Refrigerant charge, heat pump, refrigeration, extraction
According to the European Commission, heating, cooling and domestic hot water (DHW) production implies 79% of the total energy consumed in households. Moreover, as 84% of this energy is still generated from fossil fuels, it is required taking measures in order to improve the current situation. One way to increase the decarbonization in households is the use of heat pumps powered by renewable energy sources. Additionally, the energy captured by heat pumps is considered renewable when a certain efficiency value is achieved (2009/28/CE directive). Nowadays, refrigerants used by heat pumps are mainly hydrofluorocarbons (HFCs) which have a high global warming potential (GWP) and have a clear deadline defined at F-Gas EU Regulation 517/2014. For this reason, natural refrigerants will play an important role within heating, cooling and DHW production at the household sector. However, most of the natural refrigerants with acceptable thermodynamic properties are at least slightly flammable or toxic, and its use has an associated risk due to this condition. That is the cause that the amount of refrigerant charge must comply with the maximum refrigerant charge limited by regulations, and the prediction of the nominal refrigerant charge amount inside a heat pump has become an important matter within the design process of a heat pump. There already exist prediction models of refrigerant charge but, under certain conditions, they do not fit the reality. The current prediction methods which use simulation models may be improved by knowing the actual distribution of the refrigerant inside the different components of a real heat pump. In order to empirically determine the refrigerant charge amount inside each part of the heat pump, several methods can be used, but the most employed one is the “remove and weight” technique. This technique consists in extracting the refrigerant charge of each element of the heat pump in a sample cylinder in order to weight it, after isolating each component from another. A similar but less precise approach of this method is employed when recovering refrigerant in maintenance or decommissioning tasks. In this contribution, a theoretical and experimental study of different charge extraction methods is presented. In the study, every method has been analyzed according to different factors: percentage of refrigerant extracted, security measures employed, the time needed until stability is reached and cost of the technique. The results of this study will help in the selection of best extraction method according to the precision of the results needed, the available resources and the training of the staff which in the end will be performing the experiments.