Thermal control in classrooms is key to an ideal learning environment

An important consideration in the design of classrooms is the provision of good thermal conditions based on energy-efficient technologies such as natural ventilation, solar shading and intelligent building design (for the warmer months), and efficient, adjustable heating (for the colder months).

It is increasingly accepted that there is no such thing as a ‘natural’ comfort temperature. The best results with regards to cooling and heating can be achieved by providing occupants with personal and adaptive options, such as access to personally operable windows, personal control over sun shading, and possibly also desk fans and other such devices. In general terms, buildings should connect people to the outdoors as much as possible and provide shelter from it only as much as is necessary¹.

In Europe, all countries have policies for minimum indoor temperature in school classrooms set out in their legislation or standards. These minimum requirements vary from country to country, as well as by season, but range from 17°C to 20°C. Fewer European countries have standards for maximum indoor air temperature in classrooms, but for those that do, these vary from 22°C to 29°C.

For the past several decades, researchers have been studying the optimal temperature range associated with better learning outcomes. Zeiler and Boxem (2009)² carried out a thorough review in order to demonstrate the effects of thermal quality in schools on the learning performance of students.

Mendell and Heath (2005)³, meanwhile, reviewed evidence for the effect of indoor environmental quality on both performance and attendance, and Fisk (2017)⁴ did an extensive literature review about ventilation problems in schools, its impact on student performance, health and absence.

These studies found that as temperature and humidity increase, students report greater discomfort and their levels of achievement and task performance deteriorate, as a result of decreasing attention spans. High classroom temperatures have also been associated with headaches and eye, ear, nose and throat symptoms, while high humidity levels can lead to increasing incidence of mould, which can in turn cause or exacerbate a range of health problems.

Cooling solutions

Natural ventilative cooling achieved by opening windows and skylights is a fast and direct way to influence the thermal indoor environment. An open window creates increased air motion, and if the outdoor temperature is lower than the indoor temperature, then the indoor temperature will fall.

This graph from the SINPHONIE study conducted in 114 schools in 23 European countries⁴, gives a clear indication of the times at which windows are opened during the day. No evidence of the use of night ventilation was reported.

Even when the outdoor air temperature is slightly higher than indoors, the elevated air speed due to increased airflow will increase cooling of the body.

Natural ventilation for cooling can be done in two ways – day ventilation and night ventilation:

• Ventilation during the day removes excess heat from inside the building by creating high levels of movement in the air.
• Night ventilation (also referred to as night cooling) will cool down a building’s thermal mass (walls, floor, furniture, etc.) at night using cool outdoor air. The following day, less cooling energy is needed within the building as the thermal mass has already been cooled.

Orientation of the classroom and shading control also play an important part in creating consistent thermal comfort. Large windows and skylights can be oriented to allow maximum sunlight to penetrate in the winter months, and shaded with moveable shading devices to block out sunlight in the summer months as needed.

Field studies show that people in naturally ventilated buildings accept higher temperatures⁵. This effect of the body adapting to its surroundings is referred to as adaptive thermal comfort. A prerequisite for designing with adaptive thermal comfort in mind is that people can freely adapt their clothing and operate windows.

The consequence of adaptation is that thermal comfort can be achieved in warm climates without air conditioning, by using natural ventilation, solar shading and intelligent building design. In countries with the hottest summers, ceiling fans or mechanical air-conditioning units may be required in addition to natural ventilation and shading.

Heating solutions

The Clever Classrooms study (2015)⁶ found that better temperature control was achieved in winter when rooms were fitted with radiators with thermostatic controls. In contrast, underfloor heating was associated with poor heating control in individual classrooms due to longer response lag times.

The study also recommended that all methods of temperature control in classrooms be easily operable and readily accessible to teachers.

Sources

1. https://www.velux.com/article/2016/health-matters
2. Zeiler & Boxem (2009). Effects of thermal activated building systems in schools on thermal comfort in winter. Building and Environment.
3. Mendell and Heath (2005). Do Indoor Pollutants and Thermal Conditions in Schools Influence Student Performance? A Critical Review of the Literature. Indoor Air
4. Fisk (2017) The ventilation problem in schools: literature review. Indoor Air
5. de Dear and Brager (1998). Developing an Adaptive Model of Thermal Comfort and Preference. ASHRAE Transactions
6. Clever Classrooms (2015), Summary report of the HEAD project, University of Salford, Manchester