1、2009 ASHRAE 581ABSTRACT Energy cost and use have become a global concern. ASHRAE has introduced sustainability goals for energy effi-ciency and healthy indoor environments. How should we deliver such sustainability promises to air filtration in HVAC systems? There is a growing demand from end users
2、and filter manufactures to classify the air filters not only by particulate removal efficiency, but also by energy efficiency. Currently, all the filters are classified only by particulate removal efficiency and none of existing standards such as ASHRAE 52.2-2007 or EN779:2002 addresses the issue of
3、 energy efficiency. In this paper, two methods are introduced to classify the filter energy efficiency: key energy performance (kep) number and wattage. Four different models were applied to calculate the average pressure drop vs. dust loading as it is a critical variable to the energy efficiency. A
4、 new exponential model proposed in this research showed excellent consistency to experimental data of pressure drop during the dust loading process of ASHRAE 52.2 full test.INTRODUCTIONIn 2006, the ASHRAE Board of Directors approved a strategic plan to lead the advancement of sustainable building de
5、sign and operation. As William Harrison, 2008-2009 ASHRAE President, said in his speech Maintain to Sustain Delivering ASHRAEs Sustainability Promise at ASHRAE annual meeting in Salt Lake City (Harrison, 2008), sustain-ability for ASHRAE means energy efficiency and healthy, productive indoor environ
6、ments. How can we delivering such sustainability promise to air filtration in the HVAC system? We have the standards available in the industry to test general ventilation air filters for removal efficiency by particle size. ASHRAE 52.2 and EN779 are the most popular ones in the world with the former
7、 widely used in North America and the latter in Europe. But none of them has ever addressed the issues on energy efficiency. As energy becomes a global prob-lem today, there is increasing demand to establish a method generally accepted to the industry to determine how to classify a filters energy ef
8、ficiency. This paper is a preliminary research to introduce two methods which can be used in the industry for the energy classification. Experiments were made with 6 air filters (V-pack, bag, box, panel) by ASHRAE 52.2 full test and 7 representative filter media (flat sheets) by TSI 8130 Automated F
9、ilter Tester to demonstrate how to use each method to classify the energy efficiency. ENERGY EFFICIENCY CLASSIFICATIONMethod 1: kep Number Key energy performance number (kep number) is currently being discussed in Europe for the energy efficiency classification (Mayer, et al., 2008). It was defined
10、as:(1)Where is average filtration efficiency over the dust load-ing in EN779 test for a particle size of 0.4 m 3400 m3/hr (2000CFM); is the average pressure drop in Pa, i.e. (2)M is the final amount of dust loading (g), x is a variable of loaded dust (g). C is an empirical constant.kep1 FE()logPC- 1
11、00 Pa=FEPP1M- Px()0Mdx=Delivering Sustainability Promise to HVAC Air Filtration Part I: Classification of Energy Efficiency for Air FiltersChristine Sun, PhD Dan WoodmanMember ASHRAEChristine Sun is R Q is airflow rate in m3/s; is average pressure drop in Pa; t is operation time (s); is system energ
12、y efficiency, which is a product of motor efficiency, fan effi-ciency, and transmission efficiency. Currently, the state of art HVAC filtration system can reach the energy efficiencies up to 85% ( = 0.85). The typical value of is between 0.50 and 0.70 (Mayer et al., 2008). For classification of ener
13、gy effi-ciency of a single filter, the power required to run a filter can be expressed as below: (4)Where W is the power in Watts; v is face velocity (m/s); and A is the face area (m2). Set v = 2.5 m/s or 492 fpm as it is a typi-cal value used for air handling units and the standard test, we have:(5
14、)Set A = 24” 24” = 0.610 0.610 m = 0.3721 m2for a standard 24” 24” filter and system energy efficiency =0.7, then,(6)Therefore, we see the key problem to classify the filter energy efficiency is to find out how to get the average pressure drop during the use or dust loading process, no matter using
15、kep number method via Equation (1) or using wattage method via Equation (6) AVERAGE PRESSURE DROP MODELSIn reality, pressure drop curves vary with different filters. For a given filter, it is a dynamic variable which is a function of airflow, dust type and loading amount, and air conditions as shown
16、 in Equation (7).(7)Where Q is the airflow rate; K is a parameter associated with the type of dust and loading method; T is air temperature; H is air humidity; x(t) is a variable for the amount of loaded dust; and t is operation time. To simplify such complexity, the aver-age pressure drop is normal
17、ly calculated only based on the initial and final pressure drop. There are three models used in the industry to calculate the average pressure drop. They are arithmetic, geometric, and integral.For the arithmetic model, (8)Where is initial pressure drop in Pa; is final pressure drop in Pa.For the ge
18、ometric model,(9)For the integral model,(10)All these three models approximate a weighted average of the pressure drop curve using the initial and final pressure drop; however, such average pressure drop is subjective to a certain degree as it does not consider the severity of the curva-ture which a
19、ffects the actual energy performance. Figure 1 shows dust loading curves for three of six filters in this research tested by standard ASHRAE 52.2 full test. The shape of the curve was found to nearly perfectly follow the general exponential equation as expressed below. (11)Where a and b are constant
20、s associated with individual filters and x is the amount of loaded dust (g). Using the initial pres-sure drop with a second parameter to describe the curvature FEEQP t 1000=PWQP vAP =W 2.5A P =W 1.329P=Table 1. Energy and Filtration Efficiency Classification of Air Filterskep Number 3400 m3/hr (or 2
21、000CFM)Energy Efficiency Classkep 1 11 kep 0.8 20.8 kep 0.7 30.7 kep 0.6 4kep 0.6 5PPQKTHxt(),()0MM-=P12- PinitialPfinal+()=PinitialPfinalP PinitialPfinal=P Pinitial13- PfinalPinitial()+=Paebx=ASHRAE Transactions 583one can match the pressure drop curve during dust loading as seen in Figure 1. The c
22、alculated data from the exponential model showed excellent consistence to actual pressure drop measured during the ASHRAE 52.2 test. Table 2 lists the constant values of the exponential model for all six tested filters in this study.Taking Equation (11) into Equation (2), we have:(12)Table 3 lists t
23、he average pressure drop obtained from different models. The power rate was calculated based on the exponential model as it well reflected the experimental data obtained in the standard ASHRAE 52.2 test with R-squared value in the range of 0.996-0.999. The error intro-duced by using one of the other
24、 3 models is illustrated in the Max Error column of Table 3. Compared to the arithmetic and geometric models which caused the error up to 49%, the inte-gral model appeared a good model to calculate the average pressure drop for the filters investigated in this research. Table 2. a, b Values of Expon
25、ential ModelsFilters a b R-squared ValueV-pack Filter 1 79.690 0.0820 0.996V-pack Filter 2 89.490 0.0056 0.998Box Filter 55.010 0.0057 0.998Bag Filter1 44.930 0.0018 0.996Bag Filter2 36.165 0.0027 0.999Panel Filter 36.238 0.0027 0.999Table 3. (Pa) Calculated by Four Different Models and Energy Effic
26、iency in WattsTested Filters Arithmetic Geometric Integral Exponential Power (watt)Max Error (%)V-pack Filter 1 216.2 146.6 163.2 168.8 220 28V-pack Filter 2 226.3 170.5 176.7 185.0 250 22Box Filter 233.6 185.9 186.5 196.0 260 19Bag Filter1 207.5 115.2 149.9 150.3 200 38Bag Filter2 210.0 129.9 147.7
27、 140.6 190 49Panel Filter 205.0 114.6 148.3 140.9 190 46PFigure 1 ASHRAE dust loading curves.P1M- aebx xd0MaMb- ebM1()=P584 ASHRAE TransactionsWith the power wattage in Table 3, we can report the energy efficiency (round to 10). Taking V-pack Filter 1 for example, the energy efficiency is 220 watts,
28、 which indicates that the filter requires 220 watts of energy to run at 3400 m3/hr (2000CFM) airflow, which is about equivalent to lighting with 4 traditional incandescent light bulbs. ENERGY EFFICIENT AIR FILTERElectret filters are currently the most energy efficient air filters on the market (Choi
29、, 2008) as their built-in additional electrostatic charge greatly improve the filtration efficiency, especially to capture small particles as shown in Figure 2. Listed in Table 4 are seven air filter media (flat sheets) from the market, where four were pure mechanical and three were electret charged
30、. The filtration efficiency and pressure drop were measured on a TSI 8130 automated filter tester at airflow 48 l/min, using NaCl aerosols. The kep number was calculated according to Equation (1), here was the average of three efficiency readings directly from the TSI 8130. The power wattage was cal
31、culated according to Equation (6).From the power data in Table 4, electret media showed significant advantage in energy efficiency over glass fiber media and non-electet synthetic media. The challenge of elec-tret media is potential electrostatic decay during real use. Thanks to new technologies dev
32、eloped in recent years that greatly improved the stability of electrical static charge (Jans-sen et al., 2006; Tsai, 2003; Motyle et al., 2006), many eletret filters showed no notable performance decay of particulate removal efficiency in the field while providing lower pressure drop with higher ene
33、rgy efficiency over the course of their service life Sun, 2008. Electret filters have gained significant market share and are expected to grow in air filtration area as energy efficiency becomes an increasing public concern (Wang, et al., 2008).Figure 2 Particle capture mechanism in air filtration (
34、Sun, 2008).Table 4. Different Filter Media Energy EfficienciesSampleFiltration Efficiency (%)Pressure drop (Pa)kep numberEnergy Efficiency ClassificationPower(watt)Glass fiber1 87.2 850.1 0.11 5 1130Glass fiber2 98.3 970.2 0.18 5 1289PP 87.3 910.0 0.10 5 1209Polyester 48.5 138.5 0.21 5 184Charged PP
35、1 97.3 42.5 3.68 1 56Charged PP2 99.3 55.6 3.84 1 74Charged Polyester 53.8 13.4 2.01 1 18*Calculation was based on Equation (1), here C=0FEASHRAE Transactions 585CONCLUSIONEnergy cost and use have become a global concern. There is a strong demand today from end users and filter manufac-tures to add
36、energy efficiency to filter classification which is solely based on particulate removal efficiency in current stan-dards. Two methods were discussed in this paper: kep number and wattage. The wattage method proposed in this paper directly uses the power of energy needed to overcome the flow resistan
37、ce of the filters to express the energy efficiency of the filter in a standardized test. Four different models were discussed to calculate the average pressure drop, including arithmetic, geometric, integral, and exponential. The expo-nential pressure drop model proposed in this research was found e
38、xcellent to reflect the actual pressure drop along dust loading in standard ASHRAE 52.2 test, while it caused up to 49% error in power estimates when arithmetic and geometric models were used. Further filter media investigation using TSI 8130 automated filter tester demonstrated that electret media
39、are currently the most energy efficient filter material on the market over non-electret ones.REFERENCESChoi, K.J. 2008. Energy Efficient Air Filter Media, INTC08, Houston, TX, Sept. 8-11.Goel, M. and T. Goel. 1999. Future Trends of Electret Appli-cations in Energy and Environment, 10thInternational
40、Symposium on Electrets.Harrison, W. A. 2008, Maintain to Sustain - Delivering ASHRAEs Sustainability Promise, ASHRAE Meeting, Salt Lake City, June 21-25.Janssen, L. and J. Bidwell. 2006. Performance of Four Class 95 Electret Filters Against Diesel Particulate Matter, Journal of the International Soc
41、iety of Respiratory Pro-tection, Vol. 23, Spring/Summer.Mayer, M., T. Caesar, J. Klaus. 2008. Energy Efficiency Classification of Air Filters, 10th World Filtration Con-gress, Leipzig.Motyl, E., B. Lowkis. 2006. Effect of Air Humidity on Charge Decay and Lifetime of PP Electret Nonwovens, Fibers & T
42、extiles in Eastern Europe, Vol. 14, No. 5(59), January/December.Sun, C. 2008. Mechanical or Electret Filters? INTC08, Houston, TX, Sept. 8-11.Tsai, P. 2003. Novel Methods for Making Electret Media & Remediation of Charge Degredation,“ INTC 2003, Renaissance Harborplace, Baltimore, Maryland, Sep-tember 1618.Wang, A. and K. C. Hofacre. 2008. Assessment of Advanced Building Air Filtration Systems, EPA/600/R-08/032, www.epa.gov/ord, March.
