Experimental investigation on air-source transcritical CO2 heat pump water heater system at a fixed water inlet temperature

For clarify main affecting factors on air-source transcritical CO2 heat pump water heaters, and the influence extent of these main affecting factors, at fixed water inlet temperature of 12 °C, an experimental research was conducted on a prototype in a range of ambient temperatures (−15 °C–35 °C) and water outlet temperatures (55 °C–80 °C). Based on the experimental results, effect of water outlet temperatures and ambient temperatures on the optimal discharge pressure and system COP was illustrated, and with change of water outlet temperatures and ambient temperatures, variation of CO2 gas cooler outlet temperatures, evaporating temperatures and other cycle variables was presented and interpreted. According established simulation model, we conducted simulation for the prototype and the cycle respectively adopted another two gas coolers with difference heat transfer surface. As one conclusion, for an established plant, correlation for the optimal discharge pressure as the function of ambient temperatures and water outlet temperatures can be achieved by fitting numerous simulation or experimental results.

► Described effects of environmental conditions on the optimal discharge pressure and COP.
► Illustrated variation of evaporating temperatures and CO2 gas cooler outlet temperatures.
► Made simulation considering heat transfer processes and components characteristics.
► Verified the availability and accuracy of the simulation model.
► Clarified effect of gas cooler on system COP and the optimal discharge pressure.