Fraunhofer develops R290 heat pump concepts for apartment buildings

Germany – Researchers at Fraunhofer ISE have developed and tested propane heat pump concepts for replacing gas and oil heating in existing apartment buildings, including a 4.9kW apartment-level demonstrator that achieved an SCOP55 of 3.8 using 150g of R290.

The work was carried out under the LC R290 research project, with Fraunhofer ISE working alongside 20 companies from the heating industry and housing sector. A central outdoor demonstrator also reduced refrigerant charge by 20% while increasing efficiency by 15% compared with comparable heat pump units.

Potential for apartment-level systems

The project examined central and decentralised systems for indoor and outdoor installation, addressing different approaches to replacing both individual gas boilers and central heating systems.

Fraunhofer estimates that 60% of apartments in Germany’s rental housing stock in buildings with more than three dwellings have heating loads below 4kW, rising to 80% below 6kW. The report says this indicates that relatively small heat pumps could cover much of the apartment-level market.

Researchers also concluded that compact R290 heat pumps with refrigerant charges below 152g could provide a solution for replacing individual gas boilers, although integrating sufficient domestic hot water storage within the available space remains a challenge.

What’s important is a building-tailored system design including heat pump, storage, hydraulics, control, and heat distribution

Björn Nienborg, Project Coordinator, Fraunhofer ISE

Demonstrators test low-charge R290

Alongside the 4.9kW apartment unit, Fraunhofer developed central indoor and outdoor demonstrators.

The best-performing central indoor prototype achieved an SCOP55 of 4.1 with 620g of R290 and a heating output of 28kW. The 30kW outdoor demonstrator recorded an SCOP55 of 3.6 with a 2kg charge.

More than 100 propane leakage tests were also carried out across five safety concepts for indoor systems. Fraunhofer said the tests confirmed the ventilated enclosure approach covered by EN 378 and IEC 60335-2-40, while chimney and drainage concepts will be investigated further.

Research moves towards practical application

The LC R290 findings will now feed into Fraunhofer ISE’s MAMMUT project, which is developing software to support decision-making and system design for heat pumps in apartment buildings.

The system is intended particularly for HVAC installers and will link the design process with quotation generation.