Heating, cooling and
ventilation in schools
Dynamic heating needs
Before any solution can be found, it’s important to understand why these problems are so common, even when technical solutions exist. The main reason is that the requirements for adequate heating, cooling and ventilation in schools are often not fully understood at the design and implementation stage. A school building is very dynamic in terms of heating. Regular use, empty rooms at night and on weekends, and high and rapidly changing heat loads on weekdays require rapid responses from the heating system. On top of that, classrooms must be heated quickly after vacancy.
Cold radiation in classrooms
Often classrooms have large windows in order to draw in as much natural light as possible. The downside is that the window surface is cooler than other surfaces in the classroom during the heating season. This results in an asymmetry of thermal radiation, which can be uncomfortable for students sitting near the window. Radiators under the windows offset this cold radiation and prevent cold air from penetrating through the window.
Keeping a classroom cool can also present a challenge. The heat load generated by students can be on the order of 3 kW, and direct solar radiation from windows on the south façade can be as high as 400 W per window square meter if the classroom has a total window area of 10 m2. Window ventilation should be used whenever possible, for example during breaks when mechanical ventilation is not available. However, window ventilation doesn’t provide sufficient cooling and ventilation efficiency in hot outdoor conditions. In this case, mechanical cooling is required. However, the demand for cooling power is very high in classrooms, with up to 200 W per m2 of floor area. One cooling option is to use suspended ceiling tiles for cooling. These operate quietly.
Ventilation in schools
Ventilation or fresh outdoor air is required in any classroom. The amount of fresh air should be at least 4 l/s per person to keep carbon dioxide levels below 1000 ppm. High carbon dioxide levels affect concentration and learning ability. Moreover, humidity increases with the moisture supplied via the outside air. Because of the moisture load caused by human respiration and perspiration - 30 people produce about 1.5 l/h of water vapor - moisture should be removed by ventilation or dehumidification. The minimum amount of ventilation in a classroom during a lesson should be above 120 l/s.
Adequate ventilation can only be achieved with mechanical systems. These include mechanical or bidirectional ventilation and mechanical exhaust or unidirectional ventilation. In cases where bidirectional ventilation is not possible, unidirectional ventilation can be used and fresh air is supplied through ventilation radiators. The air is then filtered and preheated in the ventilation radiator.