Case studies for researchers
These scientific research-based studies inform what we have learnt in buildings that installed with fans
Last updated
These scientific research-based studies inform what we have learnt in buildings that installed with fans
Last updated
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.
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 (Luo et al., 2021).
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.
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.
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 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.
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.
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.
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.
This is a six-week study implementing ceiling fan with air conditioning in a Singaporean office building. Singapore is located at the tropical climate region, with daily mean outdoor air temperature and humidity of 26 - 29 °C [79 - 84 °F] and 75-85 %. This study examines the performance of HVAC strategy with increased cooling temperature setpoints and elevated air movement produced by ceiling fans in terms of occupants’ perception to the environment and the corresponding energy consumption. DC motor ceiling fans (Haiku I-Series 60 inches, Big Ass Fans) were used to provide air movement within the space. Figure S6 shows the office plan and ceiling fans location in the target building. Details of this field study are available in this paper (Lipczynska et al., 2018).
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).
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.
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.
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
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.
This is a 2.5 year-long field study in 4 sites, composing 8 commercial and 6 residential zones, in central California (hot / dry climate), demonstrating the difference in user behavior and energy performance for automated ceiling fans operated with air conditioning system (after renovation) when compared with the conventional air-conditioning system (before renovation). Effectiveness on the ceiling fans plus air conditioning control strategy has been demonstrated in this field study (Miller et al., 2021). The control strategy consisted of setting ceiling fans to automatically turn on for cooling before HVAC, and then operate together with air conditioning enabled raising air conditioning cooling temperature setpoints.
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.
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.
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.
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.
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.
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.
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 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.
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.
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.
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.
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.
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.
Baseline
2 Weeks
Indoor temperature setpoint 24 °C [75 °F]
Intervention
4 Weeks
Indoor temperature setpoint 24° C [75 °F] (7am-9am)
Indoor temperature setpoint 26 °C [79 °F] (9am-7pm)
Each occupant was given a fan
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.
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.
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.
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.
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.
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.
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.
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.
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.
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].
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.
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.
