Performance comparison between a single-stage and a cascade multi-functional heat pump for both air heating and hot water supply

•Performance characteristics of a multi-functional heat pump are measured.•The performance of a cascade system is compared with that of a single-stage system.•The cascade heat pump shows more stable air and water heating operation.•The cascade heat pump is more effective to provide higher water outlet temperature.

Multi heat pumps have been widely used in buildings due to their higher energy efficiency. Recently, demands for multi-functional heat pumps, which can provide heating, cooling, and water heating in a building, have been increased. In this study, a cascade multi-functional heat pump, combining a multi heat pump using R410A for air heating with a water heating unit using R134a for hot water supply, was investigated experimentally. The performance of the cascade multi-functional heat pump was measured by varying the refrigerant charge amount, EEV opening, water flow rate, and water inlet temperature. Test results were compared with those of a single-stage multi-functional heat pump using R410A for air and water heating. The cascade multi-functional heat pump adopting the water heating unit showed more stable air and water heating operations and higher water outlet temperatures than the single-stage multi-functional heat pump.