Overview of Solutions for the Low-Temperature Operation of Domestic Hot-Water Systems with a Circulation Loop

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 degrees 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 degrees 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 degrees C. These solutions can help in the transition to low-temperature district heating.

Automated summary

This article presents three recommended solutions for new DHW systems to operate at low temperatures, including limiting heating power in DHW tanks, redirecting return flow to low-temperature space heating systems, and using micro-booster heat pump systems. These solutions can help reduce return temperatures and facilitate the transition to low-temperature district heating.