NATIONAL BUREAU OF STANDARDS REPORT

6212

CAPACITY TESTS

OF

POUR 3/4-TON GASOLINE- POWERED REFRIGERATING UNITS

THERMO KING, MODEL Q9

by

Clinton W. Phillips and Paul R. Achenbach

Report to

Mechanical Engineering Division

Headquarters, Quartermaster Research and Engineering Command

Natick, Massachusetts

<NB§>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

1003-20-4832

{MBS REPORT

6212

November 7 , 1958

CAPACITY TESTS OP

OF

POUR 3/4-TON GASOLINE- POWERED REFRIGERATING UNITS

THERMO KING, MODEL Q9

by

Clinton W. Phillips and Paul R. Achenbach

Air Conditioning, Heating, and Refrigeration Section

Building Technology Division

to

Mechanical Engineering Division

Headquarters, Quartermaster Research and Engineering Command

Natick, Massachusetts

NATIONAL BUREAU Of SI

intended for use within the

to additional evaluation and

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

however, by the Government

to reproduce additional copl

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

progress accounting documents

formally published it is subjected

g, reproduction, or open-literature

issJon 1$ obtained In writing from Such permission 3s not needed,,

ly prepared If that agency wishes <NBS>

U. $, DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Capacity Tests

of

Four 3/4-Ton Gasoline-Powered Refrigerating Units

Thermo King, Model Q9

1. Introduction

Capacity tests of four Thermo King, Model Q9 3/4-ton,

gasoline-engine-driven refrigerating units were made at the

request of the Mechanical Engineering Division of the Quartermaster Research and Engineering Command, United States Army,

to determine their refrigerating capacity when used in conjunction with 21-foot military-type refrigerating semi-trailers.

Figure 1 shows one of the four Model Q9 units.

Three military-type refrigerated semi-trailers, which

had previously been tested for heat leakage by the reverse

heat-flow method, were used as calorimeters for these tests.

Figure 2 is a view of one of these trailers. The heat transmission coefficients, or "U" factors, determined for the

three vehicles in the previous trailer tests, were used for

computing the heat leakage of these same vehicles when each

was used as a calorimeter during the capacity tests of the

refrigerating units. These heat transmission factors ranged

from 56.1 to 68.3 Btu/hr (F).

This report is a summary of nine refrigerating capacity

tests, the results of which have previously been transmitted,

either verbally or by letter, to representatives of the Quartermaster Research and Engineering Command. Tests numbered 4

and 8 were made at 110 F ambient temperature and the lowest

obtainable trailer temperature. The other seven tests were

made at 110 F ambient temperature and 0 F trailer temperature.

2 . Test Procedure

Each of the gasoline-engine-driven refrigerating units

was installed in a semi-trailer which was in a test chamber

in which the desired ambient temperature could be maintained

throughout the test. The engine exhaust was connected to an

exhaust stack to conduct the fumes from the test chamber.

All temperature measurements were made by means of thermocouples and potentiometers, and all temperatures used in computing the test results were corrected by the amount of the

observed deviation of a typical thermocouple immersed in an

ice bath.

- 2 -

In the tests at 110 F ambient temperature and 0 F interior temperature, a thermostatically-controlled heater, with

shielded, resistance-type elements and a built-in blower, was

placed inside the trailer to maintain the desired interior

temperature. Electrical power supplying the heater, the blower,

and circulating fans was measured by means of separate calibrated watt hour meters.

Each test was continued for a sufficient length of time

to insure that steady rates of heat exchange between the interior and ambient air had been reached and for a six hour

period thereafter. The tabulated test results were obtained

from these six hour periods at steady state conditions.

The heat introduced into the interior of the trailer, as

computed from the measured amount of electric power supplied

to the resistance heater, the blower, and the fans, plus the

computed heat leakage of the vehicle, was taken as the net

refrigerating capacity of the Q9 refrigerating unit being

tested

3 . Test Results

The conditions under which the refrigerating capacity of

each of the four Thermo King, Model Q9, 3/4-ton refrigerating

units was determined, and the results of these nine tests are

shown in Table I.

The units bearing Serial Nos. 367 and 369 were tested as

received, without adjustment. The unit bearing Serial No. 364

was received installed in Trailer B from the Field Evaluation

Agency at Fort Lee. It had been tested there and the units

were reported to be incapable of bringing the interior of the

trailer down to a temperature of 0.0 F. In order to install

the necessary thermocouple harness on the unit, to prepare

it for the capacity tests, it was removed from the vehicle,

and while it was being prepared. Tests 3 and 4 were made,

with Model Q9 Serial No Q 367 installed in Trailer B.

The important effect of suction pressure on net cooling

capacity is indicated by comparing the results of Tests 1

and 2 on the unit with Serial No. 369 and of Tests 3 and 4

on the unit with Serial No. 367 . In the first case, a change

of 2 inches of vacuum in the suction pressure caused a vari-

-3-

ation of about 5$ in net cooling capacity with virtually no

difference in evaporator inlet temperature. In the second

case, a decrease in evaporator inlet temperature of 9.3°F

caused a decrease in suction pressure of about 2.7 psig and

a decrease in net cooling capacity of 26 percent. In each

comparison there was less than one percent change in compressor speed.

At the beginning of Test No. 5* with Model Q9 Serial No.

364 installed in Trailer it was found that this unit would..

reduce the interior temperature of the vehicle to 0.0°F. It

was found necessary to make several adjustments on the thermal

expansion valve to establish a suitable super-heat condition

and to adjust the engine speed of the unit to the design speed

of 2800 rpm. Tests 9 , 6, and 7 show the results of the capacity tests after these adjustments had been made.

Good consistency tin results was obtained in Tests 9 , 6,

and 7 at the same operating conditions on this unit. There

was only a half percent difference in net cooling capacity

among the three tests.

Test 8 was made with the Model Q9 Serial No. Ill as

received,, and installed ih Trailer C. Test No. 9 was made

after several adjustments had been made to the thermal expansion valve to establish correct super-heat. Note the lower

engine speed during Tests 8 and 9 . A comparison of the results

of Tests 8 and 9 made on the unit with Serial No, 111 shows

that a reduction of 3*2°F in the evaporator inlet air temperature caused a decrease in suction pressure of 1.5 psig and

a reduction in capacity of 9-5 percent.

Comparisons of the net cooling capacities of the four Q9

Thermo King refrigerating units of the same model provides

some information on the tolerance to be expected in a group

of such units. A comparison of Test 3 with Tests 9 , 6 ^ and 7

at the same evaporator inlet air temperature shows a variation

in capacity of 6 to 7 percent for these two units. However,

the net cooling capacity of the unit with Serial No. 369 as

indicated by Tests 1 and 2 was 7 to 11 percent below that for

the unit with Serial No. 364 and 13 to 17 percent below that

for the unit with Serial No. 367 . The net cooling capacity of the unit with Serial No. Ill,

as shown in Test No. 9 , at a compressor speed of 1750 rpm

was about equal to that of the unit with Serial No. 369 at a

compressor speed 300 rpm higher.

-4-

4. Discussion and Conclusions

The test results show that the Q9 unit, properly adjusted

for super-heat and engine speed was capable of reducing the

interior temperature of a stationary 21-foot military trailer,

as typified by the three specimens used as a calorimeter, to

a temperature below 0 ’F in an ambient temperature of 110 F.

The margin of capacity above that required to produce a cargo

space temperature of 0 F, ranged from 1500 to 3400 Btu/hr,

representing from 20$ to ^ 0% excess capacity in the several

trailers. It should be noted that the cooling loads of the

three trailers ranged from 6200 Btu/hr to 7500 Btu/hr.

In two cases, an oil leak was observed at the front crankshaft oil seal of the gasoline engine after about 100 hours of

operation. This leakage was apparently due to malfunctioning

of a pressure-equalizing device intended to relieve crackcase

pressure

The heat transmission coefficients of the trailers, used

as calorimeters for these tests, were measured using the reverse

heat loss method. In this method, the interior temperature is

raised above the ambient temperature, and the heat input is

divided by the difference in temperature to determine the heat

transmission coefficient.

More recent investigation has shown that the reverse heat

flow method does not usually indicate as great a heat transmission coefficient as is observed when the refrigerated enclosure is tested with the interior temperature lower than the

ambient dew point temperature. In most cases, the heat transmission coefficient will be greater when the interior of the

trailer is refrigerated because of the latent heat transfer

caused by condensation of water vapor entering with any leakage air which may penetrate the exterior skin.

Because of this, the computed trailer heat gains and also

the refrigerating capacities reported in Table I for the four

units may be slightly smaller than the actual values. It is

probable that this error does not exceed five percent.

It should be noted that in all cases, the units tested,

properly adjusted, and in an ambient temperature of 110 F,

were of greater capacity than needed to reduce the trailer

- 5

-

temperature to 0 F when the trailers were stationary. Tests

of commercial trailers on the road also indicate that the

cooling load of such vehicles when in motion was greater than

when tested in a stationary condition in the laboratory because

additional air and moisture entered the trailer body under the

impact of the air. This increment of additional heat gain

amounted to 20 to 30% of the heat gain measured in the laboratory.

Q9 Serial No. Ill

Test No.

Time

Date

Trailer

Head Pressure

Suction Pressure

Ambient Temp.

Cargo Space Temp.

Evaporator Inlet

Air TempEngine Speed

Compressor Speed

Fan Speed

.11

8

3j)- 0500

31- 23/56

c

Psig L75

Psig or In.HgVacj .3

F

5 F

10.3

2.7

2.7

RPM 388

RPM .765

RPM .362

Trailer Heat Gain

Electric Heat Input

Btu/hr 700

Btu/hr 750

Btu/hr 150

9

1800-2400

7/3/56

c

179

2*8 .

110.5

0.7

0.5

2363

1747

13^7

7500

1500

9000 Net Cooling Capacity

Table I

CAPACITY TESTS OF THERMO KING Q9 3/4-TOi: REFRIGERATING UNITS

Q9 Serial No. 369 369 367 367 364 364 364 111 111

Test No. 1 2 3 4 5 6 7 8 9

Time 1900-0100 0700-1300 1500-2100 1400-2000 2230-0430 1800-2400 0200-0300 2300-0500 1800-2400

Date 1/6-7/56 2/24/56 3/23/56 3/24/56 4/5-6/56 4/6/56 4/7/56 6/22-23/56 7/3/56

Trailer A A B B B B B c c

Head Pressure Psig 176 185 180 I08 185 193 190 175 179

Suction Pressure Psig or In. HgVac 2" Vac 0.0 2.5 0.4 "Vac 2.0 3.1 2.8 1.3 2.8

Ambient Temp. °F 110.3 109.9 110.9 110.4 110.4 110.4 llO.o 110.3 110.5

Cargo Space Temp. °F 0.0 -0.2 0.4 -9.5 0.2 0.4 -0.2 -2.7 0-7

Evaporator Inlet

Air Temp.

°F 1.4 1.9 0.6 -9.9 0.3 0.4+ -1.0 -2.7 0.5

Engine Speed RPM 2805 2796 2726 *2737 2825 2794 2807 2388 2363

Compressor Speed RPM 2054 2049 2014 *2025 2088 2056 2063 1765 1747

Fan Speed RPM 1543 1542 1544 *1549 1609 1571 1583 1362 13**7

Trailer Heat Gain Btu/hr 6200 6200 7250 7650 7200 7200 7250 7700 7500

Electric Heat Input Btu/hr 2650 3100 3400 0 2750 2750 2750 450 1500

Net Cooling Capacity Btu/hr 8850 9300 10650 7350

Average

9950 9950 10000 8150 9000

loCO-2400 fars.

3/2U/56

FIG.

U. s. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

• )\

NATIONAL BUREAU OF STANDARDS

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

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