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Two-stage Heat Pumps for Cold Climates

Field Test #2 of Cold-Climate Heat Pumps with Staged Compressor

Although air-source heat pumps can be used in nearly all parts of the United States, they do not generally perform well over extended periods of sub-freezing temperatures. In regions within the Pacific Northwest with sub-freezing winter temperatures, a standard air-source heat pump may not be cost effective to meet a building’s heating needs. New cold-climate designs of these heat pumps may perform well in these climates. To demonstrate their efficiency, one 4-ton and one 2.5-ton cold-climate heat pump manufactured by Hallowell were installed at residences in McCall, Idaho and Portland, Oregon. Electricity use by each heat pump and other characteristics of performance were monitored and occupant satisfaction was assessed.

Field tests found these Hallowell cold-climate heat pumps were not superior to a standard air-source heat pump. Coefficients of performance for the McCall, Idaho unit were well below industry standard. The product installed in Portland performed with a Heating Seasonal Performance Factor (HSPF) of about 7, which is slightly above the pre-2006 federal minimum standard for air-source heat pumps. Poor performance is explained by product design, faulty outdoor temperature sensors, and sizing of equipment relative to heating load.

Project Team
BPA: Kacie Bedney, Adam Hadley, Jack Callahan
Idaho Office of Energy Resources: Ken Eklund
Ecotope: Bob Davis

2007 – 2009


Field Test #1 of Cold-Climate Heat Pumps with Staged Compressor

To improve the efficiency of electricity as a fuel source for space heating, air-source heat pumps may be installed to displace heating by electric resistance equipment. However, several variables in the design and operation of air-source heat pumps – such as sizing and occupancy control – can limit their efficiency. The ability of cold-climate heat pumps to meet all of a building’s heating needs in sub-freezing temperatures could avoid the need for a secondary heating system. In this field test, a multi-stage air source heat pump, manufactured by Nyle Special Products, was installed as the central forced-air heating system at five residences in the Pacific Northwest and monitored for electricity use during the heating season.

The results of this study show the multi-capacity air-source heat pump is capable of meeting all the heating needs of homes without the use of resistance elements, even in cold-climates. However, the cold-climate heat pumps in this study did not perform as efficiently as standard air-source heat pumps. With a wide network of installers and refinements to the product, it is possible that a cold-climate heat pump could be installed without reliance on electric resistance elements for backup heating.

Project Team
BPA: Adam Hadley, Jack Callahan, Richard Stroh

2004 – 2006


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