Content area
Full Text
ABSTRACT
Within rating procedures established by the U.S. Department of Energy, benchmarks have been established for the comparative performance of heat pumps and air conditioners. The heating seasonal performance factor (HSPF) and seasonal energy efficiency ratio (SEER) index heating and cooling season performance, respectively. Although the procedures result in a highly desirable standard metric, the climate-related limitations of the published values must be understood-particularly when attempting to extend performance prediction across regions. This paper describes evaluation of climate-related variation of heat pump and air-conditioner performance. Operating seasonal efficiencies are statistically related to location-specific winter and summer design temperatures and manufacturers' equipment ratings. Implications are discussed.
HEAT PUMPS
Residential air-source heat pumps are an increasingly popular heating system in the southern United States. Over 10 million heat pumps (HPs) are currently inuse(EIA2001). The practical efficiency that air-source heat pumps achieve is a coefficient of performance (COP) of 2.0-3.0. To rate heat pumps in a standard fashion, a heating seasonal performance factor (HSPF) is determined that takes into account operation under varying outdoor temperatures as well as part-load impacts (effects of running short cycles under mild conditions). HSPF is rendered as Btu/Wh so that typical HSPFs are nominally on the order of 6.8-10 Btu/Wh (the dimensionless value of the minimum HSPF of 6.8 is COP = 1.99). HSPF is defined according to test procedures as promulgated by ARI in its Standard 210/240, as well as ASHRAE Standard 116 and the DOE Test Procedure in 10 CFR, Part 430, Appendix M (ARI 2003).
The rated/nameplate HSPF from ARI210/240 is based on the temperature in climate region IV (2000-2500 heating load hours) and the minimum design heating requirement (DHR) that is a function of machine heating capacity. This selection is favorable to limit the contribution of resistance heating because it typically results in a balance point in the 17°F to 25°F range. Although published HSPFs are linked to this climate, and specifically to 2080 heating load hours, it was never envisioned that this single value could be used to generically predict performance for all climate locations. Given the seventy of winter in much of the continental United States and the sensitivity of heat pumps to the outdoor temperature, sitespecific performance must vary significantly with climate. Although temperature bin...