EPA/600/A-96/048 95-TA33A.04 Aerosol Filtration Efficiency of Ventilation Air Cleaners James T. Hanley and David S. Ensor Research Triangle Institute P.O. 12194 Research Triangle Park, NC 27709 Leslie E. Sparks U.S. Environmental Protection Agency Air and Energy Engineering Research Laboratory Research Triangle Park, NC 27711 ------- 95-TA33A.04 INTRODUCTION The use of air cleaners has steadily moved from one of protecting equipment (such as the heat exchanger in a furnace) to one of protecting people from objectionable indoor aerosol particles (e.g., common dust and allergens). This shift has necessitated the development of new test methods for determining air cleaner filtration efficiency. Under a cooperative agreement with the U.S. Environmental Protection Agency (EPA)1 and contracts with the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)2, and the Canadian Electrical Association (CEA)\ the Research Triangle Institute (RTI) has developed a test method for measuring the fractional aerosol filtration efficiency of air cleaners. The method provides a reliable and accurate means of measuring air cleaner fractional efficiencies over the particle diameter size range of 0.01 to 10 H-m. The need for a fractional efficiency test comes from several sources: (1) the growing concern with indoor air quality (IAQ); (2) the fact that filtration efficiency is often highly particle-size dependent for particles <10 |im in diameter; (3) limitations of the current ASHRAE efficiency test (52.1-1992) which, by design, cannot differentiate between particle sizes4; and (4) that respirable particles are generally classified as those <10 p.m in diameter. Implementation of the new method will provide several benefits to the air cleaner community: Fractional efficiency data that will allow architects, building managers, and heating, ventilating, and air-conditioning (HVAC) supervisors to specify air cleaners to meet their filtration requirements; Manufacturers with a standardized fractional efficiency test of known data quality to replace the many nonstandard methods now in use; Architects and IAQ researchers with fractional filtration efficiency data required for use in air cleaning system designs and IAQ models; and The consumer with a more realistic assessment of air cleaner performance than is currently given by the single-valued efficiency and arrestance tests. Furthermore, because the new method provides a more detailed assessment of an air cleaner's performance than the current efficiency and weight arrestance tests of ASHRAE 52.1-1992, use of the new method may lead to the development of improved air cleaners. TEST DUCT The test duct, aerosol generation, and aerosol sampling systems are illustrated in Figure 1. Like an ASHRAE duct, the test duct is based on a 24 x 24 in. (610 x 610 mm) duct and accommodates the fractional efficiency tests as well as the dust loading and arrestance tests. Key features of the duct include: Positive pressure to minimize room air infiltration; 2 ------- 95-TA33A.04 Inlet air drawn from indoors to maintain temperature and humidity within the desired range; HEPA (high efficiency particulate air)-filtered inlet to remove ambient aerosol; HEPA-filtered exhaust to allow indoor discharge; Artificially generated, solid-phase, polydisperse potassium chloride (KC1) salt challenge aerosol, generated from an aqueous solution using an air-atomizing nozzle; Automated sequential upstream/downstream aerosol sampling; A downstream mixing baffle (in addition to the upstream mixing baffle) to ensure well- mixed aerosol conditions at downstream sample probes; and 180° bend in the downstream duct to bring upstream and downstream sample locations close to each other, greatly reducing sample line length and facilitating use of a single set of aerosol measurement instrumentation. AEROSOL GENERATION, SAMPLING, AND MEASUREMENT The test aerosol was composed of KC1 generated from aqueous solution. KC1 was selected because of its relatively high water solubility, high deliquescence humidity, known crystalline structure (facilitates complete drying), solid phase, and low toxicity. The aqueous solution was prepared by combining 300 g of KC1 with 1 L of distilled water. A solid-phase aerosol was desired because, due to particle bounce, solid particles tend to penetrate air cleaners at a higher rate than do liquid particles. Thus, using solid-phase aerosol particles provides a more stringent test. At particle sizes above a few micrometers, differences between aerosol penetration measured using solid- and liquid-phase aerosols can be very large for some air- cleaning devices, particularly for low efficiency filters. To span the size range from 0.01 to 10 Jim, three methods of aerosol generation and three methods of aerosol measurements were used (Table 1). This was necessary to optimize measurement accuracy over the entire size range. From 0.01 to 0.07 (im, the up- and downstream aerosol concentrations were measured with a TSI, Inc., Model 3071 Electrostatic Classifier with a Model 3020 Condensation Nucleus Counter. This instrument measures particle size based on the electrical mobility of the aerosol particles. A Laskin Nozzle using a dilute 0.1% by weight KC1 aqueous solution was used to generate the challenge aerosol. From 0.09 to 3 pim, the aerosol concentrations were measured with a Particle Measuring Systems, Inc. (PMS) LAS-X Laser Aerosol Spectrometer. This instrument measures particle size based on wide-angle light scattering using a laser light source to illuminate the particles. A Collison nebulizer containing a 20% by weight KC1 solution was used to generate the test aerosol. 3 ------- 95-TA33A.04 A Climet Instruments Company Model 226 Optical Particle Counter (OPC) with Model 8040 Multichannel Analyzer was used to measure aerosol concentrations over the range of 0.3 to 10 fim diameter. This is a wide-angle light scattering instrument that uses a high intensity white-light illumination source. The aerosol was generated by nebulizing 20% by weight aqueous KC1 solution with a two-fluid (air and water) air atomizing nozzle as illustrated in Figure 1. The aerosol output from each generator was injected into a spray tower (as shown in Figure 1). The tower served two purposes. It allowed the salt droplets to dry by providing an approximate 40 second mean residence time and it allowed larger-sized particles to fall out of the aerosol. After generation, the aerosol passed through a TSI Model 3054 aerosol neutralizer (Kr85 radioactive source) to neutralize any electrostatic charge on the aerosol (electrostatic charging is an unavoidable consequence of most aerosol generation methods). To improve the mixing of the aerosol with the air stream, the aerosol was injected counter to the airflow as illustrated in Figure 1. SYSTEM QUALIFICATION TESTS As part of a program with EPA, the new test duct was put through a series of system qualification tests to demonstrate its capability to accurately measure fractional efficiency. The purpose of these tests was to quantify that the test rig and sampling procedures were capable of providing reliable fractional penetration measurements. It is strongly recommended that such tests be included in the new test standard. Similar qualification tests are specified in the Institute of Environmental Sciences Recommended Practice "Testing ULPA Filters"5 and are an important part of any quantitative test method. Qualification tests were performed for: Airflow uniformity in the test duct, Aerosol uniformity in the test duct, Downstream detection of aerosol, Overloading tests of the OPC, 0% penetration test, 100% penetration test, Aerosol generator response time, Duct leak test, and Duct temperature and relative humidity. Table 2 summarizes the results from the system qualification tests. (In the table, "CV" is the coefficient of variation which is equal to the standard deviation of a set of measurements divided by their mean.) Also included are recommended goals for these parameters. In specifying these goals, the objective was to have tight enough control over the critical test parameters to yield accurate and reproducible results and yet not be so tight that the test becomes unrealistically difficult or expensive to perform. The recommended levels are based on a combination of judgment as to what will be required for dependable results and practical experience in trying to achieve optimum test conditions. All of the recommended levels were met or exceeded in the test duct. As data from interlaboratory comparisons become available, these goals may need to be strengthened to improve interlaboratory comparison or relaxed to increase the utility of the method. 4 ------- 95-TA33A.04 Results from the 100% penetration tests are presented in Figure 2. These tests provide a relatively stringent test of the adequacy of the overall duct, sampling, rfieasurement, and aerosol generation system. The test is performed as a normal penetration test except that no air cleaner is used. A perfect system would yield a measured penetration of 1 at all particle sizes. Deviation from 1 can occur due to particle losses in the duct, differences in the degree of aerosol uniformity (i.e., mixing) at the upstream and downstream probes, and differences in particle transport efficiency in the upstream and downstream sample lines. Results show that, at particle sizes below about 2 (im, the losses were less than 2%. Maximum loss of approximately 10% was observed in the 4 to 10 |im range. TEST PROCEDURES The penetration was calculated from the average of 10 upstream and 10 downstream samples taken sequentially (i.e., one upstream, one downstream, one upstream, one downstream, . . . until 10 each were obtained). This sequential sampling scheme minimizes the effect of aerosol generator variability. Each sample was 2 min in duration. This was based on having the sample duration long enough to obtain a minimum of 50 particles counted in each sizing channel for each upstream sample (providing a minimum total of 500 particle counts in each channel for the combined 10 upstream samples). For each test, measurements were also made with the aerosol generator off to measure the upstream and downstream background aerosol concentrations. For each test, we have the following information for each particle size: A series of background upstream and downstream measurements performed with the aerosol generator off. These are averaged to obtain Ubkg and Dbkg. A series of upstream and downstream particle counts performed with the aerosol generator on. These are averaged to obtain Uavg and Davg. A series of 0% filtration efficiency correction factors, F0. From these quantities, the filtration efficiency at each particle size was computed as: Filtration Efficiency = 1 - ( 1-F0) (Davg - Dbkg) / (Uavg - Ubkg) . RESULTS A series of triplicate tests was performed with the test air cleaners (Table 3) to illustrate the characteristic shape of the fractional efficiency curves for the various air cleaners. Under the ASHRAE program, the test air cleaners consisted of a furnace filter, a pleated-paper filter, and a two-stage electrostatic precipitator (ESP). The fractional efficiency measurements were made over the size range of 0.3-10 (im. Under the CEA program, the air cleaners consisted of a furnace filter, a single-stage ESP, a charged-media electronic air cleaner (EAC), and a two-stage ESP. The fractional efficiency measurements on the CEA program covered the size range from approximately 0.01 to 5 ------- 95-TA33A.04 10 )im. On each program, the devices were selected to cover a wide range of filtration efficiencies. Figures 3 and 4 summarize the fractional efficiency results. Table 4 shows the upstream and downstream particle counts associated with one of the pleated-paper air cleaner tests covering the 0.3 - 10 (im size range. The upstream counts were similar for the other tests with the downstream counts dependent upon the degree of particle penetration of the air cleaner. A misunderstanding often encountered in fibrous filter testing is that an air cleaner's filtration efficiency will continuously decrease as the particle size decreases. Actually, this statement holds true only over a certain range of particle sizes and this range is dependent on the filter media. For example, most media-based air filters are least efficient at particle diameters of about 0.2 to 0.3 |im. For both larger and smaller particles, efficiency increases. The increase in efficiency for larger particles results from increased effectiveness of the filtration processes to collect particles due to the physical mechanisms of inertial impaction and interception, as well as straightforward sieving of particles when the particle diameter is greater than the "pore size" of the filter. The increase in efficiency for smaller particles is caused by diffusion. Particle diffusion is the consequence of the Brownian motion that small particles undergo due to bombardment by air molecules. Particle diffusion increases rapidly with decreasing particle size. Thus, smaller particles diffuse to the filter fibers and are collected more rapidly than larger ones, resulting in increasing filtration efficiency as particle diameter decreases below 0.1 Jim. Additionally, particle bounce and reentrainment can reduce an air cleaner's efficiency for the larger particles (i.e., >3 jim diameter). These particles have sufficient kinetic energy to rebound off the air cleaner's collection surface (e.g., a fiber) and bounce their way through the air cleaner. For ESPs, particles are collected by different mechanisms than for filters. Field charging is responsible for the charging of large particles, and diffusion charging is responsible for the charging of small particles. Both processes are relatively weak in the 0.1-|im size range, resulting in a relative minimum in that range. The falloff in efficiency in the 0.01 to 0.03-|im diameter range is attributed to incomplete charging of these small-diameter particles. CONCLUSIONS AND RECOMMENDATIONS Based on the test results, the following principal conclusions are presented: The test system provides a reliable means of evaluating the fractional aerosol efficiency of air cleaners over the 0.01-10 |im diameter size range. Specification of appropriate quality control criteria, such as those presented in Table 2 (system qualification tests), are needed to ensure reliable measurements. Particle loss in the test duct appears to be <10% in the 2 to 10 (im range and <1% at smaller sizes. These losses were repeatable and relatively low in comparison to the particle removal efficiency of most air cleaners that will be tested with this method. Thus, air cleaner penetration data can be confidently corrected for these losses using the 100% penetration data. The fractional efficiency of air cleaners is highly particle-size dependent. 6 ------- 95-TA33A.04 The common furnace filter had fractional efficiencies of <20% over the 0.01 to 10 size range. The highest efficiency was seen for the 2-stage ESP which had a minimum efficiency of 62% over the entire 0.01 - 10 Jim size range. ACKNOWLEDGEMENTS The authors gratefully acknowledge the significant contributions of ASHRAE, CEA, and EPA to this effort to develop fundamental information on the fractional aerosol efficiency of air cleaners. REFERENCES 1. J.T. Hanley, "Fractional Aerosol Filtration Efficiency of In-Duct Ventilation Air Cleaners," Indoor Air, 4:169-178 (1994). 2. J.T. Hanley, D.D. Smith, D.S, Ensor, "Define a Fractional Efficiency Test Method That Is Compatible with Particulate Removal Air Cleaners Used in General Ventilation," Final Report on ASHRAE Research Project 671-RP, (1992). 3. Canadian Electrical Association, "Testing Criteria for Electronic Air Cleaners: Phase II," (1993). 4. American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. Standard 52.1-1992 "Gravimetric and Dust-Spot Procedures for Testing Air-Cleaning Devices Used in General Ventilation for Removing Particulate Matter." (1992). 5. Institute of Environmental Sciences Recommended Practice IES-RP-CC007.1 "Testing ULPA Filters," Mount Prospect, IL. 1992. 7 ------- 95-TA33A.04 Table 1 Aerosol Generators and Measurement Instrumentation Diameter Size Range, |im Aerosol Analyzer Aerosol Generator 0.01 - 0.07 TSI Model 3071 Electrical Mobility Particle Sizer with Condensation Nucleus Counter Laskin Nozzle with 0.1% by weight KC1 in distilled water. 0.09 - 3 Particle Measurement Systems Model LAS-X Laser Aerosol Spectrometer Collison nebulizer with 20% by weight KC1 in distilled water 0.3 - 10 Climet Model 226 Optical Particle Counter with Model 8040 Multichannel Analyzer Two-fluid spray nozzle 8 ------- 95-TA33A.04 / Table 2. System Qualification Measurements and Goals Parameter Level Achieved Recommended Goal Airflow Uniformity: Based on traverse measurements made over a 9-pt equal-area grid at each test flow rate. CV* = 4.1% @ 1,000 cfm** CV = 2.7% @ 2,000 cfm CV = 4.1% @ 3,000 cfm CV <5% Aerosol Uniformity: Based on traverse measurements made over a 9-pt equal-area grid at each test flow rate. CV <7% @ 1,000 cfm CV <10% @ 2,000 cfm CV <10% @ 3,000 cfm CV<10% Downstream Mixing: Based on a 9-pt perimeter injection grid and center-of-duct downstream sampling. CV = 4.6% « CV = 1.0% « CV= 1.7% « § 1,000 cfm 1 2,000 cfm 1 3,000 cfm CV <5% 0% Penetration Test: Based on HEPA filter test. <1% <1% 100% Penetration Test: Based on five replicate tests at each test flow rate. 90 to 100% for all sizing channels 90 to 110% for all sizing channels Upper Concentration Limit: Based on limiting the concentration to below the level corresponding to the onset of coincidence error. 10/cm3 (>0.3 n.m) No pre- determined level. Aerosol Generator Response Time 10 minutes No pre- determined level. Duct Leakage: Ratio of leak rate to test airflow rate. 0.12% <0.5% Duct Air Temperature 75 to 85 °F*** 50 to 100 °F Duct Relative Humidity 35 to 55% <65% Compressed Air Relative Humidity <30% <30% {*) Coefficient of variation. (**) 1,000 cfm = 0.47 m3/s. {***) °C = (°F - 32J/1.8 9 ------- 95-TA33A.04 Table 3. Description of the Test Air Cleaners Air Cleaner Flow Rate, Size Range, cfm (L/s) |j.m Pleated paper 65% dust-spot efficiency 24 x 24 x 6 in, (610 x 610 x 150 mm) 2,000 (940) o ¦ CO o Two-Stage ESP 16 x 25 x 6 in. (406 x 635 x 150 mm) 1,200 (560) 0.3- 10 Furnace Filter Spun fiberglass 24 x 24 x 1 in. (610x610x25 mm) 2,000 (940) 0.3 - 10 Two-Stage ESP 16 x 25 x 6 in. (406 x 635 x 150 mm) 1,000 (470) 0.01 - 10 Single Stage ESP 16 x 25 x 1 in. (406 x 635 x 25 mm) 1,000 (470) 0.01 - 10 Charged-Media Panel Electronic Air Cleaner 16 x 25 x 1 in. (406 x 635 x 25 mm) 1,000 (470) 0.01 - 10 Furnace Filter Spun fiberglass 16 x 25 x 1 in. (406 x 635 x 25 mm) 1,000 (470) 0.01 - 10 10 ------- 95-TA33A.04 Table 4. Upstream and Downstream Particle Counts from One Test of the Pleated-Paper Filter Particle Counts per Indicated OPC Channel (2-Minute Samples @ 0.25 cfm*) OPC Channel Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Min. Diam. (um) 0.3 0.4 0.5 0.6 0.8 1 1.5 2 3 4 5.5 6 7 8 9 Max. Diam. (um) 0.4 0.5 0.6 0.8 1 1.5 2 3 4 5.5 6 7 8 9 10 Geo. Mean Diam (um) 0.35 0.45 0.55 0.69 0.89 1.2 1.7 24 3.5 4.5 5.7 6.5 7.5 8.5 9.5 Upstream-Bkg 5 0 0 1 0 1 0 1 0 0 0 0 0 0 0 Upstream-Bkg 37 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Upstream-Bkg 6 3 1 0 2 2 4 5 3 7 3 2 1 1 0 Upstream-Bkg 21 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Upstream-Bkg 8 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Upstream 20860 20630 15350 18990 9893 16490 20470 7695 2757 1507 249 339 197 91 39 Upstream 21530 21300 15770 19620 10070 16860 21070 8050 2791 1602 244 361 192 108 58 Upstream 20340 20350 15060 18660 9839 15980 19970 7718 2695 1380 225 281 171 106 58 Upstream 20640 20410 14980 18710 9976 16020 20250 7794 2635 1511 220 360 188 122 65 Upstream 21100 20780 15580 19490 9972 16280 20930 7903 2761 1541 247 315 179 99 59 Upstream 21220 20850 15570 19280 10090 16550 20870 8124 2701 1488 240 342 189 93 62 Upstream 20690 20660 15360 18790 9846 16330 20370 7608 2739 1459 193 342 170 129 51 Upstream 20520 20310 14970 18680 9643 15920 20390 7683 2626 1504 249 327 167 100 52 Upstream 20990 20660 15530 19070 10060 16530 20580 7953 2803 1569 230 327 172 138 69 Upstream 20260 20320 14910 18690 9725 16000 20180 7632 2691 1487 240 340 157 104 50 Upstream-Bkg 142 2 0 0 0 1 0 0 0 0 0 0 0 0 0 Upstream-Bkg 168 0 0 0 0 0 2 1 0 0 0 1 1 1 0 Upstream-Bkg 157 4 1 0 1 0 2 1 0 0 0 0 0 0 0 Upstream-Bkg 142 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Upstream-Bkg 142 0 0 1 0 0 0 0 0 0 0 0 0 0 0 Downstream-Bkg 12 1 1 0 0 0 0 0 0 0 0 0 0 0 0 Downstream-Bkg 37 0 0 0 0 0 1 0 0 0 0 0 0 0 0 Downstream-Bkg 35 13 20 13 4 2 14 7 4 7 2 0 0 0 0 Downstream-Bkg 23 0 0 0 0 0 1 1 1 1 0 0 0 0 0 Downstream-Bkg 16 1 3 6 6 8 15 1 2 0 0 0 1 0 0 Downstream 17060 15830 10940 11670 4938 6056 3353 259 32 22 3 2 1 0 0 Downstream 17030 16010 10920 11640 5027 6036 3424 257 23 12 5 3 2 0 0 Downstream 17280 15840 10920 11990 5004 6021 3363 262 27 14 4 3 1 0 0 Downstream 17180 16120 10930 11580 4952 6047 3370 235 25 3 1 1 1 0 0 Downstream 17400 15980 10890 11640 5028 6124 3464 271 27 18 6 1 2 0 0 Downstream 17280 15800 10860 11590 4881 6004 3342 249 19 14 3 1 0 0 0 Downstream 16530 15270 10540 11280 4960 5851 3168 237 26 6 1 2 1 0 2 Downstream 16950 15500 10680 11330 4866 6024 3358 247 24 1 0 0 1 1 0 Downstream 17370 15790 10970 11700 5033 6007 3347 270 29 13 5 1 1 1 0 Downstream 17680 16370 11170 11930 5154 6239 3529 253 26 8 0 1 3 1 0 Downstream-Bkg 142 0 0 1 1 0 0 0 0 0 0 0 0 0 0 Downstream-Bkg 182 23 18 10 6 2 5 5 1 1 0 1 0 0 0 Downstream-Bkg 148 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Downstream-Bkg 133 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Downstream-Bkg 158 1 0 0 1 0 1 0 0 0 0 0 0 0 0 Meas. Penetration 0.82 0.77 0.71 0.61 0.50 0.37 0.16 0.03 0.01 0.01 0.01 0.00 0.01 0.00 0.00 P100 Correction Value 0.99 0.98 0.99 0.99 0.99 0.99 1.00 0.99 0.98 0.96 0.94 0.96 1.02 1.08 1.14 Corrected Penetration 0.84 0.78 0.72 0.62 0.51 0.37 0.16 0.03 0.01 0.01 0.01 0.00 0.01 0.00 0.00 (*) 0.25 cfm = 0.00012 m3/s. 11 ------- 95-TA33A.04 Exhaust ASME Nozzle Outlet Filter Bank Room Downstream Mixer Room Air OPC Device Section Backup Filter Holder 'Used When )ust-loading) Inlet Filter Bank Upstream Mixer Blower Aerosol Generator Flow Control Valve (*) Optica] Particle Counter Overview of Test Duct Configuration (Top View) Spray Nozzle Spray Tower j mF Syringe Purrp Aerosol Charge Neutnalizer Dtyii Aiomizing Air /yr" j H£PAF8ter £ br Capsules Air Control Panel Air Source I ¦* Test Dud HEPA Fiter Bank Aerosol Generation System (Side View) 90" Bend to Point Inlet Upstream Sample Lines Vafve Actuator Bail Valve interchangeable Isokinetic Sampling Tip 90* Bend to Point Inlet Upstream tectricaf Cable Downstream Pud Upstream Duct Machined 'Y* Mulichann« Analyser Data AcquMlon Computer Aerosol Sampling System (Side View) Figure 1. Schematic diagram of air cleaner test duct, aerosol generator, and sampling system. 12 ------- 95-TA33A.04 0.9- 0.8- c 0.7- 0 *| 0.6- 1 0.5- 0.4- 0.3- 0.2- - 0.1- 0.1 Particle Diameter (micrometers) 1,000cfm*--« 2,000 cfm 3,000 cfm (*) 1,000 cfm = 0.47 m3/s. Figure 2. Average results for the 100% penetration tests. 13 ------- 95-TA33A.04 100 90 80 ^ 70 > C 60 "o 3= 50 LU .2 40 15 Ll 30 20 10 0 0.01 Two-Stage ESP BDOUSSOnBl Charged-Media EAC Q. Single-Stage ESP fa* 1 a Furnace Filter i i it i 0.1 1 Particle Diameter (micrometers) 10 Figure 3. Fractional efficiency of several air cleaners over the 0.01 -10 nm diameter size range. 14 ------- 95-TA33A.04 >* O c 0) *¦¦¦ o it= LLI 100 90 80 70 60 50 | 40 co v_ ir 30 20 10 0 0.1 Two-Stage ESP a^ii Pieated-Paper Furnace Filter 10 Particle Diameter (micrometers) Figure 4. Fractional efficiency of several air cleaners over the 0.3 -10 nm diameter size range. 15 ------- 07 TECHNICAL REPORT DATA Jiiixxi-i r LA i 0 (Please read Instructions on the reverse before completir 1, REPORT NO, 2. EPA/600/A-96/048 3. 1 4, TITLE AND SUBTITLE Aerosol Filtration Efficiency of Ventilation Air Cleaners S. Rt. uni DATE 6. PERFORMING ORGANIZATION CODE 7. AUTHOR(S) J. T. Hanley and D. S. Ensor (RTI), and L. E. Sparks (EPA) 8. PERFORMING ORGANIZATION REPORT NO. 95-TA33A.04 9. PERFORMING ORGANIZATION NAME AND ADDRESS Research Triangle Institute P.O. Box 12194 Research Triangle Park, North Carolina 27709 10. PROGRAM ELEMENT NO. 11. CONTRACT/GRANT NO. CR817083 12. SPONSORING AGENCY NAME AND ADDRESS EPA, Office of Research and Development Air and Energy Engineering Research Laboratory Research Triangle Park, NC 27711 13. TYPE OF REPORT AND PERIOD COVERED Published paper; 1/92-12/94 14. SPONSORING AGENCY CODE EPA/600/13 15. supplementary notes ^EERL project officer is Leslie E. Sparks, Mail Drop 54, 919/ 541-2458. Presented at AWMA annual meeting, San Antonio, TX, 6/18-23/95. 16. abstract^.paper discusses a test method for measuring the fractional aerosol fil- tration efficiency of air cleaners. The method provides a reliable and accurate way to measure air cleaner fractional efficiencies over the particle diameter size range of 0.01 to 10 micrometers. (NOTE: The use of air cleaners has moved steadily from one of protecting equipment (e. g., the heat exchanger in a furnace) to one of protec- ting people from objectional indoor aerosol particles; e. g., common dust an aller- gens. This shift has necessitated the development of new test methods for determin- ing air cleaner filtration efficiency.) The need for a fractional efficiency test comes from several sources; (l) the growing concern with indoor air quality (IAQ); (2) that filtration efficiency is often highly particle-size dependent for particles <10 micro- meters in diameter; (3) limitations of the current American Society of Heating, Re- frigerating and Air- Conditioning Engineers (ASHRAE) efficiency test which, by de- sign, cannot differentiate between particle sizes; and (4) that respirable particles are generally classified as those <10 micrometers in diameter. 17. KEY WORDS AND DOCUMENT ANALYSIS a. DESCRIPTORS b. IDENTIFIERS/OPEN ENDED TERMS c. COSATI Field/Group Pollution Measurement Aerosols Filtration Ventilation Air Cleaners Particles Pollution Control Stationary Sources Particulate 13 B 07 D 13 A 131 14 G 18, DISTRIBUTION STATEMENT Release to Public 19. SECURITY CLASS (This Report) Unclassified 21. NO. OF PAGES 20. SECURITY CLASS (This page) Unclassified 22. PRICE EPA Form 2220-1 (9-73) ------- |