Analysis On Energy Efficiency Potential of Geothermal Heat Pump System With Shallow and Deep Borehole Heat Exchangers

Due to the great advantage of high energy efficiency and low carbon emmision over other renewable energy technology for space heating and cooling, ground-source heat pumps (GSHP) systems have been widely used in residential and commercial buildings and play an increasingly important role in fufill China carbon peak and carbon neutrality goal. Traditional GSHP system is featured with shallow borehole heat exchangers which requires a large construction area to install the underground heat exchangers array, and it poses a significant challenge to its wider application where land is scarce and densely populated. Deep borehole heat exchangers are drilled up to 1000-3000 m deep underground to extract heat from hot rock where geothermal resources storage available in the limited underground space is much large and heat exchange temperature is even higher. This paper first provides a general introduction of GSHP for cooling or heating-dominated buildings and its recent advances. Then, the hybrid ground coupled heat pump system (GCHP) with both shallow and deep borehole heat exchangers is well described. Afterwards, a detailed energy efficiency analysis and comparison of GSHPs based on various borehole heat exchanger drilling depth extending from 100m~3000m underground as well as installing configurations including single U tube, double U tubes, and coaxial tube are performed. Also, the potential to obtain better energy efficiency by optimal design and operation of the system is validated. Finally, the economic and environmental performance of a closed-loop GCHP system is also briefly summarized. It is found that the hybrid GSHP technology can be applied for heat extraction and storage with great flexibility, and the energy saving potential is significant.