The Germany-based Fraunhofer Institute for Solar Energy Systems (ISE) is developing propane (R290) air-source heat pumps designed to replace gas and oil heating systems in multi-family buildings under the LC R290 project.
The project, which is being undertaken with a consortium of 20 companies from the heating and housing sectors, seeks to develop “easy to use” and “reproducible” heat pumps. The LC R290 project is funded by Germany’s Federal Ministry for Economic Affairs and Climate Protection and will run until the end of June 2025.
Fraunhofer ISE presented initial implementation concepts at Chillventa 2024, held in Nuremberg, Germany, October 8–10. Chillventa is one of the world’s largest HVAC&R trade shows. The three concepts were designed for various building types informed by the German housing associations participating in the project. The heating load of the building types varies from 23 to 93kW (6.5 to 26.4TR), and each concept addresses different installation environments, heating capacities and building types, with a focus on minimizing the propane charge.
Low-charge, in-unit installation: This concept sees heat pumps installed within individual apartments, making it ideal for retrofitting old buildings. The system draws heat from sources such as geothermal or solar thermal energy, air collectors and low temperature heat grids, with the heat stored in a water tank.
- A laboratory tested demonstrator required only 150g of R290, reducing the risk of flammability while enabling installation in confined spaces where heat is needed, like kitchens or bathrooms.
- The system achieves a heating output of 6kW (1.7TR) at a source temperature of 0°C (32°F) and a sink temperature of 55°C (131°F) with an SCOP of 3.8.
- Development efforts are ongoing to enhance system effciency.
Centralized basement installation: This solution targets larger buildings with centralized heating systems installed in the basement. Possible heat sources include district heating, low-temperature networks or geothermal energy, which is hydraulically connected like the low-charge in-unit design concept.
- The prototype, which has already been built, provides 29.5kW (8.3TR) of heating with an SCOP of 3.65.
- The heat pump uses 830g of R290, with optimization steps planned to reduce this to 800g.
- Efficiency improvements focusing on control technology adjustments are underway.
Centralized outdoor installation: This concept is suitable for both old and new buildings and is designed to offer a heat capacity of 10–80kW (2.84–22.7kW)
- The system directly utilizes air as the heat source, and the first prototype is currently under measurement, with results expected by the end of 2024.
Final phase: Fraunhofer ISE is focused on testing and optimizing the propane-based heat pump systems to ensure they meet performance and safety targets.
- It is conducting hardware-in-the-loop simulations to assess the operational efficiency of the heat pumps under varying conditions. This involves integrating the measured performance of real heat pumps into virtual simulations of building environments and hot water tanks, enabling more accurate evaluation across different climate zones.
Quotable: “Field measurements are currently being carried out [on Fraunhofer ISE’s outdoor performance test] on the leakage behavior of propane,” said Dr. Katharina Morawietz, Heat and Cooling Technologies. “These results will provide information on how to further increase the safety of propane heat pumps.”
