NATIONAL BUREAU OF STANDARDS REPORT

6625

PERFORMANCE TESTS OF A FARR "MICROLOC"

REPLACEABLE MEDIA AIR FILTER

Manufactured byFarr Company

Los Angeles, California

by

Carl W . Coblentz

and

Paul R. Achenbach

Report to

Public Buildings Service

General Services Administration

Washington 2 5* D. C.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions ami 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,

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Publications

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

NBS PROJECT

1003-30-10630 January 8 , i960

NBS REPORT

6625

PERFORMANCE TESTS OF A FARR "MICROLOC"

REPLACEABLE MEDIA AIR FILTER

Manufactured by

Farr Company

Los Angeles, California

by

Carl W. Coblentz and Paul R. Achenbach

Air Conditionings Heating, and Refrigeration Section

Building Technology Division

to

Public Buildings Service

General Services Administration

Washington 25 ^ D. C.

NATIONAL BUREAU OF ST

intended for use yvithin the

to additional evaluation and

listing of this Report, either the Office of the Director, N< however, by the Government

to reproduce additlona! copii

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

progress 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

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Performance Test of a Farr "Microloc"

Replaceable Media Air Filter

by

Carl W. Coblentz and Paul R. Achenbach

1.

INTRODUCTION

At the request of the Public Buildings Service., General

Services Administration, the performance characteristics of a Farr "Microloc" air filter were determined. The scope of this

examination included the determination of the pressure drop and

the dust holding capacity of the filter, and separate determinations of the arrestance of Cottrell precipitate and the

particulate matter in the laboratory air.

2.

DESCRIPTION OF TEST SPECIMEN

The filter was manufactured and supplied for test purposes

by the Farr Company of Los Angeles, California. It was identified

as their model "Microloc with filter media #2." The steel frame

had face dimensions of 20" x 20 " corresponding to a face area of

2.78 sq ft and was 32" deep. The filter media consisted of five

strips, each 60 1/2 " x 18 1/2 " of felted material, approximately

5/8" thick. Each length was folded over a wedge shaped spring

steel wire frame that fitted into the housing and when the springs

were released, formed one 30-in. deep pleat. The filter medium

was supported and sealed against air leaks at the edges by perforated steel sheet. The total effective filter area was approximately 38 sq ft, i.e. the mean air velocity through the filter

media at 1000 cfm air flow rate was about 26 ft/min.

The housing was designed to hold a 20" x 20" x 2" viscid

impingement pre-filter. This test was performed without a prefilter, at the request of the General Services Administration.

3.

TEST METHOD AND PROCEDURE

Arrestance determinations were made by the NBS "Dust Spot

Method" using the following aerosols: a) the particulate matter

in the laboratory air, and, b) Cottrell precipitate. 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 ).

- 2 -

The sampling air was drawn from the center points of the

test duct one foot upstream and eight feet downstream of the

air filter assembly at equal flow rates and passed through known

areas of Whatman No. 4l filter paper. The change of opacity of

these areas was determined with a sensitive photometer which

measured the light transmission of the same area 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 aerosol, different sized areas of sampling

paper were used upstream and downstream of the filter to collect

the dust, in order to obtain a similar increase of opacity on both

samplers. The arrestance, A (in percent) was then calculated by

the formula:

where Sp and Sp are the downstream and upstram areas and AD and

AU the observed changes in opacity of the downstream and upstram

sampling papers, respectively.

A slightly different sampling procedure was used for determining the arrestance of the particulate matter in the laboratory

air. In this case, a similar increase of opacity on the two sampling papers was obtained by using similar or equal areas of the

upstram and downstream sampling papers and passing air through

the upstream sampler only part of the time while operating the

downstream sampler continuously. This was accomplished by operating the upstream sampler with an electric timer which controlled

two solenoid talve^, one in series with the sampler and the other

bypassing the sampler. The timer could be set to open the solenoid

valve in series with the upstream sampler any desired percentage

of a 5-minute cycle while bypassing the sampler during the rest of

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

the following formula:

Sp AD

A = 100 - T x x

Sp AU

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

the upstream sampler, the other values being the same as previously

indicated

-3-

The following procedure was employed in the testing of

this filter. The test specimen was assembled in accordance

with the manufacturer’s instructions and installed into the

test apparatus. Measurements were made of the pressure drop

across the filter in the range from +20% to -20%> of the rated

air flow rate of 1000 cfm. Several arrestance determinations

were then made at 1000 cfm air flow with the particulate matter

in the laboratory air as the aerosol. Thereafter, an arrestance

determination was made with Cottrell precipitate and then the

loading of the filter with Cottrell precipitate and lint in a ratio of 96 to 4, by weight, was commenced with a feed rate of

approximately 1 gram of Cottrell precipitate per 1000 cu ft of

air.

The Cottrell precipitate used had been sifted through a 100-mesh standard wire screen and the 'lint was #7 cotton linters

run through a Wiley mill with a 4 mm screen.

Further arrestance determinations with Cottrell precipitate

were made after about each 100 g additional dust were introduced

into the test apparatus. The test was terminated when the pressure drop had reached about 1.0 in. W.G. Additional determinations of the arrestance of the particulate matter in the laboratory air were made when the filter was about halfway loaded and

at the conclusion of the test.

4. TEST RESULTS

The performance data obtained at 1000 cfm air flow rate

are summarized in Table 1, presenting the pressure drop and

arrestance values for the air-borne dust in the laboratory air

and Cottrell precipitate at different dust load conditions. The

dust load shown in this table is the weight of Cottrell precipitate introduced into the test apparatus diminished by the percentage of dust fallout upstream of the filter. This fallout

was determined after the conclusion of the test by sweeping out

the test apparatus. The amount of dust swept out of the upstream

portion of the test duct was 30 g or 4.4 percent of the total of

684 grams of Cottrell precipitate and lint introduced into the

system during the test.

^r

Table 1

Performance of Farr "Microloc" Air Filter

Dust Load Pressure Drop Arrestance Aerosol

g in. W.G. % Used**

0 0.478 71.7* A

10 0.480 97.0 B

128 0.514 97.3 B

3 06 O. 58 I 95 . 8

* B

475 0.701 85.7 A

614 O .858 97 . 6

* B

654 0.975 83.3* A

* Average of two or more tests

** A - Particulate matter in laboratory air

B - Cottrell precipitate in laboratory air (Rate of

feed = 1 gram per 1000 cu ft)

It will be noted that the pressure drop of the clean filter

was 0.478 in. W.G. and increased to 0.975 in. W.G. after 654 grams

of dust had reached the specimen. Tne arrestance of Cottrell precipitate remained practically constant at 97 percent throughout

the test. The arrestance of the filter with the particulate matter

of the laboratory air used as the aerosol increased from 71.7 percent when the filter was clean to 85.7 percent at a filter load of

475 grams and then decreased again to 83.3 percent at the end of

the test.

The values of Table 1 are graphically presented in Figure 1

in which both the pressure drop and the arrestance values are

plotted against the dust load as smooth curves that approximately

fit the individual points of observation. The vertical dashed

line indicates that the dust load at 1.0 in. W.G. pressure drop

would be approximately 665 grams. The horizontal dashed lines

indicate the mean arrestance during the period in which a dust load

of 665 grams was accumulated. The mean arrestance determined for

Cottrell precipitate was 97 percent and that for air-borne dust

82.5 percent.

Table 2 shows the pressure drop of the clean test specimen

at air flow rates from 20$ above to 20$ below the rated 1000 cfm

flow. At 800 cfm air flow rate, the pressure drop decreased to

0.364 in. W.G, 24 percent below the O .478 in. W.G. at 1000 cfm

Parr - Microloc

0 100 200 300 400 500 600 700

Dust Load

-5-

air flow rate. It increased at an equal rate when the air flow

rate was increased to 1200 cfm, the pressure drop was then 0.592

in. W.G.

Table 2

Pressure Drop of Farr "Microloc" Filter When Clean

Air Plow Rate Pressure Drop

cfm in. W.G.

800 0.364

1000 0.478

1200 0.592

The effect of the operation of this filter in combination

with a panel type pre-filter cannot be predicted from this test.

It appears unlikely that such an arrangement would have much

beneficial effect on the arrestance, however, the dust holding

capacity may be increased if the filter is operated with a prefilter.

USCOMM-NBS-DC

U.S. DEPARTMENT OF COMMERCE

Frederick H. Mueller, Secretary NATIONAL BUREAU OF STANDARDS

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

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