NATIONAL BUREAU OF STANDARDS REPORT

6629

PERFORMANCE TESTS OF A FARR REPLACEABLE MEDIA

AIR FILTER, MODEL HP-2

Manufactured by

Farr Company

Los Angeles, California

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

divisions and sections on the inside of the back cover.

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 scries 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.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT MBS REPORT

1003-30-10630 January 11, I960 6629

PERFORMANCE TESTS OF A FARR REPLACEABLE MEDIA

AIR FILTER, MODEL HP-2

Manufactured by

Farr Company

Los Angeles, California

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 j D. C.

NATIONAL BUREAU OF STAF

Intended for use yvithin the Gc

to additional evaluation and rev

listing of this Report, either in the Office of the Director, Natk

however, by the Government ag

to reproduce additional copies

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

gress accounting documents

ally published it is subjected

production, or open-literature

n is obtained in writing from

ich permission is not needed,

epared if that agency wishes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Performance Test of a Farr Replaceable

Media Air Filter, Model HP-2

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 paper air filter, type HP-2, were determined. The scope

of this examination included the determination of the arrestance

of Cottrell precipitate, the pressure drop and dust holding

capacity of the filter. Some determinations of the arrestance

of atmospheric dust were also made.

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 HP-2 and consisted of a sheet steel frame

into which the filter element was fitted. This filter element

consisted of a pleated filter medium and a wire retainer that

supported each of the ten 8-in. deep pleats of the filter medium

and protected the medium from rupture or excessive dislocation

due to the air pressure. The total filtering area of the pleated

material was approximately 25 sq ft.

The filter medium was a paper product supplied in a folded

condition. After unfolding the layers, they could be inserted

into the wire retainer without great effort. A perforated steel

panel was used to secure the filter element in the holding frame,

and to provide an air seal between the reinforced edges of the

filter media and the frame. This perforated panel served as a substitute for a pre-filter which was generally used with this

filter, according to information of the representative of the

manufacturer who attended the test. The test was conducted without a pre-filter.

The weight of the complete filter was 6870 g (15 lbs, 2 oz),

when clean and it measured 20” x 20” on the outside with net dimensions of 17 5/8” x 18 ” and a net face area of 2.20 sq ft.

- 2 -

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).

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, 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 calculated by the following formula

where and are the downstream and upstream areas and AD and

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

The arrestance of particulate matter in the laboratory air

was determined by a slightly different procedure. In this case,

a similar increase of opacity on the two samplers was obtained by

using similar or equal areas of the upstream 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 that controlled two solenoid valves, 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 for the rest of the cycle. The arrestance, A (in percent) was then computed from the following

-3-

f ormula

:

A = 100 - T x x £d

AU Su

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

through the upstream sampler, the other values being the same

as indicated in the first formula.

The following procedure was employed in the testing of the

performance of this filter: After the filter was installed in

the test apparatus, a series of pressure drop measurements were

made with air flow rates ranging from 400 cfm to 1000 cfm (i.e.,

face velocities of 182 to 454 ft/min). Several arrestance determinations were then made at the rated face velocity of 250 ft/min

(550 cfm), introducing Cottrell precipitate into the air stream

at a rate of approximately 1 gram per 1000 cu ft of air. The

filter was then gradually loaded with Cottrell precipitate and

lint in a ratio of 96 parts of Cottrell precipitate to 4 parts

of lint, by weight. Further arrestance determinations were made

after about each additional 100 g of dust were introduced into

the inlet duct. This procedure was continued until a pressure

drop of 0.5 in. W.G. was reached across the filter. Then, two

determinations of the arrestance of the filter were made, using

the particulate matter in the laboratory air. Subsequently, a second filter medium was installed in the wire retainer of the

filter. It was assumed that this second filter had the same

characteristics as the first one when its weight and the pressure

drop values over the full range from 400 cfm to 1000 cfm showed

practically identical values as the first specimen, when clean.

Two more determinations of the arrestance with the particulate

matter in the laboratory air were then made on this specimen.

4. TEST RESULTS

Table 1 presents a summary of the performance data of the test

specimen operated at 550 cfm, equivalent to 250 ft/min face velocity. The dust load shown in this table is the weight of Cottrell

precipitate and lint introduced into the test apparatus divided

by the face area of the filter and diminished by the percentage

of dust fallout upstream of the filter. This fallout was determined at the conclusion of the test by sweeping out the test apparatus and calculating the ratio of fallout to the dust introduced into the system.

Table 1

Performance of Parr HP-2 Air Filter

at 250 ft/ml n Pace Velocity

Dust Load Pressure Drop Arrestance Aerosol

g/sq ft in. W.G. % Used**

0 0.044 19* A

14 0.049 80* B

42 0.069 82 B

76 0.118 87 B

116 0.229 97 B

162 0.482 98 B

162 0.494 54* A

* Average of two 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 increased from

0.044 in. W.G. with a clean filter to 0.482 in. W.G. after a dust load of 162 g/sq ft had reached the filter. The arrestance

values determined with Cottrell precipitate increased from 80

percent with the clean filter to 98 percent when the filter was

loaded to about 0.5 in. W.G. The arrestance of the filter when

using the particulate matter in the laboratory air as the aerosol

was 19 percent and 54 percent at the beginning and end of the

loading period, respectively.

The values of Table 1 are presented graphically in Figure 1

in which both pressure drop and arrestance are plotted against

the specific dust load and shown as smooth curves that approximately fit the individual points of observation. Figure 1 also

shows a vertical dashed line which indicates that the specific

dust load at 0.50 in. W.G. pressure drop would be 164 g/sq ft.

The horizontal dashed line indicates the mean arrestance, during

the period in which the capacity dust load was accumulated, to

be 89 percent.

FARR HP-2

0 20 40 60 ' 80 100 120 140 160 180

Dust Load, g/sq ft

-5-

Table 2

Pressure Drop of Clean Filter at

Different Air Flow Rates

Face Velocity- Pressure Drop, in. W.G.

ft/min 1. Specimen 2. Specimen

182

250

318

386

454

0.027

0.044

0.067

0.091

0.115

0.027

0.044

0.064

0.087

0.110

The pressure drop observed on the two clean specimens at

five different face velocities ranging from 182 ft/min (400 cfm)

to 454 ft/min (1000 cfm) is shown in Table 2. The values observed for the two media at the two lower air velocities agreed

exactly whereas the deviation ranged from 0.003 in. W.G. to

0.005 in. W.G. at the higher velocities.

USCOMM-NBS-DC

U.S. DEPARTMENT OF COMMERCE

Frederick II. Mueller, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Anlin, 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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