/o,d

NATIONAL BUREAU OF STANDARDS REPORT

6250

PERFORMANCE TESTS OF AN AUTOMATIC RENEWABLE MEDIA AIR FILTER

WITH TWO FILTER MEDIA,

CONOMATIC, MODEL 3-C90

MANUFACTURED BY

CONTINENTAL AIR FILTERS, INC.

LOUISVILLE, KENTUCKY

by

Carl W. Coblentz and Paul R. Achenbach

Report to

General Services Administration

Public Buildings Service

Washington 25* D„ Co

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBB REPORT

6250

December 23 » 1958

NBA PROJECT

1000-30-4830

PERFORMANCE TESTS OF AN AUTOMATIC RENEWABLE MEDIA AIR FILTER

WITH TWO FILTER MEDIA,

CONOMATIC, MODEL 3-C90

O MANUFACTURED BY

CONTINENTAL AIR FILTERS, INC.

LOUISVILLE, KENTUCKY

by

Carl W. Coblentz and Paul R. Achenbach

Air Conditioning, Heating and Refrigeration Section

Building Technology Division

to

General Services Administration

Public Buildings Service

Washington 25* D. d.

IMPORTANT NOTICE NATIONAL BUREAU

(

•tended for use.wjth

oaddltlqnaf eva)t/stlc llatleg of thli Report,

tee Office of the Direc however, fey the Govdi

to reproduce addition

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

progreu accounting documents

irmelly published It li tubjecled

, reproduction, or open-literature

.'Sion It obtained In writing from Such permlttlon It not needed,

t prepared If that agency withes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PERFORMANCE TESTS OF AN AUTOMATIC RENEWABLE MEDIA

AIR FILTER WITH TWO FILTER MEDIA,

CONOMATIC, MODEL 3-C90

by

Carl W. Coblentz and Paul R. Achenbach

L Introduction

At the request of the Public Buildings Service, General

Services Administration, the performance characteristics of a

Conomatic, automatically- renewable media type air filter were

determined with a glass fiber and with a plastic fiber filter

media. The scope of this investigation included the determination of arrestance of atmospheric dust and Cottrell precipitate, the dust holding capacity per unit area of filter

media and the characteristics of the automatic movement of the

filter media„

2. Description of Test Specimen

The test specimen was manufactured and supplied for test

by Continental Air Filters, Inc 0 , of Louisville, Kentucky, and

was identified as their type "Conomatic 3-C90"o It was modified

for installation in the NBS test apparatus by building a sheet

metal housing around it and providing upstream and downstream

transition sections, 24 in„ square inside, to fit the test ducto

This modification was necessary for the adaptation of the filter

and did not affect the performance of the equipment.

The "Conomatic" filter was designed to move a long blanket

or mat of filter medium across the air flow opening in the housing

by intermittent feed under automatic control „ A roll of the

clean medium was held at the top of the housing from which it

was unrolled as needed by a spool at the bottom of the housing.

The lower spool was driven by a 1/6 HP electric motor and a

reduction gear which was connected to a sprocket wheel by a

standard gear chain. This sprocket wheel was directly coupled

to the empty spool at the bottom of the housing on which the

soiled filter media was rolled up. In passing from the clean

roll at the top to the bottom roll the media was backed up by

a stationary vertical grid that prevented the media from being

stretched by the air flow as it passed across the air stream.

- 2 -

The movement of the blanket was controlled by a differential pressure switch built by the Republic Auto Gas Corporation,,

This control started the electric motor when the pressure drop

across the medium had risen to a preselected value and stopped

it when the pressure drop was reduced by an increment of almost

0„05 in. W»Go by feeding some clean media into the air stream.

The speed of the lower spool while moving the media was about

1 RPM. Depending on how much media had been wound up on the

lower spool the rate of feed of the filter media during these

periods varied from about 1 ft/min to 3 ft/min.

Two different filter media were furnished with the unit.

One was a 2-inch thick Fiberglas mat for general use and the

other one consisted of a l/2-inch thick light plastic felt for

use in food processing plants or where the user wanted to guard

against the possible contamination of the air with glass fiber

particles. The media width was 32 in. for both materials.

3 . Test Method and Procedure

Arrestance determinations were made with the NBS ’’Dust Spot

Method” using the following aerosols? (a) air drawn from the

laboratory without addition of other dust or contaminant 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 ).

For this test, the unit was installed in the test duct

and carefully sealed to prevent inleakage of air except through

the measuring orifice. The desired rate of air flow through

the filter was established and samples of air were drawn from

the center points of the test duct one foot upstream and eight

feet downstream of the test specimen at equal rates and passed

through known areas of Whatman No. 4.1 filter paper. The ratios

of the upstream and downstream filter paper areas were selected

to obtain a similar increase of opacity, and with air drawn

through both samplers for the full period, the arrestance was

computed by the following formula?

Ap AD

Ay ^ AU

A = 100 x 100
4
-3-

where A-p and A^ are the downstream and upstream filter paper areas

and AD and AU the respective changes in opacity of the samplers.

Each test with atmospheric dust required from one to two

hours and., in order to make the increase of opacity of the two

samplers more nearly equal, the upstream sampling air was drawn

through the sampler for only part of the time. If ”T" is the

percentage of the time during which air was drawn through the

upstream sampler while air through the downstream sampler was

drawn continuously, the formula for computing arrestance would

be

A = 100 -

The two filter papers used for each test were selected to

have the same opacity readings when clean.

During operation, the pressure drop of an automatic selfcleaning air filter of this type increases due to the accumulating dust load until it reaches the value at which the pressure

switch is set to operate the roller mechanism. As clean media

is then moved into the air stream, the pressure drop decreases

until the pressure switch stops the roller drive. The filter

then operates repetitively in the on-off range of the pressure

switch, the differential controlling the amount of clean media

that is moved into the air stream and the rate of dust accumulation determining the frequency of the cycles. Since the

operation of this type of filter at a high pressure drop increases

the dust load per unit area of filter media it reduces the consumption of the material but the increased blower power tends

to offset the saving on filter material. For this test, the

pressure switch was adjusted to start the roller mechanism at

about 0.50 in. W.G. and stop it at about 0.45 in. W.G. which

was in line with common operating practice for self-cleaning

air filters at a face velocity of 500 ft/min 0 The following procedure was used for determining the performance of the test specimen: The unit was installed between

the upstream and downstream sections of the test apparatus and

carefully sealed against extraneous leakage of air.

Apr AU

x 100

-4-

With the clean filter media in the air stream the pressure

drop was measured at the rated face velocity of 500 ft/min and

also at 400 and 600 ft/min 0 The arrestance of the filter at the

rated face velocity was determined first with only the particulate matter in the laboratory air as the aerosol and thereafter

with Cottrell precipitate,. The loading of the filter was performed with a mixture of 96 parts by weight of Cottrell precipitate to 4 parts of cotton lint in a concentration of one gram per

1000 cu ft of air. The Cottrell precipitate and the lint were

dispersed separately into the air stream D The lint used for this

purpose was No. 7 cotton linters previously ground in a Wiley

mill with a 4-millimeter screen. It was dispersed into the air

stream through an aspirator operating at approximately 35 psi

inlet air pressure. At intervals, the arrestance determinations

with Cottrell precipitate and with the particulate matter in the

laboratory air as the aerosol were repeated.

Markers were fastened to the filter media which could be

observed through a glass window in the test duct to determine

the amounts of clean media fed into the air stream at each roller

operation. A pilot light was connected in parallel with the

roller motor which lighted when the motor was operating the shift

mechanism. This arrangement enabled the operator to record the

pressure drop at the beginning and at the end of each advance of

the filter media and also provided information on the consumption

of filter media.

Each of the two filter mats was tested as follows. A total

of 10 arrestance values were made of the fiber glass mat until

it had advanced a total of 40 inches during 12 roller cycles.

The Dycon mat was tested during 21 roller cycles with a total

advance of 46.5 inches and 12 arrestance determinations were made

on this material. In both cases, the test was continued until

the arrestance values became steady indicating that repetitive

conditions existed during each roller cycle.

4. Test Results

The results of the tests are shown in four tables. Tables

1 and 2 summarize for the two different filter media the arrestance values determined with both the particulate matter in the

laboratory air and Cottrell precipitate. They also give the

accumulated dust loads in grams per 1 ft width of the filter media,

the total media travel and the pressure drop of the filter at the

-5-

Table 1

Summary of Arrestance Tests

Conomatic, Model 3-C90

With Fiberglas Filter Mat

Total

Dust Load Mat; Travel Pressure Drop Arrestance Aero

g/ft in. in. W 0 G 0 %

0 0 0.233 17* A

10 0 0.245 80* C

109 0 0.477 85 C

135 7-1/2 0.451 20 A

291 29 0.4l8 20 A

301 29 0.432 84 C

368 37-1/2 0.488 84 C

383 40 0.437 20 A

* Average of two tests

** Aerosol A- Particulate matter in the laboratory air.

Aerosol B- Cottrell precipitate in the laboratory air.

Table 2

Summary of Arrestance Tests

Conomatic, Model 3=090., With Dycon Filter Mat

Total

Dust Load Mat Travel Pressure Drop Arrestance

g/ft in 0 in c W„ Go %

0 0 0 „ 206

9*

10 0 o„ 217 67*

130 3-1/2 0.494 74

337 25-1/2 0.464 78

342 25-1/2 0.483 18

430 35-1/2 0.458 74*

436 35-1/2 0.470 17

498 44-1/2 0.434 20

524 46-1/2 0.475 20

Aerosol*

* Average of two tests

** Aerosol A- Particulate matter in the laboratory air„

Aerosol C- Cottrell precipitate in the laboratory air 0

>>>o>ooo

>

end of each arrestance measurement. The average initial arrestance of the Fiberglas media with atmospheric dust was 17 percent

and with Cottrell precipitate was 80 percent. As the test continued, these values increased and they leveled out at 20 percent

and 84 percent, respectively. The initial arrestance of the Dycon

mat was found to be 9 percent and 67 percent, respectively,. However, the steady state value for particulate matter in the laboratory air was also 20 percent, the same as determined for the

Fiberglas mat, and the arrestance of Cottrell precipitate was 74

percent

Tables 3 and 4 present a summary of the mat travel of the

two media during each shift and also cumulatively „ The values

for the dust loads reported in these tables were interpolated

between the 20 g loaded into the feeder hopper at one time and

are correct to within ± 3 g. It will be noted that the increments of advance of the filter mat during individual roller

cycles, varied from 1-1/2 in„ to 3 in. with the exception of the

two first advances of the Dycon mat, which were 4 and 3-1/2 inches,

respectively. The values shown for the travel of the mat are

correct to ± 1/2 in.

The differential pressure started the roller drive mechanism

at 0.494 in. W.Go at the beginning of the test with the Dycon mat,

whereas at the end of this test the cut-in pressure had decreased

to 0.480 in. W.G. and further decreased during the test of the

Fiberglas mat to 0.470 in. W.G. This condition was not noticed

during the test. It may have been caused by not properly securing the adjustment screw of the pressure switch. The differential

pressure remained practically steady during the whole test at

slightly below 0.05 in. W.G.

Fig 1 and 2 are graphs of the arrestance determinations and

of the mat travel values plotted against the dust load for the

two filter media.

The amount of Cottrell precipitate collected on a unit area

of filter media during the steady state operation of the unit

provides some measure of the consumption of filter media during

actual use. Disregarding the relatively small amounts of particulate matter collected during the tests in which the arrestance

of the filter was determined with laboratory ai^ the slope of the

straight portion of the lower curves in Fig 1 and 2 (during the

steady state condition) indicates the unit dust-holding capacity

of the filter media.

-8 -

Table 3

Dust Load, Mat Travel and Pressure Drop Characteristics

Conomatic, Model 3-C90 With Fiberglas Filter Mat

Dust Load Mat Travel, in. Pressure Drop, in. W. G.

g/ft Advance Total Before Advance After Advance

0 0 0 0.233 — 110 4 4 0.480 0.431

116 3-1/2 7-1/2 0.480 0.429

140 3 10-1/2 0.478 0.424

165 3 13-1/2 O .478 0.424

182 2-1/2 16 0.475 0.428

200 2-1/2 18 - 1/2 O .478 0.424

222 2-1/2 21 0 o 474 0.424

246 2-1/2 23-1/2 0.470 0.420

268 2-1/2 26 0.471 0.420

290 3 29 0.470 0.418

314 3 32 0.470 0.421

336 2-1/2 34-1/2 - 0.420

360 3 37-1/2 0.470 0.419

384 2

- 1/2 40 0 o 470 0.422

9

“

Table 4

Dust Load, Mat Travel and Pressure Drop Characteristics

Conomatic, Model 3-C90 With Dycon Filter Mat

Dust Load Travel of Mat, in. Pressure Drop, in. Wo G.

g/^t

' Advance Total Before Advance After Advance

0 0 0 0,206

130 3-1/2 3-1/2 0.494 0.438

145 2-1/2 6 0,490 0,444

165 3 9 0.494 0,445

190 2-1/2 n-1/2 0,495 0.446

209 2 13-1/2 0.494 0.450

230 2-1/2 16 0.493 0.446

252 2 18 0.490 0.444

270 1-1/2 19-1/2 0.490 0.443

282 2 21-1/2 0,490 0.442

299 2 23-1/2 0.488 0.444

320 2 25-1/2 0.490 0.443

340 2 27-1/2 0.490 0,440

360 2-1/2 30 0.488 0.430

376 1-1/2 31-1/2 0,480 0.436

397 2 33-1/2 0.481 0.430

410 2 35-1/2 0.480 0.432

429 2 37-1/2 0.480 0.436

446 2-1/2 40 0.480 0.432

470 2 42 0.480 0.430

492 2-1/2 44-1/2 0.480 0.431

512 2 46-1/2 - 0.430

- 10=

According to Fig 1, the Fiberglas mat traveling from position

16 inch to 40 inch, a distance 2 ft, was fed dust in the amount of

207 g/ft width, indicating a dust-holding capacity 103.5 g/sq ft.

Correspondingly, from Fig 2, the Dycon mat traveling from position

20 inch to 44 inch, a distance of 2 ft, was fed dust in the amount

of 214 g/ft width, indicating a dust-holding capacity of 107

g/sq ft.

A summary of the performance of both filter media is presented in Table 5 below.

Table 5

Summary of Test Results

Conomatic Automatic Renewable Media Air Filter

Fiberglas Mat Dycon Mat

Face Velocity,

ft/min

Pressure Drop, clean,

in. W.G.

Average Operating Pressure

500

0.233

0.475 to 0 o 425

500

0.206

Drop Range, in. W.G. 0.487 to O .438

Arrestance, %

Mat Clean: Laboratory Air 17 9

Cottrell Precipitate 80 67

Steady State: Laboratory Air 20 20

Cottrell Precipitate 84 74

Dust-Holding Capacity,

g/sq ft

Pressure Drop of Clean Filter,

103 0 5 107.0

in. W 0 G.

at 400 ft/min Face Velocity 0.169 0.148

at 600 ft/min Face Velocity O .305 0,270

GONOMATIC WITH FIBERGLAS FILTER MAT

DUST LOAD G. / FT WIDTH

CONOMATIG WITH DYCON FILTER MAT

0 IOO 200 300 400 500

DUST LOAD, G / FT WIDTH

U. S. DEPARTMENT OF COMMERCE

Lewis L. Strauss, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OE STANDARDS

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