LC150 – Development of a Refrigerant-Reduced Heat Pump Module with Propane

Heat pumps are a key heating technology of the future, and their further development is an essential part of the heat transition. This makes research into sustainable refrigerant solutions all the more important. The refrigerant propane, which has very good thermodynamic properties and a low global warming potential, offers great potential. A disadvantage is its flammability. To minimize this disadvantage, reducing the refrigerant to below 150 g is a promising approach. The aim of the LC150 ("low charge 150 g") research project funded by the by the German Federal Ministry for Economic Affairs and Energy (BMWi) is therefore to develop a standardized and refrigerant-reduced refrigeration circuit with the working fluid propane in consultation with heat pump manufacturers and suppliers.

In addition to the development of a significantly refrigerant-reduced brine-water refrigeration circuit with the working fluid propane and a market-accepted COP, a time-efficient procedure for the evaluation and design of charge-reduced refrigeration circuit components is to be developed in the project. A comprehensive database on the performance of brine-water refrigeration circuit components under refrigerant-reduced conditions will be made available to the project partners and processed for further use in simulation software. Operating strategies to achieve high efficiencies while avoiding critical conditions will be identified. A further topic of the project is the coordination of a procedure accepted by the manufacturers involved for the safety assessment of propane refrigeration circuits in the interior. The development work is supported financially and technically by a broad industrial consortium of European heat pump manufacturers. The joint development platform is intended to open up considerable cost-cutting potential for the companies involved and accelerate the industrial development of heat pumps for residential buildings.

The team has now achieved an efficiency record in the course of the project: a heating capacity of 12.8 kilowatts was achieved with only 124 grams of propane. This results in a specific refrigerant charge of approx.10g/kW. The project's goal of reducing the specific refrigerant charge to 15- 30 grams/kilowatt has thus been significantly exceeded.

The research team is also working on other levers to reduce the amount of refrigerant: the internal volume of the heat exchangers and the amount of oil required have been reduced, and additional components such as sensors have been kept to a minimum. The piping has been kept as short as possible to reduce the internal volumes.