Renewable low-temperature district heating of a new housing area in Kassel, Germany - A case study of IEA EBC Annex 64

The renewable low-temperature district heating of a new housing area in Kassel, Germany is one of the case studies of IEA EBC Annex 64 "LowEx Communties". The heat supply concept pursues the low exergy approach and is based on a low temperature district heating network in combination with central and decentralized heat sources. The district heating network is fed by a central ground-source heat pump coupled with borehole heat exchangers. The low supply temperature of 40 °C is sufficient to cover the space heating demand of 127 buildings equipped with floor heating. The low supply temperature is crucial for high efficiency of the heat pump and low heat losses of the piping network. Hygienic domestic hot water preparation requires higher temperatures of up to 60 °C and is covered by decentralized solar thermal units with electrical back-up heaters. Thus, the district heating provides only the space heating during the heating period and is not in operation during summer. Furthermore, due to the limited area for borehole heat exchangers ground regeneration is necessary in order to avoid long-term undercooling of the ground. The ground regeneration will be done during summer by cheap uncovered solar thermal collectors, which are very efficient at low supply temperatures. The paper presents the heat supply concept in detail and describes the challenges for a practical realization, as well as the aims of the research project, which shall support the detailed design of heat supply.