A Passivhaus building can in theory be heated via the fresh air supply – that is after it is heated to around 50°C. This idea of doing away with a conventional heat distribution system helped define the Passivhaus standard, but isn’t necessarily the best choice. Any heating system can be used – radiators, underfloor
heating, split system air conditioning, wood burning stove and you can use a gas boiler, a heat pump or district heating. Direct electricity for both heating and hot water is not normally possible because electricity’s high primary energy factor means this usually exceeds the Passivhaus primary energy limit of 120 kWh/(m2.a).
It makes sense to think of the heating system as primarily providing hot water, plus heating as and when needed. The efficiency of the hot water system, ie, minimising losses from storage and distribution, is significant both in terms of energy use and summer overheating. In PHPP losses that contribute to heating are considered to be part of the heating demand and not the hot water demand – so in fact the heating system itself can be providing signifi cantly less than the calculated 15 kWh/(m2.a).
Excerpt from “How to build a Passivhaus: Rules of thumb”, chapter by Alan Clarke, Passivhaus Trust, April 2015.