NATIONAL BUREAU OF STANDARDS REPORT

PERFORMANCE TESTS OF A REPLACEABLE CARTRIDGE AIR FILTER

CAMBRIDGE "AEROSOLVE" 3A-85

Manufactured by

Cambridge Filter Manufacturing Corporation

Syracuse,, New York

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

6626
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,

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 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 Scries,

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

PERFORMANCE TESTS OF A REPLACEABLE CARTRIDGE AIR FILTER

CAMBRIDGE "AEROSOLVE" 3A-85

Manufactured by

Cambridge Filter Manufacturing Corporation

Syracuse, New York

Carl W. Coblentz and Paul R. Achenbach

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

NBS PROJECT NBS REPORT

1003 - 30-10630 January 8, i 960 6626

to

Public Buildings Service

General Services Administration

Washington 25* D. C.

NATIONAL BUREAU OF S intended for use yvithln the to additional evaluation and

listing of this Report, eithei the Office of the Director, f however, by the Governmen

to reproduce additional cop

IMPORTANT NOTICE

progress accounting documents Approved for public release by the ormai|y published it is subjected

on October 9, 201 5. f prepared if that agency wishes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Performance Test of a Replaceable Cartridge Air Filter

Cambridge "Aerosolve," Model 3 A-85

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 Model 3 A-85 Cambridge "Aerosolve" replaceable cartridge air

filter were determined. The scope of this examination included

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 test specimen was manufactured and supplied for test

purposes by the Cambridge Filter Manufacturing Corporation of

Syracuse, New York, and was identified as their Model 3 A-85

’’Aerosolve” replacement cartridge. The size of the filter was

23 1/2" x 23 1/2" x 12V. The filter medium was a fiber glass

blanket, about 3/16" thick, which was glued to a supporting thin

layer of glass fibers, on the downstream side. It was arranged

in twelve pleats, each 12 in. deep, and presented an effective

filtering surface of approximately 40 sq ft. The sides of the

filter medium were glued to a corrugated cardboard frame. The

weight of the clean filter was 2480 grams (5 1/2 lbs).

The manufacturer also furnished a welded steel frame into

which the filter was to be placed during operation. When the

cartridge was inserted into this frame from the front side, each

pleat was supported for its full length on a grid of steel wires

that fitted into the pleated media to control deflection and pre

vent rupture of the media. The pressure against the filter cart

ridge that was produced by the air flow pressed the pleats of k

the filter medium against the steel wire grid and the downstream

face of the cardboard frame was pressed against a felt gasket

installed in the steel frame to prevent air leakage around the

filter.
.

* >
- 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 entitled, "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

filter under test 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

sampling papers. The arrestance, A (in percent) was then calculated by the formula:

where and Sy are the downstream and upstream areas and AD and

AU the observed changes in the opacity of the downstream and upstream 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 equal areas for the downstream and upstream sampling papers and passing air through the

upstream paper only part of the time while operating the downstream

paper continuously. This was accomplished by installing a solenoid

valve and a parallel bypass valve in the air line of the upstream

sampler and using an electric timer to open the solenoid valve

and close the bypass valve any desired percentage of a 5 -minute

cycle. The timer reversed the positions of the solenoid and bypass valves for the remainder of each 5 -minute sampling cycle.

-3-

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

following formula:

AD

A = 100 - T x —

AU

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

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

opacity of the sampling papers, as previously indicated.

The following procedure was employed in testing this

filter: The filter cartridge was inserted into the holding

frame and, instead of the usual clamps which would press the

downstream face of the cardboard frame against the felt gasket, several strips of masking tape were used to hold the

cartridge in place. This make-shift arrangement was used since

the steel holding frame was specially made to fit the test apparatus and did not have the clamps provided in the stock models.

After determining the pressure drop of the clean specimen

at air flow rates from 600 cfm to 1200 cfm, several determinations of the arrestance of the particulate matter in the laboratory air were made at the rated air flow rate of 1000 cfm.

Thereafter, two arrestance determinations with Cottrell precipitate were made and then the loading of the filter with Cottrell

precipitate and lint in a ratio of 96 to 4, by weight, commenced

at a feed rate of approximately 1 gram of Cottrell precipitate

per 1000 cu ft of air.

The Cottrell precipitate had been previously sifted through

a 100-mesh standard wire screen and the lint was prepared from

#7 cotton linters by running these through a Wiley mill with a 4 mm screen. Further arrestance determinations were made with

Cottrell precipitate after the pressure drop across the filter

nad reached 0.3 in. W.G. When the pressure drop had reached

0.5 in. W.G. and again after it reached O .85 in. W.G., further

arrestance determinations with both aerosols were made.

4. TEST RESULTS

The performance of the test specimen is summarized in Table 1

showing the dust load, the pressure drop and the arrestance of the

dust particles in the laboratory air and Cottrell precipitate at

the rated air flow rate of 1000 cfm. The dust load shown in this

table is the weight of Cottrell precipitate and lint introduced

into the test apparatus diminished by the percentage of dust

-4-

fallout upstream of the filter. This fallout was determined

by sweeping out the test apparatus at the conclusion of the

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

of the test duct was 47 g or 3.6$ of the 1307 g of Cottrell

precipitate and lint introduced during the test.

Table 1

Performance of a Model 34-85 Cambridge

"Aerosolve" Air Filter at 1000 cfm Air Flow Rate

Dust Load Pressure Drop Arrestance Aerosol

g in. W.G. $ Used**

0 0.253 69.5* A

19 0.259 97.1* B

309 0.310 98.3* B

580 0.359 ---- 920 0.511 98.3* B

940 0.520 77.4 A

1260 O.856 98.4* B

1260 0.865 84.9 A

* Average of two or more te?st s ** A - Particulate matter in laboratory air

B - Cottrell precipitate in laboratory air (Rate of

feed = 1 gram per 1000 cu ft)

The pressure drop of the clean specimen was 0.253 in. W.G.

and increased to 0.865 in. W.G. after 1260 g of dust had reached

the filter at the rated air flow rate. The arrestance of Cottrell precipitate increased from 97*1 percent when the filter

was clean to 98.3 percent after 309 g of dust had reached the

filter and then remained practically constant. The arrestance

of the particulate matter in the laboratory air increased from

69.5 percent with a clean filter to 77.4 percent at a pressure

drop of 0.520 in. W.G. and rose to 84.9 percent at the end of

the test.

The values of Table 1 are shown graphically in Figure 1,

where both the pressure drop and the arrestance values are

plotted against the dust load as smooth curves which approximately

fit the individual points of observation. The curve drawn for the

arrestance of the dust in the laboratory air indicates the average

value for the duration of the loading period was approximately

75 percent.

CAMBRIDGE MODEL 85

1000

Dust Load, g

-5-

Table 2

Pressure Drop of Clean Filter at

Different Air Flow Rates

Air Flow Rate

cfm

Pressure Drop

In. W.G.

600

800

1000

1200

0.146

0.204

0.253

0.314

Table 2 above shows the pressure drop of the clean test

specimen at air flow rates from 600 cfm to 1200 cfm. It will

be noted that the pressure drop increased over this range from

0.146 in. W.G. to 0.314 in. W.G. approximately in direct proportion to the air flow rate.

USCOMM-NBS-DC

U.S. DEPARTM ENT OF COMMERCE

Frederick If. Mueller, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Ah I in. 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

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

In general, each section carries out specialized research, development, and engineering in the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the front cover. W ASHINGTON, D.C.

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

Optics and Metrology. Photometry and Colorimetry. Photographic Technology. Length. Engineering

Metrology.

Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Molecular Kinetics. Free

Radicals Research. Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics. Atomic Physics. Neutron Physics. Radiation Theory. Radioactivity. X-rays. High

Energy Radiation. Nucleonic Instrumentation. Radiological Equipment.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic

Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics. Mass and Scale. Capacity, Density, and Fluid Meters. Combustion Controls. Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Poly- mer Structure. Plasticsr Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal

Physics.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Air Conditioning, Heating, and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat Transfer. Concreting Materials. Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics. Data Processing Systems. SEAC Engineering Group. Components and Techniques. Digital Circuitry.

Digital Systems. Analog Systems. Application Engineering.

8 Office of Basic Instrumentation. • Office of Weights and Measures. BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas Liquefaction. Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular Propagation

Services. Sun-Earth Relationships. VHF Research. Radio Warning Services. Airglow and Aurora. Radio

Astronomy and Arctic Propagation.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Research. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Propagation Obstacles Engineering. Radio-Meteorology. lx»wer Atmosphere Physics.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. High Frequency Impedance Standards. Electronic Calibration Center. Microwave Physics. Microwave Circuit Standards. Radio Communication and Systems. l,ow Frequency and Very Low Frequency Research. High Fre- quency and Very High 1' rcqucncy Research. Ultra II igh Frequency and Super High Frequency Research. Modulation Research. Anlcnnu Research. Navigation Systems. Systems Analysis. Field Operations.