Performance optimization of a cascade multi-functional heat pump in various operation modes

• Performance optimization of a cascade multi-functional heat pump is conducted.
• Control parameters are compressor speed, EEV openings, and refrigerant flow path.
• Refrigerant flow distribution into each unit is controlled by EEV openings.
• The COP in each operation mode is improved by the system optimization.

A multi-heat pump has been widely used to provide cooling and heating in a building. In addition, the demands for a cascade heat pump water heater have been increased due to its higher energy efficiency with high water temperature. In this study, a cascade multi-functional heat pump, which combines a multi-heat pump using R410A for air heating and cooling with a cascade heat pump using R134a for water heating, is considered to provide simultaneous air heating, air cooling, and water heating in a building. The performance of the cascade multi-functional heat pump was measured and analyzed in four operation modes: full-heating hot water, heating-main hot water, full-cooling hot water, and cooling-main hot water. The performance of the cascade multi-functional heat pump in each of the four operation modes was optimized by adjusting control parameters such as the compressor rotation speed and EEV opening and by modifying the refrigerant flow path.