R290 (propane) is recently understood as the most promising refrigerant for domestic heat pump applications. Propane has a Global Warming Potential (GWP) of 3 and attractive thermodynamic properties allowing energy-efficient and climate-friendly cycles designs. However, R290 is flammable, and the use of charge-reduced components and designs should be the first central step to reduce safety risks.

Within the research project LC150 (low charge heat pump 150g) the existing scientific knowledge on charge reduction was intensified by analyzing more than 30 refrigerant cycles. To understand the influence of the main components (compressor, evaporator, and condenser) on refrigerant charge, efficiency, and heating capacity those were combined differently. The cycles were evaluated at different refrigerant charges, source and sink temperatures, superheats and compressor speeds by experiment and simulation. All measurements are done with compact plate-to-plate refrigerant circuits. The results show that one significant part of the charge is defined by the compressor and the amount and kind of oil, and the second part is defined by the design and operation of the heat exchangers.

The heating capacity reaches up to 12.85kW using 124g R290. The current best solution achieves a specific heating capacity <10 g/kW with a SCOP (ErP) >4.5.

The presentation will give an overview on the methodology used to analyze the refrigerant cycles and discuss the results. This will be followed by a deeper discussion on refrigerant charge estimation in brazed plate heat exchangers (BPHE), which is not sufficiently precise in prediction for low charge systems. For this, infrared thermography, thermo-hydraulic measurements, geometrical analyses, and simulations of brazed plate heat exchangers (BPHE) will be presented and discussed.