Are we significantly oversizing domestic water systems?

There is growing dissatisfaction with the DCWS volume flow rates predicted by the UK sizing methods, particularly for sizing incoming mains and pressure boosting sets. The consequences of oversizing include increased heat loss from domestic hot water systems, thus reducing their energy efficiency, and difficulties in avoiding domestic cold water reaching unacceptably warm temperatures particularly in high rise buildings due to the slower throughput. The aim of this paper is to present measured domestic water volume flow rates and compare them with those obtained by calculation in order to investigate the magnitude of oversizing. The study revealed that the measured flow rates are on average just 20% of those calculated however BS EN 806-3 is by far the most accurate of the three methods.