Multi-objective optimised preliminary design of centrifugal compressors for Brayton high-temperature heat pumps

The ongoing global transition towards sustainable energy solutions emphasizes the need to decarbonize industrial heat production, which is traditionally reliant on fossil fuels. High-Temperature Heat Pumps (HTHPs), operating via Brayton cycles, present a viable pathway for producing heat at temperatures exceeding 200 °C, meeting the demands of sectors like chemical processing and metal manufacturing. Despite their capabilities, challenges remain in achieving compact, efficient, cost-effective designs for small-scale applications. This study investigates the feasibility of a 100 kWth Brayton HTHP system, focusing on optimizing the compressor design to maximize the Coefficient of Performance (COP) under practical constraints. A thermodynamic model was developed to define cycle parameters, which informed the design and performance evaluation of single-stage centrifugal compressors. The optimization framework considered isentropic efficiency and pressure ratios as conflicting objectives, yielding detailed insights into trade-offs. Results reveal that centrifugal compressors, constrained by inlet temperatures and mechanical limits, can meet HTHP requirements with moderate size increments (10–30 %) compared to machines operating at lower temperatures and efficient single-stage configurations for cycle temperatures up to 350 °C. Beyond this range, multi-stage designs may be necessary. The study also highlights that higher pressure ratios and thermal effectiveness of internal heat exchangers are pivotal to improving COP, albeit with economic and technical trade-offs. The findings underline the potential of Brayton HTHP in process heat electrification, demonstrating achievable performance and identifying key limitations. This research lays a foundation for future advancements in small and medium-scale, high-efficiency HTHP designs, contributing to the broader adoption of sustainable heating technologies.