Experimental Investigations of Waste Heat Utilization of High-Temperature Heat Pump Compressors

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Jeßberger, Jaromir ; Heberle, Florian ; Brüggemann, Dieter:
Experimental Investigations of Waste Heat Utilization of High-Temperature Heat Pump Compressors.
2024
Veranstaltung: 20th International Refrigeration and Air Conditioning Conference at Purdue , 15.-18.07.2024 , West Lafayette, IN, United States.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung , Paper )

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Abstract

Renewable energy sources are playing an increasingly important role in the supply of electricity. However, in the European context, renewable energy sources still play a minor role in the heating sector, with about 21 % in 2018, although this sector accounts for more than 50 % of final energy consumption (World Energy Council, 2020). In order to decarbonize the heating sector, the integration of high-temperature heat pumps (HTHPs) into renewable energy systems is a promising approach. Potential areas of application are geothermal systems or the use of waste heat from industrial processes. The goal is to utilize HTHPs to guarantee coverage during peak loads, enhance the thermal output of renewable systems, or enable waste heat utilization. Such system integration requires flexibility and robust part-load characteristics to offset significant fluctuations in demand. This study aims to examine the part-load performance of an HTHP at a laboratory scale experimentally. The test system represents a HTHP with a thermal output of 35 kW and supply temperatures of up to 130 °C. The refrigerant trans-1-Chlor-3,3,3-Trifluoropropen (R1233zd(E)), with low global warming potential (GWP) and ozone depletion potential (ODP), is used as working medium. An internal heat exchanger (IHX) as well as water-cooled cylinder heads (CHC) are implemented to investigate their potential of optimizing the performance of the test rig. The system's part load behavior is examined in a defined base scenario at a heat source temperature of 50 °C and a supply temperature of 100 °C. Additionally, increasing supply temperatures up to 130 °C are realized in conjunction with (and without) the CHC. The analysis is focused on the influence of the installed cylinder head cooling. The results show that the cylinder head cooling reduces the discharge gas temperature of the reciprocating compressor and thus ensures material-friendly operation, while the dissipated heat can be recovered and improves the efficiency of the system by up to 8 % . In addition, major influences on heat transfer can be identified, like a decrease of the pinch point in the condenser. Further recommendations for action can then be derived from this in the context of economic and technical optimization.