Engineers develop optimised propane heat pump

GERMANY: Engineers in Germany have developed a functional brine heat pump using a fully hermetic compressor with a heating capacity of 11.4kW using only 146g of propane.

This low refrigerant charge would permit it to be to installed inside buildings without undergoing extensive safety precautions. Per kilowatt of heat output, the unit requires only about one-fifth the amount of propane compared to systems on the market.

The new development is the result of a collaboration between the Fraunhofer Institute for Solar Energy Systems ISE and an industrial consortium within the LC150 (Low Charge 150g) project, which has just ended, and was funded by the German Federal Ministry for Economic Affairs and Climate Action. 

During the LC150 project a team set up, measured, evaluated and optimised more than 20 different combinations of heat exchangers and compressors. 

In October last year, the LC150 team announced it had developed a heat pump refrigerant circuit capable of achieving a maximum heating capacity of 12.8kW and a COP of 4.7 with only 124g of propane. However, this employed an automotive compressor which is not designed for the high operating hours and lifespan of a heat pump. The latest development uses a fully hermetic compressor.

“The project goal was to develop a nearly market-ready heat pump module which uses the climate-friendly refrigerant propane, does not exceed the 150g limit for indoor use and yet still provides sufficient heat for single-family homes,” explained Dr Lena Schnabel, head of the heating and cooling department at Fraunhofer ISE. “We have now achieved this goal in cooperation with our industry partners and have given them the tools to develop a market-ready heat pump.”

The team used commercially available components for the prototype with a key component being the asymmetrical plate heat exchangers, which require less refrigerant. The research team was able to significantly reduce refrigerant requirements by decreasing the amount of oil in the compressor, among other things. Additional components, such as sensors, were kept to a minimum, and pipes were kept as short as possible to reduce the amount of refrigerant required.

Multi-family heating project

In December 2022 the researchers launched the new project LCR290 to develop solutions for replacing gas and oil heating systems in multi-family houses that are easy to implement and can be broadly applied. 

The project partners aim to develop heat pump solutions for floor heating systems, central heating systems installed indoors, and heat pumps in the higher performance classes which are installed outdoors. 

For the floor heating system, the project partners will draw on the results of the LC150 project to develop suitable storage and source concepts, solutions for the connection to the hydraulic and source system, and adequate control approaches.

The budget of the new joint project is €7m. As with the LC150 project, this project is also funded by the German Federal Ministry for Economic Affairs and Climate Action. The LC290 project will run until June 30, 2025.

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