Researchers from Germany’s Fraunhofer ISE have developed an optimized heat pump propane cooling circuit for single-family homes.
Propane heat pumps intended for indoor use in private houses are now one step closer to commercialization. The German Fraunhofer ISE has successfully developed a model of a heat pump cooling circuit that uses less than 150 g of propane.
“Many heat pump manufacturers offer propane heat pumps, but mostly only for outdoor installations, as the refrigerant is subject to extensive safety regulations for indoor use due to its flammability,” Fraunhofer ISE said in a statement. “If the heat pump of a single-family house with its usual 5 kW to 10 kW output exceeds the prescribed maximum refrigerant charge of 150 grams, it can only be installed with enhanced safety measures.”
One of the best results of the Low Charge 150 g (LC150) project is an 11.4 kW heat recovery heat pump that uses only 146 g of propane, making it suitable for indoor use without extensive safeguards. According to the German research institute, the refrigerant input of the unit is 12.8 g/kW, which is about one fifth of the propane input of commercially available systems.
“The goal of the project was to develop an almost market-ready heat pump module that uses the climate-friendly refrigerant propane, does not exceed the 150 gram limit intended for indoor use, but still produces enough heat for a single-family house,” he says. Dr. Lena Schnabel, Head of Fraunhofer ISE’s Heating and Cooling Department. “We have now achieved this goal by working with our industry partners and giving them the tools to develop market-ready heat pumps.”
The research consortium established, measured, evaluated and optimized more than 20 different combinations of heat exchangers and compressors. One of the key components in reducing the amount of propane needed was the use of an asymmetric plate heat exchanger. Other factors included reducing the oil in the compressor and shortening the length of the pipes.
In October 2022, Fraunhofer ISE developed a heat pump with a heating power of 12.8 kW and which uses only 124 grams of propane. However, its refrigeration circuit was not suitable for commercialization because it used a semi-hermeneutic automatic compressor that could not run for enough hours.
The research institute now wants to develop low-load propane heat pumps for single-family home use as part of the LC290 project, which will continue until June 30, 2025. The goal of the consortium is to develop heat pump solutions for underfloor heating systems, central heating of indoor spaces. systems and efficient outdoor heat pumps.
The projects are financed by the German Federal Ministry of Economy and Climate.