NATIONAL BUREAU OF STANDARDS REPORT

4278

PERFORMANCE TESTS OF AN " AMER-glas ,{ THROWAWAY-TYPE AIR FILTER

by

Henry E. Robinson

Thomas W. Watson

Report to

General Services Administration

Public Buildings Service

Washington 25, D. C.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF 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 is suggested in the following listing

of the divisions and sections engaged in technical work. In general, each section is engaged in

specialized 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

of the back cover of this report.

Electricity and Electronics. Resistance and Reactance. Electron Tubes. Electrical Instru- ments. Magnetic Measurements. Process Technology. Engineering Electronics. Electronic

Instrumentation. Electrochemistry.

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Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics.

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Mineral Products. Porcelain and Pottery. Glass. Refractories. Enameled Metals. Concreting Materials. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Data Processing Systems. Components and Techniques. Digital Circuitry. Digital Systems.

Analogue Systems.

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Gas Liquefaction.

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Propagation Services.

Radio Propagation Engineering. Frequency Utilization Research. Tropospheric Propagation

Research.

Radio Standards. High Frequency Standards. Microwave Standards. • Office of Basic Instrumentation • Office of Weights and Measures
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

IOOO-3 O-I483 O August 10, 1955 4278

PERFORMANCE TESTS OF AN " AMER-glas

” THROWAWAY-TYPE AIR FILTER

by

Henry E. Robinson

Thomas W. Watson

Heating and. Air Conditioning Section

Building Technology Division

Report to

General Services Administration

Public Buildings Service

Washington 25, D. C e <NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, re

unless permission I)

25, D. C. Such per

cal ly prepared if t

In part, is prohibited Approved for public release by the andards , Washington Director of the National Institute of port has been specifi- Standards and Technology (NIST) eport for its own use. on October 9, 20 1 5.

PERFORMANCE TESTS OF AN "AMER-glas"

THROWAWAY-TYPE 1. AIR FILTER

INTRODUCTIONS

At the request of the Public Buildings Service,

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 American Air Filter

Company, Louisville, Kentucky, and was of the throwawaytype. It was identified as an "AMER-glas Replaceable Air

Filter", 20x20x2 inches in nominal size, and had media of

fine-fibered glass strewn in a loose pack two inches thick

covered on the faces by retainers of thin brass sheet from

which circular discs had been stamped, leaving a grid of

circular openings. The sides of the filter were enclosed

in a cardboard edging, leaving a free opening 17 15/1& x 17 7/8 inches, (2.23 ft 2

). The glass fibers were lightly

coated with a clear adhesive. The filter had actual outside dimensions of 19 5/8 x 19 5/8 x 1 7/8 inches and

weighed 1.18 lbs. when clean. The specimen filter had an

Underwriters Laboratories stamp on the cardboard edging

frame

.

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 a paper "A Test Method for Air Filters" by

R. S. Dill (ASHVE Transactions, Vol. I4I4, p 379, 1938).

#This report is submitted for information only, and is not

released for use in connection with advertising or sales

promotion.

- 2 -

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, J4 I filter paper* The areas of

the filter paper 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

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 . All light transmission measurements were made with the

photometer illumination at a constant intensity as determined by measurement on a reference of constant transmission

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

clean.

The efficiency of the filter in arresting particulate

njatter 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

- 3 - ground in a Wiley mill with a 4“mi llimeter 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, at

several rates of air flow, of the clean filter.

The performance of the filter at 800 cfm is summarized in Table 2, for both aerosols A and C. The performance of the filter in regard to aerosol C (Cottrell

precipitate in atmospheric air) is also 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 to 0.5 inch

W.G., is indicated in Table 2.

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 l/2 inch. A considerable

amount of dust had penetrated the media to a depth of approximately 1 l/2 inches; the downstream face of the media

was also founcf to be 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 /U 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 1.0 gram, or

0.26 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

- k -

of sizes up to approximately 125 microns had passed

through the filter during the dirt-loading tests. Particles much 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.

TABLE 1

PRESSURE DROP OF CLEAN OILED FILTER

AIR FACE PRESSURE

FLOW VELOCITY DROP (1)

cfm fpm inch W.G.

1200 5140 0.202

1000 1+50 0 1I4 8

800 360 .101

600 270 .062

(1) Initial values for the clean filter

TABLE 2

PERFORMANCE OF FILTER AT 800 CFM

Total

Dirt Pressure Eff. Meas.

Aerosel (1) Load (2) Drop Technique ( 3 ) Efficiency

grams inch W. G. percent

A «=, 0.101 M 11

- .101 L 12

C 7 .108 N 69

14 .113 N 70

22 .117 N 70

67 .153 N 72

II4 I .217 N 75

179 .252 N 77

290 .387 N 80

384 .505 N 82

A 381* .507 L 28

(1) Aerosol As Particulate matter in atmospheric air at NBS.

Aerosol C: Cottrell precipitate in atmospheric air

(1 gram per 1000 cf).

(2) Average mixtures I4 percent lint, 96 percent Cottrell

precipitate, by weight.

(3) Efficiency measuring techniques

L; Air sampled at equal rates through equal areas*

upstream sampling time selected to yield approximately

equal dust-spot opacities both upstream and downstream.

Ms Air sampled at equal rates through equal areas for

equal times.

Ns Air sampled at equal rates for equal times; downstream areas selected to obtain approximately equal

dust-spot opacities both upstream and downstream.

LOAD REACH IN G FILTER , GRAMS

iq:

q

FIG. I

THE NATIONAL BUREAU OF STANDARDS

Functions 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 Law 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; advisory services to Government Agencies on scientific and technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project

or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

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the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

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Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.25) and its Supplement ($0.75), available from the Superintendent of Documents, Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of

Standards, Washington 25, D. C.
NBS