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Automated hydronic balancing in space heating systems is crucial for the fourth-generation district heating transition. The current manual balancing requires labor- and time-consuming activities. This article presents the field results of an innovative electronic radiator thermostat tested on two Danish multi-family buildings. The prototypes had an additional return temperature sensor on each radiator and an algorithm was used to accurately control valve opening to ensure automated hydronic balancing. The results highlighted that the new thermostat performed as expected and helped secure the cooling of district heating temperatures —defined as the difference between supply and return temperature—4–12 °C higher during the test compared to results obtained in 2020, when the prototypes were replaced with state-of-the-art thermostats in the first building. The measurements from the other building illustrated how only two uncontrolled radiators out of 175 could contaminate the overall return temperature. The remote connection of the thermostats helped pinpoint the faults in the heating system, although the end-users were not experiencing any discomfort, and secure, after fixing the problems, a return temperature of 35 °C. Future designs may consider integrating a safety functionality to close the valve or limit the flow in case of damage or malfunction to avoid a few radiators compromising the low-temperature operation of an entire building before the cause of the problem has been identified.

Abstract The low-temperature operation of existing radiator systems connected to district heating is hindered by various factors, including non-ideal local control by users. The use of only a few of the available radiators to provide the necessary thermal comfort in an apartment is a common example. This requires a higher supply temperature and results in a high return temperature. This study investigated the potential of minimising the supply temperature of the radiator system to stimulate the use of all the available radiators in each apartment. Data from existing electronic heat cost allocators were used to detect the number of radiators not being used at any given time. A thermal/hydraulic model of the radiator system of a building was created to calculate the minimum supply temperature required according to the maximum pump operation. Energy-weighted average supply and return temperatures of 44 °C and 30 °C, respectively, could be achieved when all the radiators were used. The investigation showed that under the minimum supply temperature and a sufficient hydraulic balance, the required heat could only be delivered if all the available radiators were used. A good hydraulic balance could be secured by appropriately setting the balancing valves in each riser.

Abstract In order to reach targeted 4th generation district heating temperatures around 55 °C supply and 25 °C return, it is necessary to ensure that heating installations inside buildings are designed and operated properly. In this study we investigated the best-case of current design and operation of building installations with the aim of identifying whether there is a gap between current best-case examples and future temperature targets. The study included 7 single-family dwellings and 3 apartment buildings, that were selected based on their low district heating return temperature. Data from the building substations showed that single-family dwellings obtained return temperatures in the range from 25 to 30 °C while the apartment buildings had return temperatures in the range of 30–40 °C. This indicates that there is a gap between the best functioning heating installations in apartment buildings today, and the targeted district heating return temperatures of 25–30 °C in future 4th generation district heating networks. District heating return temperatures in the range of 30–40 °C could however be the initial ambition for the existing buildings all around Europe that are expected to be connected to new district heating systems in the near future.