A field test of medium-depth geothermal heat pump system for heating in severely cold region

Abstract

Due to the worldwide attention of fossil fuel consumption and environment pollution, geothermal is recognized to be amongst the prospering alternative energy. Previous researches mainly focused on the shallow-depth geothermal heat pump systems (SD-GHPs), while medium-depth geothermal heat pump system (MD-GHPs) lacked of the experimental support especially in severely cold region. A field test of MD-GHPs using deep borehole heat exchanger (DBHE) was conducted and verified in terms of temperature variation, heat exchange and COP. The indoor temperature remained 20 °C around even though the outdoor temperature was as low as −25.10 °C. The water supply and return water temperature on the customer side performed steadfast heating characteristics that the averages were 35.13 °C and 30.97 °C. Moreover, flow rate and borehole depth are the essential influencing factors on DBHE outlet temperatures. This suggests that lifting flow rates is a fantastic option when only considering the enhancement of the thermal extraction. The DBHE average heat exchange per meter is 1000/1200 m for 61.1/84.9 W/m and 2000 m is 152.6 W/m respectively. Besides, the average heat exchange of DBHEs for working days was 485.4 kW while during Chinese New Year Holidays was 388.6 kW. Correspondingly, the average COPs for MD-GHPs ground side were 4.5 and 5.2, respectively. Results show that MD-GHPs can be extended to severely cold regions and obtain superior performance.