Experimental analysis of the influence of the expansion valve opening on the performance of the small size CO2 solar assisted heat pump

In a Direct Expansion Solar Assisted Heat Pump (DX-SAHP), a valuable part of the energy is provided from solar radiation. The solar radiation can fluctuate during the day affecting the performance of the system. The impact of a fixed opening in the expansion device on the system performance is not well known, especially for a small size solar assisted heat pump. In this context, it is presented an experimental analysis of the influence of the expansion valve opening on the performance of a CO2 DX-SAHP. Experimental tests were carried out considering different solar radiations conditions. The value of the expansion device opening that leads to the maximum COP was almost the same, regardless of solar radiation. In consequence, it was concluded that, for a small CO2 DX-SAHP, using a basic cycle configuration a static expansion device as a capillary tube would be suitable, reducing the costs of this equipment.