### Memorandum



## Date: December 31, 2013 To: Charlie Stephens, NEEA From: Jeffrey Uslan

, Ben Larson, Bob Davis, Lucinda Gilman, Ecotope, Inc. Re: Icemaker Field Study Analysis

In 2012, NEEA asked Ecotope to study refrigerator icemaker usage. The current Department of Energy test procedure for refrigerators does not take into account the energy use of icemakers; the use per duty cycle is known from laboratory testing, but real-life use patterns are not. The goal of this study was to measure a refrigerator’s icemaker usage in the field.

To measure usage, a small logger was placed around the power wire of either the icemaker water valve or the icemaker itself. Each time the circuit was activated, an event was registered. It is worth noting that Ecotope measured not the number of times someone extracted ice from the icemaker, but the number of times the icemaker itself made more ice. Icemakers typically make five to eight cubes at a time. Kitchen temperature was also logged hourly with a separate logger located away from the refrigerator, range and other heat-generating appliances. Outside temperatures were gathered from local weather stations.

Ninety sites were metered in Washington, Idaho and Oregon. Half of the sites metered had through-door icemakers and half had in-freezer icemakers. Refrigerators in the study were

manufactured between 2001 and 201 1

. Fieldwork began in March 2012; sites were removed from the field in August 2012. Usable data were gathered from eighty-four sites.

The results of our analysis were somewhat surprising. Icemaker use did not correlate with many

of the factors that one would initial ly postulate. For example, higher icemaker usage did not correlate with outdoor temperature, the number of people in a house, or even the number of adults in a house. However, there were correlations with cooling zone, kitchen temperature, and the type of icemaker (through-door vs. in-freezer). These results indicate to us that behavior – how often a household chooses, for whatever reason, to use ice – is an important driver of icemaker usage.

Throughout the analysis, we generally present the results in terms of annual icemaker cycles, daily cycles, annual energy use, or daily energy use. The field metering period lasted roughly four months at each site but never covered an entire year. To calculate annual cycles, we scaled up the number of cycles observed in the measured period by the number of days not observed.

## The method relies on the simple assumption that the daily average of icemaker usage over the

course of the year will be the same as it was over the time period studied. Having not observed, by definition, the unmetered months, we have no way of testing this assertion. For the information presented on the daily cycles, we do not scale the data, instead presenting only the data observed during the metered period. Throughout the memo, results are expressed as means; graphs show the mean result with a 90% confidence interval overlaid. By that we mean the
interval within which we are 90% confident the true value will fall inside.



# Number of Annual Cycles, Average, and Range

On average, icemakers cycle 1102 times per year or 3 times per day. Icemaker cycles ranged

from a minimum of 60 cycles per year to a maximum of 3441 ; at the 25 th 

## percentile the icemaker cycled 4 70 times per year and at the 75 th 

## percentile, 1507 times per year. The top three sites show an unusually large number of cycles per year; it is possible that there is a problem with the
icemaker at these sites.

Figure 1 . Number of Annual Cycles

## We investigated additional possible explanations for the number of cycles. There were no

correlations to manufacturer, volume or year of manufacture. The number of annual cycles does not seem to trend upward or downward according to manufacture date. More icemaker cycles are seen in refrigerators manufactured between 2004-2007, the middle of our range, but there is no obvious explanation for the pattern

. The number of annual cycles does not seem to trend upward or downward according to refrigerator volume or make.

Table 1 . Annual Cycles by Manufacture Date

Manufacture Date Bin Annual Cycles

Mean EB n 2000

- 2003 1097 189 19
2004

- 2007 1197 160 33 2008

- 2012 948 139 29



## Table 2. Annual Cycles by Volume

Volume (ft 3 ) Annual Cycles
Mean EB n 18

- 19 878 126 9
20

- 21 1061 196 25
22

- 23 776 189 5
24

- 25 1172 142 35 26 + 1215 364 6



## Table 3. Annual Cycles by Make

Refrigerator Make Annual Cycles
Mean EB n Amana 1260 440 5 Frigidaire 660 137 6 General Electric 1538 275 13 Kenmore 1285 275 23 Kitchen Aid 862 237 6 LG 658 321 2 Maytag 629 216 8 Samsung 1221 277 4 Whirlpool 978 249 11



# Icemaker Cycle Impact on Energy U se

There is a fairly strong correlation between refrigerator energy usage and the number of annual cycles (see Figure 2 ). This relationship is clear for all refrigerators taken together, and for through-door icemakers, but it is not as strong for in-freezer icemakers (see Table 2 ). This muddiness may be due to a low number of high energy users in the latter group; the high energy

## users have fewer icemaker cycles per year, but there are only 4 refrigerators in this group. A

regression analysis for this group showed that there was still a significant relationship between energy use and icemaker cycles.

Figure 2 . Annual Cycles by Total Refrigerator Energy Usage

Table 2 . Annual Cycles by Total Refrigerator Energy Usage

Annual Kwh Annual Cycles

Mean EB n 400 884 124 19 500 1056 156 27 600 1235 244 14

Annual Kwh Annual Cycles for In Freezer Ice Dispensers

Mean EB n 400 794 139 13 500 815 145 12
600 676 239 4

Annual Kwh Annual Cycles for Through Door Ice Dispensers

Mean EB n 400 1079 249 6 500 1250 250 15 600 1458 306 10

## Certainly, the number of icemaker cycles contributes to energy consumption, but the extent to

which it contributes to the energy consumption of the entire refrigerator in this study is not clear. There are other factors involved, such as overall refrigerator/freezer efficiency and individual
household behavior.



# Regional Impact

We assessed the data for any variations based on geography or climate and found correlations with cooling zone.

Icemaker cycles show no statistical differences by state. Table 3 shows the difference in cycles by state. Washington has slightly fewer cycles on average but is within the error bounds of the other two states’ averages. The sites in Washington were generally in cooler climate zones which could explain the slightly lower mean value. Nevertheless, the differences are not significant.

Table 3 . Annual Cycles by State

S tate Annual Cycle

Mean EB n ID 1358 176 7 OR 1097 156 27
WA 1067 132 47



## Icemaker cycles are strongly dependent on heating and cooling zones. This is intuitively apparent for cooling zones, but given that our measurements were taken primarily in summer months we believe the dependence on heating zone is merely a product of the correlation between heating zones and cooling zones- the correlation is 0 .65 which is to say that most of the cooling zone 2 sites are also located in heating zone 2 instead of heating zone 1.

## Figure 3 . Annual Cycles by Cooling Zone

Table 4 . Annual Cycles by Cooling Zone

Cooling Climate Zones Annual Cycles

Mean EB n

1 920 90 61
2 1655 223 20

## Figure 4 . Annual Energy by Cooling Zone

Table 5 . Annual Energy by Cooling Zone

Cooling Climate Zones Annual kWh

Mean EB n

1 577 19 58

2 641 55 18

## Figure 5 . Annual Cycles by Heating Zone

Table 6 . Annual Cycles by Heating Zone

Heating Climate Zone Annual Cycles

Mean EB n 1 981 93 69
2 1893 264 11



# Inhabitant Demographics

A regression analysis on the number of occupants showed that neither the number of occupants nor the number of adults (age 19+) in a household had any significant impact on the number of annual cycles observed. There was a slight correlation with the age of the occupants – children seem to contribute to fewer ice making cycles than adults. In the regression analysis on number of occupants, the constant term dominates the model. Additional linear regression analyses, with and without a constant, show that the statistically significant age groups are ages 19 to 64 and ages 65+.

## Table 7. Annual Cycles by Number of Occupants

Occupants Annual Cycles

Mean EB n 1 660 139 12
2 1105 127 38 3 1059 249 15
4 1603 303 11



## Table 8 . Annual Cycles by Number of Adults

Adults Annual cycles

Mean EB n 1 640 119 14
2 1224 117 54
3 1070 325 10



# Seasonal Impact

There is a seasonal impact on icemaker use. Use was higher in July and August by 3 -8 ice cubes per day. This probably represents 1-2 additional iced drinks. Use was also somewhat higher in April, but we can find no explanation for this. These findings are robust even when outliers are
excluded.

Figure 6 . Daily Cycles by Month

## Table 9 . Daily Cycles by Month

M onth Daily Cycles

Mean EB n Apr 6.01 0.17 827 May 5.37 0.12 1137 Jun 5.59 0.14 1103
Jul 6.67 0.15 1260 Aug 6.61 0.23 582



# Temperature

There does not seem to be a relationship between icemaker cycles and outdoor temperature. Neither daily maximum nor daily average outdoor temperatures drive icemaker usage; there is a weak relationship with minimum outdoor temperature, but that may be spurious. A better predictor is indoor (kitchen) temperature.

Table 10

. Daily Cycles by Outdoor Temperature Bin

Temperature Bins Daily Cycles

Mean EB n 40 6.9 0.9 43 45 6.1 0.3 226 50 5.1 0.2 564 55 5.5 0.2 606 60 5.7 0.2 522
65 5.4 0.3 237 70 4.9 0.4 81

## Figure 7

. Daily Cycles by Indoor Temperature Bin

Table 11

. Daily Cycles by Indoor Temperature Bin

Indoor Temperature Daily Cycles

Mean EB n 62 4.1 0.4 32
64 5.1 0.4 98 66 5.4 0.3 228 68 5.4 0.2 695 70 5.6 0.1 1060
72 6.2 0.2 983
74 6.5 0.2 836 76 6.4 0.2 528 78 6.6 0.4 250 80 6.5 0.6 110 82 7.3 0.8 54
84 9.1 1.7 21



# Through-Door vs. In-Freezer Ice Dispensers

There is a difference between the annual ice making cycles of refrigerators with and without through-door dispensers. Through-door ice dispensers have more annual ice making cycles than

in -freezer dispensers. It is certainly easier to obtain ice from a through-door ice dispenser;

## however, whether the ease of access drives ice use or whether people who have a tendency to use

ice preferentially select through-door icemakers is unknown. Figure 8 and Table 12 show the average number of cycles; Figure 9 and Table 13 show median cycles.

There is also a difference between the annual energy use of refrigerators with and without through-door dispensers. Through-door ice dispenser refrigerators use more energy annually. Unlike duty cycles, energy use has been annualized using a trigonometric fit method (discussed in Appendix A below).

Figure 8 . Average Annual Cycles by Ice Dispenser Type

Table 12

. Average Annual Cycles by Ice Dispenser Type

Ice Dispenser Annual Cycles
Mean EB n In Freezer 866 112 39 Through

- door 1321 140 42

## Figure 9

. Median Annual Cycles by Ice Dispenser Type

Table 13

. Median Annual Cycles by Ice Dispenser Type

Ice Dispenser Annual Cycles

25th Quartile Median 75th Quartile n

In Freezer 397 610 1179 39 Through Door 618 1009 2023 42

## Figure 10 . Refrigerator Energy Use by Ice Dispenser Type

Table 14 . Refrigerator Energy Use by Ice Dispenser Type

Ice Dispenser Annual kWh
Mean EB n In Freezer 535 20 36 Through

- door 642 30 40



# Ice Dispenser and Cooling Zone

The dependence on delivery method and cooling zone suggests taking a deeper look at the combination of the two factors. Below is an investigation of each factor when the other is held constant. A visual and tabular inspection shows that both energy consumption and ice making cycles are dependent on either cooling zone or delivery system even when the other factor is held constant, the only exception being energy consumption of in-freezer ice makers among cooling

zones.

## Figure 11 . Annual Cycles by Ice Dispenser and Cooling Zone

Table 15 . Annual Cycles by Ice Dispenser and Cooling Zone

Annual Cycles Cooling Zone Ice Dispenser 1 2 n In Freezer Mean 734 1375 39
EB 103 331 Through Door Mean 1113 1843 42
EB 141 299

## Figure 12 . Annual Energy by Ice Dispenser and Cooling Zone

Table 16 . Annual Energy by Ice Dispenser and Cooling Zone

Annual Energy (kWh) Cooling Zone Ice Dispenser 1 2 n In Freezer Mean 537 529 36
EB 25 28 Through Door Mean 616 712 40
EB 27 83



# Annual Refrigerator Energy U se

Table 17 shows four different quantifications of annual refrigerator energy use. The table contains the rated energy from DOE testing; the annual use, which is based on the measured data linearly extrapolated to the full year; the hypothetical annual use if the indoor temperature were always within the 69°F to 71 °F range; and the trigonometric fit average annual use, our best estimate of actual energy, as described in Appendix A.

## Table 17 . Rated and Measured Energy Use

Annual kWh
Mean EB n Rated annual kWh 546 9 89 Annual kWh 592 20 76 Annual kWh Within Temp Range 581 18 75 Trig Fit Average kWh 543 1 9 82



## Using an analysis of variance test, we compared rated annual kWh and raw observed annual kWh. Our analysis of variance produced a p-value of 0.029; this indicates that the rated energy use of refrigerators and observed annual energy use are not significantly related.

However, when observed annual energy use is restricted to times when the kitchen temperature is between 69°F and 71°F, we find a p-value of 0.079. This indicates that the rated annual energy use is significantly related to the actual energy use. Kitchen temperature is within 69°F and 71°F, 23% of the time averaged across all sites. This is within one degree of the DOE test condition – refrigerators are tested at 90°F and no door openings and closings, with the assumption that that corresponds to an actual kitchen temperature of 70°F with regular door openings and closings.

Figure 14 . Rated vs. Actual Energy Use

## When we perform an analysis of variance test comparing the rated energy kWh to the

trigonometric fitted prediction, we find a p-value of 0.87. This indicates that the rated annual energy use is significantly related to the actual energy use.

Looking at these comparisons, we see that rated energy use is approximately 35 kWh lower than annual energy use when the refrigerators are operating at a kitchen temperature between 69- 71°F. It is 3 kWh higher than the annualized kWh ratings across all temperatures. Thus, it is a good estimate of energy use compared to the Department of Energy standard, and very close to

real-world observations.



# Conclusions

Icemaker use is not driven by as many factors as we believed at the onset of the study. Teenagers are not a driver of icemaker use; inhabitant demographics generally do not appear to be a driver of icemaker use; outdoor temperature is not a driver of icemaker use. The primary factors are indoor temperature, the ease of access to the ice – whether it is through-door or in the

freezer – and climate zone. The fact that climate zone is a driver of icemaker use while outdoor temperature is not as curious. Icemaker use also has a correlation with overall refrigerator

energy use.

The study had certain limitations. We did not study the energy use of the icemaker independently of the refrigerator as a whole due to budgetary constraints. We had relatively few homes with high occupancy rates (>3 people per home). Our only stratification was on the type of refrigerator –

through-door vs. in-freezer. However, our data are robust enough to support the conclusions given.

# Appendix A. Energy Use: Annualized Projections

Our data are predominantly taken from summer months. Given the observed dependence on months we would expect to see a seasonal change in energy use from the data if observations spanned the entire year. In order to come up with a fair annual estimate accounting for the colder months of the year we have implemented a linear regression on trigonometric terms. This

method has been used in other Northwest studies 1 

## (and elsewhere). Our fit methodology was based on an article by Nicholas Cox published in the Stata journal 2 

## . Scaling the entire year as a
unit we fit sine and cosine terms.

This allows us to approximate the energy use of the entire year. An initial fit yielded two annual peaks so the fit was reproduced to halve the period, forcing a single annual peak. As expected, the fit finds the peak during the summer. The trigonometric fit captures the seasonal variation in kitchen temperature, placing more use in the summer when the kitchen is warmer and less in the

winter when it is cooler.

Figure 15

. Example Trigonometric Fit of Refrigerator Power1 

### Roos, C. and D. Baylon. May, 1993. Non-Space Heating Electrical Consumption in Manufactured

Homes . Residential Construction Demonstration Project, Cycle II. Prepared for Bonneville Power Administration under Contract No. DE-AM79-91BP13330.

2 

### Cox, N. “Speaking Stata: In Praise of Trigonometric Predictors,” Stata Journal 6 (2006) 561-579.