Experimental exergy and energy analysis of a novel high-temperature heat pump with scroll compressor for waste heat recovery

The industrial sector demands novel sustainable energy systems to advance in its decarbonisation and meet the targets of the Paris Agreement for the climate change mitigation. High-Temperature Heat Pumps (HTHPs) are being investigated as a feasible energy conversion technology alternative to traditional fossil fuel boilers. This paper presents the first experimental results of an HTHP prototype equipped with a modified scroll compressor and internal heat exchanger (IHX). The elements of the main and secondary circuits are presented, as well as the test methodology and heat balances are exposed. The tests have been performed using HFC-245fa at heat source temperatures between 60 and 80 degrees C, and heat sink temperatures between 90 and 140 degrees C. The heating capacity and coefficient of performance (COP) varied between 10.9 and 17.5 kW and between 2.23 and 3.41, respectively. An exergetic analysis indicated that the expansion valve was the component with the worst second law efficiency and the compressor presented the highest potential improvement over the other cycle components. A computational analysis of low global warming potential (GWP) refrigerant alternatives was carried out, which confirmed the benefits of using an internal heat exchanger (IHX) and the good performances of the low-GWP refrigerants: HCFO-1224yd(Z), HCFO-1233zd(E), and HFO-1336mzz(Z). Finally, we proved that the proposed system can save up to 57% of the equivalent CO2 emissions of a natural gas boiler. This paper provides a reference for the high-temperature heat pump recovery of the low-grade waste heat from industrial energy processes.