Development and test: Future-proof substation designs for the low-temperature operation of domestic hot water systems with a circulation loop

• Published in: Energy and buildings Vol. 298; p. 113490
• Main Authors: Yang, Qinjiang, Salenbien, Robbe, Motoasca, Emilia, Smith, Kevin, Tunzi, Michele
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2023
• Subjects: Circulation loss booster; Decoupling; Domestic hot water system; Low-temperature district heating; Low-temperature district heating; Domestic hot water system; Decoupling; Circulation loss booster
• ISSN: 0378-7788
• DOI: 10.1016/j.enbuild.2023.113490

•Future-proof domestic hot water substations ready for 4th generation district heating.•Separate heat exchangers decouple the heating of the cold water and the circulation.•Low district heating return temperatures can be achieved by the booster heat pump.•The booster heat pump is a coupling point of the electricity grid and heating system. On the transition toward low-temperature district heating (DH), generation sectors, distribution networks, and building consumers should all be adapted to low-temperature operation conditions. However, a bottleneck in lowering DH return temperatures is the domestic hot water (DHW) system with a circulation loop in multifamily buildings. Existing systems with a single heat exchanger often led to elevated return temperatures because of the reheating of the circulation loop. This study developed several innovative designs for future-proof DHW substations that decouple the heating of cold water and circulation flows, ensuring lower DH return temperatures in large multifamily buildings. First, a theoretical analysis was performed for benchmarking the return temperature for various proposed design configurations under low-temperature operation conditions; then, the proposed configurations were tested for a Danish multifamily building connected to a medium–low-temperature DH network. In the field tests, compared to a typical DHW substation with a single heat exchanger, the proposed configuration with the circulation loss booster reduced the average DH return temperature from 46.4 °C to 34.1 °C and 27.9 °C for parallel or serial connections, respectively. Economic analysis confirms the viability of the proposed solution, with a payback period ranging from 3.4 to 7.9 years.