Conversion area ‘Lagarde’ in Bamberg, Germany
Since the withdrawal of the US army in 2014, the city of Bamberg has planned to develop and integrate the former military area (Lagarde Campus), which consists of existing and new building stocks, into the existing city structure. Above all, the urban and architectural identity should be preserved during the planning process, at the same time the energy system should be reinterpreted in a contemporary way. Thereby, the energy supply of the Lagarde Campus should be primarily based on renewable energies, which generate heat and power in the quarter itself, in order to contribute to the local climate goal, within the German national framework of the funding programme ‘Wärmenetzsysteme 4.0’ (Kaiser and Loskarn, 2019 / Kaiser and Loskarn, 2019a).
The purpose of the feasibility study was to develop a cold district heating system (CDH), which supplies low temperature heat from near-surface geothermal collectors to decentralized heat pumps, located in the connected buildings, based on a thermal-hydraulic analysis with the simulation environment TRNSYS.
The main heat supply of the cold district heating network is supplied by a combination of near-surface geothermal collectors and different heat sources, such as sewage (about 12°C) and drinking water networks (8– 14°C). Due to the limited area of undisturbed ground, geothermal collectors are buried horizontally under buildings, 3.6 meters deep in the ground. Regarding the heat supply with near-surface geothermal collectors, the distribution networks are designed with a supply temperature of 1°C and a return temperature of -2°C in the winter periods. Because of the low temperatures, the system is intended to be operated with a brine. For the additional heat gain through the distribution networks, plastic pipes without thermal insulation are used for the CDH. Besides the CDH, PV-modules are implemented to cover the local electricity demand of household devices and partly that of the decentralized heat pumps.
The results of the simulation study show that the network temperature is significantly affected by the ground temperature during the operation of the CDH. Thereby, the operation of cold distribution networks with a supply temperature of around 1°C in the winter periods and ca. 10°C during the summer months allows an annual heat gain of ca. 19 MWh/a through distribution pipes, which corresponds to around 1% of the total heat demand (ca. 1,820 MWh/a).
However, the simulation results of near-surface geothermal collectors indicated that the limited amount of heat sources from sewage and drinking water networks could lead to the icing over of ground collectors in freezing weather. For this reason, further integration of heat sources such as ice storages, PVT-Modules etc. are investigated in the second phase of the study.