Thermodynamic competitiveness of high temperature vapor compression heat pumps for boiler substitution

Replacement of fossil fuel-fired boilers for generation of high-temperature water and steam is of paramount importance for reaching a fossil-free economy. Heat pumps could be possible substitutes, but the presently marketed solutions are mainly limited to low-temperature applications. This paper compares the thermodynamic performance of various High-Temperature Heat Pumps (HTHP) based on the vapor compression cycle with natural gas boilers for assessing their technical feasibility and competitiveness as future replacements.

Different cycle configurations and natural refrigerants were compared based on the coefficient of system performance and exergetic efficiency. Moreover, the technical feasibility of the most interesting cycles was discussed based on current technologies. The results showed that HTHP are promising substitutes for gas boilers for heat production of temperatures up to 180 °C.

In particular, ammonia cycles were preferable for source and sink temperatures lower than 60 °C and 110 °C, respectively, while water was a better-working fluid at higher temperatures. The complete exergy analysis showed different behaviors for various natural refrigerants in the working domain but confirmed the results identified by the energy analysis.

In any case, the technological analysis showed that further improvement of compressor technologies is required for making these solutions competitive.