Cold Climate Heat Pump Using Tandem Vapor-Injection Compressors

Abstract

Conventional air-source heat pumps (ASHPs) experience rather poor performance in cold climate areas. The heating capacity and efficiency of conventional ASHPs decrease significantly as the outdoor temperature decreases. The major R&D challenges are to limit this ASHP heating capacity and efficiency degradation at low and extremely low ambient temperatures. Vapor injection (VI) compressors are able to provide better efficiency and larger capacity at low ambient temperatures. A prototype air-source cold climate heat pump (CCHP), using tandem vapor injection (VI) compressors and inter-stage flash tank, was developed. The CCHP has two identical VI compressors in parallel, which works with a two-stage indoor blower and two-stage thermostat. At moderately low ambient temperatures, only one compressor is called, and at extremely low ambient temperatures, both the compressors are used. The prototype was installed in Fairbanks, Alaska and underwent field testing for six months. The CCHP successfully operated down to −30 °F (−35 °C) and was able to meet the building heating load with good efficiency in a wide range of ambient temperatures. At −30 °F (−35 °C), the CCHP delivered 75% heat pump capacity, relative to the capacity at 47 °F (8.3 °C), and the heat pump COP was 1.8. This paper will introduce the CCHP development and field testing results.

This manuscript has been authored by UT-Battelle LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, Irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).