NATIONAL BUREAU OF STANDARDS REPORT

6692

PERFORMANCE TESTS OF TWO THROW-AWAY TYPE

"DUST-STOP" AIR FILTERS

Manufactured by

Owens-Corning Fiberglas Corporation

Toledo., Ohio

by

Carl W. Coblentz

and

Paul R. Achenbach

Report to

Public Buildings Service

General Services Administration

Washington 25/ D. C.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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; in- vention 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. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the

Bureau’s unique competence is required. The scope of activities is suggested by the listing of

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Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers. These 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 periodicals available from

the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary

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

data for determining the best frequencies to use for radio communications throughout the world.

There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series,

Handbooks, Miscellaneous Publications, and Technical Notes. 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 ($1.50), available from the Superintendent

of Documents, Government Printing Office, Washington 25, D.C.
NATBONAL BUREAU OF STANDARDS REPORT

NIBS PROJECT NBS REPORT

1003-30-10630 March 22, i 960 6692

PERFORMANCE TESTS OF TWO THROW-AWAY TYPE

"DUST-STOP” AIR FILTERS

Manufactured by

Owens-Corning Fiberglas Corporation

Toledo, Ohio

by

Carl W. Coblentz and Paul R. Achenbach

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

to

Public Buildings Service

General Services Administration

Washington 25., D.-C.

IMPORTANT NOTICE

NATIONAL BUREAU OF

intended for use within t to additional evaluation a listing of this RepoFt, eitt the Office of the Director, however, by the Governm

to reproduce additional c

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

,r progress accounting documents

formally published it is subjected

ng, reproduction, or open-literature mission is obtained in writing from

2 . Such permission is not needed,

illy prepared if that agency wishes

U. S. DEPARTMENT OF COMMERCE
' *
PERFORMANCE TESTS OF TWO THROW-AWAY TYPE

"DUST-STOP" AIR FILTERS

by

C. W. Coblentz and P. R. Achenbach

1.

INTRODUCTION

At the request of the Public Buildings Service, General

Services Administration, the performance characteristics of

two specimens of the throw-away type "Dust-Stop" air filters,

1-inch thick, were determined. The scope of this investigation included the determination of the arrestance of Cottrell

precipitate and of the particulate matter in the laboratory

air, the dust holding capacity and the pressure drop at 370

ft/min face velocity. The pressure drop across the clean filter for a range of face velocities was also measured.

2.

DESCRIPTION OF TEST SPECIMENS

The test specimens were manufactured by the Owens-Corning

Fiberglas Corporation of Toledo, Ohio, and bore the trade name,

"Dust-Stop." They were supplied by the manufacturer. The nominal size of the filter was 20 x 20 x 1 inches; the actual size

was 19 5/8 x 19 5/8 x 15/16 inches with a net face area of

17 7/8 inches square, i.e. 2.22 sq ft. The filter media consisted of a pack of glass fibers which were treated with an

oily adhesive and were supported on both faces by thin brass

sheet retainers, perforated with 1 1/2 inch diameter cut-outs.

The retainers and media were held together with cardboard frames.

Each filter weighed 377 grams (13-3 oz). The two specimens were

of the same design and supposedly identical in construction.

3.

TEST METHOD AND PROCEDURE

The performance of the test specimens was determined at a face velocity of 370 ft/min or 822 cfm. The arrestance measurements were conducted in accordance with the NBS ”Dust--Spot

Method" described in a paper entitled, "A Test Method for Air

Filters” by R. S. Dill, (ASHVE Transactions, Vol. 44, p. 379.?

1938).

For testing, each filter was installed in the test apparatus and carefully sealed to prevent inleakage of air except

through the measuring orifice. The desired rate of air flow
'* '
- 2 -

through the filter was established and samples of air were

drawn from the center points of the test duct two feet upstream and eight feet downstream of the test specimen at

equal rates and passed through known areas of Whatman No. 4l

filter paper. The change of the opacity of these areas was

determined with a sensitive photometer which measured the

light transmission of the same spot on each sampling paper

before and after the test. The two sampling papers used for

each test were selected to have the same light transmission

readings when clean.

For determining the arrestance of the filter with Cottrell precipitate as the test dust, different size areas of

sampling papers were used upstream and downstream of the filter in order to obtain a similar increase of opacity on both

sampling papers. The arrestance, A (in percent), was then

calculated by the formula

where Sp and Sp are the upstream and downstream sampling areas

and AU and AD the observed changes in the opacity of the upstream and downstream sampling papers, respectively.

For determining the arrestance of the particulate matter

in the laboratory air, equal sampling areas were used for the

upstream and downstream samplers. A similar increase of the

opacity of the upstream and downstream filter papers was then

obtained by passing the sampling air through the upstream paper

only part of the time while operating the downstream sampler

continuously. This was accomplished by installing one solenoid

valve in the upstream sampling line and another one as a bypass. The valves were operated by an electric timer and a relay so that one was open while the other one was closed during

any desired percentage of the 5-^inute timer cycle, reversing

the position of the two halves during the remainder of the

cycle. The arrestance, A (in percent), was then determined

with the following formula:

A = 100 - T x

AU

where T is the percentage of time during which air was drawn

through the upstream sampler, AU and AD being the changes of

opacity of the sampling papers, as previously indicated.

- 3

-

At the conclusion of the test of each specimen, the fallout of dust that occurred upstream of the filter was determined by sweeping out this part of the test apparatus. The

dust load was then calculated as the average amount of dust

and lint that reached the filter per unit area, i.e. the weight

that was introduced into the test apparatus divided by the net

face area of the filter and multiplied by the fraction of the

total dust introduced into the apparatus at the termination of

the test that reached the filter, according to the formula:

D = ^0 x

D

T

~ F

A Dip

where: D = Dust load of the filter at the time when Dq grams

of dust have been introduced into the test apparatus, g/sq ft

Djp = Total dust introduced into the test apparatus during

the test, grams

F = Dust fall-out in the upstream portion of the test

apparatus at the end of the test, grams

A = Net face area of filter, sq ft

At the end of the test, when Dq = D,p ,

D

1 =

dT - P

A

Before introducing test dust, the pressure drop of the first

test specimens was determined at five different air flow rates

from All cfm to 1233 cfm, i.e. at the rated air flow rate and

25$ and 50$ above and below this flow. Thereafter, two determinations of the arrestance of the particulate matter in the laboratory air were made, followed by two arrestance determinations

with Cottrell precipitate.

The Cottrell precipitate had been sifted through a 100-mesh

screen to remove particles larger than 150 micron size. During

the loading of the test specimen, lint was introduced into the

test apparatus in a ratio of 4 parts to 96 parts of Cottrell precipitate, by weight. The lint was prepared from #7 cotton linters by running these through a Wiley mill with a 4 mm screen.

-4-

Cottrell precipitate was introduced into the test apparatus at

a rate of 1 gram per 1000 cu ft of air.

Arrestance determinations with Cottrell precipitate were

repeated after the introduction of each increment of approximately 80 grams of dust and lint until the pressure drop across

the filter reached 0.5 in. W.G. At this time., two more arrestance determinations were made using the particulate matter in

the laboratory air as the aerosol. The test on the first specimen was then terminated and the second specimen was installed

in the test apparatus. The arrestance of this filter was determined only with Cottrell precipitate and the test was conducted in a similar manner, except that arrestance determinations

were made at longer intervals.

4. TEST RESULTS

The performance of the test specimens is summarized in

Tables 1 and 2 showing the dust load, the pressure drop and

the arrestance of Cottrell precipitate and also of the particulate matter in the laboratory air at the rated face velocity

of 370 ft/min, corresponding to an air flow rate of 822 cfm.

Table 1

Performance of Specimen 1, "Dust-Stop" Throw-Away Filter

Load Pressure Drop Arresta:

g/sq ft in. W. G. ~w~

0 0.080 8*A

5 0.088 58*

28 0.136 59*

59 O.I87 58*

93 0.237 58

134 0.317 57

192 0.451 61

197 0.470 —

206 0.500 —

210 0.501 55*

212 0.503 4* A

* Average arrestance of two determinations.

VThe particulate matter in the laboratory air was used as the

aerosol, Cottrell precipitate was the test dust in all other

test s

.
-
-5-

Table 2

Performance of Specimen 2, "Dust-Stop” Throw-Away Filter

Load Pressure Drop Arrest

g/sq ft in. W. G. ~W

0 0.080

5 O.O83 57*

72 0.198 57

111 0.249 —

170 0.351 61*

205 0.449 —

225 0.508 60

* Average arrestance of two determinations.

The pressure drop of each filter when clean was 0.080 in.

W.G. and increased to 0.5 in. W.G. after a dust load of slightly

over 200 g/sq ft had been attained. Figure 1 is a graphical

presentation of these two tables and shows that the pressure

curves of the two specimens agree at the lower values. It will

be noted that the pressure curve of filter #1 appears to flatten significantly when a pressure drop of 0.5 in. W.G. was

reached coincidental with a sharp drop of the observed arrestance., indicating that, at that time, dust was probably carried

through the filter medium.

The arrestance of the particulate matter in the laboratory

air determined for the first test specimen was 8 percent when

the filter was clean and 4 percent when the filter was loaded.

This decrease of arrestance also suggests that dust was pulled

off the filter at that time, because the arrestance of such filters for atmospheric dust is usually higher when loaded than

initially.

The relation of face velocity to pressure drop for the

clean filter is shown in Table 3-

Table 3

Pressure Drop at Different Air Flow Rates,

"Dust-Stop" Throw-Away Filter

Flow Rate Face Velocity Pressure Drop

cfm ft/mi

n

in. W. G.

411 185 0.027

617 277 0.051

822 370 0.080

1028 463 0.126

1233 555 0.157

- 6 -

It was noticed at the termination of each test

filter media had ‘forced away from the upstream grid

of approximately 2 inches at the center of the test

that the

a distance

specimens

.

USCOMM-NBS-DC

t

4±

4-i- 4—

|—

ILS. DEPARTMENT OF COMMERCE

Frederick H. Mueller, 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 major laboratories in Washington, D.C., and

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