On the circulation heat losses in domestic hot water systems in residential buildings

Abstract

The share of domestic hot water (DHW) systems in total energy consumption of buildings, especially in Nearly Zero-Energy Buildings (NZEBs), is rising and will continue doing so in the future, because most energy efficient measures are dedicated for heating/cooling systems. Besides, the amount of detailed field research on DHW systems is limited in comparison to heating/cooling systems. This article identifies the problem of excessive heat losses in the circulation lines of the DHW installation in residential buildings supplied from the district heating network. The analysis used the measurement and operational data for the summer season, i.e. the period of May–September 2018 for nine multi-family buildings located in Lublin (Poland). The buildings are divided into three groups according to the cubic volume: below 5000 m3, 5000 ÷ 10,000 m3 and above 10,000 m3. The research was conducted in two variants. Method I concerns the heat losses from circulation only at night and days, when hours with the power needed to heat DHW is lower than assumed values on the basis of DHW consumption, while method II covers all hours of the day. The obtained average results of circular heat losses range from 9.36 ÷ 25.38 % for method I and 22.96 ÷ 69.14 % for method II. The largest energy losses were recorded in the summer months, mainly August and July, while the smallest losses were recorded for May, June and September during the school year. The obtained calculations and their results are the basis for determining the information on the dependence of heat losses on circulation pipes and the size of buildings.