NATIONAL BUREAU OF STANDARDS REPORT

7772

PERFORMANCE TEST OF THE ROLL-O-TRON

ELECTRONIC AIR CLEANER, MODEL #3~50HV

manufactured by

American Air Filter Company

Louisville, Kentucky

by

Carl W. Coblentz and Paul R. Achenbach

Report to

Public Buildings Service

General Services Administration

Washington, D. C.

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

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

' l orvs-m ^ ~

‘ JV , . V NBS REPORT

December 26 > 1 962

PERFORMANCE TEST OF THE ROLL-O-TRON

ELECTRONIC AIR CLEANER, MODEL #3-50HV

manufactured by

American Air Filter Company

Louisville, Kentucky

Carl W. Coblentz and Paul R. Achenbach

Mechanical Systems Section

Building Research Division

Public Buildings Service

General Services Administration

Washington, D* C.*

by

to

IMPORTANT NOTICE

NATIONAL BUREAU OF S' progress accounting documents

1 1 A j reps uyutuun? ui up"ii*nici <uui c

listing of this Heport, elthei Director of the National Institute of ssion is obtained In writing from

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
'

:

•
Performance Test of the Roll-O-Tron

Electronic Air Cleaner,, Model 3-50HV

Manufactured by

American Air Filter Company

Louisville, Kentucky

by

C. Wo Coblentz and P. R. Achenbach

1 . INTRODUCTION

At the request of the General Services. Administration,

Public Buildings Service, the performance characteristics of

the Roll-O-Tron electronic air cleaner. Model #3-50HV, were

determined. The scope of this examination included the

determination of the arrestance of the particulate matter in

the laboratory air and the pressure drop of the unit, the

electrical characteristics of the agglomerator and the dustholding capacity of the collector at a face velocity of 500

ft/min.

2. DESCRIPTION OF TEST SPECIMEN

The test specimen was manufactured and supplied for test

purposes by the American Air Filter .Company of Louisville,

Kentucky, and was identified as their Roll-O-Tron, Model

#3-50HV. The equipment was a combination of an electrostatic

precipitator and an automatic renewable media air filter,

designed to be used in series. By operating the electrostatic

precipitator without adhesive on the collection plates* only

a small dust load could accumulate on them. It operated on

the principle that the electrostatic precipitator collected

•small air borne dust particles and agglomerated them on the

collector plates. Then, after dust had been deposited to a certain thickness, it is blown off the collector plates by

the air stream and drawn into the automatic renewable filter

downstream of the precipitator, where the rather large

agglomerations are arrested in the glass fiber mat in a

much higher proportion than the individual dust particles

would have been.
fjx
- 2 -

The test specimen wa3 designed for an air flow rate of

5,000 cfm at a face velocity of 500 ft/min. By reducing the

open area to 24 x 24 in. to match the cross section of the

test duct while maintaining the 500 ft/in. face velocity the

performance characteristics of the device were not significantly

altered while the air flow rate of 2,000 cfm was commensurate

with the capacity of the NBS test apparatus.

The. two Identical agglomerator units comprising the

electrostatic precipitator were Installed one above the other

in the same housing used for the automatic renewable filter.

The individual agglomerator units as well as the renewable

glass fiber medium were essentially the same design as those

of the Electrocell and Roll-O-Matic units, respectively,

manufactured by the American Air Filter Company and previously

described in NBS Reports 6952 and 6947 . The type SG-5V power

pack used a full-wave voltage-doubler rectifier circuit for

the ionizer supply and a half-wave rectifier for the plate

supply.

3. TEST METHOD AND PROCEDURE

The arrestance determinations of the test specimen were

made with the particulate matter in the laboratory air as the

aerosol using the NBS Dust Spot Method as described in a

paper by R. S. Dill entitled "A Test Method for Air Filters”

(ASHVE Transactions, Vol. 44, p. 379, 1938).

The device was installed in the test apparatus and carefully sealed to prevent bypass of air or inward leakage into

the test apparatus except through the measuring orifice.

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. 41

filter paper. The light transmission of each sampling paper

was measured before and after each arrestance determination on

the same area of the papers. 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
smnn 1

1

-
-3-

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~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 formula:

A = 100 - T x AD

AU

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

through the upstream sampler,, and AU and AD are the observed

changes in the opacity of the upstream and downstream sampling

paper., respectively.

Arrestance determinations were made at the beginning and

at the end of the test and at several intermediate loading

conditions. The filter was loaded with Cottrell precipitate

to which cotton linters were added in a ratio of 4 parts to

every 96 parts of Cottrell precipitate. The Cottrell

precipitate had been previously • sifted through a 100-mesh

screen and was injected into the air stream at a ratio of 1

gram per 1,000 cu. ft. of air. The lint was prepared by

grinding No. 7 cotton linters through a Wiley mill with a

4-millimeter screen.

The pressure drop across the device was recorded at the

beginning of the test., after the introduction of each 20-gram

increment of Cottrell precipitate into the test duct, and after

each arrestance determination.

The power pack was connected to the laboratory electric

supply line through a variable voltage transformer and the

inoizer and plate voltages were measured with the input

voltage adjusted to 115 volts. While the input voltage

to the power pack was allowed to drift with the line voltage

between readings, it was adjusted to its original value before

subsequent readings of the D.C. potentials, which were taken

with an electrostatic kilovoltmeter . With the input voltage
.
-4-

to the power pack adjusted to 115 volts transformer taps were

selected that furnished an ionizer potential of 13,300 volts

and a plate voltage of 5*400 volts.

A number of arrestance determinations were made during the

early part of the test which indicated an average value of

88 percent. In order to improve the arrestance of the unit

the factory representative, who attended the test, changed the

ionizer wires to a smaller size and placed a metal strip, about

1 inch wide between the two agglomerator sections to close an

air gap between them. These modifications were made to improve

the ionization without increasing the potential and also

to prevent the flow of un-ionized aerosol between the two

sections of the agglomerator.

4. TEST RESULTS

Table 1 shows the performance of the device during the

second half of the test. While 1376g of dust, i.e. 688g/ft.

width, were introduced into the test apparatus the media

advanced 27 in. in 6 increments ranging from 3 1/2 in. to

5 1/2 in.- Seven arrestance determinations made during this

time showed values ranging from 89.7 percent to 91.2 percent,

averaging 90.7 percent.

The medium was then advanced approximately 3 ft. and

another arrestance determination was made using a clean

portion of the media as the collector. The arrestance was

90\9 percent, then, indicating that the loading condition did

not measurably affect the arrestance of . the device. When the

metal strip that had been placed between the two agglomerator

sections to close an air gap was removed, the arrestance

decreased to. 88.7 percent. This indicates that un-ionized

aerosol leaking between the two agglomerator sections had

reduced the arrestance significantly. Though not experimentally

proven, it appears that the installation of this metal strip

had a larger effect in improving the arrestance than the

increase in size of the ionizing wires.

The pressure drop across the complete device ranged from

0.352 to 0.460 in. W.G. during the test. The average pressure

drop at the beginning of the media advance cycle was 0.458 in.

W.G. and at the end of the advance cycle was 0.370 in. W.G.,

corresponding to an average pressure differential of 0.088 in.

W.G.
'
-5-

The ”Dust-Holding Capacity” of the filter media, i.e.

the dust load received per unit area, was computed from Figure

1. This figure shows the cumulative advance values plotted

against the cumulative dust load and the straight line that best

fitted the individual points of the observation. The slope of this

line expressed the dust-holding capacity of the mat. According

to the graph, while the media advanced 2

in., from the 20-inch

position to the 46-inch position, the dust load increased from

967g/ft. width to l637g/ft. width or by 670g/ft. width. The dustholding capacity, D, was therefore:

D = 670 x ^

= 309g/sq.ft.

USCOMM-NBS-DC

TABLE 1

Performance of Roll-O-Tron Electronic Air Cleaner

Model #3-50HV

Dust Load

g/ft . width

Mat Travel , In*

Advance ' Total

Pressure Drop,

Start

in. W.G.

End

Arrestance

%

937 — 19 1/2 0.360 0.360 90.9

937 — 19 1/2 0.360 O. 36O 91.2

1062 / 3 1/2 23 0.458 O .388 —

1166 5 1/2 28 1/2 0.460 0.352 —

1312 4 32 1/2 0.458 O .370 —

1427 5

• 36 1/2 0.459 0.380

1438 — 36 1/2 0.398 0.398 89.8

1438 — 36 1/2 0.398 0.398 . 89.7

1520 5 4l 1/2 0 . 458 ' 0.370 —

1608 — 4l 1/2 0.439 0.439 91-1

1625- 5 46 1/2 0.454. 0.360 -- 1625 — 46 1/2 0.360 0.360 90.7

1625 — 46 1/2 0.360 0.360 91.2

Dust

Load

.

grams

per

foot

widt

MAT TRAVEL V/S DUST LOAD

MAT TRAVEL, inches

U. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

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

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