Heat pump system design


The aftercooling concept is an innovative district heating substation for large multi-apartment buildings where the domestic hot water preparation and reheating of the circulation flows are decoupled and obtained in two separate heat exchangers connected in parallel. The primary return temperature flow from the circulation heat exchanger is further aftercooled by the space heating system before returning to the district heating network. The concept provides a reduced return temperature to the district heating network.


The key ability of the future district heating system is to operate at lower network temperatures. The aftercooling system reduces the return temperature from the building, and this is often a precondition for being able to reduce the district heating supply temperature. Lower network temperatures make it possible to utilise low temperature surplus energy sources that otherwise would be wasted or would require a temperature lift by e.g., a heat pump. Further it reduces the thermal distribution losses from the district heating network. The potential for district heating return temperature reduction is 4-8°C on yearly level for typical buildings, which is significant.
Operating diagram of the aftercooling system


This innovation focuses on the development of the aftercooling concept and the analysis of the district heating return reduction potential. The developed aftercooling system is relevant where a traditional district heating substation is to be installed or to be updated, typical residential and commercial buildings, and where there is domestic hot water circulation service provided. Critical for the deployment of the concept is that the district heating utilities establishes an economic bonus scheme awarding a reduced district heating return temperature. This is the case in Denmark and partly in Sweden, but it’s not widely spread.


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