NBSIR 74-547

Ice Quality and Energy Utilization

Efficiency Tests of Four Commercial

Ice Makers

William J. Mulroy and John W. Grimes

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

March 11, 1974

Final Report

Prepared for

S. Army Natick Laboratories

Natick, Massachusetts 01760

NBSIR 74-547

ICE QUALITY AND ENERGY UTIUZATION

EFFICIENCY TESTS OF FOUR COMMERCIAL

ICE MAKERS

William J. Mulroy and John W. Grimes

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington. D. C. 20234

March 27. 1974

Final Report

Prepared for

U. S. Army Natick Laboratories

Natick, Massachusetts 01760

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent. Secretaiy

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director
V,

..."1*1' f-
Ice Quality and Energy Utilization Efficiency Tests

of Four Commercial Ice Makers

William J. Mulroy and John W. Grimes

Thermal Engineering Systems Section

Building Environment Division

Center for Building Technology

Institute for Applied Technology

ABSTRACT

At the request of the United States Army Natick Laboratories, the

Center for Building Technology tested four commercial ice making machines

for their ice-making process efficiency and for the latent heat of fusion

clarity, and purity of the ice which they produced. This was done to pro

vide quality estimation guidelines for field testing of these units and

to indicate the ranges of ice quality and machine efficiency that could

be expected.

Key Words: Calorimetry; heat of fusion; ice; ice machine

tests; ice makers; latent heat; refrigeration

equipment
Table of Contents

Page

1. Introduction 1

5 2. Test Specimens 1

3. Test Apparatus and Procedure 2

3.1 Test Apparatus 2

3.2 Test Procedure ..... 3

3.2.1 Latent Heat of Fusion Measurements 3

3.2.2 Efficiency and Ice Production Rate Measurements . 3

10 4. Test Results » 3

4.1 Calorimeter Calibration .... 3

4.2 Latent Heat of Fusion Measurements 4

4.3 Observations 4

4o4 Efficiency and Ice Production Rate Measurements 4

5. Discussion and Conclusions 5

6 . Acknowledgment 5 15

Table I Latent Heat of Fusion Measurements 6

Table II Efficiency and Ice Production Rate Measurements .... 7

ii
1. Introduction

The Thermal Engineering Systems Section of the Center for Building

Technology of the National Bureau of Standards (NBS) was requested by

U. S. Army Natick Laboratories through Project Order No. AMXRED 73-314

dated May 18, 1973 to develop testing and rating methods for measuring

^ the ice production of ice makers under field conditions.

Electrical power consumption and pounds per hour of machine output are relatively simple to measure. They are determined by using a watthour meter and small platform scale. The output of these machines, however, has some water content so that a simple weight measurement of the

machine output is not a measurement of the ice output. The accurate determination of the water content of the ice requires a laboratory calorimeter.

In this project, calorimeter measurements were made of ice produced

10 in several different sizes and by different processes to determine the

probable magnitude of the moisture content likely to be encountered in

the field and also to provide rule-of -thumb values for estimating this

variable

.

Measurements were also made of the electrical power required to

operate these machines so that thermal efficiencies for the various ice

making processes tested could be calculated.

15 2. Test Specimens

Four commercial ice makers were tested. Three of these were new machines provided especially for these tests by U. S. Army Natick Laboratories and the fourth was NBS property which had been used as a laboratory ice maker for approximately 3 years. These machines were chosen

to provide samples of three different sizes of ice particles, cubes,

flakes, and crushed ice produced by two basic methods, batch and continuous operation.

20

Machine B-1 produced cube ice by a batch process in which ice was formed by spraying water into inverted, refrigerated molds and then

harvested by warming the molds with water which had been heated by con- denser heat during the refrigeration cycle. The ice cubes were cylinders

approximately 1 1/4 inches in diameter and 1 1/2 inches long.

Machine B-2 produced flake ice in a batch process by freezing water

into refrigerated flat plates, harvesting the flat ice sheets with hot

gas, and then breaking the sheet ice into flakes in a mechanical, motor25 driven cracker. The ice flakes were approximately 3/16 inch thick and

varied in size from roughly 1/4 inch in diameter to 1 inch in diameter

with the average diameter about 5/8 inch.
10

15

20

Machine C-1 produced ice in a continuous process by scraping the

interior of a refrigerated drum on which the ice was frozen with a motor

driven worm which also compressed the ice and forced it through a 3/8

inch by 5/8 inch rectangular die. This rectangular, extruded rod of ice was then broken into sections of diced ice varying from 1/2 inch to 2

inches in length.

Machine C-2 produced ice in a continuous process by scraping ice

from a refrigerated surface. The crushed ice particles produced were irregularly shaped and approximately 1/4 inch in diameter.

The batch process machines recirculated the water which was frozen

during the refrigeration cycle; dumped the remaining water and took a supply of fresh water at the end of each batch. Dumping this water re- sulted in some lost efficiency but produced clearer ice by eliminating

impurities in the water.

The continuous process machines have no waste water. The nature of

their cycles prevents their producing clear ice even if the water impurities were not frozen.

Test Apparatus and Procedure

3.1 Test Apparatus

The primary objective of this test series was to determine the latent

heat of fusion of the ice produced by these machines, i.e., the moisture

content (wetness) of the ice, and secondarily to determine their ice production rate. For this reason the primary effort was to construct and

operate a calorimeter for measuring the ice sample latent heat of fusion.

Figure 1 illustrates the calorimeter that was constructed for latent

heat of fusion measurements. The calorimeter was heavily insulated (approximately 4 inches of urethane foam) so that the energy used to melt

the test ice sample would be provided by metered electric heat instead

of sensible heat gain through the calorimeter walls. The circulating

pump was provided to insure uniform conditions within the calorimeter.

In addition to the calorimeter apparatus, calibrated, commercial

watt-hour meters were used to measure the ice making machine power re- quirements and a beam balance with a smallest division of 1/100 pound was used to weigh ice samples.

2
3.2 Test Procedure

3.2.1 Latent Heat of Fusion Measurements

At the start of a test the calorimeter was filled to the drain and

its interior heated to 40 °F. The drain was then plugged, the ice sample

to be tested weighed and added, and the temperature again lieated to 40 °F.

Since the sensible ^heat gain to the calorimeter was negligible both be- cause of its heavy insulation and because the surrounding temperature was

held to 32 °F by the test laboratory refrigeration system, the latent heat

of fusion for the total sample was the electrical power input to the calorimeter required to return it to its original state.

The calorimeter filled to its drain held approximately 40 pounds of

water. Ice test samples ranged in weight from 7 to 12 pounds.

Samples of standard ice which had been stored at a subfreezing temperature were used to check the accuracy of the test setup on each test

day. Since these samples were subcooled, a mathematical correction for

sensible cooling was applied to the calculations for these calibration

tests. The ordinary test samples from the machines were assumed to be near saturation and their temperatures were not measured.

3.2.2 Efficiency and Ice Production Rate Measurements

The ice production rate test was not performed at standard test con- ditions. Normal laboratory supply water was used. Water and ambient

temperatures stayed substantially constant during the two months in which

these tests were performed.

Each test reflects approximately one 8 hour day's continuous operation for the machine with the ice production weighed and the power con- sumption read hourly.

4. Test Results

4.1 Calorimeter Calibration

Calibration of the calorimeter using standardized ice was performed

on 10 different days.

The average value was sufficiently close to the expected value of

144 Btu/lb that no correction factor was applied to the test results.

The range of values measured indicates that the accuracy of a single

calorimeter test could be expected to be better tlian 3%.

3
The

Table I. individual test results are summarized in the first column of

4.2 Latent Heat of Fusion Measurements

Measured latent heats of fusion for samples of ice from the four

machines tested are summarized in Table I. The calculated ice quality

included in the table is defined as the latent heat of fusion for the

test sample divided by that of the standard ice and is equivalent to

the percent of the ice sample that is actually ice instead of water.

In addition to the tests listed in Table I, tests were made of ice

samples from machines B-1 and B-2 that had been stored overnight in thei

mcchines's storage bins. Values of 142.4 and 137.0 Btu/lb were measured

for the aged ice from these two machines, respectively, indicating that

there is no appreciable difference between fresh and aged ice.

4.3 Observations

The ice produced by the batch process machines, B-1 and B-2, was

clear in appearance whereas that produced by the continuous scraping and

compacting processes was translucent.

No off taste or noticeable odor or discoloration was imparted to th

ice by any of these machines.

4.4 Efficiency and Ice Production Rate Measurements

Table II lists the results of the ice production rate and efficienc

tests. The coefficient of performance listed in the table was obtained

by dividing the heat equivalent of the ice production rate by that of

power consumption after both had been converted to similar units.

The Ibs/hr of ice produced is the actual measured weight and is

not corrected to 144 Btu/lb ice equivalent. All tests were performed

with an ambient air temperature surrounding the machine of approximately

68 °F and a water supply temperature of approximately 72 °F.

In addition to the tabulated results, measurements were also made

of the power requirement of the harvesting motor on machine C-1 (88

watts) and of the heat lost in the blow-down water on machine B-1 (624

Btu/hr)

.
5. Discussions and Conclusions

The ice from the batch type machines was clearly higher in quality

than from the continuous machines. The continuous process of scraping

and compacting ice from a plate on which running water is continuously

being frozen results in unclear ice with included water.

^ The highest and lowest values of ice quality (percent ice in sample)

were 98 percent and 82 percent, respectively, a range of 16 percent. The

data in Table I indicate that good rule-of-thumb values for ice quality

would be 96 percent for batch type machines and 83 percent for continuous

process machines. Since ice from batch machines does not have included

water as does ice from continuous machines, its moisture content would be

expected to vary with cube surface area. No appreciable difference was observed between fresh and aged ice.

Machine C-1 with the highest coefficient of performance (twice that

10 of the second most efficient machine) produced the lowest quality ice.

Conversely machine B-1 produced the highest quality ice but had the lowest efficiency. This would suggest that it is possible to trade off ice

quality for increased efficiency.

Rejecting a large amount of cold blow-down water at the end of a batch, as machine B-1 did, results in a major loss of efficiency. This

loss could be reduced without loss of ice clarity by fitting an efficient

heat exchanger onto the machine.

15 High quality, clear ice is also promoted by a low temperature on the

freezing surface on which the ice is formed. This is directly related

to ef f iciency--the thermal efficiency of a compression refrigeration

system falling off with lowering evaporator temperatures.

The difference in efficiencies between machines C-1 and C-2 which

produced similar quality ice by similar processes indicates that lowered

ice quality does not mean an automatic efficiency increase. Careful design is necessary to achieve this end.

20 No off taste or noticeable odor or discoloration was imparted to the

ice by any of these machines.

6. Acknowledgment

Appreciation is expressed to David K. Ward and Boyd L. Shomaker

for constructing the special equipment required for these tests and

attending to the daily operation of this test series.

25

5
Table I Latent Heat of Fusion Measurements

Standard Machine Machine Machine Machine

Date Ice B-1 B-2 C-2 C-1

1/16/74 145.4 137.8 123.0 121.6

1/15/74 144.9 122 .1

1/14/74 148.1 143.2 134.8

1/8/74 144.0 140.3 119.2

1/7/74 . 146.8 122 .8 116.4

1/4/74 • 145.3 127.2

12/28/73 . 144.2 123.0 114.7

12/27/73 145.2 144.3 125.8

• '12/26/73 141.7 135.1

11/15/73 144.3 135.2

15 Average,

Btu/lb 145.0 142.6 135.7 123.6 119.5

Quality,

percent 100 98 94 85 82

10

6
Table II Efficiency and Ice Production Rate Measurements

Ice

Production Energy

Rate Consumption Efficiency

Machine Ib/hr W (c.o.p.)

10

C-1

B-2

C-2

B-1

30.4

17.5

3.0

5.3

1,010

1,300

280

660

1.06

0.54

0.39

0.34

7
o

.J u 8
NBS-n4A IREV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLIC A l lON OK KhPORTNO.

NBS IR 74-547

2. Ciov't Acrcs.sioii No.

3. Ret ipient'.s Acces.sion No.

4. TITH; ANO .SUBTITLl

Ice Quality and Energy Utilization Efficiency Tests of Four

Commercial Ice Makers

5. Publication Date March 1974

6. Performing Organization < <,)(lc

7. AUTHOR(S)

William J. Mulroy and John W, Grimes

8. Pi- r f

I .f Mil [jg Organ. Rcpori No. NBS T R 74-')4 7

9. PKRFORMINt, ORt.ANI/.ATlON NAMf- ANP ADOKKSs

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Proi<-( I Ta.sk/Worlc Utnl N. 4624400

11. ( ontract Giant No.

12. Sponsoring Organization Name and Complete Address (Street, City, Slate, ZIP)

U. S. Army Natick Laboratories

Natick, Massachusetts 01760

13. Type of Report St P<riod Covert d Final, 4/18/73 - 6/30/7^f

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTtS

16. ABSTRACT (A 200-word or leaa l*ctu»l auttmsry ol moat si^^Hicmnt irtiorwation. H document irtclud«a « »i0tificmt

bibliography or litarature aurvey, mentiort it here.)

At the request of the United States Army Natick Laboratories, the Center for Building

Technology tested four conmercial ice making machines for their ice-making process efficiency and for the latent heat of fusion, clarity, and purity of the ice which they

produced. This was done to provide quality estimation guidelines for field testing of

these units and to indicate the ranges of ice quality and machine efficiency that could

be expected.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only tfin first letter of the first key word unless a prop'sc name, separated by semicolons

)

Calorimetry; heat of fusion; ice; ice machine tests; ice makers; latent heat; refrigeration equipment

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