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 significantly less than the calculated 15kWh/ (m2 .a).

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