NATIONAL BUREAU OF STANDARDS REPORT

6673

AIR DELIVERY AND ARRESTANCE TESTS OF A

"PURITRON" AIR CLEANER, MODEL F-20

Manufactured by

Michael Electric Company

New Haven, Connecticut

by

Carl W. Coblentz

and

Paul R. Achenbach

Report to

Bureau of Medicine

Food and Drug Administration

Department of Health, Education, and Welfare

Washington, D. C.

<NBS>

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; in- vention 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. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the

Bureau’s unique competence is required. The scope of activities is suggested by the fisting of

divisions and sections on the inside of the back cover.

Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers. These 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 periodicals available from

the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary

and preliminary reports on work in progress; and Basic Radio Propagation Predictions provides

data for determining the best frequencies to use for radio communications throughout the world.

There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series,

'Handbooks, Miscellaneous Publications, and Technical Notes. 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 ($1.50), available from the Superintendent

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

NBS PROJECT NBS REPORT

1000-30-10630 February 24, i960 6673

AIR DELIVERY AND ARRESTANCE TESTS OF A

"PURITRON" AIR CLEANER, MODEL F-20

Manufactured by

Michael Electric Company

New Haven, Connecticut

hy

Carl W. Coblentz and Paul R. Achenbach

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

to

Bureau of Medicine

Food and Drug Administration

Department of Health, Education, and Welfare

Washington, D. C.

NATIONAL BUREAU Of STA

Intended for use within the G to -additional evaluation and re listing of this Report, either Ir the Office of the Director, Nat however, by the Government t to reproduce additional copies

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 201 5.

ogress accounting .documents

Tally published It Is subjected

sproductlon, 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
,

•
AIR DELIVERY AND ARRESTANCE TESTS OF A

’’PURITRON” AIR CLEANER, MODEL F-20

by

C. W. Coblentz and P. R. Achenbach

1. INTRODUCTION

At the request of the Bureau of Medicine, Food and Drug

Administration of the Department of Health, Education and Welfare, tests were made of the air cleaning characteristics of a Puritron Air Cleaner manufactured by the Michael Electric Co.

Inc. of New Haven, Connecticut. The scope of the investigation

was limited to measurements of the arrestance of atmospheric

dust, the air delivery of the unit with the filter in a clean

condition and also with it partially loaded with dust and lint,

and qualitative observations of the arrestance of ragweed pollens

and tobacco smoke.

2. DESCRIPTION OF TEST SPECIMEN

The test specimen was a Puritron model F-20, manufactured

by Michael Electric Company, Inc., New Haven, Connecticut. It

was supplied to the National Bureau of Standards by the Food and

Drug Administration, Bureau of Medicine and was Identified as

their specimen 47-603P, 11-26-58, AJB. The overall dimensions

of the unit were 9 1/2” long, 7” high, and 7 1/8” deep. An outlet grille 2 5/16” wide and 2 5/8” high protruded 3/8” from the

front side. Air entered the casing through five 3" long louvers

on the top of the unit. The housing was made of sheet steel with

a gray enamel coating. Figure 1 is a three-quarter view of the

specimen showing the inlet louvers and outlet grille.

The incoming air passed around three germicidal lamps of 4

watts each, made by General Electric Co., and then through a ”Dust-Stop” fiber glass air filter made by the Owens-Corning

Corp. The outside dimensions of the filter were 6” x 4” x 7/8”

thick with an effective face area of approximately 2) 1/4” x

4 1/4”. The downstream side of the filter was placed against

the 2 1/2” I.D. intake opening of the fan housing. The rotating

element of the fan consisted of a flat steel sheet about 3” x 1”

which was attached to the shaft of an electric motor, along the

shorter center line of the sheet to form a paddle-wheel type of

element. The unit was equipped with an electric cord for connection to an ordinary convenience outlet.
.

*
Figure

- 2 -

3. DESCRIPTION OF TESTS

3.1 Determination of the Air Flow Rate

Measurement of the air velocity at the plane of the outlet

grille, using a thermocouple anemometer, produced readings over

a range from 700 to below 100 ft/min. Five directional v&tie.s

turned slightly upward and a 1/4” wide vertical brace in the

center of the outlet apparently produced secondary vortices at

the grille. Due to this non-uniformity of the velocity at the

face of the grille, it was necessary to determine the velocity

at a large number of stations to obtain an average.

A cardboard collar 2 5/8" x 2 3/8" was placed snugly around

the grille. It projected 7/8” at the top and 13/16” at the bottom in order to provide a vertical outlet plane. The collar was

then marked at 1/4-inch intervals along the top and one side to

identify a measurement pattern consisting of 90 equal areas.

The velocity pressure of the air stream was determined with

a 1/16” O.D. nickel impact tube and a micromanometer that could

be read to the nearest 0.001 in. W.G. The nozzle end of the impact tube was 10 in. long, thus avoiding a disturbance of the air

flow. It was placed successively at the center of the marked

square areas in the outlet plane of the cardboard collar. There

was a strip of 1/16” width left around the periphery of the collar

not covered by the 90 squares. Disregarding the air flow through

the area of this strip, the total air flow rate of the unit, Q (cfm),

was then the sum of the air flow rates determined for each individual square, q (cfm)

Q = £q (cfm)

where: q = a x v (cfm)

a = (1/4 x 1/12) 2 (sq ft)

v = 4008 x (ft/min) for air at standard conditions

h = the velocity head determined at the center of each 1/4”

square (in. W.G.)

Therefore

:
,

1
-3-

or

Q = (1/4 x 1/12) 2 x 4008 x £/h~

Q = 1.735 x £ l/h" cfm

When making these velocity pressure measurements with the

clean filter in place* positive velocity pressures could be observed in 62 squares. The lower 1/2" of the outlet showed either

zero or a negative velocity pressure which indicated that air was

aspirated into a portion of the outlet. A suction pressure of

0,004 in. W.G. was observed in several squares corresponding to

an inward flow velocity of approximately 231 ft/min. In computing

the total air delivery* both the inward air flow and the air flow

in the 1/16" wide strip at the periphery were neglected. Either

of the two amounted to less than 5 percent of the total air flow

rate* and the inward flow in the lower part of the collar was estimated to be higher than the outward flow along the upper edge.

The velocity in the peripheral strip at the sides of the collar

was near zero at all places. The air flow rate* thus determined*

for the unit with a clean filter was 12.3 cfm. This value is believed correct to ±1 cfm.

The Puritron unit was then installed in the test duct of the

NBS air filter apparatus and Cottrell precipitate and cotton lint*

in a ratio of 96 to 4 by weight* was introduced while the Puritron

was operated. After the weight of the filter had increased by 2.7

grams* another series of velocity measurements was made using the

same stations of observation. A total air flow rate of 7-84 cfm

was calculated from positive pressure heads observed in 64 individual squares. No aspirating air flow was observed in the lower

section of the outlet during this test. Based on the velocity

patterns in a vertical plane observed during this test and the

preceding test with a clean filter* it was estimated that the

average air flow rate in the remaining 26 squares did not exceed

100 ft/min. On this basis* the total air flow rate did not exceed 8.97 cfm for this test. An air velocity of 100 ft/min corresponds to a velocity head of 0.00067 in- W. G. * which is below

the sensitivity of the micromanometer used. On the basis of these

observations* the total air flow rate with a load of 2.7 grams of

dust was between 7-8 cfm and 9-0 cfm. This dust load corresponds

to a value of about 40 grams/sq ft of face area and is less than

that which can be accumulated on similar filters for air conditioning purposes at full load by a factor of three or four.
’

-

: V

.

'
-4-

3.2 Determination of Arrestance

Arrestance determinations were made by the NBS ’’Dust Spot

Method” using the particulate matter in the laboratory air as

the aerosol. The test method is described in the paper, "A Test

Method for Air Filters,” by R. S. Dill (ASHVE Transactions,

Vol. 44, p. 339, 1938).

The Puritron was placed on a table and operated from the

115-volt electric service. The upstream and downstream samples

of air were drawn from the vicinity of the air inlet louvers and

about 2 in. horizontally from the center of the upper edge of

the outlet grille, respectively. The sampling air was passed

through known areas of Whatman No. 4l filter paper at very nearly

equal flow rates as determined with two calibrated orifice flow

meters. The change of opacity of the exposed areas of the sampling papers was determined with a sensitive photometer which

measured the light transmission of the same area on each 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. The arrestance. A, was then calculated by the formula:

fD ADh

x 0 x —- x 100, percent

S U AU J

where: F^ = flow rate of downstream sampling air

Fy = flow rate of upstream sampling air

S-p = collection area on downstream filter paper

= collection area -on upstream filter paper

AD = change in opacity of downstream sample

AU = change in opacity of upstream sample

The tests were conducted with a clean filter in a calorimeter

room where the relative humidity could be raised above that normally

prevailing in a heated room during the heating season. Six arrestance determinations were made at the normal relative humidity

and four measurements of the arrestance were made at higher relative humidity.

In order to determine the effect of the ultraviolet lamps on

the arrestance of the unit, half of these tests were made with the

lamps removed and the other half with the lamps operating. Table 1

shows the values of the arrestance determined under these conditions.

-5-

Table 1

Arrestance of Particulate Matter in the Laboratory Air

Relative Humidity 21 1 CM OJ tR 54-60^

Ultraviolet Lamps In out in out

Arrestance, %

Test Series 1 19.7 21.6 31.4 CM

1

—

1

Test Series 2 19.9 30.7 40.2 41.6

Test Series 3 22.7 16.4

Average Arrestance, % 20.8 22.9 35.8 41.4

Although there was some variation in the arrestance values

determined for repetitive tests under the same conditions, it

appears that the arrestance was a little higher on the average

when the germicidal lamps were removed than when they were in

and operating, at both the higher and lower level of relative

humidity. The arrestance at the higher humidity level was definitely larger than at the low humidity level.

3.3 Removal of Cigarette Smoke and Ragweed Pollen

After making the arrestance tests, but prior to loading the

filter with the 2.7 grams of dust and lint, cigarette smoke was

blown from the mouth of a staff member through a paper straw into

the vicinity of the intake louvers of the operating specimen.

Figure 1 shows the procedure used and the qualitative result. The

photograph clearly shows a significant amount of the smoke emerging from the outlet grille after having penetrated the test specimen with the filter in place and the ultraviolet lamps operating.

Ragweed pollen was also introduced into the test specimen and

a microscopic slide was mounted approximately 1 in. from the outlet

grille. This slide was prepared with an adhesive and the deposit

by the effluent was exmained with a microscope. It showed after

each of several tests that ragweed pollen had passed through the

Puritron device and was deposited on the microscopic slide. No

quantitative data on the arrestance of ragweed pollen were obtained.

- 6 -

4. DISCUSSION AND CONCLUSIONS

a) The air delivery determined with a clean filter was 12.3

cfm ±1 cfm and, with a filter loaded with 2.7 grams of dust, was

8.4 cfm ±0.6 cfm.

b) The arrestance of particulate matter in the laboratory

air was lower when the germicidal lamps were installed and operating, than when they were removed. This difference may have been

caused by a somewhat higher air flow rate that probably resulted

from elimination of the flow resistance of the three lamps.

The arrestance increased by about 80 percent when the relative humidity level was increased from the range of 21-22$ to the

range of 5^-60$.

c) Cigarette smoke blown at the inlet of the unit could be

seen leaving the outlet grille as shown in Figure 1. The penetration of ragweed pollen fed into the unit was indicated by the

deposit of such pollen on a microscopic slide that had been mounted

close to the outlet grille.

d) An advertising folder for Puritron states that the Model

F-20 is suitable for a room with dimensions of 15’ x 15' • Such

a room, with an 8’ ceiling height, would have a volume of 1800

cubic feet. It is not unusual for residential living spaces to

have an outdoor air leakage of 1 airchange per hour, which, for

the example cited, would be equivalent to 30 cfm of outdoor air.

A calculation can be made to determine how much the Puritron

could reduce the particulate matter in a room of this size with an

outdoor air leakage of 30 cfm and no contribution to contamination

from inside the room, as follows:

If C 0 is the volumetric concentration of particulate matter

in the outdoor air, the total particulates entering the room per

minute would be 30 C 0

.

If Cp is the steady state volumetric concentration of particulates in the room after the Puritron has been operating for a sufficiently long time, the total particulates leaving the room

per minute would be:

30 Cj_ + 12 x .36 x Cp assuming that the Puritron was circulating 12 cfm and had an arrestance of 36$.

-7-

Under steady state conditions, the total rate of entry and

removal of particulates would be equal or

30 C

± + 12 x .36 x C

± = 30 C 0

and C

± = 0.87 C 0

If particulate matter was contributed to the air from activities in the room, the interior concentration would be a higher

percentage of the outdoor concentration, and could exceed the outdoor concentration under certain conditions.

USCOMM-NBS-DC

U S. DEPARTMENT OF COMMERCE

Frederick H. Mueller, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Amin, 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 and Electronics. Resistance and Reactance. Electron Devices. Electrical Instruments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Photographic Technology. Length. Engineering

Metrology.

Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Molecular Kinetics. Free

Radicals Research. Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics. Atomic Physics. Neutron Physics. Radiation Theory. Radioactivity. X-rays. High

Energy Radiation. Nucleonic Instrumentation. Radiological Equipment.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic

Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. 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. Poly- mer Structure. Plastics. Dental Research. MelaUurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal

Physics.

Minerul Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Air Conditioning, Heating, and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat Transfer. Concreting Materials.

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

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

Digital Systems. Analog 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. VHF Research. Radio Warning Services. Airglow and Atirora. Radio

Astronomy and Arctic Propagation.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Research. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Propagation Obstacles Engineering. Radio-Meteorology. Lower Atmosphere Physics.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. High Frequently Impedance Standards. Electronic Calibration Center. Microwave Physics. Microwave Circuit Standards. Radio Cominnnisialson and Systems. Low Frequency and Very Low Frequency Research. High Fre- quency and Very High Frequency Research. Ultra II igh Frequency and Super High Frequency Research. Modulation Research. Antenna Research. Navigation Systems. Systems Analysis. Field Operations.
NBS