Ceiling Fans vs. Air Conditioning: A Pilot Study in Classrooms

Keywords: classrooms, thermal comfort, passive cooling, ceiling fans, mobile air conditioning

Summary

In a Dutch primary school, there have been complaints about heat in the summer. Ahead of improving the HVAC system in the building, the school wants to improve summer comfort with simple measures. In a pilot study, the effectiveness and practical applicability of mobile air conditioning units and ceiling fans were compared.

Introduction

Thermal comfort in schools is crucial for overall well-being of students and teachers. High ambient temperatures can lead to discomfort and reduced cognitive performance [1]. Therefore, finding cost-effective and practical solutions to manage indoor thermal comfort during the summer months is essential.

In 2024, we were approached by a Dutch primary school facing complaints about summer heat and indoor air quality. Ahead of improving the HVAC system more radically in the future, the school wanted to enhance summer comfort at short notice with simple measures. To prevent unnecessary expenses for approximately 50 classrooms on potentially ineffective solutions, a pilot study was proposed to assess the effectiveness of two alternatives.

Prior to the pilot, various solutions were considered, taking into account e.g. costs, energy consumption, noise level, cooling effect, security, and practical feasibility. Since the school initially considered installing mobile air conditioners, this was taken as the starting point. These units are popular for their ability to provide immediate cooling and their portability. However, their high energy consumption and noise levels can be drawbacks. Ceiling fans were added to the study as a low-cost alternative. Ceiling fans are a passive cooling solution that improve thermal comfort by increasing the air speed. They are inexpensive to install, are a factor or 10 more energy efficient than mobile air conditioning units and are relatively easy to use [2]. All of these factors make ceiling fans an attractive option for schools.

The aim of the pilot was to gain insight into the effectiveness of ceiling fans and mobile air conditioning to improve summer comfort in a classroom context.

Methods

Pilot Classrooms

The pilot was conducted in four adjacent classrooms. Two additional classrooms served as reference spaces without any cooling measures. All classrooms were located on the top floor and oriented towards the South/West to assure a worst-case situation in terms of external heat load. The classrooms already had sunscreens and operable windows for passive cooling.

Two pilot classrooms were equipped with mobile air conditioning units (Comfort Line Aircobreeze R290) with a cooling capacity of 3.4 kW (Figure 1). These units have a noise level (when used at maximum setting) of 64 dB(A), which is significantly higher than the recommended 35 dB for installations in classrooms. The warm air from the condenser of the units was vented outside through a panel fitted in the sliding window. This setup allowed for a straightforward installation but raised concerns about burglary risk for future installation on the ground floor.

Two other classrooms were fitted with remote controlled 3-speed ceiling fans (Create Wind Sail 90W silent XL Ø163 cm), see Figure 2. The fans had volumetric flow capacities of 5400, 8160, and 12000 m³/h at speed settings 1, 2, and 3, respectively; noise level in the highest setting was 48 dB(A). The CBE Fan Tool [3] was used to determine the fan configuration. One Wind Sail fan per classroom was likely to be sufficient. The fans were expected to reduce the perceived temperature by 2 to 4 degrees Celsius, assuming elevated airspeeds of up to 1,5 m/s in the occupied zone [3,4].

Figure 1. Mobile air conditioning unit with exhaust via a panel between the sliding windows.

Figure 2. WindSail Ceiling fan.

Monitoring Indoor Climate

The study monitored the objective and perceived indoor climate through continuous temperature measurements, thermal comfort measurements, and interviews with teachers.

Continuous temperature measurements provided data on the effectiveness of the cooling solutions over time. The temperature measurements were performed using Aranet Pro sensors. The measurement results were compared with the Class C requirements for the indoor climate in Dutch schools [5]. For classrooms with active cooling, a maximum temperature of 27°C applies. For classrooms without active cooling adaptive temperature requirements apply (maximum indoor operative temperature = 0.33 times running mean outdoor temperature + 20,4°C).

Thermal comfort measurements offered insights into the predicted comfort levels experienced by occupants. Measurements of air temperature, radiant temperature, relative humidity, and air velocity were conducted at the workstation of the teacher in 3 classrooms using a Testo 400 IAQ and comfort kit. During the measurements, the sunshades were closed to limit the effect of solar radiation (increased radiant temperature). The measurements outcomes were used to calculate the PMV (Predicted Mean Vote) according to the methodology in ASHRAE 55 [6] using a clo value of 0,5 and a metabolism of 1,2 met. Results were compared with the Category C requirements from ISO 7730 (−0,7 < PMV < +0,7) [4].

Interviews added a qualitative dimension to the study, capturing the personal experiences of the people that worked in the classrooms during the test period. For practical reasons these interviews were limited to the teachers.

Monitoring took place during and after a week of warm summer weather. During the week of 25 June to 2 July 2024, the maximum outdoor temperatures during the day ranged from 17,3°C to 30,0°C, and the minimum outdoor temperature (day and night) was between 10,5°C and 17,2°C.

Results

Temperature Measurements

The results of the continuous temperature measurements are summarised in Table 1. During this summer week, the temperature in the original situation exceeded the temperature threshold for approximately 70% of school hours. In the classrooms with a ceiling fan, the percentage of temperature exceedances was significantly reduced compared to the situation in the reference rooms (34-50%). Classrooms with mobile air conditioning units almost met the comfort requirements, with only 3-8% of the time exceeding the threshold temperature of 27°C.

Table 1. Summary of temperature measurements (REF: reference, CF: Ceiling fan, MAC: Mobile air conditioning).

Thermal Comfort Measurements

The results of the PMV assessments are summarised in Table 2. In a classroom without any cooling, the PMV was around +1 (+0,92 to +1,17). With the ceiling fan turned on, the air temperature in the classroom remained more or less the same, but the PMV-value dropped to +0,69 due to an increase of air velocity. In the classroom with mobile air conditioning, the PMV-value was even lower (+0,33), due to the lower air temperature there.

Table 2. Summary of thermal comfort measurements and the calculated PMV. (REF: reference, CF: Ceiling fan, MAC: Mobile air conditioning).

Teacher Interviews

Teachers in classrooms with mobile air conditioning units clearly appreciated the cooling effects but were bothered by the noise, which (they said) sometimes even distracted students.

Teachers in classrooms with ceiling fans also reported a positive impact on temperature perception; they even said to prefer fans over air conditioning units due to the lower noise levels. However, they did remark that fans could not be set to the highest speed (setting 3) due to paper to be blown away. The teachers in these classrooms admitted that they initially thought to prefer mobile air conditioning, but after the pilot they preferred to keep the ceiling fans instead.

Discussion

Measurement data indicate that both cooling solutions had a positive impact on indoor thermal comfort. Ceiling fans reduced the percentage of time that temperatures exceeded the comfort threshold by approximately half, while mobile air conditioning units nearly eliminated temperature exceedances. The thermal comfort assessment shows that with the ceiling fan, an acceptable comfort level (Class C) is achieved. With the mobile air conditioning, a higher quality level (Class B), is reached in terms of thermal comfort but at the expense of extra noise hindrance. This shows that both solutions are effective to improve summer comfort, but mobile air conditioning units provide lower air temperatures.

All presented measurements are performed at the teacher’s desk. We expect somewhat different and diverse results in the thermal comfort assessment for other positions in the classroom e.g. there were students are sitting. For the ceiling fan, the highest cooling effect is reached underneath the fan, while the desk of the teacher was positioned in the zone with lower air speeds which implies a relatively small cooling effect compared to the cooling effect at certain student workstations (Figure 3).

Also, the mobile air conditioning will not provide a uniform thermal situation throughout the space. Close to the unit higher air speeds will result in extra cooling effects.

Figure 3. Cooling effect of the WindSail ceiling fan. [3]

In the interviews, teachers mention that they did not use the fan at speed level 3 because of papers blown away. They did not have complaints about draught; in speed level 2 the measured air velocities at the teacher’s workstation were not higher than 0,19 m/s, which is well below the Category C summer threshold of ISO 7730 [4]. Note that normally in summer situations draught complaints anyhow will be avoided if users have control over the settings of the system / the airspeed [4]. The latter is the case with both the ceiling fan and the mobile air conditioning unit.

Conclusions

The study concluded that both cooling solutions are viable options for improving thermal comfort in classrooms to, at least, an acceptable level. Ceiling fans are recommended in general for their cost-effectiveness and energy efficiency, while mobile air conditioning units are suggested for environments where higher levels of cooling are required. While mobile air conditioning units were appreciated by the teachers for their superior cooling performance, ceiling fans were preferred for their quieter operation. The noise generated by air conditioning units was a significant concern, particularly in classrooms with students who are easily distracted. The final choice between the two solutions might depend on factors such as budget, energy performance requirements, and noise tolerance.

For a cost-effective and energy-efficient solution, ceiling fans are recommended. They can be used in all classrooms and remain beneficial even with future HVAC system improvements (think e.g. of combinations of ceiling fans with centrally cooled mechanical ventilation). For environments where higher thermal comfort levels are needed temporarily, mobile air conditioning units can be considered, but quieter models should be selected than the ones used for this pilot study.

References

Wargocki, P., Porras-Salazar, J. A., & Contreras-Espinoza, S. (2019). The relationship between classroom temperature and children’s performance in school. Building and Environment, 157, 197-204.

Arens E., Turner, S., Zhang, H., & Paliaga, G. 2009. Moving air for comfort. ASHRAE Journal, May 51 (25), 8 – 18.

Raftery, P. (2019) CBE Fan Tool, cbe.berkeley.edu/fan-tool. Center for the Built Environment, University of California Berkeley, US.

ISO 7730:2005 Ergonomics of the thermal environment – Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria.

RVO (2021) Programma van Eisen Frisse Scholen 2021. Rijksdienst voor Ondernemend Nederland, Utrecht, The Netherlands.

ANSI/ASHRAE 55: 2023 Thermal Environmental Conditions for Human Occupancy.