A specially-designed test platform and method to study the operation performance of medium-depth geothermal heat pump systems (MD-GHPs) in newly-constructed project

Abstract

Medium-depth geothermal heat pump systems (MD-GHPs) use deep borehole ground heat exchangers (DBHEs) to extract heat from the medium-depth geothermal energy with depth of 2–3 km. To study the local geothermal condition and operation performance of MD-GHPs, so as to guide the system design and operation control, a test platform and method are raised and applied in a newly-constructed project, where a DBHE with depth of 2750 m is constructed. Results show that the maximum heat extraction rate of DBHE reaches 450 kW with inlet and outlet water temperature of 5.0 ℃ and 18.9 ℃, and the maximum heat supply rate of heat pump reaches 600 kW with supply and return water temperature of 51.8 ℃ and 40.6 ℃ under continuous operation mode. Then the energy efficiency of heat pump (COP) can still remain higher than 3.60 with renewable energy utilization rate higher than 72.2 % in this maximum load condition. Besides, the DBHE still extracts heat from outside ground to store heat when the heat pump system shuts off, thus the transient maximum heat extraction rate could reach 600 kW or even higher under intermittent operation mode. Finally, the optimization direction of DBHE and heat pump systems are analyzed, so as to improve the overall operation performance of MD-GHPs and achieve better energy conservation effect.