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Ventilation, heating and hot water in passive houses!
April 6, 2016

Ventilation, heating and hot water in passive houses!

The performance of the ventilation system is considered an integral element of the primary Passivhaus heating demand calculation, though the rest of the services are not. You can think of this as being because the main intake and exhaust ducts, carrying cold air, actually form part of the building’s external envelope. So in keeping with the emphasis on compact form, the designer needs to be aware of these ducts and how to make them as short as possible at an early stage in design. The impetus for using MVHR may have come from the opportunity for heat recovery but now we recognise that the main benefit of these ventilation systems is basically good ventilation. The Passivhaus standard sets detailed criteria for airflow rates, noise levels and commissioning which, if followed, will lead to ventilation that works well. The ventilation section of this guide provides specific details about designing ventilation to the Passivhaus standard.

A Passivhaus does need some heating – this is implicit in the standard, which is in terms of annual heating demand or peak heat load, after taking account of solar and internal heat gains. However, the amount of heating is very small – much less than a standard new building, and far less than the 20th Century buildings our heating systems have developed in. It should be possible to heat a Passivhaus by heating the ventilation supply air, but this doesn’t mean you should do it. There is often a mismatch between where you want air and where you need to supply heat, so it can be easier to separate them. Also neither boilers nor heat pumps are well suited to supplying the steady low level of heating power required by air heating.In fact the heating system is one area where you can reduce costs compared with a conventional building and still retain conventional suppliers and technologies – simply use a gas boiler but with fewer and smaller radiators.

Excerpt from “How to build a Passivhaus: Rules of thumb”, Passivhaus Trust, April 2015