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High performance heat pump designed for cold climates

A high performance prototype heat pump, designed for cold climates, is set to be developed by Purdue University, with the resulting technology potentially halving heating bills.

Eckhard Groll, professor of mechanical engineering, who is working on the project, says: “With this technology we can maintain the efficiency of the heat pump even when it gets cold outside.”

The technology works by modifying the conventional vapour-compression cycle behind standard air conditioning and refrigeration.

The project will investigate two cooling approaches during the compression process. In one, large amounts of oil are injected into the compressor to absorb heat generated throughout the compression stage.

In the second, a mixture of liquid and vapour refrigerant from the expansion stage is injected at various points during compression to provide cooling. The added steps improve the compression process while also reducing energy losses due to friction in the expansion stage.

The system is designed to precisely control the flow of refrigerant from the evaporation stage into the compression stage using a series of small valves, while a scroll compressor, which uses a rotating, scroll shaped mechanism is used to compress refrigerant.

Domestic heat pumps normally use reciprocating compressors, in which a piston compresses the refrigerant.

Mr Groll says: “You can’t inject a liquid into a reciprocating compressor, whereas you can with a scroll compressor, which is uniquely suited for this modification.”

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