Integration of space heating and hot water supply in low temperature district heating

District heating may supply many consumers efficiently, but the heat loss from the pipes to the ground is a challenge. The heat loss may be lowered by decreasing the network temperatures for which reason low temperature networks are proposed for future district heating. The heating demand of the consumers involves both domestic hot water and space heating.

Space heating may be provided at low temperature in low energy buildings. Domestic hot water, however, needs sufficient temperatures to avoid growth of legionella. If the network temperature is below the demand temperature, supplementary heating is required by the consumer. We study conventional district heating at different temperatures and compare the energy and exergetic efficiency and annual heating cost to solutions that utilize electricity for supplementary heating of domestic hot water in low temperature district heating.

This includes direct electric heating and three heat pump solutions applying R134a and R744. The results show that conventional solutions at lowest possible temperature have the highest exergetic efficiency of 28% and lowest annual cost of € 690 for a 159 m2 house. The best low temperature system is an R134a heat pump with hot water storage on the district heating side, which reaches 25% exergetic efficiency.