OAK RIDGE, Tenn. — The U.S. Department of Energy’s (DOE’s) Oak Ridge National Laboratory (ORNL), collaborating with Emerson Climate Technologies, developed a prototype for an air-source heat pump for the colder regions of the country — one that heats better and uses significantly less energy.

The technology also enhances air-source heat pump efficiency and comfort in milder climates where heat pumps are already common, which means significant national primary energy savings (about .04 quads annually) and greenhouse gas reductions (2.4 million metric tons annually) are possible.


Air-source heat pumps are well established in southern parts of the country where winters are relatively mild. The problem is that the heating capacity and efficiency of conventional air-source heat pumps decrease significantly as the outdoor temperature drops and the demand for home heating increases. Consequently, supplemental electric resistance heat must be used, decreasing the heating performance. In this project, ORNL researchers developed a heat pump that minimizes the loss of heating capacity and the drop in efficiency in low temperatures while maximizing heating comfort.

Exhaustive research led to a prototype that’s both cost-effective and highly efficient at heating the home, even in cold outdoor temperatures. The heart of the prototype is a new scroll compressor, developed by Emerson, which is optimized for low ambient heating performance and reliable under such operating conditions. The design used tandem compressors (two parallel, equal-size, and single-speed scroll compressors) and other features to achieve the target performance. A single compressor operates for cooling and for heating in mild conditions, but when outdoor temperatures plummet, both compressors kick in.


The research team’s innovative concept shows promising results. The prototype was field-tested in early 2015 in an occupied house in Sidney, Ohio, that had been previously equipped with a conventional air-source heat pump. During the coldest month, the prototype maintained comfortable temperatures in the home while reaping 40 percent in energy savings. When outdoor temperatures plunged to -13°F, the prototype kept the house warm without any reliance on supplemental electric resistance heat.

In fact, the technology is so efficient — and cost effective — that it already beat DOE’s 2020 goal, achieving a 1.077 primary seasonal coefficient of performance or COP (goal was 1.07), and $18 installed cost premium per kBtuh (goal was $25).


Emerson is one of the nation’s largest domestic manufacturers of compressors for residential and light commercial HVAC equipment and is currently marketing its cold climate-optimized compressor to air-source heat pump manufacturers. The ORNL prototype provides manufacturers with an example of how to integrate the new compressors into an air-source heat pump design that achieves exceptional cold climate performance.

“This project is an excellent example of how collaboration between industry and a national lab can benefit the general population,” said Hung Pham, director of integrated technologies at Emerson Climate Technologies. “Together we developed the most cost-effective air-source heat pump option for cold climates, which will have a bright future displacing space heating derived from oil, propane, and electric furnaces. In addition, air-source heat pumps in mild climates can also be improved by the underlying technology.”

The collaboration between ORNL and Emerson was conducted under a Cooperative Research and Development Agreement (CRADA). The DOE Building Technologies Office sponsored ORNL’s effort within the CRADA and Emerson was self-funded.

Publication date: 5/20/2016

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