# NIST Technical Note 1697



# Energy Consumption of Automatic
Ice Makers Installed in Domestic Refrigerators
Revision 1

David A. Yashar Ki-Jung Parkii 

# NIST Technical Note 1697



# Energy Consumption of Automatic
Ice Makers Installed in Domestic Refrigerators
Revision 1

David A. Yashar Ki-Jung Park Energy and Environment Division Engineering Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899-7321

November 2011

U.S. Department of Commerce John Bryson, Secretary

National Institute of Standards and Technology Patrick D. Gallagher, Directoriii ENERGY CONSUMPTION OF AUTOMAT IC ICE MAKERS INSTALLED IN

DOMESTIC REFRIGERATORS

David A. Yashar and Ki-Jung Park

National Institute of Standards and Technology

Gaithersburg, MD 20899

Abstract

This study examines the energy consumption of automatic ice makers installed in

domestic refrigerators. Th e purpose of this research is to determine a method of

measuring the energy consumption of automatic ice makers that will generate a

repeatable and reproducible result. This study examined four refrigerator-freezers of

different configurations, one top-mount unit, one side-by-side unit, and two French-door

units with bottom freezers. The component s and operational modes of each ice maker

varied among the test subjects. This st udy examined each automatic ice maker and its

components, and discussed how the operation of each component contributed to the

overall energy consumption.

Two of the units had a single-speed compressor that maintained the compartments within

a range of temperatures by switching on and o ff (cycling). Since this type of unit draws

considerable power when the compressor operate s and very little when it doesn’t, a good

representation for energy consumption can only be obtained over a number of complete

compressor cycles. However, the unit’s ice maker also produces cyclic variation in

power draw; therefore accurate measurem ent of the ice maker energy consumption

should also be obtained over a number of comp lete ice making cycles. Since the units’

compressor cycles and the ice making cycles are not coincident, it is difficult to

determine the ice making energy usin g a predefined test period.

The other two units employed inverter-dri ven, variable-speed compressors, which

maintained a constant, part-load condition with out cycling on and off. Determination ofiv the ice making energy consumption for these uni ts was rather straightforward since data

could be examined over several complete ice making cycles.

We also examined the conditions which affect the ice making energy consumption. The

results of these tests showed that the ice ma king energy consumption is influenced by the

operating temperatures inside the cabinets. Th e results also showed that when their ice

maker is switched from a mode where it is not producing ice to one where it is actively

producing ice, some units exhibit temperat ure changes inside the cabinets without

changing the thermostat settings. For these reasons, it may not be feasible to prescribe an

ice making test at a specific thermostat setti ng, rather the results of multiple tests should

be interpolated to a predefined set of compartment temperatures.

The measurements showed that only approximately one half of the energy used by a

refrigerator to operate an automatic ice maker is actually used to freeze water into ice; the

other half is a result of usi ng heaters to free the ice from th e ice maker. The process of

freeing ice from the molds may be accomplis hed by other, less energy intensive means;

therefore, it is expected that introduci ng an ice making energy test will result in

significant reductions of field energy use.

Our measurements indicate that the ice ma king energy consumption varies widely from

product to product. The most efficient product tested consumed approximately

0.249 kWh per kilogram of ice produced under th e test conditions used in this study,

while the least efficient product consumed a pproximately 0.375 kWh per kilogram of ice.

Variations in ice maker design and control algorithms played a large role in the ice

production rate, which influenced the ic e-making energy consumption. The annual

energy consumption attributed to automatic ice makers added approximately 11 % - 20 %

to the rated energy consumption value for each refrigerator, as determined by a regulatory

test method. This value is based on the product of the measured ice making energy

consumption per unit mass of ice produced and a consumer driven household ice

consumption factor provided by a trade organization.v This study shows that it is po ssible to develop a test met hod for rating the energy use of

automatic ice makers. In order to develop a test method that result s in a repeatable and

reproducible test result, the test must compar e the energy consumed by a refrigerator with

and without the ice maker being operated and the refrigerator maintaining comparable

temperature conditions. Furthermore, data must be collected over a sufficiently long test

period in order to reduce the influence of the refrigerator’s compressor cycles operating

at a different frequency from the ice maker’s cycles.

Keywords: energy consumption, ice maker, refrigeratorvi Preamble

In April 2011, we published NIST Tec hnical Note 1697 which described energy

consumption tests of automatic ice makers insta lled in four domestic refrigerators. After

the completion of that study and publication of the results, we determined through

discussions with manufacturers of the test subjects that two of the tested refrigerators

were defective. It is important to note that, although defectiv e, the test subjects

performed their functions without indication th at would be obvious in field operation. In

order to assure the utility of the information disseminated from this study, we replaced or

repaired the defective refrigerators and repeat ed the tests. This report supersedes the

original NIST Technical Note 1697 and replaces the results and analysis derived from the

tests of the defective test units.

During the original study we noted that th e refrigerator, known as the side-by-side

refrigerator-freezer, was not producing as much ice as was expected. Through

examination of this unit, the source of the malfunction was identified as a leaky

connection between the solenoid va lve that controls the flow of water to the refrigerator

and the tube that delivers the supplied water to the ice-maker. This leaky connection was

located at the exit point of the solenoid, near the bottom of the refrigerator, and water that

dripped from the connection was ultimately rout ed to the same reservoir that receives the

water runoff from the periodic defrosting of the evaporator. This leaky connection was

repaired with an adhesive and the refrigerator was reexamined.

The manufacturer of first refrigerator used in this study, known as the top mount

refrigerator-freezer, also brought it to our atte ntion that the ice pr oduction rate under the

test conditions was much lower than the rate it was designed to produce. We examined

the refrigerator and were unable to determ ine the cause of the malfunction without

destroying it; therefore we purchased a ne w refrigerator of the same model as a

replacement.vii These two units were tested according to the methods outlined in the Technical

Note 1697, but the results are quite different since these units are not defective.

Chapter 3 and Chapter 4 of this study were rewritten with data and analysis determined

from the new data sets. Minor changes we re also made to Chapter 7, Chapter 8, and

Chapter 9 of this report in consid eration of the updated information.

We also made one additional minor change to the document. In the initial study, we

explored the possibility of us ing a purely calculation based a pproach as an alternative to

measuring the energy consumed due to the production of ice. To perform these

calculations, a value for the coefficient of performance (COP) of a refrigerator was

needed. A value of 1.8 was used to perfor m the calculations, since this was the best

estimate that could be provided by manufacturers. The use of this value was cautioned in

the previous publication by the statement “It should be emph asized that this assumed

COP is merely a placeholder assumption and has no verifiable basis.” Since the original

publication was released, additional info rmation was shared between several

manufacturers which suggest that this value is too high; therefore the calculations were

performed again with a COP value of unit y. This new value has resulted in minor

changes in Chapter 1, Chapter 3, Chapter 4, Chapter 5, and Chapter 6.viii Acknowledgement

This work was sponsored by the United Stat es Department of Energy. Dr. W. Vance

Payne contributed to the test apparatus design, op eration, and data acquisition. Mr. John

Wamsley provided technician s upport throughout various phases of this project. Ms.

Natascha Milesi Ferretti of NIST and Dr. Detlef Westphalen of Navigant Consulting Inc.

provided technical commentary on the draft of this report.ix Table of Contents

Abstract ...................................................................................................................... ........ iii

Preamble ...................................................................................................................... ...... vi

Acknowledgement ........................................................................................................... vii i

Table of Contents ............................................................................................................. .. ix

List of Figures ............................................................................................................... .... xii

List of Tables ................................................................................................................ ... xiv

Nomenclature .................................................................................................................. ...xv

1. Introduction ......................................................................................................................1

2. Test Setup and Data Acquisition ......................................................................................6

3. Experimental Results for Top Mount Refrigerator Freezer .............................................8

3.1 Top Mount Refrigerator Freezer with No Ice Production .........................................8

3.1.1 Mid Setting Results ............................................................................................. 8

3.1.2 Warm Setting Results .........................................................................................9

3.1.3 Combined Test Results for T op Mount Refrigerator Freezer with No Ice

Production ..........................................................................................................9

3.2 Top Mount Refrigerator Freezer with Ice Production .............................................10

3.2.1 Mid Setting Results ...........................................................................................10

3.2.2 Cold Setting Results ..........................................................................................12

3.2.3 Mixed Setting Results .......................................................................................14

3.3 Calculation Based Method .......................................................................................16

3.4 Test Length Determination ......................................................................................17

3.5 Summary ..................................................................................................................22

4. Experimental Results for Side- by-Side Refrigerator Freezer ........................................24

4.1 Side-by-Side Refrigerator Freezer with No Ice Production .....................................25

4.1.1 Mid Setting Results ...........................................................................................25

4.1.2 Cold Setting Results ..........................................................................................25

4.1.3 Combined Test Results for Side-by-Side Refriger ator with No Ice

Production ........................................................................................................27

4.2 Side-by-Side Refrigerat or Freezer with Ice Production ...........................................27

4.2.1 Mid Setting Results ...........................................................................................28x 4.2.2 Cold Setting Results ..........................................................................................30

4.3 Calculation Based Method for Estimating Ice-Maker Energy .................................31

4.4 Test Length Determination ......................................................................................32

4.5 Summary ..................................................................................................................36

5. Experimental Results for French Door Refrigerator Freezer #1 ....................................37

5.1 French Door Refrigerator Freezer #1 with No Ice Production ................................38

5.1.1 Mid Setting Results ...........................................................................................38

5.1.2 Cold Setting Results ..........................................................................................39

5.1.3 Mixed Setting Results .......................................................................................40

5.1.4 Combined Test Results for French Door Refrigerator Freezer #1 with

No Ice Production .............................................................................................40

5.2 French Door Refrigerator Freezer #1 with Ice Production ......................................40

5.2.1 Mid Setting Results ...........................................................................................40

5.2.2 Cold Setting Results ..........................................................................................43

5.2.3 Mixed Setting Results .......................................................................................44

5.3 Calculation Based Method .......................................................................................46

5.4 Summary ..................................................................................................................46

6. Experimental Results for French Door Refrigerator Freezer #2 ....................................49

6.1 French Door Refrigerator Freezer #2 with No Ice Production ................................50

6.1.1 Mid Setting Results ...........................................................................................50

6.1.2 Cold Setting Results ..........................................................................................50

6.1.3 Mixed Setting Results .......................................................................................51

6.1.4 Combined Test Results for Fr ench Door Refrigerator Freezer #2 with

No Ice Production .............................................................................................51

6.2 French Door Refrigerator Freezer #2 with Ice Production ......................................51

6.2.1 Mid Setting Results ...........................................................................................52

6.2.2 Cold Setting Results ..........................................................................................54

6.2.3 Mixed Setting Results .......................................................................................55

6.3 Calculation Based Method .......................................................................................57

6.4 Summary ..................................................................................................................58

7. Observations ..................................................................................................................60xi 8. Recommendations for Ice-Making Energy Consumption Test .....................................62

9. Open Items for Future Consideration ............................................................................63

10. References ....................................................................................................................64

Appendix : Uncertainty Analysis .......................................................................................65xii List of Figures

3.1 Top Mount Refrigerator Freezer ..................................................................................8

3.2 Power Signatures of Top Mount Unit under Test ......................................................10

3.3 Temperature Response to Ice Maker Operation ........................................................11

3.4 Refrigerator Power at Co ld Setting with Ice Production ...........................................13

3.5 Graphical Representation of Triangular Interpolation ...............................................15

3.6 Average Power Draw Over Full Compressor Cycle – Top Mount Unit Test #1 .......18

3.7 Instantaneous and Cumu lative Average Power Draw

Top Mount Unit Test #1 ............................................................................................19

3.8 Ice Production Rate - Top Mount Unit Test #1 .........................................................20

3.9 Instantaneous and Cumu lative Average Power Draw

Top Mount Unit Test #2 ............................................................................................21

3.10 Ice Production Rate - Top Mount Unit Test #2 .........................................................21

4.1 Side by Side Re frigerator Freezer ..............................................................................24

4.2 Power Signature of Side-by-Side Unit - Cold Setting ...............................................26

4.3 Temperature Response of Si de-by-Side Unit - Cold Setting .....................................26

4.4 Refrigerator Power at Mi d Setting with Ice Production

for Side-by-Side Refrigerator Freezer .......................................................................28

4.5 Temperature Response to Mid Setting with Ice Production

for Side-by-Side Refrigerator Freezer .......................................................................29

4.6 Temperature and Power of Side- by-Side Unit under Coldest Setting .......................30

4.7 Average Power Draw Over 12 Whole Compressor Cycle

Side-by-Side Unit Test #1 ..........................................................................................32

4.8 Instantaneous and Cumu lative Average Power Draw

Side-by-Side Unit Test #1 ..........................................................................................33

4.9 Ice Production Rate - Side-by-Side Unit Test #1 .......................................................34

4.10 Instantaneous and Cumula tive Average Power Draw

Side-by-Side Unit Test #2 ..........................................................................................35

4.11 Ice Production Rate - Side-by-Side Unit Test #2 .......................................................36

5.1 French Door Unit #1 ..................................................................................................37

5.2 Refrigerator Power during Defrost – French Door Unit #1 .......................................39xiii 5.3 Refrigerator Power During Ice Production at Mid Setting

for French Door Unit #1 ............................................................................................41

5.4 Temperature Response During Ice Production at Mid Setting for
French Door Unit #1 ..................................................................................................4 2

5.5 Power Response During Ice Production at Cold Setting French Door Unit #1 .........43

6.1 French Door Unit #2 ..................................................................................................49

6.2 Power Response for Ice Production at Mid Setting for French Door Unit #2 ...........52

6.3 Temperature Response to Ic e Production at Mid Setting for

French Door Unit #2 ..................................................................................................5 3

6.4 Power for Ice Production at Cold Setting French Door Unit #2 ................................54

6.5 Refrigerator Power with I ce Production at Mixed Setting for

French Door Unit #2 ..................................................................................................5 5

6.6 Refrigerator and Freezer Compartmen t Temperatures with Ice Production at Warm/Cold Setting for French Door Unit #2 .............................................................56xiv List of Tables

2.1 Measurement uncertainty ...............................................................................................6

3.1 Ice making energy by various methods – top mount refrig erator freezer ....................23

4.1 Ice making energy by various methods – side by side refrigerator freezer .................36

5.1 Ice making energy by various methods – french door unit #1 .....................................47

5.2 Energy consumption error associated w ith first batch – french door unit #1 ..............48

6.1 Ice making energy by various methods – french door unit #2 .....................................58

6.2 Energy consumption error associated w ith first batch – french door unit #2 ..............59xv Nomenclature

E

Energy Consumption ......................................................................................... kWh/yr

P Power ...................................................................................................................... .... W

T

Temperature ............................................................................................................... .. oC

m Mass ............................................................................................................................kg

U

Uncertainty .............................................................. consistent with measured quantity1 

### 1: Introduction Cyclic type automatic ice makers produce i ce within one of the compartments of a domestic refrigerating appliance. They are directly connected to a source of water and continuously produce batches of i ce and store it in a low temperat ure bin. At the present, these devices are rendered inoperative during the regulated energy consumption test (10 Code of Federal Regulations Part 430, S ubpart B, Appendix A1, 2010) therefore the energy used to make ice is not measured. This is because ice making energy was not included in the basic energy consumption test (AHAM, 1979). The use of cyclic automatic ice makers do, however, have a sign ificant impact on the product’s energy use, which effectively goes undetected under current regulatory test procedure.

A cyclic type automatic ice maker consists of several components that enable repetitive cycling of three distinct seque ntial processes: (1) delivering of water into the ice maker, (2) freezing of water into ice, and (3) harvesting or removal of the ice from the molds in which it was frozen. The operation of these devi ces is halted when a sensor indicates that the ice storage bin is filled to its limit and can no longer accept new ice. The energy consumption associated with cyclic type au tomatic ice makers can be broken down into four categories. The first category is the ener gy used to deliver water into the ice maker; this is generally accomplished by energizing a solenoid valve. The second category is related to the additional load the refrigerato r’s vapor compression system must handle to extract thermal energy from the water in order to cool and freeze it. This second category of energy consumption is equa l to the extracted thermal energy, the enthalpy difference between the water entering the system and th e frozen ice, divided by the appliance’s Coefficient of Performance (COP). The thir d category consists of the energy required to
free the ice from the molds and deliver it to the storage bin. Most commonly, this is done by using electric resistance h eaters to melt the interface be tween each ice cube and the mold where it was formed. The last category is related to the additional load to the appliance’s vapor compression system needed to remove any thermal energy introduced to the cabinet through the other steps. Most commonly, this is the thermal energy introduced by ice heaters used to free the ice from the molds divi ded by the appliance’s
COP.

Limited research exists in literature on energy consumption measurement of cyclic
automatic ice makers. Meier and Martinez (1996) attempted to quantify the energy consumed by automatic ice makers by producing approximately 500 g of ice and subtracting off the energy consumed under similar conditions with the ice maker inoperative. The approach used in this study, however, did no t consider the variability of the mass of ice produced during the test, which was as much as 12 %, nor did it consider the temperature changes in the cabinets during ice maker operation. Another study by Haider et al. (1996) showed a more comp rehensive evaluation of ice maker energy consumption. In this study, the researchers compared the energy consumption with and without the ice maker operating under two temp erature settings and normalized the ice maker energy to the measured quantity of i ce produced during the test. Although these authors did acknowledge substantial differences in compartm ent temperatures when the ice maker was rendered operative while using si milar thermostat settings, and substantial2 differences in ice production rates with di fferent thermostat se ttings, they did not interpolate the results of their measurements to a common condition.

These studies, however, were quite useful and have shown that the energy use associated with cyclic automatic ice makers is quite substantial compared to the total energy used by a domestic refrigerating appliance. These stud ies also suggested that energy used to cool
and freeze water into ice does not constitute th e majority of their energy consumption. Both studies show that the energy require d to cool and freeze water into ice is approximately half of the total energy cons umption of cyclic automatic ice makers.



### Considerations for Developing an Automatic Ice Maker Energy Test Theoretically, it should be relatively simple to extract the energy used by a cyclic automatic ice maker simply by performing the basic energy consumption test with and without the ice maker op erating, and examining the difference of the measurement results. In practice, however, there ar e several issues that comp licate the development of a repeatable test. Some of the specific points are outlined below.

1)

U Ice-making cycles are not typically coin cident with the appliance’s compressor cycles

U . Most domestic refrigerator-freezers use a single-speed compressor that operates intermittently to maintain th e compartment(s) within a range of temperatures. In order to accurately measure the energy consumption for a unit using this type of compressor, the power must be averaged over a whole number of complete ‘on’ and ‘off’ compressor cycl es during an energy consumption test. Attempting to quantify the energy consum ption with anything short of a whole number of compressor cycles introduces sy stematic error. Each ice-making cycle produces a discrete amount of ice, which is not obtained until the harvest step. Therefore, attempting to characterize the energy consumption of a cyclic automatic ice maker with anything short of a whole number of ice-making cycles will also introduce error. Ice-making cy cles are generally independent of the compressor cycles; therefore any method used to measure an automatic ice maker’s energy consumption must compromise between these two constraints. The error caused by this tradeoff can be reduced by extending the test period,
which increases the number of whole compressor and ice making cycles under
consideration.

Furthermore, heat is removed from wate r at varying rates during the ice making process. Most cyclic automatic ice make rs operate in such a way that water is frozen by cooling it with cold air. During the compressor ‘o n’ time periods, the cold air near the ice molds is usually be ing circulated by fans; therefore the heat
transfer mode used to remove thermal energy is forced convection. The heat transfer coefficients are roughly two orders of magnitude lower during the compressor ‘off’ periods because the fans are not running and heat is transferred to the surrounding air via free convection. Also, the air temperature oscillates during the compressor cycles (decreasing temperatures during the on cycles and increasing temperatures during the off cycl es) and the temperature of the water in the molds is continuously decreasing as it approaches a frozen state. Therefore,3 as the water is cooled and frozen into ice, the heat transf er rate governing the production of ice varies widely because of the variations in heat transfer coefficients, water temperature, and air temp erature. This aspect has an influence on the repeatability of an ice-making energy measurement and it compounds the effect of the non-coincident compressor and ice-making cycles because it is dependent on the temporal phase shift between the ice-making cycles and the compressor cycles.

2)

U Cabinet temperatures may depart from steady-state operation in response to ice-maker operation

U . When an automatic ice maker inside an appliance is rendered operative, one or more of th e appliance’s compartments may exhibit some type of temperature change. This response varies by product configuration and control algorithm. Cert ain units respond in such a way that water introduced into the ice maker’s mold in one compartment results in a much higher temperature in that compartment due to the thermal load of the warm, unfrozen water. Other units respond in such a wa y that they overcompensate for this load and actually cool this compartment below the temperature that was maintained before ice making was initiated. Another variation is that the cabinet’s control system will simply have difficulty balanc ing the load between the fresh food and freezer compartments when making ice, th erefore inducing a temporary departure from the steady-state temperature of both the fresh food and frozen compartments. It should be noted that the most highly s ophisticated state-of-the-art units with electronic controls generally do not exhi bit temperature changes of the same magnitude as the traditional mechanically-c ontrolled units. This aspect raises the question of whether or not to consider cabinet temperature departures during ice making. This can be done by interpolating the results of multiple ice-making tests to calculate the ice-making capacity and en ergy consumption at a set of standard temperatures. This could then be a un iform basis for comparison with the basic energy test. The aspect of temperature departure should be considered in some way; however, there are at least two reasona ble methods to consider this aspect. One method is to perform multiple ice-maki ng tests and interpolate the results of these tests to a given target temperature. Another method is to perform a single ice-making energy consumption measurement and use the recorded temperatures from that data as a target set of temperatures for interpolation with the baseline energy consumption measurements (without making ice). Therefore this could consist of a single ice-making measuremen t in addition to the already existing energy consumption measurements.

3)

U Determination of an appropriate inlet water temperature

U . The temperature of water supplied to the cabinet has an impact on the overall ice-making energy consumption because it is di rectly related to the amount of energy that must be extracted to freeze it into ice. In a typi cal household installation, water is supplied
to the cabinet via direct connection to a water source generally maintained between 10 oC and 21 oC (50 oF and 70 oF). However, water in the supply lines to the cabinet moves very slowly whic h causes the water to reach thermal equilibrium with the environment before entering the cabinet. Therefore,4 attempting to supply water to the cabinet at any temperature other than the ambient temperature in the test chambe r is not feasible. The ambient room temperature during the current energy c onsumption tests is 32.2 oC (90.0 oF). Using 32.2 oC (90.0 oF) as the temperature of the water entering the ice maker is an atypical condition and may present a biased challenge to a unit under test; however, using a temperature more represen tative of field conditions would result in greater test burden.

4)

U Determination of how to treat interactions with defrost cycles

U . Most domestic refrigerators periodically undergo a cycle that removes accumulated frost from the evaporator. During this period of opera tion, the power consumption and cabinet temperatures undergo deviations from st eady state operation. When a defrost cycle occurs during a time when an ice maker is rendered operational, analyzing the energy consumption measurement data can get quite complicated because these are two transient phenomena working against each other within the cabinet. Without going into a great level of detail , it is undesirable to use data that encompasses any portion of a defrost sequence when examining the ice making energy. This is a complication because th e test operator generally has no control over the timing of a defrost cycle and cannot easily structure data collection to avoid defrost periods. Furthermore, in many cases the production of ice shortens the time between successive defrost sequences because many refrigerators employ some type of demand defrost and the s upply of water into the ice maker often generates an accelerated demand for defrosting.

5)

U Non-standard ice production rate. Every model of automatic ice maker produces ice at its own rate, therefore it may pr oduce a biased evaluation to rate such a device on the basis of energy consumed pe r unit of time. The more appropriate approach is to rate them by ice-maki ng energy per unit mass of ice produced.
This metric can later be converted to energy/time base d on a standardized usage factor of mass of ice per unit time. With this in mind, it is important to note that while testing in a 32.2 oC (90 oF) ambient would reduce the test burden, the amount of energy that must be removed from the water to freeze it is greater than what would normally be expected in fiel d operation, and the refrigeration system
COP would be lower as well – both eff ects increase the measured energy use associated with ice making. Therefore, th e rate at which the unit can produce ice under test conditions would likely be smaller than in the field.

Because of all of these known difficulties, ther e have also been suggestions that a purely calculation-based approach for determining ice maker energy use might yield a better result. The suggested approach is to ta bulate the energy used by each of the cyclic automatic ice maker’s components and add that to the additional compressor work which is the total thermal load (energy removal from water/ice plus the load from any heaters used) divided by the system’s COP. This appr oach will also be investigated as an option to gauge ice maker energy consumption.5 This study examines the ice-making energy asso ciated with cyclic automatic ice makers installed in four different styl es of domestic refr igerator-freezers. The objective of this study is to facilitate the establishment of a robust, repeatable ice making energy consumption measurement method that would be applicable to cyclic automatic ice makers and would not substantially increase the test burden beyond th at of the currently regulated energy consumption test. This study characterizes the energy consumption attributed to four automatic cyclic ice ma kers by examining the difference between the energy consumption of each refrigerator-f reezer with the ice maker operative and inoperative. Various interpolation methods ar e examined and their merits and drawbacks are compared. Specifically, we examined the energy consumption of an automatic ice maker by (1) examining the ice-making and non ice-making energy consumption of a unit at a single set of temperature se ttings; (2) examining the ice-making and non ice-making energy consumption of a unit using multiple measurements and interpolating the results to a common set of operational conditions, this was performed using two different interpolation methods; a nd (3) a purely calculation based approach.

During the data analysis, the individual da ta sets were examined to determine an appropriate length of time for data colle ction, since steady state operation does not generally exist.6 

### 2: Test Setup and Data Acquisition The test setup was constructed in accordan ce with the Department of Energy’s (DOE) test procedure outlined in 10 Code of Federal Regulations Part 430, Subpart B, Appendix A1, 2010. There was one slight modifi cation to this setup; a continuous water supply was connected to the unit under test to supply water to the automatic ice maker.
Two identical test cells were construc ted to simultaneously measure the energy consumption of two refrigerators. Each te st cell consists of a thermally non-conductive platform and a vertical wall adjacent to one ed ge of the platform. Each refrigerator is mounted on top of the platform w ith its rear adjacent to the ve rtical wall. All faces of the test cells were painted dull bl ack to minimize the radiant heat transfer to and from each refrigerator during testing.

The test cells were placed in an enviro nmental chamber, which was large enough to
house two test cells and all of the necessary data acquisition hardware. This environmental chamber was capable of provi ding controlled ambient temperature and humidity over long periods of time with lit tle supervision, as nece ssitated by the lengthy test periods of domestic refrigerat or energy consumption measurements.

Water supply lines were connected to each te st unit. The temperature of the water supplied to each unit was not controlled, but the tube connecting each line to a refrigerator was sufficiently l ong to allow the water to equilib rate with the temperature in the chamber. This was verified by inserti ng two T-type thermocouples into each water line just upstream of the refrigerator connection.

All of the temperature and humi dity data were gathered us ing a personal computer and a multiplexed data acquisition unit. The electrical energy input was monitored using a separate personal computer dedicated to two digital power meters, on e connected to each test unit. All temperatures were sampled every 30 s, and the power was sampled every two seconds. Table 2.1 lists the measured quant ities and the uncertainty associated with 95 % confidence. The equations used to calculate the measurement uncertainty are shown in the Appendix.

Table 2.1: Measurement uncertainty Measured quantity Measurement device Uncertainty at 95 %
confidence Temperature Thermocouples ± 0.1 ° C (0.2 ° F)

Power Watt-meter ± 0.5 % of reading Energy Watt-meter ± 0.5 % of reading

Mass Digital scale ± 5 g

The dry-bulb temperature in the environm ental chamber was maintained at 32.2 oC (90.0 oF) in accordance with the US DOE test procedure. Throughout the duration of the tests, the analysis was performed to charac terize the performance of the test subjects while maintaining cabinet temperatures of 3.9 oC (39 oF) in the refrigerator compartment and -17.8 oC (0 oF) in the freezer compartment. These target temperatures are different from the current Department of Energy test procedure, 7.2 oC (45 oF ) in the refrigerator7 compartment and -15 oC (5 oF) in the freezer co mpartment, but will be incorporated in the new test procedure, which will be requ ired for rating products starting in 2014 (75FR78810), therefore it is of greater interest to use these new temperatures. It is important to note, however, that the test units in this study were rated using the current target temperatures, therefore it is expected that they consume more energy during the non-ice making tests than their rated sp ecification at differe nt temperatures.

In total, four domestic refrigerator-freezer s were used for this study. The units were selected to provide information spanning a variety of designs and features that are expected to influence ice making energy cons umption. The first unit in this study is a top-mount refrigerator-freezer w ith an ice maker located in the freezer compartment. The second unit is a side-by-side refrigerator-fre ezer with an automatic ice maker mounted on the door of the freezer, and it dispenses ice th rough the freezer door. The third and fourth units are French door style units, whose freeze r compartments are located beneath their refrigerator compartments. The third unit pr oduces ice by directing some cold air from the freezer to an insulated ice-making sub-compartment in the refrigerator compartment. Lastly, the fourth unit produces ice by means of a separate ice making evaporator in an insulated ice making sub-compartment located in the refrigerator compartment8 

### 3: Experimental Results for Top Mount Refrigerator Freezer The first test unit is a 600 L (21 ft 3 ) top mount, energy star rated model shown in Fig. 3.1.
It has variable defros t control, mechanical thermostat control, and a single-speed compressor. The unit has a factory installe d cyclic automatic ice maker, which was
connected to an external wate r supply and produces and stores ice in a bin located in the freezer compartment. The unit was outfitted w ith three thermocouples in the refrigerator compartment and three thermocouples in the freezer compartment, as shown below. The compartment temperatures used for the calculations that follow were the average of the time averaged values reported from the three thermocouples located in each compartment during the test duration.

Figure 3.1 Top Mount Refrigerator Freezer

The minimum and maximum time between defro st cycles for this unit is 8 hours and 96 hours of compressor run time, respectively. Ac cording to the procedure outlined in the current DOE energy test procedure, these valu es result in a calculated average time between defrost of 30 hours of compressor run time.

3.1 Top Mount Refrigerator Freezer with No Ice Production

U 3.1.1 Mid Setting Results During the first test, the energy consumption was measured with the thermostats set to the median setting for each compartment a nd the icemaker rendered inoperative. The following results were obtained:9 Steady state cyclic operation time: 10801 seconds = 03:00:01 Measured refrigerator compartmen t temperature: (4.0 ± 0.1) oC Measured freezer compartment te mperature: (-18.4 ± 0.1) oC Energy expended during the test period: (164.2 ± 0.8) watt-hours

Alternatively, this can be expressed as an average steady state power of (54.72 ± 0.27) W at the measured temperatures.

The defrost sequence for this unit consisted of (a) defrost heater switching on, (b) defrost heater switching off, (c) period of no power draw, (d) compressor on – recovery cycle, and (e) the following compressor off cycle. Measurements during this sequence yielded the following results:

Defrost time: 8153 seconds = 02:15:53 Energy expended during defrost period: (257.4 ± 1.3) watt-hours

Combining the results of these two portions of the test, assuming that the average time between defrosts is 30 hours of compressor run time, we arrive at the total energy consumption of (498.9 ± 2.5) kWh/yr at the measured temperatures.

U 3.1.2 Cold Setting Results Since the temperatures in the refrigerator comp artments for the first test was warmer than the target temperature, the thermostat was se t to the coldest setting and the measurements were performed again. The following results were obtained:

Steady state cyclic operation time: 12069 seconds = 03:21:09 Measured refrigerator compartm ent temperature: (3.0 ± 0.1) oC Measured freezer compartment temperature: (-20.6± 0.1) oC Energy expended during the test period: (199.2 ± 1.0) watt-hours

Alternatively, this can be expressed as an average steady state power of (59.4 ± 0.3) W at the measured temperatures.

Defrost time: 9858 seconds = 02:44:18 Energy expended during defrost period: (298.7 ± 1.5) watt-hours

These values resulted in the total energy consumption of (540.3 ± 2.7) kWh/yr at the measured temperatures.

U 3.1.3 Combined Test Results for Top Mount Re frigerator Freezer with No Ice Production
We then combined the results of the measuremen ts at the first thermostat setting with the results at the second thermostat setting and inte rpolated to the target temperatures. When interpolating to the refriger ator target temperature of 3.9 oC, the calculated energy consumption was (503.0 ± 2.5) kWh/yr; when interpolating to th e freezer target temperature of -17.8 oC, the energy cons umption was (491.4 ± 2.5) kWh/yr. The10 maximum of these two values is declared as the baseline energy consumption: (503.0 ± 2.5) kWh/yr.

It is also useful for late r calculations to note that th e energy consumption obtained through interpolation if the defrost energy was not considered. In this case, the calculations were performe d with the steady state ope rational average power of (54.7 ± 0.3) W ((479.2 ± 2.4) kWh/yr) from the mid/mid setting and (59.4 ± 0.3) W ((520.4 ± 2.6) kWh/yr) from the cold/cold sett ing rather than the total values which included the contribution of the defrost cycles. Here, negating the energy from periodic defrosting shows the energy consumption fo r this unit to be (483.5 ± 2.6) kWh/yr.

3.2 Top Mount Refrigerator Freezer with Ice Production With the baseline energy consumption charac terized, we next performed a series of measurements to examine the energy consump tion attributed to the production of ice by
the automatic ice maker.

U 3.2.1 Mid Setting Results

U The thermostat was set to the median position for each compartment and the ice maker was rendered operative. Water was supplied to the unit at a temperature of 32.2 oC. The power signature of this unit showed a few differences compared to the measurements with the ice maker inoperative. Fig. 3.2 s hows the power drawn by the unit with the thermostats set to the median setting with (a) ice maker inoperative and (b) ice maker operative.

Figure 3.2 Power Signatures of Top Mount Unit under Test11 The first difference between the signatures for the two different ice-maker settings is that the compressor on cycle is longer while the uni t is producing ice; this is due to the additional cooling load. The second differen ce is the power consum ed by the ice-maker components. There are two separate energy- consuming actions that are engaged during the process of ice making and harvesting. Th e first block of energy is consumed by the ice mold ejection heater, which draws appr oximately 190 W for a period of 90 seconds. This heater is used to heat up the tray in wh ich the ice is formed so that it can be freed and dropped from the mold into the storage bin. The second device is a solenoid valve, which is powered up to allow water to flow from the supply into the ice molds; this solenoid draws approximately 28 W for a period of 10 seconds. It is also very important to note that the ice making cycle, which c onsists of the time pe riod starting from the solenoid valve fill through the operation of th e ice ejection heater, is not synchronized with the compressor cycle. Since the results of all measured quantities are averaged over
a whole number of successive co mpressor cycles, it is desirabl e to record data over the longest attainable time period in order to increase the number of whole compressor cycles. Extending the data set in this manner increases the accuracy of the results by reducing the effects of the incomplete ice making cycles.

Another aspect of the ice-making test data was that the additional load to the freezer compartment resulted in an elevated temperat ure in this compartment. Fig. 3.3 shows the temperatures measured during the ice-making test. At a certain time (approximately 130 000 seconds on the graph) the ice maker au tomatically halted i ce production due to the ice storage bin reaching its fill limit. After this point the freezer compartment temperature decreased by approximately 2 K wh ich resulted in a temperature similar to that seen during the test at the same thermost at setting test with the ice maker inoperative.

Figure 3.3 Temperature Respons e to Ice Maker Operation12 The data recorded during the time period encompassing 31 whole compressor cycles and all ice production showed the following results:

Steady state cyclic operation time: 127278 seconds = 35:21:18 Measured refrigerator compartm ent temperature: (3.7 ± 0.1) oC Measured freezer compartment te mperature: (-16.2 ± 0.1) oC Mass of ice produced: (2.46 ± 0.005) kg Ice production rate: (69.6 ± 0.2) grams per hour Energy expended during the te st period: (2.41 ± 0.01) kWh

Alternatively, this can be expressed as an average steady state power of (68.21 ± 0.34) W at the measured temperatures.

Single Data Point Method for Measuring Ice-Maker Energy Consumption The first proposed approach to quantifyi ng the ice-making energy is to compare the steady state energy consumption with both thermo stats set to their medi an setting for both ice producing and ice maker inoperative condition s. In this case, the difference between the average power with a nd without ice making was:

(68.21 ± 0.34) W – (54.72 ± 0.27) W = (13.49 ± 0.43) W

The energy used to produce ice in this configuration can then be calculated from the mass of ice, the differential powe r and the test period time.



### ( ) ( ) ( ) 0.0135 kW 35.355 h
2.46 kg = (0.194 ± 0.006) kWh/kg

The uncertainty of ± 0.006 kWh/kg was calculate d using the individual uncertainties of the measured quantities. This notat ion is used thr oughout this report.

This, however, may not be the best approach to estimate the ice-making energy because the temperatures realized in this unit changed considerably in response to the activation
of the ice maker.

U 3.2.2 Cold Setting Results The next approach was to attempt to use an interpolated energy (and ice production rate) using a second set of measurements. Since the internal temperature of the freezer compartment was warmer than the target temp erature, we set the thermostats of each compartment to the coldest se tting. When this unit was operated with the compartments set to their coldest temperatures and warm water introduced into the freezer through the ice maker, the automatic defrost control algorithm made the un it operate with the compressor running 100 % of the time and with a very short time between defrost periods. This mode did not allow the unit to oper ate in a steady state mode long enough to produce a significant set of useable data. Th erefore, the thermostats were set to a13 position slightly warmer than the coldest posi tion as a means to achieve a steady cyclic operation.

The power measurements are shown in Fig. 3.4. The useable portion of this data set
occurs between the two defros t events. The operation of the ice mold ejection heater is clearly visible in this figure , and its deployment can be used as a counter for the number of ice making cycles during the test.

Figure 3.4 Refrigerator Power at Cold Setting with Ice Production

The data from this set of measurements must be used to estimate the marginal energy consumption due to ice making; therefore we have to consider only the steady state operation portion, i.e. that which in not influe nced by either defrost events. We need to calculate the relevant values averaged over a whole number of compressor cycles operating at steady state; theref ore, we prorated the ice maki ng events of the entire data collection period to determine the ice produced during the 11 events that occurred during the period of steady operation.

Single cycle operation time: 38765 seconds = 10:46:04 Measured refrigerator compartm ent temperature: (-2.4 ± 0.1) oC Measured freezer compartment te mperature: (-18.1 ± 0.1) oC Mass of ice produced: (0.961 ± 0.005) kg Ice production rate: (89.2 ± 1.4) grams per hour Energy expended during the test period: (836.2 ± 4.2) watt-hours14 Average steady state power of (77.65 ± 0.4) W

Two Data Point Method for Measuring Ice-Maker Energy Consumption Now, the energy consumption at the specified target temperatures is calculated based on
the results of the mid/mid and cold/cold se tting tests. For th is calculation, the interpolated values for a freezer temperatur e of -17.8 oC are an energy consumption of (667.2 ± 3.9) kWh/yr. Since the ice production ra te varied between th ese two tests, it was necessary to estimate the ice production at the target temperatures by some means. Therefore, the ice production ra te at the target temperatures was estimated using a linear interpolation approach, this effectively weight ed the measured ice production rates in the same proportion as the measured energy. The ic e production rate at the target conditions was calculated as (754.3 ± 7.8) kg/ yr. However, these interpolated values occur at a refrigerator compartment temper ature of 2.6 oC, which manifests itself as a penalty on the energy consumption value because it is colder than the target temperature. Regardless, comparing these values to the non-defrost in fluenced data for th e tests without ice production results in the following values:

Energy consumption difference: (667.2 ± 3.9) kWh/yr - (483.5 ± 2.4) kWh/yr = (193.7 ± 4.6) kWh/yr Ice production rate: (754.3 ± 7.8) kg/yr Ice production energy: (0.257 ± 0.006) kWh/kg

It should again be noted that this unit has difficulty contro lling the internal compartment temperatures during the ice pr oduction phase, and that opera ting this unit at the same thermostat settings with and without i ce production does not result in the same compartment temperatures. This is because ice production places a large processing load onto the duty of the freezer compartment w ithout any addition to the refrigerator compartment’s duty. Also, the mechanical th ermostat used by this unit has difficulty balancing the cooling load requirements between the comp artments in ice production
mode.

U 3.2.3 Mixed Setting Results

U In order to attempt to obtain a more accura te representation of the ice-making energy,
another data set was taken with the freezer co mpartment set at the coldest setting and the refrigerator compartment set at its median se tting. By using three data points, a more accurate triangular inter polation method (ASNZ, 2007) can be applied in lieu of the linear interpolation method. The following values were obtained from this data set.

Steady state cyclic operation time: 39379 seconds = 10:56:19 Measured refrigerator compartm ent temperature: (4.7 ± 0.1) oC Measured freezer compartment te mperature: (-17.2 ± 0.1) oC Mass of ice produced: (0.962 ± 0.005) kg Ice production rate: (87.9 ± 1.1)) grams per hour Energy expended during the test period: (854.4 ± 4.3) watt-hours Average steady state power: (78.1 ± 0.43) W15 Three Data Point Method for Measuring Ice Maker Energy Consumption The triangular interpolation method is based on the idea that one can estimate the energy consumption of a two compartment cabinet at a specific pair of internal temperatures by using three data points that form a triangle ar ound that pair of temperatures. Using the three measured data points, the position of a theoretical fourth data point (T4) is calculated, which lies at the intersection of a lin e joining two of the da ta points with a line joining the third data point to the target set of temperatures. This theoretical data point serves as a basis to calculate the energy cons umption at the target set of temperatures. Fig. 3.5 below shows the data points in graphical form. For this particular unit, however, the mechanical thermostat had limited ability to control the compartment temperatures during ice production. Therefore, we were unable to acquire a third data set that graphically forms a triangle with the other da ta sets that contains the set of target temperatures of 3.9 oC and -17.8 oC; this is w hy the target temperatures lie outside of the triangle formed by the three measured data sets. The mathematics outlined in this method can still be applied to extrapolate the data to the target temperatures.

Figure 3.5 Graphical Representati on of Triangular Interpolation

Using this approach, values for the ener gy consumption and ice production rates were calculated as if they were obtained at the target temp erature conditions. Energy consumption: (700 ± 12) kWh/yr Ice production rate: (808 ± 21) kg/yr16 Comparing this to the baseline energy cons umption value without ice productions, the
result is:

Energy consumption difference: (700 ± 12) kWh/yr - (483.5 ± 2.4) kWh/yr = (216.5 ± 12) kWh/yr Ice production energy: (0.268 ± 0.015) kWh/kg

In this case, the value determined by three poi nt triangular interpola tion is similar to the value obtained through two point linear interpol ation. This is because the refrigerator temperature realized through two point inter polation, 2.6 oC, is rela tively close to the target refrigerator temperature of 3.9 oC.

All of the above methods estimate the amount of energy consumed for the purposes of making ice while excluding the interactions between the ice production and the defrost sequence. It is very difficult to separate out the ice-making energy if these interactions are considered; particularly since ice maki ng may, but does not necessarily occur during the defrost sequence. Also, this particul ar unit shows that ope rating the ice maker
influences the automatic defrost control scheme, which may not be the case for all refrigerator freezers, and it is therefore quest ionable whether this interaction could be neglected. Furthermore, since ice maki ng is prompted by user interaction and automatically halted when the storage bin is filled, it is difficult to determine the significance of these interacti ons during field use. Obvious ly, ice production is a much less efficient process during the time period th at the defrost heater is operating, but this situation may have limited occurrence.

3.3 Calculation Based Method The last method examined for determining ice-maker energy consumption is a simplified calculation approach. There are four components contributing to energy consumption during ice production: (1) energy used by the solenoid valve to deliver water to the ice molds, (2) the energy consumed to run the refrigeration cycle to meet the demand of removing heat from the water, (3) the energy us ed by the ice mold ejection heaters to free the ice from the molds, and (4) the energy used to run the refrigeration cycle to meet the
demands of the additional load cont ribution of the ej ection heaters.

Each data set taken with the ice maker opera tive was started with the ice bin empty and logged until the bin reached its shut off limit. The first data set showed 3.28 kg of ice produced through 23 cycles, the second show ed 2.99 kg in 21 cycles, and the third showed 2.85 kg in 20 cycles. Therefore, this unit produces an average of 142.5 grams of ice during each cycle.

The solenoid valve draws 28 W for a period of 10 seconds to deliver water to the molds, which results in 280 joules per ice-making cy cle. The ice ejection heater draws 190 watt for a period of 90 seconds to free the ice fr om the molds, which results in 17,100 joules per ice-making cycle. The total energy c onsumed by these components is therefore 17,380 joules per ice-making cycle. Considerin g the mass of ice produced per cycle, this can be expressed as 122.0 kJ/kg of ice produ ced. Also, the energy consumed by the ice17 ejection heater is ultimately dissipated as h eat into the freezer cabinet; therefore it must
be considered an additional heat load to be processed by the refrigeration system.

The energy required to cool 32.2 oC water to freezing is comprise d of three parts. First, approximately 135 kJ/kg of energy is required to reduce the water’s temperature to 0 oC. Then 334 kJ/kg of energy is required to freeze it into ice. Lastly the ice must be cooled down to the freezer temperature (-17.8 oC) by ex pelling an additional 36 kJ/kg. In total, this accounts for 505 kJ of energy per kilogram of ice.

The proposed calculation method relies on an assumed value for a Coefficient of Performance (COP). At any given set of operating conditions, m odern products operate with a somewhat broad range of COP’s and it is difficult to select a representative value that is applicable for all app liances. Also, it should be not ed that the COP used in the calculation approach is not the COP of the te st unit itself, but rather the COP of ice making within the test unit which will be lower that the system COP due to other thermodynamic losses between the evaporator and the ice maker. For the sake of exploring the calculation approach, we will us e an assumed COP value of unity, i.e. that the system can remove one unit of heat for ev ery unit of electrical input. It should be emphasized that this assumed COP is merely a placeholder assumption and has no
verifiable basis.

While making ice, this refrigeration system must meet the additional demand of 627 kJ of heat per kg of ice produced (505 kJ for c ooling and freezing the water plus 122.0 kJ for the load from the ejection heaters). Using the assumed value of the COP, the additional electrical input to th e system required to meet this load is 627 kJ/kg of ice produced. Adding in the energy consumed by the solenoid and ejection heater brings the total load to 749 kJ/kg; or in altern ative units 0.208 kWh/kg.

3.4 Test Length Determination The main point of this exercise is to ex amine the power response from the unit while making ice in a little more detail in order to determine how much data needs to be recorded to properly calculate the energy consumption. Fig. 3.6 shows the average power drawn during each full compressor cycle whil e the unit was operating at the mid/mid setting and producing ice.18 Figure 3.6 Average Power Draw Over Full Compressor Cycles – Top Mount Unit Test #1

Throughout this test period, there was either zero or one batch of ice harvested during each compressor cycle. The compressor cycles that included a harvest event drew, on average, about 5 W more than the compressor cy cles that didn’t include a harvest event.

Fig. 3.7 shows this same data plotted as the cumulative average power draw versus time; the instantaneous power is also shown in the figure. Here, the beginning of this data is coincident with the compressor switching on; therefore each local minimum point on the plot is indicative of another compressor on switch. Consequently, each local minimum also represents the cumulative average pow er draw over a whole number of compressor cycles. We can see that as time elapses, the local minima of cumulative average power draw asymptotically approaches a value of approximately 68.2 W. This value represents the average power draw needed to mainta in the temperatures in the cabinet and simultaneously produce ice over a sufficiently long test period, which is one of the values
that is of interest to this study. It is interesting to not e that the running average stays within 1 % of the final value after only 2 compressor cycles and 1 ice ejection cycles were recorded. This means that the average power could be determined in a very short test period.19 Figure 3.7 Instantaneous and Cumulative Average Power Draw Top Mount Unit Test #1

Fig. 3.8 shows the ice production rate, defined as the cumulative quant ity of ice produced since the beginning of the test period divi ded by the test period length. Fig. 3.8 shows that while the cumulative average power is stable after 4 compre ssor cycles, the ice production rate is not as stable on a time scal e. Instead, the ice pr oduction mechanism is directly related to the amount of time that the compresso r is running; therefore the periods of time when the compressor is not r unning are effectively nul l or slow bands in the production of ice.

The value of 69.6 grams per hour was reported fo r this data set base d on the total length of the data set, however, the saw tooth pattern indicates that if we were able to extend this data set for an infinite amount of time, the reported ice production rate would lie somewhere between 68.5 grams per hour and 71.6 grams per hour. Since the reported
value is less than 3 % from either of thes e limits; however, the da ta required to achieve
this took over 35 hours to collect.20 Figure 3.8 Ice Production Rate - Top Mount Unit Test #1

We also performed a similar analysis on the second set of ice making data. During the collection of this data set, the moisture a ddition to the cabinet from the operation of the ice maker caused the unit to undergo defrost cycles more frequently, thereby limiting the amount of useful data. Fig. 3.9 shows the instantaneous and cumu lative average power draw for this data set. This figure shows that the average power can be determined to
within 1 % of the final value after the third compressor cycl e, less than 5 hours of data collection. Fig. 3.10, however, shows that th e ice production rate is not as easy to determine by these methods. This figure s hows that the saw tooth pattern is still oscillating between 84.9 grams per hour and 95.5 grams per hour. The reported value of 89.2 grams per hour determined by the entire leng th of the useable data set, is less than
7 % from either of these limits.21 Figure 3.9 Instantaneous and Cumulative Average Power Draw Top Mount Unit Test #2

Figure 3.10 Ice Production Rate Top Mount Unit Test #222 A similar analysis was also performed on the thir d data set. Similar to the other data sets, the average power remained within 1 % of the reported value after only three compressor cycles, less than 5 hours of data collection. The ice production rate , however, was still bounded by the limits of 81.7 grams per hour an d 91.9 grams per hour at the end of the
data set.

3.5 Summary The ice-making energy was calculated by four methods as shown in Table 3.1. Also shown in the table is the energy impact of producing a representative consumer usage factor of 0.816 kg of ice per day (AHAM, 2009). It should be noted that this usage factor was based on a very limited sample of survey data and will likely be revised after further studies have been completed.

The first method was to compare the differen ce in energy consumed with the thermostats set to their median positions. This method re sulted in a large departure from the non-ice producing freezer temperature because of the co ntrol system used in this cabinet. The freezer temperature in this compartment wa s more than 2 oC warmer during the ice production process, which effectively biased the energy consumption results because it reduced the cooling load dur ing the ice-making test.

The second method attempted to characteri ze the ice-making energy by using the twopoint interpolation method for two energy consumption measurements, and comparing these results to the baseline energy test resu lts without accounting for the defrost energy. This method attempted to mitigate the effect s of the elevated freezer temperature during ice production. Because of the nature of th e thermostat used in this system, it was difficult to finely control the temperatur es during the ice-making tests, and this interpolation method resulted in a value that would represent the energy required to make ice while maintaining the appropriate freezer temperature and a refrigerator temperature that was more slightly colder than the target temperature.

The third method attempted to characteri ze the ice-making energy by using the threepoint triangular interpola tion method. The controllability of the cabinet made it impossible to actually triangulate around the specified set point; how ever, extrapolation of these data points should result in a reasonable estimate of the ice-making energy, depending on the linearity of the relati onship between ice production rates and compartment temperatures. Upon initial examin ation of the results, it is surprising that this method returned a value of ice making energy that is higher than the two point interpolation method. After considering the limits on our ability to determine the ice production rates for the second and third data sets, however, the results seem reasonable.

The final method was a simple calculation method based on the amount of energy required to process the ice-making load, and to power the auxiliary devices required to make and store ice. This method relies heavily on an assumed COP value which is a parameter that is not readily available for a given test subject.23 Table 3.1 Ice making energy by various met hods – top mount refrigerator freezer

Method Ice making energy kWh/kg kWh/yr % of baseline energy 1 Median position only 0.194 58 12%
2 Median and coldest positions 0. 257 77 15 %

3 Triangular Interpolation 0. 268 80 16 %
4 Calculation 0. 208 62 12 %

A point for consideration is the ice make r’s influence on the defrost controller. Alteration of the defrost control period will have influence the overall energy consumption. There is a wide variety of i nput that the current technology may use for
variable automatic defrost controllers. Th e input used can range from measurement of ice on the evaporator, internal compartment temperatures, ambient temperatures, air humidity levels, door openings, data collected during previous opera tion, etc.; therefore, some defrost control algorithms may be str ongly affected by the operation of ice makers and some may be completely unaffected. This particular unit was strongly influenced by the ice maker’s operation, but this effect was not considered in this analysis. This effect is worthy of investigation, howev er, and it should be revisited at some point in the future.24 

### 4: Experimental Results for Si de-by-Side Refrigerator Freezer This unit is a 760 L (27 ft 3 ) side-by-side, energy st ar rated model. It has variable defrost control, electronic thermostat control, and a single-speed compressor. The unit has a factory installed ice maker, which is connect ed to an external wa ter supply and produces
and stores ice in a bin located on the inside of the door to the freezer compartment. This ice maker was equipped with an ON/OFF switch and is capable of producing ice at three different rates. For the purposes of these tests, all non-ice produc tion test data were
recorded with the ice maker switch set to the “ON” position and the bail arm forced to sense a full bin condition. The ice production rate was set to th e highest setting.

The unit was outfitted with th ree thermocouples in the refrigerator compartment and five thermocouples in the freezer compartment, as shown in Fig. 4.1. The compartment temperatures used for the calculations that follow are the average of the time averaged values reported from each thermocouple during the test duration.

Figure 4.1 Side-by-Side Refrigerator Freezer

The manufacturer provided the minimum and maximum time between defrosts for this unit as 7 hours and 50 hours of compressor run time, respectively. According to the method outlined in the current DOE energy te st procedure, these values result in a calculated average time between defrosts of 22.4 hours of compressor run time.25 4.1 Side-by-Side Refrigerator Fr eezer with No Ice Production

U 4.1.1 Mid Setting Results This unit’s electronically controlled ther mostat was capable of setting the freezer temperature between -21.1 oC and -13.3 oC, and the refrigerator temperature between 0.6 oC and 7.8 oC. During the first measurem ent, each compartment’s thermostat was set to its median temperature setting, -17.2 oC for the freezer compartment and 3.9 oC for the refrigerator compartment. Examination of the test data showed that the temperatures in the refrigerator and freezer compartment temper ature changes were not in sync; i.e. the refrigerator compartment would get colder a nd the freezer got warmer and vice versa. This suggests that this unit suppl ies cold air to the compartments in an alternating pattern. From an energy test point of view, this feat ure showed itself as a series of secondary cycles (both power and temper ature) that occurred while the compressor was operating. For the purposes of these tests, each peri od during which the compressor was running was considered as a single compressor “ON” cycle, regardless of the number of times it shifted the cooling load between compartmen ts. The following results were obtained:

Steady state cyclic operation time: 14290 seconds = 03:58:10 Measured refrigerator compartm ent temperature: (4.2 ± 0.1) oC Measured freezer compartment te mperature: (-17.7 ± 0.1) oC Energy expended during the test period: (401.1 ± 2.0) watt-hours

Alternatively, this can be expressed as an average steady state power of (101.1 ± 0.5) W at the measured temperatures.

The defrost sequence for this unit consisted of (a) defrost heater switching on, (b) defrost heater switching off, (c) period of no power draw, (d) compressor on – recovery cycle, and (e) the following compressor off cycle. Measurements during this sequence yielded the following results:

Defrost time: 9355 seconds = 02:35:55 Energy expended during defrost period: (399.9 ± 2.0) watt-hours

Combining the results of these two portions of the test, assuming that the average time between defrost is 22.4 hours, we arrive at the total ener gy consumption of (912 ± 4.6) kWh/yr at the measured temperatures.

U 4.1.2 Cold Setting Results Since the temperatures in both compartments fo r this test were warmer than the target temperatures, the thermostat was set to the coldest setting for each compartment, 0.6 oC for the refrigerator and -21.1 oC for the freezer, and the measurements were performed again. The power signature from this data set and the temperatures recorded in the refrigerator and freezer compartm ent are shown in Figs. 4.2 and 4.3.26 Figure 4.2 Power Signature of Side -by-Side unit - Cold Setting

Figure 4.3 Temperature Response of Side-by-Side unit - Cold Setting27 By examining the temperature response to the compressor power draw, we can see that the unit shifts its cooling load between refr igerator and freezer compartments a number of times during each compressor “ON” cycle. The cyclic operation shows that the electrical load increases and the freezer temperature in creases while cooling is supplied to the refrigerator compartment, and that the elec trical load decreases and the refrigerator temperature increases while it is not.

The following results were obtained:

Steady state cyclic operation time: 20715 seconds = 05:45:15 Measured refrigerator compartm ent temperature: (-2.0 ± 0.1) oC Measured freezer compartment te mperature: (-21.5 ± 0.1) oC Energy expended during the test period: (729.9 ± 3.6) watt-hours

Alternatively, this can be expressed as an average steady state power of (126.8 ± 0.6) W at the measured temperatures.

Defrost time: 18882 seconds = 05:14:42 Energy expended during defrost period: (776.8 ± 3.9) watt-hours

These values resulted in the total energy consumption of (1133 ± 6) kWh/yr at the measured temperatures.

U 4.1.3 Combined Test Results for Side-by-Si de Refrigerator with No Ice Production
The results of the measurements at the firs t thermostat setting were combined with the results at the second thermostat setting and inte rpolated to the target temperatures. When interpolating to the refriger ator target temperature of 3.9 oC, the calculated energy consumption was (923 ± 3) kWh/yr; when inte rpolating to the freezer target temperature of -17.8 oC, the energy consumption was (918 ± 6) kWh/yr. The maximum of these two
values is declared as the base line energy consumption: (923 ± 3) kWh/yr. It is important to note that the interpolation results using th e refrigerator temperature target and that using the freezer temperature target are very close to each other, therefore using the triangular interpolation method will not result in improved accuracy.

It is also useful for late r calculations to note the ener gy consumption obtained through interpolation if the defrost energy was not cons idered. In this case, the calculations were performed with the steady st ate operational average power of (101.1 ± 0.5) W (mid/mid setting) and (126.8 ± 0.6) W (cold/cold settin g) rather than the total values. Here, negating the energy from peri odic defrosting shows the ener gy consumption for this unit to be (897 ± 3) kWh/yr.

4.2 Side-by-Side Refrigerator Freezer with Ice Production With the baseline energy consumption charac terized, we next performed a series of measurements to examine the energy consump tion attributed to the production of ice by
the automatic ice maker.28 U 4.2.1 Mid Setting Results The thermostat was set to the median position for each compartment and the ice maker was rendered active. Water was supplied to the unit at a temperature of 32.2 oC.

Figs. 4.4 and 4.5 show the power and temperat ures measured during the test. These figures demonstrate the complexity of the operati on of this unit. The first point to note is that the compressor cyclic pattern changes peri odically, this is because of the nature of
the electronic thermostatic cont roller used in this system. This controller monitors the temperatures in both compartments and supplie s cooling to each one based on its needs. Satisfying both of these compartments need s simultaneously results in the operational mode switching as shown in the figures.

The power signature of this unit also show s the operational energy consumed by the ice making components. The ice ejection heater operates at approximately 130 W for a period of 150 seconds (19.5 kJ). After the ice is freed from the mold, a plastic rod is swept through each mold and pushes the fro zen cubes to the storage bin. Then the solenoid valve opens to deliver water to the molds; this process consumes approximately 32 W for 4 seconds (128 J).

Figure 4.4 Refrigerator Power at Mid Setting with Ice Production for Side-by-Side Re frigerator Freezer29 Figure 4.5 Temperature Response to Mid Setting with Ice Production for Side-by-Side Re frigerator Freezer

The data was recorded for the maximum am ount of time that could be logged while avoiding a defrost cycle. The data was also reduced to allo w a whole number of compressor cycles; the ice production cycles were agai n treated as secondary.

Steady state cyclic operation time: 80801 seconds = 22:26:41 Measured refrigerator compartm ent temperature: (3.1 ± 0.1) oC Measured freezer compartment te mperature: (-17.7 ± 0.1) oC Mass of ice produced: (1.81 ± 0.005) kg Ice production rate: (80. 6 ± 0.23) grams per hour Energy expended during the te st period: (2.91 ± 0.01) kWh Average Power drawn during test period: (129.5 ± 0.6) W

Single Data Point Method for Measuring Ice-Maker Energy Consumption The first proposed approach to quantifyi ng the ice-making energy is to compare the steady state energy consumption with both thermo stats set to their medi an setting for both ice producing and ice maker inoperative conditi ons. Since this particular unit had an electronic thermostat, the compartment temper atures measured during the tests at the median temperature settings were simila r regardless of whether the ice maker was producing ice or not; therefore, it is thought that this met hod should provide a fairly good comparison. In this case, the di fferential power consumption was:

(129.5 ± 0.6) W – (101.1 ± 0.5) W = (28.4 ± 0.8) W30 The energy used to produce ice in this configuration can then be calculated from the mass of ice, the differential powe r and the test period time.



### ( ) ( ) ( ) 0.0284 kW 22.44 h

= 1.81 kg ( 0.352 ± 0.01) kWh/kg

U 4.2.2 Cold Setting Results The next approach was to attempt to use an interpolated energy (and ice production rate) using a second set of measurements. Since the internal temperature of the freezer compartment was slightly warmer than the ta rget freezer temperature, the thermostats of each compartment were set to the coldest se tting for the second measurement. This caused the unit to operate w ith the compressor running 100 % of the time and caused the unit to initiate a defrost cycl e after every 7 hours of compressor run time; the operation is shown graphically in Fig. 4.6.

Figure 4.6 Temperature and Power of Side -by-Side Unit under Coldest Settings

The compressor does not cycle under these condi tions and with this very short time between defrost cycles this unit never achieve s steady state operation as defined in the test procedure. We must therefore select a te st period that consists of the longest period of time during which ice was actively produced wit hout the influence of the defrost cycle.

The first and second ice ejection events occur shortly after the depl oyment of the defrost heater and the freezer compartment is underg oing its recovery, therefore it is not desirable to use data prior to either of these in stances. It is also im portant to note that the31 freezer and refrigerator compartm ent temperatures exhibit a cyclic pattern as the cooling load is periodically shifted between these comp artments. We will therefore select the test period that begins at the instance the unit begins to supply cold air to the freezer compartment after the second ice ejection even t and ends at the in stance that the unit begins to supply cold air to the freezer compar tment just prior to the next defrost event.

The following results were obtained:

Steady state cyclic operation time: 15198 seconds = 04:13:18 Measured refrigerator compartm ent temperature: (-2.3 ± 0.1) oC Measured freezer compartment te mperature: (-19.4 ± 0.1) oC Mass of ice produced: (0.467 ± 0.005) kg Ice production rate: (110.5 ± 0.6) grams per hour Energy expended during the te st period: (0.625 ± 0.003) kWh Average Power drawn during test period: (148.0 ± 0.8) W

Two Data Point Method for Measuring Ice-Maker Energy Consumption Now, the energy consumption at the specified target temperatures is calculated based on
the results of the mid/mid and cold/cold setti ng tests. For this cal culation, the results show that the interpolated values for a freezer temperature of -17.8 oC are an energy consumption of (1144 ± 9) kWh/yr and an interpolated ice production rate of (721.5 ± 14.5) kg/yr. The interpolation resu lts using the refrigerator compartment temperatures are again very close to th e interpolation results using the freezer temperatures. Comparing these values to those calculated from the tests without ice production (not considering defrost periods ) results in the fo llowing values:

Energy consumption difference: (1144 ± 9) kWh/yr - (897 ± 3) kWh/yr = (247 ± 10) kWh/yr Ice production rate: (721.5 ± 14.5) kg/yr Ice production energy: (0.342 ± 0.013) kWh/kg

4.3 Calculation Based Method for Estimating Ice-Maker Energy The next method of estimating ice-maker ener gy was a simplified calculation approach. Each data set taken with the ice maker opera tive was started with the ice bin empty and logged until the bin reached its shut off limit. The first data set showed 1.90 kg of ice produced through 20 cycles, the second show ed 1.96 kg in 21 cycles. Averaging the results of these two tests yields a producti on rate of 94.1 grams of ice per cycle (3.86 kg in 41 cycles).

As mentioned earlier, the solenoid valve cons umes 128 Joules per cycle, or 1.36 kJ/kg of ice produced. The ice ejection heater cons umes 19.5 kJ, or 207.2 kJ/kg, which is then dissipated into the freezer compartment. Th erefore, the total energy consumed by these components is 208.6 kJ/kg of ice produced. C onsidering the heat load for freezing water into ice and the removal of the dissipated heat from the ejection heaters, the total demand of additional cooling to the refrigeration system is 713.6 kJ/kg. Assuming that the refrigerating system operates with a COP of 1.0, this translates to 713.6 kJ/kg. Finally,32 adding in the energy consumed by the solenoi d, ejection rod, and ejec tion heater brings the total load to 922.2 kJ/kg; or in alternative units 0.256 kWh/kg.

4.4 Test Length Determination As with the previous test subject, we ex amined the power consumed by the unit while making ice in a little more detail in order to determine how much data needs to be recorded to properly calculate the energy consumption. Fig. 4.7 shows the average power consumed during each full compressor cycle while the unit was operating at the mid/mid setting and producing ice.

Figure 4.7 Average Power Draw Over 12 Whol e Compressor Cycle – Side by Side Unit
Test #1

This data set encompasses 12 compressor cycles that occurred while the unit was producing ice. Eight of these compressor cycl es each produced two batches of ice, while the remaining four compressor cycles each produ ced one batch. It is interesting to note
that while there was variation in the numb er of batches of ice produced during each compressor cycle, the average power consum ed during each compressor cycle did not vary by much. The compressor cycle with the largest deviation from the mean was within 2 % of the average of all 12 compressor cycles.

Fig. 4.8 shows the data plotted as both in stantaneous power (pink) and cumulative average power draw (blue) versus time for this cabinet under the mid/mid thermostat setting. This figure shows that the cumula tive average power draw changes by less than 1 % between successive compressor cycles thro ughout the entire data set. The results33 showed that, under these conditions, it is possible produce a reasonable energy consumption result using only one comp ressor cycle, about 2 hours of data.

Figure 4.8 Instantaneous and Cumulative Average Power Draw Side-by-Side Unit Test #1

The ice production rate, however, is not as quick to stabilize. Fig. 4.9 shows the ice production rate, defined as the cumulative quant ity of ice produced since the beginning of the test period divided by the test period lengt h, versus time for the same data set. The value of 80.6 grams per hour was reported base d on the total length of the test period, however, the saw tooth pattern in the figure suggests that the true value lies somewhere between 80.4 grams per hour and 84.9 grams per hour.34 Figure 4.9 Ice Production Rate - Side-by-Side Unit Test #1

An analysis of the ice making energy to quantity of ice produced was performed using
the second data set. This data set did not encompass any compressor off cycles, since operating this unit at the cold est setting with ice production caused it the compressor to run 100 % of the time. Therefore, we used an alternative approach based on temperature cycles. Fig. 4.10 shows the data plotted as both instantaneous power (red) and cumulative average power draw (blue) versus time for this cabinet under the coldest thermostat setting. This figure shows that the oscillations in cumulative average power draw change by less than 1 % between successi ve temperature cycles after the fourth cycle. The results showed that, under these conditions, it is possible produce a reasonable energy consumption resu lt using about 3 hours of data.35 Figure 4.10 Instantaneous and Cumu lative Average Power Draw Side-by-Side Unit Test #2

Fig. 4.11 shows the ice production rate for this same data set. The value of 110.5 grams per hour was reported based on the total length of the test period, however, the saw tooth pattern in the figure suggests that the true value lies so mewhere between 92.0 grams per hour and 114.9 grams per hour.36 Figure 4.11 Ice Production Rate - Side-by-Side Unit Test #2

4.5 Summary Table 4.1 shows the ice making energy was calcu lated by three methods. Also shown in Table 4.1 is the annual energy impact of producing 0.816 kg of ice per day.

Table 4.1 Ice making energy by various methods – side by side refrigerator freezer

Method Ice making energy kWh/kg kWh/yr % of baseline energy 1 Median position only 0.352 105 11 % 2 Two point interpolation 0.342 102 11 %
3 Calculation 0.256 76 8 %37 

### 5: Experimental Results for Fren ch Door Refrigerator Freezer #1 This unit is an 800 liter (28 c ubic foot) French door, energy star rated model with through
the door ice and water service. It has variable defrost co ntrol, electronic thermostat control, and a variab le-speed compressor. The unit ha s a factory installed ice maker which is located in the upper portion of the refrigerator compartment. The ice maker is
connected to an external wate r supply and produces and stores ice in a bin also located in the refrigerator compartment. The ice maker for this unit has a dedicated evaporator and produces ice without displacing cold air fr om the freezer compartment. The unit was outfitted with three thermocouples in the refri gerator compartment, as shown below, and five thermocouples in the freezer compartment. The compartment temperatures used for the calculations that follow are the average of the time averaged values reported from each thermocouple during the test duration.

Figure 5.1 French Door Unit #1

The minimum and maximum time between defro st for this unit are 6 hours and 96 hours of compressor run time, respectiv ely. According to the proc edure outlined in the current38 DOE energy test procedure, these values result in a calculated average time between defrost of 24 hours of compressor run time.

This unit also has an automatically controll ed anti-sweat heater, which responds to the ambient humidity condition. The humidity levels were maintained below 8 oC dew point for all tests performed in this study in order to ensure that this feature would not consume electricity outside the scope of this set of experiments.

5.1 French Door Refrigerator Freezer #1 with No Ice Production

U 5.1.1 Mid Setting Results

U During the first test, the energy consumption wa s measured at with the thermostat set to the median setting for each compartment. Th e fact that this unit had a variable-speed compressor facilitated the characteriza tion of energy consumption because the compressor did not undergo period ic cycles; rather it mainta ined part load continuous operation to stabilize the temperatures in the cabinets. The following results were
obtained:

Steady state operation time: 40145 seconds = 11:09:05 Measured refrigerator compartm ent temperature: (6.9 ± 0.1) oC Measured freezer compartment te mperature: (-17.9 ± 0.1) oC Energy expended during the test period: (629.2 ± 3.1) watt-hours

Alternatively, this can be expressed as an average steady state power of (56.42 ± 0.28) W at the measured temperatures. In alternative units, (494.3 ± 2.5) kWh/yr.

The defrost sequence for this unit consisted of (a) defrost heater switching on, (b) defrost heater switching off, (c) period of no power draw, (d) a recovery cycle – high compressor power, and (e) return to steady state – part load compressor power. The sequence is shown below in Fig. 5.2.39 Figure 5.2 Refrigerator Power duri ng Defrost – French Door Unit #1

Measurements during this sequenc e yielded the following results:

Defrost time: 3598 seconds = 00:59:58 Energy expended during defrost period: (205.3 ± 1.0) watt-hours

Combining the results of these two portions of the test, assuming that the average time between defrost is 24 hours, we arrive at the total energy consumption of (521.5 ± 2.6) kWh/yr at the measured temper atures. It should be noted that the calculations used to arrive at this number are based on an assumption that the compressor operates 50% of the time; which is not va lid for a variable speed compressor which operates 100% of the time under part load conditions.

U 5.1.2 Cold Setting Results

U The second set of tests were conducted with the thermostat for each compartment set to the coldest setting. The follo wing results were obtained:

Steady state operation time: 89901 seconds = 24:58:21 Measured refrigerator compartm ent temperature: (4.4 ± 0.1) oC Measured freezer compartment te mperature: (-22.7 ± 0.1) oC Energy expended during the test period: (1756.4 ± 8.8) watt-hours

Alternatively, this can be expressed as an average steady state power of (70.33 ± 0.35) W at the measured temperatures , or (616.1 ± 3.1) kWh/yr.40 Measurements during this sequenc e yielded the following results:

Defrost time: 5426 seconds = 01:30:26 Energy expended during defrost period: (266.7 ± 1.3) watt-hours

Incorporating the defrost energy results in an overall energy consumption value of (645.4 ± 3.2) kWh/yr at these temperatures.

U 5.1.3 Mixed Setting Results

U Since the thermostat for this unit was programmed to optimize performance while simultaneously maintaining temperatures of 7.2 oC and -15.0 oC in the refrigerator and freezer, respectively, a third data set was take n with the refrigerator set to the coldest setting and the freezer set to the warmest setting. The third data set resulted in the following values:

Steady state operation time: 39733 seconds = 11:02:13 Measured refrigerator compartm ent temperature: (2.4 ± 0.1) oC Measured freezer compartment te mperature: (-15.7 ± 0.1) oC Energy expended during the test period: (673.5 ± 3.4) watt-hours

Alternatively, this can be expressed as an average steady state power of (61.0 ± 0.3) W at the measured temperatures, or (534.5 ± 2.7) kWh/yr. Measurements during this sequence yielded the following results:

Defrost time: 4304 seconds = 01:11:44 Energy expended during defrost period: (250.9 ± 1.3) watt-hours

Incorporating the defrost energy results in an overall energy consumption value of (567.0 ± 2.8) kWh/yr at these temperatures.

U 5.1.4 Combined Test Results for French D oor Refrigerator Freezer #1 with No Ice
Production The steady operation values from these three da ta sets were used to calculate the energy consumption at -17.8 oC and 3.9 oC using th e three point interpol ation method; this resulted in an energy consumption value of (544 ± 5) kWh/yr. The total energy consumption, including the defros t energy, was (574 ± 5) kWh/yr.

5.2 French Door Refrigerator Freezer #1 with Ice Production With the baseline energy consumption charac terized, we next performed a series of measurements to examine the energy consump tion attributed to the production of ice by
the automatic ice maker.

U 5.2.1 Mid Setting Results

U First, the thermostat was set to the medi an position for each compartment and the ice maker was rendered operative. Water was supplie d to the unit at a temperature of 32.2 oC. Fig. 5.3 shows the power signature of this unit while making ice under these conditions.41 Figure 5.3 Refrigerator Power During Ice Production at Mid Setting for
French Door Unit #1

Starting from an empty ice bin condition, the ice maker operated for less than 14 000 seconds before ceasing ice production by sens ing a full bin. During this ice production period, the freezer temperature deviated from its measured temperat ure prior to the ice making period, shown in Fig. 5.4. It is noted that each ice making cycle appears to include two successive ejection heater ope ration periods followed by the solenoid operation. Each time the heater is powere d on, it consumes 150 W for approximately 120 seconds; the solenoid consumes 40 W for 4 sec onds. It is also noted that the freezer compartment became slightly colder for a short period, which was followed by a period of increasing freezer temperature. This is documented merely to illustrate that the ice making period is a transient period during whic h time the unit tries to adjust operation to produce ice while maintaining th e prescribed conditions. For this reason, it was generally not possible to acquire a data set that encompasses real steady state operation.42 Figure 5.4 Temperature Response During Ice Production at Mid Setting for
French Door Unit #1

Since this unit had a variable-speed comp ressor, it was not necessary to consider compressor cycles, and the ice making energy wa s calculated by the considering all of the ice making cycles. The test period is then de scribed as starting from the ice maker being cued to produce ice until the moment that the ice maker halts production based on it sensing a full bin condition. This is clea rly visible on the figure above showing the power signature.

Operation time: 13920 seconds = 03:52:00 Measured refrigerator compartm ent temperature: (6.2 ± 0.1) oC Measured freezer compartment te mperature: (-18.8 ± 0.1) oC Mass of ice produced: (0.69 ± 0.005) kg Ice production rate: (178.5 ± 1.3) grams per hour Energy expended during the test period: (503.0 ± 2.5) watt-hours

Alternatively, this can be expressed as an average steady state power of (130.1 ± 0.7) W at the measured temperatures; or (1139.5 ± 5.7) kWh/yr.

Single Data Point Method for Measuring Ice Maker Energy Consumption The first proposed approach to quantifyi ng the ice making energy is to compare the steady state energy consumption with both thermo stats set to their medi an setting for both ice producing and ice maker inoperative condition s. In this case, the differential power consumption was:43 (130.1 ± 0.7) W – (56.42 ± 0.28) W = (73.7 ± 0.8) W

The energy used to produce ice in this configuration can then be calculated from the mass of ice, the differential powe r and the test period time.



### ( ) ( ) ( ) 0.0737 kW 3.867 h
0.69 kg = 0.413 kWh/kg (± 0.005 kWh/kg)

In this case, the measured temperature in both compartments was colder than the measured temperature during the first test (s ame setting but no ice production), therefore the results of this ice-making test also include the additional load of maintaining slightly colder temperatures.

U 5.2.2 Cold Setting Results

U The next approach was to attempt to use an interpolated energy (and ice production rate) using this and two other sets of measurem ents. We set the thermostats of each compartment to the coldest se tting for the second ice making data set. The figure below shows the power signature record ed during this measurement.

Figure 5.5 Power Response During Ice Production at Cold Setting for
French Door Unit #1

Under these test conditions, the unit does not abruptly shift back to the steady operation after it ceased ice production due to the full bin condition as was the case with the44 previous measurement. Rather it gradually reduced the compressor power until reaching the steady operation condition. The figure shows that ice production ceases at approximately 10 000 seconds, but the unit does not recover from the ice production until approximately 20 000 seconds. If we take the test period to be that of the ice production period only, we obtain the following values:

Operation time: 9906 seconds = 02:45:06 Measured refrigerator compartm ent temperature: (3.5 ± 0.1) oC Measured freezer compartment te mperature: (-22.3 ± 0.1) oC Mass of ice produced: (0.55 ± 0.005) kg Ice production rate: (199.9 ± 1.8) grams per hour Energy expended during the test period: (436.0 ± 2.2) watt-hours

Alternatively, this can be expressed as an average steady state power of (158.5 ± 0.8) W at the measured temperatures; or (1388.1 ± 6.9) kWh/yr.

If the recovery period is included as part of the analysis, th e following values are
obtained:

Operation time: 20000 seconds = 05:33:20 Measured refrigerator compartm ent temperature: (3.4 ± 0.1) oC Measured freezer compartment te mperature: (-23.0 ± 0.1) oC Mass of ice produced: (0.55 ± 0.005) kg Ice production rate: (99.0 ± 0.9) grams per hour Energy expended during the test period: (747.0 ± 3.7) watt-hours

Alternatively, this can be expressed as an average steady state power of (134.5 ± 0.7) W at the measured temperatures; or (1177.8 ± 5.9) kWh/yr.

Inclusion of the recovery period resulted in a colder freezer temper ature and lower energy consumption, but also lower ice production rate.

U 5.2.3 Mixed Setting Results

U The final measurement for this unit was performed with the freezer set to the warmest setting and the refrigerator set to the coldest setting. This data set, like that from the mid/mid setting with ice production, showed an abrupt reduction in compressor speed at the time that it ceased ice production. The following data were obtained from these

measurements:

Operation time: 11039 seconds = 03:03:59 Measured refrigerator compartm ent temperature: (2.9 ± 0.1) oC Measured freezer compartment te mperature: (-17.1 ± 0.1) oC Mass of ice produced: (0.56 ± 0.005) kg Ice production rate: (182.6 ± 1.6) grams per hour Energy expended during the test period: (395.2 ± 2.0) watt-hours45 Alternatively, this can be expressed as an average steady state power of (128.9 ± 0.6) W at the measured temperatures; or (1128.9 ± 5.6) kWh/yr.

Three Data Point Method for Measuring Ice Maker Energy Consumption By applying the three poin t interpolation method for bot h the energy consumption and the ice production rate, the fo llowing values were obtained for conditions representative of 3.9 oC in the refrigerator and -17.8 oC in the freezer. The following data shows the
overall results of the calcul ations using both possible ice production periods from the cold/cold setting data (i.e., with and without the r ecovery period).

U Ice production period only Energy consumption at T freeze = -17.8 oC and T fridge = 3.9 oC (1142 ± 7) kWh/yr = (130.4 ± 0.8) W Ice production rate at T freeze = -17.8 oC and T fridge = 3.9 oC (182 ± 1) grams per hour

U Ice production and recovery periods Energy consumption at T freeze = -17.8 oC and T fridge = 3.9 oC (1134 ± 4) kWh/yr = (129.5 ± 0.5) W Ice production rate at T freeze = -17.8 oC and T fridge = 3.9 oC (179 ± 2) grams per hour

The results differ by 0.7 % on energy a nd 1.7 % on ice production rate. These calculations show that the result is largel y unaffected by the inclusion of the recovery period for this unit; however, this may not hol d true for a unit with a more aggressive recovery schedule.

The following results were obtained by compari ng the triangularly in terpolated results
from the tests with a nd without ice production.

(130.4 ± 0.8) W – (62.1 ± 1.7) W = (68.3 ± 1.9) W

The energy used to produce ice in this configuration can then be calculated from the mass of ice, the differential powe r and the test period time.



### ( )

0.0683 kW

= kg 0.182 h ⎛ ⎞ ⎜ ⎟ ⎝ ⎠ ( 0.375 ± 0.011) kWh/kg

Next, it is also intere sting to calculate the ice making energy by triangular interpolation of the non-ice making data to the temperatures realized during the ice making tests. First, the ice making test data at the mid/mid setti ng resulted in temperatur es of 6.2 oC in the refrigerator and -18.8 oC in the freezer. Triangularly in terpolating the non-ice making data points to these temperatures, we calcu late a value of (59.48 ± 0.35) W, which is (70.6 ± 0.8) W less than the average power seen during the mid/mid test with ice production. Dividing th is differential power by the i ce production rate, the ice making46 energy at T

B fridge

B =6.2 oC and T

B freeze

B =-18.8 oC is (0.396 ± 0.005) kWh/kg. Similarly, the ice making energy was calculated at the coldest and mixed settings as well. The coldest setting, at T

B fridge

B =3.5 oC and T

B freeze

B =-22.3 oC is (0.436 ± 0.020) kWh/kg; the mixed setting,

at T

B fridge

B =2.9 oC and T

B freeze

B =-17.1 oC is (0.363 ± 0.005) kWh/k g. These results illustrate the dependence of the ice-making energy on the co mpartment temperatures. It is for this reason that a fixed set of temperature condi tions should be used in order to form a repeatable basis for an ice-making energy test.

5.3 Calculation Based Method Lastly, the theoretical ice-making energy was calculated using the simplified calculation approach. Each data set taken with the ice maker operative was started with the ice bin empty and logged until the bin reached its shut off limit. The first data set showed 0.69 kg of ice produced through 10 cycles, th e second showed 0.55 kg in 8 cycles, and the third showed 0.56 kg in 8 cycles. On av erage, this unit produces 69.2 grams of ice during each cycle.

The solenoid valve draws 40 W for a period of 4 seconds to deliver water to the molds, which results in 160 Joules during each ice-ma king cycle, or 2.31 kJ/kg of ice produced. The ice ejection heater draws 150 watt for two 120 second periods to free the ice from the molds which results in 36,000 Joules per ice making cycle, or 520.2 kJ/kg of ice produced. The total energy consumed by thes e components is therefore 522.5 kJ/kg of ice produced. Also, the energy consumed by the ice ejection heater is ultimately dissipated as heat into the ice-making compar tment; therefore it must be considered an additional heat load to be pro cessed by the refrigeration system.

The energy required to cool 32.2 oC water to freezing accounts for 505 kJ/kg. The refrigeration system must therefore meet the additional demand to remove 1025 kJ of heat per kg of ice produced. Using the a ssumed COP of 1, the additional compressor duty to remove this heat will total 1025 kJ/kg. Adding in the energy consumed by the solenoid and ejection heater bri ngs the total load to 1547.5 kJ/ kg; or in alternative units 0.303 kWh/kg.

5.4 Summary The ice-making energy was calculated by thre e methods as shown in Table 5.1. Also shown in the table is the energy imp act of producing 0.816 kg of ice per day.

The first method was to compare the differen ce in energy consumed with the thermostats set to their median positions. This method resulted in a temporary, relatively small departure from the non-ice producing freezer temp erature because of the control system
used in this cabinet. The second method at tempted to characterize the ice making energy by using the three-point interpolation met hod and various temperature conditions. The final method was a simple calculation method based on the amount of energy required to process the ice making load, and to power th e auxiliary devices required to make and store ice. This method relies heavily on an assumed COP value of unity. The values in the table below are shown in comparison to the baseline energy of 574 kWh/yr.47 Table 5.1 Ice making energy by various methods – french door unit #1

Method Ice making energy kWh/kg kWh/yr % of baseline energy 1 Median position only 0.413 123.0 21.4 % 2 Triangular Interpolation (3.9 oC/-17.8 oC) 0.375 112.0 19.5 %

Triangulation (M/M) (6.2/-18.8) 0.396 118.3 20.6 % Triangulation (C/C) (3.5/-22.3) 0.436 129.9 22.6 %

Triangulation (C/W) (2.9/-17.1) 0.363 108.4 18.9 %

3 Calculation 0.430 128.0 22.3 %

Error Associated with Inco mplete Ice Maker Cycling This product has a variable speed compressor which greatly simplifies the recognition of energy associated with the ice maker. In this case, the compressor power maintains a steady part-load condition th roughout its operation, and ther e is no compressor cycling. Since there is no compressor cycling, the analysis was conducted using a whole number of ice making cycles and there is no error a ssociated with incomplete cycling in this

manner.

There is, however, a certain le vel of error due to the first batch of ice harvested upon the initiation of ice production. Once initiated, the ice maker be gins by harvesting a batch of cubes, but the energy used to cool and freeze water into this set of cubes was expended long before the ice maker was rendered operative . Therefore, the energy recorded for the
first batch of ice cubes is me rely that of the ejection heater. This should have a much smaller impact on the end result than the error associated with the units employing cycling compressors, particularly since the ej ection heaters are such a large portion of the total energy used by the ice maker. However, this particular unit does not take many ice making cycles to fill the ice bin, theref ore this aspect is significant here.

The heaters for this unit use a total of 36 kJ to harvest each batch of ice, which weighed approximately 69 grams. Therefore, in each measurement the energy recorded for the first batch of ice was only 0.149 kJ/kg. If the ma ss of the first batch of ice is subtracted from each data set along with the ejection heater power, the following results shown in Table 5.2 are obtained, which are slightly higher than those shown in Table 5.1.48 Table 5.2 Energy consumption error associated with first batch
french door unit #1

Method kWh/kg
Measured

Value Value Excluding
First Batch Difference

1 Median position only 0.413 0.443 7.3 %

2 Triangular Interpolation 0.374 0.403 7.8 %

Although it is not difficult to correct for the firs t batch of ice in this case, it may not be possible for every unit because it may not alwa ys be possible to determine the number of cubes harvested in each cycle, etc. as was s een with the other test subjects. There is, however, a simple approach to avoid this type of error entirely at the onset of testing. If the water supplied to the cabinet is interrupt ed, the ice molds would be emptied prior to the beginning of the data co llection period. Therefore, one could begin the test by opening the water supply and then rendering the ice maker operative. After rendering the ice maker operative, the ejection heaters woul d operate and then the solenoid valve would fill the molds with water for the first batch of ice. The test period would then begin at the
first solenoid event and end after the last batc h of ice is harvested, thereby consisting of a whole number of ice-making cycles.49 

### 6: Experimental Results for Fren ch Door Refrigerator Freezer #2 This unit, shown in Fig. 6.1, is a 765 liter ( 27 cubic foot) French door, energy star rated model with through the door i ce and water service. It ha s variable defrost control, electronic thermostat control, and a variable -speed compressor. The unit has a factoryinstalled ice maker which is located in the uppe r portion of the refrigerator compartment.
It is connected to an external water s upply and produces ice in the ceiling of the refrigerator compartment and stores it in a bin located in the door of the refrigerator compartment. This unit freezes ice using a se t of small ducts inside the walls of the cabinets to bring cold air from the freezer co mpartment located beneath the refrigerator compartment. The compartment temperatures used for the calculations that follow are the average of the time averaged values re ported from each thermocouple during the test
duration.

Figure 6.1 French Door Unit #2

The minimum and maximum time between de frost for this unit are 8 and 96 hours of compressor run time, respectively. According to the method outlined in the current DOE50 energy test procedure, these values result in a calculated average tim e between defrost of 30 hours of compressor run time.

This unit also has an automatically controll ed anti-sweat heater, which responds to the ambient humidity condition. The manufacturer provided the control algorithm for this feature, and we maintained a de w point below 8 oC for all tests in order to ensure that this feature would not consume electricity outsi de the scope of this set of tests.

6.1 French Door Refrigerator Freezer #2 with No Ice Production

U 6.1.1 Mid Setting Results

U During the first test, the energy consumption wa s measured at with the thermostat set to the median setting for each compartment. The following results were obtained:

Steady state operation time: 13497 seconds = 03:44:57 Measured refrigerator compartm ent temperature: (3.7 ± 0.1) oC Measured freezer compartment te mperature: (-16.8 ± 0.1) oC Energy expended during the test period: (237.2 ± 1.2) watt-hours

Alternatively, this can be expressed as an average steady state power of (63.28 ± 0.32) W at the measured temperatures. In alternative units, (554.3 ± 2.8) kWh/yr.

Measurements during the defrost sequ ence yielded the following results:

Defrost time: 8701 seconds = 02:25:01 Energy expended during defrost period: (303.3 ± 1.5) watt-hours

Combining the results of these two portions of the test, assuming that the average time between defrost is 30 hours, we arrive at the total energy consumption of (576.3 ± 2.9) kWh/yr at the measured temperatures.

U 6.1.2 Cold Setting Results

U The second set of tests were conducted with the thermostat for each compartment set to the coldest setting. During this test, the compressor did not cycle on and off, but did exhibit temperature and power oscillations due to the part load compressor speed and the periodic cooling load shifts be tween the refrigerator and freezer compartment. In order to ensure that the most repeatable result was captured, the test period used consisted of a whole number of these oscillations. The following results were obtained:

Steady state operation time: 13622 seconds = 03:47:02 Measured refrigerator compartm ent temperature: (-1.2 ± 0.1) oC Measured freezer compartment te mperature: (-20.0 ± 0.1) oC Energy expended during the test period: (287.7 ± 1.4) watt-hours

Alternatively, this can be expressed as an average steady state power of (76.04 ± 0.38) W at the measured temperatures , or (666.1 ± 3.3) kWh/yr.51 Measurements during the defrost sequ ence yielded the following results:

Defrost time: 14400 seconds = 04:00:00 (no cycling condition) Energy expended during defrost period: (450.9 ± 2.3) watt-hours

Incorporating the defrost energy results in an overall energy consumption value of (687.6 ± 3.4) kWh/yr at these temperatures.

U 6.1.3 Mixed Setting Results

U The thermostat for this unit was programmed in order to optimize performance while simultaneously maintaining temperatures of 7.2 oC and -15.0 oC in the refrigerator and freezer, respectively. Therefore, a third data se t was taken with the refrigerator set to the warmest setting and the freezer se t to the coldest setting in order to appropriate data for the three point interpolation method. These se ttings resulted in the compressor operating at part load conditions, but w ith periodic cycling. Because of this, the data was reduced using a whole number of complete compressor cy cles. The third data set resulted in the following values:

Steady state operation time: 33243 seconds = 03:44:57 Measured refrigerator compartm ent temperature: (7.2 ± 0.1) oC Measured freezer compartment te mperature: (-20.3 ± 0.1) oC Energy expended during the test period: (640.4 ± 3.2) watt-hours

Alternatively, this can be expressed as an average steady state power of (69.35 ± 0.35) W at the measured temperatures, or (607.5 ± 3.0) kWh/yr. Measurements during the defrost sequence yielded the following results:

Defrost time: 23818 seconds = 06:36:58 Energy expended during defrost period: (615.0 ± 3.1) watt-hours

Incorporating the defrost energy results in an overall energy consumption value of (630.3 ± 3.2) kWh/yr at these temperatures.

U 6.1.4 Combined Test Results for French D oor Refrigerator Freezer #2 with No Ice
Production The steady operation values from these three da ta sets were used to calculate the energy consumption at -17.8 oC and 3.9 oC using th e three point interpolation method which resulted in an energy consumption value of (576 ± 3) kWh/yr. The total energy consumption, including the defros t energy, was (598 ± 3) kWh/yr.

6.2 French Door Refrigerator Freezer #2 with Ice Production With the baseline energy consumption charac terized, we next performed a series of measurements to examine the energy consump tion attributed to the production of ice by
the automatic ice maker.

U52 6.2.1 Mid Setting Results

U The thermostat was set to the median position for each compartment and the ice maker was rendered operative. Water was supplied to the unit at a temperature of 32.2 oC. Fig. 6.2 shows the power signature of this un it while making ice under these conditions.

Figure 6.2 Refrigerator Power for Ice Production at Mid Setting for
French Door Unit #2

Starting from an empty ice bin condition, the ice maker operated for less than 44 000 seconds before undergoing a defrost period. This unit continued to produce ice during the defrost and recovery period, however, only th e data leading up to the defrost was used for this analysis in order to separate out the effects of the defrost cycle. In total, 2.37 kg of ice was produced during 40 ice making cycles ; 26 of these cycles occurred before the defrost; therefore the mass of 1.54 kg was used fo r this analysis. Each time the heater is powered on, it consumes 165 W for approximately 70 seconds, and the solenoid
consumes 50 W for 4 seconds.

It is also noted that the freezer compartment became slightly warmer for a short period near the beginning of the data set, when the ice maker was switched on, and gradually decreased over the duration of the test period. This temperature increase was in response to the additional load realized by the freezer compartment as cold air was bled off to produce ice in the ice maker. It is also interesting to not e that the temperature in the refrigerator compartment became slightly colder when the ice maker was rendered operative. This is because the ice maker is located in the refrigerator compartment and53 the additional supply of cold air needed to freeze ice has a cooling effect on the entire
compartment.

Figure 6.3 Temperature Response to Ice Production at Mid Setting for
French Door Unit #2

Since the compressor maintained a part load condition throughout the data set and did not switch on and off, it was not necessary to consider compressor cycles and the ice-making energy was calculated by consider ing all of the ice making cycl es prior to the defrost. The test period is then described as starting from the ice maker being cued to produce ice
until the moment that the defrost heater was ac tivated. This is clearly visible on Fig. 6.3.

Operation time: 41273 seconds = 11:27:53 Measured refrigerator compartm ent temperature: (3.2 ± 0.1) oC Measured freezer compartment te mperature: (-16.8 ± 0.1) oC Mass of ice produced: (1.54 ± 0.005) kg Ice production rate: (134 .37 ± 0.44) grams per hour Energy expended during the test period: (1052.0 ± 5.3) watt-hours

Alternatively, this can be expressed as an average steady state power of (91.79 ± 0.46) W at the measured temperatures; or (804.1 ± 4.0) kWh/yr.

Single Data Point Method for Measuring Ice-Maker Energy Consumption The first proposed approach to quantifyi ng the ice making energy is to compare the steady state energy consumption with both thermo stats set to their medi an setting for both ice producing and ice maker inoperative condition s. In this case, the differential power consumption was:54 (91.79 ± 0.46) W – (63.28 ± 0.32) W = (28.51 ± 0.56) W

The energy used to produce ice in this configuration can then be calculated from the mass of ice, the differential powe r and the test period time.



### ( ) ( ) ( ) 0.02851 kW 11.46 h

= 1.54 kg ( 0.212 ± 0.004) kWh/kg

Comparing the temperature results of the test s at the median setting shows that this particular unit maintained fairly consistent compartment temperatures whether or not the unit was producing ice. Alt hough there was some transient be havior at the onset of ice making, the time averaged values showed that the freezer compartment temperature remained nearly identical temperatures, but the refrigerator compartment temperature was approximately 0.5 oC colder while making ice.

U 6.2.2 Cold Setting Results

U The next approach was to attempt to use an interpolated energy (and ice production rate) using three sets of measurements. We set the thermostats of each compartment to the coldest setting for the second ice making data set. Fig. 6.4 shows the power signature recorded during this measurement. This figure shows that the compressor power fluctuates under these conditions; this is because this unit constantly adjusts the compressor speed in order to maintain constant temperatures in the compartments. We averaged the data over the en tire data set in order to dampen out these effects.

Figure 6.4 Power for Ice Production at Cold Setting
French Door Unit #255 Operation time: 54928 seconds = 15:15:28 Measured refrigerator compartm ent temperature: (-0.1 ± 0.1) oC Measured freezer compartment te mperature: (-18.2 ± 0.1) oC Mass of ice produced: (1.800 ± 0.005) kg Ice production rate: (117 .97 ± 0.33) grams per hour Energy expended during the test period: (1541.9 ± 7.7) watt-hours

Alternatively, this can be expressed as an average steady state power of (101.06 ± 0.51) W at the measured te mperatures; or (885.3 ± 4.4) kWh/yr.

U 6.2.3 Mixed Setting Results

U The final measurement for this unit was perf ormed with the freezer set to the coldest setting and the refrigerator set to the warmes t setting. This data set showed a gradual change in temperatures duri ng the initiation and terminati on of ice production. It also displayed an abrupt reduction in compressor sp eed and a return to periodic oscillation at the time that it ceased ice production, shown in Fig. 6.5.

Figure 6.5 Refrigerator Power with Ice Production at Mixed Setting for
French Door Unit #256 Figure 6.6 Refrigerator and Fr eezer Compartment Temperatures with Ice Production at Warm/Cold Setting for French Door Unit #2

The following data were obtained from these measurements:

Operation time: 48398 seconds = 13:26:38 Measured refrigerator compartm ent temperature: (5.4 ± 0.1) oC Measured freezer compartment te mperature: (-18.4 ± 0.1) oC Mass of ice produced: (1.57 ± 0.005) kg Ice production rate: (116.9 ± 0.4) grams per hour Energy expended during the test period: (1324.1 ± 6.6) watt-hours

Alternatively, this can be expressed as an average steady state power of (98.5 ± 0.5) W at the measured temperatures; or (862.8 ± 4.3) kWh/yr.

Three Data Point Method for Measuring Ice-Maker Energy Consumption By applying the three poin t interpolation method for bot h the energy consumption and the ice production rate, the fo llowing values were obtained for conditions representative of 3.9 oC in the refrigerator and -17.8 oC in the freezer.

Energy consumption: (845 ± 4) kWh/yr ((96.4 ± 0.5) W) Ice production rate: (2.96 ± 0.02) kg/day ((123.3 ± 0.9) grams per hour)

The following results were obtained by compari ng the triangularly in terpolated results
from the tests with a nd without ice production.57 (96.4 ± 0.5) W – (65.8 ± 0.3) W = (30.6 ± 0.6) W

The energy used to produce ice in this configuration can then be calculated from the mass of ice, the differential powe r and the test period time.



### ( )

0.0306 kW

= kg 0.1233 h ⎛ ⎞ ⎜ ⎟ ⎝ ⎠ ( 0.248 ± 0.005) kWh/kg

Next, it is of interest to ca lculate the ice-making energy by tr iangular interpolation of the non ice-making data to the temperatures reali zed during the ice-making tests. First, the ice making test data at the mid/mid setting re sulted in temperatures of 3.2 oC in the refrigerator and -16.8 oC in the freezer. Triangularly in terpolating the non-ice making data points to these temperatures, we calcu late a value of (63.7 ± 0.5) W, which is (28.1 ± 0.7) W less than the average power seen during the mid/mid test with ice production. Dividing th is differential power by the i ce production rate, the ice making energy at T

B fridge

B =3.2 oC and T

B freeze

B =-16.8 oC is (0.209 ± 0.005) kWh/kg. Similarly, the ice-making energy was calculated at the coldest and mixed settings as well. The coldest setting, at T

B fridge

B =-0.1 oC and T

B freeze

B =-18.2 oC is (0.260 ± 0.009) kWh/kg; the mixed setting, at T

B fridge

B =5.4 oC and T

B freeze

B =-18.4 oC is (0.278 ± 0.005) kWh/kg. These results confirm the observation from the previous uni t that the ice-making energy is fairly dependent on the refrigerator and freezer compartment temperatures.

6.3 Calculation Based Method Lastly, the theoretical ice-making energy was calculated using the simplified calculation approach. Each data set taken with the ice maker operative was started with the ice bin empty and logged until the bin reached its shut off limit. The first data set showed 1.54 kg of ice produced through 26 cycles, th e second showed 1.8 kg in 36 cycles, and the third showed 1.57 kg in 32 cycles. On av erage, this unit produ ces 52.2 grams of ice during each cycle.

The solenoid valve draws 50 W for a period of 4 seconds to deliver water to the molds which results in 200 Joules, or 3.83 kJ/kg of ice produced. The ice ejection heater draws 165 W for 70 second periods to free the ice fr om the molds which results in 11,550 Joules, or 221.26 kJ/kg of ice produced. The total energy consumed by these components is therefore 225.10 kJ/kg of ice produced. Als o, the energy consumed by the ice ejection heater is ultimately dissipated as heat into the ice-making compartment; therefore it must
be considered an additional heat load to be processed by the refrigeration system.

Considering the energy required to cool 32.2 oC water to freezing a nd the additional load of the heaters, the refrigeration system must therefore meet the a dditional demand of to remove 726 kJ of heat per kg of ice pr oduced. Using the assumed COP of 1, the additional compressor duty to remove this h eat will total 726 kJ/kg. Adding in the energy consumed by the solenoid and ejection heater br ings the total load to 951.1 kJ/kg; or in alternative units 0.264 kWh/kg.58 6.4 Summary The ice making energy was calculated by 4 methods as shown in Table 6.1. the table also shows the energy impact of producing 0.816 kg of ice per day.

The first method was to compare the differen ce in energy consumed with the thermostats set to their median positions. This method resulted in a temporary departure from the refrigerator cabinet temperature because of th e control system used in this cabinet. The second method attempts to characterize the i ce making energy by using the various threepoint interpolation methods. The final me thod was a simple calculation method based on the amount of energy required to process the ice making load, and to power the auxiliary devices required to make and store ice. The values in Ta ble 6.1 are shown in comparison to the baseline energy of 598 kWh/yr.

Table 6.1 Ice making energy by various methods – french door unit #2

Method Ice making energy kWh/kg kWh/yr % of baseline energy 1 Median position only 0.212 63.1 10.6 % 2 Triangulation (3.9/-17.8) 0.248 74.1 12.4 %

Triangulation (M/M) (3.2/-16.8) 0.209 62.2 10.4 % Triangulation (C/C) (-0.1/-18.2) 0.260 78.0 13.0 %

Triangulation (W/C) (5.4/-18.4) 0.278 82.8 13.8 %

3 Calculation 0.264 78.7 13.2 %

Error Associated with Inco mplete Ice-Maker Cycling This product, like the other French door un it, has a variable-speed compressor which simplified the recognition of energy associated with the ice maker because the compressor never cycled off during ice production. Since there was no compressor cycling during the ice-making te sts, the analysis was conduc ted using a whole number of ice-making cycles and there is no error associated with incomplete cycling.

As was the case with the French Door Refrig erator Freezer Unit #1, the level of error due to the first batch of ice harvested upon the initi ation of ice production is examined in this section. Performing a similar analysis yields significant results. As mentioned in the previous section, however, th e influence of this first batch of ice on the energy consumption can be easily eliminated by using the valve approach described in the previous section of this report.59 Table 6.2 Energy consumption error associated with first batch
french door unit #2

Method kWh/kg
Measured

Value Value Excluding
First Batch Difference

1 Median position only 0.212 0.219 3.3 % 2 Triangular Interpolation 0.248 0.257 3.6 %60 

### 7: Observations Four refrigerators with automatic ice makers we re examined in this study to evaluate test procedure options for determining ener gy consumption due to ice production by
automatic ice makers. The units varied in configuration, technol ogical sophistication, and most importantly ice-making energy consumption. This study centered on an approach that was based on usi ng the longest attainable period of test data that included steady state or cyclic operation. The length of the test period for each data set was limited by either a complete filling of the ic e storage bin or by an interruption of steady operation due to a defrost event.

The first two units analyzed employed a single-speed compressor that maintained temperature by cycling on and off. For th ese units, the ice-making cycles did not typically coincide with the compressor cycl es, which compromised the reproducibility of the test data. However, the reproducibility of the end result is stri ctly a function of the
number of undisturbed sequential cycles that can be found within a data set. A unit with a very large ice storage bin operating in su ch a way that it shows a long time between defrost events will be simpler to evaluate than one with a small storage bin or a short time
between defrost events.

The second two units studied were French door units. These units were particularly interesting because they produce ice inside the refrigerator compartment rather than the freezer compartment, which was expected to result in less efficient ice production. However, these are high-end units that empl oy sophisticated features. They both use inverter-driven variable-speed compressors, which are more efficient than single-speed compressors. These units ultimately show ed similar ice-making energy consumption values when compared to the units that made ice in the freezer. One particularly interesting aspect of the units with variab le-speed compressors is that the ice-making cycles can be easily separated from the data because the compressors do not cycle on and off. This greatly simplifies the dete rmination of ice making energy.

This study also considered a purely calculati on-based approach to estimate the ice-maker energy consumption. This method proved to be undesirable because the ice making energy consumption must be based on the actu al mass of ice produced, which must be a measured quantity. Also, this approach is based on an assumed COP of the system, which is not a traceable or reliable quantity.

The data showed that the compartment temperatures often deviate from their set points when the ice maker is rendered operative. Furthermore, the ice-making energy consumption generally varies with the compar tment temperatures. For this reason, it is recommended that the ice-making energy be de termined at a specified standard set of cabinet temperatures in order to have a good basis for comparis on of products. It is also suggested that a three point triangular inter polation method could be used to determine the ice-making energy consumption if tw o point interpolatio n does not closely approximate the target refrigerator and freezer temperatures simultaneously.61 The most reliable and cross-comparative results were those obtained using the interpolation methods and th e target temperatures of 3.9 oC in the refrigerator
and -17.8 oC in the freezer. Examination of these results shows that the measured ice maker energy consumption ranges from 0. 375 kWh/kg down to 0.248 kWh/kg. In general, roughly quarter of the energy e xpended during the ice pr oduction process was due to the operation of electric resistance heat ers, and it is estimated that approximately one third of the remaining energy was expended to remove the heat added by these heaters. In other words, approximately half of the total energy used to make ice is actually used to cool and freeze water into ice, the other half is used to remove it from the
molds. This indicates that there are substantial opportunitie s for efficiency improvements merely by optimizing the operati on of the heaters associated with the ice makers or by eliminating them altogether and using an alternative method to free the ice from the
molds.

It should also be noted that the theoretical limit of ice-making energy is merely the difference between the inlet water’s enthalpy and that of the ice in its final state, divided by the vapor compression system’s COP. The enthalpy difference is a firm parameter of 505 kJ/kg for water entering the ice maker at 32.2 oC (90 oF) and being brought to a final temperature of -17.8 oC (0 oF). The COP is limited by the Carnot efficiency of a vapor compression cycle operating between a conde nsing temperature of 32.2 oC and an evaporating temperature of - 17.8 oC, at these conditions COP

B Carnot

B is 5.1. Therefore, the theoretical limit of ice making energy consumption is 99 kJ/kg or 0.028 kWh/kg. Although this is an unattainable limit in practice, it provides insight to the fact that the best technology evaluated in this study is an order of magni tude less efficient than the
theoretical limit.62 

### 8: Recommendations for Ice-Ma king Energy Consumption Test Through this study, several key aspects of a repeatable, reproducible ice-making energy consumption test have been determined. In order to minimize overall test burden, the several parameters of an ice-making energy consumption test can be aligned with the basic energy consumption test for domestic refrigerating appliances including ambient temperature in test chamber of 32.2 oC (90 oF) and water inlet temperature of 32.2 oC (90 oF), since it is not practical to deliver wa ter to the test unit at a temperature different
from the ambient condition.

The ice-making energy consumption should be determined by measuring the energy consumption of the unit while actively producing ice and subtracting the energy consumption of the unit while not actively produ cing ice. Interpolation of the results of
individual measurements to a set of compartment temperatures , specifically 3.9 oC in the refrigerator compartment and -17.8 oC in the freezer compartment, could be used as a means to unify the conditions at which the te st results are based. The ice production rate should be interpolated to these temperatures by the same means.

The result of the ice-making energy consumpti on measurement is then defined as the icemaking energy consumption at the specified target temperatures divided by the ice production rate at the specified target temperatures.

The test period for the ice-making energy cons umption test must include enough data to ensure a repeatable and reproducible measurement. This is a difficult parameter to define for units that use a single-speed comp ressor that maintains conditions in the compartments by switching on and off. The recommendation for this type of unit is to perform the energy consumption test over a whole number of compressor cycles and to calculate the cumulative average of the power draw and the ice produc tion rate. The data set is considered sufficiently long if this parameter does not change significantly when another compressor cycle is included in the analysis.

If a defrost event interrupts the data set, only the portion of the da ta collected during the steady operation period should be used. Th e mass of ice produced during the steady portion may be estimated by multiplying the to tal mass of ice produ ced by the proportion of ice-making cycles that o ccurred during this period.

For the case of a variable-speed compressor, the test is grea tly simplified because the test period is not affected by compressor cycles. In this case, the water supply line should be outfitted with a valve that can stop the supply of water to the cabinet. With the valve shut, the ice maker can be operated until the ice molds are emptied. The ice-making energy consumption test can begin by opening th e water supply valve and simultaneously rendering the ice maker operative. The test cab inet will then begin operation of the ice maker with an empty bin condition, and the test period can be taken from the first solenoid opening to the last ice ejection heat er operation; a whole number of ice-making cycles.63 

### 9: Open Items for Future Consideration Through this study, several issues became a pparent for consideration of future investigation. The first step is to validate the recomm ended methodology through additional testing. We will consider the developed measurement techniques as an adequate tool for rating these products if the results of multiple measurements of several automatic ice makers can be repr oduced at different laboratories.

Another issue is that the measurement techni ques must be validated for use with other styles of automatic ice makers. Four styles of automatic ice makers were examined in the present study, the energy use of each was heav ily influenced by electric resistance heaters
used to free frozen ice from the ice maker. Other technologies curren tly exist for ejecting ice from the ice makers, and it is of interest to examine test data for such units to ensure that such a method is appli cable for these technologies.

The objective of an automatic ice maker is to produce a quantity of ice, not maintain a specific condition; therefore, it is not appropria te to measure the amount of energy that an automatic ice maker uses during a specified am ount of time. Instead, such products must be rated on their ice-making energy cons umption, which is the amount of energy expended normalized to the amount of ice pr oduced. However, the value of ice-making energy consumption can be s caled to an appropriate annualized energy consumption using a usage factor that repr esents the amount of ice that the units ac tually produce in a typical residential setting. To date, there is limited information regarding consumer usage of automatic ice makers and it is reco mmended that studies be conducted to seek
this information.

Throughout this study, the effects of ice maki ng on the contribution of energy related to periodic defrosting was not c onsidered. Operation of auto matic ice makers may, under certain conditions, strongly impact the defros t frequency of certain refrigerator designs. This is a secondary issue but is very complex and would be difficult to factor into a rated energy consumption value for an ice maker; how ever, the impact may be quite substantial as evidenced by some of the un its examined in this study.

Finally, this study relied on an assumption th at the ice production rate at the specific target temperatures could be estimated by inte rpolating the results of the measurements in the same manner as energy consumption. Although this method is a good first approximation, it is necessary to either verify this met hod or to quantify the error associate with this approach.64 

### 10: References
AHAM, 1979. ANSI/AHAM HRF-1-1979, American National Standard for Household Refrigerators and Household Freezers. Ch icago: Association of Home Appliance
Manufacturers.

AHAM, 2009. AHAM Update to DOE on Status of Ice Maker Energy Test Procedure. November 19, 2009.

ASNZ, 2007. ASNZ 4474.1 Performance of household electrical appliances— Refrigerating appliances. Part 1 Energy Consumption and Performance.

Uniform Test Method for Measuring the Ener gy Consumption of Electric Refrigerators and Electric Refrigerator-Freezers, 10 Fe deral Register 430, Subpart B, Appendix A1 (01JAN2010), pp. 159-167.

Haider, I., Feng, H., and Radermacher, R., 1996. Experimental Results of a Household Automatic Icemaker in a Refrigerator/Fre ezer. ASHRAE Transactions: Symposia, SA96-7-3, pp. 541-545.

Meier, A. and Martinez, M., 1996. Energy Use of Ice Making in Domestic Refrigerators. ASHRAE Transactions, Vol., 102, Pr. 2, pp. 1071-1076.65 

### Appendix: Uncertainty Analysis

The equation used to calculate the energy cons umption using 2 point interpolation is as
follows:


## ( ) ( )

1 22 1

1 2 ref ref E T T ET T E T T −− −

=

−

Where E is the energy consumption (kWh/yr) and T is the compartment temperature (oC), the subscripts 1 and 2 refer to the data point and ‘ref’ refers to the standardized reference temperature at which the equation calculates the energy consumption.

In order to calculate the propagation of meas urement uncertainty, it is necessary to take the partial derivatives of energy with respect to each measured quantity:



### ( ) 

## ( )
( ) 12 2

2

1 1 2 ref E ET T E

T T T − − ∂

= ∂

− 

## ( ) ( ) 2

1 12 ref T T E

E T T − ∂

= ∂ −



### ( ) 

## ( )
( ) 12 1

2

2 1 2 ref E ET T E

T T T − − ∂

= ∂

− 

## ( ) ( )

1

2 12 ref T T E

E T T − ∂

= ∂ −

And the uncertainty of the cal culated energy consumption is:

1 12 2

222 2

112 2 ET E T E EE E E UU U U U TE T E ⎛ ⎞⎛ ⎞⎛ ⎞⎛ ⎞

∂∂ ∂ ∂
= +++ ⎜ ⎟⎜ ⎟⎜ ⎟⎜ ⎟

∂∂ ∂ ∂ ⎝ ⎠⎝ ⎠⎝ ⎠⎝ ⎠

Where U is the uncertainty of the value sp ecified by the accompanying subscript, in the same units as the quantity.66 The uncertainty analysis for the triangular interpolation appro ach is much more complicated since; it incorporates the measurements from both compartments simultaneously. The subscripts ‘A’ and ‘B’ are used to denote Refrigerator and Freezer compartments. The first step is to calculate the location of a theore tical fourth point from the following relationship:



### ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1

2 13 1 3 1 2

4 1

2 31 31 2 xA B xB A B B B B B xB

A xB B

A xA A A A A A xA TT T TT T T T T T T T T TT TT TT TT − ⎛ ⎞ ⎛ ⎞

− − −− = − −+

−

⎜ ⎟ ⎜ ⎟ ⎜ ⎟

− − −− ⎝ ⎠ ⎝ ⎠

Or alternatively written:

123 12 1 2 1 3 231 23 3 1 3 2
4

12 1 21 23 32 3 1 3 A A B A A xB A xA B A xA B A A B A A xB A xA B A xA B
A

A B A xB A B A B A B A xB xA B xA B TT T TT T TTT TTT T TT T TT TTT TTT T TT TT TT TT TT TT TT TT −+−−+ +−

= −−+ − ++−

The partial derivatives of T

B A4

B

with respect to each of the other measured temperatures

are:



### ( ) ( )

( )( ) 23 2 2 3 4

1 12 1 21 23 32 3 1 3

2 1 2 3 1 2 1 21 32 3 1 2 3 3 13 2

12 1 21 A B A xB xA B xA B A

A A B A xB A B A B A B A xB xA B xA B

B xB A A B A A xB A xA B A xA B A A B A A xB A xA B A xA B

A B A xB A B TT TT TT TT T

T TT TT T T TT TT TT TT TT

T T TTT TTT TTT TTT TTT TTT TTT TTT

TT TT TT T −+− ∂

= ∂ −−+ − ++−

−− − + − − + + −

−−+ 

### ( ) 2

23 32 3 1 3 A B A B A xB xA B xA B

T TT TT TT TT − ++−



### ( ) ( )

( )( ) 13 1 31 3 4

2 12 1 21 23 32 3 1 3

1 3 123 12 1 2 1 3 231 23 3 1 3 2

12 1 21 A B A xB A B A xB A

A A B A xB A B A B A B A xB xA B xA B

B B A A B A A xB A xA B A xA B A A B A A xB A xA B A xA B

A B A xB A B TT TT TT TT T

T TT TT T T T T TT TT TT TT

T T TTT TTT TTT TTT TTT TTT TTT TTT

TT TT TT −−+ ∂

= ∂ −−+ − ++−

−+ − + − − + + −

− −−+ 

### ( ) 2

23 32 3 1 3 A B A B A xB xA B xA B TT TT TT TT TT − ++−



### ( ) ( )

( )( ) 21 2 1 2 4

3 12 1 21 23 32 3 1 3

2 1 2 3 1 2 1 21 32 3 1 2 3 3 13 2

12 1 21 A B A xB xA B xA B A

A A B A xB A B A B A B A xB xA B xA B

B xB A A B A A xB A xA B A xA B A A B A A xB A xA B A xA B

A B A xB A B TT TT TT TT T

T TT TT TT TT TT TT TT TT

T T TTT TTT TTT TTT TTT TTT TTT TTT

TT TT TT −+ +− ∂

= ∂ −−+ − ++−

−+ − + − − + + −

−

− − 

### ( ) 2

23 32 3 1 3 A B A B A xB xA B xA B TT TT TT TT TT + − ++−



### ( ) ( )

( )( ) 23 3 4

1 12 1 21 23 32 3 1 3

2 123 12 1 2 1 3 231 23 3 1 3 2

12 1 21 23 32 A A A xA A

B A B A xB A B A B A B A xB xA B xA B

A xA A A B A A xB A xA B A xA B A A B A A xB A xA B A xA B

A B A xB A B A B A B TT TT T

T TT TT T T T T TT TT TT TT

T T TT T TT T TTT TTT T TT T TT TTT TTT

TT TT TT TT TT − + ∂

= ∂ −−+ − ++−

−+ − + − − + + −

− −−+ − 

### ( ) 2

3 13 A xB xA B xA B TT TT TT ++−67 

### ( ) ( )

( )( ) 1 3 4

2 12 1 21 23 32 3 1 3

1 3 123 12 1 2 1 3 231 23 3 1 3 2

12 1 21 23 32 A xA A xA A

B A B A xB A B A B A B A xB xA B xA B

A A A A B A A xB A xA B A xA B A A B A A xB A xA B A xA B

A B A xB A B A B A B TT TT T

T TT TT TT T T TT TT TT TT

T T TTT TTT TTT TTT TTT TTT TTT TTT

TT TT TT T T TT T − ∂

= ∂ −−+ − ++−

− −+−−+ +−

− −−+ − + 

### ( ) 2

3 13 A xB xA B xA B

T TT TT + −



### ( ) ( )

( )( ) 12 1 4

3 12 1 21 23 32 3 1 3

2 123 12 1 2 1 3 231 23 3 1 3 2

12 1 21 23 32 A A A xA A

B A B A xB A B A B A B A xB xA B xA B

A xA A A B A A xB A xA B A xA B A A B A A xB A xA B A xA B

A B A xB A B A B A B TT TT T

T TT TT T T TT TT TT TT TT

T T TTT TTT TTT TTT TTT TTT TTT TTT

TT TT TT TT TT T − ∂

= ∂ −−+ − ++−

− −+−−+ +−

− −−+ − + 

### ( ) 2

3 13 A xB xA B xA B

T TT TT + −

The uncertainty of the temperature in compartment A is:

4 1 1 2 2 22 22

44 4 44 4
23 23

12 3 12 3 A AA A AA A
T AA A BB B

AA A BB B TT T TT T UUU U UU U TT T TT T ⎛⎞ ⎛⎞ ⎛ ⎞⎛ ⎞ ⎛ ⎞⎛ ⎞

∂∂ ∂ ∂∂ ∂
= + + ++ + ⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟⎜ ⎟

∂∂ ∂ ∂∂ ∂ ⎝ ⎠⎝ ⎠ ⎝ ⎠⎝ ⎠ ⎝ ⎠ ⎝ ⎠

Once the uncertainty of Temperature T

B A4

B

is defined, the uncertainty of the corresponding energy, E

B 4

B , can be calculated from the equation for E

B 4

B .



### ( ) ( ) ( ) 4 1

4 1 31

3 1 A A

A A T T EE EE T T ⎡ ⎤

− =+ − ⎢ ⎥

− ⎣ ⎦

The partial derivatives of E

B 4

B with respect to each measured quantity are:



### ( ) ( ) 4 1 4

1 31 1 A A

A A T T E

E T T − ∂

= − ∂ −



### ( ) ( ) 4 1 4

3 31 A A

A A T T E

E T T − ∂

= ∂ −



### ( ) ( ) ( ) ( ) 4 1 4
3 1 2

1 31 3 1 1 A A

A AA A A T T E E E T TT T T ⎛ ⎞

− ∂

− ⎜ ⎟ =− + ∂ −

− ⎝ ⎠



### ( )( ) ( ) 31 4 1 4

2

3 3 1 A A

A A A E ET T E

T T T − − ∂

= − ∂

−68 

### ( ) ( ) 3 1 4

4 31 A AA E E E

T TT − ∂

= ∂ −

The uncertainty of E

B 4

B is therefore:

41 3 1 3 4 2 2 22 2

44 4 4 4

13 1 3 4 AA A EE E T T T

AAA EE E E E UUU U U U EET T T ⎛⎞ ⎛ ⎞ ⎛⎞ ⎛ ⎞ ⎛ ⎞

∂∂ ∂ ∂ ∂
= ++ + + ⎜⎟ ⎜ ⎟ ⎜⎟ ⎜ ⎟ ⎜ ⎟

∂∂∂ ∂ ∂ ⎝⎠ ⎝ ⎠ ⎝ ⎠ ⎝⎠ ⎝ ⎠

Finally, the uncertainty of the overall energy consumption at the triangulated coordinates can be calculated from its equation:



### ( ) ( ) ( ) 2

2 42

4 2 xA A

x
A A T T EE EE T T ⎡ ⎤

− =+ − ⎢ ⎥

− ⎣ ⎦

The partial derivatives of E

B x

B with respect to each measured quantity are:



### ( ) ( ) 2

2 42 1 xA A x

A A T T E

E TT − ∂

= − ∂ −



### ( ) ( ) 2

4 42 xA A x

A A T T E

E T T − ∂

= ∂ −



### ( ) 24 2 44 4

2

2 4 2 x A xA A xA

A A A E ET ET ET ET

T T T ∂ −−+

= ∂

−



### ( ) 2 22 42 4

2

4 4 2 x xA A A xA

A A A E ET ET ET ET

T T T ∂ −+−

= ∂

−

The uncertainty of E

B x

B is therefore:

24 2 4 22 2 2

24 2 4 x A A xx x x EE E T T

A A EE E E UU U U U EET T ⎛ ⎞⎛ ⎞⎛ ⎞⎛ ⎞

∂∂ ∂ ∂
= ++ + ⎜ ⎟⎜ ⎟⎜ ⎟⎜ ⎟

∂∂∂ ∂ ⎝ ⎠⎝ ⎠⎝ ⎠⎝ ⎠