NATIONAL BUREAU OF STANDARDS REPOR1

7892

PERFORMANCE TEST OF A WESTINGHOUSE ELECTROSTATIC

AIR CLEANER, PRECIPITRON VB-012

manufactured by

Westinghouse Electric Corporation

Staunton., Virginia

by

Ca^l W. Coblentz and Paul R. Achenbach

Report to

General Services Administration

Public Buildings Service

Washington 25 ^ D.C.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

1003-30-10630 May 31, 1963

NBS REPORT

7892

PERFORMANCE TEST OF A WESTINGHOUSE ELECTROSTATIC

AIR CLEANER, PRECIPITRON VB-012

manufactured by

Westinghouse Electric Corporation

Staunton, Virginia

by

Carl W. Coblentz and Paul R. Achenbach

Mechanical Systems Section

Building Research Division

to

General Services Administration

Public Buildings Service

Washington 25 * D.C.

IMPORTANT NOTICE NATIONAL BUREAU OF SI

for use within the Government,

and review. For this reason, tt whole or in part, is not authc Bureau of Standards, Washing

the Report has been specificall

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

ess accounting documents intended

; subjected to additional evaluation

2 listing of this Report, either in le Office of the Director, National

y the Government agency for which

copies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PERFORMANCE TEST OF A WESTINGHOUSE ELECTROSTATIC

AIR CLEANER, PRECIPITRON VB-012

by

Carl W. Coblentz and Paul R. Achenbach

1. INTRODUCTION

At the request of the Public Buildings Service, General

Services Administration, the performance characteristics of

an electrostatic air cleaner, Precipitron VB-012, manufactured by the Westinghouse Electric Corporation, Staunton,

Virginia, were determined. The scope of this examination

included the determination of the arrestance of the particulate matter in the laboratory air at different face

velocities and at different ionizer potentials, as well as

the determination of the pressure drop of the device and

its electric current requirements.

2. DESCRIPTION OF THE TEST SPECIMEN

The test specimen was supplied by the Air Conditioning

Division of Westinghouse Electric Corporation, Staunton,

Virginia. It was a redesign of this company’s commercial

electrostatic precipitator which was described in NBS

Report 6498, dated August 5 j> 1959. The device was designed

for use in residences with forced hot air heating systems

where a higher degree of air purification is desired than

can be obtained with the conventional type of furnace

filters

.

The outside dimensions of the filter were 28 x 22 1/2 x

18 1/2 in., the air inlet measured 24 x 18 1/4 in., and the

outlet measured 16 3/16 x 14 1/4 in. The air flowed first

through the pre-filter which consisted of two identical

pleated foam filters, installed side by side, each about

15 3/4 x 10 3/4 1 3/4 in. with a total media area of about

3.4 sq. ft. The medium was made of plastic foam approximately
- 2-

45 pores per square inch and 1/8 in. thick. Each of the

two ionizer and collector sections had a face area of

13 1/4 x 10 3/4 in., i.e., 2 sq. ft. total face area for

the two sections. There were 7 ionizer wires in each

section. The 31 collector plates in each section were

10 3/4 in. long and spaced 0.34 in. center-to~center, with

a total plate area of approximately 65 sq. ft. The prefilters as well as the ionizer and collector sections could

be removed individually from the housing for the purpose of

cleaning.

The frames of the ionizer and collector sections were

grounded to the housing, while the ionizer wires and the

charged plates were connected to the positive side of the

power pack by means of insulated contact springs mounted

inside the panel door. The power pack was installed inside

the housing and was equipped with a rheostat in series with

the primary winding of the transformer to adjust the ionizer

voltage according to the operating conditions. The transformer output was rectified by means of a conventional halfwave doubler arrangement. Both ionizer wires and collector

plates were operated at the same D.C. potential.

After completion of the test, it was noted that the performance determined with the test specimen did not agree with

the values observed in the factory laboratories. It was

then found that the outlet area should have been enlarged to

permit free passage of the effluent air over the full width

of the collector sections. The housing was designed for

devices with different air flow rates and had an original

outlet opening commensurate with a single ionizer - collector set. It was to be cut out when installed to

match the existing duct system, but it should not be smaller

than the collector area. The outlet area was enlarged

from 16 3/16 x 14 1/8 In. to 22 1/2 x 14 1/8 in., I.e.,

from approximately 0.8 to 1.2 times the face area.
-3-

3. TEST METHOD AND PROCEDURE

The arrestance determinations were made in accordance with

the NBS Dust Spot Method described in a paper by R, S. Dill

entitled "A Test Method for Air Filters” (ASHVE Transactions* Vol. 44* p. 379 j 1938). After the device was

installed in the air filter test apparatus* it was carefully

sealed to prevent inward leakage through cracks. Samples

of air were drawn from the center points of the test duct

2 feet upstream and 8 feet downstream of the filter at

equal rates and passed through equal areas of Whatman No. 4l

filter paper. The light transmission of each sampling

paper was measured before and after each arrestance determination on the same area of the paper. The two papers

used for any one arrestance determination were selected

to have the same light transmission when clean. A similar

increase of the opacity of the two sampling papers was

obtained by passing the sampling air through the upstream

paper only part of the time while operating the downstream

sampler continuously. This was accomplished by installing

one solenoid valve in the upstream sampling line and

another one in a line bypassing the sampler. The solenoid

valves were operated by an electric timer and a relay so

that one was open while the other one was closed during

any desired percentage of the 5-roinute timer cycle*

reversing the position of the two valves during the

remainder of the cycle. The arrestance* A (in percent)*

was then determined with the formula:

AD

A = 100 - T x

where T is the percentage of time during which air drawn

through the upstream sampler* and AU and AD are the

observed changes in the opacity of the upstream and downstream sampling paper* respectively.
-4-

The power pack was connected to the laboratory electric

supply line through a variable transformer and the performance of the device was determined at four different

input voltages to the power pack ranging from 90 volts to

120 volts with a fixed medium setting of the series rheostat.

The ionizer potential was measured with an electrostatic

kilovoltmeter . The input current was also observed.

Arrestance measurements were conducted at six air flow

rates ranging from 600 cfm to 1600 cfm in 200 cfm steps,

i.e., at face velocities of 300 ft/min. to 800 ft/min.

corresponding to the 2 sq . ft. free area of the inoizer

and collector sections.

After a series of arrestance determinations had been made

with the particulate matter in the laboratory air as the

aerosol, it was planned to determine the dust-holding

capacity of the device by introducing Cottrell precipitate

at a rate of 1 gram per 1000 cu. ft. of air. This test

had to be discontinued when it was noticed that the feeding

of Cottrell precipitate produced an excessive arcing of

the device and that the arcing decreased only to approximately one discharge per second when the potential was

lowered to 7*200 volts.

4. TEST RESULTS

The arrestance values determined at different face velocities

and ionizer voltages with the original outlet area of 16 3/16

x 14 1/4 in. are shown in Table 1.

TABLE 1

Observed Arrestance Values at Different Face

Velocities and Ionizer Voltages

Voltage

Supply Ionizer 300

Face Velocity, ft/min.

400 500 600 700 800

90 7, 450 93.5 76.8 69.5

100 7,850 — 86.5 80 .

6

69.0

no 8,200 — 88.8 — — 120 8,550 95.0 .94.2 90.6 86.8 -- 79.4
- 5

-

By plotting the arrestance values and ionizer voltages in

Figure 1 , a family of smooth curves could be drawn that

show with acceptable accuracy the arrestance at each of

the six face velocities at varying ionizer voltages. It

will be noted that the highest arrestance values of 95.0

percent was observed at the lowest face velocity of 300

ft/min. and the lowest arrestance of 69 percent was determined at 800 ft/min. face velocity. The effect of the

ionizer voltage became increasingly greater with higher

face velocity* whereas the difference of arrestance between

the lowest recommended ionizer voltage of 7*500 volts and the

highest of 8.500 volts was only about 1.4 percent (93.6 - 95-0 percent) at 300 ft/min. face velocity* the difference

at 800 ft/min. face velocity was approximately 16. 7 percent

(63.0 - 79.7 percent).

The dashed curves in Figure 2 were obtained by crossplotting from Figure 1 the values of arrestance and face

velocity for three selected ionizer voltages. The convergence of these curves at the lowest observed face velocity

indicated a small difference in arrestance resulting from

changes of the ionizer voltage* as revealed by an almost

flat curve in Figure 1 . Also shown in Figure 2 are three

arrestance values observed after the outlet area was

increased from 16 3/16 x 14 1/8 in. to 22 1/2 x 14 1/8 in,*

and a family of three solid lines was drawn analogous to

the dashed lines to present a close approximation to the

performance that could be expected for a range of face

velocities and ionizer voltages when the device was

operated with the correct outlet area. Values taken from

Figure 2 are shown in Table 2 . TABLE 2

Arrestance Values at Different Face

Velocities and Ionizer Voltages

(Extrapolated from Fig. 2 * for Enlarged Outlet Area)

Ionizer Face Veclcity* ft/min.

Voltage 300 400 500 600 700 800

7*500 94.0 90.9 86.2 8l.O 75.5 70.0*

8*000 94.8 92.7 89.4 85.7 81. 8 77-9

8*500 95.6 94.7 92 . 7

* ' 90.2 87.5 84 . 7

* Observed values
- 6 -

The above values, though determined by a graphical

similarity procedure, are believed to correspond to the

arrestance of the device when operated at the design outlet area within about ±1/2 percent.

The overall performance of the power pack is shown in Table

3, indicating the effect of the supply voltage on the

ionizer voltage, the maximum and minimum values obtained

by means of the adjustable series rheostat, and the values

of the supply current demand.

TABLE 3

Performance of Power Pack

AC SUPPLY IONIZER

CHARACTERISTICS VOLT. RANGE TEST VALUES

Current Amp. DC AC

Volts Min. Max. Min. Max. Voltage Amp

.

90 0.22 0.33 7,000 7*900 7,450 0.26

100 0.26 0.40 7*300 8,350 7,850 0.32

110 0.30 0.47 7,650 8,750 8,200 0.37

120 0.34 0.55 7*950 9*100 8,550 0.42

It will be noted that an increase of 30 percent in the ionize

voltage. from 7, 000 volts to 9*100 volts. produced ia supply

current increase from 0.22 amp. to 0.55 amp., i.e., 150 percent. However, no change of the ionizer voltage nor the

supply current was observed as an effect of a change in the

air flow rate.

No discharges in the ionizer or collector were noticed when

the device was operated with laboratory air. When Cottrell

precipitate was added to the air stream, the arcing produced

drops of the ionizer voltage to about half its operating

value with a noticeable increase in the supply current.
-7-

The pressure drop across the test specimen is shown in Table

4 at different face velocities and with the original outlet

area of 16 3/16 x 14 1/4 in. and also after the outlet area

was enlarged to 22 1/2 x 14 1/4 in.

TABLE 4

Pressure Drop across Filter

Face Velocity Pressure Drop, in. W.G.

ft/min. Prig. Outlet Enlarged Outlet

300 0.058 0.055

400 0.093 0.080

500 0.140 0.115

600 0.193 0.161

700 0.255 0.210

800 0.320 0.265

The values presented in this table are plotted as smooth

curves in Figure 3 showing that the decrease in pressure

drop resulting from enlarging the outlet area was insignificant when the device was operated at low air flow rates,

but becomes quite considerable at the higher flow rates.

/Vrrestance v/s Plate Voltage at Different Face Velocities

! Veloc

Si

Face Velocity, ft/min

Pressure Drop v/s Air Flow Rate

^ H- ;-H-l

-r t H-f-t—f Ht —•» T I 1-.—H 1 —M- -• *-)-! r-r—!

1

Face Velocity ft/min

U. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A.‘V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C.,and

Boulder, Colorado, 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 of the

front cover. WASHINGTON, D C.

Electricity. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurements.

Dielectrics. High Voltage. Absolute Electrical Measurements.

Metrology. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering Metrology.

Mass and Volume.

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Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. Combustion

Controls.

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Inorganic Solids. Engineering Ceramics. Glass. Solid State Chemistry. Crystal Growth. Physical Properties.

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Radio Standards Engineering. High Frequency Electrical Standards. High Frequency Calibration Services. High

Frequency Impedance Standards. Microwave Calibration Services. Microwave Circuit Standards. Low Frequency

Calibration Services.

Joint Institute for Laboratory Astrophysics- NBS Group (Univ. of Colo.).
J