NATIONAL BUREAU OF STANDARDS REPORT

3259

PERFORMANCE TESTS OF A WESTINGHOUSE

PRECIPITRON ELECTRONIC AIR CLEANER

Henry E 0 Robinson

Thomas W„ Watson

Report to

General Services Administration

Public Buildings Service

Washington 25, D. C.

0. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

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^Office of Basic Instrumentation ^Office of Weights and Measures.
-/7fi r"

NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1000-30-4^37 April 26, 1954 3259

PERFORMANCE TESTS OF A WESTINGHOUSE

PRECIPITRON ELECTRONIC AIR CLEANER

TYPE FA-22

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, reprlntl

unless permission isobta

25, D. C, Such permlssi

cal ly prepared If that a

a a c ii- i .1 rt, Is prohibited Approved tor public release by the J rds, Washington Director of the National Institute of „ a8 been speclfl . Standards and Technology (NIST) for its own U 3 e. on October 9, 20 1

5

.

PERFORMANCE TESTS OF A WESTINGHOUSE TYPE FA-22

PRECIPITRON ELECTRONIC AIR CLEANER

lo 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,,

The cleaner was manufactured by the Westinghouse

Electric Corporation, Sturtevant Division, Hyde Park,

Boston 36 , Massachusetts, and was of the electrostatic

type. It was identified as a Westinghouse Precipitron

Type FA-22 with two type CA-12 cells, Style 15595&7, rated

velocity 333 feet per minute (1332 CFM total). The power

pack had the following nameplate data:

The test unit had a housing with actual outside dimensions of 24x24 - 1/4 inches and was 26 - 1/2 inches long, and was

rated as having 4 sq. ft. of transverse area, i.e., 1332 CFM

air delivery at 333 fpm velocity. The upstream and downstream

faces had flanges 30 inches square matching those of the duct

of the test apparatus. The face openings were 20x22-1/2

inches upstream and 20x20-1/2 inches downstream. The downstream face was adapted to receive a nominal 24x24x1 inch

after-filter, which for this unit was a 24x23 - 1 /16x1 inch

2. DESCRIPTION OF THE FILTER SPECIMEN

Precipitron Power Pack

Type M

Volts 115

Cycles 60-50

Style No. I 56O6OI

.Amps 0.3 Watts 90

Phase 1

Ionizer volts 12,300 Plate 5,500

- 2 -

"A-Lum-O-Aire” aluminum wool (dry type) air filter manufactured by the Carey Electronics Engineering Co® of Springfield, Ohio„

There were two similar filter cells in the housing,

each having actual outside dimensions of 11-7/8 inches in

height, 15 inches in length, and 22 inches in width, and

each containing 61 aluminum plates spaced approximately

5./l6-inch apart, presenting a total surface area of approximately 120 square feet for each cello The manufacturer

supplied a piece of 0 o 025 inch aluminum angle 1-1/2x1/2x22

inches in size, which was inserted beneath and around the

downstream bottom edge of the top cell, with the 1-1/4 inch

dimension parallel to the direction of air flow, for the

purpose of preventing oil blow-off from the upper plates

®

The manufacturer furnished an adhesive (a water-emulsifying oil) designated as Tf Precipitron Adhesive T-675" , and

an applicator for oiling the collecting plates of the cells

by spraying them from the upstream face® In accordance

with the request of the manufacturer’s representative, the

” A-Lum-O-Aire” after-filter was oiled in preparation for the

test by immersing the filter in an oil and letting excess

oil drain off with the filter standing on edge for 18 hours

prior to the test® The adhesive supplied by Westinghouse

for spraying the collecting plates was not sufficient in

quantity for immersing the after-filter, so a suitable

water-emulsifying oil was selected for this purpose from a

group of oils that had been submitted by manufacturers for

oiling viscid impingement air filters®

The power pack, connected to a 115-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 a highresistance voltmeter which was compared with 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; (b) kerosene lamp smoke; and (c) Cottrell

precipitate® The test method is described in the paper

- 3 -

TT A Test Method for Air Filters" by R. S. Dill (ASHVE Transactions, Vol. 44, Po 379, 193$) o The test duct and arrangement are shown in Figure 1. A baffle made of two 3-inch

wide sl^tts wa^ 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 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

Efficiency, percent = 100 1 _ # ^2 _ ^oo _ 10^2

L *2 °1 J0

1

where 0^ and O2 were the opacities of the dust-spots upstream

and downstream, respectively, and tj and t

2 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.

- 4

-

If the opacities of the dust-spots differed, the value of the

efficiency was calculated by means of the formula above, with

the ratio ^2/Ap substituted for the ratio where A2

and Aj 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 115 volts; ionizer 13.2 kv; plates 6.1 kv) . 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 open 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 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

dirt-loading process was continued until afraut 900 grarfls of

the lint and Cottrell precipitate mixture had been fed (i.e.,

2/3 gram per CFM of unit rating)

.

- 5 -

At suitable periods as the dirt-loading process progressed, strips of transparent cellulose 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 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 (10X),

by transmitted light were made of sections of the tapes corresponding to a position at mid-height in the test duct.

One of the filter cells 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 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

10X enlargements of the center 3/4xl-inch section of each

of the cellophane tapes located at the three similarlynumbered stations described under Test Method and Procedure.

The tapes 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 165 grams, as shown in Table 2. After

- 6 -

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 only one 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 8 times per hour at the end of the load

ing 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 face velocity at which

it was operated, as shown in Table 1. At the rated velocity

(333 fpm) , the average efficiency on atmospheric air (92.2

percent), and that on oil lamp smoke (91.£ percent), were

very nearly the same. 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 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 dense aluminum wool 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 after-filter. It is

noted in Table 2 that in the dirt-loading test, the pressure

drop of the complete unit increased by 0.057 inch W.G. for

a total dirt-load of 3$7 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

.

- 7

-

B. Cleanability

The filter cells were 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.

C. General

Upon completion of the dirt-loading test, the unit

was removed from the test duct and examined. Dirt deposits were heaviest on the ionizer bars, and on the upstream edges and first 3 or 4 inches of the collector

plates, the thickness of the deposits being up to about

1/32 inch. A continuous, but thinner, layer of dirt was

deposited over the remaining area of the collector plates,

extending to the after edge. Considerable bridging of

lint fibers from one collector plate to another, spanning

the gap between them, was observed; such bridging appeared to be most extensive in alternate plate spacings.

Some lint fibers were observed to extend downstream for

as much as 1/2 inch from the aft edges of the plates.

The dirt (dust) deposits on the plates appeared to be

well saturated with oil; there was little or no perceptible difference in amount of deposit on the various collector plates, except for the difference mentioned in regard to lint bridging.

The upstream face of the after-filter showed considerable amounts of lint, deposited more heavily over

certain areas or patches of the face. The after-filter

media was darkened by a light deposit of dust; it was evident that many of the dust 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 cellophane tape samples obtained at stations (1),

(2) and (3), as shown in Photographs No. 1, 2 and 3, respectively, indicate in a general way the performance of

the complete unit. 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 1+00 microns, as

well as many fibers of lint. (In these photographs, l/l6

inch corresponds to an actual dimension of about 160 microns.)

Photograph No. 2, for the tape 15 inches downstream of the

unit, shows several large particles up to about 150 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 8 ft downstream of the unit, shows

an absence of the larger particles of Photograph 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 unit in arresting Cottrell precipitate, as is also indicated by the discoloration test 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 or kerosene lamp smoke. 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 or kerosene smoke. Nevertheless, the downstream tapes, and the deposits on the afterfilter, 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.

No evidence of oil droplet entrainment in the effluent

air was observed, either by microscopic examination of the

downstream cellophane tapes, or by examination of the test

duct downstream of the unit after the tests.

Table 1

Face

Velocity

Inlet

Aerosol*

Ionizer

Voltage

Plate

Voltage

Pressure

Drop

Duration

of Test Efficiency

fpm kv kv inch WG Minutes percent

333 A 0 0 0.145 15 6.3**

333 A 13.2 6.1 .145 120 92.3

333 A 13.2 6.2 .142 130 92.1

333 A 13.3 6.2 .142 130 92.3

266 A 13.2 6.1 oON ro o 130 95.5

400 A 13.3 6.2 .190 130 33.0

333 S 13.3 6.2 .133 30 91.9

333 S 13.3 6.2 .133 20 91.9

333 S 13.3 6.2 .133 20 91.6

333 C 13.3 6.2 .139 3 98.3

333 C 13.3 6.2 .139 10 98.5

333 C 13.3 6.2 .139 10 93.6

* 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.

Table 2

Face

Velocity

Dirt

Load*

Ionizer

Voltage

Plate

Voltage

Pressure

Drop Efficiency**

fpm grams kv kv inch W.G. percent

333 41 13.5 6.2 0.139 98 . 5 (avg.)

165 13.5 6.3 .150 97.3

321 - - .153 98.5

44# 13.4 6.2 .1 58 9 8.8

561 - - . 166 98.0

731 - - .181 97.9

812 13.0 6 .

0

.196 97.2

887 13.3 6.2 .196 97.9

* Average mixture: 3.9$ lint, 96.1$ Cottrell precipitate

by weight.

** Efficiency determined with 100$ Cottrell precipitate.

Lint,

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VERTICAL SECTION

Air Filler Test Apparatus

Figure 1

Photograph No

Photograph No. 2

Photograph No. 3

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

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

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available from the Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of Standards, Washington 25, D. C.
NBS