Heat pumps are fundamental to decarbonize the building heating sector. To reduce the emissions of greenhouse gases into the atmosphere, a prototype heat pump working with carbon dioxide (R-744) as refrigerant is presented. However, R-744 heat pumps have to operate a trans-critical cycle to produce hot water and this penalizes their performance compared to systems operating subcritical cycles.

The present prototype adopts several innovative solutions: a double heat source at the evaporator and the electricity production by means of photovoltaic-thermal modules. Indeed, the present heat pump water heater for residential building applications can work with the s ...