Scientists back hydrocarbon heat pumps

As the debate over the revisions to the F-gas regulation rumbles on, a group of more than 40 scientists from 24 different universities and research institutes in Europe have signed a position paper supporting the use of hydrocarbons as refrigerants in heat pumps.

The researchers argue that hydrocarbons such as propane and isobutane are just as good or better refrigerants than synthetic ones. However, because these fluids are more flammable than the synthetic fluids, special safety precautions must be considered in the design, during service, and in the factories where the heat pumps are manufactured.

Indeed, many stakeholders have observed that although the technology and market for hydrocarbon-based air-to-water heat pumps is fairly well developed, the same is not true for air-to-air heat pumps, such as splits and VRF systems.

Björn Palm is a professor in the division of applied thermodynamics and refrigeration at the KTH Royal Institute of Technology, and one of the signatories of the paper. As noted in the document, he believes a longer transition period may be necessary for air-to-air systems.

“This is particularly difficult for multi-split systems where the refrigerant charges can be quite large,” he says. “I do not see a future for multi-split systems using any type of flammable refrigerant. Instead, I expect to see hydronic systems used for distributing heating or cooling within a building.”

As for smaller split systems, Palm says it may be possible to decrease the charge to acceptable limits.

“There is a research project ongoing here in Stockholm with the aim of demonstrating a split system with less than 150g of propane,” he says. “This requires novel technical solutions for the heat exchangers, the compressor, and for the expansion device. I also see a possibility for other technical solutions, such as quick-closing valves limiting the releasable charge in case of leakage.

“We are now starting up an IEA HPT Annex dedicated to safety of flammable refrigerants, and we hope for large participation from countries all over the world. There are many ideas about how to increase the safety, but they need to be investigated and verified before the regulations can be adapted.”

In terms of how to best facilitate a transition away from synthetic refrigerants, Palm expects exponential growth in the demand for heat pumps in Europe in the coming years due to the embargo on gas imports from Russia.

“My understanding is that the manufacturers have already understood this expansion cannot be based on the use of synthetic refrigerants,” he says. “But the industry needs support in the transition, and the best way is to ensure that there is sufficient government funding for research in this area.”

Palm points to the German government’s €7 million (AUD$11.4 million) grant for developing propane heat pumps to Fraunhofer ISE.

“Another interesting piece of news indicating the direction for the future is that Rheinmetal won a €770 million (AUD$1,250 million) contract for propane compressors based on technology from the automotive industry.

The position paper has been sent to members of the European Parliament’s Committee on Environment, Public Health and Food Safety (ENVI), and to all Swedish EU MPs as an input before the decision on the F-gas regulation, which is to be taken by the parliament by the end of March.

Image courtesy of KTH.

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