Performance analysis of a rooftop, air-to-air heat pump working with CO2

The air-conditioning sector for large buildings and shopping centers is developing a growing interest in rooftop heat pumps due to their easy installation. Instead of the application of HFC refrigerants, carbon dioxide (CO2) could be an interesting perspective in this sector for environmental reasons. This work presents new performance data of an air-to-air heat pump roof-top system working with a trans-critical carbon dioxide cycle during the heating season. In particular, the experimental results showed how the heating power and the coefficient of performance are affected by the air temperature at the inlet of the gas cooler and by part load working conditions. A thermodynamic analysis pointed out the direct and indirect effects of fans speed and air flow temperatures on the performance, defining a performance map and the optimal range of application of such systems.