Overview of solutions for the low-temperature operation of domestic hot-water systems with a circulation loop

Theofanis Benakopoulos*, William Vergo, Michele Tunzi, Robbe Salenbien, Svend Svendsen

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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The operation of typical domestic hot water (DHW) systems with a storage tank and circulation loop, according to the regulations for hygiene and comfort, results in a significant heat demand at high operating temperatures that leads to high return temperatures to the district heating system. This article presents the potential for the low-temperature operation of new DHW solutions based on energy balance calculations and some tests in real buildings. The main results are three recommended solutions depending on combinations of the following three criteria: district heating supply temperature, relative circulation heat loss due to the use of hot water, and the existence of a low-temperature space heating system. The first solution, based on a heating power limitation in DHW tanks, with a safety functionality, may secure the required DHW temperature at all times, resulting in the limited heating power of the tank, extended reheating periods, and a DH return temperature of below 30 °C. The second solution, based on the redirection of the return flow from the DHW system to the low-temperature space heating system, can cool the return temperature to the level of the space heating system return temperature below 35 °C. The third solution, based on the use of a micro-booster heat pump system, can deliver circulation heat loss and result in a low return temperature below 35 °C. These solutions can help in the transition to low-temperature district heating.

Original languageEnglish
Article number3350
Issue number11
Number of pages26
Publication statusPublished - 2021

Bibliographical note

Funding Information:
Funding: This research was funded by VITO NV and Technical University of Denmark, Department of Civil Engineering (DTU_PhD_1701_contract) and the Danish national EUDP grants—J.nr. 64019-0554—for the project “Improved operation of heating systems in multistorey building to realize low temperatures in district heating networks”.


  • Circulation heat loss
  • Domestic hot water systems
  • Heat exchanger
  • Low return temperature
  • Micro-booster heat pump
  • Storage tank


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