, and energy saving estimation

Although many studies have shown that elevated air movement can improve the occupants’ perceived air quality (; ; ), studies on the relationship between air movement and indoor air quality are comparatively limited. Increased air movement does not remove indoor pollutants from a space like ventilation does. However, air movement changes the airflow pattern in the space, which can reduce an occupant’s exposure to indoor pollutants and infectious agents in several ways: as discussed below.

Firstly, air movement changes the room airflow pattern by redistributing the supply air, thus diluting local sources of pollutants in the room. In spaces with stagnant air where the ventilation effectiveness is lower than 1, the sources of air pollutants can accumulate in the room locally. Using air-moving devices, such as ceiling fans, the air within the space can be fully mixed, resulting in the ventilation effectiveness of the room to approach 1 (which is a measure of complete air mixing) (, Table 6-B) and lowering of the air pollutants levels. However, for other rooms with ventilation effectiveness above 1, such as displacement ventilation (), using large fans will decrease the effectiveness of indoor pollutants removal by design using such systems.

Increasing air movement has been reported to impact the dynamics of indoor air. Using a ceiling fan or a larger stand fan, air pollutants in the room were fully mixed resulting in a more uniformed but lower pollutant concentration (). The authors reported that the air pollutant released from a source was dispersed much faster and reached a more uniform concentration within the space using a fan blowing directly to the source than without a fan. In a recent study on indoor airborne transmission of the SARS-CoV-2 virus, fan use was found to help disperse viruses from the breathing zone to the unoccupied upper part of the room, thus, potentially lowering infection risk. Another study shows that using ceiling fans reduced the pollutant concentration in the exposed person’s breathing zone by more than 20% (). For upper-room ultraviolet germicidal irradiation system (UVGI) systems typically relies on the natural convection of air within the space to disinfect microorganisms brought from the breathing zone up to the irradiated zones near the ceiling. Using ceiling fans greatly improved the UVGI effectiveness system by mixing the microorganisms-laden air up to the irradiation zone, thus disinfecting them at a higher rate compared to those without using ceiling fans (; ; ; ).

Secondly, elevated air movement increases the deposition rate of airborne particles onto indoor surfaces such as fan blades and room furniture, floor, ceiling and walls (; ). This process can be understood by the reduction in boundary layer thickness because of increased air movement, thus facilitating the mass transfer of particles onto the surfaces. Although resuspension of particles may also increase with increased air movement (), the resuspension rate is several orders lower than that of deposition. The air movement needed to resuspend deposited from surfaces into the air is typically on an order of 10 m/s () which is higher than most fan speeds.

Lastly, the World Health Organization (WHO) recommends using stand fans (or pedestal fans) by placing them close to an open window to enhance ventilation for naturally ventilated spaces (). Evaporation of airborne droplets and water-containing particles can be enhanced via air movement. A simulation study on the ejection process of saliva droplets in the air to mimic real events of human cough showed that increased air velocity will result in the saliva droplets going further with a decreased concentration and liquid droplet size in the wind direction (). For infectious bioaerosols, this evaporation process and increased mechanical stress may decrease microorganisms' viability within the airborne droplets. In indoor spaces that adopt increased air movement and elevated temperature, the higher air temperature and relative humidity (RH) may affect viability of airborne microorganisms (; ). have noted that RH controls droplet evaporation. The evaporation affects droplet chemistry (solutes become more concentrated as water is lost) which in turn affects the virion’s microenvironment and viability. For SARS-CoV-2, changing the room temperature and relative humidity from 23 °C [73 °F] and 40% to 28 °C [82 °F] and 60 % will reduce the virus half-life from 44.8 minutes to 22.6 minutes ().

Fans are effective for comfort cooling and air circulation. However, fan applications are highly dependent on the design intent for desire air speed and distribution, and any physical environment limitations. Understanding the elevated air movement design intent is the prerequisite in selecting an adequate fan type for a particular space.

Design intents for air speed and distribution

Figure 32 outlines the key considerations for defining the fan design intents. These design intents are divided into four types, namely personal control, targeted, variability, and uniformity. Table 4 outlines the description of fan applications in each design intent category. The table also provides example application types, example target air speeds, and additional considerations for each design intent approach. For any of the described design intent, the ideal condition should include the automation of fan with the possibility of user override. This would allow, ideally, for fans to be activated automatically according to room occupancy and indoor temperature conditions, but maintain occupants control, allowing them to make temporary changes to fit their needs.

Even under identical environmental conditions, occupant comfort needs vary significantly based on individual preference and expectation, clothing levels, and metabolic rates. “Personal control” design emphasizes the goal of fan system to provide thermal comfort for a single occupant, while the adjustment of fans is unlikely affecting other occupants. In such a case, the design intent of air speed and distribution are not particularly relevant, as the subject has full control of the fan speed, airflow direction (i.e., relocate a desk fan position), and operation schedule according to their own needs. One example would be a private office where the single occupant has control over the fan and another one would be an open plan office where every occupant has a small desk fan (see classification of control levels in the “” section).

In general, design intent of “Variability” has its advantage at multi-occupant space where occupants have flexibility to adjust fans operation based on their desire thermal comfort needs, or they are free to move around and choose their preferrable locations or thermal conditions. In many cases the variability in air speeds created by a fan can help improve overall occupant comfort. For example, a manually adjustable ceiling fan that serves multiple persons within the space for different thermal needs (e.g., adjusts higher fan speed for transient period, but lower speed at steady condition). Another example is in spaces where occupants can easily move around, such as a lobby, gymnasium or cafeteria, variability is likely beneficial as the comfort needs of different occupants can be met by choosing their location in the space.

In spaces where there are variable or transient occupancies, non-uniform thermal conditions, or spaces with specific thermal requirements due to architectural features or activity levels, “Targeted” air movement may provide more comfort. For example, the thermal comfort impact of increased solar radiation near a poorly shaded, highly glazed façade could be offset by locating ceiling fans near the façade, but the areas further from the façade might not need any or fewer ceiling fans. Other examples could be to locate ceiling fans over a dance floor area instead of the audience or directing air circulators to the exercise area in a gym and not directed to the front desk.

Design intent of “Uniformity” (i.e., more regular control) emphasizes uniform air speeds and consistent thermal comfort experience applied in multi-occupant spaces where occupants do not have flexibility to control fan or change their location, especially when occupants will be staying in those areas for extended periods. Uniform air speed and distribution are applied because there is no way of guaranteeing that the person who feels the warmest happens to be the one who is located where the air speeds are highest in the room. Examples here include a shared office with fixed assigned seats, classrooms, and allocated seating dining areas.

Table 4. Recommended guidelines classified by design intent for fan applications.

Fan type considerations

There is no absolute rule to be applied on how to select a suitable fan. In practice, fan selection criteria are mainly dependent on design intent of air speed and distribution, purpose of elevated air movement (i.e., direct cooling across human body or air circulation), and any limitations of fan usage in space.

If the above limitations do not apply, ceiling fans are likely to be recommended. Figure 33 shows that ceiling fans work effectively in different design intents summarized in Figure 32. Ceiling fans can be arranged to provide uniform air speed and distribution within a multi-occupancy space when the occupants do not have control of the fans. Alternatively, in spaces where ceiling fan speed can be centrally or manually adjusted, or occupants can freely move around to satisfy their variable thermal comfort needs, uniform air distribution is less important, and variability is recommended. In single occupancy rooms, the occupant can be given full control of the ceiling for fulfilling different air speed demands at different times of the day or throughout the year, in this case ceiling fans can provide personal control. While in a particular area that has special thermal demands, ceiling fans can be pre-set/adjusted with stronger air movement or located only over the most demanding area so, by design, higher air speed target part of the space and lower air speed reaches its adjacencies.

Within a space, different types of fans can be integrated to maximize occupants’ comfort and to achieve multiple design intents. For example, ceiling fans can provide a uniformly low speed background air movement for all occupants in a large open space, while individual fan allow additional personal control to further improve occupants’ local thermal comfort at whenever it is necessary (e.g., at transient condition or near the window).

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There are multiple fan types available in the market, but ceiling fans outweigh their benefits over the other fan types in terms of air circulation effectiveness and low energy consumption, especially for serving multiple occupants within the same space. In addition, installation and operation of ceiling fans are specific to building design and different from other portable fan options. Therefore, this guide highlights a separate section for ceiling fans, while other fan choices (i.e., other air movement devices) will be clustered in another section.

Ceiling fan options

The following sections describe the different types of ceiling fans, and the features that differentiate ceiling fan models.

Fan types

A part of the "" from the US Department of Energy (DOE) defines a variety of ceiling fan types. This guide focuses on several of them defined below:

Standard ceiling fan: any ceiling fan with a diameter greater than 45 cm [18 in] but no more than 2.1 m [7 ft], and with the lowest point of the fan blades more than 25 cm [10 in] below the ceiling. A standard ceiling fan does not exceed the limits outlined in Table 1 below.

Large-diameter ceiling fan: any ceiling fan that is greater than 2.1 m [7 ft] in diameter. These are often also known as High Volume Low Speed (HVLS) fans.

Small-diameter ceiling fan: any ceiling fan that is more than 46 cm [18 in] in diameter but less than or equal to 2.1 m [7 ft] in diameter, and with an airflow of at least 0.87 m³/s [1840 CFM] and a rotational speed of more than 1.5 Hz [90 rpm] at its highest speed.

High-speed small-diameter ceiling fan: any small-diameter ceiling fan that has a blade thickness of less than 3.2 mm [12.6 in] at the edge or a maximum tip speed greater than the applicable limit specified in Table 1 below.

Low-speed small-diameter ceiling fan: any small-diameter ceiling fan that has a blade thickness greater than or equal to 3.2 mm [12.6 in] at the edge and a maximum tip speed less than or equal to the applicable limit specified in Table 1 below. (“Standard ceiling fans”, defined above, are a type of low-speed small-diameter ceiling fan).

Hugger ceiling fan: any low-speed small-diameter ceiling fan for which the lowest point on the fan blades is less than or equal to 25 cm [10 in] from the ceiling.

Very-small-diameter ceiling fan: any ceiling fan with one or more fan heads, each of which has a blade span of 46 cm [18 in] or less, and with an airflow of at least 0.87 m³/s [1840 CFM] and a rotational speed of more than 1.5 Hz [90 rpm] at its highest speed.

Highly decorative ceiling fan: any ceiling fan with a maximum rotational speed of 1.5 Hz [90 rpm] and less than 0.87 m³/s [1840 CFM] airflow at high speed

Note that while these DOE definitions include a variety of sub-categories for small-diameter fans, any fan larger than 2.1 m [7 ft] in diameter is simply a “large-diameter” fan, with no further differentiation.

Table 1. Ceiling Fan Blade and Tip Speed Criteria (Adapted from DOE Definitions).

The DOE also defines a variety of other specialty ceiling fan types (including belt-driven ceiling fans, centrifugal ceiling fans, multi-head ceiling fans, and oscillating ceiling fans), but those specialty types are not the subject of this guide. This guide primarily focusses on two main ceiling fan types, defined above as “standard ceiling fans” and “large-diameter ceiling fans”. However, much of the discussion in this guide will also be relevant to the other small-diameter ceiling fan types beyond the “standard” definition, and there is significant overlap between many of the small-diameter ceiling fan sub-categories. Note, for example, that “standard ceiling fans” are a type of low-speed small-diameter ceiling fan, and “hugger ceiling fans” are essentially equivalent to standard ceiling fans but with fan blades mounted closer to the ceiling (despite the negative effect on efficiency) for suitability in spaces with lower ceiling heights.

Though standard ceiling fans are more applied in residential applications, they are equally effective for comfort cooling in most non-residential applications (including offices, classrooms, gyms, hospitality, etc.) where they can be positioned near the occupants. Large-diameter ceiling fans require higher ceilings (typically at least 3.3 m [11 ft]) and larger spaces free from obstructions to accommodate their increased diameter. As a result, large-diameter ceiling fans are most often found in non-residential commercial and industrial applications.

Although the fan type definitions from the DOE focus on fan diameter, in the case of specific fan products there is some overlap in terms of applications and fan styles. Some large-diameter fans are available in styles that are more frequently associated with standard fans, and some manufacturers have HVLS fan models in diameters less than 2.1 m [7 ft]. Additionally, there are some large-diameter fans that have a relatively low maximum rotational speed and thus, meet blade tip speed and thickness requirements for mounting below 3 m [10 ft], though these also have a relatively low maximum airflow.

Blade type and blade number

Blade shape, number of blades, and blade pitch are important factors in increasing energy efficiency while maximizing airflow through the fan blades. There are two main types of blades shapes shown in Figure 8 below. Blade shapes have evolved over time from flat to airfoil-style blades to become more energy efficient and maximize air movement. As the name implies, flat ceiling fan blades are flat panels mounted at a fixed angle, whereas airfoil blades are like airplane wings in section. Like the cross-section of an aircraft wing, the curvature of the airfoil blades helps increase airflow through the ceiling fan, minimizing air turbulence at the trailing edge of the blade common to flat blades. Airfoil-style blades are thus typically more efficient and quieter than flat blades. However, flat blades are cheaper to manufacture. Note that flat blades will perform equally whether the fan is operating in the forwards (blowing down) or reverse (blowing upwards) direction. In contrast, airfoil blades will not operate as efficiently in reverse, and will typically have a lower airflow when doing so. Some fan models have blades that can be manually attached in inverted position or can mechanically invert the blade while it is attached to the fan, which allows for improved efficiency when operating in reverse.

The number of blades is an important factor in increasing airflow of ceiling fans. Nevertheless, the increased weight and drag due to the blades can cause a loss in energy efficiency. Standard fans typically have between 3 and 5 blades, though some models have as few as 2 blades or up to 6 blades. Large-diameter fans typically have 6 or 8 blades, with some models having as few as 3 blades.

Similarly, increasing the blade’s angle may also increase airflow at the cost of energy efficiency. Academic modeling studies have found the optimal blade angle to be 8-10 ° for residential fans. Manufacturers recommend 12-15 °. Some airfoil-style blades also vary the blade angle over the length of the fan blade, with steeper angles toward the center of the fan to maximize airflow for the low blade speed in this region and reducing to shallower angles toward the tips where the blade speed is high to limit drag and maximize energy efficiency.

Motor and drives

There are three main types of motors used in ceiling fans: AC induction, permanent magnet DC (PMDC), and brushless direct current (DC) motors. Generally, there are very large percentage efficiency savings when changing from AC to DC motors for small fans, and far less of an effect for large diameter fans. AC induction works with electromagnets outside the motor that creates a rotating magnetic field causing motor rotation through induction. The benefits are that it provides constant and even airflow and it is cheaper than DC motors. PMDC has magnets located on the motor creating a stationary magnetic field. A segmented commutator rotates within the magnetic field creating a mechanical switching of current direction. The benefit is being more energy efficient than AC motors and providing constant force over a wider range of speeds than AC motors. Brushless DC work with permanent magnets rotated in motor creating a rotating magnetic field. The current direction in the stator is switched in relation to the magnetic field to create rotation. This is the most energy efficient motor types (for small motors on small diameter fans, a DC motor often will use 70 % less energy than an AC motor), most quiet, and has a longer service life than PMDC motors, with the same benefit of enabling a wider range of air speed.

Fans may also be either direct drive or gear driven. Almost all small-diameter fans are direct drive, but large-diameter ceiling fans may either be direct-drive or gear-driven. Direct-drive fans are quieter than gear-driven fans, which have a more refined appearance, and reduced operating cost. However, direct-drive fans do provide less airflow and it may be harder to replace the motors. Due to this, direct-drive fans are typically used in situations where sound level and aesthetics are a concern, and less airflow is needed.

On the other hand, gear-driven fans allow for higher motor power and are often used in situations where maximizing airflow is a priority over sound levels or aesthetics. This is well suited for industrial settings where ceilings are high and there is little or no air conditioning.

Understanding ceiling fan metrics

Several factors determine a ceiling fan’s performance, as well as its suitability to a given application. Some of the most critical factors are described in the following sections.

Diameter and rotational speed

All other factors being equal, a larger diameter fan will produce greater airflow through the fan than a smaller diameter fan at the same rotational speed. Figure 10 shows a range of example fans of varying diameters and the range of possible airflows and rotational speeds at which those fans can operate. In general, higher airflow through the fan generally results in higher average air speeds in the space. Additionally, larger fan diameters increase the uniformity of air speeds throughout a space. Lastly, larger diameter fans increase the depth of the boundary layer of air moving along the floor in the spreading zone outside the fan blades. This figure also highlights the differences between fan models even if they have the same diameter. Comparing the Type G and Type F fans, of equal diameter (2.4 m [8 ft]), it shows the range of performance varies by fan type. The Type G fan has a higher maximum airflow, a lower minimum airflow, and a higher rotational speed for any particular airflow.

For any particular fan, airflow is linear with rotational speed, as Figure 10 also shows. Additionally, the air speed at any point in the space is also directly linear with fan rotational speed. So, if a point in the room measures 0.5 m/s [100 fpm] when the fan is rotating at 1.3 Hz [80 rpm], it will measure approximately 0.25 m/s [50 fpm] at 0.7 Hz [40 rpm]. This relationship begins to break down at very low air speed, very low rotational speeds, or where the fan blade height is unusually far from the floor (e.g., > 3 m [10 ft]).

Power and fan efficacy

Fans that can turn down to a low rotational speed and maintain good motor efficiency at that speed can operate very efficiently under those conditions. There are several fans in the market with an efficacy of over 0.47 m³/s·W [1000 CFM/W] at their lowest operating speed. Other fans typically have a relatively high minimum speed, and often also have poor motor efficiency at that speed, and these fans benefit less from speed reduction. Generally, the ability of a fan to operate efficiently at lower speed improves as the diameter increases, as Figure 12 demonstrates.

However, there is considerable variation in performance between models of fans with the same diameter, as Figure 13 shows. This also demonstrates that there is a wide range of turndown ratios (minimum speed divided by maximum speed) among different fan models at the same diameter. Some fans can operate at or below 20% of their maximum rotational speed, while others cannot run below 50% of their maximum rotational speed. This is also apparent in the MAEDbS data, as Figure 14 shows.

Airflow

Airflow direction

All fans sold in the USA are required to be reversible, and thus, fans can run in either direction – forwards, blowing downwards towards the floor, or in reverse, blowing upwards towards the ceiling. Many standard ceiling fans will have a switch on either the wall switch, remote control, or on the motor housing to change the direction between downwards and upwards. For some models this functionality will be provided in the control system or smartphone app. Most applications are for fans blowing downwards, as this is by far the most common and efficient way of creating air movement in the occupied space. Reversing a fan so that it blows upwards against the ceiling requires that the space containing the fan (or fans) is bounded by a ceiling and walls on all sides. This creates a similar recirculation cell as blowing the fan downwards, but it avoids creating a region of high air speeds directly under the fan. Running fans in reverse has the effect of creating a much lower, but much more uniform air speed distribution in the space, which can be desirable in some applications.

One application of running fans in reverse is to mix air the room when elevated air speed in the occupied zone is not desirable. One example is destratifying spaces in the heating season. Many fans have a relatively high minimum rotational speed and if these fans run in the downwards direction, the resulting air speeds may cause a draft on the occupants directly below the fan. This can be remedied by running the fan in reverse. Note here that there are also fans that have a very low minimum speed, allowing them to run forwards without creating a draft on the occupants, while still effectively de-stratifying the space. This uses less power to destratify than a fan with a higher minimum speed running in reverse. Another application of running fans in reverse is when elevated air speed in the region directly under the fan is perceived as excessive for some reason, such as causing paper to blow off a desk.

The ratio of airflow through a fan in the upwards vs. downwards direction depends on the fan type and associated blade geometry. Some fans have highly optimized blade designs that blow downwards efficiently. Here, the blade geometry is not symmetrical when the fan reverses direction, and these do not generate as much airflow at the same rotational speed and power when operated in reverse. Other fans, such as those with a less efficient but symmetrical blade geometry (e.g., flat blades) or those whose blades can be inverted and re-attached to the fan (making the blade geometry symmetrical in reverse), will generate approximately the same airflow operating in reverse.

For context, based on full scale laboratory testing the area weighted average air speed for seated and standing occupants with a fan blowing upwards ranged from 30 to 70% that of the same fan blowing downwards at the same speed in the same room. In cases where the blade geometry is symmetrical (flat blades, or inverted blades), the area weighted average air speed was approximately 60-70% that of the downwards case. Obstructions in the flow from the fan (e.g., furniture, ceiling obstructions, etc.) will likely have a significant effect on these percentages.

Fan air speed

The fan air speed is calculated by dividing the rated airflow of the fan by its diameter. It represents the average air speed that passes through the circle swept by the fan blades. Thus, as with rated airflow, fan air speed varies linearly with fan rotational speed, in other words the airflow rate of a ceiling fan can be scaled (up or down) by its rotational speed. Fan air speed is a useful metric as it is more directly representative of the air speeds that will occur in the space. For example, the maximum air speed at any location and height in the room will typically be within 1.3 to 1.5 times the fan air speed, and it will occur below the fan blade tip, slightly inside the fan blade diameter. That applies regardless of fan diameter. Unlike fan rotational speed, airflow, or power consumption, the concept of fan air speed is also very useful as it allows designers to directly compare fans with different diameters to one other. Figure 16 presents an example from MAEDbs that fans with higher maximum fan air speeds will yield higher maximum air speeds in the room regardless of fan diameter. By using the fan air speed as a metric instead of the rated airflow (see Figure 15), one can directly compare fans to each other even if the diameter differs substantially. This is useful in cases when the design target is the maximum air speed directly underneath the fan.

Levels of speed control

Most standard fans typically have several fixed fan speed levels. Though some of these fans have a wide range of speed levels (6 or more), most fans have just 3 (see Figure 17). These are typically standard fans with AC motors, whereas DC motor fans tend to have more speed levels. Large diameter fans are typically variable speed regardless of motor type.

The minimum rotational speed on fans with just 3 speed levels is typically still quite high, and often the minimum speed may generate 0.75 m/s [150 fpm] seated average directly under the fan, equivalent to over 2.8 °C [5 °F] cooling effect. Having a high minimum speed can be problematic in some applications, such where there are occupants located directly under the fans for extended periods of time (e.g., an office) or when the fan is used to destratify a space in heating mode. The reason is that the minimum speed may generate too much of a cooling effect for the occupants when temperatures are mild or cool, and they cannot reduce the speed further without switching the fan off. In contrast, a high minimum speed is less of a concern in transiently occupied spaces, spaces where occupants can move freely around. Overall, in most applications, it is desirable to have more levels of speed control, particularly a minimum level that is slow enough that it generates low air speeds directly under the fan. A reasonable approximation is that the minimum fan air speed should be below 0.4 m/s [80 fpm], or a 1.7 °C [3 °F] cooling effect at the minimum allowed blade height, depending on the specifics of the application.

Uniformity of air speeds

The amount of variation of the air speeds in a space is an important design consideration. Figure 18 below shows the measured air speeds in a cross section through a 5.5 x 5.5 m [18 x 18 ft] room with a 1.5 m [5 ft] diameter ceiling fan located at the center of the room. The airflow ‘jet’ from the fan immediately narrows to a slightly smaller diameter than the fan blades. The jet then impinges on the floor, creating a stagnation point, and then spreads radially outwards along the floor. Smaller diameter fans have a relatively shallow spreading zone. For the case shown below, the air speed in the spreading zone is still high along the floor at a distance of one fan diameter from the fan center. However, the air speeds are almost unaffected by the fan at a height of 0.5 to 0.7 m at the same location. In contrast, larger diameter fans have a deeper spreading zone. For fans at or above 3m [10 ft] in diameter, the height of the spreading zone at a distance of one fan diameter from the fan center is approximately the height of an average person. However, large diameter fans have lower air speeds directly under the fan center, near the stagnation point. As Figure 19 shows, the larger the ratio of fan diameter to room size is, the more uniform the distribution of air speeds will be in the room.

IP rating, damp rated, and wet rated

For a motor, drive, and controller combination, it may be useful to check the IP (Ingress Protection) Rating of the fan defined by IEC Standard 60529. The IP rating describes how well an electrical enclosure keeps water and solids out. A direct drive or gear-driven fan with a higher IP rating means that the fan is suited to running in harsh environments or conditions, which may be required for the application under consideration.

Similarly, any ceiling fans in outdoor applications must be rated for outdoor use. UL (Underwriters Laboratories) provides “Damp Location” and “Wet Location” ratings for electrical products such as lighting and ceiling fans. Damp rated ceiling fans can be installed in covered locations where they may be exposed to moisture but cannot be directly exposed to water such as rain or a hose. Wet rated ceiling fans can be directly exposed to rain or washed down with a hose.

Controls

Controls for ceiling fans run the gamut from basic manual on-off and speed controls, to fully automated onboard controls that are also integrated with the building automation system. In any scenario the design and specification of ceiling fans must address a variety of controls considerations. Will the fans be fully manual or automated? Will occupants have control over the fans, and if so how and where? If the fans are automatically controlled, what will the setpoints or triggers be? How much variation in fan speed is necessary for the application? How will ceiling fan controls interface with the HVAC system? These questions must all be considered when planning controls for ceiling fans.

Control needs and priorities will vary from application to application. The following sections provide guidance through the most common decisions related to controls when designing and specifying ceiling fans.

User interface

One of the most important control considerations for implementing ceiling fans is how the occupants will control the fans. Typical user interface options are listed below. Note that it is common for ceiling fan installations to combine several of the control types listed below in a single application.

Pull chain: adjust a fan’s speed or light level by pull chain located on the fan. Typically, each fan will have two chains, one for the light, and one to turn the fan on or off and adjust the fan speed, typically through just 3 speed levels. Typically, only used in residential applications.

Wired wall control: slide controls or knobs on the wall connecting to wiring in order to control fan speed and light levels. Wall controls may be preferable for fans with greater fan speed variability or dimmable lighting.

Wireless IR remote control or detachable wall control: wall control or remotes tuned to create a frequency combination enabling wireless control of fan speed and light levels. Like wired wall controls, wireless controls can support greater fan speed variability and dimmable lighting. Wireless controls eliminate the need for hardwired connections, which can be costly in retrofit scenarios, but they also typically use batteries that will need to replace regularly, and if detachable, they can be lost or misplaced.

Wi-Fi or Bluetooth Connectivity via Phone App or Internet: some fans have smartphone apps or web interfaces that use Bluetooth or Wi-Fi networks to control fan speed, light levels, and other settings. This may be especially advantageous for controlling multiple fans in a space or throughout a building but may be less ideal for spaces where multiple people will need access to fan controls. Additionally, note that many fan models can be retrofit with a controller that adds Wi-Fi or Bluetooth control capabilities.

Building automation system interface: some fans may also be controlled through building automation system interface. This approach may be ideal for applications where access to fan control needs to be limited to building management and maintenance staff, such as assembly and hospitality spaces.

Figure 20 demonstrates some examples of wall mounted control for ceiling fan that are not particularly clear to the user. For example, the controls are not labelled as controlling the ceiling fan and as such are indistinguishable from a dimmable light switch in many cases. It is important to ensure that wall mounted fan controls are clearly visible to the occupant(s), located near the fan they control and near the thermostat in the room, intuitive (e.g., levels increase vertically from off to maximum speed), and clearly differentiated from other controls, like lighting controls.

Types of control automation

In addition to the user control interfaces listed above, there are a range of options and strategies for ceiling fan control automation. Listed below are some automation strategies that can be implemented for ceiling fans. As with control interfaces, many of these automation strategies can be used in combination. However, the automation options available for any given application will sometimes depend on the capabilities of the chosen ceiling fan model.

The simplest is the manual control option, where there is no automation and fan control is fully manual based on occupant inputs. The schedule option allows to set when the fans are operating, typically at a fixed speed. For example, if a room is generally only used during weekday business hours, a schedule could be set to automatically turn on each weekday morning and turn off at night. Automation based on occupancy option ensures that a fan only operates when the space is occupied. The fans only provide a cooling sensation if an occupant is there to feel it. This control option can be applied in different ways: by a wall switch “vacancy” or “occupancy” sensing; by integration with building automation system (BAS) occupancy sensors (e.g., via power relay, 0-10 V input or BACnet interface to fan); or on-board occupancy sensor (available in some products). Another option is temperature sensing, which allows fans to be programmed to turn on at certain temperature thresholds, and increase speed with temperature, automating the thermal comfort control in a similar manner to a thermostat for a traditional HVAC system. This option can be applied when manufacturer provided wall controller with built in temperature sensor (or remote temperature probe); by integration with building automation system (BAS) occupancy sensors (e.g., via power relay, 0-10 V input or BACnet interface to fan); or on-board occupancy sensor (available in some products). Learning behaviors and/or preference controls can also be used when ceiling fans are equipped with programming that learns user preferences over time. For example, if a user frequently turns off the fan when the room temperature drops to 23 °C [73 °F] the fan will “learn” this user preference and start to automatically turn off at that temperature.

Additional considerations for choosing a control type

There is amperage restriction to a wall control unit which limits the number of ceiling fans that can be controlled together at once. For example, a wall control unit with an amperage of 5 amps could only control at most 5 fans at once if the load of one fan is about 1 A. In general, the number of fans that may be in a space at once is limited by the National Electric Code standards. The standard mandates that a circuit breaker does not carry more than 80% of its rated current. This means that for a standard circuit breaker with 15-20 A, the circuit breaker will only allow about 12 fans (80 % of 15). To allow for more fans to be controlled at once, fans are often daisy-chained together. When fans are daisy-chained, a control device controls one master fan, and the rest of the fans are controlled by the master fan by a variable-frequency drive.

When using wireless wall controls or remote controls, each fan that is controlled must have a receiver. Additionally, for each new fan desired to be controlled simultaneously with the existing fans, a new receiver must be purchased. The frequency settings must then be reset for the receiver and remote control to match.

Ceiling fan costs

Like many building products, ceiling fan costs can vary widely depending on size, material, motor type, and other characteristics. Standard ceiling fans can range from less than US$100 for basic off-the-shelf models to over US$1,000 for more specialized fans with more decorative features, higher quality materials, and/or automated onboard control systems. In general, fans with DC motors tend to be more expensive than fans with AC motors, but DC motors also tend to be more energy efficient, quieter, and more durable than AC motor fans due to better bearings and build quality. A wide range of high quality, efficient standard fans with DC motors are currently available from US$400 upwards. Large-diameter ceiling fans start at approximately US$3,000 and increase in cost with fan diameter and performance characteristics. There is relatively little difference in performance between DC and AC motors for the larger motor sizes associated with large-diameter fans.

Installation costs can vary widely depending on the fan (assembly time, weight and diameter), the space conditions, and whether the installation is a new construction or a retrofit. Very approximately, it can take a professional anywhere from 30 minutes to 3 hours to assemble and install a single ceiling fan depending on the selected model and site conditions. On the low end of that estimate, the time required to install a ceiling fan is simply the labor cost to assemble the ceiling fan and connect it to an existing junction box. On the other hand, a variety of factors can make ceiling fan installations more complicated, and therefore more expensive. The need for additional structural bracing in spaces with suspended ceilings, the need for additional people to handle and install larger fan models, running new wiring for power and controls in retrofit scenarios, and the need for mechanical lifts for installations in spaces with high ceilings are just a few of the factors that can add complication and cost for ceiling fan installations. In retrofit scenarios, if there is already an electrical box in place, installation costs may be minimal, but if new wiring and junction boxes are needed, the installation is likely to be more complicated and more costly. The variations in installation costs also consider external factors beyond the fan installation, such as long travel times to the demonstration sites (several hours each way), and the size and efficiencies of each of the installation projects (e.g., larger jobs had lower average per fan costs since external factors are averaged over a larger number of fans).

Environmental conditions

ASHRAE Standard 55 (2020)

specify the combinations of indoor thermal environmental factors and personal factors that will produce satisfactory thermal environmental conditions for a majority of the occupants within the space. The ASHRAE 55 is applicable worldwide and incorporated in other countries standards (e.g., the )

ASHRAE 55 (2020) outlines methods to determine satisfactory thermal conditions. The analytical comfort zone method predicts the thermal sensation mean vote (PMV) of a representative occupant based on the six factors indicated in the previous section (Factors of thermal comfort). is an index that predicts the average vote of thermal sensation on a scale from –3 (cold) to +3 (hot), where a score of 0 would be considered neutral condition, not too cool nor too warm. The standard defines the interval between –0.5 and +0.5 PMV as required condition to achieve thermal comfort. This model is applicable for air speed up to 0.2 m/s [40 fpm]. For higher air speed the Elevated Air Speed Comfort Zone Method should be applied. This method uses the same six factors and is defined based on the same comfortable interval of ± 0.5 PMV. However, the thermal conditions are calculated based on the Standard Effective Temperature (SET) index which is more reliable for considering the heat loss effect of increased air speed. ASHRAE 55 (2020) also includes the Adaptive Model, which is applicable for natural conditioned spaces where occupants can open and close external openings and can adjust their clothes (e.g., take of a jacket). This model considers the increment of air speed can offset the maximum temperature limits in a space.

ASHRAE 55 (2020) presents a Design Thermal Environmental Control Classification that ranks spaces with more control options in a higher level for occupant comfort. This captures the beneficial effects of increased opportunities for local and group level control of thermal comfort as indicated in Table 5. The standard also determines desk fans should have to be capable of providing air speed at the occupant’s head/face/upper body within range of 0.36 to 0.8 m/s [71 to 160 fpm].

Table 5. ASHRAE 55-2020 Comfort control classification levels (CCCLs)

Green Mark Scheme - Singapore

Green Mark is a green building certification scheme established by the Building and Construction Authority (BCA) tailored for tropical climate aiming to raise standards in energy performance and emphasis on other sustainability outcomes. Singapore is located in the Tropics with a yearly average outdoor air temperature around 30 °C [86 °F], which indicates a great potential for application of increased air movement.

In section, strategy of hybrid cooling system (i.e., increasing temperature setpoint in HVAC system with provision of elevated air speed by ceiling fans and/or individual fans) is highlighted to enhance thermal comfort in air-conditioned non-residential buildings. Thermal comfort can be achieved by controlling the temperature of conditioned air and by adjusting air speed via fans. The allows for the use of elevated temperatures in a Hybrid cooling system, with increased air speed to meet thermal comfort criteria (-0.5 < PMV < 0.5, and/or PPD < 10 %) through ASHRAE Standard 55, ISO 7730, or EN 15251 (substituted by EN 16798) methodologies. This setpoint temperature operates in the fan-integrate AC system is higher than the setpoint recommended in the , i.e., room temperature should be maintained within 23-25 °C [73-77 °F], for conventional air-conditioning (without fan) settings, meaning that energy saving through increased temperature setpoint in the HVAC system is achievable.

Ceiling fans testing regulations

Small-diameter fans: Method for ENERGY STAR qualified ceiling fans

Large-diameter fans: AMCA Standard 230

A major consideration in using the DOE metric is when the fan operates at a very low speed. Power consumption is proportional to the cube of flow rate. Therefore, slowing down a fan would reduce the input power and airflow, but the reduction in input power is higher than airflow. Low airflow fans with inefficient motors can still achieve high DOE metric values. Conversely, high airflow fans (at the same diameter), even equipped with more efficient motors, are more difficult to comply with the DOE metric.

Large-diameter fans: Ceiling Fan Energy Index (CFEI)

The reference fan is a conceptual fan that relates all fans to a common baseline, producing the airflow and fan pressure required at a specified electrical input power. According to the standard, large-diameter ceiling fans should have a CFEI greater than or equal to: (a) 1.00 at high (i.e., 100 %) fan speed and (b) 1.31 at 40 % of fan speed.

ASHRAE Standard 216

This standard provides a consistent industry-standard practice for determining ceiling fan performance characteristics. Manufacturers can use Standard 216 test procedures to test their products and provide standardized performance data for use in specification and simulation of fan performance. Standard 216 test procedures should also be used for any full-scale fan test mock-ups. In conjunction with the Design Thermal Environmental Control Classification of ASHRAE Standard 55, this standard supports the implementation of ceiling fans as an option for thermal comfort control in buildings.

IEC 60879:2019

Fire safety and installation

Fire code requirements

The primary concern with ceiling fans in relation to the fire code is the interaction with fire sprinklers. For the most part, standard ceiling fans in typical residential and non-residential applications have few limitations in relation to fire sprinklers, while large-diameter ceiling fans require a higher degree of integration with fire suppression systems.

Per NFPA 13, for ceiling fans less than 1.5 m [60 in] in diameter where the blades are less than 50 % of the swept area in plan view, fire sprinklers can be located without regard to the fan blades (Ref: NFPA 13 2016 sections 8.6.5.2.1.10, 8.7.5.2.1.6, 8.8.5.2.1.9, 8.9.5.2.1.6; NFPA 13 2019 sections 10.2.7.2.1.10, 11.2.5.2.1.9, 12.1.10.2.1.9). Since the above requirement specifically calls out “fan blades,” there may be cases where other parts of the ceiling fan, such as motor housing or mounting pendants (or fan blades that are less than 50% open in plan view), are considered obstructions to fire sprinklers. In most cases, for any motor housing, mounting pendant, or other part of the fan that is 46 cm [18 in] or less below the level of the sprinkler deflector, the so-called “rule of three” applies, where sprinklers must be placed away from the obstruction a minimum distance of three times the maximum dimension of the obstruction, up to 61 cm [24 in] (Ref: NFPA 13 2016 section 8.6.5.2.1.3; NFPA 13 2019 section 10.2.7.2.1.3). In other words, if the motor housing of a ceiling fan is 18 cm [7 in] in diameter, any fire sprinklers should be located at least 53 cm [21 in] from the motor housing. In the 2019 version of NFPA 13, for extended coverage sprinklers and residential sprinklers, this requirement is increased to a distance of four times the maximum dimension of the obstruction, up to 91 cm [36 in] (Ref: NFPA 13 2019 sections 11.2.5.2.1.3 and 12.1.10.2.1.3).

NFPA 13R requirements are more explicit about sprinkler locations in relation to obstructions such as ceiling fans. In these cases, the standards require pendant sprinklers to be a minimum of 1 m [3 ft] from any ceiling fan (Ref: NFPA 13R 2016 and 2019 section 6.4.6.3.4.1), and sidewall sprinklers to be at least 1.5 m [5 ft] from any ceiling fan (Ref: NFPA 13R 2016 and 2019 section 6.4.6.3.5.1). Though the standards do not explicitly state where those distances are measured from, this is typically interpreted as being the distance from the center point of the ceiling fan.

For larger format fans, NFPA 13 lays out more detailed requirements: (1) Fans must be no more than 7 m [24 ft] in diameter; (2) Each fan must be approximately centered between four adjacent sprinklers; (3) The vertical distance from fan blade to sprinkler deflector must be at least 1 m [3 ft]; and (iv) All fans must be interlocked to shut down immediately upon receiving a waterflow signal from the alarm system in accordance with the requirements of NFPA 72.

The California Fire Codes also specify that smoke alarms and smoke detectors shall not be installed withing a 36-inch (91 cm) horizontal path from the tip of the bade of a ceiling-suspended (paddle) fan unless the room configuration restricts meeting this requirement (907.2.11.8)

While this section covers requirements as they apply in the California Fire Code, adapted from NFPA Standards, specific requirements may vary by local jurisdiction. Always consult local codes for requirements for a specific project.

Seismic requirements

In many applications, standard ceiling fans attached directly to a structural ceiling do not require any further seismic bracing or restraint. However, applications with large-diameter ceiling fans, suspended ceilings, long suspension rods, or other special conditions may require additional seismic support.

Energy information label for ceiling fan

The Energy Protection Act (EPA) requires any ceiling fan to be tested in approved laboratory before it can be sold in the United States. The airflow and corresponding wattage at different operating speeds of the ceiling fan will be tested. Thereafter, the fan will be given an airflow rating (cubic feet per min), electricity use rating (watt, excludes lights), and an airflow efficiency rating (cubic feet per minute per watt). All the numbers will be printed on an energy Information label outside the fan packaging. This label helps the fan buyers to clarify the efficiency of fan products and to compare their needs between fan types.

Most studies of ceiling fans have been performed in laboratories, but there are some studies performed in buildings. We discuss them in this section to provide useful information about the application of fans in realistic conditions.

Air speed measurement in 4 commercial buildings in California

Background

This study conducted a detailed assessment of air speed performance by ceiling fans in 4 commercial buildings in California. Different ceiling fan operation modes such as fan rotational speed, operating direction, and the number of operating fans were considered; aiming to demonstrate the magnitude and distribution of air speed, cooling effects, and any potential influencing factors in commercial building settings. Detailed of this field study is available in this paper ().

Study methods

Field measurements of air speed were conducted in 4 commercial buildings installed with ceiling fans between May 2018 and March 2020. Table S1 summarizes the buildings and ceiling fans characteristics tested in this study. In each site, air speed from ceiling fans was measured with different operation modes, including airflow directions (upward and downward), fan speed levels (high, medium, and off), and the number of operating fans at the same time. Air speed was measured typically at occupied locations with four heights from floor level (i.e., 0.1 m, 0.6 m, 1.1 m, and 1.7 m [0.3, 2, 3.6 and 5.6 ft]). The cooling effect provided by the ceiling fan was estimated.

Table S1. Tested buildings and ceiling fans information.

Air speed distribution overview

The height averaged air speed superimposed on floor plans with the ceiling fan layout and furniture in the 4 buildings (see Figure S1). In general, higher air speeds were found under or near the downward operating ceiling fan and decreased proportionally to the distance from the fans. Potential factors that vary the air speed are fan diameter, number of fans in operation, distance from ceiling fan centers, fan rotational speed, and fan operation direction.

Flow direction, rotational speed, and fan number

Figure S2 demonstrates the air speed performance under different test conditions. Ceiling fans operating in the downward direction produced higher mean air speeds (0.2-1.8 m/s [40-350 fpm]) than the upward direction (0.2-0.5 m/s [40-100 fpm]). However, a more uniform airflow within the occupied zone was found when fans are blowing upwards (i.e., smaller variation in air speed distribution). The variation of air speeds is mainly influenced by measurement height. Generally, fans operating downwards create negative vertical gradients (i.e., air speed the fastest at ankle height and the slowest at head height), while a positive gradient is observed directly under the fan. In contrast, upwards operating fans provide higher air speed at the head height of occupant than at the ankle level, but a negative gradient is observed in the return air path (e.g., near walls or at the confluence of airflows with multiple fans). Priority should be given to downward blowing fans if the thermal comfort design requirements are to maximize cooling efficiency in space, or to minimize energy consumption. Conversely, upward blowing fans allow better airflow uniformity across vertical and horizontal dimensions. In addition, designers should pay attention to the fan blade design (with symmetrical blade geometry or inverted installation fan) if the fans are intended to operate upward in the design stage.

As described earlier in this guide, air speed generated by ceiling fan increases linearly with the fan rotational speed. The field measurement also confirmed higher mean air speed in all sites when ceiling fans are operating at higher speed. In addition, when ceiling fans were rotating at higher speed, the resulting air speed was found dispersed in wider range, meaning that a larger air speed gradient was created regardless of airflow direction.

The SC and FC buildings allow air speed measurement with reduced number of fans in operation. Results showed the mean air speed is positively proportional to the square root of the number of operating ceiling fans. For the SC building, the mean air speed dropped by 32 % when reducing 4 fans to 2 fans. For the FC buildings, the mean air speed decreased by 15-25 % and 23-46 % when reducing 26 ceiling fans to 14 and 9 fans respectively.

Cooling effect

Cooling effect is the temperature reduction (in °C or °F) perceived by the occupant with elevated air speed compared to the condition without air movement under the same temperature. Figure S3 summarizes the magnitude of cooling effect for each testing condition and building. At the same rotational speed, the cooling effect with upward flow (1-2 °C [2-4 °F]) was lower than the downward flow condition (2-4 °C [4-7 °F]), resulting in a 19-76 % reduction, especially with increased number of operating ceiling fans within the space. The uniformity of the cooling effect depends on the layout and number of the operating fans. The highest cooling effect was found under the operating fans and generally reduced as the distance from the fan increased. These are important findings since one ultimate function of ceiling fan is to offset the thermal sensation of increasing the cooling setpoint temperature in air-conditioned space.

Multiple fan interaction

The room’s air speed magnitude and its distribution are affected by multiple ceiling fans operated simultaneously. Figure S4 shows the air speed contours when three fans were arranged linearly (left) or diagonally (right) with the same space. The three grey lines represent the air speed measurement horizontally every 0.2 m [0.6 ft] and vertically at 0.1, 0.6, 1.1, and 1.7 m [0.3, 2, 3.6, 5.6 ft] distance. For each fan arrangement (i.e., linear or diagonal), the average air speeds among the three sections and the percentage of low (< 0.3 m/s [60 fpm]), medium (0.3 - 1.2 m/s [60 - 240 fpm]), and high (> 1.2 m/s [240 fpm]) air speed is presented. The results suggest multiple fans operated at diagonal layout could provide higher average air speed (0.54 m/s [105 fpm]) and higher percentage of medium air speed (72.3 %), resulting in more uniformity of air speed than fans arranged at linear layout.

Effects of furniture

Furniture is an important aspect for elevated air speed by ceiling fans design in real buildings. Lower average air speed was found at on-site measurement when compared to the simulated air speed profile using the CBE Ceiling Fan Design Tool for similar fans and room configuration setting. It suggested that presence of furniture in space would impede the air movement path in real buildings, leading to overestimation of air speed in the simulation model. An increased percentage of furniture in space would reduce the actual air speed performance, leading to larger differences between the predicted and measured air speeds. In addition, furniture also affects the vertical profile of air speed. Figure S5 compares the on-site average air speed with and without tables at four measurement height. It showed the presence of tables blocked downward-moving air from the ceiling fan, resulting in faster air speed (0.05 - 0.1 m/s [10 - 20 fpm) above table level, but lower air speed (0.24 m/s reduction [47 fpm]) at ankle height.

Insights from this study

This study demonstrates on-site air speed measurement results in four buildings. The results are helpful for building practitioners to plan for existing and future building design staging with ceiling fans. Some important highlights include: (i) downward airflow fans setting is prioritized with higher air speed and cooling effect in space, but upward flow setting could provide better air speed uniformity; (ii) evenly-placed fans layout is beneficial for the magnitude and uniformity of air speeds in space; and (iii) presence of furniture would impede the air speed distribution by fan, resulting in lower actual air speed on-site when compared to the predicted air speed profile using simulation tool.

Commercial building in Singapore

Background

Study methods

The study lasted for 6 weeks from May – July 2016. It examines occupants’ perception to the environment and corresponding energy consumption in HVAC system under three conditions: (i) typical air-conditioning settings at 23 °C [73 °F] without fan, (ii) increased cooling temperature setpoint to 26 °C [79 °F] with elevated air movement by fans, and (iii) repeated condition (ii) but increased temperature to 27 °C [81 °F]. Occupants were able to adjust the ceiling fan speed freely anytime in condition (ii) and (iii). Air temperature and humidity data were recorded for both indoor and outdoor conditions. HVAC energy consumption through fan coil units and the ceiling fans was captured for 16 days throughout the study period. For the condition at 27 °C [81 °F], the fan coil units were turned off to achieve the target indoor temperature.

Subjective survey was conducted to characterize occupants’ thermal comfort (thermal sensation, acceptability, and preference), air movement (acceptability and preference), and self-reported well-being (i.e., concentration ability, level of sleepiness, and perceived productivity).

Thermal acceptability and preference

Figure S7 summarizes the survey results on subjects’ thermal acceptability and thermal preference. Highest thermal acceptability (91 %) was reported when the cooling temperature setpoint was at 26 °C [79 °F] and ceiling fan were in operation. This was the only condition that met the requirements of ASHRAE 55 for widely accepted indoor environmental conditions (i.e., acceptability >80 %). Further increasing the cooling temperature setpoint to 27 °C [81 °F] with air conditioning turned off reduced thermal acceptability to 77 %, but this acceptability rate was still found higher than the conventional HVAC setting (at 23 °C [73 °F] without fan) in Singapore (which generated 58 % acceptance).

A total of 78 % of occupants preferred “no change” in thermal conditions, implying they were considered adequate at 26 °C [79 °F] with fans control. In conventional air-conditioned settings, i.e., 23 °C [73 °F] without fans, 63 % of the respondents preferred a “warmer” working environment. This indicates conventional air conditioning setting could generate overcooling, as higher thermal unacceptability rate was found when compared to other conditions with ceiling fans. When air conditioning was turned off at 27 °C [81 °F] indoor temperature, 54 % of the occupants preferred a “cooler” environment even when ceiling fans were in operation, showing a performance limitation, which means temperatures above 26 °C would decrease occupants’ comfort.

Self-reported well-being

Figure S8 plots the occupant’s self-reported level of sleepiness, concentration, and work productivity, for the 3 tested thermal conditions. In general, participants reported relatively alert, easy to concentrate, and high in productivity in all conditions. Statistically, the median of most cases was significantly different (p < 0.05), but the effect of all these differences is negligible. It means that increasing room temperature and air movement in workspace will not bring any observable downside to subject’s alertness, level of concentration, and productivity when compared to conventional air conditioning office operating at cooler temperature setpoint without fan.

HVAC energy usage

Table S2 presents the recorded daily electrical energy usage for the fan coil units and the ceiling fans. Time-averaged total daily energy consumption (for the fan coils and ceiling fans when included) at 23 °C [73 °F] without ceiling fan and at 26 °C [79 °F] with ceiling fans were 34.5 kWh and 23.6 KWh respectively. This means increasing the cooling temperature setpoint by 3 °C [5 °F] with ceiling fans available, approximately saved 32 % of energy in the HVAC system. In addition, it is highlighted that the energy use for operating the ceiling fans consumed less than 1 % of the total energy consumption. Turning off the air conditioning system, and fully depending on the elevated air speed from ceiling fan for cooling did not substantially increase the ceiling fans energy consumption (~ 0.16 kWh).

Table S2 Daily consumption of electrical energy during the field study

Insights from this study

This field study shows an example of a real workspace in tropical climate region that with ceiling fan operating with air conditioning system. The study proved that increasing the setpoint temperature from 23 °C [73 °F] to 26 °C [79 °F] and including ceiling fans operation not only resulted in substantial HVAC energy saving, but also enhanced occupants’ thermal comfort. In addition, it showed employee’s alertness, concentration and work productivity were not hindered by the increase of cooling setpoint temperature, nor the air movement in working environment. More importantly, this study was conducted in Singapore with yearly round hot and humid climate, which implies this intervention (AC + Fan) can satisfy occupants’ comfort even in tropical climate region, been applicable to all other climate conditions.

Commercial and residential buildings in California

Background

Study methods

The study was mainly composed of three stages: baseline, retrofit, and intervention. The baseline period lasted one year from Jul 2017 – June 2018. During this period, the indoor and outdoor temperature, relative humidity, lighting, and the current draw from the air-conditioning system (compressors and fan coils) were recorded in the target buildings. Also, on-site occupants’ thermal comfort responses were surveyed. During the retrofit period, June – July 2018, 99 automated ceiling fans were installed in each of the selected buildings. Thereafter, in the intervention period, from July 2018 – October 2019, the target buildings were operated with both automated ceiling fans and the HVAC system. In the intervention period, the same physical measurement (both environmental parameters and energy consumption with ceiling fans) and subjective survey conducted in the baseline period were repeated. Figure S9 indicates the field study timeline.

The automated ceiling fans installed in this study were all integrated with brushless direct current motor, with power consumption ranging from 2 to 53 W depending on fan size. The installed fans operate automatically based on infrared sensors on the fan hub detecting temperature and occupancy. Also, the fans were configured to operate when spaces were occupied or reaching above the adjustable temperature setpoint at 23.3 °C [74 °F]. The fan speed increased with temperature up to an adjustable maximum automatic level, then the air conditioning turned on to cool the space. Figure S9 visualizes the control strategy. At all times, occupants could manually override the fan control using handheld remotes or smartphone apps.

Indoor / Outdoor temperature

Figure S10 shows an increased indoor temperature during the intervention (AC + fans) compared to the baseline period (AC only) period by an average of 1.9 °C [3.4 °F] across all sites and all hours. Assuming ‘still air’ conditions during the baseline period (air speeds < 0.05 m/s [10 fpm]), and air speeds up to 0.5 m/s [100 fpm] in the intervention period, the respective comfort temperature ranges estimated from ASHRAE Standard 55 in typical office conditions are 22.2 - 25.6 °C [72 - 78 °F] and 22.2 - 28.3 °C [72 - 83 °F]. For the baseline period, 46 % of the hours from all sites (including unoccupied hours) were within the comfort temperature range, while 84 % of the hours in the intervention period with ceiling fans were within the comfort temperature range. This result suggests that occupants could be more comfortable in conditions where ceiling fans are operating together with air conditioning at a higher cooling setpoint.

Subjects’ responses to thermal comfort

To verify the occupants’ actual thermal comfort perception, subjective surveys were conducted in one out of the four sites before and after the installation of ceiling fans. Subjects responded to the thermal comfort question in a 5-point Likert scale: Too warm, comfortably warm, comfortable, comfortably cool, and too cool. Any responses given to the middle three scales are considered comfortable. The results in Figure S11 suggest 82 % of the occupants found themselves comfortable at 22 °C (72 °F) indoor temperature with air conditioning. The percentage of comfortable occupants increased to 93 % in the intervention period where air conditioning was operating at 26 °C [79 °F] setpoint temperature together with ceiling fans. This result gives evidence that the intervention could enhance subjects’ thermal comfort compared to the condition operated only with air conditioning.

HVAC power consumption

Figure S12 summarizes the recorded power consumption for the compressor from HVAC system and for the ceiling fans in all sites. The measured power is normalized by floor area to allow the proper comparison of the energy savings. The normalized mean compressor power consumption for the intervention (AC + fans) is 1.8 W/m² [0.6 Btu/h·ft²], which demonstrated 36 % energy saving during the cooling season (April – October) when compared to baseline conditions (2.8 W/m² [0.9 Btu/h·ft²]. During the warmer months, June – September, the overall energy savings between at 4 – 9pm increased to 41 %.

Ceiling fans were frequently operated during occupancy periods in most zones, resulting in an average operation during 81% and 45% of occupied hours in commercial and residential zones respectively. When averaging across all zones and hours, the normalized mean ceiling fan power was 0.04 W/m² [0.01 Btu/h·ft²], equivalent to only 2 % of the compressor power consumption during the same period. These results reveal two important findings: (i) in practice, huge energy saving potential can be achieved with ceiling fans operating with air conditioning compared to a condition with air conditioning operating alone; and (ii) ceiling fans energy consumption is negligible compared to the energy used in HVAC compressor.

Meanwhile, detailed field study data suggested that the energy saving potential between intervention and baseline condition could be affected by changes in occupancy frequency and duration. Lower energy saving potential is especially found in residential and irregular occupancy commercial buildings. The regularly occupied commercial spaces that maintained comparable staffing and working hours were less affected by this source of variation.

Insights from this study

This field study demonstrated substantial energy saving potential and improved occupant comfort by the implementation of air movement and air conditioning. Through this field work, we learnt that energy savings and cost effectiveness can be maximized by targeting zones with high cooling demand. Cost can be reduced when this intervention is implemented to new construction at design stage as opposed to retrofit project.

In commercial buildings, the design tip is to ensure air conditioning cooling setpoint remains above fan cooling setpoint by introducing interlock for this control. In residential buildings, especially in bedrooms, the motion-based or infrared-based occupancy sensors in automated ceiling fans may not function properly when occupants are sleeping with blankets.

Zero Energy Building (ZEB) Plus in Singapore

Background

This is a detailed study on cooperating ceiling fans, desk fans, and air conditioning systems in the Zero Energy Building (ZEB) Plus office at the Building and Construction Authority (BCA) in Singapore for thermal satisfaction improvement and cooling energy reduction (see Figure S13). The BCA ZEB Plus is a Green Mark Platinum certified office building renovated in 2019. It is a living laboratory demonstration of an energy-efficient building design and technology solutions in the tropics.

Study methods

Before the retrofit, the first floor of this building was a gallery exhibition using a conventional air-conditioning system. The retrofitted office is approximately 675 m² that can accommodate 51 occupants, integrating multiple energy-efficient technologies such as high-efficient lighting control, smart power management, and especially fan-integrated AC system. Fans, desks and HVAC ducts layout is shown in Figure S14. The ceiling fans provide the base air movement to satisfy most of the occupants, while personal desk fans are available for each occupant to maximize workstation micro-environment control.

The study was conducted in 3 phases. In phase 1, we set a temperature setpoint at 26 °C [79 °F] and increase air movement using ceiling and desk fans for 4 weeks to allow the occupants to adapt to the new indoor temperature setting. In phase 2, we aimed to identify the optimal temperature setpoint with personal adjustable air movement by fans. To achieve this, we varied the indoor temperature between 26-28.5°C [79-83 °F] and allowed occupants to operate fans (both ceiling and desk fans) based on their preferences for 4 weeks. During this period, we studied subjects’ satisfaction with the indoor temperature and air movement using the right-here-right-now survey, i.e., How satisfied are you with the temperature and air movement? Participants are required to answer these questions in a three-point satisfaction scale: “Satisfied / Neither satisfied nor dissatisfied / Dissatisfied”. In phase 3, we conducted a longitudinal measurement for 11 consecutive weeks to thoroughly evaluate the thermal comfort and energy-saving impact of the optimal condition evaluated in phase 2. During phase 3, we alternated the environment and operated system between (i) the new fan-integrated AC system at 26.5 °C [80 °F] indoor temperature setpoint and (ii) conventional AC system at 24 °C [75 °F] temperature setpoint. We also sent a daily survey to the occupants asking their immediate satisfaction with temperature and air movement within the office environment. Detailed energy consumption from the HVAC system (chiller, AHUs, pumps, and cooling tower) and fans (ceiling and desk) were measured for energy-saving comparison.

Thermal comfort

Thermal comfort is a critical requirement to evaluate the effectiveness of the fan-integrated AC system. Based on the experimental results in phase 2, we found the optimal temperature setpoint at ZEB Plus with ceiling fans to elevate air speed in the open plan office was 26.5 °C ± 0.5 °C [80 °F ± 1 °F]. Meanwhile, personal desk fans were provided in each workstation to meet additional cooling needs. Subjective survey on occupants’ satisfaction with temperature was conducted in ZEB Plus at 26.5 °C [80 °F] (with fans) and compared with 10 other conventional AC offices in Singapore at 24 °C [75 °F] (without fans) in Figure S15. We found 68 % of the occupants in ZEB Plus were satisfied with the indoor temperature. Additionally, the dissatisfaction with temperature for fan-integrated AC workspace has been reduced by 14 % when compared with conventional AC offices. This demonstrates an improved temperature satisfaction in ZEB Plus with fans despite the workspace being 2.5 °C [5 °F] warmer than common AC offices.

Figure S16 showed the results, in phase 3 of the study, when we asked occupants which thermal environment they would prefer between the conditions (i) 24 °C without fans and (ii) 26.5 °C with fans. People who preferred no change (these are the people that are comfortable) increased from 55 % (24 °C without fans condition) to 77 % (26.5 °C and fan-integrated AC condition), indicating that fan-integrated AC gained higher preference of occupants. Moreover, 33 % of occupants preferred a slightly warmer or warmer under 24 °C condition which pointed out the potential discomfort in overcooling conditions. When the setpoint temperature was raised to 26.5 °C with elevated air movement, this negative preference was reduced from 33 % to 9 %. The result provided quantitative evidence that the increased air movement with fans, in general, will not initiate excessing discomfort to the occupants at higher temperature conditions. The fan-integrated AC system worked well in terms of temperature and air movement satisfaction when the occupants were given sufficient long time in adapting to the new system.

Energy performance

Besides thermal comfort, energy performance of the fan-integrated AC system has also been investigated. The yearly average outdoor temperature of Singapore is between 25 °C and 31 °C [77 °F and 88 °F]. Air conditioning is necessary in office buildings to maintain thermal comfort. The ZEB Plus was installed with a variable air volume (VAV) air conditioning system and served by three air handling units. The cooling setpoint temperatures were about 23 °C [73 °F] and 26-27 °C [79-81 °F] before and after retrofitting with ceiling fans installed.

In phase 3 of the thermal comfort experiment, we conducted an 11-week study and alternated the office condition between 2 settings: 24 °C without fan and 26.5 °C with both ceiling and desk fans. All the energy measurement data of the air-conditioning system and fans were recorded to directly compare energy performance. Figure S17 shows the energy use intensity (EUI) of HVAC sub-systems including chillers, pumps, AHU, cooling towers and fans in two cases: i) baseline scenario at 24 °C without fan and ii) proposed scenario at 26.5 °C with both ceiling and desk fans. We found the total EUI for the HVAC system is 36.6 kWh/m²·yr and 25 kWh/m²·yr, respectively, for the baseline and proposed scenarios. A 32 % reduction in energy usage (11.6 kWh/m²·yr) is observed in the proposed scenario. The significant energy saving comes from chiller energy usage, then AHU fan and pump. Meanwhile, ceiling and desk fans use only 3.5 % of total energy usage (0.88 kWh/m²·yr). These findings suggest that increasing air movement with fans is an energy-efficient complementary technology to conventional air conditioning in office buildings in the tropics. In fact, energy use in ZEB Plus is lower than 90 % of the office buildings in Singapore based on the building energy benchmarks for commercial buildings from 2017.

Capital cost saving between conventional AC and fan-integrated AC system

Potential cost savings accrued from using fan-integrated AC system are mainly derived from two factors: (i) smaller capacity of AC components and (ii) reduced supply air ducting. To compare the potential cost saving, we redesigned the conventional air-conditioning system with extended supply air duct for air distribution and selected adequate chiller and air handling unit size to support the original design cooling load (air temperature at 24 °C [73 °F]) and estimated the potential construction cost based on average market rate. Figure S18 shows a sector in ZEB Plus comparing the existing installed system layout with ceiling fans (Figure S18b) versus what would be the conventional AC system layout without fans and with more ducts (Figure S18a). This same process was done for the whole floor plan to estimate cost saving.

First, the fan-integrated AC system is operating at indoor temperature setpoints between 25-28 °C [77-82 °F] and supply air temperature between 14-17 °C [57-63 °F]. Instead of the typical chilled water supply temperature at 7 °C [45 °F], the fan-integrated AC system can operate at much higher chilled water supply temperature up to 11 °C [52 °F]. This means that smaller size chiller and AHU can be used in the fan-integrated system approach.

Ceiling and desk fans could mix the zone air more uniformly than the supply air diffusers. The supply air ducts used for distributing diffusers within the occupied zone can be reduced significantly (i.e., only the main supply air duct is needed) when the space is provided with fans. Consequently, a smaller AHU fan size can be selected due to a reduction of static pressure required in the supply air duct.

When compared with the conventional AC system (e.g., Figure S18a), we roughly estimated an overall cost savings of reduced size in chiller (~22 %), reduced size in AHUs (~25 %), and minimized duct work (~25 %) in the fan-integrated AC system design (e.g., Figure S18b) in ZEB Plus. It is worth noting that the capital investments for purchasing and installing ceiling fans in this project are trivial when compared to the above cost savings. In addition, the electricity tariff saving for the HVAC system operating at higher setpoint temperatures (i.e., approximately 25-30 % when increased from 24 °C to 26.5 °C [from 73 °F to 81 °F]) should also be considered.

Insights from this study

This study is the first large-scale deployment of a fan-integrated AC system in office space in Singapore. It demonstrates that the ceiling and desk fans can be integrated efficiently with the HVAC system in tropical climates to achieve better thermal comfort while reducing energy consumption significantly. Besides, the cost saving in initial investment and operation reveals a huge advantage of the fan-integrated AC system over the conventional design. From our experience, the location of ceiling fans should be designed properly to uniformly mix the cooling air for all occupants and to avoid the visual flickering or strobing effect between the lighting fixtures and the operating fans. Lastly, desk fans should be provided for higher granularity of air movement adjustment based on individual needs, especially during the transient period from outdoor to indoor conditions.

Non-ceiling fans study in Singapore

Background

Ceiling fan installation for some buildings is not possible due to limited floor to ceiling height. This case study explored the effectiveness of non-ceiling fan options (i.e., desk fan, towel fan, and pedestal fan) for the application of higher temperature cooling with elevated air speed in a retrofit application.

Study method

Field measurement was carried out in VENTUS, an office building, located at the National University of Singapore (NUS) (See Figure S19). Around 40 occupants doing administration work participated in this study. Before the study, each occupant was given a chance to select one out of four fan types, including desk fan, clip on fan, tower fan, and pedestal fan (see Figure S20), based on their personal preference. These fans have been pre-tested to increase air movement towards occupants and to compensate potential thermal discomfort due to higher temperature setpoint in the workspace. An introductory session was given to the occupants on the study objectives, procedures, and what should be done before the experiment.

The entire study was divided into two stages: (i) the baseline settings (2 weeks) and (ii) the intervention settings (4 weeks). Table S3 summarizes the conditions for both baseline and intervention settings. The baseline settings referred to the conventional air-conditioning system in VENTUS’s workspace with temperature setpoint at 24 °C [75 °F] without any fan. In the intervention settings, the indoor temperature was set to 24 °C [75 °F] between 7am - 9am before being increased to 26 °C [79 °F] between 9am - 7pm. A lower temperature set in the morning aimed to improve occupants’ initial perception to the thermal environment when they first came into the office. Personal fans were provided to compensate for potential thermal discomfort due to the elevated temperature in space at the beginning of the intervention setting. Each occupant could select one out four fan types as shown in Figure S20, including desk fan, clip on fan, tower fan, and pedestal fan. A duration of four weeks given to the intervention settings is targeted to provide sufficient time for the occupants to adapt to working under higher indoor temperature setpoint with elevated air speed via fans.

Table S3. Experiment settings, duration, and conditions.

Physical measurements were conducted to verify the indoor environmental status between baseline and intervention settings. Indoor air temperature, relative humidity, carbon dioxide (CO2) concentration and outdoor air temperature were recorded in a 5-minute interval. Indoor sensors were placed at 1.3 m height above ground level and approximately 0.6 m away from the occupants. Sensitivity of the sensors were: temperature (+/- 0.5 °C [0.9 °F]), relative humidity (+/- 2 %), and CO2 (+/- 50 ppm).

Additionally, subjective surveys via web-based platform were conducted to obtain individual’s preference with their perceived environment and perception for the usage of fans. Subject’s satisfaction regarding thermal comfort, indoor air quality, and overall environment was evaluated using a 5 – point satisfaction scale (Very dissatisfied / Dissatisfied / Neither satisfied nor dissatisfied / Satisfied / Very satisfied). We asked the occupants about their fan usage experience regarding the comfortability of air movement generated by fans, noise level, spatial occupation of fans, and overall happiness in using fans. The subjects were instructed to answer these questions using a 5 – point scale (Strongly disagree / Disagree / Neither agree nor Disagree / Agree / Strongly agree). The environmental satisfaction survey was conducted after both baseline and intervention stages, while the fan related survey was only conducted after the intervention stage.

Physical measurements

Figure S21 summarizes the measured indoor temperature, relative humidity, and CO2 concentration within the studied zone for both baseline (AC only) and intervention (AC + fans) settings. The mean (min – max) temperature recorded in the baseline and intervention settings was, respectively, 23.1 °C (21.5-25.3 °C) [73.6 °F (70.7-77.5 °F)] and 25.6 °C (25.2-29.2 °C) [78.1 °F (77.4-77.5 °F)]. In the intervention setting, higher temperature levels were occasionally observed in the morning at around 7am right after the air-conditioning system started. The mean (min – max) relative humidity for the baseline and intervention settings was, respectively, 61% (56-71 %) and 68 % (62-76 %). We observed the mean humidity in intervention setting has increased by 7 % when compared to baseline. This could be due to the increased off coil temperature setpoint from the air handling unit, where less moisture is being removed from cooling coil, but the indoor latent load remains. Lastly, we found a higher mean (min – max) CO2 concentration in the intervention setting 820 ppm (700-920 ppm) than in baseline condition 770 ppm (670-900 ppm). Nevertheless, these recorded CO2 levels were all well below the general CO2 threshold (i.e., 1000 ppm) for good indoor air quality in office premises.

Environmental satisfaction

Figure S22 compares the occupant’s satisfaction with thermal comfort, indoor air quality (IAQ), and the overall environment between baseline and intervention settings. We found the thermal comfort satisfaction in the intervention settings has increased from 56 % to 64 %, while thermal dissatisfaction has decreased from 21 % to 9 % when compared to the baseline. The results suggest that occupants are thermally more satisfied under higher temperature setpoint (26 °C [79 °F]) with ability to operate personal fans than in the conventional AC setting at lower temperature (24 °C [75 °F]). The additional 3 % of “very dissatisfied” responses in the intervention settings could be due to individual’s higher sensitivity to a high indoor temperature resulting from the morning period when the air conditioning just started and have not reached the setpoint yet (max temperatures > 28 °C [82 °F] in the intervention period, see Figure S21). The percentage of satisfactory IAQ has increased from 62 % in baseline to 70 % in the intervention settings, while the percentage of dissatisfaction remained 12 %. In general, we observed an improvement for IAQ in the when subjects can adjust the air speed around them. Meanwhile, an additional 3 % of the subjects responded “very dissatisfied” for IAQ during the intervention. This could be associated with the increased relative humidity in space which returns a sense of stuffiness in the air. Lastly, we found the overall satisfaction has increased from 59 % to 70 %, while dissatisfaction decreased from 12 % to 6 %, when compared the intervention to the baseline settings. These results showed occupants in the tropics are satisfied with higher temperature workspace when they are given personal fans to adjust their surrounding air speed.

Fan selection and users’ feedback

Figure S23 illustrates the occupant’s preference regarding the fan types available in this study. We found 18 subjects selected a desk fan, 9 of them picked a pedestal fan, 5 of them took a tower fan, and the remaining 3 chose a clip-on fan. Spatial constraint could be a reason for more subjects selecting desk fan instead of pedestal and tower fans. Despite the small size of clip-on fan, the placed location is limited along the desk’s edge, and simply unavailable to be placed in front of the subjects (i.e., desk with partition in the front). In this study, occupants were free to select the fan speed based on their own preference. The average air speed perceived by each occupant is not identical.

Figure S24 presents the subject’s feedback regarding their fan usage experience, including how comfortable is the air movement generated by fans, fans noise level, spatial consideration, and overall happiness in using fans. The results showed 54 % of the occupants were thermally comfortable, while 21 % reported uncomfortable, with the air movement from personal fans. Also, we found 53 % of the participants were satisfied with the noise level generated by the fans. Only 17 % of the subjects reported the fans were noisy, among which 50 % of them were using a desk fan, 25 % was using a pedestal fan, and the rest was using a tower fan. We found 8 out of 39 participants (~21 %) responded that the fans have taken up too much of their working space. 5 out of these 8 participants were holding a desk fan and the other 3 were holding a tower fan. It also suggests that approximately 28 % of the desk fan holders and 60 % of the tower fan holders felt the fans are spatially too occupied.

Overall, we found 62 % of occupants (i.e., 25 out of 40) are satisfied with the use of personal fans under higher temperature workspace environment, where only 12 % (i.e., 5 out of 40) of them showed dissatisfaction. In addition, among these 5 dissatisfied individuals, 2 of them also reported thermally uncomfortable when in using fan, 2 of them claimed the fans have taken up too much of their working space, while the remaining one just anyhow not happy with the fan. These findings generally support the idea of using personal fans in workspace with higher temperature setpoint.

Other occupants’ feedback

During the study, we engaged with some of the occupants to obtain general feedback. In the middle of the intervention period, some participants have reported difficulties in thermally adapting to the new condition, even though personal fans were provided. Thermal dissatisfaction responses were reported early in the morning when the air-conditioning system just started (i.e., temperature may increase up to 29 °C [84 °F]) and during the transient period when occupants were entering the office from outdoor. In addition, some occupants felt that the indoor air was stuffy and there is inadequate air circulation. Nevertheless, such complaints were reduced significantly towards the end of the experiment.

Recommendations

Based on what we have learnt from this field experiment, there are several recommendations to smoothen the transition between traditional air-conditioning systems (without fan) to fan-integrate air-conditioning settings in real buildings.

1. Sufficient communication with the occupants is important. Before the implementation of the fan-integrated air-conditioning approach, an introduction session given to all occupants to explain the rationales, procedures, precautions, expectation, and flexibility (e.g., clothing) is necessary. This session will help the occupants to prepare for the upcoming changes. In addition, continuous monitoring of occupants’ feedback regarding thermal comfort, indoor air quality, and the usage of fans is critical. It provides hints to the management officers on how to react and satisfy occupants’ needs during the transitional period.

2. Selecting a suitable fan is critical. From our experience, the personal fans being selected for workspace usage should be quiet and not too bulky (i.e., limited discomfort in acoustic and occupied space). It would be best if a few fan choices were provided for the occupants to select based on their own preference.

3. Preparation for additional fans. Additional fans can be deployed in common areas, such as meeting rooms, receptions, and pantries, where different activity occupant levels are expected.

4. Avoids aggressive change in temperature setpoint. During the early stage of the intervention, the increase in temperature setpoint shall not be too large. For example, if the conventional temperature setpoint is 24 °C [75 °F] and the new targeted setpoint with fans is 26 °C [79 °F], we suggest to first to increase the temperature to 25 °C [77 °F] for one or two weeks, followed by 26 °C [79 °F] if the occupants’ feedback is positive. The benefits are two-fold: (i) it allows the occupants to progressively adapt to the temperature change, and (ii) it provides a buffer for management officers to collect and resolve occupants’ feedback before any further actions are to be taken. Each step change of temperature setpoint is recommended to not exceed 1 °C [1.8 °F].

5. Occupants need time for adaptation. Occupants are used to the conventional air-conditioning setting in the workspace. The concept of increasing convective and evaporative heat loss through higher air speed is physiologically valid, but it takes time for the occupants to adapt to this new cooling strategy. It is expected that some occupants would take longer time for adaptation and reflect thermal discomfort during the early stage of system transformation. Facility managers are advised to be patient and try to resolve the reasons for dissatisfaction. For example, occupants may adopt flexible clothing policy, increase background air circulation, or even temporarily reduce the temperature setpoint in a particular hot day. With respect to the space and system settings, the occupant’s adaptation period can be varied.

Insights from this study

This study demonstrates the feasibility for using personal fans (i.e., desk, clip-on, pedestal, and tower fans) to compensate potential thermal discomfort under higher temperature (up to 26 °C [79 °F]) workspace in Singapore. Positive feedback on thermal satisfaction, air quality satisfaction, overall environment satisfaction, and overall happiness from the occupants has been confirmed with the use of fans in the workspace. The findings are beneficial to the buildings that are attempting to adopt higher temperature cooling with elevated air speed strategy but limited to ceiling fans installation (i.e., insufficient floor-to-ceiling height) and major renovations (i.e., high cost). Precautions have been raised when selecting personal fans, including flexibility of fan choices, noise level, and spatial consideration. Lastly, an adaptation period for the occupants is acknowledged when transforming from conventional air-conditioning system to fan-integrated air-conditioning system.

Coastal Biology Building

The Bullitt Center

Franco Center

This work was partly funded by the industry consortium members of the , and partly by the through the SinBerBEST program.

We thank Samuel Foo, Chuan Seng Lee, Yang Lim Lem, Komang Narendra, Majid Sapar, Yvonne Soh, Kiat Leong Tan, and Irene Yong for their valuable comments and support. We want to thank , , and for the valuable discussions on the use of fans.

This work is based on decades of research on fans. We want to thank some of the key researchers that helped in this process: Edward Arens, Gail Brager, Carlos Roa Duarte, Lindsay Graham, Charlie Huizenga, Ollie Jay, David Lehrer, Aleksandra Lipczyńska, Shuo Liu, Arsens Krikor Melikov, Asit Mishra, Jovan Pantelic, Chandra Sekhar, Costas Spanos, William W Nazaroff, Gwelen Paliaga, Tom Parkinson, Dongyun Rim, Federico Tartarini, Kwok Wai Tham, Yan Bing, Le Yin, and Hui Zhang.

Conflict of interests

The Center for the Built Environment (CBE) at the University of California, Berkeley, with which some of the authors are affiliated, is advised and funded, in part, by many partners that represent a diversity of organizations from the building industry, including manufacturers, building owners, facility managers, contractors, architects, engineers, government agencies, and utilities.