A propane heat pump with compact bionic heat exchangers

Heat pumps are increasingly used for space heating and production of domestic water, especially in Europe. The European F-Gas Regulation requires a phase-down of fluorinated greenhouse gases. Propane (R290) is an interesting alternative to those refrigerant, since it has excellent thermodynamic properties. Nevertheless, it is a highly inflammable substance and its use requires some precautions.

The German research organization Fraunhofer recently developed a propane heat pump with a very low volume of refrigerant, thanks to highly compact finned heat exchangers. They are composed of parallel channels which absorb or radiate heat. The refrigerant circulates in those channels, and the vapor-liquid ratio must be identical in all channels to guarantee they operate efficiently. It was made possible thanks to a distributor with a bionic structure, instead of conventional Venturi distributors. This bionic distributor has a "continuously branching structure like the branches and twigs of a tree, which ensures even distribution of the refrigerant into the individual evaporator channels, even with a small volume of refrigerant", according to Dr. Lena Schabel, who is at the head of the department for heating and cooling technologies at Fraunhofer Institute for Solar Energy Systems. This structure improves the efficiency of the heat exchanger, and therefore of the heat pump.

A specialized compressor is also used to reduce the risks of explosion. All its ignition sources are encapsulated.

For further information, please read the press release of Fraunhofer.