1、2008 ASHRAE 187ABSTRACTThe objective of this study was to assess the performanceof residential furnace blowers for both heating, cooling and airdistribution applications and to compare their performance atDOE/ARI rating conditions (for AFUE and SEER) and at realinstalled conditions. A testing progra
2、m was undertaken at twolaboratories to compare the performance of furnace blowersover a range of static pressure differences that included stan-dard rating points and measured field test pressures. Threedifferent combinations of blowers and residential furnaceswere tested. The laboratory test result
3、s for blower power andairflow were combined with DOE2 models of building loads,models of air conditioner performance, standby power, as wellas igniter and combustion air blower power to determinepotential energy and peak demand impacts. The results showdistinct differences between the two types of f
4、urnace blowermotor technology: Permanent Split Capacitor (PSC) and moreefficient Brushless Permanent Magnet (BPM). The high staticpressure differences in real installations reduce the advantagethat BPM driven blowers have at DOE/ARI rating conditionssuch that for cooling the two motor technologies h
5、ave essen-tially the same power consumption although the reduction inairflow for the PSC driven blower results in 10% lower airconditioner efficiency. For heating, the advantage of the BPMblower is approximately halved when changing from standardtest conditions to installed conditions, although the
6、BPMblower has the advantage of maintaining airflow that avoidsthe safety implications of the PSC blowers lower airflow. TheBPM blower retains its advantage for multi-speed systems thatcan operate for significant numbers of hours in low-fire mode.To better reflect blower performance it is recommended
7、 thatappliance rating test procedures be amended to use realisticsystem static pressures of between 0.5 and 0.8 in. water (125and 200 Pa) and that utility rebate programs ensure thatrebates are provided for multi-speed systems and/or systemsthat have a field measured low static pressure difference b
8、elow0.5 in. water (125 Pa).INTRODUCTIONThe blowers in residential furnaces typically move heatedor cooled air through a duct system that distributes the air andthen returns it to the furnace. Usually the blowers are doubleinlet models with air entering the centrifugal blower wheel atboth sides. The
9、motor mounts inside one side of the blower.Some systems also use the central blower to distribute venti-lation air or to mix air to improve comfort and reduce stratifi-cation.Although furnaces, air conditioners and heat pumps havebecome significantly more efficient over the last couple ofdecades, re
10、sidential forced air system blowers have not expe-rienced similar improvement. The most common blowershave been shown by field testing to have efficiencies of only10% to 15% (Phillips 1998 and 1995, and Gusdorf et al. 2002).These low efficiencies indicate that there is significant roomfor improvemen
11、t of both electric motor and the aerodynamicperformance of furnace blowers.The U.S. Environmental Protection Agency (EPA) andthe California Energy Commission (CEC) are both consider-ing accounting for the electricity use of furnaces and furnaceblowers. The EPA requirements are still being decided, b
12、ut arelikely to either be a fixed kWh/year number (available from theGAMA Directory (GAMA 2006) or kWh/year proportionalto the furnace output or input. For example, the GAMA direc-tory already lists “electrically efficient” furnaces whose elec-Comparing Residential Furnace Blowers for Rating and Ins
13、talled PerformanceIain S. Walker, PhDMember ASHRAEIain S. Walker is a staff scientist at Lawrence Berkeley National Laboratory, Berkeley, CA.NY-08-0252008, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Volume 114,
14、Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.188 ASHRAE Transactionstrical consumption is 2% or less of total annual energyconsumption. This approach therefore uses test
15、 data fromfurnaces evaluated at the AFUE rating conditions of extremelylow external static pressure. The CEC proposal for the 2008California Residential Building Efficiency Standards is torequire field testing of airflow and power consumption and usea W/1000 cfm metric (Wilcox 2006), where credit wo
16、uld begiven for systems using less than 400 W/1000 cfm (whilesimultaneously requiring more than 350 cfm/ton of coolingcapacity). The CEC proposal has the advantage of testingsystems as they are actually installed.An important consideration in analyzing forced airsystem blowers is that essentially al
17、l of the wasted electricityis manifested as heat. This extra heat reduces air conditioningcooling performance and effectively acts as an electric supple-ment to fossil-fueled furnaces. For heat pumps, this heatsubstitutes for vapor compression-based high COP heatingand effectively reduces the COP of
18、 the heat pump.This study combines the results of field tests to determinetypical operating conditions with detailed laboratory perfor-mance mapping to determine the power consumption of theblowers. Additional calculations and modeling were used toaccount for the interactions of the blowers with HVA
19、C equip-ment to account for performance issues such as the extra heat-ing effect of the blowers and the effect on air conditionerperformance with airflow.The results of this study are important to several constit-uents. From a national and state public policy point of view, ifthe EPA and CEC wish to
20、 make informed decisions regardingblower performance it is critical that actual field performanceis documented and understood. This allows the setting ofreasonable performance expectations and credits for betterperformance. If utilities (an the commissions that overseethem) want to have rebate progr
21、ams for more energy efficientblowers they need to know how blowers really perform inhouses so that the rebates can be justified. A better understand-ing of the key aspects of blower performance also allows anyrebate programs to better define the blowers that are rebated(for example, differentiating
22、between single and variablespeed) and the appropriate level of rebate. CHARACTERISTICS OF RESIDENTIAL BLOWERSThere are two types of blowers used in residentialfurnaces. Both blowers have similar blower wheels but theyhave different electric motors: Permanent Split Capacitor(PSC) and Brushless Perman
23、ent Magnet (BPM).PSC BlowerPermanent split capacitor motor driven blowers are by far(90% of the residential market) the dominant motor used inresidential furnace blowers used today. The single-phase PSCmotors are six-pole induction motors with a synchronous rota-tion speed of 1200 rpm. They can oper
24、ate at several fixedspeeds over a range of airflow rates, with highest airflowsabout 1.5 times the lowest airflows. The speed is set by usingdifferent electric current taps that result in different slip, or lagfrom synchronous speed, of the rotor. Different speeds arenecessary to match the different
25、 airflow requirements for heat-ing and cooling operation, and allow a single blower to havea wider range of applications than if it operated at a singlespeed. The blower wheel has many narrow chord forwardcurved bent sheet metal blades, with large gaps between thewheel and housing. The housing has o
26、ne opening on each sidewith the direct drive motor located in one of these openings,and a rectangular discharge. This side entry means that theairflow pattern inside the air handler cabinet is fairly convo-luted as air typically enters the bottom of the cabinet, flowsaround the housing, then changes
27、 direction 90 to enter theblower wheel. Also, unlike older belt-drive blowers, themounting of the electric motor in the inlet restricts the flow onthat side of the fan.Variable Speed BPM BlowerBrushless permanent magnet motors electronicallycontrol the rotating stator field by shifting the field to
28、differentcoils in the windings. The rotor consists of permanent magnetsdirectly mounted on the shaft of the motor. By varying the volt-age and frequency of the electrical current to the stator coils,the motor can be made to rotate over a wide range of speedsand torques. The blower and motor combinat
29、ion can providea constant airflow across a wide range of static pressuresthrough programming controls based on the performance ofthe blower. A key characteristic related to the wide speed range ofBPM blowers is their ability to operate at much lower airflowrates, making them more suitable for contin
30、uous fan operationused for mixing and/or distribution of ventilation air. The abil-ity to operate at much lower airflows (usually about 2.5 timesless than the maximum airflow) results in the use of consider-ably less power at low fan speeds. The blower wheel and hous-ing are the same as those used w
31、ith PSC blowers. BLOWER PERFORMANCE METRIC The most useful blower performance metric combinesboth airflow (L/s or cfm) and power consumption (W). Twocombinations are in common usage: L/s/W (cfm/W) or Watts/m3(Watts/1000 cfm). When interpreting the results, it isimportant to realize that there is a l
32、imit on L/s/W (cfm/W)ratings for 100% efficient operation. The limit is 1000 L/s/Wper Pascal (8.5 cfm/W per inch of water). At a typical operat-ing pressure difference of 125 Pa (0.5 in. water), the limit is 8L/s/W (17 cfm/W). At lower pressures, the limit increases andat higher pressures it decreas
33、es. This dependence of the cfm/W limit on pressure is illustrated graphically in Figure 1.Clearly, there are large potential benefits for low static pres-sure systems.ASHRAE Transactions 189FIELD STUDIES Field studies by many researchers (see the Field TestingBibliography) have shown that existing f
34、ans in residential airhandlers typically consume about 500W, supply about 1 L/s/W (2 cfm/W), and have efficiencies on the order of 10% to15%. The results of a recently completed California EnergyCommission field survey (Wilcox 2006) that focused on newconstruction in California showed similar result
35、s of 1 L/s/W (2cfm/W), but even higher power consumption, with an averageof about 700W per system, due to larger systems beinginstalled in new homes. In cooling mode these systems had amedian static pressure difference of 200 Pa (0.8 in. water). A Canada Mortgage and Housing Corporation (CMHC1993) s
36、tudy showed that typical furnace fan efficiencies are onthe order of 15%, but poor cabinet and duct design can reducethis to about 7%. The spread from best to worst systems wason the order of ten to one indicating that performance dependsstrongly on individual installations. Another Canadian studyby
37、 Phillips (1998 however, these general conclusions can bebroadly applied based on input from furnace manufacturersand the test results from other unpublished studies. Specificfurnace/blower combinations will have different airflow char-acteristics, efficiency ratings and pressure difference sensitiv
38、-ity, but the general trends and observations will still apply.Analysis of the detailed laboratory investigations and energyuse analysis in this study has shown that:BPM and PSC blowers have distinctly different perfor-mance characteristics that must be accounted for whenproposing performance specif
39、ications. BPM blowers have better performance in terms of main-taining airflow at typical system pressures and reducedpower consumption compared to PSC blowers. How-ever, the advantage for BPM blowers is marginal at highpressures above about 200 Pa (0.8 in. water).As system pressures increase, the P
40、SC blower powerconsumption decreases but the airflow is reduced. Power consumption for PSC and BPM blowers are verydifferent at current rating conditions, but the differencesare reduced significantly in real installations due to ductstatic pressures that are much higher than at rating con-ditions.Fi
41、gure 8 Summary of total energy consumption for fourblower furnace design options for three ductsystems design conditions.194 ASHRAE TransactionsAnnual energy use is about the same for PSC and BPMblowers in typical field installations with single-stageheating or cooling equipment, whereas the BPM blo
42、weris about 30% better at rating conditions.Two-stage equipment that operates for a significant frac-tion of the year at lower capacity and airflow has thebiggest potential benefit from the use of a BPM blower. Use of BPM blowers in place of PSC blowers in highpressure drop systems will allow design
43、 flow rates to bemet, but may in fact increase energy consumption unlessa systems approach is taken.To better reflect blower performance it is recommendedthat appliance rating test procedures be amended to userealistic system static pressures of between 0.5 and 0.8in. water (125 and 200 Pa) and that
44、 utility rebate pro-grams ensure that rebates are provided for using a BPMblower instead of a PSC blower in multi-speed systemsand/or systems that have a field measured low staticpressure difference below 0.5 in. water (125 Pa).BPM blowers have a big advantage over PSC blowers atlow airflows used fo
45、r mixing and air distribution, usingabout one fifth the power.One important utility issue with BPM blowers is theirlower power factor that leads to increased generationand distribution costs. For PSC blowers, the power fac-tor ranged from 0.7 to 0.9, with the lower power factorsat high-speed setting
46、s and high pressures. For BPMblowers the power factors range from 0.53 to 0.62 withhigher power factors at higher speed.As well as the external static pressure effects, the air-flow patterns within blower door cabinets also affectperformance. Side entry, particularly on the motor sideof the blower s
47、hould be avoided. Restrictive cabinetsthat have little clearance around the blower also reduceblower performance. Airflow reductions are about 15%,with similar reductions in L/s/W (cfm/W) ratings whenclearance is reduced to about 25 mm (1 inch). From the national or state appliance rating and public
48、policy viewpoint, this study indicates that considerable careneeds to be taken when developing rating requirements, andthat currently available data may be inadequate. Until changesare made to current ratings, or new rating procedures aredeveloped, efficiency labels (and other consumer informa-tion)
49、, rebates and/or tax credits may be misrepresentative. RECOMMENDATIONS FOR FUTURE WORKOnly a small sample of furnaces were evaluated in thelaboratory tests. To be more definitive, it would be a good ideato test more furnaces from a range of manufacturers. In addi-tion, furnaces over a range of capacities should be tested to seeif the general results from the testing described in this reportare applicable in all cases. Lastly, the energy analysis could beextended to cover other climate zones with different ratios ofheating to cooling.ACKNOWLEDGMENTSThe following individuals contributed to
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