Staged control of domestic hot water storage tanks to support district heating efficiency

Abdelkarim Tahiri*, Kevin Michael Smith, Jan Eric Thorsen, Christian Anker Hviid, Svend Svendsen

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Storage tanks are commonly used for domestic hot water (DHW) preparation in large buildings supplied by district heating (DH), especially to cope with peak demand. The charging control of DHW tank systems is often suboptimal, increasing return temperatures and harming the overall DH operation efficiency. This paper presents two novel control concepts to optimise DHW tank charging, satisfying comfort and hygienic requirements without leading to excessive DH flows. The first, more complex control concept employs the smart energy meter sometimes used for DHW billing. It inspired the development of a second, broadly implementable control concept employing a staged proportional gain with an added temperature sensor. The authors tested and refined this staged-gain concept using a validated Modelica model of a real DHW system in a Danish multistory residential building. The authors subsequently implemented the staged-gain control concept in the field, successfully reducing the energy-weighted DH return temperature by 7 °C and the total DH flow by 23.6% compared to the conventional thermostatic control. This analysis accounted for the variation in DHW tapping, DHW temperature, DH supply temperature, and cold water temperature. Furthermore, the performance was robust to relaxed settings of the valve constraints, demonstrating minimal configuration requirements for new implementations.
Original languageEnglish
Article number125493
Number of pages12
Publication statusPublished - 2023


  • Domestic hot water tank
  • Control strategy
  • Modelica model
  • District heating
  • Return temperature


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