Paper No 498 – Analysis of the performance of a heat pump with subcooling control as a function of the refrigerant charge – 14th IEA Heat Pump Conference, Chicago, USA
When using hydrocarbons like propane (R290) as a refrigerant in heat pumps, it is critical to detect if the system is undercharged to find potential leaks, as they are flammable. This is specially challenging in reversible air-to-water heat pumps where a liquid receiver to compensate for the charge fluctuations is commonly installed. This liquid receiver introduces some tolerance of the system to charge fluctuations which are desirable from the system performance point of view but also makes especially difficult the pre-diagnosis of a possible leak. This study has experimentally characterized the performance with different refrigerant charge levels of a reversible air-to-water propane heat pump with a liquid receiver at the compressor inlet and a variable-speed compressor. It has different control strategies: superheat control for cooling and subcooling for heating mode. The work shows the evolution of the most important system variables like discharge, condensation, and evaporation temperature, as well as subcooling and superheat, and which could be the impact on the system performance. Finally, the use of compressor speed as a tool to diagnose potential system undercharge faults have been pointed out as a promising strategy.