Low charge 150g heat pump with R-290 as refrigerant 
Fraunhofer ISE developed a brine to water heat pump which provides 5-10kW heating capacity which fits the regulations in a long dated scale regarding the F-gas regulations and the legal restrictions for flammable refrigerants. Propane has a global worming potential of three and counts as a natural refrigerant. Propane is not expected to be regulated beyond security concerns. Therefore it was chosen as refrigerant for this project and the charge limited to 150g, resulting in 0,45kg of CO2 equivalent. The reduction of charge was achieved with different approaches and technics. The main goal was to minimize the inner volume on the refrigerant side in all components and tubes. The components with the highest impact regarding charge are the two main heat exchangers and the liquid line. The following steps were taken to optimize the inner volumes. Firstly the heat exchangers were chosen with an asymmetric plate profile and long thermal length. Secondly the liquid line was designed as short and thin as possible. Thirdly the filter dryer in the liquid line was shifted to the suction line. Another strong impact on the charge is the absorption of refrigerant in the oil. The oil is mostly present in the compressor sump and partially in the refrigerant circuit. To reduce the absorbed quantities of the oil, the amount of oil was minimized by reducing the security buffer and the positioning of components to prevent oil retention in the refrigerant circuit. Additionally pressure and temperature are impacting the absorption of refrigerant in the oil, which naturally leads to consideration of these parameters for the biggest gross of oil, the oil sump in the compressor. Therefore two different compressors were investigated. A suction gas cooled scroll compressor and a hot gas cooled twin rotary compressor. Both were inverter driven. The tested operation points were B0/W35, B0/W55 and B0/W65. As secondary goals, reduced installation space even with increased volumes due to sensors and other measurement equipment, were defined. The outer dimensions needed were reduced to 700 x 300 x 600 mm.
--- Datum: 22.10.2019 Uhrzeit: 16:35 - 17:00 Uhr Ort: Saal Brüssel, NCC Mitte