An economic-energetic-environmental evaluation algorithm for hybrid mid-depth geothermal heating system

Low-carbon and high-efficiency mid-depth ground-source heat pumps become a promising heating option for cold regions in China towards carbon neutral. However, system-level evaluation algorithm that incorporates multiple influences are needed. Hence, an economic-energetic-environmental evaluation algorithm for a hybrid mid-depth geothermal heating system was established. It couples load characteristics and reflects the impact of design parameters, geological conditions, and fluctuating factors on three evaluation indicators. The economic performance increases initially as heat pump load ratio and hole depth grow but is more sensitive to the former. A recommended design parameters’ zone is given for the general case. Moreover, when the load ratio is 0.65 and the depth is 2750 m, the maximum relative NPV reaches 88.4 million CNY. The peak value of carbon reduction revenue, 54.7 CNY/tCO₂, appears near the load ratio of 0.63 and the depth of 3300 m. The valley of heating cost, −15.9 CNY/GJ, occurs near the load ratio of 0.66 and the depth of 2600 m. The break-even point of geothermal gradient has a positive linear relationship with the hole completion cost, by which investing feasibility can be determined. Fluctuating factors have a significant impact on the above indicators but will not change the profit-loss status.