With comfortable indoor temperatures increasingly considered a criterion for rentability, it makes sense for property owners to invest in indoor climate comfort. The new white paper, ‘Cooling buildings efficiently’, shows how we can build or renovate properties today to ensure they continue to offer a high level of comfort in the climate of the future.
According to the Climate CH2025 scenarios (in German), average temperatures in Switzerland will have increased by 2.9 degrees Celsius by 2024 compared to pre-industrial times (1871 to 1900). This puts Switzerland above the global average of 1.3 degrees Celsius. The climate scenarios predict how our climate could change compared to pre-industrial times in the event of global warming levels of +1.5, 2 or 3 degrees Celsius. Unless we manage to reduce greenhouse gas emissions significantly, this means that Switzerland will see an increase of 4.9 degrees Celsius in the most extreme global warming scenario of 3 degrees Celsius.
More hot days and tropical nights
Hot days with temperatures of 30 degrees Celsius or higher are already a more frequent occurrence than in the last century. Urban residents are hardest hit by the heat. Given the extensive sealing of urban areas, surfaces heat up significantly during the day. This results in ‘heat islands’ that make it more difficult for indoor spaces to cool down overnight.
Impact on interior comfort and health
High temperatures have a negative effect on interior comfort. However, how humans perceive comfort varies from one person to another. It is not just the air temperature that influences comfort, but also air currents, temperature differences within the room and humidity. For most people, indoor comfort means temperatures between 22 and 26.5 degrees Celsius, which is why the Swiss Society of Engineers and Architects (SIA) suggests this range as a guide for room temperatures in the summer.
Cooling requirements of buildings
According to the report entitled ‘Climate scenarios for the interior climate of the future' (in German), the effect of climatic change differs depending on location and building use. In practically all cases, both residential buildings and office buildings will require active cooling in the future, i.e. a cooling system that runs on electricity.
The study ‘ClimaBau – Planning in the face of climate change' (in German) investigated how future climate conditions will affect the energy requirements of residential buildings in Switzerland by 2100. While energy requirements for heating are falling, the focus is shifting to providing energy for cooling. It is likely that, as early as the middle of this century, the cooling demand in new residential buildings on the Swiss Plateau will be higher in particularly hot years than the heating demand. In southern Switzerland, heating demand will be almost insignificant compared to the cooling demand.
Among other things, the planning framework is defined by the Model Cantonal Regulations in the Energy Sector (MuKEn). These require buildings and facilities to consume as little energy as possible. Standard SIA 384/4 ‘Air conditioning cooling systems in buildings – Principles and requirements' (in German) also serves as a basis for the planning, construction and operation of air conditioning cooling systems, and requires a holistic approach.
A new building that is planned today should still be functional towards the end of the century. According to one study (in German), the following points, amongst others, should be included in the project brief: analysis of exterior and interior comfort; requirements for protection against summer overheating; maximum acceptable indoor temperatures; demonstration of thermal comfort.
If indoor climate comfort in existing buildings no longer meets current or future requirements in summer, the following measures should be considered and prioritised: protection against summer overheating; passive cooling through night cooling or free cooling/geocooling; active cooling, such as the use of chillers.
Cost-effectiveness
It pays for property owners to invest in indoor climate comfort. As summers get hotter, indoor temperatures are becoming an increasingly important criterion for the rentability of properties. Opting for an integrated cooling and heating supply leads to lower investment costs than having separate cooling systems. In addition, properties capable of maintaining a pleasant indoor climate over the long term are future-proof, increase in market value and are likely to generate higher rental income.
Protection against summer overheating
Windows: Large window surfaces enable passive heat gain in winter. In summer, on the other hand, insufficiently shaded and/or energy-inefficient windows can accelerate the overheating of indoor spaces. Minergie recommends that windows account for 20 to 30 per cent of the facade in residential buildings and 30 to 40 per cent in office buildings.
Shading: Direct sunlight can be prevented by blinds, shutters, awnings or a canopy. At the same time, the sun protection should allow enough daylight into the building’s interior and enable solar heat gain in winter.
Insulation: To slow or prevent heat penetration, it is necessary to have a well-insulated building envelope. Many existing buildings show room for improvement in this regard.
Facade and roof greening: Greening can reduce heat development on the building envelope. Plants provide shade for roof and facade surfaces and draw heat from their surroundings by evaporating water through their leaves.
Passive cooling
Night cooling: The easiest way to cool a building without using energy is to ventilate it through the windows at night and early in the morning. The cooler night air that flows through the room absorbs the heat and transports it outside.
Free cooling/geocooling: During free cooling, only the circulation pump runs. The water absorbs thermal energy as it circulates through the rooms and the room temperature drops. The heat is then transferred to the energy source used for heating – usually to groundwater, the ground (geocooling) or to a thermal network with a low operating temperature (‘anergy network’).
Active cooling
Reversible heat pump: In reverse mode, the heat pump provides cooling instead of heating. This can be circulated through a panel distribution system to cool the rooms. The cooling effect is similar to that of free cooling, but more energy is consumed because the compressor is running.
Air conditioning unit: Air conditioning systems or units are relatively uncommon in Switzerland. These systems are actually air-to-air heat pumps that heat or cool the air directly. Although they do this quickly, a larger amount of energy is required.
With comfortable indoor temperatures increasingly considered a criterion for rentability, it makes sense for property owners to invest in indoor climate comfort. The new white paper, ‘Cooling buildings efficiently’, shows how we can build or renovate properties today to ensure they continue to offer a high level of comfort in the climate of the future.
