NATIONAL BUREAU OF STANDARDS REPORT

5833

PERFORMANCE TESTS OF A TRION HOC

HIGH CAPACITY ELECTRONIC AIR CLEANER

(No. 25 Cell)

by

Thomas W. Watson and Henry E. Robinson

Report to

General Services Administration

Public Buildings Service

Washington 25, D. C.

<MBS>

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 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; 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 Energy

Commission. 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 Bureau’s work take the form of either actual equipment and devices or published papers 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, 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, 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

1000-30-4890

NBS REPORT

April 1, 1958 5833

PERFORMANCE TESTS OF A TRION HOC

HIGH CAPACITY ELECTRONIC AIR CLEANER

(No. 25 Cell)

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.

by

IMPORTANT NOTICE

NATIONAL BUREAU OF STAf

Intended for use within the G(

to additional evaluation and re» listing of this Report, either in the Office of the Director, Nath however, by the Government a| to reproduce additional copies

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

ogress accounting documents

lally published It is subjected

eproductlon, or open-literature on Is obtained in writing from

iuch permission is not needed,

repared if that agency wishes

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
1 ••

• •••*
PERFORMANCE TESTS OF A TRION HCC

HIGH CAPACITY ELECTRONIC AIR CLEANER

(No. 25 Cell)

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

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 two

aerosols (atmospheric air and Cottrell precipitate), pressure

drop, dirt load performance characteristics, and cleanability

of the specimen.

2. DESCRIPTION OF THE FILTER SPECIMEN

The cleaner was manufactured by Trion, Inc., of McKees

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

was identified by the manufacturer's representative as a

"Trion HCC High Capacity Cell Model 15 with No. 25 Cell."

The power pack furnished was a laboratory type pack, Serial

No. 7T157 , having a variable voltage adjustment to obtain

desired settings for the tests. The power pack nameplate

data furnished by the manufacturer were as follows:

Type A

60 cycles, 110 volts

Ionizer volts 17*5 kv D.C., Plate 8.7 kv D.C.

Maximum output 24 milliamps

The test unit had a housing with transverse outside

dimensions 24 1/2 by 22 1/4 inches and was 23 7/16 inches

long. The upstream and downstream faces had special flanges

for joining the unit to the flanges of the test apparatus.

Near the downstream face, the housing was adapted to receive

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

released for use in connection with advertising or sales

promotion

.

- 2 -

an afterfilter, which for this unit was a 23 by 21 7/8 by 7/8

inch viscid impingement type air filter (Airsan AF150) manufactured by the Air Filter Corporation of Milwaukee, Wisconsin.

The afterfilter had a net face area of 3*03 square feet.

The filter cell of the unit was 2b inches in height,

22 1/16 inches in width, and 17 7/8 inches in length, and

contained 63 aluminum plates (32 plates 21 1/b by 10 3A

inches, and 31 plates 23 1/16 10 3 A inches in dimension)

spaced about 5/16 inch on centers, presenting a total surface area of approximately 206 square feet. The gross inlet

area of the ionizer assembly was 2.57 square feet, and the

gross cell transverse area was 3*68 square feet.

The manufacturer furnished an adhesive, designated as

EAC-2 "Socony Mobile Par 3000 hot water emulsion type,"

with which the collector plates were oiled by spraying them

from both the upstream and downstream faces. The afterfilter

was oiled in preparation for the test by spraying the media

from the upstream and downstream sides with the same adhesive.

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

was adjusted by the manufacturer's representative to recommended settings prior to the tests; the ionizer and plate

voltages that resulted were measured by means of an accurate

electrostatic voltmeter.

3. TEST METHOD AND PROCEDURE

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

drawn through 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. bb

,

p. 379> 1938). 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 feet downstream of the test assembly 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 assembly at equal rates and passed through

known areas of Whatman No. bl filter paper. For the atmospheric air tests, the samples were drawn at equal rates

through equal areas of filter paper (3A-inch diameter spots).

The downstream sample was drawn continuously during the test;

-3-

the upstream sample was drawn intermittently in a number of

one-minute periods uniformly distributed over the duration

of the test, aggregating one-tenth 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 a photometer 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

where 0y and C>2 were the opacities of the dust-spots upstream

and downstream, respectively, and ty and t2 were the aggregate times during which the upstream and downstream samples,

respectively, were drawn.

For the efficiency tests with Cottrell precipitate as

the 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 ratio A2 /Ay substituted for the ratio

ti/t2, where A2 and Ay were the areas of the dust-spots downstream and upstream, respectivedy

.

The foTTowing 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 17. M- kv; plates 8.5 kv). Two deter

minations 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 open window. A determination of efficiency with the unit not energized was also

made. Following these, single determinations were made,

using outdoor air, at air flows 20 percent greater, and 20

percent less than the rated air flow.

Following these, two efficiency determinations were

made at the rated air flow, 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

Efficiency, percent = 100

-b

had been obtained, the process was begun of loading the unit

with a mixture of b 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 4—

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 dirtloading process was continued until 124-5 grams of the lint

and Cottrell precipitate mixture had been fed (i.e., 2/3

gram per cfm of unit rating).

At suitable periods as the dirt-loading process progressed, strips of transparent cellophane adhesive tape

(3/4— inch wide) were stretched vertically across the test

duct near its axis, with the adhesive side facing upstream.

Tapes were located at two positions, (1) 12 inches upstream

and (2) 15 inches downstream of the test unit. 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.

The filter cell was removed from the test unit 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 afterfilter

was determined separately, by the same means.

4. TEST RESULTS

A summary of the test data giving efficiencies in percent with the two aerosols and the pressure drop of the

complete unit, including the afterfilter, in inch W.G. , at

several rates of air flow, is given in Table 1. A summary

of the test data obtained in the dirt-loading test conducted at 184-0 cfm is given in Table 2.

Throughout the tests with atmospheric air, electrical

sparking or flashing in the unit audible to the ear occurred,

on the average, about two times per hour. However, during

-5-

the Cottrell and lint loading test) electrical sparking or

flashing occurred intermittently, the frequency increasing

from about 10 to 15 times per minute at the start to about

50 to 90 times per minute at the end of the loading test.

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 air flow at which it was

operated, as shown in Table 1. At the rated air flow (1840

cfm) , the average efficiency on atmospheric air was 91.7 percent. 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.

The efficiency of the unit in arresting Cottrell pre~

cipitate, initially at a value of 98.6 percent, as shown in

Tables 1 and 2, decreased with dirt-loading t(^ about 95*5

percent, later rising to about 97 percent at the end of the

test. The slightly lower values of efficiency were obtained

when the ionizer and plate voltages had decreased to 16.2 and

8.1 kv, respectively. At the same time, the ionizer current

as indicated by the power pack milliammeter was variable,

ranging from 1.4- to 2.5 milliamps. Occasionally throughout

the loading test the milliammeter read full scale (10 ma)

momentarily, returning to the lower value upon shorting or

flashing of the unit. An efficiency determination made with

atmospheric air at the end of the dirt-loading test indicated

that the unit had an efficiency of 88.6 percent on this aerosol when the unit was heavily laden with dirt.

The greater part of the pressure drop through the complete unit was due to the resistance of the aft'erf ilter . It

is noted in Table 2 that in the dirt-loading test, the pressure drop of the complete unit increased by 0.51 inch W.G.

for a total load of 1245 grams. Pressure drop measurements

made at the conclusion of the dirt loading test showed the

pressure drop across the cell to be 0.06 inch W.G., and that

across the afterfilter to be 0.68 inch W.G. The rise was due

chiefly to an increase in the pressure drop of the afterfilter, as a result of an accumulation of cotton lint and of

comparatively large particles of Cottrell precipitate on its

media

.

- 6 -

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 afterfilter

was also satisfactorily cleaned using the same procedure.

C. General.

On completion of the dirt-loading test, the unit was

removed from the test duct and examined. The ionizer assembly and bars, and the insulators, were coated with a moderate

layer of dust and lint. Dirt deposits on the collector

plates were heaviest one inch downstream from the upstream

edges and on the next three to four inches of the plates,

the thickness of the deposits being about 1/32 inch. The

heaviest deposits were observed on the negative plates. A

continuous but thinner layer of dirt was deposited over the

remaining area of the collector plates, extending to the aft

edges. There were a few instances of lint bridging between

the collector plates near the aft edges near the bottom of

the cell.

The upstream face of the afterfilter revealed considerable deposits of lint uniformly deposited over the whole airpassing area. The afterfilter was uniformly darkened by a dust deposit on its upstream face.

The dirt (dust) deposits on the electrostatic unit and

on the afterfilter appeared to be well saturated with oil.

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

section downstream of the unit was carefully swept out with

a fine brush. The amount of material obtained from this

sweeping was 0.8 gram.

Cellophane tapes, stretched across the test duct downstream of the filter unit with the adhesive side facing

upstream, indicated upon visual and microscopic examination

after exposure to the air stream throughout the dirt-loading

test, that a few particles up to about 200 microns in size

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

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

papers and tapes obtained in tests with both aerosols.

Comparison of the numbers of particles on the upstream

and downstream tapes indicated, in an obvious way, a high

order of efficiency for the unit in arresting Cottrell precipitate, as is also indicated by the dust spot efficiency

- 7 -

results presented in Table 2. The latter results show a considerably higher efficiency for the unit when Cottrell precipitate was being received in the air stream than when the

aerosol was outdoor air. The overall efficiency of the unit

on particles of the sizes found in Cottrell precipitate

appears therefore to be better than on the finer particles in

outdoor air. Nevertheless, the downstream tapes, and the

deposits on the afterfilter, showed that a few quite large

particles of dust 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 downstream tapes indicated, a few large particles

of dust passed unarrested through the afterfilter. Assuming

that one of the functions of the afterfilter is to arrest as

much as possible of the material escaping the electrostatic

unit, the arrestance characteristics of the afterfilter are

of major importance in determining the presence or absence,

in the air leaving the complete unit, of such particulate

matter

.

Table 1

Air

Flow

Inlet

Aerosol*

Ionizer

Voltage

Plate

Voltage

Output

Current

Pressure Duration

Drop of Test Efficiency

cfm kv kv ma in. W.G . min. percent

1840 A 0 0 0 0.240 40 4 , 2 * *

1840 A 17.4 8.7 2.0 .240 180 91.5

1840 A 17.4 8.5 2.0 .240 220 91.8

1472 A 17.4 8.5 2.0 .160 220 96.2

2208 A 17.2 8.5 2.0 • 335 180 85.7

1840 C 17.2 8.4 2.0 .230 11 98.5

1840 C 17.2 8.4 2.0 .232 12 98.6

*A = Particulate matter in atmospheric air at NBS

.

C = Cottrell precipitate in atmospheric air (1 gram/1000 cf )

.

** Since the unit was not energized, the efficiency was

chiefly that of the afterfilter.

Table 2

Air Dirt Ionizer

Flow Load* Voltage

cfm gram kv

1840 37 17.2

230 17.0

441 16.2

632 16.0

843 16.2

1074 16.2

1245 16.5

1245 16 .

6

Plate Ionizer

Voltage Current

kv ma

8.4 2.0

8.4 2.0 to 4.0

8.3 1.7 to 3.0

7.6 1.5 to 2.3

8.1 1.4 to 2.0

8.1 1.6 to 2.5

8.3 1.4 to 2.4

8.4 1.2

Pressure

Drop Efficiency**

in. W.G. percent

0.230 98.6(avg .

)

.252 98.4

.292 97.9

.345 97.7

.437 95.7

.590 95.4

.740 97.1

.760 88.6(a)

*Average mixture: 4.0 percent lint, 96 percent Cottrell

precipitate by weight.

**Efficiency determined with 100 percent

(a) Efficiency determined with aerosol

with the unit dirty.

Cottrell precipitate.

"A” as in Table 1,

DUST

rr

r

k

7/vvy. y/S/S//////S/TT?/777/ /////////////s////////////////////7/7//A

To

~E" n-> Blow

6-l{" 12- 0 Y'

Up Stream Duct Down Stream Duct

SIDE ELEVATION

Up Stream Duct Filter Frame

VERTICAL SECTION

VERTICAL SECTION

Air Fi If er Test Apparatus

Figure I

U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Ashn, Director VUE NATIONAL BUREAU OF STANDARDS

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

D. C., and its major field laboratories in Boulder, Colorado, is suggested in the following listing of

the divisions and sections engaged in technical work. In general, each section carries out spe- cialized 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 front cover of this report.

WASHINGTON, D. C.

Electricity and Electronics. Resistance and Reactance. Electron Tubes. Electrical Instruments,

Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation.

Electrochemistry.

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

Technology. Length. Engineering Metrology.

Heat and Power. Temperature Physics, Thermodynamics. Cryogenic Physics, Rheology

and Lubrication. Engine Fuels,

Atomic and Radiation Physics, Spectroscope/. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics. Atomic Physics. Nuclear Physics, Radioactivity. X-rays. Betatron. Nucleonic Instrumentation. Radiological Equipment. AEC Radiation Instruments. 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 Controls.

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.

Metal Physics.

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

Materials, Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Condi--

tioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics, Numerical Analysis, Computation. Statistical Engineering. Mathematical Physics.

Data Processing Systems, SEAC Engineering Group. Components and Techniques. Digital

Circuitry. Digital Systems, Analogue 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,

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Systems.

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

Systems Application Engineering,

Radio Standards, Radio Frequencies. Microwave Frequencies. High Frequency Electrical

Standards. Radio Broadcast Service. High Frequency Impedance Standards. Calibration

Center, Microwave Physics Microwave Circuit Standards.