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NATIONAL BUREAU OF STANDARDS REPORT

THE DEVELOPMENT OF A RATING METHOD

FOR REFRIGERATED TRUCKS

by

C c W. Phillips

Mechanical Systems Section

Building Research Division

Transportation and Facilities Research Division

U.S. Department of Agriculture

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

7441

Progress Report

on

Report to
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NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT NBS REPORT

7i 1003-12-10131

1003-12-10434

February 13* 1962

Progress Report

on

THE DEVELOPMENT OF A RATING METHOD

FOR REFRIGERATED TRUCKS

by

C„ W. Phillips

Report to

Transportation and Facilities Research Division

U.S. Department of Agriculture

IMPORTANT NOTICE

NATIONAL BUREAU OF STAND

intended for use within the Gov<

to additional evaluation and revie

listing of this Report, either in w

the Office of the Director, Nation however, by the Government age

to reproduce additional copies fo

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

ess accounting documents

iy published it is subjected

oduction, or open-literature

is obtained in writing from

h permission is not needed,

lared if that agency wishes

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Progress Report

on

THE DEVELOPMENT OF A RATING METHOD

FOR REFRIGERATED TRUCKS

For The Quarter Ending December 31* 1961

by

C. W. Phillips

PURPOSE:

(1) To develop a method for rating refrigerated truck

bodies with respect to cooling load, that will take into

account the effects of air leakage, moisture weight gain,

solar radiation, and air and moisture exchange due to opening of the body doors.

(2) To study a selected number of different types of

body construction and insulation as represented by vehicles

specially constructed by cooperating manufacturers according

to a predetermined schedule.

BACKGROUND:

In an earlier project a rating method for refrigerated

trailers was developed to evaluate the cooling load, air

leakage and moisture gain of these vehicles intended for

long-haul highway transportation of frozen foods.

Certain differences were noted between usage of highway

trailers and local delivery trucks which indicated that different test procedures should be used for rating the two types of

vehicles

The highway trailers operate day and night, usually at

road speeds, and are opened for loading and unloading only at

terminals or major transfer points. The additional cooling

load caused by strong solar radiation while the vehicle was

stationary was probably less than that caused by air leakage

when the vehicle was in motion, and doors are opened infrequently, if at all, during a trip.

Delivery trucks are stationary for the most part, operate

primarily during daylight hours, and are subjected to a wide

variety of door opening schedules during the working period.
- 2 -

Thus, the rating method for trailers required means for

simulating the effect of forward motion, but not solar radiation or door openings. The rating method for trucks, in contrast, requires means for simulating the effect of solar

radiation and door openings, but not necessarily the effect

of forward motion. It is to be recognized that' there are

exceptions to the general case.

The Mechanical Systems Section, NBS, Transportation and

Facilities Research Division, USDA, and the Truck Body and

Equipment Association have, beginning July 1, I960, sponsored

a cooperative effort to develop a suitable method for rating

refrigerated trucks taking into account the factors just outlined. The project is being carried out at NBS, under direc-.

tion of the Mechanical Systems Section.

As in the case of the trailer rating method, standard

rating conditions of 100°F ambient temperature at 50$ relative

humidity and 0°F interior temperature were selected.

A project steering committee was appointed, consisting of

representatives from interested industry and government organizations. To date, two meetings of the project steering committee have been held, on October 14, I960, and on June 19*1961.

Project accomplishments prior to this reporting period

include (l) Assembly of the comparison heater - heat sink

apparatus for simultaneous measurement in two ways of the

amount of cooling capacity needed to maintain the test truck

interior temperature at 0°F. Figure 1 shows some of this

equipment. (2) Preparation of the test facilities and instruments needed to conduct the tests and to measure the cooling

load and weight gain of the vehicles under study. Figure 2

shows some of the instruments. (3) Measurement of the cooling

load, weight gain rate, and air leakage of the first three

trucks submitted as test specimens. Figure 3 shows a truck

installed for test. Results of these tests were discussed at

the June 19, 1961, project steering committee meeting.

Tasks Accomplished During This Reporting Period

Installation was completed of a specially designed perforated ceiling incorporating air volume controlling means. to

provide draft-free air cooling of the test space when simulated

solar radiation tests are made. Figure 4 shows this ceiling.

Apparatus to provide simulated solar radiation was designed,

constructed and installed, including controls and instruments

for regulating and measuring the applied thermal radiation.
-3“

The Idea of a rotating mechanism to duplicate the effect

of the daily sun movement over a vehicle was discarded in favor

of adjustable stationary banks of electric heating elements

and parabolic reflectors facing each of two sides and the top

of a test truck. To simulate the effect of sun movement during

the day, the voltage applied to the heaters was varied. Each

bank was 9' high and 15 ' long and consisted of 45 parabolic

reflectors l'x3' at the bank face. Each reflector was equipped

with an 8l-ohm helical electric resistance coil wound around a 7mm o.d. glass tube mounted in the reflector so that the heater

axis was at the focus of the parabolic reflector.

The heating elements were designed so they operated without visible radiation at 208 volts. Maximum heat dissipation

of each heater, including both convective losses and radiant

transfer, was about 600 Btu/hr per foot of reflector length,

or 600 Btu per square foot of projected reflector area.. The

total heat release of one bank of 45 heaters operating at

maximum design voltage would be approximately 83,000 Btu/hr.

Figure 5 shows construction of the individual reflectorheater assembly, and Figure 6 shows the three banks installed

in the test room. Also In Figure 6 can be seen two of the

three scales used to measure the weight change of a truck

under test. Figure J shows one of the test trucks in the

test room for simulated solar load tests.

Previous observations of truck and trailer skin temperatures

exposed to bright summer sunlight at NBS had indicated temperatures as high as yO°F above ambient, and this value was selected

arbitrarily as an approximate upper roof skin temperature limit

for the simulated solar tests.

To establish a pattern for cyclic variation of the simulated solar energy, values of hourly insolation on a vertical

east and west surface and on a horizontal (roof) surface were

taken from U.S. Weather Bureau curves, as shown in Figure 8,

for June 21 at latitude 40°N. Such a solar day extends from

4:4QAM to 7»20PM, with maximum insolation values of 235 Btu/hr

(Ft^) on a vertical east wall at 7:30AM and on a vertical west

wall at 4:30PM, and 320 Btu/hr(Ft2 ) on a horizontal surface at

noon.

The wavelength of maximum emission of thermal energy is

a function of the temperature of the emitting source and is

between 0.3 and 0.7 micron for sunshine at the earth surface,

depending on the effect of the atmosphere.
- 4-

The measured temperature of one of the heater' rods

operating at the maximum voltage necessary for test was

700°F. At this temperature the wavelength of maximum

emission is about 4.5 micron. As the voltage is lowered,

the temperature of the heater approaches the ambient

temperature of 100°F, at which temperature the wavelength

of maximum emission is about 9-3 micron. The significance

of selecting a radiation source at temperatures of 700°F

or lower is related to the capacity of various surfaces to

absorb radiant energy. Surfaces covered with nonmetallic

paint, such as most truck bodies, regardless of color, will

absorb about the same fraction of radiation at the wavelengths above 4 microns as dark-painted surfaces will absorb

at the shorter wavelengths of solar radiation. For this

reason it was considered unnecessary to repaint any of the

painted vehicles in order to establish similar conditions

for the simulated solar tests. Metallic surfaces such as

aluminum or stainless steel, or metallic-painted surfaces

would require special consideration. All the vehicles

received to date for the test series have been painted with

nonmetallic paints.

For these tests it was desired to determine the effect

of similar solar insolation, regardless of the finish of the

test vehicle, on the various types or methods of construction

of the various truck bodies in the test series. By using the

lower temperature longer wavelength radiation source for the

simulated solar tests, all vehicles tested should absorb radiation as if they were painted with dark paint and exposed to

solar radiation of equal intensity. It was not an intended

purpose of these tests to determine what type of surface treatment was the best for minimizing the heat gain due to solar

exposure,

Earlier tests at NBS of insulated metal covered panels

exposed to sunlight have shown that gloss-white enamel surfaces

were more effective than bright mill-finish aluminum or stainless steel surfaces in reducing the rise in skin temperature

due to solar radiation. Some dark-painted surfaces were of

similar effectiveness as the metallic surfaces in limiting the

skin temperature rise due to solar heating. An examination of

the emissivity factors for various surfaces at various wavelengths explains this. Depending on their brightness, metallic

surfaces will absorb from 10 to §5 percent of the energy at the

short wavelengths of Bunshine compared to an absorption ranging

from 65 to 80 percent for dark-painted surfaces at the same

wavelengths.
-5-

For longer wavelength radiation, metallic surfaces at a temperature of 100°F, again depending on brightness, are capable of radiating from 10 to 30 percent as much energy as a perfect black radiator, while dark-painted surfaces can radiate from 85 to 95 percent as much energy as a perfect black

radiator.

Of the radiant energy absorbed by a surface over insulation such as an insulated truck wall, only a small percentage

will actually be transferred through the insulation; while a high percentage of the energy will be radiated to surrounding

lower temperatures or given up to convective air movement at

the surface. The metallic surfaces absorb less solar energy

than the dark painted surfaces but in turn are less able to

radiate the energy which they do absorb tending to minimize

the difference in the amount of energy transmitted through the

surface. As each surface is heated above ambient air temperature, it loses additional heat to convective air currents in

proportion to the difference in temperature between the surface

and the air.

Although most of this reporting period was utilized in

completing the construction and adjustment of the simulated

solar apparatus, simulated solar heat gain tests were completed on one of the trucks previously measured for heat gain

without solar load. Tills truck was identified in earlier

reports as truck "C"

The maximum observed increase in measured heat transmisskn

caused by the simulated solar heating for this truck was about

16 percent averaged over a four-hour period with the peak occur

ring about four hours after noon of the simulated solar cycle.

Figure 9 shows the average relationship between the time of the

simulated solar cycle and the measured heat gain for several

daily cycles. Figure 10 shows the average temperature of the

two sides and roof before, during and after a simulated solar

cycle. The temperatures shown are the average of eight thermocouples each on the east wall and roof, and seven thermocouples

on the west wall. Each thermocouple, representing an equal

area, was attached to the exterior of the surface by soldering,

after which the area affected by soldering was painted to match

the original surface. The west wall had one less thermocouple

Included in the average because the brine lines for the cooling

coil entered the wall so close to one thermocouple that it was

not indicative of normal skin temperature.
- 6 -

Radiation measurements were made with three special

radiometers, one mounted near to and parallel to each of the

three surfaces affected by the simulated solar energy. These

measurements are being analyzed for possible use in establishing criteria for duplicating the simulated solar tests on other

vehicles and in other test laboratories. Also under study are

measurements of two other devices used to interpret the intensity of the net radiant energy directed toward the vehicle skin

during a simulated solar cycle.

At the close of the reporting period the first vehicle was

being removed from the test facility, and a second vehicle.

Truck "A" in earlier reports, was being prepared for installation

for simulated solar tests.

During this reporting period some additional work was done

in modifying and refining the helium-trace measuring instrument

to be used to measure the air exchange due to various door-opening schedules . Preliminary tests have indicated that the heliumtrace technique can be used for this measurement. Figure 11

shows the Instrument and sensing element as it appeared prior

to the most recent modification to reduce the number of adjustment dials required for operation.

The fourth vehicle to be studied in the project series,

an ice cream truck furnished by the Hackney Company, Wilson,

North Carolina, was received in December. This vehicle is

insulated with foamed-in-place polyurethane

.

FUTURE PLANS:

Simulated solar heat gain tests will be performed on some

of the other vehicles on hand for study.

The study of air exchange during various door opening

schedules, using the helium-trace Instrument will be started.

Study of suitable means for measuring the effective radiation intensity will be continued and the techniques for measuring the additional refrigerating capacity required by various

door opening schedules will be investigated.

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Figure

4

»





HOURLY

INSOLATION

ON

CLOUDLESS

DAYS

JUNE

21,

LATITUDE

40°

NORTH

OlflNIW) 13 0S/n±g‘N0l±V10SNI

SOLAR

TIME

INCREASE

IN

COOLING

LOAD

CAUSED

BY

SIMULATED

SOLAR

CYCLE

(AVERAGE

OF

TWO

CONSECUTIVE

TESTS)

0300

0500

0700

0900

MOON

1300

1500

1700

1900

2100

2300

0100

0300

SOLAR

TIME

SURFACE

TEMPERATURES

DURING

SIMULATED

SOLAR

TEST

OIOO

0300

0500

0700

0900

1100 N

1300

1500

1700

1900

2100

2300

SOLAR

TIME

Figure

11

51. 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.

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

Mass and Scale. Volumetry and Densimetry.

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.

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

Controls. ' Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal Physics. Electrolysis and Metal Deposition.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Crystal Growth. Physical

Properties. Constitution and Microstructure. Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials. Codes and Safety Standards. Heat Transfer. Inorganic 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. Solid State Physics. Electron Physics. Atomic Physics.

Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation. Physical. Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Molecular Kinetjcs. Mass Spectrometry.

Office of Weights and Measures. BOULDER, COLO.

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Cryogenic Technical Services. 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. Radio Propagation Engineering. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements.

Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. Radio and Microwave Materials. Atomic Frequency ana Time Interval Standards. Electronic Calibration Center. Millimeter-Wave Research.

Microwave Circuit Standards. Radio -Systems. Applied Electromagnetic Theory. High Frequency and Very High Frequency Research. Modulation

Research. Antenna Research. Navigation Systems.

Upper Atmosphere and Space Physics. Upper Atmosphere and Plasma Physics. Ionosphere and Exosphere

Scatter. Airglow and Aurora. Ionospheric Raaio Astronomy.