Thermodynamic Tradeoffs in Brayton High-Temperature Heat Pumps: Impact of Compressor Performance and Heat Exchanger Size

Abstract High-temperature heat pumps (HTHPs) are a standard solution to electrify and decarbonize process heat production. To date, commercial HTHP technologies cannot operate much beyond 200 °C, but new solutions that can go beyond this threshold are being increasingly researched. Brayton HTHPs are one such solution, leveraging on the expectation that they could feature a maximum heat production temperature of up to 400 °C with components of reasonable size and performance. However Brayton HTHPs produce heat over an extensive range of temperatures. Therefore, the average heat production temperature is a parameter that better quantifies Brayton HTHP performance and can be of great importance for process integration. This average temperature can be increased at the cost of coefficients of performance (COP) reduction, primarily if intercooled compression is added to the basic thermodynamic cycle. The paper explores the tradeoff between performance and heat production temperature, considering practical limitations on the heat exchanger dimension. Additionally, the analysis focuses on the compressor design, investigating its performance in function of the specific operating conditions of Brayton HTHP. The obtained results comprehensively characterize Brayton HTHP performance and improve the understanding of this novel heat-pumping technology.