The importance of hot water system design in the Passivhaus
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Abstract
The default assumptions in PHPP [PHPP 2007] already put the energy demand for hot water higher than that for space heating. Our analysis of actual water use shows that in the UK hot water use is typically at least 30% higher per person than is assumed in PHPP. Also the losses associated with hot water generation are considerable, with a calculated 5kWh/(m2.a) being the best acheived and over 10kWh/(m2.a) more usual in modern low energy houses. Monitored data from completed low energy houses (at Stamford Brook) have shown higher losses than this in practice [Wingfield et al 2008]. So for occupancy levels assumed in PHPP (35m2/person) the total energy demand of the hot water system is usually at least 30kWh/(m2.a), double the passivhaus heating demand of 15kWh(m2.a).