Comparative Assessment of the Thermodynamic Performance and Application Area of Mechanical Vapor Compression and Joule Brayton High Temperature Heat Pumps
High-temperature heat pumps (HTHPs) providing heat at up to 150°C are already available and can be used to decarbonize a large share of industrial heat demand. Increasing the temperature that HTHPs can deliver will allow for an increase in this share further. However, for reaching temperatures higher than the critical temperature of most refrigerants, the conventional closed refrigeration vapor-compression thermodynamic cycle working with traditional refrigerants is no longer a feasible option. This paper investigates and compares two promising cycles for delivering heat above 150°C: open cycle mechanical vapor compression (MVC) (R718) HTHP and Joule-Brayton (R729, R740, R744) HTHP. Hereby, centrifugal compressors and turboexpanders are considered. Thermodynamic models of the proposed HTHPs are developed with a CoolProp interface. These models are used to study the thermodynamic performance of the MVC and the Joule-Brayton HTHP, including the COP, maximum temperature, and required compressor pressure ratio and peripheral speed. The three-stage MVC HTHP achieves condensation temperatures of up to 350°C with high superheating at the compressor outlet of 500°C. Moreover, the MVC has a high COP (2-10) for large temperature lift (160-30 K). The Joule-Brayton HTHP generates high-temperature heat (150-500°C) with a reasonable COP (2.2-1.35). Based on the results, guidelines for selecting a HTHP are given with regards to the characteristics of the waste heat carrier and the process heat carrier. The MVC HTHP is recommended for steam generation and applications when the waste heat source is low pressure steam. The Joule-Brayton HTHP is recommended if sensible heat is required with a large temperature rise of the process heat carrier and a large temperature drop of the waste heat carrier. Finally, the study indicates the application area where MVC and Joule-Brayton HTHP can decarbonize process heat demand at up to 500°C.