Critical review of heat pump prototype operation

In the testing facilities of SPF Institute for Solar Technology (SPF) the performance of the following heat pump prototypes was tested under different working conditions and operation modes: (R744) CO2-ice heat pump, (R290) propane-ice heat pump, and (R290) propane-dual source heat pump (see Figure 1and Figure 2). The experiments analysed in detail the effects of different operating parameters on the overall coefficient of performance, heat duty, and compressor energy consumption.

The CO2-ice heat pump includes a rotary compressor coupled to an inverter, the tri-partite brazed plate gas cooler, an evaporator, an internal heat exchanger, an ejector, a throttling valve, and a liquid separator. The heat pump unit is designed with a capacity of 10 kW, 8 kW, and 10 kW under only domestic hot water, only space heating, and simultaneous domestic hot water and space heating modes to provide the tap water heating and space heating water up to 70 °C and 35 °C, respectively. According to the results, the CO2-ice heat pump shows good performance for high DHW demand with large temperature differences at the gas cooler if the inlet temperature of the gas cooler is low (10 °C to 20 °C, such typical temperature level of fresh water). In DHW mode, the COP varies between 3.6 and 4.3 for set temperatures of 55 °C to 65 °C.

The propane-ice heat pump prototype is designed with a capacity of 10 kW and consists of a scroll compressor with inverter, two plate heat exchangers in the heat sink side (desuperheater and condenser), an evaporator, an internal heat exchanger, and several expansion valves. Similarly to the CO2-ice heat pump, the propane-ice heat pump was studied at a steady state for only space heating operation, only domestic hot water operation, and simultaneous domestic hot water and space heating operation. The results indicate that the COP for space heating temperature 30/35 °C ranges between 4.4 and 5.4. However, the COP of the unit for domestic hot water with a set temperature of 65 °C drops to between 2.5 and 2.8.

The propane-dual source heat pump with a capacity of 10 kW is designed and manufactured to use both air and/or water/brine coming from geothermal boreholes as heat source/sink, allowing to test this unit under heating and cooling working modes. The results of the propane-dual source heat pump indicate a slightly lower heat duty than the requirements under the design conditions (70 Hz.), while the COP/EER varies between 3.2 and 3.7, depending on the operating mode.

More information about the experiments, the methods and results can be found on D5.5 on TRI-HP’s website.

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