NATIONAL BUREAU OF STANDARDS REPORT

5827

PERFORMANCE TESTS OF A FARR CO. "ROLL-KLEEN"

AUTOMATIC RENEWABLE MEDIA AIR FILTER

by

Thomas W. Watson and Henry E. Robinson

/i

i

Report to

General Services Administration

Public Buildings Service

Washington 25, D. C.

<nb|>

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 F,aw 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; invention 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. A major portion of the Bureau’s work is performed

for other Government Agencies, particular!) the Department of Defense and the Atomic EnergyCommission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the back cover.

Reports and Publications

The results of the Rureau’s work take the form of either actual equipment and devices or published paj>ers and reports. Reports arc issued to the sponsoring agency of a particular project

or program. Published 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 monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, llandhooks. Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau's publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards (#1.25) ami its Supplement (#0.75), available from the Superintendent of Documents, Government Printing Office, Washington 25, D. C.

Inquiries regarding the Bureau’s reports should be addressed to the Office of Technical Information, National Bureau of Standards, Washington 25. D. C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1000-30-^890 March 28, 1958 5827

PERFORMANCE TESTS OF A FARR CO. "ROLL-KLEEN"

AUTOMATIC RENEWABLE MEDIA AIR FILTER

by

Thomas W. Watson and Henry E. Robinson

Heat Transfer Section

Building Technology Division

Report to

General Services Administration

Public Buildings Service

Washington 25, D. C.

IMPORTANT NOTICE

NATIONAL BUREAU OF ST, intended for use within the

to additional evaluation and r listing of this Report, either i the Office of the Director, Na

however, by the Government

to reproduce additional copie

irogress accounting documents

Approved for public release by the

rmal b published it is subjected r J reproduction, or open-literature

Director or the National Institute of slon is obtained In writing from Standards and Technology (NIST) Such permission Is not needed, on October 9, 201 5.

prepared lf as' nc> "isl,e *

<NBS>

U. S. DEPARTMENT OF COMMERCE

PERFORMANCE TESTS OF A FARR CO. "ROLL-KLEEN"

AUTOMATIC RENEWABLE MEDIA AIR FILTER

by

Thomas W. Watson and. Henry E. Robinson

1. INTRODUCTION*

At the request of the Public Buildings Service, General

Services Administration, the performance characteristics of

automatic renewable media type air filters were determined

to provide information to assist in the preparation of new

air filter specifications.

The test results presented herein were obtained on a specimen renewable media type air filter, submitted by its

manufacturer at the request of the Public Buildings Service,

and included determinations of dust arresting efficiency

with two aerosols (atmospheric air and Cottrell precipitate),

pressure drop, dirt load.; performance characteristics, and

movement of the media.

2. DESCRIPTION OF THE FILTER SPECIMEN

The filter was manufactured by the Farr Company of Los

Angeles, California, and was of the automatic renewable

media type. It was identified by the manufacturer's representative as a Farr "Roll-Kleen" Air Filter, Special Model

3-70 (3 ft. wide by 7 ft. high) capacity 2080 cfm at 520

fpm inlet face velocity.

The test unit had a housing with actual outside dimensions of 36 inches in width, 84 inches in height, and

26 3/8 inches in length. Special upstream and downstream

transitions, with flanges 30 inches square, matching those

of the duct of the test apparatus, were used to adapt the

unit for test. The air inlet and outlet openings formed by

these transitions were 24 inches square (4.0 sq. ft.).

The "Roll-Kleen 1

’ filter is designed to move a long

blanket or strip of filtering media across the air flow

opening in the housing, in a manner similar to that in

which strip film is moved in a box camera. A roll of

*This report is submitted for information only, and is not

released for use in connection with advertising or sales

promotion

.

- 2 -

clean blanket media is held at the top of the housing, from

which the m'bdia is unrolled as needed by a wind-up roller or

spool at the bottom of the housing, driven by a gear motor

drive directly connected by means of a standard roller

chain. In passing from the top to the bottom roller, the

media slides over a stationary back-up grid of 3 hy 6 inch

mesh wire. The drive motor characteristics are given as

hO watts, 110 volts, 60 cycles, 1 phase.

The filtering media, designated as Farr "Modiglas

E3D," consists of a long strip or blanket (3h inches wide

and about 2 inches thick when uncompressed) of interlaced

matted and bonded fine glass fibers. The blanket is bonded

on the downstream side to a flame-proof four-mesh fabric

sheet. The fibers are uniformly coated with a tricresylphosphate adhesive. As furnished on a spool, the blanket

is tightly rolled and compressed in thickness, but expands

upon being unrolled for use.

The unit is designed so that the shift drive mechanism

is intermittently energized by means of an adjustable differential pressure switch actuated by the pressure drop

through the filtering media. A differential pressure

switch (Dwyer No. 1626.1; Range 0.15 to 1.00 inch W.G. ; 15

amps; 125 , 260, A60 v a-c) was used for the tests reported

here. The pressure control was adjusted to energize the

drive motor when the pressure drop reached a value of about

0.50 inch W.G. , and to open the drive motor circuit when

the movement of clean media into the air stream lowered the

pressure drop to about 0.43 inch W.G. Motion of the media

during periods of shift occurred at the rate of about 55 ft.

per hour

.

3. TEST METHOD AND PROCEDURE

Efficiency determinations were made by the NBS "DustSpot Method" using the following aerosols: (a) outdoor

atmospheric air drawn through the laboratory without

addition of other dust or contaminant; and (b) Cottrell

precipitate dispersed in the outdoor atmospheric air. The

test method is described in the paper "A Test Method for Air

Filters" by R. S. Dill (ASHVE Transactions, Vol. Ah, p. 379,

1938). The test duct and arrangement are shown in Figure 1.

A baffle made of two 3-inch wide slats at right angles to

each other was located in the duct about 3 1/2 ft. downstream of the test assembly to intermix the air discharged

from it.
*

.
-3-

For these tests, the unit was installed in the test

duct and its exterior housing was carefully sealed to prevent inleakage of air. The desired rate of air flow

through the air cleaner was established and samples of air

were drawn from the center of the test duct, at points one

foot upstream and eight feet downstream of the air cleaner

assembly, at equal rates for equal times, and passed through

known areas of Whatman No. 4l filter paper. The filter

papers used in the upstream and downstream positions were

selected to have the same light transmission readings when

clean, as determined by means of a photometer using transmitted light. Using filter paper sampling areas downstream

equal to 30 percent of the filter paper area upstream, an

efficiency of 70 percent would be indicated if the upstream

and downstream dust-spots on the papers had the same opacity,

as indicated by the change in the light transmissions of the

dust-spot areas before and after the sample was drawn. If

the opacities of the dust-spots differed, the efficiency was

calculated by means of the formula

Efficiency, percent = 100

where Aq and A2 were the areas of the dust-spots upstream

and downstream, respectively, and 0]_ and 02 were the opacities of the dust-spots upstream and downstream, respectively.

An air filter of this kind equipped with a differential

pressure switch to actuate the media shift mechanism operates

at a sort of "steady-state" condition, in which the pressure

drop slowly increases to an upper limit as dust is received,

and is then rapidly reduced to a somewhat lower limit as clean

media is moved into the air stream due to action of the pressure switch. An average pressure drop is thus maintained by

intermittent shifting of the media as the pressure drop through

the filter changes within these limits. It is evident that the

dirtiness of the filter media as it is moved out of the air

stream is dependent on the magnitude of the average pressure

drop at which the unit is adjusted to operate, and that the

rate of usage of media therefore depends on it. Further,

since dust-arresting efficiency of this type of media increases

slightly as the media becomes choked with dirt, the efficiency

of the unit may be affected by the operating pressure drop. In

order that the tests represent conditions reasonably appropriate for service applications, the differential pressure

control was adjusted to yield an average pressure drop of the

magnitude commonly experienced with automatic self-cleaning

air filters (about 0.46 inch W.G.).

n ^2 . Ai 0i

-4-

The following procedure was used in these tests. The

clean unit was installed in tandem between the upstream and

downstream sections of the test duct, and all discoverable air

leaks were sealed. The differential pressure control was adjusted to actuate the media shift drive-motor when the pressure drop across the media increased to 0.50 inch W.G; its

operating differential was such that the control opened the

drive-motor circuit when the pressure drop decreased to 0.4-3

inch W.G.

With the filtering media in the air stream all clean, the

pressure drop was measured at several face velocities, and the

efficiency of the filter on atmospheric air was determined at

rated face velocity. Next, the efficiency was determined with

100 percent Cottrell precipitate. The process of dirt-loading

the filter at rated face velocity was then begun, using a mixture of 96 percent Cottrell precipitate and 4 percent cotton

lint by weight, separately dispersed into the air stream at a concentration of 1.0 gram of mixture per 1000 cf of air. The

lint used for this purpose was No. 7 cotton linters previously

ground in a Wiley mill with a 4-millimeter screen; the required

weight of lint was dispersed into the air stream every 10-12

minutes through an aspirator operating at approximately 35 psi

gage inlet air pressure.

When the pressure drop of the filter reached the upper

limit of the differential pressure- switch, and thereafter fluctuated about the average value established by the control setting, the filter operation became substantially "steady-state."

Readings of pressure drop just before and after the shifts of

the media, and of the media travel as indicated by a mark on

the curtain, were recorded from this point on; occasional

measurements of dust-arresting efficiency were also made as

this condition was continued. Some of these determinations

were made so that a shift of the media occurred during the

air-sampling period, and some were made without such a shift.

As shown in Figure 2, after the filter had been operated

at a dirt concentration of 1.0 gram per 1000 cf, for a period

in which approximately 240 grams of dirt per foot width of

filter were fed, the dirt concentration was reduced to 0.5

gram per 1000 cf, with occasional efficiency measurements

being made. Thin was continued until the amount of dirt fed

increased from 240 to 364 grams per foot width of filter. At

this stage, the efficiency of the filter with atmospheric air

as the aerosol was again measured.

During the tests, at appropriate times, strips of 3/4

inch cellophane adhesive tape were stretched across the

test duct with the adhesive side facing upstream to catch

samples of dust particles approaching in the air stream.

-5-

The tapes were placed in the duct at a position 15 inches

downstream of the downstream flange of the test unit, or

about 20 inches downstream of the filtering media of the

unit

.

4. TEST RESULTS AND DISCUSSION

Tabulated in Table 1 are measurements, at four face

velocities, of the pressure drop through the filter when

the media was clean, and average values of the efficiency

of the unit on atmospheric air and on Cottrell precipitate

for the filter when clean and when dirt-loaded to the

"steady-state" condition corresponding to an average pressure drop of about 0.47 inch W.G. at rated face velocity.

The operating performance of the unit at 520 fpm face

velocity is summarized in Table 2 and in Figure 2. Referring to Figure 2, it is seen that the pressure drop

increased gradually from its initial value, as dirt was fed

to the filter, to a value of about 0.50 inch W.G. At this

point the differential pressure control caused about six

inches of new clean media to be shifted into the air stream,

which lowered the pressure drop to about 0.43 inch W.G*

Thereafter, the unit operated automatically in a "steadystate" condition with the pressure drop varying between

maximum and minimum values of 0.50 and 0.43 inch W.G.

,

respectively. The travel of the media as this process continued is also shown; it is seen that the plotted points

describe a substantially straight line having constant slope,

i.e., that the use of media per gram of dust received per

foot of filter width was substantially constant. The efficiency of the filter on Cottrell precipitate in atmospheric

air is shown at the top of Figure 2. It increased from an

initial value of 75 percent to an approximately steady value

of 84 percent for the "steady-state" operating condition.

The results above were obtained with the filter being

loaded with a dirt mixture at a concentration of 1.0 gram

per 1000 cf of air. When the test was continued with the

dirt concentration reduced to 0.5 gram per 1000 cf, substantially the same results were obtained, as shown on the

right-hand portion of Figure 2, although the time required

to feed a given quantity of dirt was doubled because of the

halved concentration.

For a filter of this type, with a filter curtain H feet

from top to bottom of the air-passing area, receiving at a face velocity of V fpm an aerosol having a dust concentration
.•

1

'
- 6 -

of C grams per 1000 cf, the rate of dirt-loading, S, is

given by

S = ^qqq" = 0.06 VHC grams/hr per ft of media width (a)

If T is the average rate of travel of media in feet per

hour, the "burden", B, or weight of dust received by a

square foot of the media by the time it leaves the air

stream, is given by

6 OHVC n VHC = S

1000T U,UD

T T

(b)

For the "steady-state" operating condition shown in

Figure 2, S/T is given in effect by the inverse slope of the

line showing media travel versus total dust received per

foot of media width, in appropriate units. Table 2 gives

the values of S , T, and B derived from the data plotted in

Figure 2 and from the elapsed-time records of the tests,

for the "steady-state" operating condition for both aerosol

dirt concentrations. It is seen that the value of the burden B is very nearly the same for the tests at the two concentrations .

It would be expected on general grounds that for the

same filtering media, face velocity, and aerosol, the burden B would be affected chiefly by the pressure drop at

which the unit was operated. The fact that almost identical burdens resulted for two dirt concentrations for the

same average pressure drop gives support for the use of a relation like equation (b) for making estimates of media

usage for various possible values of the dirt concentration

C or for units of various heights of exposed filtering

blanket. It should be recognized, however, that B (here

about 50 grams/sq. ft.) may have a quite different value

for some other operating pressure drop or face velocity,

or for some other aerosol or filtering media.

The results show plainly that for a unit equipped with

a differential pressure switch controlling the media

shifting mechanism, the use of media is proportional to the

concentration or amount of dirt being received. For a unit

equipped with a timer-clock, the rate of use of media would

be constant and unresponsive to dirt loading rates, and the

pressure drop would rise and fall in magnitude with increase

oil decrease in dirt concentration.

-7-

The efficiency of the unit appeared to be unaffected

by movement of the media during an efficiency measurement.

After the unit had been removed from the test duct, the

section of the duct five feet long downstream of the

flanges, and upstream of a 3/4- inch thick wood strip

fastened flat across the bottom of the test duct, was carefully swept out with a fine brush. The amount of material

obtained from the duct by this sweeping was l8.0 grams, or

2.5 percent of the dirt load reaching the filter, constituting the fall-out in the first five feet of the duct

from the air passed through the filter. This material

consisted for the most part of large dust particles with

some few glass fibers.

Cellophane tapes, stretched across the test duct with

the adhesive side facing upstream, indicated upon visual

and microscopic examination after exposure to the air stream

that some particles of sizes up to approximately 125 microns

had passed through. the filter during the dirt-loading tests.

Particles smaller than five microns were observed in quantity by microscopic examination of the downstream filter

papers obtained in tests with both aerosols. No lint was

observed on the tapes during these tests.

The intermittent shifting action of the media occurred

without significant noise.
.
TABLE 1

Initial and Final Performance of Air Filter

Face Air Pressure Average Efficiency

Velocity Flow Droo ( 1 ) Atmosoheric Air Cottrell Preciaitate

fpm cfm inch W.G. percent percent

250 1000 0.076

375 1500 .141

520 2080 .234 10 75

625 2 500 .318

520 2080 .47 ± . 042) 232

)

842)

1 ) Pressure drop of the clean filter.

2 ) Values for the filter at "steady-state" condition when

dirt-loaded with a mixture of 96 percent Cottrell precipitate and A percent lint by weight.

TABLE 2

Summary of Performance with Cottrell Precipitate at 520 cfm

Condition Initial "Steady-State" "Steady-Stati

Duration, hours 0.85 3.1 4.2

Aerosol cone. , (C)

,

gram/1000 cf 1.0 1.0 0.5

Avg. efficiency,

percent 75.6 83.8 84.6

Avg. pressure drop,

inch W.G.

Pressure drop, inch W.G.

0.240

5

0.465 0.466

avg. max. /avg. min.

Rate of dirt ldg.*, (S),

grams/hr. per ft. of

0.503/. 427 0.505/.427

media width

Rate of travel of media,

62.4 31.2

(T), ft. /hr.

"Steady-state" burden*

1.25 0.61

on media , (B)

,

grams/ft

.

2 - 50.0 51.0

*Dirt load: 4 percent lint, 96 percent Cottrell precititate

by weight.

SJSCOHM-NES-DC
-
Up Stream Duct Filter Frame

VERTICAL SECTION

VERTICAL SECTION

Air Filfer Test Apparatus

Figure I

DUST

CONCENTRATION

GRAM/IOOO

CF

U. S. DEPARTMENT OF COMMERCE

Sinclair Works. Secretary

NATIONAL nUHEAU OF STANDARDS

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

The scope of activities of the National Bureau of Standards at its headquarters in Washington,

D. C., and its major laboratories in Boulder, Colo., 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 front cover. WASHINGTON, D. C.

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

Optics gnd Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Engineering Metrology.

ITeat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Engine

Fuels. Free Radicals Research.

Atomic and Radiation Physics, Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics. Atomic Physics. Neutron Physics. Nuclear Physics. Radioactivity. X-rays. Betatron. 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. Polymer Structure. Plastics. Dental Research.

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

Metal Physics.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Concreting Materials. 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.

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.

• 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. VII F Research.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Systems.

Navigation Systems. Radio Noise. Tropospheric Measurements. Tropospheric Analysis.

Radio Systems Application Engineering. Radio Meteorology.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. High

Frequency Impedance Standards. Calibration Center. Microwave Physics. Microwave Circuit

Standards.