NATIONAL BUREAU OF STANDARDS REPORT

3203

CAPACITY TESTS OF TWO REFRIGERATION COMPRESSORS

THERMO-KING, MODEL 4R AND UNIVERSAL',. MODEL VFP

by

Minoru Fujii

Co W. Phillips

Po R. Achenbach

Report to

Headquarters, U. S. Marine Corps

Department of the Navy

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

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G- i^iS3

NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1000-30-4^30 April 2, 1954 3203

CAPACITY TESTS OF TWO REFRIGERATION COMPRESSORS

THERMO-KING, MODEL 4R AND UNIVERSAL, MODEL VFP

by

Minpru Fujii

C. W. Phillips

P. R. Achenbach

Heating and Air Conditioning Section

Building Technology Division

to

Supply Branch

Headquarters, U. S. Marine Corps

Department of the Navy

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprli

unless permission is ob

25, D.C, Such permls

cal ly prepared If that

Approved for public release by the ,a,ti ls P

roh|bl,e<l Director of the National Institute of ,ard, ' Wa8hlnRton

Standards and Technology (NIST)

' has ^

e6n spedfi

rt for Its own use. on October 9, 201 5.

CAPACITY TESTS OF TWO REFRIGERATION COMPRESSORS

THERMO-KING, MODEL 4R AND UNIVERSAL, MODEL VFP

by

Minoru Fujii, C„ W„ Phillips and P„ R„ Achenbach —— 1

, Abstract

Determinations were made of the net refrigerating

capacity of a Marine Corps standard Thermo-King

refrigerating unit for a 600 cu„ fto warehouse at

refrigerator temperatures of 0°F and 35°F and with

an ambient temperature of 110°F o Subsequently the

capacity of the compressor was measured with a

secondary refrigerant calorimeter for each of the

two operating conditions,. The capacity of a

Universal, Model VFP, compressor was measured with

the calorimeter for a range of speed from 1600 rpm

to 3000 rpm to determine whether or not it could

be substituted for the Thermo-King compressor in

the standard warehouse refrigerating unite It was

found that the Universal compressor produced a

capacity equal to that of the Thermo-King compressor

at approximately equal theoretical displacement,

but the required rotative speed for the Universal

compressor was in the range from 2700 rpm to 3000

rpm because of its smaller bore and stroke,, Two

specimens of the Universal compressor failed mechanically during the tests; a connecting rode broke

on one specimen7 and the eccentric assembly separated

from the crankshaft in the other specimen,, Because

of these failures it was concluded that the Universal

compressor could not be expected to function satisfactorily in the standard Thermo-King warehouse unit,,

lo INTRODUCTION

At the request of the U„ S« Marine Corps, as outlined

by letter dated September 13, 1953, capacity tests were made

of a Marine Corps standard Thermo-King refrigerating unit

for a 600 cu„ ft„ refrigerated warehouse and calorimetric

measurements were made of both the original compressor in

this unit and a proposed alternate compressor furnished by
'

.

• t

.

:
- 2 -

the Engineer Supply Section, Supply Branch, Headquarters U„ S„

Marine Corps

.

A primary purpose of the tests was to determine if the proposed alternate compressor could be used satisfactorily in place

of the original compressor in the Marine Corps standard refrigerating unite The compressor originally installed in the unit, was a

Thermo-King Model 4R, manufactured by the U 0 So Thermo Control

Company of Minneapolis, Minnesota 0 The alternate compressor, a

Universal Model VFP, was manufactured by Tecumseb Products Company

of Tecumseh, Michigan,,

Tests were made to obtain the following information:

lo Refrigerating capacity of the refrigerating unit in an

ambient temperature of 110°F with refrigerator temperatures of 0°F and 35°F, respectively 0

2 0 Capacity of the Thermo-King compressor alone as measured

by calorimeter for conditions of suction pressure, discharge pressure, suction gas temperature, and speed identical to those observed during the tests of the entire unit.

3. Capacity of the Universal Compressor as measured by

calorimeter, at various speeds ranging from 1600 rpm

to 3000 rpm with other conditions the same as for the

Thermo-King compressor,,

4o Comparison of the general construction and performance

of the two compressors in order to evaluate their relative merits for application to the Marine Corps standard

refrigerating unit„

2 o TEST SPECIMEN

The specimen refrigerating unit, Thermo-King Model MQ 51

was of the plug-type, of nominal one-ton -: capacity equipped with

a gasoline engine drive which was designed to refrigerate a 600

cu 0 ft 0 sectional walk-in box in the field where a source of

electric power was not available for refrigeration purposes

„

The 600 cu& ft. box used for these tests was manufactured by

Hussman Refrigeration, Inc„ of St „ Louis, Missouri,, The unit

was powered by a straight four-cylinder four-cycle engine manufactured by Crosley Motors of Cincinnati, Ohio,, Components of

the refrigeration circuit, such as compressor, condenser, evaporator and blowers were manufactured by the U„. S„ Thermo Control
* ;'Vv. ;

r

.

,:

• -

•

. .

V

'

'
Company,, The compressor, Model 4R, had four cylinders with

bore and stroke of 2-1/4 in, and 1-3/3 in, respectively • The

compressor was coupled directly to the engine and the evaporator and condenser fans were driven by two double-V belts

.

The refrigerant used was dichlorodifluoromethane

,

The Universal compressor, Model TFP, manufactured by the

Tecumseh Products Company failed mechanically during the test

and another compressor was submitted by the manufacturer’s

representative o The two compressors were practically identical except that the design of the crankcase and the crank

shaft seal varied slightly,, Each compressor had four cylinders

with bore and stroke of 1-3/4 inch,,

3„ TEST PROCEDURE

The Thermo-King Model MQ51 plug-type gasoline-enginedriven warehouse-refrigerating unit was designed for a nominal capacity of one ton (12,000 Btu/hr) under conditions of

0°F warehouse temperature and 110°F ambient temperature,,

Since there are losses in a refrigerating system the compressor must produce a capacity greater than the net capacity

available in the refrigerated space,, For this reason it was

necessary to: (1) measure the net refrigerating capacity of

the assembled unit under specified conditions (2) observe the

exact conditions existing at the original compressor during

such test (3) remove the original compressor from the unit and

measure its refrigerating capacity under these identical 1

conditions--before the next step /4) which was to determine

the speed required for the alternate compressor to deliver the - same or more capacity than the original, all other conditions ' being the same,,

The Model MQ 51 Thermo-King refrigerating unit with ThermoKing compressor, Model 4R, was mounted in the 600 cu„ ft „ test

warehouse. The entire system was operated in a room where the

ambient temperature was controlled at the desired level. By

adjusting an internal heat load the warehouse temperature was

also maintained at the desired level.

Prior to the capacity tests, a reverse heat-flow test was

made to determine the rate of heat transfer through the warehouse

wall, which constitutes part of the refrigerating load. The refrigerating unit was in place but was not operated during this

test. The ambient temperature was held at 30°F and the warehouse temperature was maintained at l30°F while observations of

temperatures and the amount of heat required to maintain this

temperature difference were made at 30 minute' intervals for

six hours after a steady state condition was reached.
*

** < l •<
- 4

-

For the two capacity tests the refrigerating unit was operated in an ambient temperature of 110°F while the warehouse

temperatures were maintained at 0°F and 35°F, respectively

„

In addition to the above observations, pressures, speeds and

gasoline consumption were measured

„

Compressor capacities were determined by use of a secondary refrigerant calorimeter in accord with the method outlined

in the A.S.R.E. Standard No 0 23-R, Methods of Rating and Testing

Refrigerant CompressorSo The liquid refrigerant quantity method,

as described in the A.S.R.E. Standards No e 23-R, was employed

to check the capacity determined by the primary test method.

The conditions of the refrigerant (pressure and temperature)

entering and leaving the compressor during tests of the entire

unit in the warehouse were duplicated for these calorimeter

tests of the compressors alone. These conditions were:

suction gas temperature of #1°F and suction and discharge pressures of 0 o 6 psig and 177 psig respectively for the first series

of tests, corresponding to a refrigerator temperature of 0°F;

and 13 »1 psig and 211 psig respectively, with the same suction

gas temperature for the second series of tests, corresponding

to a refrigerator temperature of 35°F.

For the first series of test, the speed of the Universal

compressor was varied from 1750 rpm to 3000 rpm in approximately

250 rpm increments for successive tests. For the latter series

of tests the compressor speed was varied from 1600 rpm to 2350

rnm in increments of approximately 250 rpm for successive tests.

Tests at more than one speed were made only on the Universal

compressor ( s ) during both series and the second series was terminated at 2350 rpm because of the mechanical failure of the ~- second Uniyersal compressor. The first Universal compressor

failed mechanically during the second test in the first series.

The Thermo-King compressor was tested once for each series

of tests, at 2300 rpm and 2100 rpm respectively, which were the

original speeds of the compressor as installed in the unit during the unit capacity tests. Capacity tests of the Thermo-King

compressor at various speeds were not requested. One additional

test of the Thermo-King compressor was made at an A.S.R.E.

Standard Rating condition for reference purposes^ The standard

rating selected called for conditions of: suction pressure 4«5

•psig; discharge pressure 117 psig; and suction gas temperature

65°F. * '

For all compressor calorimeter tests, an oil separator was

used in the discharge line to keep the oil out of the calorimeter

and thus simplify! capacity measurements. However, the oil was

returned to" the suction line to simulate normal oil return in

- 5 -

the Thermo-King refrigeration unit 0 A shunt-wound 5 H,P,

direct-current variable-spped motor was used to drive the

compressor in all but one of the calorimeter tests , After

the calorimeter reached steady state conditions, the compressor under test was run for two hours, and observations

of temperature, pressure, speed, voltage, current, power

consumption and liquid refrigerant flow were made every

twenty minutes

,

Calibrated thermocouples, pressure gages, and other

instruments were used for the various measurements,

4, TEST RESULTS

The heat transmission factor of the 600 cu, ft, warehouse

used to test the ‘unit was found to be 59o5 Btu/°F(HR) 0 The capacity tests showed that the Thermo-King MQ51 re,

A

frigerating' unit had capacities of '19,100 Btu/hr at 0°F warehouse temperature and 23,900 Btu/hr at 35°F warehouse temperature with an ambient temperature of 110°F o in each case. The

results are tabulated in Table l c Table 1 ' also shows the' results^ of the' Thermo *-K in g com^y

'pressor capacity-tests determined ’-by -calorimeter measurements,

1. • • w . by - e primary -

;b: od j ..

: : sd

^n:h; The maximum deviation between the primary and secondary

methods used in all calorimeter tests reported was 3 <>3% of the

capacities indicated ‘by the primary method as described under

Test Procedure,

Table 2 shows the results of the capacity tests of the

Universal compressor on the secondary refrigerant calorimeter.

The capacity versus speed of the two models of refrigeration compressors is plotted in Fig, 1 for the two series of

tests.

The lower curve shows the observed capacities for the

Universal Model VFP compressor for various speeds and at the

conditions established for a 0°F warehouse and 110°F ambient

temperature'.

The upper curve shows the observed capacities for the

same compressor for various speeds and at the conditions established for a 35 b F warehouse and 110°F ambient temperature.

The curve is extrapolated as a straight line from 2300 rpm to

3000 rpm.

The observed capacities of the Thermo-King Model MQ51

unit was 23,900 Btu/hr at 20$4 compressor rpm for conditions

of 35°F warehouse temperature and 110°F ambient temperature,

and the capacity was 10,100 Btu/hr at 2291 compressor rpm for

conditions of 0°F warehouse temperature and 110°F ambient

temperature

,

The Thermo-King Model 4& compressor, when tested on the

calorimeter at the same suction and discharge conditions

showed capacities of 13,700 Btu/hr at 229$ rpm for conditions

corresponding to the lower warehouse temperature and 24, $00

Btu/hr at 2096 rpm under conditions corresponding to the higher warehouse temperature. The characteristic of the governor

on the Thermo-King MQ51 unit was such that an appreciable

speed change was required to establish a different throttle

position on the gasoline engine. This accounts for the difference of about 200 rpm in compressor speed between the tests

at 0°F and 35°F warehouse temperature.

The capacity observed during a third test of this compressor was 27,900 Btu/hr at 2404 rpm under conditions of 4.3

psig suction pressure 117 psig discharge and 62,0°F suction

gas temperature. These conditions approximated one of the

standard A,S,R,E, rating points, A test of the Universal compressor would have been made under these conditions and at a speed which would produce equivalent theoretical displacement

if both of the Universal samples submitted had not failed

mechanically.

During the tests of the Universal compressor ( s ) it was

observed that the quantity of oil circulated through the

system by the compressor increased noticeably as the oil 'level

approached the maximum level allowed. Other conditions being

equal this increase in oil circulation tended to increase the

compressor temperature.

The Thermo-King Model 4R compressor was equipped with a built-in pressure-limiting device in the suction which modulated

the flow of suction gas to the cylinders so that the pressure in

the crankcase and cylinders was limited to approximately 19

psig, during the suction stroke for normal operation. In addition the modulating valve could be closed by means of a builtin solenoid valve blocking flow of all gas to the crankcase or

cylinders to unload the compressor,

A test at 3000 rpm was attempted initially with the first

Universal compressor submitted to match the theoretical displacement of the Thermo-King compressor. However, the speed

was unstable so the first test was made at a speed of 1746

rpm (test 1, Table 2), This compressor failed mechanically

during the course of the second test being made with it.

- 7 -

At the time of failure the compressor had been operated for

45 minutes at 1500 rpm and then 30 minutes at 1995 rpm during the second test when one of the connecting rods broke

just below the wrist pin bearing,,

Test 1 was repeated and a total of ten runs were made

with the second Universal compressor submitted,, The second

compressor failed at 3000 rpm after running for three hours

at that speedo In this case the eccentric assembly separated

at the point where it was locked to the shaft,, This caused

damage to other parts,, The damaged compressor parts are

shown in Fig„ 2„

No dynamometer tests were made of the compressors to determine the power required to drive them* Observations of

the total power input to the motor used during the calorimeter

tests were made, however,, Considering the fact that various

pulley and belt combinations were employed at various stages

of the tests, and considering further that the motor losses

are not known, these total power measurements are not suitable

for determining the absolute power requirements but are

definitely of value in establishing relative power requirement

Fig, 3 shows the power consumed by the motor which operated the compressors under test„ Three tests were made of the

Thermo-King Model 4R compressor, one at conditions corresponding to 0 °F warehouse temperature, one at conditions correspond

ing to 35 °F warehouse temperature and one at 4°

3

psig suction

pressure, 177 psig discharge pressure, 62 °F suction gas temper

ature at a speed of 2404 rpm 0 Power consumed for the three

tests was 41o0, 5$9$ and 5739 watts respectively

„

For the series of tests of the Universal compressor ( sT

at conditions corresponding to 0 °F warehouse temperature, the

power consumption ranged from 2746 watts (avg) at 1747 rpm

(avg) to 456$ watts at 3029 rpm„

The series of tests of the Universal compressor at conditions corresponding to 35 °F warehouse temperature was interrupted by mechanical failure of the test specimen,, Observed

power consumption for the tests run ranged from 375$ watts at

1625 rpm to' 5614 watts at 2343 rpm„ The extrapolation of this

curve, as shown by the dotted line on Fig„ 3 indicates an expected power input of 7010 watts at 2740 rpm (2740 rpm is the

speed of the Universal necessary for equivalent displacement

to the Thermo-King at 2096 rpm) , and an expected power input

of 65OO scants at 2595 rpm, at which speed the extrapolated

capacity curve (see Fig 0 1 ) indicates equivalent capacity to

the Thermo-King compressor operating at 2096 rpm„

From these values , the refrigerating capacity per watt

input to the driving motor was 3°3 Btu(hr)/watt for the

Thermo-King compressor and 3oG Btu(hr)/watt for the Universal compressor at conditions corresponding to 0°F warehouse

temperature „ For condition corresponding to 3 5°B warehouse

temperature , the ratio was 4o2 *ptu( hr ) /watt for the ThermoKing compressor compound to 3o£ Btu(hr)/watt for the Universal

compressor ( extrapolated

)

0

5o DISCUSSION AND CONCLUSION

Under identical conditions, except for speed, the capacity

of the Universal compressor ( s ) had a linear relationship with

speed, within the range of both series of tests, as shown in

Figo lo

Since the capacity curve for the first series of tests

shown in Figo 1 was a straight line at least up to 3000 rpm,

it was assumed to be reasonable that the same characteristic

would hold true for the portion of the second series of tests

that could not be made because of mechanical failure of the , two Universal compressors submitted 0 Accordingly, the extrapfor the upper curve in Figo- 1 was shown as a straight

line 0 Within the speed range from 1600 rpm to 3000 rpm it is

probable that a similar linear relationship existed for the

Thermo-King compressor as for the Universal compressor ( s

)

e Because of the difference in theoretical displacement the

Thermo-King compressor had greater capacity for equal speeds

than the Universal compressor 0 The displacement of the ThermoKing compressor was 21 0 9 cu Q in 0 /rev 0 and of the Universal was

l6 0 B cu 0 in 0 /reVo Accordingly the speed at which the Universal

would have to operate to have equivalent theoretical displacement to the Thermo-King operating at 2100, 2300 and 2400 rpm

would be 2740, 3000, and 3130 rpm respectively 0

n- The capacity of the Thermo-King compressor at 2300 rpm,

when the suction pressure and discharge pressure was 0 o 4 psig

and 177 psig, was equal to that of the Universal compressor at

3000 rpm as shown in Fig 0 1 G This Was in agreement with the

displacements of the two compressors 0 However, following the

extrapolated portion of the curve for the other -series of tests

at a suction pressure of 13 d psig and discharge pressure of

211 psig the capacity of the Thermo-King compressor at 2100

rpm was lower than ifhat predicted for the Universal compressor

at the speed of equal theoretical displacement, 2720 rpm 0

This indicated inconsistency is not fully explained by the

test data but it suggests the possibility that the extrapolated durve should not actually be a straight line„

Mechanical failure of two specimens of the Universal

Model VFP compressor was observed, and in both cases at

speeds below the minimum speed required to produce a capacity

equal to that of the Thermo-King Model 4R compressor,, These

failures are the primary basis for the conclusion that the

Universal Model VFP compressor cannot be expected to function

satisfactorily in the Thermo-King Model MQ51 warehouse refrigerating unite

From observations of the total power input to the motor

(including belt and motor losses) used to drive the ThermoKing and Universal compressors in the calorimeter tests, it

appeared that approximately 10 percent more power was required

for the Universal compressor than for the Thermo-King compressor for equivalent capacity 0 In view of the mechanical failures of the Universal compressors it was not considered essential to study other problems such as drives, mounts, compressor body cooling, fi^,

weight, etCo, related to substitution of the Universal Model

VFP for the original Thermo=King Model 4R compressor,,

17 Test at

1

2

TABLE 1

THERMO-KING MODEL MQ51 , KNIT CAPACITY TEST

Test

Net Refrigerating Capacity

Btu/hr

Compressor

Speed

rpm

Condenser

Fan Speed

rpm

Evaporator

Fan Speed

rpm

Warehouse

Temp.

Ojt

Ambient

Temp.

op

Suction

Pressure

PSlG

Discharge

Pressure

PS! G

Suction

Gas Temp.

Op

Temp, of

Liquid

Entering

Exp. Valve

op

Gasoline

Consumption

lb/hr

i 10,100 2291 1471 1234 -0.8 109.6 0.6 177 79.6 56.1 6.2

2 23.900 2084 1319 1094 34.3 109.7 13.0 211 82.8 83.4 6.7

THEHMO-KING MODEL 4h, COMPRESSOR CAPACITY TEST

Test

Compressor

Capacity

Btu/hr

Compressor

Speed

rpm

Suction

Pressure

PSlG

Discharge

Pressure

PSlG

Suet ion

Gas Temp.

op

Temp, of Liquid

Entering Exp. Valve

°F

Compressor

Ambient Temp.

Op

1 13.700 2299 0.4 177 81.2 111.4 91.5

2 24,800 2096 13.1 211 81.2 117.1 112.1

3 27.900 24o4 4.3 117 62.0 84.8 89.0

UNIVERSAL

MODEL

VEP,

COMPRESSOR

CAPACITY

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