The experimental investigation on a novel transcritical CO₂ heat pump combined system for space heating

Performance improvement methods attending to sub-cool CO₂ at the gas-cooler outlet to improve the system COP and reduce the optimum discharge pressure by combining another system have been popular recently. In this paper, a novel transcritical CO₂ heat pump combined system prototype was developed and experimentally investigated. Experimental data demonstrated that an optimal discharge pressure existed for the both individual systems in the proposed combined system. The frequency ratio of the two compressors was found to have a great influence on the system performance and an optimal ratio also existed according to the experimental data. When the ambient temperature increased from −20 °C to 0 °C, the system COP increased by 22%. The comparison results showed the combined system could improve the COP up to 15.3% comparing to the standard transcritical CO₂ heat pump system and that the optimal discharge pressure was decreased by up to 39%.