ASHRAE AN-04-5-2-2004 How Much Energy Could Residential Furnace Air Handlers Save 《有多少能源可以通过住宿炉空气处理挽救?》.pdf
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1、AN-04-5-2 How Much Energy Could Residential Furnace Air Handlers Save? Harvey M. Sachs, Ph.D. Member ASHRAE ABSTRACT Available information indicates that improving the air- handler motors and fan systems in residential furnaces and heat pumps promises substantial, cost-efective eficiency gains (hund
2、reds of kWh per year). Unfortunately, the manda- tory test methods used give on ineficient units use several times more. The savingspotential is comparable to the electricity use of a 2001-compliant refrigerator (about 500 kWh/yr). INTRODUCTION The air handler of residential split systems includes t
3、he cabinet (below the furnace in an upflow furnace), the fan, and the fan motor. Improvements could result from changes in aerodynamics, the fan, motor, and/or motor controls. Such measures show potential for substantial, cost-effective effi- ciency gains. During the heating cycle, the difference be
4、tween an advanced fardmotor system and an ordinary one is approx- imately the total energy consumption of a 2001 -compliant refrigerator: in the range of 500 kilowatt-hours per year (kWh/ yr). In the air-conditioning mode in “average” climates, we estimate that the better air-handler motors reduce d
5、emand by about 250 watts (including the benefits of reduced heat rejec- tion by the fan motor) and save 200 kWh in a typical cooling climate (Sachs and Smith 2003). In this paper, many numbers are “engineering estimates.” In some cases, actual data are proprietary and unpublished. In others, uncerta
6、inties arise from gaps between field measurements and predictions that would be made from rating methods. Thus, our conclusions should be taken as indicators of opportunities and additional Sandy Smith, Ph.D. Table 1. An Indication of Electricity Savings Potential for the Most Efficient Condensing F
7、urnaces* Based on 114 furnaces listed in ACEEE (ZOOI), which only considered AFUE. The “high” use group is inferred to use PSC motors, and the “low” use group to be equipped with ECPM motors. research needs rather than definitive results for regulatory purposes. Gas furnace electricity consumption v
8、aries greatly, even within size classes. To illustrate this, one estimator of electri- cal use by furnaces is Eae, the annual electrical consumption computed according to the annual fuel utilization efficiency (AFUE, ASHRAE 2000) test protocol. Table 1 shows the aver- age value of Eae for extremely
9、efficient condensing fumaces (AFUE almost all 94% or better), taken from ACEEE (2001 I). Routes to Improved Performance Most residential units use permanent split capacitor (PSC) motors. Typically, multiple taps give fixed speed . Pp. 24-27, table titled “Most Eficient Gas Furnaces. Harvey M. Sachs
10、is director of the Buildings Program and Sandy Smith is senior research associate at American Council for an Energy-E%- cient Economy (ACEEE), Washington, D.C. 02004 ASHRAE. 43 1 Table 2. Efficiency Estimates for 1/2 Horsepower PSC and ECPM Motors* Technology Based on discussions with industry autho
11、rities. See also Nadel et al. (2002, “Efficiency (Oh) up to 82%” from . options. The electronically commutated DC permanent magnet motor (ECPM, ECM? ICM, DCPM, and other terms) has 5% to 10% of the “premium” market.3 The ECPM motor costs substantially more today, but it offers many benefits, includi
12、ng continuously variable speeds-and much higher efficiency. Table 2 compares efficiency for % horsepower versions of the two motor types. The efficiencies noted are electrical energy conversion efficiencies, or “wire-to-shaft” rather than “wire-to-air” effi- ciencies. The efficiency of fractional ho
13、rsepower motors (4 hp) is not governed by national EPAct standards (NEMA 1997), and the relevant standard (NEMA 2002) does not include non-induction single-phase fractional motors, such as permanent magnet motors. Thus, estimates in this paper are based on reviews of manufacturers literature4 and di
14、scussions with industry experts. Conventionally, residential systems use high-speed fan operation in air-conditioning mode and a lower speed for heat- ing. This is required because the contrast between the supply air temperature and the desired room temperature is much smaller in cooling than heatin
15、g: roughly 20F (1 1 OC) in cool- ing and 5OoF-7O0F (28OC-39”C) in heating with gas or oil fuel. Thus, getting the same effect requires moving more air mass in cooling, which is accomplished through higher fan speeds. Ironically, because the air-handler fan is located in the condi- tioned airstream,
16、reducing electricity used in heating will slightly increase gas consumption. On the other hand, the decreased heat rejection by an efficient motor in the cooling cycle decreases compressor work and electricity used for cool- ing, improving efficiency. ECMm is a trademark of one manufacturer. Estimat
17、e based on roughly 300,000 ECMyr (10-year average ACHR 20031) and roughly 4.5 million new furnaces (GAMA data) plus roughly 1.5 million new heat pumps (AM data) per year. Calling it 400,000 ECM for 2002 to allow for increasing market share would give about 9%. As an example, one efficiency graph in
18、a product brochure shows a remarkable 70% efficiency at 400 rpm (about 150 watts) and peak efficiency of 82% at . 12. The artificially high number ofmodels makes inferences ofstatis- tical robustness inadvisable. furnaces and because there is little difference in the two numbers across the range of
19、furnace efficiencies considered. Indeed, although total range is fairly small-90% to 96+%- roughly 85% (of common updraft models) have efficiencies no higher than 93%. The scatter plot of Eue (electricity use) versus furnace capacity suggested a “trough” or “valley” with few models. Empirically, thi
20、s seemed to separate a graph region of systems with high electrical efficiency/low Eae from a graph area with much higher electricity use. When we plot- ted the data for the best 20% (lowest kwhyr) in each size class against the most inefficient 20% (most kWWyr) within capac- ity classes, there were
21、 clear differences. To further explore this pattern, we created an informal efficiency metric, the electricity use ratio or EUR. This is the ratio of the annual electricity use, Eae, divided by the fumace capacity, in thousands of Bhuh (kBtu/h). For a furnace with Eae = 500 kWhyr and 50,000 Bhuh (50
22、 kBtdh) capacity, EUR = 500/50 = 1 O. EUR has two operational virtues: (1) EUR “normalizes” electricity use across furnace capacities, and (2) everything needed for assessing EUR is available in the stan- dard columns of the GAMA on-line database for gas furnaces. EUR can be used to select high- eff
23、iciency electrical furnaces. Table 4 tabulates these data by furnace size.13 The average saving, across all sizes, is 5 1 1 kWh/yr. For purposes of this study, we use 500 kWhyr as the average elec- tricity saving in the heating season by high-efficiency furnace air handlers. In contrast, GE uses 894
24、 kwh as the national average (GE 2001). This value is decremented by the esti- mated fraction of condensing furnaces sold in relatively warm climates (Kendall 2002b). We assumed 90% conversion effi- ciency for gas condensing furnaces. The sales-weighted aver- age may be higher, which would make ACEE
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