NATIONAL BUREAU OF STANDARDS REPORT

4972

PERFORMANCE TESTS OF A ’’DUST-STOP”

THROWAWAY-TYPE AIR FILTER

by

Thomas W. Watson

Henry E . Robinson

Report to

General Services Administration

Public Buildings Service

Washington 25, D. C.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OE COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its headquarters in Washington,

D. C., and its major field laboratories in Boulder, Colorado, is suggested in the following listing of

the divisions and sections engaged in technical work. In general, each section carries out spe- cialized research, development, and engineering in the field indicated by its title. A brief

description of the activities, and of the resultant reports and publications, appears on the

inside back cover of this report.

WASHINGTON, D. C.

Electricity and Electronics. Resistance and Reactance. Electron Tubes. Electrical Instruments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation.

Electrochemistry.

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Technology. Length. Engineering Metrology.

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and Lubrication. Engine Fuels.

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• Office of Basic Instrumentation • Office of Weights and Measures

BOULDER, COLORADO

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Navigation Systems. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Radio

Systems Application Engineering.

Radio Standards. Radio Frequencies. Microwave Frequencies. High Frequency Electrical

Standards. Radio Broadcast Service. High Frequency Impedance Standards. Calibration

Center. Microwave Physics. Microwave Circuit Standards.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1000-30-4830 January 18, 1957 4972

PERFORMANCE TESTS OF A ’’DUST-STOP”

THROWAWAY-TYPE AIR FILTER

by

Thomas W« Watson

Henry E . Robinson

Heating and Air Conditioning Section

Building Technology Division

to

General Services Administration

Public Buildings Service

Washington 25, D. C.

IMPORTANT NOTICE

NATIONAL BUREAU OF ST

intended for use within the

to additional evaluation and

listing of this Report, either the Office of the Director, N

however, by the Government

to reproduce additional copi

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

)rogress accounting documents

rmally published it is subjected

reproduction, or open-literature

sion is obtained in writing from Such permission is not needed,

prepared if that agency wishes

<nb|>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PERFORMANCE TESTS OF A ’’DUST-STOP"

THROWAWAY-TYPE AIR FILTER

by

Thomas W. Watson and Henry E. Robinson

1. INTRODUCTION*

At the request of the Public Buildings Service j General

Services Administration, the performance characteristics of

throwaway-type air filters were determined to provide information to assist in the preparation of new air filter specifications . The test results presented herein were obtained on a

specimen throwaway-type air filter submitted by its manufacturer at the request of the Public Buildings Service and

included determinations of dust arresting efficiency with two

aerosols (atmospheric air and Cottrell precipitate), pressure

drop and dirt load,

2. DESCRIPTION OF THE FILTER SPECIMEN

The filter was manufactured by the Owens-Corning Fiberglas Corporation, Toledo, Ohio and was of the throwaWay-type

,

It was identified as a ’’Dust-Stop’’ replaceable-type air filter, 20 X 20 X 2 inches in nominal size and had media of finefibered glass strewn in a loose pack about two inches thick

covered on the faces by retainers of thin brass sheet, from

which circular discs had been stamped, leaving a grid of circu

lar openings. The sides of the filter were enclosed in a card

board edging, leaving a free opening 17 15/16 inches square

(2.23 ft^) . The fibers were lightly coated with an adhesive.

The filter had actual outside dimensions of 19 5/8 x 19 5/8 x

17/8 inches and weighed 1.07 pounds when clean.

This report is submitted for information only, and is not

released for use in connection with advertising or sales

promotion.
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The present ”Dust-Stop” filter was stated to have

fibered and more flexible media than earlier Dust-Stop

and is lighter in weight and has a larger face opening

flow.

a finerf liters

,

for air

3, TEST METHOD AND PROCEDURE

Efficiency determinations were made by the NBS "DustSpot Method** using the following aerosols: (a) outdoor atmospheric air drawn through the laboratory without addition of

other dust or contaminant; and (b) Cottrell precipitate , dispersed in the outdoor atmospheric air. The test method is

described in the paper "A Test Method for Air Filters" by

R, S. Dill (ASHVE Transactions, Vol, 44, p, 379, 1938),

For these tests, the filter was installed in the apparatus and the desired rate of air flow through the cleaner was

established. Samples of air were drawn from the center of the

test duct, at points one foot upstream and eight feet downstream of the filter and passed through known areas of Whatman

No, 41 filter paper. The areas of the filter papers used

upstream and downstream and the times during which the air

was sampled upstream and downstream were selected experimentally so that the change in transmission of light through the

two filter paper spots would be about the same. The filter

efficiency was calculated by means of the formula

Efficiency, percent = 100 1

^2 ^2

^1 '^2

where A represents the dust spot area, 0 the change in light

transmittance of the filter paper as measured before and after

the deposition of dust, and T the time during which the air

sample was drawn. Subscripts 1 and 2 refer to the upstream

and downstream positions, respectively.

Three efficiency-measuring techniques or modifications

based on the above formula were used, depending on the apparent

efficiency of the filter with the different aerosols. For the

tests made, techniques L, M and N were used, as indicated in

table 2.
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All light transmission measurements were made with the

photometer illujninat ion at a, constant intensity as determined by measurement on a reference of constant transmission

characteristics. The filter papers used upstream and downstream were selected to have equal light transmissions when

clean

The efficiency of the filter in arresting particulate

matter in atmospheric air was determined by means of two

tests of the L and M types, as described in table 2, with

the filter clean. Following these, the efficiency of the

filter in arresting Cottrell precipitate was measured by

means of two N-type tests, after which was begun the process of loading the filter with a mixture of four percent

of cotton lint and 96 percent of Cottrell precipitate, by

weight, separately dispersed in the air stream. The lint

used for this purpose was No . 7 cotton linters previously

ground in a Wiley mill with a four-millimeter screen. At

suitable periods as the loading progressed, the efficiency

of the filter was determined using Cottrell precipitate in

outdoor air. Pressure drops were recorded at intervals

during the test. The dirt-loading was continued until the

pressure drop increased to approximately 0.50 inch W. G. The

efficiency was again determined with Cottrell precipitate

and then with atmospheric air as the aerosols.

4 . TEST RESULTS

Table 1 presents data as to the pressure drop of the

clean filter at several rates of air flow.

The performance of the filter at 800 cubic feet per minute is summarized in table 2 for two aerosols. The performance

of the filter in regard to aerosol C (Cottrell precipitate

in atmospheric air) is shown graphically in figure 1. The

efficiency of the filter in arresting aerosol A (atmospheric

particulate matter) , both initially and after its resistance

had been increased by dirt-loading to 0.5 inch W. G. , is indicated in table 2.
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Observation of the filter at the end of the dirt-loading

test revealed that the greater part of the arrested lint was

found on the upstream face and had not penetrated the media

beyond a depth of about 1/4 inch. A considerable amount of

dust had penetrated the media to a depth of approximately one

inch; the downstream face of the media was uniformly darkened

with dust. No lint was visible on the downstream face of the

media

After the unit had been removed from the test duct, the

section of the duct five feet long downstream of the unit, and

upstream of a 3/4 inch thick wood strip fastened flat across

the bottom of the test duct, was carefully swept out with a

fine brush. The amount of material obtained from the duct by

this sweeping was 11.8 grams, or 4.1 percent of the dust load

reaching the filter, constituting the fall-out in the first

five feet of the duct from the air passed through the filter,

and consisting for the most part of large dust particles.

Cellophane tapes, stretched across the test duct downstream of the filter with the adhesive side facing upstream,

indicated upon visual and microscopic examination after exposure to the air stream that some particles of sizes up to

approximately 150 microns had passed through the filter during

the dirt-loading tests. Particles smaller than five microns

were observed in quantity by microscopic examination of the

downstream filter papers obtained in tests with both aerosols.

No lint was observed on the tapes during these tests.
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Table 1

PRESSURE DROP OF CLEAN FILTER

Air Face Pressure

Flow Ve locity Drop( 1)

cfm fpm inch W.G.

1200 540 0o225

1000 450 . 170

800 360 .121

600 270 .076

(1) Init ial values for the clean filter.
,r
Table 2

PERFORMANCE OF FILTER AT 800 CFM

Aerosol (1)

Total

Dirt

Load (2)

Pressure

Drop

Eff. Meas,

Technique (3) Efficiency

grams inch W. G. percent

A _ 0.121 M 10

- . 121 L 11

C 7 . 129 N 74

14 . 137 N 73

81 .207 N 78

159 .291 N 81

217 .377 N 83

287 .523 N 83

A 287 .523 M 12

(1) Aerosol A; Particulate matter in atmospheric air at NBS

Aerosol Ct Cottrell precipitate in atmospheric air

(1 gram per 1000 cubic feet).

(2) Average mixture: 3.8 percent lint, 96 „

percent Cottrell

precipitate by weight.

(3) Efficiency measuring technique:

L: Air sampled at equal rates through equal areas;

upstream sampling time selected to yield approximately equal dust-spot opacities of the upstream

and downstream filter papers.

M: Air sampled at equal rates through equal areas

for equal times.

N: Air sampled at equal rates for equal times; downstream areas selected to yield approximately equal

dust-spot opacities of the upstream and downstream

filter papers.
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EFFICIENCY,

PERCENT

D 200 300

LOAD REACHING FILTER, GRAMS

THE NATIONAL BUREAU OF STANDARDS

Funclions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public I,aw 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advi.sory services to Government Agencies on scientific and technical

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Inquiri(“s regarding the Bureau’s reports should be addressed to the Office of Technical Information, National Bureau of Standards, Washington 25, D. C.