Efficient Propane Heat Pump Replaces Gas and Oil Heating Systems in Apartment Buildings

The Fraunhofer Institute for Solar Energy Systems ISE, alongside industry partners, successfully developed and presented a groundbreaking solution for replacing gas and oil heating systems in multi-family homes. As part of the "LC R290" project, Fraunhofer ISE focused on the use of propane (R290) heat pumps, a more environmentally friendly refrigerant, to provide energy-efficient heating solutions for existing buildings. With a consortium of twenty companies from the heating and housing sectors, the research team developed and tested various implementation concepts, which were unveiled at the Chillventa trade fair in Nuremberg from October 8 to 10, 2024.

Diverse Heating Solutions for Multi-Family Homes

The project’s research began by selecting a range of sample buildings from the portfolios of participating housing associations. These buildings represented a wide array of the German housing stock, with heating loads ranging from 23 to 93 kW. The wide range of building types allowed the research team to develop scalable propane heat pumps suitable for both small apartments and larger complexes. A key challenge was providing solutions for apartments that used individual gas heating systems, particularly in low-income housing, where minimizing retrofitting and space requirements was critical.

Three Application Concepts Demonstrated

During the project, Fraunhofer ISE built several demonstrators to test the direct replacement of fossil fuel heating systems in apartment buildings using propane heat pumps. The first conceptual approach involved a decentralized solution that used hydraulically connected heat sources such as geothermal energy, solar thermal energy, district heating, or air collectors. A demonstrator using just 150 grams of propane was constructed and tested, achieving a heating output of 6 kW and demonstrating an impressive seasonal coefficient of performance (SCOP55) of 3.8 at a source temperature of 0°C and a sink temperature of 55°C.

The second approach focused on centrally installed heat pumps located inside the building’s basement. Using a heat source such as geothermal energy or solar thermal energy, this solution achieved a heating output of 29.5 kW with 830 grams of propane. Efficiency was rated at SCOP55 = 3.65, with the potential for further improvements by optimizing control strategies. The research team aims to reduce the propane charge to 800 grams while increasing SCOP to 3.7 in future optimizations.

The third concept introduced a centralized, externally installed propane heat pump for multi-family homes. Measurements of the first prototype are ongoing, with initial results expected later in the year.

Propane Leak Testing and Safety Enhancements

As part of the ongoing research, Fraunhofer ISE conducted extensive tests on the leakage behavior of propane. These measurements, performed at an outdoor test field, are crucial for enhancing the safety of propane heat pumps and minimizing the quantity of refrigerant required. These efforts build on the outcomes of a previous project, "LC150," aimed at minimizing propane use in heating systems.

Next Steps: Real-World Testing and Functional Verification

In the final phase of the "LC R290" project, the system will undergo further testing under realistic operating conditions. The hardware-in-the-loop (HIL) method will be used to simulate system behavior over an entire year, providing valuable data on the performance and efficiency of the heat pumps. This method connects real heat pump hardware with a virtual model of the building and hot water system, offering a detailed analysis of system functionality and control models.

Fraunhofer ISE and its partners have made significant strides toward replacing traditional gas and oil heating systems with propane heat pumps in multi-family homes. The results from this project highlight the potential for R290-based systems to deliver energy-efficient, environmentally friendly heating solutions, helping the housing sector reduce its carbon footprint while maintaining cost-effective operations.

The "LC R290" project is funded by the Federal Ministry for Economic Affairs and Climate Protection and will run until the end of June 2025.