ASHRAE AN-04-5-3-2004 Heat Pump System Performance in Northern Climates《在北方的气候下的热泵系统的性能》.pdf
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1、AN-04-5-3 Heat Pump System Performance in Northern Climates Paul W. Francisco Member ASHRAE Bob Davis David Baylon Larry Palmiter ABSTRACT Single-value ratings for heat pumps and air conditioners have become industry standards and are widely used by consumers, designers, and program managers for equ
2、ipment selection and prediction ofperformance. On the heating side, the standard rating is the heating seasonal performance factor (HSPF), and on the cooling side the standard rating is the seasonal equipment eficiency ratio (SEER). These values are determined under set conditions. However, the actu
3、alperfor- mance of the equipment depends on the climate in which it is being used. Furthermore, the overall energy use can begreatly impacted by factors such as control strategy and duct losses. This paperpresents the results of computer modeling using the bin method to estimate the impact of climat
4、e, certain common control strategies, sizing approaches, and duct losses on the HSPF of heat pumps in two climates in the northwest United States. Comparisons with jeld data and observations show impacts on heat pump performance consistent with modeling results. INTRODUCTION As energy prices increas
5、e, people are paying more atten- tion to the seasonal efficiency of heat pumps and air condi- tioners. This efficiency is often characterized by a single number, which is determined at a specific set of test condi- tions. For heat pumps, this number is the HSPF (heating season performance factor), a
6、nd for air conditioners the number is the SEER (seasonal energy efficiency ratio). These values are used by consumers to compare conditioning systems, by program managers and regulators to predict The SEER rating uses the results of operating the air conditioner at three different conditions (AN 199
7、4). All of them are done at 82F outdoor temperature and 80F indoor temperature at the indoor coil, for a sensible load temperature difference of only 2F. Two of the tests are done with low indoor humidity (dry coil)+ne of these is done at steady- state conditions (typically about 10 to 15 minutes af
8、ter the unit has begun operation); the other is done with the compressor operating for 6 minutes and then off for 24 minutes. These two results are used to determine the part-load factor, which accounts for losses due to the cycling of the compressor. The third test is done with higher indoor humidi
9、ty such that the coil is wet and is also done under steady-state conditions. The SEER rating is the EER (energy efficiency ratio, defined as the ratio of the compressor output in kBtuh to the power input in kW) for this third test multiplied by the part-load factor. The fact that the SEER rating is
10、higher than the commonly published EER rating is because the commonly published EER rating test is performed at 95F outdoor dry-bulb. The HSPF uses a similar technique to get the part-load factor as that used in determining the SEER (AM 1994). The HSPF test, however, uses a much broader range of con
11、ditions to get the rating. Compressor efficiencies at both 17F and 47F are used, as well as the defrost penalty at 35“F, using a 90-minute defrost cycle. The data are applied to multiple design loads and in multiple climates, using a bin calculation technique. This results in many different HSPF rat
12、ings for each piece of equipment. The rating that is published is based on the U.S. Department of Energy Climate Region IV using the minimum design load. savings and establish incentives, and by designers to specify equipment. Despite the broad use of these single-value ratings, the actual seasonal
13、performance of a specific piece of equipment P.W. Francisco is a research specialist at the Building Research Council, School of Architecture, University of Illinois, Champaign. D. Baylon is president, B. Davis is a research scientist, and L. Palmiter is senior scientist at Ecotope, Inc., Seattle, W
14、ash. 442 02004 ASHRAE. can be very different from the ratings provided. One of the primary causes of this is that the conditions under which the rating tests are performed may not represent the location of interest. For example, if the equipment is located in a climate that differs significantly fro
15、m the climate selected for publi- cation of HSPF values, the seasonal efficiency of the heat pump may be very different from the stated rating. The differ- ences between a specific climate and the rating conditions can result in either an improvement or a reduction in seasonal performance. This fact
16、 is well known among experts, but the way in which these ratings are used suggests that this infor- mation is not common knowledge among users, practitioners, and policy-makers (for example see EPA 1998 and ICC 1998). Another factor that can affect the actual performance of a heat pump is the contro
17、l strategy, especially on the heating side. The point at which the backup heating comes on can have a major impact on the actual energy use of a heat pump, since the efficiencies of electric resistance (100%) and natural gas combustion (typically about 80% for standard gas furnaces, 95% for condensi
18、ng types) are both much less than the effi- ciency of a compressor (capacity divided by power input, usually 200% to 400% at the standard rating points). Averag- ing the backup contribution into the overall performance will reduce the apparent equipment efficiency. Backup heat is considered in HSPF
19、ratings, with the assumption that the backup heat only comes on when necessary. Experience with the manner in which systems get installed in the Pacific North- west shows that the desire to ensure customer comfort or prevent customer complaints results in significantly greater use of backup heat. Du
20、ct losses can also have a major effect on the system performance. Duct losses cause the system to run longer than it would otherwise and on the heating side can cause the backup to be required at warmer temperatures than if there were no duct losses. This effect was evaluated for air condi- tioners
21、under hot conditions by Walker et al. (1998), who found that, even with good sizing and installation, the deliv- ered cooling under the conditions evaluated could be as much as 50% lower than the rated output. Palmiter and Francisco (1997) showed that duct losses in the heating mode had a larger imp
22、act on the system efficiency for heat pumps than for furnaces, with the efficiency loss often double that for furnaces for the same duct leakage. This is because delivery tempera- tures are much lower for compressors than for furnaces and extra load is often made up by backup heating elements. This
23、paper describes the results of computer simulations to investigate the performance of heat pump systems for given ratings, installation practices, and duct systems in two loca- tions in the Pacific Northwest-Seattle and Spokane, Wash- ington. These computer simulations use a bin method calculation,
24、similar to that used in the determination of the HSPF ratings, to estimate the efficiency of the heating system at each bin and then combine the results to provide a seasonal efficiency calculation. No cooling season results are reported in this paper, though a similar method can be applied. Results
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