In the summer heat, your own four walls can quickly become an oven. The information program Zukunft Altbau, funded by the Baden-Württemberg Ministry of the Environment, gives tips on what you can do to prevent interior rooms from overheating.
Window with sun protection glass
An important element in heat protection is modern heat protection or sun protection glazing. Triple glazing with a very thin, metallic coating on the glass ensures that large parts of the sun’s heat do not get into the house. The g value (g for total energy transmittance) shows how good the protection against overheating caused by excessive solar radiation is. With normal thermal insulation glass, the value is 0.55 – that means: 55 percent of the sun’s heat gets into the house.
Modern triple glazing has a value of around 0.5, sun protection glasses up to 0.2. “Accordingly, between 50 and 80 percent of the sun’s heat stays outside,” says Waldemar Dörr from the Baden-Württemberg Glass Window Facade Association. “Low g-values are required where a lot of sun falls on the windows during the day on hot days, for example with exposed south-facing windows, but also some east and west windows.” On the north side, they are not really worth it, except for skylights. However, very low g-values are not desirable in winter when solar radiation is welcome for energy gain.
Heat regulation via sun protection elements and night-time ventilation
Even more important is the shading of the window surfaces by sun protection elements such as lowered roller shutters and blinds, extended awnings and closed window shutters. Especially if these are attached to the outside, this further reduces the heat input. Longer roof overhangs and balconies help to ensure that less intense, high-lying sun hits the windows in summer.
“Airing during the cooler hours at night also plays a key role,” explains Dörr. “The remaining heat in the house is then simply ventilated out.” For this purpose, homeowners should ventilate the room laterally, i.e. open the opposite windows wide at the same time. The warm room air is quickly exchanged for the cooler air and the building can cool down.
Storage masses and insulation keep the heat out of the apartment
If there are storage masses inside the house, heat waves can be survived better. They ensure heat buffering for several hours during the hot hours of the day and cool down again at night when the window is open. Examples are screeds, solid exterior and interior walls in the attic instead of lightweight walls or clay plaster instead of plasterboard in the roof structure.
Thermal insulation is also worthwhile to reduce the amount of heat entering the house in summer. It slows down the flow of heat from the outside to the inside – and in the opposite direction in winter. Good insulation of the exterior walls and roof can reduce the room temperature in summer by up to ten degrees Celsius.
Green roofs and facades as well as cooling from the ground
Green roofs and green facades also lower the temperature in the house. They act like a heat shield. Due to the evaporation of water on hot summer days, the air in the immediate vicinity cools down. A well-functioning green facade can reduce the ambient temperature by up to five degrees Celsius. This avoids extreme temperatures inside and at the same time has a positive effect on the climate around the house.
If there is still a need for cooling afterwards, homeowners should not use an air conditioner – it consumes a lot of electricity. Cooling with a heat pump is better. It not only heats effectively in winter, but can also cool the house in summer. There are two ways of lowering the temperature in the house with heat pumps: passive and active cooling.
Heat pumps can also cool
A geothermal heat pump is required for passive cooling. “The heat pump itself remains switched off, the heat is simply conducted via the radiators and the circulating pumps into the cooler ground,” says Frank Hettler from Zukunft Altbau. “That lowers the temperature in the rooms by up to three degrees.” More cooling is not possible, but usually not necessary if you have taken the heat protection precautions to heart. Then the electricity costs remain low.
Active cooling, on the other hand, works with many heat pumps. With active cooling, the heat pump with cooling circuit and compressor is active. This increases the cooling capacity, but also increases electricity costs. Therefore, if active cooling is required, it is best to use the solar power from your own roof directly for this purpose.