Heat Pumps Architecture Optimization For Enhanced Medium Temperature Geothermal Heat Use in District Heating

Use of geothermal heat in distric heating allows increasing the share of renewable energy use. However, in many cases, this share is limited by the district heating required temperature and seasonnal load variation. Heat pumps permit upgrading geothermal heat by increasing further the temperature while pumping residual heat from the network return. Therefore not only they substitute boilers for upgrading the temperature but also increase the capacity of the geothermal heat source by reducing the return temperature. This paper presents a methodology for heat pumps architecture optimization enhancing the use of geothermal heat. The methodology allows considering two optimisation objectives: total cost and renewable energy share. Heat pumps are modeled by considering their partial load behavior. Many architecture options are considered involving the disposal heat pumps in serie and in parallel. A case study is presented optimizing the use of a 60°C georthemal source connected to a district in the north of France. The geothermal well has two constraints: a limited mass flowrate and a minimal reinjection temperature of 26°C. Both investment and operating costs are considered for the optimisation while a minimum renewable energy share is set as a constraint