Temperature matching method of selecting working fluids for geothermal heat pumps

The fact, that some areas need district heating through heat pumps and at the same time recover residual heat from geothermal water, presents a new working condition: feed water temperature of heat network 80 °C, return water temperature 65 °C; discarded geothermal water temperature 40 °C and its emission standard temperature below 30 °C. But none of known pure refrigerants and mixtures can meet this requirement. The paper introduces a novel approach named temperature-matching method, which provides a direction in selecting high-performance working fluids for further research. It is shown from the results that the mean COPs of binary and ternary mixtures are 4.85 and 4.74 respectively, but that of pure refrigerants is 4.12 under the same ambient condition. This point indicates that temperature matching contributes to energy saving. The novel approach to high-performance working fluids can be conveniently introduced into other working conditions.