By Josh Perry, Editor
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Researchers at the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg, Germany have created a heat pump that uses propane rather than standard synthetic refrigerants that they believe is more environmentally-friendly and efficient.

The newly developed heat pump distributor takes its inspiration from the branching limbs of a tree. (Fraunhofer ISE)

According to a report from the institute, 40% of Germany’s energy consumption goes to heating and hot water and heat pumps represent a sustainable method for reducing dependence on climate-damaging fossil fuels.

Heat pumps extract heat from the ground, groundwater or ambient air and use it to heat homes or water.

“To achieve this, the heated, vaporized refrigerant is compressed, which raises its temperature and pressure,” the article explained. “The hot refrigerant gas releases its heat into water and condenses. The warm water flows into underfloor heating systems, radiators or hot water storage tanks, while the liquid refrigerant, now cool, flows back into a so-called evaporator, where it once again absorbs heat energy. The cycle then starts again from the beginning.”

Typically, refrigerants with synthetic fluorinated greenhouse gases are used. Propane is becoming more common in air conditioning and refrigeration applications, but its flammability makes it difficult to use in heating cycles. To make propane safe, only small amounts of the refrigerant can be included.

To accommodate this, researchers created compact, brazed, finned heat exchangers that function with small amounts of liquid and transfer the heat from one fluid to another. The parallel channels in the heat exchangers circulate the refrigerant so that it absorbs heat in one section and radiates it in another.

For this to work, the vapor-liquid ratio has to be identical in all channels. A distributor with a bionic structure was created to ensure the balance stays correct. The distributor was based on the branches and twigs of a tree, evenly distributing refrigerant into the evaporator channels and also ensuring that the entire surface of the heat exchanger is used, which improves efficiency.

Another safety measure that researchers included was a specialized compressor with the ignition sources encapsulated to prevent explosions.