Renewable energy as an auxiliary to heat pumps: Performance evaluation of hybrid solar-geothermal-systems

The aim of this study is to combine renewable energy sources with heat pumps so that the usage of electricity needed to operate heat pumps is minimized along with associated fuel combustion. The aforementioned objective leads to reduce the energy consumption, the operational cost and the environmental impact of the heat pump. To minimize the usage of electricity, it is proposed that the heat pump (HP) system is combined by two renewable energy systems, a Solar Air Heater (SAH) and a Geothermal Well Water (G). To enrich this study, five prospective combinations of Heat Pump (HP), Solar Air Heater (SAH) placed Upstream (U) and Downstream (D) of the condenser, and Geothermal Water Well (G) were investigated. Hereafter, these five combinations are referred as HP-G, HP-S-U, HP-S-D, HP-G-S-U and HP-G-S-D. The thermal modeling of the aforementioned combinations in addition to baseline HP were developed and examined using an in-house computational code. To ensure that the input data used in the computational code are reliable, experiments were conducted to validate that the geothermal water temperature is higher than the ambient temperature in winter, in addition to confirming the analytical thermal modeling of the solar air heater. Numerical analyses and associated parametric studies revealed that the combination of Solar Air Heater (SAH) and a Geothermal Well Water (G) can efficiently increase the performance of the system by reducing the power needed to operate the compressor of HP. The gain in COP was found to be 48, 43, 81, 105 and 191 % for HP-G, HP-S-U, HP-S-D, HP-G-S-U and HP-G-S-D respectively. In addition, results revealed that the most efficient system is the (HP-G-S-D) for all simulated conditions and assumptions with a gain in COP that can reach up to 191 % in comparison to the baseline heat pump system.