Hybrid ground source absorption heat pump in cold regions: Thermal balance keeping and borehole number reduction

Thermal imbalance of ground source electrical heat pump (GSEHP) leads to cold accumulation in cold regions. Ground source absorption heat pump (GSAHP) can relieve the thermal imbalance, but may cause heat accumulation in the warmer parts of cold regions. Hybrid GSAHP (HGSAHP) integrated with a cooling tower is proposed to solve this problem. Hourly simulations of single-effect HGSAHP and generator absorber heat exchange (GAX) cycle HGSAHP are conducted, and are compared with hybrid GSEHP (HGSEHP). Results show that the thermal balance can be well kept by HGSAHP, with imbalance ratio reduced from 60-80% to within 20%, and soil temperature variation staying within 3 °C after 20 years' operation. Moreover, HGSAHPs are advantageous in heating mode and inferior to HGSEHP in cooling mode. The annual performance of GAX-cycle HGSAHP is very close to that of HGSEHP in Beijing, while being 17.5% higher than that of HGSEHP in colder regions like Shenyang. Compared with HGSEHP, the required borehole number and occupied land areas can be reduced by 37-52% by single-effect HGSAHP and reduced by 20-38% by GAX-cycle HGSAHP. Additionally, the lifecycle cost of GAX-cycle HGSAHP (coal) is the lowest, while GAX-cycle HGSAHP (gas) is cheaper than conventional HGSEHP (gas) assisted by an auxiliary boiler.