Experimental investigation into the performance of a water-source carbon dioxide heat pump system integrated with hydrate energy storage

In the context of the Kigali Amendment and carbon neutrality, carbon dioxide-based water-source heat pump systems hold significant development potential. To enhance the cooling performance of carbon dioxide-based water source heat pump systems, a novel carbon dioxide-based system with hydrate storage is presented. By leveraging latent heat storage technology, the system aims to achieve peak load shifting and improve the year-round operational energy efficiency of carbon dioxide-based water source heat pump systems. In this study, a small-capacity carbon dioxide-based water source heat pump system test setup with hydrate storage is constructed, and experimental tests on cooling and cold storage performance are carried out. The results demonstrated that the cooling performance of the modified system is approximately 19.4 % higher than that of conventional systems. In addition, the system operates in a non-steady state during the cold storage process due to the participation of carbon dioxide in the hydrate formation, which reduces the flow of carbon dioxide circulating in the system. The system’s average coefficient of performance during the cold storage process is approximately 2.54, with a gas cooler inlet-water temperature of 32 °C. In addition, the predictive correlations of compressor frequency, gas cooler water-inlet temperature, gas cooler water-inlet flow rate, and evaporation temperature on the optimal discharge pressure are fitted. The determination of the predictive correlation lays the foundation for future seasonal operation regulation strategies for carbon dioxide-based water source heat pump systems between transcritical and subcritical cycles.