58 ASHRAEJou rna l ash rae .o rg Augus t 2006

Global StandardsFor Filter TestingTheISOandtheIECarecooperatingwiththeEuropeanUnionsCEN(seeTable 1 foracronymdefinitions)andotherstandardsorganizationstocreateglobalstandardsforbuildingairfilters.The

UnitedStates,throughANSI,isrepresentedonISOTechnicalCom-

mittee(TC)142,CleaningEquipmentforAirandOtherGases,Work-

ingGroup(WG)3,GeneralVentilationFilters.Thisgroupiswriting

anISOstandardforatestmethodforgeneralventilationairfilters.

Severalothercountriesareparticipatingandthelistisbeingupdated

continuously(seeISO/TC142Websiteforthelatestinformation).

By Paolo Tronville, Ph.D., Associate Member ASHRAE; and Richard D. Rivers, Fellow ASHRAE

A review of the major U.S., European, and international standards in the air-cleaning field should help ASHRAE members in designing and specifying air

filter systems in the global HVAC market. We encourage members to help develop international standards in this technology as they have with Society standards.

In this article, we discuss test standards for particulate and gaseous contaminant air filters in general ventilation systems. Usually, along with test standards are filter rating systems, which also need to be understood by filter specifiers.

Test Standards and Rating Systems For Particulate Filters

Filters used for building general venti-lation are tested at the time of their market introduction, and subsequently for quality control. ASHRAE Standard 52.1-1992, Gravimetric and Dust-Spot Procedures

About the AuthorsPaolo Tronville, Ph.D., is an assistant professor at Politecnico di Torino in Torino, Italy. He is chairman of ISO/TC 142, Cleaning Equipment for Air and Other Gases. Richard D. Rivers is president of EQS in Louisville, Ky.

2006 American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Journal (Vol. 48, August 2006). For personal use only. Additional distribution in either paper or digital form is not permitted without ASHRAEs permission.

Augus t 2006 ASHRAEJou rna l 59

Table 2: Comparison between ANSI/ASHRAE Standard 52.2-1999 and EN 779:2002.

Item ANSI/ASHRAEStandard52.2-1999 EN779:2002

Test Duct1 Straight allowed, return bend preferred; Straight specified; positive and negative pressure positive pressure only; ducts permitted, with leakage evaluation; more rather strict dimensioning; conductive walls dimensional freedom; conductive walls

Test Air Room or recirculated air; Room, recirculated or outdoor air; 10C 30C, 20% 65% RH RH < 75%, temperature not specified

Test Aerosol Dry, approximately spherical, polydisperse Liquid, spherical, polydisperse KCl (potassium chloride) DEHS (diethylhexyl sebacate)

Sampling Primary/secondary and diluters allowed; upstream and downstream lines must have same geometry, be rigid and conductive; deviation from isokinetic flow condition is specified.

Discrete Particle Optical or aerodynamic counters allowed, Optical counter specified; 0.2 m 3.0 m inCounter or Counters a matched pair of counters upstream and downstream, a minimum of 5 diameter ranges in near-logarithmic or single counter, switched; 0.3 10 m steps; specifies a single counter switched in 12 set diameter ranges. between upstream and downstream.

Test Stand Both standards require items 1 13. Standard 52.2-1999 also requires items 14 17.Qualification Tests2 (1) air velocity uniformity; (2) aerosol uniformity; (3) particle counter size accuracy; (4) particle counter overload- ing; (5) particle counter zero; (6) zero filter efficiency; (7) 100% filter efficiency; (8) aerosol generator response time; (9) neutralizer activity; (10) manometer calibration; (11) dust feeder airflow; (12) duct leakage; (13) efficiency and stability of final filter; (14) effectiveness of downstream mixing; (15) upstream/downstream correlation ratio; (16) upper limit of aerosol count; (17) empty test section pressure drop.

Maintenance Tests Both standards require repetition of Qualification Tests 1 12 at various intervals. ASHRAE 52.2 also requires periodic repetition of Tests 13 and 16, and adds two others: (18) check of the dust feeder venturi throat dimension for wear, and (9) evaluation of the resistance and arrestance and particle-size efficiency of a group of reference filters.

Electrified Fiber Mention of possible decay of electrostatic effects, no Includes procedure for conditioning filter to inhibit

Filter Testing recommendation. Addendum on a preconditioning electrostatic effects and allow measurement of non-

procedure to eliminate electrostatic effects is

electrified efficiency. under discussion.

Dust and Fiber Flow of HEPA-filtered air is continuedShedding after the efficiency test following an increment Discussed but not specified. of dust loading for 20 minutes. Particle count indicates amount of shedding.

Notes1. With positive pressurization, the static pressure inside the test duct is above the pressure outside the duct; with negative, the static pressure inside the duct is below the pressure outside.2. The upstream/downstream correlation ratio is the ratio (upstream count/downstream count) when no filter is between the upstream and downstream samplers. This ratio, computed for each size range, is used to correct the efficiency calculation for differences in between upstream and downstream sampling line losses.

Abbrev. Organization Location InternetSite

ANSI American National Standards Institute USA www.ansi.org

AFNOR Association Franaise de Normalisation France www.afnor.fr

BSI British Standards Institution UK www.bsi-global.com

CEN

Comit Europen de Normalisation European Committee for Standardization

Belgium www.cenorm.be

CSA Canadian Standards Association Canada www.csa.ca

DIN Deutsches Institut fr Normung Germany www2.nabau.din.de

DOD U.S. Department of Defense USA www.dod.gov

DOE U.S. Department of Energy USA www.energy.gov

IEC International Electrotechnical Commission Switzerland www.iec.ch

IEST Institute of Environmental Sciences and Technology USA www.iest.org

ISO International Organization for Standardization Switzerland www.iso.ch

MIL-STD Military Standard (USA) (Document source) USA www.dsp.dla.mil

SAE Society of Automotive Engineers USA www.sae.org

UNI Ente Nazionale Italiano di Unificazione Italy www.uni.comTable 1: Abbreviations and Internet sites for standards oganizations.

60 ASHRAEJou rna l ash rae .o rg Augus t 2006

for Testing Air-Cleaning Devices Used in General Ventilation for Removing Par-ticulate Matter, and CENs EN 779:1993, Particulate Air Filters for General Venti-lation Requirements, Testing, Marking, were quite similar standards, specifying several tests. These included filter resis-tance as a function of flow; resistance rise when a coarse synthetic dust was fed to the filter; dust removal efficiency (arres-tance) on the same synthetic dust at each fed increment; and efficiency on ambient atmospheric dust (atmospheric dust spot test), at each increment of dust fed.

For many years, these tests served to characterize and compare filters but failed to evaluate an important filter character-istic: the efficiency of the filter at specific particle sizes. In addition, the dust-loading information was merely comparative.

One cannot predict the service life of a filter from the dust-holding capacity provided by the two standards, because the dust used for the loading test does not represent what is found in actual air-handling systems.

The first of these inadequacies has essentially been overcome for revisions of both standards: ANSI/ASHRAE Standard 52.2-1999, Method of Testing

General Ventilation Air Cleaning Devices for Removal Efficiency by Particle Size, and EN 779:2002, Particulate Filters for General Ventilation: Determination of the Filtration Performance, include methods that determine filter efficiency vs. par-ticle diameter. The problem of a better simulant for real dust in air-handling systems is the subject of the completed ASHRAE Research Project RP-1190.1 The results of this study could influence future revisions of ASHRAE standards.

Standard 52.2-1999 and EN 779:2002 are detailed although not identical. Table 2 compares the standards. The similarity between the standards and the involve-ment of U.S. representatives on ISO/TC142/WG3 offers the possibility that a global standard for this class of filters can be written soon.

Many manufacturers still use Stan-dard 52.1-1992, testing by its methods and publishing ratings based on them. Standard 52.2-1999 and EN 779:2002 make use of the arrestance and dust-loading procedures from Standard 52.1-1992 almost verbatim. Standard 52.1-1992 retains the atmospheric dust spot test, and also includes a procedure that evaluates automatic self-renewing

Table 3: Classes defined by ANSI/ASHRAE Standard 52.2-1999.

AverageEfficiency(E), Average MinimumMERV PercentinDiameterRange Arrestance, Final 0.3m1.0m 1.0m3.0m 3.0m10.0m (A) Resistance

1 n/a n/a

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filters (e.g., roll-type filters). Annex A of EN 779:2002 includes procedures for evaluating the electrostatic augmenta-tion of aerodynamic filtration, which could be adversely influenced by many unknown factors, such as the capture of small particles and captured conductive or oily particles. A proposed addendum to Standard 52.2-1999 dealing with this problem completed its first public review in December 2004 and is still under discussion inside ASHRAE Standing Standards Project Committee 52.2.

Both EN 779:2002 and Standard 52.2-1999 include classification systems for general ventilation filters. Table 3 shows the MERV levels found in Standard 52.2-1999, and Table 4 shows the F and G Classes found in EN 779:2002. The system used by EN 779:2002 is simpler, placing filters in categories determined by their arrestance (for coarse filters) and by their efficiency on 0.4 m DEHS particles (for fine filters). This size was chosen because it approximately matches the dust spot efficiency value measured in Standard 52.1-1992 that is widely used.

The Standard 52.2-1999 MERV (Mini-mum Efficiency Reporting Value) system requires several steps. First, the efficiency in all 12 particle size ranges is determined at each dust increment during the dust-load-ing procedure. The minima for efficiency for each size range may occur for a clean filter, or at some specific dust load, so the second step is to select the minimum values throughout the loading procedure.

The next step is to average the mini-mum efficiencies in three size groups: 0.3 1 m, 1 3 m and 3 10 m. For a filter to rate a given MERV level, these minima must exceed the values listed for that level in Table 3. Note, however, that only MERV levels 13 and above make use of all three particle size ranges, and the lowest MERV levels are still based on average arrestance, rather than the count procedure just described.

There is no exact correspondence between any of the categories in the two rating systems. Standard 52.2-1999 provides in its Appendix E a table that attempts to correlate its MERV ratings with Standard 52.1-1992 arrestance, dust spot efficiencies, and the ratings for HEPA

and ULPA filters tested according to other standards. Table 5 lists the approximate equivalents given in Standard 52.2-1999 Appendix E, to which we have added the approximately equivalent EN 779:2002 and EN 1822:19982 ratings. Complaints have been raised as to whether the final resistance specified by the ASHRAE table for loadingwhich influences average efficiencies as well as dust sheddingare realistic. The final resistances specified by EN 779:2002 are even higher (450 Pa [1.8 in. w.g. for F filters) than those specified by Standard 52.2-1999.

Test Standards for Gaseous Contaminant Filters

Test standards for general ventilation gaseous contaminant filters have not progressed as far as those for particulate filters. Many reasons exist for this. Gas-eous contaminants may be toxic, odorous, annoying, and damaging or disastrous for manufacturing processes or building ma-terials. These effects and the performance of adsorptive and chemisorptive filters depend on physical and chemical proper-ties of individual contaminants; on their concentrations; on the temperature and humidity of the airstream reaching the fil-ter; and on the cumulative exposure of the filter media, to mention a few factors.

Hundreds of contaminants are of serious concern, and each has different properties. Standards writers must select a limited number of test contaminants that represent those found in field applications, and also select test conditions that are representa-tive and sufficiently realistic to give mean-ingful evaluations of filter media.

A group of standards has been pro-duced by American Society for Testing Materials (ASTM) to provide quality control of many properties of gaseous contaminant adsorption filter media. However, the ASTM standards that evalu-ate the mass of contaminant that a given mass of adsorptive media captures and/or holds (D5228-92:2000, D5160-95:2003, D5742-95:2000, and D6646-03:2003,36 for example) use contaminant concentra-tions far higher than those that prevail in HVAC systems, and do not measure contaminant penetrations through filters in the course of their loading with the

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62 ASHRAEJou rna l ash rae .o rg Augus t 2006

Class Final Average Average Resistance Arrestance,(A) Efficiency(E) On0.4mParticles G1 250 Pa 50%#A#65% n/a

G2 250 Pa 65%#A#80% n/a

G3 250 Pa 80%#A#90% n/a

G4 250 Pa 90%#A n/a

F5 450 Pa n/a 40#E#60

F6 450 Pa n/a 60#E#80

F7 450 Pa n/a 80#E#90

F8 450 Pa n/a 90#E#95

F9 450 Pa n/a 95#E

Table 4: G and F Classifications defined by EN 779:2002.

ASHRAE Approx.ASHRAEEN779: EN1822: Standard Standard52.1Values2002 1998 52.2 Avg.DustSpot Arrestance

Classes Classes MERV Efficiency

20 n/a n/a n/a H14

19 n/a n/a n/a H14

18 n/a n/a n/a H13

17 n/a n/a n/a H13

16 n/a n/a n/a H10

15 >95% n/a F9 n/a

14 90% 95% >98% F8 n/a

13 80% 90% >98% F7 n/a

12 70% 75% >95% F6 n/a

11 60% 65% >95% F6 n/a

10 50% 55% >95% F5 n/a

9 40% 45% >90% G4 n/a

8 30% 35% >90% G4 n/a

7 25% 30% >90% G4 n/a

6