Methods for Refrigerant Charge Determination in Residential Heat Pumps - presentation of IEA HPT Annex 64

Detecting and quantifying refrigerant leakages in residential heat pumps at an early stage is a major stake to maintain their efficiency and extend their lifespan. It is also of great interest in terms of safety when using flammable refrigerants. Several methods already exist. However, most focus on refrigerating or air-conditioning systems involving fixed-speed compressors and fixed orifice valves, lacking the dynamic aspects of more recent devices tending to smooth out the impacts of a leakage on the system.

The results presented here are part of a thesis work dedicated to the development of a method to determine in real time the refrigerant charge of a residential heat pump. The presentation first provides a brief insight on the state of the art of refrigerant charge determination methods and highlights two promising ones. Then the presentation focuses on the two-stage evaluation of both methods. First, a numerical evaluation, thanks to the development of a virtual test bench, is presented. Then, an extensive experimental evaluation of these two methods, carried out in climatic chambers, is exposed. The system studied is a typical residential Heat Pump: split air-to-water heat pump filled with R-32 and equipped with a variable-speed compressor and an electronic expansion valve. This experimental evaluation, consisting in tests in stationary conditions as well as in scenario-based Hardware-In-the-Loop dynamic ones, shows the difficulty of both evaluated methods in assessing the charge of the studied heat pump. For such adaptative technology, very resistant to refrigerant loss, the presented study highlights the need of new specific methods. It will be particularly challenging to develop a method suitable for systems filled with very low charge of flammable refrigerant.