Purdue University Research Could Cut Winter Heating Bills in Half

It's hard for many of us to think about frigid winter temperatures as some of the nation is in the middle of a summer heat wave. Winter will be here before you know it and people in cold northern climates will be fighting to keep their homes warm.

Researchers at Purdue University are working on a new research project that promises the potential to cut heating bill in half for people who live in very cold climates. The research involves changes to the way heat pumps operate to make them more efficient in extreme cold temperatures. The technology also promises to expand the geographic range in which heat pumps are capable of operating.

The researchers are studying two cooling processes during the compression process. One of the cooling processes injects a "relatively large" amount of oil into the compressor to absorb heat generated in the compression stage. The second injects a mix of liquid and vapor refrigerant from the expansion stage at various points during compression to provide cooling. This injection of other materials required a redesign of the traditional piston-driver reciprocating compressor to a new scroll-compressor design.

Professor Groll said, "You can't inject a liquid into a reciprocating compressor, whereas you can with a scroll compressor, which is uniquely suited for this modification. Also, an important part of our project will be to determine the efficiency of a machine that pumps liquid while also compressing gas, so there will be a lot of computational modeling involved."

"With this technology we can maintain the efficiency of the heat pump even when it gets pretty cold outside," said Eckhard Groll, a professor of mechanical engineering who is working on the project with Braun and W. Travis Horton, an assistant professor of civil engineering.

The $1.3 million research project is funded by the U.S. Department of Energy and hopes to result in a prototype design at the end of its three-year span. Along with Purdue University, the project is being worked on by Emerson Climate Technologies Inc. and Carrier Corp. Emerson is working on the research end of the project and Carrier will integrate the prototype design into a new heat pump providing the completed system.

Doctoral students Margaret Mathison and Ian Bell are participating in the project and will present research papers on the project at the 13th International Refrigeration and Air Conditioning Conference. The tech created during the research project reportedly works by modifying the currently used vapor-compression cycle that a normal air conditioning and refrigeration system uses. This process has four stages with refrigerant compressed as a vapor that condenses into a liquid, and then expanding to a mix of vapor and liquid, finally evaporating.

Part of the research on the project is into the development of a series of valves that can precisely control the injection of refrigerant into the new compressor. The project stems from research into the Ericsson cycle. Purdue is also working on a similar project with the California Energy Commission.