Field studies of domestic hot water comfort in semi-detached houses during summertime

The paper describes measurements performed in three district heating (DH) substations in semidetached houses. In all these houses more than 40 % of the domestic hot water (DHW) tappings turned out to be shorter than 10 s. The fraction of total energy used to heat this water varied between 2.4 % and 10.2 %, indicating a large influence of households' daily habits. For 60-78 % of tappings, the total amount of supplied DH water volume was below 2.5 litres, which underlines the importance of using small volume pulses for the energy metering. When analysing the off-load behaviour of the DH substations it was established that radiator circuit control valves for the most part of the studied period were working on/off. During periods when there was no radiator load, the primary supply temperature was typically 50-60 degrees C, which was higher than expected. The differences in supply temperature level between the substations might be caused by leaking valves or by differences in off-load set point temperature of DHW control valves. Furthermore, the measurements indicate large differences among DHW controllers regarding the characteristics of the feed-forward control. In more than 80 % of the tappings with duration of more than 10 s, an outgoing DHW temperature of at least 40 degrees C was obtained within a maximum of 10 s. However, depending on the house studied, in 17-55 % of those tappings the monitored DHW temperature did not reach the level of at least 50 degrees C, as required by the Swedish District Heating Association