The GAX Heat Pump

The GAX heat pump which is based on a generator-absorber heat exchange (GAX) cycle, is envisioned as the technology of the future because of its energy efficiency (as much as a 40% improvement over existing technologies), lower maintenance, and use of environmentally benign refrigerants. DOE is working with industry to develop commercially available GAX heat pumps, and a complete GAX heat pump prototype was put into full operation at Oak Ridge National Laboratory (ORNL) in January 1998. In addition, DOE is partnering with a consortium of four gas utilities to commercialize gas-fueled GAX technology. The consortium, called Unitary Gas Heating and Cooling Products, will develop and test prototypes and introduce its new products to consumers.

ORNL's heat pump consists of a Phillips Engineering prototype outdoor assembly coupled to a standard off-the-shelf Robur/Century indoor unit (for chillers). The heating output was more than 68,000 Btu/h, with indoor air delivery temperatures of 98 to 99F. The GAX outdoor unit was delivering hot water at 120F to the indoor unit. Because these air delivery temperatures are above skin temperature, the air from the indoor unit feels warm, unlike air delivered by conventional heat pumps. It is expected that a complete production GAX heat pump with a properly sized and matched indoor fan-coil-cabinet unit will offer even better performance than this prototype.

The GAX heat pump provides a major jump in energy efficiency in the heating mode but not in the cooling mode (heating gas COP of 1.5 at 47F and cooling gas COP of 0.7 at 95F). Therefore, the GAX heat pump is marketable primarily in the middle and northern United States. ORNL is also working on developing the Hi-Cool heat pump, which is suitable for the more cooling-dominated southern states.

GAX heat pumps are 40–50%
more efficient than other
high-efficiency technologies.
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