Most effective measures to combat heat indoors

Due to climate change, homes are increasingly becoming unacceptably hot, especially during heat waves and therefore create health risks for citizens. To combat heat indoors, active cooling systems, such as air conditioning, are very effective. However, this also comes with negative effects such as increasing energy demand, the use of cooling liquid and releasing heat into the surrounding outdoor environment. Housing associations in particular want to know how they can take possible overheating into account when renovating homes (e.g., for the energy transition). That is why, on behalf of the national government, it was investigated which characteristics on three different levels (the urban area, the building, and the inhabitant) make homes especially vulnerable to heat and which measures can limit that heat.

Desk research (literature study, simulation study and panel discussion) has been carried out in which different situations and the effectiveness of heat-reducing measures have been compared and ranged. For two common housing types in the Netherlands that cover a substantial part of the Dutch housing stock owned by housing corporations, the hourly temperature has been simulated for a representative summer. This was done for many combinations of factors like: green surroundings or urban heat islands effects, solar heat gain (windows, sunscreens), insulation, green roofs, ventilation and use of curtains.

The research shows that the entrance of sun in particular determines overheating of houses and that measures that reduce solar heat gain therefore have the greatest positive effect. Orientation of the house, location and size of windows, and sunscreens are key factors in preventing heat gain. Purge ventilation during the night is the second most important measure, as this helps cooling the house. For this reason night time city temperatures are important. Better insight in those urban night time temperatures is required. The study also showed that human behaviour is an important factor. Correct ventilation and use of sunscreen have a large impact on overheating of houses. Finally, the focus on thermal insulation without sufficient attention on ventilation greatly increases the risks of overheating. The outcome of the research is presented in a guideline for housing associations that ranges the measures in very effective, medium effective and undesirable actions.