NATIONAL BUREAU OF STANDARDS REPORT

8673

PERFORMANCE TESTS OF TWO DEEP-BED HIGH EFFICIENCY AIR FILTERS

Conosac 85, Model 8 -sac- 24 and

Conosac 95, Model 9- sac- 24

manufactured by

Continental Air Filters, Inc.

Louisville, Kentucky

Report to

General Services Administration

Public Buildings Service

Washington, D. C.

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

by

Joseph C. Davis

and

Charles M. Hunt
THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards is a principal focal point in the Federal Government for assuring

maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. Its responsibilities include development and maintenance of the national stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials; development of methods

for testing materials, mechanisms, and structures, and making such tests as may be necessary, particularly for government agencies; cooperation in the establishment of standard practices for incorporation in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; assistance

to industry, business, and consumers in the development and acceptance of commercial standards and

simplified trade practice recommendations; administration of programs in cooperation with United

States business groups and standards organizations for the development of international standards of

practice; and maintenance of a clearinghouse for the collection and dissemination of scientific, technical, and engineering information. The scope of the Bureau’s activities is suggested in the following

listing of its four Institutes and their organizational units. Institute for Basic Standards. Applied Mathematics. Electricity. Metrology. Mechanics. Heat. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radiation Physics. Radio Standards

Laboratory:* Radio Standards Physics; Radio Standards Engineering. Office of Standard Reference

Data. Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic Materials. Reactor Radiations. Cryogenics.* Materials Evaluation Laboratory. Office of Standard Refer- ence Materials. Institute for Applied Technology. Building Research. Information Technology. Performance Test Development. Electronic Instrumentation. Textile and Apparel Technology Center. Technical Analysis.

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* Located at Boulder, Colorado 80301. ** Located at 5285 Port Royal Road, Springfield, Virginia 22171.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

421.03-30-4215628 August 17, 1965

NBS REPORT

8673

PERFORMANCE TESTS

OF TOO DEEP- BED HIGH EFFICIENCY AIR FILTERS

Conosac 85, Model 8-sac-24 and

Conosac 95, Model 9-sac-24

manufactured byContinental Air Filters, Inc.

Louisville, Kentucky

by

Joseph C. Davis

and

Charles M. Hunt

to

General Services Administration

Public Buildings Service

Washington, D. C.

NATIONAL BUREAU OF STAND/

for use within the Government. Befor and review. For this reason, the publ whole or in part, is not authorized i Bureau of Standards, Washington, D C

the Report has been specifically prepa

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

ounting documents intended

:ted to additional evaluation

g of this Report, either in

:e of the Director, National Government agency for which

for its own use. <Qras>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PERFORMANCE TESTS OF TWO DEEP- BED HIGH EFFICIENCY AIR FILTERS

Conosac 85, Model 8-sac- 24 and

Conosac 95, Model 9-sac-24

manufactured by

Continental Air Filters, Inc.

Louisville, Kentucky

1 . Introduction

At the request of the General Services Administration, the performance characteristics of a Continental Conosac 85 Filter, Model

8-sac-24, and two Conosac 95, Model 9-sac-24, were determined. These

filters were of the deep-bed panel type employing a replaceable medium.

The filters were manufactured by the Continental Air Filters, Inc.,

Louisville, Kentucky. The scope of the investigation included the

determination of the arrestance of the particulate matter of the laboratory air by the filters, and the pressure drop across the filters at

the rated air flow rate of 2000 cfm as the dust load was gradually

increased from zero to a final value corresponding to a pressure drop

of 1.0 in. W.G. for both Models 8-sac-24 and 9-sac-24.

2 . Description of Test Specimens

The filters were manufactured and supplied by the Continental Air

Filters, Inc. of Louisville, Kentucky. They were identified as "Conosac 95", Model 9-sac-24, made with a yellow fine glass fiber media

(Owens Corning FM 003), and "Conosac 85", Model 8-sac-24, made with a pink medium glass fiber media (Owens Corning FM 004). In each specimen, the filter medium was secured to No. 20 mesh dacron. The filter

mat with its dacron mesh backing was formed into six pockets, 35 inches

deep and 31 inches wide, presenting an effective filtering surface of

approximately 90 sq. ft.

o The gross face area of each of the filter units was 3.84 ft. , but the enclosing edges of the metal frame reduced the net face area

to 22" x 22", or 3.36 ft. 2

At a rated air flow of 2000 cfm, the net face velocity was approximately 600 ft/min and the average velocity through the filter medium

was about 22 ft/rain.

The manufacturer furnished square frames made of 2- x 3/4- inch

steel angle, electro-galvanized, into which the filter units were

placed during operation. The frames had overall dimensions of 24" x

24", with polyurethane gaskets to prevent air leakage when the filters

were in operation. The weight of the clean filters was approximately

1800 grams (4 lbs.).

- 1-
3” Test Method and Procedure

The filter under test was installed in the test apparatus and

carefully sealed to prevent by-pass of air or inward flow of air into

the test apparatus except through the measuring orifice at the en- trance to the test duct. The construction of both filters was such

that the method of mounting was important. To obtain maximum performance of each filter, it was necessary that the pleats did not sag

materially, that their extension during the testing was not impeded

by faulty fastening of the media to their frames, and that none of

the pleats remained collapsed in the air stream. It is suggested that

these precautions be taken during use of these filters in government

installations

.

The filters were tested at an air flow rate of 2000 cfm. The

arrestance determinations of each specimen were made with the NBS Dust

Spot Method described in a paper by R. S. Dill entitled, "A Test

Method for Air Filters" (ASHVE Transactions, Vol. 44, page 379, 1938).

After establishing the correct air flow rate through the filter,

samples of air were drawn from the center points of the test duct 2 feet upstream and 8 feet downstream of the test specimen. Each sample

of air was passed through Whatman No. 41 filter paper. Arrestance

determinations were made with the particulate matter in the laboratory

air as the aerosol.

The light transmission of the sampling papers was measured on the same part of each paper before and after test, and the two sampling

papers used for any one arrestance determination were selected to have

the same light transmission when clean.

Since there is a higher aerosol concentration upstream from the

test filter than downstream, it is necessary to adjust sampling to

obtain approximately equal discoloration of the upstream and downstream

sampling papers. In most of these tests this was accomplished through

the use of sampling plates of different areas to hold the upstream and

downstream sampling filters. Percent arrestance, A, was then calculated

by the relationship,

/ Sd ab\

A - (i - x

ffuj 100

where Sj and S

y are the downstream and upstream sampling areas, and AD

and A U are the respective change in opacity of the downstream and upstream sampling papers.

With one of the Model 9-sac-24 filters, sampling was done both

with sampling plates of different areas and with a timer, and the re- sults of the two methods were compared. In the timer method, upstream

sampling is intermittent while downstream sampling is continuous

- 2

-
throughout the sampling period. Percent arrestance, A, is calculated

by the formula,

where t is the fraction of the total time sampled upstream, and the

other symbols have the same meaning as before.

Arrestance measurements were made with each filter in the unloaded

condition and after adding increasing increments of a test dust con- sisting of 96 parts of Cottrell precipitate and 4 parts cotton lint.

The Cottrell precipitate had previously been sifted through a 100-mesh

sieve, while the lint was prepared by grinding No. 7 cotton linters

through a Wiley mill with a 4-millimeter screen.

The pressure drop across the filter under test was recorded at the

beginning of the test, after each arrestance determination, and after

each increment of Cottrell precipitate and lint that was introduced into

the test duct. The test was terminated when the pressure drop reached

approximately 1.0 in. W.G. across the filter.

100

4 . Test Results

The test results obtained with the Conosac 85 Model 8-sac-24- filters are summarized in Table 1.
Table 1„ Performance Characteristics

of Conosac 85 Model 8-sac-24 Filters

at 2000 cfm Air Flow Rate

Nominal dust loada A K Arrestance"'

Pressure drop across filter

Cottrell

precipitate Lint Total

Grams Grams Grams Percent Inches W. G.

1st Filter

0 0 0 77.3 0.546

140 5.8 146 79.1 .588

360 14.9 375 79.6 .642

600 24.9 625 81,3 .710

840 34.9 875 83.4 .800

1080 44.8 1125 84.9 .900

1260 52.3 1312 87.5 1.026

Average arrestance0 82.0%

2nd Filter

0 0 0 76.5 .562

a Nominal dust load is the total cumulative weight of Co ttrell precipitate

and lint introduced into the test duct. The actual s i retained by the

filter is less than the nominal load by the amount wl.i ch passes the filter

UArrestance values obtained with atmospheric dust using sampling plates

of different area downstream and upstream.

cAverage arrestance, A,

ship

,

is based upon a graphical estimate of the relationA =

L Total

dL

L Total

/"L Total

where A is the arrestance at a nominal load of L, and -^AdL is the area under the carve of arrestance vs, load.

In Figure 1 arrestance and pressure drop across the Conosac 85

Model 8-sae.-24 filter are plotted as functions of nominal dust load.

From the upper curve an average arrestance of 82.0 percent is calculated. From the lower curve the amount of test dust required to produce a pressure drop of 1.0 in. W. G. is estimated to be 1280 grams.

This corresponds to 381 grams per ft^ of net face area or 14.2 grams

per ft^ of filter media.

The test results obtained with the 9-sae-24 filters are presented

in Table 2.

- 4 -
i!

Table 2, Performance Characteristics

of Conosac 95 Model 9-sac-24 Filters

at 2000 cfm Air Flow Rate

Nominal dust loada Cottrell

Arrestance^

Average

Sampling (Sampling plate Pressure drop

precipitate Lint Total plate Timer and timer) across filter

Grams Grams Grams percent Inches W.G.

1st Filter

0 0 0 --- 89.6 •—

0.606

140 5.8 146 --- 91.9 --- .640

280 11.6 292 --- 91.5 — .684

480 19.9 500 — 91.2 --- .766

620 25.7 646 --- 92.0 — .852

860 35.7

Average arrestance0 92.0%

896 93.4 1.012

2nd Filter

0 0 0 90.3 91.3 90.8 0.598

140 5.8 146 90.3 90.0 90.2 . 646

280 11.6 292 91.3 91.4 91.4 .690

480 19.9 500 91.2 90.9 91.1 .766

680 28.2 708 93.9 --- --- .870

880

Average arrestance

36.5

; c 92.2%

917 94.5 94 .

4

94.5 1.020

3rd Filter

0 0 0 90.1 ----- --- .580

a ’ c See footnotes at bottom of Table 1.

In Figure 2 the data for the first two Conosac 95 Model 9-sac-24

filters are presented graphically, as an average. From the upper curves average arrestance values of 92.0 and 92.2 percent were obtained for

the first and second filters, respectively. The close agreement between

the two values may be somewhat fortuitous in view of the scatter of

individual points. Scatter of individual points greater than this has

been reported for some deep-bed- type filters in. NBS Report No. 8001, and

it was suggested to be due to dislocation of the dust in the filter pockets when the air flow was cut off.

- 5

-
5 . Summary

Some of the pertinent data relating to the performance of the

8~sac-24 and filters is summarized in Table 3.

Table 3. Summary of Performance of Conosac Filters

Conosac 85 Conosac 95

Model No. 8"Sac~24 9

- &&.xy- 2.4 1 2

' 1 2 3

Air flow rate (cfm) 2000 2000

!'2000

f 2000 2000

Initial pressure drop (in. W«G.

)

0.546 0.562 ' 0.606

9 0.598 0.580

Recommended final pressure drop (in. W.G.

)

1.0 1.0 ' 1.0

1 1.0 1.0

Dust load at 1.0 inch pressure drop (grams) 1280 --

' 850

S 890 ---

Estimated net face area (ft^) 3.36 3.36 ' 3.36

! 3.36 3.36

Estimated filter area (ft^) 90 90 ' 90

8 90 90

Initial arrestance with atmospheric dust

(percent) 77.3 76.5

1

' 89.6

f 90.8 90.1

Average arrestance with atmospheric dust

(percent) 82.0 ---

1

? 92.0

i 92.1 ---

USCGMM-NBS-BC

- 6-
PRESSURE

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CWTXMtmL All FILT1S