The LC150 project, carried out by Fraunhofer ISE from October 2020 to June 2023, aimed to develop compact heat‑pump circuits that use the environmentally friendly refrigerant R290 (propane) with a maximum charge of 150 g. The goal was to enable installation of these heat pumps in any room without spatial restrictions while delivering a heating capacity of 5–10 kW. All prototypes were designed as water‑to‑water heat pumps and were evaluated for both refrigerant efficiency and thermal performance. The most successful circuit achieved a specific refrigerant charge of less than 10 g kW⁻¹ while delivering 12.8 kW of heating power, thereby surpassing the target of 150 g. Thermal efficiency was benchmarked against a minimum SCOP of 4.3 at sink temperatures between 24 °C and 35 °C and a source temperature of 0 °C, and all measured circuits met or exceeded this requirement. Detailed tables in the report list the characteristic performance metrics for each tested circuit.

Technical work encompassed the design and fabrication of heat exchangers, selection and testing of compressors, and oil characterization to ensure compatibility with R290. Component combinations were systematically varied and assembled into test rigs, followed by a comprehensive measurement campaign that evaluated heat‑transfer performance, pressure behaviour, and refrigerant charge distribution. The project also investigated safety aspects of propane use. Experiments simulated leak scenarios and measured the dispersion of R290 in a test room. Results showed that a release height of 2.2 m significantly reduced risk due to dilution effects, confirming that higher installation levels can mitigate safety concerns. These findings are intended to inform future design guidelines for propane‑based heat pumps.

Collaboration was structured around an industry advisory board comprising nine European heat‑pump manufacturers. The board guided the project’s direction, reviewed interim results, and helped align the development with market needs. Fraunhofer ISE led the research, development, testing, and data analysis, while the advisory board provided industry expertise and facilitated the translation of laboratory findings into commercially viable solutions. The project was funded by a decision of the German Bundestag through the Federal Ministry for Economic Affairs and Climate Action, which supported the initiative’s objective of advancing low‑carbon heating technologies. The partnership model enabled rapid iteration and ensured that the developed circuits would meet the expectations of a broad European market. The final report also documents several publications, conference presentations, and press releases that disseminated the project’s outcomes to the scientific community and the public.