NATIONAL BUREAU OF STANDARDS REPORT

7800

AIR DELIVERY PERFORMANCE OF A RITTLING UNIT VENTILATOR

UNDER ISOTHERMAL CONDITIONS

manufactured by

The Rittling Corporation

Hamburg, New York

by

Joseph C. Davis

Report to

Government of the District of Columbia

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 019, 1950. Those include (lie 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; invention 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 listing of divisions and sections on the inside of

the back cover.

Publications

The results of the Bureau’s research are published either in the Bureau's own series of

publications or in the journals of professional and scientific societies. The Bureau publishes

three periodicals available from the Government Printing Office: The Journal of Research,

published in four separate sections, presents complete s< ientifie and technical papers; the Technical News Bulletin presents summary and preliminary reports on work in progress; and the

Central Radio Propagation Laboratory Ionospheric Predictions provides data for determining

the best frequencies to use for radio communications throughout the world. There are also

five series oi nonperiodical publications: Monographs, Applied Mathematics Series, Handbooks.

Miscellaneous Publications, and Technical Notes.

A complete listing of the Bureau’s publications can be found in National Bureau of Standards Circular 460, Publications of the National Bureau of Standards, 1901 to June 1947 ($1.25;,

and the Supplement to National Bureau of Standards Circular 460, July 1947 to June 1957

(SI. 50), and Miscellaneous Publication 240, July 1957 to June 1960 (includes Titles of Papers

Published in Outside Journals 1950 to 1959) ($2.25); available from the Superintendent of

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

NBS PROJECT NBS REPORT

1003-30-10630 June 17, 1963 7800

AIR DELIVERY PERFORMANCE OF A RITTLING UNIT VENTILATOR

UNDER ISOTHERMAL CONDITIONS

* manufactured by.

The Rittling Corporation

Hamburg , New York

hy

Joseph C. Davis

Mechanical Systems Section

Building Research Division

Report to

Government of the District of Columbia

Washington,, D.C.

NATIONAL BUREAU OF f for use within the Governmenl

and review. For this reason, whole or in part, is not autl Bureau of Standards, Washin

the Report has been specifica

IMPORTANT NOTICE

;ress accounting documents intended

A j r 1 1 ,, is subjected to additional evaluation Approved for public release by the re listing of this Report, either in Director of the National Institute of the Office of the Director, National Standards and Technology (NIST)

on October 9, 2015.

by the Government agency for which

I copies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

AIR DELIVERY PERFORMANCE OF A RITTLING UNIT VENTILATOR

UNDER ISOTHERMAL CONDITIONS

by

Joseph C. Davis

1. INTRODUCTION

In accordance with a request from Mr. Richard C.

Crutchfield., Chief; Office of Design and Engineering

Department of Buildings and Grounds; Government of the

District of Columbia; tests were made on a unit ventilator manufactured by the Rittling Corporation of

Hamburg; New York. These tests were performed in compliance with specifications supplied by the Government

of the District of Columbia. The other two unit ventilators made by different manufacturers previously

tested by the National Bureau of Standards under similar

arrangements and in accordance with the specifications

noted above; each had a nominal air delivery rate of 1000

cfm. The nominal rating of the subject unit ventilator

was 750 cfm. Because of this difference in unit size and

structure; it was not feasible to compare sound pressure

noise level test results of the 750 cfm units with the

sound pressure test results of the two 1000 cfm units.

The authorization letter of January 16, 1963 states that

the noise level tests should not be performed.

The unit ventilator was selected by representatives

of the District Government from a number of the same

models which were being installed in one of the District

schools. The test specimen was identified as Model No.

SM 7532 and Serial No. 70^-6. Only tests pertaining to

air delivery were performed; no evaluation was made of

its heating performance. Figure 1 is a view of the front

and right end of the unit. The discharge grille can also

be seen in the figure.

- 2 -

The air delivery from the unit to the schoolroom can be

100 percent fresh air, 100 percent recirculated air or any

proportion of fresh air to recirculated air between these

amounts. During normal operation, the proportion is

regulated by automatic control of dampers, but during testing,

the dampers were set manually at selected positions to

maintain fixed proportions of fresh air to recirculated air.

The name-plate voltage was 115 volts. The supply

voltage to the permanent split-capacitor motor driving the

four centrifugal blowers, was adjustable by the use of taps

on a transformer. In order to attain maximum air delivery

rate of 610 cfm when the impressed voltage on the transformer was 115 volts, it was necessary to use transformer

tap No. 1 as specified by a representative of the Rittling

Company. The impressed voltage on the transformer was maintained at the constant value of 115 volts by means of a variac for all tests.

2. METHODS OF TESTING

Air delivery from the supply grille of the unit was

measured by means of a pitot tube. The pitot tube measurements were made at 50 equally-spaced positions in the crosssectional area of a duct having the same cross-sectional area

as the gross area of the supply grille and a length of about

4 feet. The duct was attached at an angle conforming to

the angle of discharge of the air as determined during one

of the tests. The length of 4 feet was necessary to produce

reasonable mixing of the air and to minimize the number of

very low pressure differences observed during pitot readings

on a shorter duct.

The frictional resistance encountered by the moving

air in the duct of 4 feet length at the discharge grille was

not appreciable. Since the duct was fixed at an angle

conforming to the angle of discharge, there was little effect

due to air-Impingement on the walls. Reference to the Guide

for 1961 of the American Society of Heating, Refrigerating

and Air Conditioning Engineers, will show that at an air

velocity of 350 fpm and for a duct of this length and of

6 inch diameter, the pressure drop due to resistance is only

about 0.002 inches W e G. The duct at the discharge grille and

at the fresh-air grille can be seen in Figure 2.

-3-

Figure 2 shows the pitot tube in position for measurement at the top of the duct at the discharge grille.

Measurements were made with the impact opening and the

static pressure holes of the pitot tube below the crosssectional plane at the end of the duct.

Impact pressure readings obtained by the pitot tube

were observed on a sensitive inclined manometer which had

been calibrated against a Hook gage.

Once the proper transformer tap was selected to

obtain a maximum air delivery rate with the fresh air

damper 100 percent open, the rotational speed of the

blowers was measured. This measurement was made with a

stroboscope and also with a tachometer. The tachometer

was applied to the blower shaft with as little pressure

as possible, consistent with no slippage in order not to

affect the motor speed. A negligible deviation in current

from that occuring without the use of the 4 foot duct

indicated little change in load during the speed measurement . Air delivery rates through the discharge grille

were measured under the following positions of the sliding

outdoor-air damper:

100 percent open

50 percent open

25 percent open

100 percent closed

For tests with all fresh-air damper positions, the voltage

impressed on the transformer was maintained at 115 volts

and rotational speed measured and checked in the same

fashion.

With the fresh-air damper 100 percent open, the

starting current of the unit was measured by means of an

oscilloscope. This instrument was calibrated in terms of

-4-

current as a function of vertical displacement of the

electron beam on the screen. During steady operation,

temperatures of the motor casing were measured with a calibrated copper-constantan thermocouple and semi-precision

potentiometer. Impressed transformer voltage, motor

current, and energy usage readings were made every 30

minutes of the test. A watthour meter was used for

determining the average power requirement. Wet- and drybulb determinations were made using a sling psychrometer

having a new, clean wick for each test.

The air leakage through the recirculating-air damper

system was measured when the fresh air damper was in the

wide open position. To measure the small quantity of air

leakage occurring in this unit under these conditions, the

air that was leaking was forced to pass through a round 3-

inch duct connected to a plenum fitted over the return air

opening. The 3 inch tube was somewhat flattened to

accomodate it to the plenum. The rate of air flow was

measured with the pitot tube and manometer mentioned above.

All openings at other points in the housing where air

leakage into the blowers could occur, were sealed.

To test the unit for ability to prevent "blow-through"

of winds from outdoors to the schoolroom, smoke-laden air

was forced directly toward the outdoor-air intake grille at

a velocity of 47 mph over about 33 percent of the grille

area. The test was repeated for an adjacent one-thrid of

the grille area, and then finally for the remaining third.

The smoke-laden air was directed at the outdoor intake

grille by a blower with a discharge duct measuring 8 by

8 inches. Sudden application of the air stream to each

zone of 1/3 of the grille area was accomplished by suddenly

raising a damper in the 8 by 8 inch duct, which caused a

momentary rush of air similar to a gust of wind greater

than 47 mph. This test was performed with the outdoor-air

damper 100 percent open, 50 percent open, 25 percent open,

and fully closed. Detection of amount of "blow-through" was

made by looking for an issue of smoke at the recirculatingair grille.

All tests were performed with the outdoor grille and

medium-mesh screen assembly attached to the unit. A 6-inch

duct connected the grille to the screen assembly replacing

the opening in the masonry in the wall of the school during

normal use.

The angle of discharge of the air leaving the discharge

grille was measured with a protractor which was sighted

against 20 threads placed at representative positions in

the grille.

The air delivery of the unit in every case was

calculated using the observed temperature and moisture

content of the air. Since a centrifugal blower is essentially

a constant volume device at a given fan speed regardless

of air density* the volume rate of air delivery would have

been the same if the ambient air had been at standard conditions. The 50 pitot tube readings measured differences

between total and static pressure in 50 areas of approximately

equal size comprising the total grille area. Pressure

difference was determined for each area and the velocity was

calculated from the average pressure difference for all

areas in accordance with the relation:

v - 4005 ~\A

Density of "St anda rd Air

Density of Ambient Air

where h is the average difference between total

pressure and static pressure* in. of water* as

measured with the pitot tube.

3. TEST SPECIFICATIONS

The specifications supplied by the Government of the

District of Columbia* modified to conform to the nominal

rating of 750 cfm* are presented in the following paragraphs.

The tests are to determine that each unit tested

delivers the specified amount of air In cubic feet per minute

(cfm) corrected to standard air conditions. Tests of heating

coil capacity are not required.

The units chosen for testing will be models with room

or recirculated air admitted through louvered lower front

panels. All units are to be tested at free delivery (no

external resistance on unit discharge). Air deflection

vanes* If provided* should be set for no lateral deflection.

Units will be fitted with standard discharge grille normally

furnished.

- 6 -

Units to be tested will be floor mounted models of a size designed to deliver 75 O cfm standard air.

Units shall be tested with standard size outdoor air

intake of standard construction (normally offered by the

manufacturer) in the correct position set at normal distance

from the outdoor air opening to the unit (approximately 6

inches from bird screen side of louver to unit).

Units will be fitted with a clean, permanent type

filter. All units tested should be tested with filters

which are identical in construction and resistance

characteristics

.

During tests, records should be kept of fan motor

voltage, watts, amperes and temperature rise. Peak motor

starting current should be recorded for each unit tested.

Preferably the tests should be conducted in a room

of ambient temperature of approximately 70 °F.

A. Determine fan rpm required to deliver 750 cfm standard

air with outdoor air damper 100 percent open and room

air damper closed. Also, determine amount of air

leakage thru room air damper at this condition.

B. Set fan at the rpm obtained in Test A above and determine cfm at several damper positions with outdoor air

damper 100 percent open to completely closed. Room

air damper will vary inversely from completely closed

to 100 percent open.

C. Test "blow-through" prevention performance, which

should prevent gusts of outdoor air from blowing

through the unit room air intake louver into the

room, by setting the outdoor-air damper at various

positions and blowing high velocity air through the

outdoor air opening of the unit. Tests should be made

with unit fans operating at the rpm determined in

Test A above at free delivery into the room.

D. At 75O cfm standard air delivery, the units shall be

tested for operating noise level by an approved method.

Each unit test for noise level shall be identical as

to method.

- 7

-

E, At free delivery into the room through a standard*

normally furnished discharge grille* determine the angle

of discharge leaving the unit and the average leaving

velocity of the air. This test shall be performed with

the unit delivering 750 cfm standard air. Deflector

vanes, if provided* shall be set for no lateral deflection.

4 . TEST RESULTS

The following test results are reported t TEST A. (l) The test specimen did not circulate the required amount of air* 750 cfm* at the maximum ' blower speed attainable. The maximum speed

attainable at an impressed voltage of 115 volts

was 750 rpm* with outdoor air damper open and

room air damper closed. The observed air

delivery rate for this condition was 610 cfm. ,

( 2 ) Amount of air leakage through room air damper , at this condition was 30 cfm.

TEST B. The air delivery rate from the discharge duct* the

fan speed* the motor current* and motor power were observed

for several positions of the outdoor damper and at constant

impressed voltage. The results are summarized in the

following table: *.

; Rotational

Position of Speed of Air Motor Impressed Power

Out do or- Air Damper Pan Quantity* Current Voltage Input

(T'rans. .Displacement) (rpm) (cfm) (amp) (volts

)

(watts)

100 percent open 750 610 1.35 115 140

50 percent open 700 700 1.50 115 155

25 percent open 685 740 1.57 115 ' 155

100 percent closed 720 570 1.45 115 • 150

Due to the low values of air velocity encountered in this unit

the uncertainty in the values of air delivery rate may be as

much as 10 percent.

- 8 -

Ambient

Air Temperatures

Position of Average

Out door- Air Damper Dry Bulb Wet-Bulb Value for ~VK

( Trans"7 Displa cement ) P’fT (in. H^O)

100 percent open 78*3 55 .4 .0854

50 percent open 72.4 49.0 .0987

25 percent open 76.0 51.6 .1043

100 percent closed 79-3 54.8 .0799

Cross-sectional area of discharge duct 1.79 sq.ft.

TEST C. There was no evidence of ’’blow-through” when

smoke-laden air was forced directly into the outdoor-air

intake grille at a velocity of 47 mph over about 33 percent of the grille area for outdoor damper positions of

100 percent open, 50 percent open, 25 percent open, and

100 percent closed (transverse displacement).

TEST D. The noise level test was not requested.

TEST E. The angle of discharge of the air through the

discharge grille was 50 ±5 degrees referenced to the

horizontal. The average leaving velocity with the outdoor damper 100 percent open was 350 fpm. Because of

the low velocity at some positions of the grille, the'

threads used to measure the angle of discharge failed to

respond the the air movement and lay flat on the grille.

While the unit was operating with the outdoor-air

damper 100 percent open, peak starting current was 2.5

±5 amperes. The maximum temperature rise of the motor

casing was 37°^ above the temperature of 55°F* the

temperature of the motor casing at the beginning of the

test. The maximum temperature was reached after 2.5

hours of operation

5. APPENDIX

The following information on components of the unit

ventilator was supplied by the manufacturer, or taken

from name plates.

-9-

Motor name plate : Split capacitor type motor.

Century, rated, 1/12 HP, 775 rpm, 115 volt, single phase,

60 cycle, type CX, frame H 52Z, 2.0 amperes, EMI 657-F,

Code 1, Spec. 28469, Serial No. B4E0AM cont. 55 °C

connection diagram C 41797, thermal protection NOT SP 10.

Unit name plate : Model No. SM 7532, Serial No. 7046^

115 volts, 2.2 amperes, Ph 1, and 60 cycle.

i/

Fan : Four centrifugal fans, manufactured by Revcor

Blower Company, 8 In. in diameter, 4 1/2 in. wide. Model

No. C-762-450 HD. Direct driven from motor.

Filters ; Smith Lifetime Air Filter, manufactured by

Smith Filter Corporation, Moline, Illinois. Size 6 3/4”

x 1” x 43 1/2” (two) one for outside air and one for

recirculated room air. (Permanent type.)

1/ Information furnished by Mr. Holliday, F. C. Clifford

Company, Washington, D.C., supplier of Rlttling Unit

Ventilator.

USCOHM-NBS-DC

Figure


>STS
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.

Heat. Temperature Physics. Heat Measurements. Cryogenic Physics. Equation of State. Statistical Physics.

Radiation Physics. X-ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.

Nucleonic Instrumentation. Neutron Physics.

Analytical and Inorganic Chemistry. Pure Substances. Spectrochemistry. Solution Chemistry. Standard Refer- ence Materials. Applied Analytical Research. Crystal Chemistry.

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

Controls. Polymers. Macromolecules: Synthesis and Structure. Polymer Chemistry. PolymeF Physics. Polymer Characterization. Polymer Evaluation and Testing. Applied Polymer Standards and Research. Dental Research.

Metallurgy. Engineering Metallurgy. Metal Reactions. Metal Physics. Electrolysis and Metal Deposition.

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

Crystallo gr aphy.

Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials.

Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. Metallic Building Materials. Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics. Operations Research. Data Processing Systems. Components and Techniques. Computer Technology. Measurements Automation.

Engineering Applications. Systems Analysis.

Atomic Physics. Spectroscopy. Infrared Spectroscopy. Far Ultraviolet Physics. Solid State Physics. Electron

Physics. Atomic Physics. Plasma Spectroscopy.

Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation.

Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Ele- mentary Processes. Mass Spectrometry. Photochemistry and Radiation Chemistry.

Office of Weights and Measures. BOULDER, COLO.

CRYOGENIC ENGINEERING LABORATORY

Cryogenic Processes. Cryogenic Properties of Solids. Cryogenic Technical Services. Properties of Cryogenic

Fluids. CENTRAL RADIO PROPAGATION LABORATORY

Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere Research. Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. Vertical Soundings Research.

Troposphere and Space Telecommunications. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Spectrum Utilization Research. Radio-Meteorology. Lower Atmosphere

Physics.

Radio Systems. Applied Electromagnetic Theory. High Frequency and Very High Frequency Research. Fre- quency Utilization. Modulation Research. Antenna Research. Radiodetermination.

Upper Atmosphere and Space Physics. Upper Atmosphere and Plasma Physics. High Latitude Ionosphere

Physics. Ionosphere and Exosphere Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.

RADIO STANDARDS LABORATORY

Radio Standards Physics. Frequency and Time Disseminations. Radio and Microwave Materials. Atomic Fre- quency and Time-Interval Standards. Radio Plasma. Microwave Physics.

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 Grotq> (Univ. of Colo.).

USC0MM-N6S-DC