Energy efficiency of domestic hot water distribution system

The aim of paper is to analyze the thermal losses of domestic hot water (DHW) distribution system. There were used calculation methods by valid EN standard for energy performance of building. The analysis of energy performance was done for multi-dwelling house with 5 floors with total number of flats 32 (two-room and three-room flats on the 2nd to 5th floors). There are total 86 residents in the house and the average consumption of DHW is at 40 litres per person and day. The object of analysis is the application of electric heat cables in order to maintenance domestic hot water temperature. The results are compared with traditional DHW distribution system with circulation loop. Energy need for DHW, thermal losses from the DHW distribution system and thermal losses from the DHW storage vessel were calculated in order to analyse the selected variants of DHW systems. From results is clear that DHW distribution system with circulation loop represents significant part of system energy need. In case of classic DHW distribution system with circulation loop the distribution thermal losses are about 30 % from energy need for DHW preparation. In case of electric heat cables application the rate of distribution thermal losses were reduced to 15 % from energy need for DHW preparation. The reached energy saving was not displayed in the operation costs of DHW system. In case of heat cables utilisation the electric energy consumption in DHW system is higher and it caused the increasing the operation costs about 8 %. In case that all energy requirements of DHW system (both variants) are covered by electricity the operation costs of DHW system with electric heat cables would be reduced by 10 % at average.