Numerical investigation of the heating efficiency of CO2 heat pump water heater system in cold environments.

This paper introduces a novel a CO₂ mechanical subcooling heat pump water heater (MSHPWH) to improve the heating performance in low temperatures. By utilizing a mechanical subcooling (MS) cycle, additional heat is supplied to cooling water, improving system efficiency. The study evaluates the heating COP (COP_h), power consumption and temperature of hot water under various steady-state operating conditions. Results indicate that the COPh of the MSHPWH increases by 44% to 57% compared to conventional HPWH as ambient temperatures range from -25 ℃ to -5 ℃. The MS cycle proves beneficial, with a subcooling range of 4 ℃ to 20 ℃. Adjusting the refrigerant mass flow rate ratio enhances heating output and hot water temperature. Changes in the mass flow rate ratio impact COP_h and the temperature of hot water concurrently. This research highlights the innovative MS cycle's significant role in enhancing CO₂ heat pump water heater performance in cold climates, showcasing its potential as an eco-friendly and efficient heating solution. [ABSTRACT FROM AUTHOR]