ASHRAE AN-04-5-1-2004 Energy-Saving Opportunities in Residential Air-Handler Efficiency《住宅空调搬运效率的节能机会》.pdf
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1、AN-04-5- 1 Energy-Saving Opportun it es in Residential Air-Handler Efficiency Mark A. Kendall ABSTRACT This paper demonstrates the technical considerations that are important to understanding the energy-saving potential of encouraging the use ofbrushless direct current (BDC) motors in residential ai
2、r handlers. Energy savings estimates are provided, and the regulations that are already in place are explained. Some misperceptions about the testing and opera- tion of residential furnaces and air conditioners are also covered. Usingone set ofparameters that assume typical cyclic operation, the con
3、sumer payback of purchasing BDC circu- lating fan motors rather than standardpermanent split capac- itor motors is 26 years. This drops to just under 4 years if the fan is operated continuously. INTRODUCTION An air handler is the component in a central heating or cooling system that is responsible f
4、or circulating conditioned air through the conditioned space. The air handler is usually part of the central furnace or indoor unit on a heat pump. In cases where there is no furnace, but there is a central air condi- tioner, the air handler is a distinct piece of equipment. The standard air handler
5、 utilizes a centrifugal blower and a permanent split capacitor (PSC) motor. The PSC motor oper- ates on alternating current. Speed control, which is required for fans that operate at one speed during the cooling season and at another during the heating season, is accomplished by applying voltage to
6、different sets of motor windings. This introduces slip, which slows the motor down, but at a consid- erable efficiency penalty. A PSC motor operating at part speed draws almost as much power as one operating at full speed. A competing motor technology found in many high-end air handlers is the brush
7、less direct-current (BDC) motor. The BDC motors construction and its speed-control technique are inherently more efficient than the PSC motor, but there is a substantial price premium. Some advocates of energy efficiency, utilities, legisla- tures, and regulators have considered requiring or promoti
8、ng more efficient air handlers based on BDC technology. Many of these promoters presume that the air handler is not regulated, or is under-regulated, by the federal government, and that additional energy savings can result from the promotion of efficient air handlers as distinct from the air conditi
9、oning or heating systems they serve. There are several points that must be considered when deciding whether to apply additional regulation or incentive to promote more efficient air handlers. There are also some common misperceptions about the way in which furnaces and air conditioners are tested an
10、d how air-handler electricity consumption is measured. These factors lead to lower net energy savings and higher incremental equipment prices than might first be apparent. ENERGY SAVINGS DURING THE HEATING SEASON In 1997 there were 56.6 million residences in the United States equipped with a central
11、 warm air furnace. Ofthose, 35.1 million were installed in combination with a central air condi- tioner. In the remaining 2 1.5 million homes, only a central furnace is present. Homes with a central air conditioner but no central furnace number 12.1 million. Other homes with air handlers include tho
12、se heated and cooled by electric heat pumps, which number 10.5 million (EIA 1997). Since the air handler and the furnace are one and the same in over 7 1% of all households with air handlers, improving the electrical efficiency of the air handler results in electricity Mark A. Kendall is the vice pr
13、esident, Technical Affairs, Gas Appliance Manufacturers Association, Arlington, Va. 02004 ASHRAE. 425 Table 1. Typical Furnace Electrical Consumption Characteristics AFUE 80% When Equipped with a When Equipped with Electricity Use Metric Stages PSC Fan Motor a BDC Fan Motor Savings E, kWh (GJ) 1 730
14、 (2.6) 420 (1.5) 42% 2 590 (2.1) 180 (0.6) 67% BE, W 1 450 250 47% 2 - LOW 320 60 79% 2 - HIGH 450 160 58% 90% EA, kwh (GJ) 1 660 (2.4) 470 (1.7) 38% 2 620 (2.2) 250 (0.9) 63% savings during the heating season. However, while electricity savings are substantial, they are offset by increased fuel con
15、sumption. BE, W The Efficiency Advantage of BDC Motors A survey of seven residential furnace manufacturers in 2002 quantified the electricity savings that can be achieved in typical single- and two-stage residential furnaces with BDC motors. The results are presented in Table 1. Respondents provided
16、 average annual electricity consumption, EAE, and blower power consumption, BE, as measured by the federal test procedure for their “most sold” furnace models. The survey requested efficiency certification test data for nominal 75 kBtu/h (22 kW) input furnaces capable of accom- modating a 3-ton (1 1
17、 kW) cooling system. Savings shown are the average of savings compared to products from the same manufacturer rather than across manufacturers. Since there are no single-stage BDC furnaces available today, the results represent an estimate based on comparative BDC-PSC perfor- mance data. These data
18、reveal that the common single-stage furnace, if it were equipped with a BDC motor, would save 3 10 kWh/ yr (0.9 GJ/yr), or 42%, compared to an identical PSC- equipped model. For condensing funiaces, the savings would be less at 190 kWh/yr (0.7 GJ/yr), or 38%. Using average national retail electricit
19、y prices of $0.0841 per kWh ($23.3/ GJ) (DOE 2003), this corresponds to an annual electricity cost savings of $26 for noncondensing funiaces and $16 for condensing furnaces. The power consumption of a typical furnace circulating fan motor in heating mode is 400 W. At 30% efficiency, the motor suppli
20、es 280 W of supplementary electric resistance heat. A BDC motor operating in low speed at 70% efficiency would supply the equivalent of a 40 W resistance heater-a savings of 240 W. If all 56.6 million central furnaces operated simultaneously, their circulating fan motors would generate 15.8 GW in su
21、pplementary resistance heat. Contrast that with 1 550 330 44% 2 - LOW 400 120 77% 2 - HIGH 580 320 44% the 13 million electric resistance furnaces in the US. (EIA 1997). If all operated simultaneously, assuming 1 O kW each, they would produce 130 GW of resistance heat, nearly 10 times the power cons
22、umption of all central furnace fan motors. When combined with two-stage gas controls and two- speed inducer motors that allow the fumace to operate at two different capacities to better match the heating load, electricity savings are even more substantial. The data also show that electricity savings
23、 almost double those for single-stage equip- ment can be achieved by using BDC motors in combination with two-stage controls. So, the typical two-stage noncon- densing furnace equipped with a BDC, which is available today, would save 4 1 O kWhiyr (1.5 GJ/yr), or 67%, versus the single-stage version.
24、 Electricity Savings Are Offset by Increased Fuel Use While these electricity savings are impressive, consumers do not receive the full benefit in terms of energy savings or util- ity cost savings. Increasing the efficiency of the fan motor reduces the amount of heat it generates. For fumaces in the
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