NATIONAL BUREAU OF STANDARDS REPORT

PERFORMANCE TESTS OF A TRION

ELECTRIC AIR FILTER

Henry E, Robinson

Thomas W. Watson

Report to

General Services Administration

Public Buildings Service

Washington 25, D. C,

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

3336

by
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Aslin, Director

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards is suggested in the following listing of

the divisions and sections engaged in technical work. In general, each section is engaged in specialized research, development, and engineering in the field indicated by its title. A brief description

of the activities, and of the resultant reports and publications, appears on the inside of the back

cover of this report.

Electricity. Resistance and Reactance Measurements. Electrical Instruments. Magnetic

Measurements. Electrochemistry.

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

Technology. Length. Engineering Metrology.

Heat and Power. Temperature Measurements. Thermodynamics. Cryogenic Physics. Engines

and Lubrication. Engine Fuels. Cryogenic Engineering.

Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics. Atomic Physics. Neutron Measurements. Infrared Spectros- copy. Nuclear Physics. Radioactivity. X-Ray. Betatron. Nucleonic Instrumentation. Radiological Equipment. Atomic Energy Commission Radiation Instruments Branch.

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

Inorganic Chemistry. Electrodeposition. Gas Chemistry. Physical Chemistry. Thermochemistry.

Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics. Mass

and Scale. Capacity, Density, and Fluid Meters. Combustion Control.

Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Organic Plastics. Dental Research.

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

Mineral Products. Porcelain and Pottery. Glass. Refractories. Enameled Metals. Concreting

Materials. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering.

Electronics. Engineering Electronics. Electron Tubes. Electronic Computers. Electronic

Instrumentation. Process Technology.

Radio Propagation. Upper Atmosphere Research. Ionospheric Research. Regular Propagation

Services. Frequency Utilization Research. Tropospheric Propagation Research. High Frequency

Standards. Microwave Standards.

^Office of Basic Instrumentation ^Office of Weights and Measures.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

1000-30-4^37 June 7, 1954

NBS REPORT

3336

PERFORMANCE TESTS OF A TRION

ELECTRIC AIR FILTER

by

Henry E, Robinson

Thomas W. Watson

Heating and Air Conditioning Section

Building Technology Division

to

General Services Administration

Public Buildings Service

Washington 25, D, C.

NBS

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, r

unless permission

25, D, C. Such p(

cally prepared If

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

]r in part, is prohibited

Standards, Washington

report has been specifireport for its own use.
(

j

(

. il
PERFORMANCE TESTS OF A TRION MODEL NO.

g-102-00 ELECTRIC AIR FILTER

1. INTRODUCTION

At the request of the Public Buildings Service, General Services

Administration, the performance characteristics of electrostatic air

cleaners 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

electrostatic filter unit submitted by its manufacturer at the request of the Public Buildings Service and included determinations of

dust arresting efficiency with three aerosols (atmospheric air,

kerosene lamp smoke, and Cottrell precipitate), pressure drop, specific dirt load and cleanability of the specimen.

2. DESCRIPTION OF THE FILTER SPECIMEN

The cleaner was manufactured by Trion, Inc., 1000 Island Avenue,

McKees Rocks, Pennsylvania, and was of the electrostatic type. It

was identified as a Trion Electric Air Filter, Model No. ^-102-00

with one cell, rated velocity 333 feet per minute (1332 CFM total

capacity) . The power pack nameplate data furnished by the manufacturer were as follows:

Type B 60 cycles 110 volts 5 amps

Ionizer volts 13 • 5 kv Plate 6.7 kv

Maximum output 9 ina

The test unit had a housing with actual outside dimensions of

25 1/4 X 27 1/2 inches and was 24 l/^ inches long. It was rated as

having 4 sq. ft, of transverse area, i. e., 1332 CFM air delivery

at 333 fpm velocity. The face openings were 22 1/S x 24 inches upstream and IS 3 /^ X IS 5 /^ inches downstream. The downstream face

was adapted to receive a nominal 20 x 20 x 1 inch after-filter, which

for this unit was a 19 1/2 x 19 l/2 x 7/S inch viscid impingement

type air filter, manufactured by the Research Products Corporation

of Madison, Wisconsin.

The unit had a filter cell, 23 3/4 inches in height, IS inches in

length, and 22 l/S inches in width, containing 51 aluminum plates

spaced approximately 3/^-inch apart, presenting a total surface area

of approximately I6 S square feet.

The manufacturer furnished an adhesive (a water-emulsifying oil)

designated as ’^Trion No. 36 S”, and an applicator for oiling the

collecting plates of the cell by spraying them from both the upstream
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and dovmstream face. The after-filter was oiled in preparation

for the test by immersing the filter in the oil and letting the

excess drain off with the filter standing on edge for 1^ hours

prior to the test.

The power pack, connected to a 110-volt 60-cycle supply, was

adjusted by the manufacturer’s representative to a setting of 1.6

milliamperes on the power pack instrument; the ionizer and plate

voltages that resulted were measured by means of a high-resistance

voltmeter which was compared with an accurate electrostatic voltEfficiency determinations were made by the NBS ”Dust-Spot Method”

using the following aerosols: (a) outdoor air drawn through the

laboratory without addition of other dust or contaminant; (b) kerosene

lamp smoke; and (c) Cottrell precipitate. The test method is described in the paper ”A Test Method for Air Filters” by R. S. Dill

(ASHVE Transactions, Vol. 44, Po 379, 193^) • The test duct and

arrangement are shown in Figure 1, A baffle made of two 3-inch wide

slats was located in the duct about 3-1/2 ft downstream of the test

unit to intermix the air discharged from it.

For these tests, the unit was installed in the test duct and

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 points of the test duct one foot upstream

and eight feet downstream of the air cleaner at equal rates and passed

through known areas of Whatman No, 41 filter paper. For the atmospheric

air and oil lamp smoke tests, the samples were drawn at equal rates

through equal areas of filter paper (3/4-inch diameter spots). The

downstream sample was drawn continuously during the test; the upstream

sample was drawn intermittently in a number of one-minute periods

uniformly distributed over the duration of the test, aggregating onetenth of the downstream sampling period. Under these conditions an

efficiency of 90 percent would be indicated if the upstream and downstream dust-spots on the filter 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, which were determined

by means of aph.tometer using transmitted light. The filter papers

used in the upstream and downstream positions were selected to have

the same light transmission readings when clean. If the opacities

of the dust-spots differed, the efficiency was calculated by means

of the formula

meter

3c TEST METHOD AND PROCEDURE

Efficiency, percent 100
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where 0

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were the opacities of the dust-spots upstream

and downstreamf respectively, and t^ and t 2 were the aggregate

times during which the upstream and downstream samples, respectively, were drawn.

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aerosol, the samples upstream and downstream were drawn at equal

rates and for equal times but unequal dust-spot areas were used

to obtain opacities that were approximately equal. If the opacities

of the dust-spots differed, the value of the efficiency was calculated by means of the formula above, with the radio ^ 2/^1

substituted for the ratio ^l/t2 , where A 2 and were the areas

of the dust-spots downstream and upstream respectively.

The following procedure was employed in these tests. After

the clean and oiled unit had been installed in the test duct, and

all discoverable air leaks into its housing had been sealed, its

input and output voltages were adjusted to recommended values by

a representative of the manufacturer; (input 110 volts; ionizer

15.2 kv; plates 7.0 kv; output current 1.6 ma.). Three determinations of the efficiency of the clean unit were made at the rated

velocity, using as the aerosol outdoor air drawn into the test

duct through a nearby window. A determination of efficiency with

the unit not energized was also made. Following these, single determinations were made, using outdoor air, at velocities 20 percent

greater, and 20 percent less than the rated velocity.

Next, three efficiency determinations were made at rated velocity,

using as the aerosol outdoor air with the addition of kerosene smoke

generated by an open lamp flame near the inlet to the test duct.

Following these, three efficiency determinations were made at

rated velocity, using as an aerosol outdoor air in which was dispersed

Cottrell precipitate at a concentration of one gram per thousand

cubic feet of air. When these had been obtained, the process was

begun of loading the unit with a mixture of 4 percent cotton lint

and 96 percent Cottrell precipitate, by weight, separately dispersed

into the air stream. The lint used for this purpose was No. 7 cotton

linters previously ground in a Wiley mill with a A-millimeter screen;

the lint was dispersed into the air stream through an aspirator

operating at approximately 35 psi inlet air pressure. At suitable

periods as loading progressed,, the efficiency of the unit was determined using 100 percent Cottrell precipitate in outdoor air. In

these tests, and during the loading process, the, rate of feed of the

dispersant was one gram per thousand cubic feet of air. The pressure

drop and the ionizer and plate voltages of the unit were recorded

at intervals during the tests. The dirt-loading process was continued until about 900 grams of the lint and Cottrell precipitate

mixture had been fed (i.e., 2/3 gram per CFM of unit rating).
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At suitable periods as the dirt-loading process progressed,

strips of transparent cellulose adhesive tape (3/4 in wide) were

stretched vertically across the test duct near its axis, with the

adhesive side facing upstream. Tapes were located at three positions

(1) 12 inches upstream, (2) 15 inches downstream, and (3) S ft downstream, of the test unit; the tapes at stations (1) and (3) were in

the same longitudinal positions in the test duct as the inlets to

the upstream and downstream sampling tubes. The adhesive surface

of such a tape captured a sample of the particulate matter in the

air flowing past it, and after suitable times of exposure to the

aerosol, scrutiny of the tapes by eye and with a microscope afforded

considerable information as to the vertical distribution, the nature,

number, and size of the particles caught at the various stations.

Photographic enlargements (lOX), by transmitted light were made of

sections of the tapes corresponding to a position at mid-height in

the test duct.

The filter cell was removed from the test unit after the tests

and cleaned by means of a stream of cold water from a high pressure

hose nozzle, directed at and into the cell plates from both ends of

the unit. The cleanability of the after-filter was determined

separately, by the same means.

4. TEST RESULTS

A summary of the test data, giving efficiencies in percent

with the three aerosols, and the pressure drop of the complete unit

including the after-filter, in inch W.G., at rates of air flow

corresponding to various face velocities, is given in Table 1. Also,

a summary of the test data obtained in the dirt-loading test conducted

at the rated face velocity of 333 fpm is given in Table 2.

Photographs No. 1, 2 and 3 included in this report are lOX enlargement of the center 3/4 x 1-inch sections of cellophane tapes

located at the three similarly numbered stations described under

Test Method and Procedure. Tapes Nos. 2 and 3 were exposed at their

respective stations simultaneously during the dirt-loading test for

a period in which 124 grams of mixture were fed to the test unit.

This exposure was during the interval in which the dirt-load increased

from 41 to I 65 grams, as shown in Table 2. Photograph No. 1 shows

a tape exposed at station No. 1 for an equal length of time. After

exposure the tapes were carefully removed from the test duct for

photographing and microscopic study.

Throughout the tests with atmospheric air and oil lamp smoke

there was no observed instance of electrical sparking or flashing

in the unit audible to the ear. However, during the Cottrell and

lint loading test electrical sparking or flashing occurred intermittently, the frequency increasing from about one to three times

per hour at the start to about 6 or 10 times per hour at the end

of the loading test.
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5 . SUMMARY

A. Performance

The efficiency of the air cleaner in arresting the particulate

matter existent in atmospheric air drawn through the unit varied

considerably with the face velocity at which it was operated, as

shown in Table 1. At the rated velocity (333 fpm) , the average

efficiency on atmospheric air (90.2 percent), and that on oil lamp

smoke (^9.6 percent^ were very nearly the sameo The efficiencies

are reported to three significant figures obtained from the test

data. In reporting thus, however, it is considered desirable to

point out that an uncertainty on the order of one or two percent

is possible in determining efficiencies, although in these results

the differences between comparable efficiency values were consistently of a lesser magnitude.

The efficiency of the unit in arresting Cottrell precipitate,

initially at a high value of about 9^ percent, as shown in Tables

1 and 2, decreased with dirt-loading to under 90 percent, later

rising to just above 90 percent. The lower values of efficiency

were obtained when the ionizer, and especially the plate, voltages

had decreased considerably under their initial adjusted values.

At the same time, the output current, as indicated by the powerpack milliammeter , was approximately triple the value observed

when the unit was less loaded with dirt.

The pressure drop through the test unit decreased slightly

during the tests reported in Table 1. It is believed that this

was due to slight drainage of oil from the after-filter media to

the lower retaining frame. The greater part of the pressure drop

through the complete unit was due to the resistance of the afterfilter. It is noted in Table 2 that in the dirt-loading test, the

pressure drop of the complete unit increased by 0,140 inch W,G, for

a total dirt-load of 915 grams. This rise was due chiefly to an

increase in the pressure drop of the after-filter, as a result of

an accumulation of cotton lint and of comparatively large particles

of Cottrell precipitate on its media,

B. Cleanability

The filter was subjected* to the cleaning process described

under Test Method and Procedure, No difficulty was experienced

in thoroughly cleaning the ionizer and collector sections of the

unit, using moderate care. The after-filter was also satisfactorily

cleaned using the same procedure.
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C, General

On completion of the dirt-loading test, the unit was removed from the test duct and examined. The ionizer structure

and bars, and the insulators, were generally coated with a

moderate layer of dust and lint. The collector plates were well

covered with an oily deposit of dust and lint, with a slightly

thicker deposit on the plates for a distance of two or three

inches from the leading edge. There was a slight amount of

bridging of the plate spaces by lint fibers, such bridging being

chiefly near the bottom and aft edges of the plates. Lint fibers

extended downstream as much as 1/2 inch from the aft edges of the

plates, •

The upstream face of the after-filter showed considerable

amounts of lint, deposited more heavily at the tops and bottoms

of six vertical strips about 1 1/2 inches wide. The after-filter

media was darkened on its upstream face by a moderate deposit of

dust particles; it was evident that many of the particles were

relatively large, but because fine particles are less readily observed, it cannot be stated that many fine particles were not also

present. The downstream face of the after-filter was observed to

be slightly darkened uniformly by dust.

The dirt (dust) deposits on the electrostatic unit, and on

the after-filter, appeared to be well-saturated with oil. Microscopic examination of the cellophane tape exposed at station (2)

showed a few droplets of what appeared to be oil, but the number

and amount of such droplets were so small that oil entrainment in

the effluent air is considered of no practical importance.

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

downstream section of the latter was carefully swept out with a

fine brush. The amount of material obtained from the duct by this

sweeping was S grams, consisting almost wholly of fairly large dust

particles, with little observable lint.

The cellophane tape samples shown in Photographs 1, 2 and 3,

corresponding to stations (Ij, (2) and (3), respectively, indicate

in a general way the perfori ” ' ’ lete unit at the rated

Photograph 1 was obtained at a different time than those in Photographs 2 and 3, but was exposed for an equal length of time, and

may be considered as representative for the upstream station.

Photograph No. 1 shows many particles under 5 microns in actual

size, and a distribution of larger particles up to a few as large

as 400 microns, as well as many fibers of lint. (In these photographs, l/l6 inch corresponds to an actual dimension of about

ionizer and plate voltages The tape shown in
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l60 microns.) Photograph No. 2, for the tape 15 inches downstream of the unit, shows many large particles up to about 300

microns in size, and a few lint fibers, but very few fine dust

particles considering their number upstream of the unit. Photograph No. 3, for the tape ^ ft downstream of the unit, shows an

absence of the larger particles of Photograph No. 2, which apparently settled out of the air stream, although a few fibers of

lint remained.

Comparison of the numbers of particles on the upstream and

downstream tapes indicates, in an obvious way, a high order of

efficiency for the relatively clean unit in arresting Cottrell

precipitate, as is also indicated by the earlier discoloration

test results presented in Table 2. The latter results show that

the relatively clean unit had a considerably higher efficiency

when Cottrell precipitate was being received in the air stream

than when the aerosol was outdoor air or kerosene lamp smoke.

The overall efficiency of the relatively clean unit on particles

of the sizes found in Cottrell precipitate appears therefore to

have been better than on the finer particles in outdoor air or

kerosene smoke. Nevertheless, the downstream tapes, and the

deposits on the after-filter, show that many quite large particles

of dust and lint escaped beyond the electrostatic unit. Whether

the large particles were passed through the unit because they were

not arrested at all, or were caught and later dislodged from the

collector plates by electrical sparking, is not known from these

tests.

As the photographs show, many large particles and some lint

passed unarrested through the after-filter. Assuming that one of

the functions of the after-filter is to arrest as much as possible

of the material escaping the electrostatic unit, the arrestance

characteristics of the after-filter are of major importance in determining the presence, in the air leaving the complete unit, of

such particulate matter as is shown in the downstream tape photographs.
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Table 1

Face

Velocity

Inlet

Aerosol*

Ionizer

Voltage

Plate

Voltage

Output

Current

Pressure

Drop

Duration

of Test Efficiency

fpm kv kv milliamps inch WG minutes percent

333 A 0 0 0 o.uo 20 4.6**

333 A 15.1 6.9 1.7 .140 ISO 90.9

333 A 15.1 7.0 1.7 .13^ ISO 90.0

335 A 15.1 7.0 1.7 .13^ ISO S9.S

266 A 15.2 7.0 1.6 .0S9 ISO 94.8

400 A 15.1 7.0 1.6 .1^^9 ISO S4 .

4

333 S 15.1 7.0 1.6 .135 20 90.7

333 S 15.1 7.0 1.6 .135 20 S9.6

333 S 15.1 7.0 1.6 .135 20 SS.5

333 C 15.0 7.0 1.7 .135 10 97.6

333 C 15.0 7.0 1.7 .137 9 98.5

333 C 15.0 7.0 1.7 .13^ 10 98.5

*A = Particulate matter in atmospheric air at NBS.

S = Kerosene lamp smoke in atmospheric air.

C = Cottrell precipitate in atmospheric air (1 gram/1000 CF) ** Since unit was not energized, the efficiency was chiefly that of

the after-filter.
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Table 2

Face

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Dirt

Load’*'

Ionizer

Voltae:e

Plate

Voltase

Output

Current

Pressure

Drop Efficiency*'-'

fpm grams kv kv milliamps , inch WG percent

333 41 15.0 7.0 1.7 0.13s 9S.2 (avgo)

165 14.9 6.^ 1.9 .141 94.4

21t 14.6 6.3 2.3 .142 91.9

419 14.1 5 .^ 3.3 .153 90.0

490 13.0 4 * ^ 6.0 .170 -

561 13.1 4.9 5 .S .IS3 87.3

703 13.6 5.2 5.5 .212 87.4

S44 13.5 4 . ^ 5.4 .257 90.1

900 13.5 5.0 5.5 .273 90.

s

915 13.3 5.0 5.0 .27s 90.4

’{'Average mixture: 3.9^ lint, 96.1^ Cottrell precipitate by weight.

Efficiency determined with 100% Cottrell precipitate.
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Filter Frame

VERTICAL SECTION

Arr Filf er Test Apparatus

Figure 1

Photograph No 1

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Photograph No, 2

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Photograph No. 3

THE NATIONAL El KEAU OF STANDARDS

Funclions and Activities

The functions of the National Hun'aii of Standards an- ^>et forth in die Act of (ion<rre<s, March

3, 1901, as amended h\ Congress in Puhlie !,a\v 619. 1930. d liesc include the dcvelopnienl and

maintenance of the national standards of measurenumt and the provision of means and mcihods

for making measurements consistent with these standards; tlie determination of jiln sical 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, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are 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 j)ublishes 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, Handbooks, 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) and its Supplement ($0.75), available from the Superintendent of Documents, Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific PublicationSj National Bureau of

Standards, Washington 25, D. C.