Experimental characterization of a carbon-dioxide dual source heat pump

Heat pumps represent a key factor in the electrification of heating and cooling and are crucial for the energy transition towards low-carbon systems. The adoption of innovative solutions, such as multi-source configurations and low-GWP refrigerants like carbon dioxide also improve sustainability and system efficiency. The studied system is a dual-source (air/sun), reversible carbon-dioxide heat pump installed at the ENEA Research Center in Casaccia. The prototype, with about 10 kW of heating capacity, is designed to provide chilled water during the summer season and hot water for both space heating in winter and sanitary water production and integrates two strings of five photovoltaic thermal hybrid solar panels to both produce electricity and assist the evaporation process. This paper presents dynamic heating-mode tests for space heating in climatic zone D, focusing on the cooling effect of the panels and its impact on their performance. Steady-state tests validated the dynamic tests findings, showing an average improvement in electrical efficiency of 8.06%. Finally, thermal imaging on panel surfaces with the heat pump off and on revealed a surface temperature drop from 50°C to 25°C corresponding to roughly 0.52% efficiency gain per degree Celsius reduction.