The use of environmental energy to supply heating results in less carbon dioxide emissions. Therefore, heat pumps are a key heating technology for the future. But they still primarily use refrigerants that are harmful to the environment. Researchers at Fraunhofer ISE have developed a climate-friendly alternative, which uses propane, a natural gas with a greenhouse gas potential that is about 500 times less than conventional refrigerants. Another advantage is that the new brine-to-water prototype requires only one fourth of the refrigerant compared to conventional heat pumps available on the market at the same power. A propane heat pump based on this development would be the first-of-a-kind in Germany that is permitted for indoor use without implementing additional safety measures.
For the heat pump industry, new refrigerants are especially important: As of January 1, 2020 first bans on harmful refrigerants take effect in the European Union, as the EU Regulation No. 517/2014 aims to decrease emissions from refrigerants. Therefore, heat pump manufacturers and institutes are searching frantically for alternatives to conventional refrigerants. Most of the new alternatives are either poisonous or flammable and therefore belong to safety groups with stricter requirements. As coolant, propane is climate friendly, relatively inexpensive, available worldwide and leads to high coefficients of performance. Due to its flammability, however, the safety regulations for its use in heat pumps are quite elaborate. The newly developed heat pump at Fraunhofer ISE (working name LC150) reaches eight kilowatts of heating power with 150 grams of propane. It can be installed inside the building without additional safety requirements. Each kilowatt requires about 20 grams of propane, compared to commercially available systems that use 80 to 90 grams coolant.
“The objective of our work is to develop a heat pump that uses a climate-friendly refrigerant and at the same time achieves high power and efficiency using the lowest possible refrigerant amount,” says Dr. Lena Schnabel, Department Head of Heating and Cooling Technology at Fraunhofer ISE. The Fraunhofer ISE researchers used components which were available on the market to build the prototype. Asymmetrical plate heat exchangers were used for the reduction of the used refrigerant. Since most of the refrigerant is located in the heat exchangers and pipe system, the optimization of the heat exchanger has a great effect. The refrigerant demand was also reduced by decreasing the amount of oil in the compressor.
Efficient heat pump using the climate-friendly refrigerant propane developed at Fraunhofer ISE for indoor installations. ©Fraunhofer ISE