NATIONAL BUREAU OF STANDARDS REPORT

6875

PERFORMANCE TEST OF AN ELECTRO-AIR

ELECTROSTATIC AIR CLEANER, MODEL 20-1

by

Carl W. Coblentz and Paul R. Achenbach

Report to

General Services Administration

Public Buildings Service

Washington 25 j, D. C.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OE STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the Nation^ 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 und methods for making measurements consistent with these standards; the determination of physical constants and

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Publications

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

NIBS PROJECT MBS REPORT

1003-30-10630 June 20, i 960 6875

PERFORMANCE TEST OF AN ELECTRO-AIR

ELECTROSTATIC AIR CLEANER, MODEL 20-1

by

Carl W„ Coblent z and Paul R. Achenbach

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

to

General Services Administration

Public Buildings Service

Washington 25., D. C,

IMPORTANT NOTICE

NATIONAL BUREAU OF S' intended for use within the

to additional evaluation and

listing of this Report, either the Office of the Director, N

however, by the Governmenl

to reproduce additional copi

progress accounting documents Approved for public release by the ,rmal| y published it is subjected

. . r , reproduction, or open-literature

Director of the National Institute Of , s j on j $ obtained in writing from Standards and Technology (NIST) Such permission is not needed, on October 9, 2015. prepared if that agency wishes

S. DEPARTMENT OF COMMERCE

PERFORMANCE TEST OF AN ELECTRO- AIR.

ELECTROSTATIC AIR CLEANER,, MODEL 20-1

by

Carl W. Coblent z and Paul R. Achenbach

1. INTRODUCTION

At the request of the Public Buildings Service, General

Services Administration, the performance characteristics of an

Electro-Air electrostatic air cleaner were determined. The

scope of this examination included the determination of the arrestance of the particulate matter in the laboratory air and of

Cottrell precipitate, the pressure drop, and the dust holding

capacity of the specimen.

2. DESCRIPTION OF TEST SPECIMEN

The air cleaner was manufactured and supplied for test purposes by the Electro-Air Cleaner Company of McKees Rocks, Penna,,

and was designated as Model 20-1.

The collector cell assembly was 23 13/16” high and 19 1/2”

wide, presenting a gross face area of 3*23 sq ft. The frame of

the cell as well as the 29 charged and 28 grounded plates were

made of aluminum. The plates were spaced 5/16” center to center

and measured 10 3/4" x 23”. Each plate was 0„ 020” thick and had

two V-shaped reinforcing crimps. There were II ionization wires

separated by elongated pear-shaped separators. The cell was

equipped with an after-filter, type Airsan AF 150, 18 1/4” x

22” x 1", Before installation Into the test apparatus, the cell

was sprayed with an adhesive, type DAX, furnished by the manufacturer.

The power pack was designed to supply a potential of 8,2 KV

to both ionizer wires and collector plates. Two 200-watt light

bulbs in series with the primary transformer winding functioned

as a ballast when the plate current increased during plate discharges. Overload protection for the power pack was provided

by a 2.4 amp breaker switch and a 2 amp fuse. The actual line

current could be observed on an ammeter with a range of 0-2

amperes. The adjustment of the electrostatic potential was accomplished with a rheostat in the primary of the transformer.

- 2 -

The high voltage output of the transformer was rectified with

a full-wave selenium rectifier which was shunted by a bleeding

resistor to prevent shock from, residual energy.,

The arrestance measurements were made in accordance with

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

and entitled "A Test Method for Air Filters/’ (ASHVE Transactions^ Vol. 44, p. 379 5 1938)*

For test purposes, the collector cell was installed in the

test apparatus and carefully sealed to prevent inward leakage

of air except through the measuring orifice. The desired rate

of air flow through the filter was established and samples of

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

upstream and eight feet downstream of the test specimen at equal

rates and passed through known areas of Whatman No. 4l filter

paper. The change of the opacity of these areas was determined

with a sensitive photometer which measured the light transmission

of the same spot on each sampling paper before and after the test.

The two sampling papers used for each test were selected to have

the same light transmission readings when clean.

For determining the arrestance of the filter, with Cottrell

precipitate as the test- dust, different size areas of sampling

papers were used upstream and downstream of the filter in order

to obtain a similar increase of opacity on both sampling papers.

The arrestance, A (in percent), was then calculated by the

formula

where S-g and Sg are the upstream, and downstream sampling areas

and AU and AD the observed changes in the opacity of the upstream

and downstream sampling papers, respectively.

For determining the arrestance of the particulate matter in

the laboratory air, equal, sampling areas were used for the upstream and downstream samplers. A similar increase of the opacity of the upstream and downstream filter papers was then obtained by passing the sampling air through the upstream paper

3 . TEST METHOD AND PROCEDURE

A

(
.
“ 3

-

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 as a by-pass.

The 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-minute 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 following

formula

A = 100 - T x AD

AU

where T is the percentage of time during which air was drawn

through the upstream sampler, AU and AD being the changes of

opacity of the sampling papers, as previously indicated.

The power pack was connected to the laboratory electric

line through a variable voltage transformer. The rheostat of

the power pack was adjusted so that the energizing voltage was

8.2 KV at 117 volts input. The rheostat setting was not changed

during the test and the plate potential was measured with an

electrostatic kilovolt-meter at an input voltage of 117 ± 1/4

volts

.

The tests were attended by two representatives of the manufacturer, who suggested minor modifications to the arrangements

of the collector cell in the test apparatus after observing that

the arrestance values at various air flow rates were considerably

lower than had been expected. When no improvement of the arrestance was observed, it was agreed that an earlier model of

the test specimen would be retested to ascertain whether there

was any discrepancy in the test procedure or a malfunction of

the test apparatus. This older cell had been tested at the NBS

in 1957 and had at that time an arrestance of 91.2$ using a 2”

thick after-filter. When it was now tested with a 1 ” thick after

filter, the arrestance was 90 . 5 $. This was accepted by the manufacturer's representatives as evidence that the apparatus was

functioning satisfactorily.

A total of twenty arrestance determinations were made using

either the particulate matter of the laboratory air or Cottrell

precipitate as the aerosol. After making two arrestance determinations, each at the rated air flow rate of 1650 cfm (510 ft/

min gross face velocity) and at 20 percent below and above this

4-

air flow rate, the filter was loaded with Cottrell precipitate

and lint to a dust load of about 2/3 grams per cfm rated flow

rate, i.e. 1095 grams. A number of arrestance determinations

were made at selected intervals while the device was being

loaded and a final determination was made at the end of the

test

.

4. TEST RESULTS

A summary of the test results is presented in Table 1,

which shows the air flow rates, cumulative dust loads, plate

and ionizer voltages and the supply current of the power pack,

the combined pressure drop across the collector cell and after

filter and the arrestance values determined with Cottrell precipitate and with the particulate matter in the laboratory air.

The effect of the dust load on the pressure drop and on

the arrestance are plotted in Fig. 1; the effect of the air

flow rate on the arrestance of the filter before loading is

plotted in Fig. 2.

The pressure drop across the device increased from 0.307

in. W.G. to 1.11 in. W.G. as the filter was being loaded to a final value of 1095 grams/sq ft of Cottrell precipitate and

lint, corresponding to 2/3 grams per cfm rated air flow. During

this time the arrestance of atmospheric air borne dust decreased

approximately linearly from 88.8 percent to 84.2 percent, whereas

the arrestance of Cottrell precipitate decreased from 98 . 0 percent to 97-1 percent.

The arrestance of the particulate matter in the laboratory

air at 1320 cfm. air flow rate was 92.4 percent and at 1980 cfm

84.8 percent. These flow rates are 20 percent below and above

the rated 1650 cfm.

An examination of the collector cell after the conclusion

of the test showed that all plates were evenly covered with a light layer of dust. However, there was a large number of

bridges up to about 3/8 in. wide between the plates, apparently

formed by lint particles. These bridges were especially numerous near the downstream sides of the collector plates. Practically no bridges were found in the first two inches at the inlet

end of the collector cells. As many as 22 bridges were counted

between two adjacent plates.

-5-

Table 1

Performance of Electro-Air,, Model 20-1

(Gross Face Area 3-23 sq ft)

Ionizer

Air and

Flow Dust Plate Pressure Aerosol

Rate Load Voltage Current Drop Arrestance Used

cfm g KV amp in. W.G. **

1320 0 8.2 0.55 0.205 92.4* A

1650 0 8.2 0.55 0.307 88 . 8

* A

1980 0 8.2 0.55 0.436 84.8* A

1650 32 8.2 0.60 0.308 98 . 0* B

1650 373 8.2 0.60 0.394 87.8 A

1650 452 7-9 0.65 0.432 97-6* B

1650 659 7.8 0.65 0.559 85.8 A

1650 1095 7-7 0.65 1.11 97-1* B

1650 1095 8.2 0.63 1.13 84.2 A

* Average of two or more tests

.

** A - Particulate matter in laboratory air.

B - Cottrell precipitate in laboratory air.

USCOMM-NBS-DC

6oo 700

Dust Load, grams per square foot

500 1000 1100

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ELECTRO - AIR Model 20-1

1500 1600 1800 2000

Air Flow Rate

UiS. DEPARTMENT OF COMMERCE

Frederick H. Mueller, Secretary NATIONAL BUREAU OF STANDARDS

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

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