Simulation-based investigation of active regeneration in a novel dual-source heat pump refrigerant cycle
Dual-source heat pumps serve as a complex compromise to reduce individual disadvantages of traditional airand ground-source heat pumps. One way to reduce net energy extraction and therefore space requirements compared to ground-source HPs is by adding refrigerant cycle-based active regeneration. In this paper, instead of using solar thermal regeneration, a refrigerant cycle-based procedure is introduced and investigated. Serially connecting two heat sinks on different temperature levels allows subcooling of the refrigerant before expansion. An experimental investigation is conducted, showing the condensation shifts and therefore more heating power being delivered to the low temperature heat sink. Only 23 % is delivered to the high temperature sink. Two ways of controlling the ratio between the heating power between these two heat sinks are investigated with a verified physical simulation: First, changing the refrigerant charge affects the ratio of heating power to the heat sinks. Increasing the refrigerant charge floods the condenser and shifts condensation and therefore 81 % of heating power happens in the high temperature heat exchanger. This yields high total heating powers and efficiencies but is inherently less flexible; Second, adding a mid-expansion valve between the two heat sinks allows for flexible control and a wide range of heating power ratios. While total heating power and efficiency are reduced by up to 10 %, the high temperature heat sink receives between 22 to 73 % of the total heating power, demonstrating the high flexibility. This allows integration of refrigerant cycle-based active regeneration with flexible power outputs into a dual-source heat pump to reduce ground-source heat exchanger sizes.