Heat pumps with propane are "highly explosive", some heating engineers are blocked, and there are also different positions in the heat pump association. What's with that?
Frankfurt/Freiburg – For climate protection and independence from fossil fuels, the German government has set itself the goal of installing six million heat pumps by 2030. One problem with climate-friendly heating systems is the refrigerants used in the pumps, some of which are highly questionable – they are highly toxic PFAS, so-called "poisons of the century". A Europe-wide ban is already being planned, it would affect the majority of the heat pumps installed so far.
The fact is that there is an environmentally and climate-friendly alternative to the dangerous PFAS: propane. But this brings with it other problems. The Federal Association of Heat Pumps BWP criticizes the safety risk of propane, as it can ignite relatively easily, it says. And some heating engineers are also blocking themselves and citing safety concerns about propane: One heating engineer recently even warned against "highly explosive" heat pumps. But is that true? The air conditioning technology expert Dr. Lena Schnabel from the Fraunhofer Institute ISE in Freiburg commented on this in an interview with fr.de from IPPEN. MEDIA.
Air conditioning expert Dr.-Ing. Lena Schnabel estimates the danger posed by propane heat pumps to be very low. (Symbolic image) © Lena Schnabel/Daniel Reinhardt/dpa/Montage
Heating law in Germany: Efficiency record for heat pump with propane in the quantity of five lighters
Last year, the Fraunhofer Institute set a record for a heat pump with the refrigerant propane: With only 124 grams of propane, a maximum heating output of 12.8 kilowatts and an efficiency of 4.7 (ratio of heat generated to electricity used) was achieved. The amount of refrigerant required per kilowatt of heating capacity "is roughly equivalent to the amount of propane in five lighters," explained project manager Clemens Dankwerth at the time, namely a tiny 9.7 grams. By comparison, commercially available heat pumps require about 60 grams of propane per kilowatt.
Does such a small amount really pose a risk of explosion? "Propane gas is flammable, so of course it's potentially dangerous. But that's the same with a gas burner. The residual risk cannot be eliminated 100 percent anywhere, not even when operating a car," says Schnabel. She heads the Heating and Cooling Technology department, which was involved in the propane heat pump project "LC 150" at the Fraunhofer Institute for Solar Energy Systems.
Since 1994, every refrigerator in every household has been containing the equally flammable refrigerant isobutane.
Dr. Lena Schnabel, Head of Heating and Cooling Technology, Fraunhofer Fraunhofer Institute
Heat pumps with propane: Dangers completely overestimated, according to expert – sophisticated safety technology
"When companies develop devices, risk assessments are made, worst-case scenarios are run through and appropriate technical measures are taken to avoid such cases and prevent damage to body and soul," says Schnabel. "Of course, propane can escape from the pump if a large block of concrete or a heavy tree falls on the device. This case is very unlikely, but it is played out as such a scenario by the developers, evaluated in its possible effects and appropriate security measures are derived from it," she explains.
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The climate expert continues: "Since 1994, every refrigerator in every household in Germany has contained the refrigerant isobutane, another highly flammable hydrocarbon like propane, with an average of about 100 grams per appliance. Here, too, the manufacturers have of course ensured that the event that the gas ignites can practically not occur. This is also the case in the manufacture of heat pumps."
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Energy transition: "Extremely unfair to base risk assessment on a single case that has occurred so far"
Schnabel is not aware of any major accidents with propane-powered heat pumps. "There was an incident in Berlin, about five years ago. It was a very exotic system in which the propane was routed directly through the pipes in the house, which nobody does anymore." There, a house had been destroyed by an uncontrolled gas leak over the floor and its ignition. "But it is extremely unfair to hang the risk assessment on this one case," says the air conditioning technician. Again and again, misconceptions circulate about heat pumps, which experts have to clarify.
"Very sophisticated" technology of propane heat pumps for outdoor use
"I think the variants of propane pumps that are installed outside are very mature." In the case of devices that are intended for indoor use, however, a lot must and will happen in the next two to three years, Schnabel promises. She admits that there is still some catching up to do at this point: "Indoor heat pumps are subject to higher safety requirements, and planning and construction are more complex."
Above all, it will be a matter of developing complex solutions in the context of renovations in apartment buildings. So far, the industry's involvement has been rather cautious, "because there has been a lack of planning security and perspective so far". Habeck's heating law, for which the cabinet gave the green light, and which now has to pass the Bundestag and Bundesrat, is therefore an important step.
What are the benefits and properties of propane as a refrigerant?
- Propane (R290) is a climate-friendly refrigerant that contributes neither to ozone depletion nor to the greenhouse effect.
- Propane has very good thermodynamic properties, which lead to energy-saving operation and high efficiency.
- Heat pumps with propane have low maintenance costs, no leak tests.
- However, the use of propane in heat pumps requires additional safety precautions due to its flammability, such as the careful connection of components and the use of special compressors.
- Safe operation of the system even at high outside temperatures.
- When planning the pump, care should be taken to keep the amount of refrigerant as low as possible in order to minimize safety risks.
- The installation of propane heat pumps is subject to stricter requirements, such as a minimum distance from windows, doors and vents.
- The subsidy for heat pumps that run on natural refrigerants such as propane is subsidized with up to 40 percent of the investment costs.
- From 2028, heat pumps in Germany will only be subsidized if they use a natural refrigerant, which makes the use of propane increasingly attractive.
Habeck's heating law: Transitional solutions and exemptions "extremely sensible"
The climate engineer therefore considers the transitional periods and exemptions provided for in the planned heating law to be extremely sensible: "In this transitional period, the six million heat pumps proclaimed by the government can be installed outdoors for the time being, where it is technically feasible. During this time, the industry can calmly develop solutions to the more complex problems. In a few years, these can then be installed where it has been difficult so far – indoors and in existing multi-family buildings." And where a higher heating load, which is becoming a decisive factor due to Habeck's plans, is required, and a higher amount of coolant is required.
"Propane gas heat pump answers a major problem"
One component will certainly be the 124-gram propane model developed by Fraunhofer ISE over the past two years. For comparison, a camping gas cartridge contains 180 grams of propane. "We are convinced that we have been able to answer a major problem." The findings are now being incorporated into developments in the industry – with appropriate rigorous safety tests and technical measures to ensure that no ignitable mixture can be produced outside the device, both indoors and outdoors. This would mean that the heat pump system, of which some energy experts say there is no alternative, would then also have a secure future with the refrigerant propane.
