International. The Fraunhofer Institute for Solar Energy Systems ISE is developing a compact and cost-effective cooling circuit for heat pumps using propane as a refrigerant in the research project "LC150 Development of a heat pump module with propane coolant reduction", funded by the German Federal Ministry for Economic Affairs and Energy BMWi.
Heat pumps will be the most important heating technology of the future. To accelerate market penetration, heat pump manufacturers are working to reduce costs and find sustainable refrigerants. A large industrial consortium of European heat pump manufacturers financially supports and technically accompanies the development of the project. The joint development platform is intended to open up considerable cost-cutting potential to participating companies and accelerate the industrial development of heat pumps for residential buildings.
The aim of the project is to develop a standardized cooling circuit with low refrigerant load in cooperation with heat pump manufacturers and suppliers. The standardized unit must be qualified for different components.
"Currently, the industry is working in parallel on the many aspects related to the conversion of propane heat pumps. Thermodynamically, propane is classified as a very suitable refrigerant, however, because it is flammable, it might need more safety measures. Reducing the volume of refrigerant required is therefore obvious and also possible to a large extent, as our preliminary work has shown," explains Dr. Lena Schnabel, Head of the Heating and Cooling Technology Department at Fraunhofer ISE.
Simultaneous requirements for high efficiency and operational reliability pose a challenge. Here, the project wants to create technical responses and accumulate design expertise through extensive measurement and simulation campaigns, to which participating partners will have priority access. The acceleration of the market for heat pump units is absolutely necessary for the energy transition. Support for this will be provided by joint development of security tests, addressing development issues together with component suppliers and, at best, through joint production.
Joint platform development
So far, each European manufacturer has developed its own refrigerant circuit for each of the different refrigerants and performance classes. The LC150 project is breaking new ground with its joint development platform that enables significant cost reductions through increased quantities and automated production. As in the automotive sector, synergies will now be identified between manufacturers in the heat pump sector so that standardized parts can be used in the cooling circuit. Based on the knowledge acquired, a modular design can be developed for different series and performance classes, thus opening up more synergies.
Propane as a natural refrigerant
The EU regulation on fluorinated greenhouse gases calls for a 70% reduction in harmful emissions from refrigerants by 2030 compared to 1990. For heat pump manufacturers, propane is becoming increasingly important as a natural refrigerant. It is widely available and has excellent thermodynamic properties, allowing for greater efficiency (ratio of useful heat generated to energy used for generation) compared to conventional heat pumps. At the same time, the GWP global warming potential of 3 is 500 times lower than the GWP of the most commonly used classic fluorinated refrigerants today.
In 2019, as part of a potential study, Fraunhofer ISE managed to develop a saltwater cooling circuit using commercially available components. The circuit requires only 150 grams of propane for a heating capacity of 8 kW, which corresponds to a 75 percent coolant reduction compared to systems on the market. A heat pump based on this concept could be placed inside the house, as a refrigerator, without additional safety precautions. "We are confident that this refrigerant reduction can also be achieved for other capabilities and operating points when singular components are customized for propane use," says Dr. Peter Schossig. The project addresses the optimization of performance, efficiency and operational stability. The decisive factors for overall optimization are the use of heat exchangers, compressors and piping systems with reduced refrigerant load and the development of operating modes that allow the refrigerant to be well distributed throughout all components.
The Project Consortium
The project is being carried out in Fraunhofer ISE. An advisory board with industry members will jointly participate in the discussion of the task and work plan, thus ensuring relevance to the practice. The following companies intend to participate in the project, funding and advisory board: Vaillant, Kermi GmbH, Bosch Thermotechnik GmbH, Viessmann Werke Allendorf GmbH, BDR Thermea and ait-deutschland GmbH.
The project is 75 percent funded by the Federal Ministry of Economic Affairs and Energy BMWi (funding code 03EN4001A).
Source: Fraunhofer ISE.
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