[Darmstadt, Germany] On hot summer days, Passive House buildings can be noticeably cooler than conventional buildings. The excellent level of thermal insulation keeps the heat out, coupled with effective strategies such as “passive night cooling” ensure com-fort in the summer months. Providing proof of a pleasant indoor climate in summer is also one of the requirements for quality assurance for Passive House certification. "Nu-merous practical examples in different climate zones very clearly show that Passive House buildings have a pleasant and cool indoor climate during heat waves. However, professional planning is crucial for this", says Zeno Bastian of the Passive House In-stitute.
Good planning is essential
A common problem in summer is overheating. With climate change in mind, this problem is only set to intensify in the future. It is sometimes thought that well-insulated buildings are prone to overheating. However, this claim is un-justified. "There may certainly be isolated cases of well-insulated buildings that become overheated in summer. However, through careful planning par-ticularly using the planning tool PHPP, this problem can be avoided from the outset. Buildings with little or no insulation will definitely become overheated. Not only will these buildings be warm in the summer, they will also be too cold in the winter," explains Zeno Bastian, head of building certification at the Passive House Institute.
With perfect beach weather, especially con-ventional buildings become overheated.
"Passive" cooling measures
The Passive House Standard is suitable for various climatic conditions, including cold, temper-ate and also warm and humid climates. It can thus be applied anywhere in the world. Passive House buildings, among other things, are characterised by their high quality thermal insulation, triple-glazed windows, and an airtight building envelope. In winter, heat recovery by the ventila-tion system ensures that the air entering the building is preheated. What keeps heat inside the building in winter also helps in the summer: heat enters the building more slowly. “Passive” cool-ing measures ensure that a Passive House building does not heat up at all ? or only heats up slowly ? during a heat wave in the summer. These can also be helpful in conventional buildings for maintaining summer comfort without any additional active cooling:
* The first and foremost measure against heat-ing up is exterior shading elements. For this reason, Venetian blinds or roller blinds should be kept closed for as long as possible on hot days. This is also applicable in older buildings. Here, the heat gain through the walls and roof is significantly higher, though.
* Passive night cooling: during the course of a hot summer day, even Passive House build-ings can become warmer. The easiest way to remove this heat is at night by simply opening the windows. The warm air can be flushed out and the inside of the building will cool down; the walls and ceilings will keep this cool tem-perature for the following summer day. This option is also possible in old buildings. How-ever, in a Passive House this cool state is maintained for much longer.
* If it is not possible to open the windows, then cool outdoor air can also be drawn into the
home at night via the ventilation system (summer bypass). However, window ventila-tion is more effective because it introduces bigger amounts of air into the building com-
pared to the summer bypass of the ventilation system.
* After night-time cooling, when it is cooler inside compared to the outside, the heat recov-ery of the ventilation system in a Passive House building ensures that pre-cooled fresh air enters the house: the ventilation system transfers the heat of the outdoor air to the extract air before it comes into the building. The extract air is removed towards the outside, and only the pre-cooled air comes into the building. This option is only possible in a Passive House with a heat recovery ventilation system.
* Energy efficient household appliances and energy-saving lighting not only reduce the electricity bill, they also produce less unnecessary waste heat, so that the building remains cool for longer in the summer.
* Hot water pipes must be well-insulated. This not only reduces energy losses but also minimises the heating up of rooms in summer.
Practice has shown that Passive House buildings such as those in the Bahnstadt in Heidelberg have a pleasantly cool indoor climate even during hot periods in summer. However, proper planning is crucial Passive House Institute
When a Passive House certifier is entrusted with the task of checking the planning, the certifier will also examine the summer behaviour of the building. If the criteria for summer comfort are not met, the certifier will request modification of the planning. In some cases, additional measures or active cooling may be necessary. For example, if summer ventilation strategies in inner cities are not feasible due to traffic noise or burglary protection, when extreme climatic conditions prevail in warm and humid climate zones, or if there is an altered requirement for comfort.
Hot and humid climate zones
In hot and humid climate zones all the “passive” measures to reduce overheating described above support the Air Conditioning systems which do cooling and dehumidification. Therefore, the cooling load and cooling energy demand in Passive House buildings is much smaller than in conventional buildings. Careful planning of all features and the calculation of cooling load are thus crucial.
Combined with renewable energy
Due to the small cooling load, a small cooling unit with a low output and therefore low electricity con-sumption will be sufficient for a Passive House building. "A photovoltaic system generates a lot of electricity particularly on hot summer days. Anyone who installs these on the roof can power the Passive House building's cooling unit through this self-generated renewable energy", says Zeno Bastian. The Passive House Institute recommends that expert advice should be sought before retro-fitting or installation of an active cooling system.
Cooling in Greece
Stefan Pallantzas is also very interested in the summer comfort in his Passive House retrofit in Greece. Temperatures over 33 degrees are normal in summer in Athens. Therefore, for the 95 square meters of his home, Pallantzas has installed a 2-kW split unit for heating and cooling. "The results were good. The single unit has managed to cool the whole residence without any problem. The temperatures measured inside and outside the building were very close to the ones used in PHPP. The highest temperature measured in summer was 25,70°C." says Pallantzas.
Comfort in New York
Matthew Brouwers of Rochester, New York, USA, is also very pleased with the comfort of his passive house during prolonged periods of heat:“ We are certainly satisfying any concerns of comfort with a spot source cooling unit,” writes Matthew in a recent article on Heat and Humidity in his Rochester Passive House Blog.
Source: The Passive House Institute