NATIONAL BUREAU OF STANDARDS REPORT

3790

EFFECT OF ENGINE AND FAN SPEEDS ON THE CAPACITY OF THE

1/3-TON THERMO KING REFRIGERATING UNIT, MODEL Q15G

by

C. W. Phillips

Minoru Fujii

P. R. Achenbach

Report to

Mechanical Engineering Division

Headquarters, Quartermaster Research & Development Command

Natick, Mass*

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

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A. \ . Astin, Director

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1003~20-4$32 November 12, 1954 3790

EFFECT OF ENGINE AND FAN SPEEDS ON THE CAPACITY OF THE

1/3-TON THERMO KING REFRIGERATING UNIT, MODEL Q15G

by

C. W. Phillips

Minoru Fujii

P* R. Achenbach

Heating and Air Conditioning Section

Building Technology Division

to

Mechanical Engineering Division

Headquarters, Quartermaster Research Sc Development Command

Natick, Mass*

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, r

unless permission

25, D.C. Such pi

cal ly prepared If

A in , 1 , ,, or In part, is prohibited Approved tor public release by the

. . Standards, Washington Director ot the National Institute ot

report has been specifi- Standards and Technology (NIST) report for lts own use , on October 9,2015.

EFFECT OF ENGINE AND FAN SPEEDS ON THE CAPACITY OF THE

1/3-TON THERMO KING REFRIGERATING UNIT, MODEL Q15G.

by

C. W. Phillips, Minoru Fujii, and P. R. Achenbach

ABSTRACT

A study was made of the effect of engine and fan

speeds on the net refrigerating capacity of a plugtype refrigerating unit manufactured by the U. S.

Thermo Control Company, The stock unit is beltdrivai by a gasoline engine thus fixing the speed

ratios between engine and compressor and between

engine and evaporator and condenser fans. In addition to studying the unit as furnished the effect of

independently varying the fan speeds was evaluated

using a separate fan drive. The results showed that

there were optimum speeds for both the compressor and

fans. The maximum net refrigerating capacity was

obtained at an engine speed of about 2300 rpm with

the pulleys provided on the unit. This was very

close to the design speed of the unit. However,

the design speed of the fans was too high resulting

in a loss of net capacity at all engine speeds because of the excessive amount of energy dissipated

in the refrigerator by the evaporator fan. The maximum net refrigerating capacity was observed for a fan

speed of about 1100 rpm at each of three engine speeds

in the range from 1&00 rpm to 3000 rpm. The net refrigerating capacity was increased from 4700 Btu/hr to

5350 Btu/hr by decreasing the fan speed from 2100 rpm

to 1100 rpm with an engine speed of 2400 rpm in each

case. The net refrigerating capacity increased almost uniformly with increase in compressor speed in

the range from 1200 rpm to 2000 rpm when the fan

speed was held constant indicating rather uniform

volumetric efficiency and good valve performance in

this range of speed. Experience with the test specimen

indicated that the belt drive needed some improvement

and that certain components of the engine and some of

the controls should be more accessible.
~!'V'

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1. INTRODUCTION

At the request of the Office of The Quartermaster General

tests were made as outlined in letters dated January 24th, May 2,

1951 and December 1, 1952, of a l/3-ton gasoline-engine driven

refrigerating unit, Model Q15G, of the plug type manufactured

by the U„ S. Thermo Control Company of Minneapolis, Minnesota,

It was tested in a 150 cubic foot, portable, walk-in refrigerator

of the type usually equipped with this size refrigerating unit in

the field* The refrigerator was employed as a calorimeter for the

purpose of thtese tests.

The purposes of this investigation can be divided into three

main parts as follows:

A. Measurement of the net refrigerating capacity of the

unit at design compressor speed for a range of ambient

temperatures from 70°F to 110°F and at refrigerator

temperatures of 35°F, 0°F, and the lowest temperature

attainable without internal load in the refrigerator.

B. Investigation of the effect of changing the compressor

speed on net refrigerating capacity when the speed ratios

between the compressor, and the evaporator and condenser

fans remained fixed at the design value. Investigation

of the effect in the net refrigerating capacity of changing the compressor speed independently of the fan speeds

and vice versa.

C. Observation of the mechanical features of the refrigerating unit with regard to their suitability for military

purposes.

The results observed with respect to the above three objectives are reported in Parts A, B, and C of the section on Test

Results, respectively.

2. DESCRIPTION OF TEST SPECIMEN

The specimen refrigerating unit was identified as follows:

(NBS Test Specimen 54-51)

U. S. Thermo Control Co., Minneapolis, Minnesota

l/3»Ton

Model Q15G

Serial Number

The unit was of the plug-in type and used Freon 12 as the

refrigerant. The compressor was identified as Thermo-Kifig,
.
- 2 -

Model 2R, Serial Number 1051. The refrigerating unit was driven

by a gasoline engine manufactured by D. W. Onan & Sons, Inc. of

Minneapolis, Minnesota with the following nameplate data;

Model CK-MS

Specification 190J

Serial Number 31-430271

Maximum Horsepower 10.1 at 3,000 rpm

The condenser fan was of the propeller type made of cast

aluminum. It had 10 blades, 5-5/3" long, and the diameter was

17 inches. Ambient air was drawn through the condenser, forced

around the engine and compressor and discharged from the top and

sides of the condensing unit section.

The evaporator fan was of the centrifugal type made of aluminum plates. The fan wheel was 14-1/2 inches in diameter and 1-3/4

inches in width. There were 17 fan blades which were 1-1/2 inches

long. The air was drawn into the evaporator from the front and

discharged from the top of the evaporator section.

The condenser and evaporator fans were mounted on opposite

ends of a common shaft. The pulleys of the engine, idler, fans

and compressor were connected in that order in a clockwise direction by two V-belts. The diameters of the pulleys were 6-3/4",

7", 7-3/$" and 10", respectively.

Five photographs of the specimen refrigerating unit are

attached as Figures 1-5 inclusive. Figure 1 and Figure 2 show

the exterior views of the condenser and evaporator sections,

respectively. Figure 3 is a three-quarter view showing the

condenser section with the perforated panels removed. Figure 4

is a left side view of the condenser section showing the relative

locations of the engine, condenser fan, and compressor. Figure 5

is the side view of the evaporator section showing the location of

the evaporator fan.

The physical dimensions of the refrigerating unit were as

follows;

(1) Gross weight, without battery, lb. 533®

5
>“

-
- 3 -

(2) Overall dimension, include

battery, in»

(3) Condensing unit section

without battery, in.

(4) Evaporator section, in.

(5) Plug Section, in.

(6) Compressor:

a) Model

b) Serial Number

c) Type

d) Bore, in.

e) Stroke, in.

f) Speed, rpm, design

g) Displacement, cu. in.

(7) Condenser:

a) Width, in.

b) Height, in.

e) Depth, in.

d) Fin size, in.

e) Fin spacing

f) Tube size, in.

g) Number of tubes

h) Series or parallel

i) Primary surface

area, sq. ft.

j) Secondary surface

area, sq. ft.

k) Total surface

area, sq. ft.

l) Ratio primary to total

surface, %

m) Tube material

n) Fin material

Wi dth Height Depth

34 59-3/8 32-1/4

34 50 19

27=1/2 28 10-1/4

28 28 3

2R

1051

2 cylinder vertical

2-1/4

1-3/4

1680

13.91

27

23-1/2

1-3/4

23-1/2 X 1-3/4

10 per inch

3/S O.D.

4S

24 tubes in series per circuit,

2 circuits in parallel

10.6

134.3

144.9

7.3

Copper

Aluminum

- 4

-

(3) Engine:

a) Model number

b) Specification

c) Serial number

d) Type

e) Material

f) Speed, rpm, design

g) Hated maximum brake

horse power at 3000 rpm

h) Lubrication

i) Fuel system

j) Ignition system

k) Cooling system

1)

Governor

(9) Evaporator:

a) Width, in*

b) Height, in.

c) Depth, in.

d) Fin size, in.

e) Fin spacing

f) Tube size, in.

g) Number of tubes

h) Series or parallel

i) Primary surface area,

sq. ft.

j) Secondary surface area,

sq . ft.

k) Total surface area,

sq. ft.

l) Ratio primary to total

surface, %

m) Tube material

n) Fin material

CK-MS

190J

31-430271

4 cycle 2 cylinder opposed

horizontal, air-cooled

Aluminum

2400

10.1

Force feed

Pump feed to carburetor

Special 12 -volt motor-generator

built into flywheel of engine

provided automatic starting,

battery charging and ignition.

Fan on armature of engine generator forced air over engine

block and finned cylinder heads

as directed by engine housing.

Pierce Governor Company - GC1403 2 1

24

25

4

4 x 25

3 per inch

1/2 0.D,

30

20 tubes in series per circuit

20.9

24.3

245,7

3.5

Copper

Aluminum

- 5 -

3. TEST PROCEDURE

The specimen refrigerating unit was installed in a 150 cu, ft.

portable, walk-in refrigerator for the capacity tests, which was

located in a test room where the ambient temperature could be controlled. Refrigerator temperature was maintained at the desired

level by an electronic rheostat controlling the input to electric

heaters which were used for the internal load. The heat output of

these heaters was measured by means of watthour meters in the supply

circuits. Temperatures were measured by means of calibrated thermocouples using an electronic, constant-balance type potentiometer.

The engine speeds were varied by adjusting the governor. The

compressor, fan, idler, and engine were connected with a pair of

double-faced V-belts during Part A of the tests. Therefore, the

compressor and fan speeds were proportional to the engine speed as

determined by the pulley ratio. During Part B of the tests, the compressor was driven by the gasoline engine and the fans were driven

with a single V-belt by a 3/4 H.P. direct current motor installed on

top of the condenser section. The idler was eliminated and the engine

and compressor were connected with two V-belts using the original

pulleys. The condensate drain fitting had to be removed in order to

permit installation of these belts# The objective of this modification was to provide independent control of the fan and compressor

speeds so the fan speed could be determined for each engine speed

that would result in the maximum net refrigerating capacity* The

fan speeds were regulated by variable external field resistance and

all speeds were measured by means of a stroboscopic tachometer.

After steady state test conditions were reached, they were

maintained for an average period of about 5 hours while observations

of pressures, temperatures, speeds, voltage, electric current and

wattage were made at 30 minute intervals.

During the course of the capacity tests, some operational

difficulties were encountered. They were recorded when they occurred

for reporting as a part of the operating experience with this unit.
'
4. TEST RESULTS

Part A

In preparation for the capacity tests, a test was made

to determine the heat transmission factor of the 150 cubic

foot, portable, walk-in refrigerator in Btu per hour per

degree cemperature difference. Refrigerator temperature

averaged 35®3°F and the ambient temperature averaged 136*2 C F

for eleven hours during steady state conditions. ^ The heat

transmission factor was computed to be 23*62 Btu/'nr (°F temperature difference),,

Results of the capacity tests with various engine speeds

and proportional fan speeds at a refrigerator temperature of

0°F and an ambient temperature of 110°F are summarized in

Table 1 and shown graphically in Fig. 6. The engine speed

bore an average ratio of 1.56 to 1 to the compressor speed

and 1.11 to 1 to the fan speed during these tests. However,

these ratios did not remain constant for all tests indicating

that belt slippage was occurring during some tests. This

problem is discussed in Fart C of this report*

Fig. 6 shows that the net refrigerating capacity reached

a maximum value of about 4700 Btu/hr at an engine speed in the

neighborhood of 2300 rpm. The net refrigerating capacity

decreased for speeds above and below 2300 rpm reaching a value

of l/3-ton or 4000 Btu/hr at engine speeds of about 1760 rpm

and 2920 rpm*

It would be expected that the total refrigerating capacit

of the compressor would increase proportionally with engine

speed if the volumetric efficiency remained constant* However, the power required to drive the evaporator fan would

increase as the cube of the fan speed or the engine speed.

Consequently, at some engine speed the rate of increase of com

pressor capacity would be eoual to the rate of increase of

evaporator fan power * Above this speed the net refrigerating

capacity would decrease assuming that the heat transfer co~

efficient of the evaporator surfaces remained constant through

out the speed range. This optimum engine speed was about

2300 rpm on the test specimen which was approximately the design speed of the unit

.

Table 1 shows that the comparative differences between

inlet and outlet air on the evaporator and between inlet and
[
- 7

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outlet air on the condenser remained reasonably steady

in the engine speed range from 1$00 rpm to 2700 rpm.

This indicates that the total heat transfer in each of

these components increased steadily with increase in

engine speed since the air delivery of a fan in a given

circuit is proportional to the fan speed,, There was about

a 20 percent decrease in the temperature difference between inlet and discharge air of the evaporator at an

engine speed of 3000 rpm as compared to the lower engine

speeds indicating a decrease in the net refrigerating

capacity.

The slow rise in discharge pressure and the gradual

decrease in suction pressure with increased engine speed

indicate a steady increase in the total amount of heat

transferred by the condenser and evaporator, respectively.

The greater air flow over the condenser and evaporator

surfaces does not significantly change the heat transfer

coefficient inside these heat exchangers. Consequently,

a greater temperature head was recuired to exchange more

heat between the refrigerant and these surfaces.

If it were assumed that the compressor capacity was

directly proportional to engine speed and the power absorbed by the evaporator fan directly proportional to the

cube of the fan speed during this series of tests, the net

refrigerating capacity of the unit could be expressed by

an equation of the form:

R = AS - BS3 where

R is the net refrigerating capacity in Btu/hr

S is the engine speed in rpm

A and B are constants which can be evaluated using

the observed values of R and S for two test conditions.

Using values of R taken from the curve in Fig. 6 for

S = 2100 and 2400 rpm, respectively the following relationship is obtained:

R = 3.09S - 0.00197S3

(1)

From this equation values of the net refrigerating

capacity at other engine speeds in the range of the tests

have been computed and plotted in Fig. 6. The computed

values fit the curve drawn through the observed values

very well except at engine speeds near 1800 rpm indicating that equation (1) adequately represents the relationship between net refrigerating capacity and speed over

most of the speed range tried.

The discharge and suction pressures and the air

temperatures at the outlet of evaporator and condenser

were probably affected to a small extent by the belt

slippage revealed during some of the tests but these effects

are considered small compared to the broader capacity trends

caused by compressor displacement and power comsumption of

the fans.

Fig. 7 shows the hourly gasoline consumption of the

unit plotted against the engine speed. The relationship

was approximately linear over the range of the tests. The

gasoline consumption per ton of net refrigerating capacity

increased steadily over the range of speed shown in Fig. 7

and was slightly more than twice as great for a speed of

3000 rpm as for a speed of 1800 rpm.

The relation between the net refrigerating capacity

of the Thermo King Q15G unit and refrigerator temperature

is shown in Fig. 8 for four different ambient temperatures

ranging from ?0°F to 125°F. At each ambient temperature

tests were made with refrigerator temperatures of 35°F,

0°F, and the lowest temperature that could be attained without internal heat load. The observed results are summarized

in Table 2.

The engine was operated at a speed of about 1700 rpm

for these tests corresponding to compressor and fan speeds

of about 1200 rpm and 1600 rpm respectively. However, there

was more than 100 rpm speed variation during the series of

tests for each of the components: engine, compressor, and

fans. These variations were caused by belt slippage in

some cases but depended also on the amount of load on the

engine. It was observed that the speed of the engine changed

with engine load considerably for a given governor setting.

- 9

Fig. 3 shows that the net refrigerating capacity varied

approximately in linear relation to the refrigerator temperature at each ambient temperature » The capacity curves at the

four ambient temperatures are nearly parallel, converging

slightly as the refrigerator temperature decreased. On the

average the net refrigerating capacity increased 140 Btu/hr

per degree rise in refrigerator temperature for the three higher

ambient temperatures. At an ambient temperature of 125°F the

net refrigerating capacity increased 117 Btu/hr for each degree

rise in refrigerator temperature.

Part B

Capacity tests were made to determine the optimum fan

speeds at various engine speeds and the results are summarized

in Table 3» The refrigerator temperature and the ambient temperature were maintained at about 0°F and 110°F respectively

during the tests. Speeds of the fan and engine were controlled

independently for each test. Fan speeds were varied from 500 rpm

to 2100 rpm and engine speeds from 1300 rpm to 3000 rpm at

300 rpm intervals.

Figure 9 shows the net refrigerating capacity plotted

against engine speed for average fan speeds of 334 rpm 3 1353 rpm

and 2097 rpm. At each fan speed the unit capacity increased

approximately in direct proportion to the increase in engine

speed in the range from 1300 rpm to 3000 rpm. Each curve drops

slightly at the higher engine speeds. This is probably accounted

for by the increase in compression ratio that occurred with increase in engine speed. Table 3 shows that the discharge pressure

increased and the suction pressure decreased as the engine speed

increased for any constant value of fan speed. This was to be

expected because greater temperature difference between air and

refrigerant would be required in both evaporator and condenser to

transfer greater quantities of heat as the engine and compressor

speeds increased.

A comparison of Fig. 6 and Fig. 9 reveals the effect of

proportional and constant fan speed on net refrigerating capacity

at any given engine speed. Net refrigerating capacity is plotted

against engine speed in both figures, but in Fig. 6 the fan speed

was increased proportionally with the engine speed whereas in

Fig. 9 the fan speed remained constant while the engine speed was

increased. This comparison shows that the greater refrigerating

capacity produced by increased engine and compressor speed was
_

.
- 10 -

quickly offset by the greater amounts of fan energy dissipated in the refrigerator by the evaporator fan.

The marked curve in Fig. 6 shows approximately how the

net refrigerating capacity would increase with engine speed

if the fan speed remained constant at 1500 rpm, the fan

speed corresponding to the lowest value of engine speed on the

solid curve. The marked curve is based on the data in Table 3*

The difference in capacity represented by the two curves in

Fig» 6 is a measure of the increased energy dissipated in the

refrigerator by the evaporator fan when the fan speed is increased proportionally with the engine speed as compared to

constant fan speed. The difference amounted to 1600 Btu/nr

at an engine speed of 3000 rpm.

Figure 9 shows that the net refrigerating capacity at

any given engine speed increased in the range of fan speed

from 834 rpm to 1062 rpm, but began to decrease in the range

of fan speed between 1062 rpm and 1353 rpm and decreased quite

significantly for a fan speed of 2097 rpm. This relationship

is revealed more clearly in Fig. 10 where net refrigerating

capacity is plotted against fan speed for three engine speeds.

Fig. 10 shows that the net refrigerating capacity increased

with fan speed up to a value of about 1100 rpm after which it

decreased rather rapidly with further increase in fan speed.

Table 3 shows that the compression ratio decreased as the

fan speed was increased for any constant value of engine speed.

This was th^ result of better heat transfer in both evaporator

and condenser. The pumping capacity of the compressor increased

as the compression ratios decreased even though the compressor

speed remained constant and the increase in compressor capacity

was greater than the increase in evaporator fan power for fan

speeds up to 1100 rpm. Above this fan speed the energy dissipated

by the evaporator fan increased more rapidly than the compressor

capacity so the net refrigerating capacity decreased.

If the data in Table 3 are plotted to show the relation

of compression ratio to fan speed at constant compressor speed,

it is revealed that the curve approximates a straight line*

Calorimeter studies of other compressors have shown that the

capacity of a compressor decreases almost linearly with increase in compression ratio. These two facts can be combined
I ’ '
- 11 -

in the following equation to show how the total refrigerating

capacity of the compressor in the Thermo King unit might be

affected by the fan speeds*

Rt

= A - BS where

R is the total refrigerating capacity of the compressor

S is the fan speed

A and B are constants

However , the net refrigerating effect of the unit would

be equal to the difference between the total refrigerating

capacity of the compressor and the heat dissipated by the evaporator fan inside the refrigerator* But since the fan power is

proportional to the cube of the fan speeds the net refrigerating

capacity of the unit could be expressed by an equation of the

form:

R - A + BS - CS^ where

R is the net refrigerating capacity in Btu/hr

S is the fan speed in rpra

A, B and C are constants which can be evaluated

using the observed values of R and S

for three test conditions at constant

engine speed*

Using values of R taken from the curve in Fig* 10 for

S

35 £00, 1300 and 2100 rpm respectively, and an engine speed

of 3030 rpm, the following relationship is obtained:

R - 4572 + 1.326S - 0*26 x 10“ S (2)

From this equation values of the net refrigerating capacity

at other fan speeds in the range between £00 and 2100 rpm have

been computed and plotted in Fig. 10 * The computed values lie

near the curve drawn through the observed values for an engine

speed of 3030 rpm, although the curvature of the line through

the computed values is slightly different and the fan speed

- 12 =

corresponding to the maximum value of capacity is a little

higher for equation 2 than for the observed data. The rela=

tively good agreement of the computed and observed values

indicates that an equation similar to equation 2 represents

the relation between net refrigerating capacity and fan speed

of the Thermo King unit at constant engine speed.

If the theoretical relation between volumetric efficiency

and compression ratio is used instead of the linear relation

assumed in equation (2), an equation of the following form

results? 1

"TToST 3

E - A <= BP => GS where (3)

R is the net refrigerating capacity in Etu/hr

S is the fan speed in rpm

P is the compression ratio of the compressor

A 3 B 5 and C are constants which can be evaluated if

three sets of observed values of P s and S a,re substituted in the equation.

It was found that the curve described by equation (3) does

not fit the observed data plotted in Fig s 10 any better than the

curve for equation (2) and equation (3) requires a knowledge

of the relation between compression ratio and fan speed for the

unit under test* A more comprehensive study of the performance

characteristics of the various components in the Thermo King

unit might reveal an equation that better describes the relation

between net refrigerating capacity and fan speed than either

equation (2) or (3).

Part G

A number of defects and mechanical failures were observed

during the course of the tests. These are described below.

The joint between rubber and glass in the sight glass in

the liquid refrigerant line was loose causing the unit to lose

its refrigerant charge during the storage period prior to the

tests, A close coupling of the double flare nut type between

- 13 -

the receiver valve and the sight glass split during the

tests causing loss of refrigerant.

Considerable difficulty was experienced with the belt

drives. When the unit was first started for test, it was

found that the belts were loose and the compressor pulley

was not aligned with the engine pulley. As a result the

belts did not ride down in the groove of the compressor

pulley. The belts became loose twice during the course of

the tests indicating that the automatic belt-tightener did

not function properly. The spring furnished on the belttightener was replaced with a turnbuckle and a short spring

one inch in diameter made of l/$-inch tempered wire. This

modification prevented further difficulty with belt slippage.

It was observed, however, that the arc of belt contact on

the compressor pulley was small because of the relative positions of

the pulleys on the engine, compressor, fans and the idler.

The battery charging rate was initially observed to

be 12.5 amperes. It was reduced to 2.5 amperes in accordance

with the manufacturer's instructions. It was observed that

the batteries required daily filling with water even after the

charging rate was reduced.

Considerable maintenance was required on the distributor

points to keep the engine in operation. The distributor was

not readily accessible. Considering the frequent need for

servicing, attention should be given to a relocation of some

of these components.

The manually-operated hot gas defrost valve was not readily

accessible. It was located in a place which caused the operator

to be burned by the refrigerant line at the condenser inlet when

opening the valve. A relocation of the thermometer on the

control panel and changing the position of the defrost valve

handle would remove this hazard.

The metal side panel had to be removed from the unit to

start the engine, adjust the thermostat, or fill the gasoline

tank. If these functions could be performed through an access

opening, the operator would be more likely to leave the side

panel on the unit®
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wt
- 14 -

5. DISCUSSION AND CONCLUSIONS

This study of the relation between net refrigerating

capacity and engine and fan speeds for the l/3~ton Thermo

King refrigerating unit, Model Q15G, showed that there were

optimum speeds for both components. The maximum net refrigerating capacity was obtained at an engine speed of about 2300

rpm with the pulleys provided on the unit. This speed was

very close to the design speed of the unit. However, the

design speed of the fans was too high resulting in a loss of

net capacity at all engine speeds, because of the excessive

energy dissipated in the refrigerator by the evaporator fan.

The maximum net refrigerating capacity of the unit was observed for a fan speed of about 1100 rpm at each of three

engine speeds, viz, 1&00 rpm, 2400 rpm and 3000 rpm. The net

refrigerating capacity was increased from 4700 Btu/hr to

5350 Btu/hr by decreasing the fan speed from 2100 rpm to 1100

rpm with an engine speed of 2400 rpm in each case. Therefore,

it is recommended that the pulley on the fan shaft be reduced

in diameter to provide a fan speed of approximately 1100 rpm,

at the design engine speed, thereby increasing the capacity

and reducing the load on the engine.

The net refrigerating capacity increased almost uniformly

with increase in compressor speed in the range from 1200 rpm

to 2000 rpm when the fan speed was held constant indicating

rather uniform volumetric efficiency and good valve performance

in this range of speed. These results suggest the possibility

of using the same compressor for more than one duty by adjusting the compressor speed to the anticipated load.

Experience with the test specimen indicated that the

belt drive needed some improvement and that accessibility

had been sacrificed to compactness in a few important respects.
tm-
EFFECT OF COMPRESSOR SPEED ON UNIT

CAPACITY AT CONSTANT REFRIGERATOR AND AMBIENT TEMPERATURES

Test No. _1 __2 3 4 _j> _6

Net Refrigerating, capacity,

Btu/hr 4060 4670 4690 4470 3940 3730

Engine Speed, r.p.m. 1735 2099 ! 2364 2693 2973 2974

Compressor Speed, r.p.m. 1120 1339 1526 1301 1910 1935

Fan Speed, r.p.m. 1590 1353 2103 2423 2912 2656

Ratio of Engine Speed to

Comp. Speed 1.59 I .64 1.55 1.49 1.56 1.54

Ratio of Engine Speed to

Fan Speed 1.12 1.13 1.12 1.11 1.02 1.12

Gasoline Consumption, lb/hr 3.2 4.0 4.3 6.2 7.4 6.5

Discharge Pressure, psig. 205 211 214 219 226 226

Suction Pressure, psig. 4.4 5.0 4.2 3.3 2.9 2.9

Avg. Refrigerator Temp.,°F 0.0 0.2 0.1 0.2 0.3 0.2

Avg. Ambient Temp., °F 110.7 109.9 109.0 110.9 110.7 P-10.3

Suction Gas Temp., °F 32.2 76.5 78.7 78.7 78.9 73.3

Temp, of Air Entering

Condenser, °F 117.5 113.2 119.2 117.9 117.9 p.13.1

Temp, of Air Leaving

Condenser, °F 124.6 126.3

1 126 .

1

125.9 125.8 126.5

Temp, of Air Entering

Evaporator, °F 1.7 1.9 2.5 I 1.5 1.6 1.7

Temp, of Air Leaving

Evaporator, °F -3.3 -3.1 - 2.9 1

1 -3.6 -2.6 -2.2

TABLE 1
'

'

.

,* •

'
»rirrrnv*T PITHFAII OF STANDARDS

TEST NO.

Net Refrg.-

Engine Spe

Compressor

Fan Speed

Gasoline C Avg. Refrg

Avg. Ambie

Discharge

Suction Pi

Compressic

Suction Gs

Temp, of I ing Conde

Temp, of / ing Conde

Temp, of / ing Evapc

Temp, of l Ing Evapf

^Vacuum, 1
• . > '
EFFECT OF AMBIENT TEMPERATURE AND REFRIGERATOR TEMPERATURE ON UNIT CAPACITY

AT CONSTANT COMPRESSOR AND FAN SPEEDS

TEST NO. Units

Net Refrg. Capacity Btu/hr

Engine Speed r.p.m.

Compressor Speed r.p.m.

Fan Speed r.p.m.

Gasoline Consumption lb/hr

Avg. Refrg. Temp. °F

Avg. Ambient Temp. °F

Discharge Pressure psig.

Suction Pressure psig.

Compression Ratio

Suction Gas Temp. °F

Temp, of Air Entering Condenser °F

Temp, of Air Leaving Condenser °F

Temp, of Air Entering Evaporator °F

Temp, of Air Leaving Evaporator °F

1 2 3 4

10,570 5,280 5,440 2,230

1,726 1,804 1,779 1,801

1,127 1,257 1,191 1,186

1,529 1,657 1,601 1,581

3.4 3.1 3.2 £.7

36.4 1.3 0.7 -22.7

71.3 71.1 71.5 71.5

170 130 127 116

17.2 4.3 4.6 6.0*

5.30 7.64 7.37 11.20

64.6 57.9 55.8 62.1

34.4 77.9 79.1 76.8

91.1 82.0 31.9 77.6

38.6 2.6 1.7 -21.7

22.8 -4.9 -5.9 -25.1

5 6 7 8

10,040 4,360 2,530 8,620

1,701 1,741 1,764 1,613

1,205 1,067 1,136 1,151

1,605 1,447 1,521 1,526

3.6 3.1 2.3 4.0

35.2 0.7 -16.3 34.8

91.0 91.4 90.8 109.8

174 165 153 225

17.0 5.5 0.5* 19.0

5.96 8.66 11.70 7.12

72.6 70.2 74.3 81.7

100. g 97.9 95.7 119.3

108.0 100.6 96.1 126.8

37.5 2.1 -15.4 36.8

22.7 -4.6 -18.8 23.9

9 10 11 12

3,990 2,770 7,490 3040

1,699 1.726 1,693 170S

1,215 1,225 1,199 1211

1,605 1,626 1,601 1608

2.6 2.3 4.1 3.3

0.1 -6.7 35.5 -2.5

110.2 110.5 124.1 126.3

188 188 261 224

6.5 2.8 19.0 5.5

9.59 11.65 8.20 11.87

79.4 85.2 88.1 90.9

117.2 116.1 133.9 131.9

120.2 117.7 HO. 6 134.7

1.0 -5.6 37.1 -1.6

-4.8 -9.7 26.0 -5.6

^Vacuum, In. Hg.

TABLE 2

htthf.au OF STANDARDS

Nominal Engine

Test No,

Net Refrigerate

ing CapacityEngine Speed

Compressor Spec

Pan Speed

Gasoline Consumption

Avg. Refrigera

Tempe rature

Avg, Ambient

Temperature

Discharge Pres- sure Suction Pressuj

Compression Ra' Suction Gas Tei

perature

Temperature of

Entering Cone ser Temperature of

Air Leaving

Condenser

Air Temperature

Diff, across Condenser

Temperature of

Air Entering

Evaporator

Tempe rature of

Air Leaving

Evaporator

Air Temperature

Diff, Across

Evaporator

EFFECT OF FAN SPEED OK NET REFRIGERATING CAPACITY AT CONSTANT ENGINE SPEED

Nominal Engine Speed. RPK 1800 2100 24-00 2700 1000

Test No. Units 1 2 3 4 5 6 7 8 9 10 11 12 13 l4 15 16 17

Net Refrigerat- Btu/hr 4220 4498 3374 4972 4264 3785 ; 4427 5016 5063 5304 5408 4721 4210 4584 54g4 5669 4993

ing Capacity

Engine Speed r.p.m. 1841 1828 1809 2107 2095 2089 2435 2400 2421 2428 2396 2435 2400 . 2687 3030 3045 3014

Compressor Speed r.p.m. 1230 1210 1213 1388 1390 1387 1600 1580 1595 1608 1570 1601 1589 1763 2005 2015 1996

Fan Speed

Gasoline Conr e p„m. 828 1354 2114 1355 1718 2089 515 675

4.0

831 1013 1062

4.2

1718 2084 2110 844 1350 2086

sumption

Avg. Refrigerator

lb/ hr 3.1 3.3 2.9 3.5 3.6 3.7

-0.4

3.9 3.9 3.9 4.3 4.0 ,

1 4.6 4.8 4.8 5.0

Temperature ®F -1.3 0.0 -0.1 -0.1 -0.3 0.1 0.0 -0.1 -0.5 -0.2 1.3 -0.2 -0.5 0.1 -0.3 0.2

Avg. Ambient

Temperature

Discharge PresOp io4.g 109.8 111.6 107.4 110.9 111.2

186

107.9

194

107.2

194

110.0

196

109.3 105.6 111.5 111.6 ill0,7 110,8

!

109.9 108.0

sure psig 194 189 187 192 187. 193 191 192 195 190 201 193 203

Suction Pressure psig 2.4 3.5 5.0 3.0 3.5 3.6 | l.l 1"Hg 1.9 1.5 2.2 1.6 2.9 2.7 1.8 1.0"Hg 0.7"Hg 2.2

Compression Ratio

Suction Gas Tem12.27 11.25 10.28 11.73 11.13 11.02

74.3 |

14.83 12.64

78.4

13. 08

69.7

12.35

72.4

12.70 11.80 12.11

79.4

12.47 j 15.30 14.55 12.95

perature °F 73.2 75.9 79.2 : 72.7 76.6 70.5 72.6 73.8 77.2 73.3 75.6 74.8

Temperature of Air ! Entering Conden- i 117.6 119.0 ser op 118.8 118.0 118.0 : 118.9 117.5 H7.6 j 1118.3 119.1 117.2 117.9 118.9 120.1 118.9 118.5 118.2

Temperature of

Air Leaving

Condenser ©F 131.3 125.5 123.1

j L28.2 124.8 122.6

i 133.3 131.6 130.0 129.2 128.8 129.3 126.2

j124.9 131.6 127.1 128.6

Air Temperature I Diff. across Condenser op 12.5 7.5 5.1 9.3 7.3 5.0 15.0 12.5 12.8 n.3 9.9 9.2 7.3 7.3 13.1 8.9 9.6

Temperature of : Air Entering

Evaporator ©F 0.1 1.0 0.7 0.8 l.l 0.6 “ - 2.1 0.9 1.0 2.6 0.7

1 0.3 1.1 0.5 1.5

Temps rature of

Air Leaving

Evaporator Op -9.7 - 6.3 -2.8 -7.3 -4.2 -3.5 - 15.5 -7.3 -11.3 -9.8 -9.6 -3.2 -3.6 -5.0 -12.8 -9.0 -4.3

Air Temperature

Diff. Aero 88

Evaporator Op 9.8 7.3 3.5 8.1 5.3 4.1 - - 13.4 10.7 10 . 6 . 5.8 4.3 i 5.3 13.9 9.5 5.8

TAP L E A j

1

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; 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. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project or program. Published 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 monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

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

which provides data for determining the best frequencies to use for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.00). Information on calibration services and fees can be

found in NBS Circular 483, Testing by the National Bureau of Standards (25 cents). Both are available from the Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of Standards, Washington 25, D. C.
NBS