Abstract
District heating (DH) systems are one of the main components of future energy systems as they can significantly contribute to the transition towards a 100% renewable-based supply. Employing heat pumps in the substation of DH end-users has already been investigated, finding the periodic use of heat pumps an economic challenge. This work proposes neighborhood-scale heat pumps in an ultralow-temperature DH system to increase their utilization factor and thereby, improving the cost-effectiveness. As such, triple-pipes (TPs) are used instead of conventional twin-pipes (TwPs) to separate hot water (HW) line from space heating (SH) line, decreasing the size of heat pumps and the rate of losses. Heat pumps only increase the temperature of the HW supply line. The suggested DH system is designed and analyzed thermodynamically for a sample network, and the results are compared with a low-temperature DH system, as the most important competitor to the proposed solution. The results show that the proposed system is better than the competing solution in terms of an overall efficiency point of view. For three typical hot/medium/cold days in the network, the daily thermal losses of the proposed and low-temperature systems are 155.2/557.5/913.4 kWh and 182.3/692.8/1053.2 kWh, respectively.
•Triple-pipes and decentralized heat pumps are analyzed in district heating systems.•Performance of this system is compared to low-temperature district heating system.•Proposed solution offers a lower rate of heat loss and better energy efficiency.•Effectiveness is larger when the operation load is higher, e.g. a winter day.