7

- i CHAPTER 7

. ENERGY USE ANALYSIS

TABLE OF CO NTENTS

7.1 INTRODUCTION

................................ ................................ ................................ ........... 7

- 1

7.2 CONSUMER SAMPLE

................................ ................................ ................................ ... 7

- 1

7.3 STANDBY POWER CONSUM PTION

................................ ................................ .......... 7

- 2

7.3.1 Annual Energy Consumption by Efficiency Level

................................ .......................... 7

- 3

7.3.2 Variability of Annual Energy Consumption

................................ ................................ .... 7

- 4

LIST OF T ABLES

Table 7.2.1 RECS 2005 Sample Statistics

................................ ................................ .............. 7

- 1

Table 7.3.1 Number of Meals Cooked per Day Based on RECS Sample

.............................. 7

- 3

Table 7.3.2 RECS Microwave Oven Use Percentage

................................ ............................. 7

- 3

Table 7.3.3 Microwave Ovens and Countertop Combination Ovens: Annual Energy Consumption by Standby Power Level

................................ ................................ 7

- 4

Table 7.3.4 Over the Range Combination Ovens: Annual Energy Consumption by Standby Power Level

................................ ................................ ........................... 7

- 4

LIST OF FIGURE

Figure 7.3.2 Range of Annual Energy Use for Microwave Ovens and Countertop

Combination Ovens

................................ ................................ ............................. 7

- 5 Figure 7.3.3 Range of Annual Energy Use for Over the Range Combi nation Ovens

.............. 7

- 57-1 CHAPTER 7. ENERGY USE ANALYSIS

7.1 INTRODUCTION

To carry out the life

- cycle cost (LCC) and payback period (PBP) analyses descri bed in chapter 8, DOE must determine the energy savings to consumers from more efficient products. This chapter describes how DOE determined the annual standby energy consumption of microwave ovens for use in the LCC and PBP analyses.

The engineering analysis described in chapter 5 reports energy use based on the DOE test procedure. This test provides standardized results that serve as the basis for comparing the performance of different appliances used under the same conditions. Actual usage in the fi eld varies depending on the conditions in which the appliances are operated.

To establish a reasonable range of energy consumption of microwave ovens in the field,

DOE primarily use d data from the Energy Information Administration (EIA)’s 2005 Residential
Energy Consumption Survey (RECS 2005 )

. 1 RECS is a national sample survey of housing units
that collects statistical information on the consumption of and expenditures for energy in housing units along w ith data on energy

- related characteristics of the housing units and occupants. RECS 2005 collected data on 4,381 housing units and was constructed by EIA to be a national representation of the household population in the United States.

7.2 CONSUMER SAMPLE

The subset of RECS 2005 records used for the microwave oven sample met the following

criteria:

**•** The household had a microwave

Because RECS 2005 provides no means of determining the type of microwave present in a given household, DOE use d the same sample fo r both product classes. The RECS reported saturation of microwave ovens in 2005 was 88 percent.

Table 7.2.1 RECS 2005 Sample Statistics

Product Class Selection Criterion No. of

Records No. of U.S.

Households
Represented (million)

All Has Microwave = Yes 3835 97.77-2 7.3 STANDBY POWER CONSUM PTION

To estimate the annual energy use associated with standby power ( E

SP ) for both product classes, DOE used the following expression where the standby power is multiplied by the number of hours in a year the microwave oven is in stan dby mode:

SP SP SP Hours P E **× =** 

Where:

P

SP = standby power (watts), and

Hours SP = hours in a year the microwave oven is in standby mode (kWh/yr).

The annual standby hours equal the total hours in a year less the number of hours the

microwav e oven is in active operation. DOE determined the hours of active operation ( Hours ACTIVE ) with the following expression:

RECS NOPR ACTIVE Use Hours Hours **× =** 

Where:

Hours NOPR = average microwave operating hours from the NOPR, and

Use RECS = relative usage factor.

In the previous NOPR for cooking products, DOE determined the average hours of
operation for microwaves ( Hours NOPR ) to be 71 hours per year. 2 DOE has no reason to believe
that this number has changed.

Fo r each household, RECS 2005 provides information on the frequency of microwave oven usage and the number of hot meals prepared per day. DOE calculated the RECS usage factor ( Use RECS ) for each household in the sample using the following expression:



## ( **)**

AVG RECS RECS RECS Use Freq Meals Use / **× =** 

Where:

Meals RECS = RECS reported household hot meals per day,
Freq RECS = RECS reported microwave use frequency, and

Use AVG = Weighted average usage factor.

The weighted average usage factor was calculated using the following expression:7-3 

## ∑ **∑ ×**  **×**

**=**

RECS RECS AVG AVG

AVG Weight Weight Freq Meals Use

Where:

Meals AVG = Average household hot meals per day,
Freq AVG = Average microwave use frequency, and Weight = RECS household weight.

The responses in RECS for Meals RECS and Freq RECS fall into o ne of the bins shown in

Tables 7.3.1 and 7 .3.2, respectively. For each question, DOE assumed a uniform or triangular distribution within the boundaries of each bin and randomly assigned a value from within the appropriate range to each sample household. For the calculati on of the average usage factor ( Use AVG )

, DOE used the average values from the respective bins.

Table 7.3.1 Number of Meals Cooked per Day Based on RECS Sample

Bin Description Meals per day

Min Max

0 Doesn't cook/Never cooks 0 .0 0.0

1 Three or more times a day 3.0 4.0

2 two times a day 1.0 3.0

3 Once a day 0.5 1.5

4 A few times each week 0.2 0.8

5 About once a week 0.1 0.2

6 Less than once a week 0.0 0.1

Table 7.3.2 RECS Microwave Oven Use Percentage

Bin Amount of food cooked in

the microwave Use Percentage

Min Max

1 Most or all 90% 100%

2 About half 25% 75%

3 Some or very little 20% 30%

4 Used only for snacks, defrosting, or reheating

food 5% 25%

7.3.1 Annual Energy Consumption by Efficiency Level

Tables 7.3.3 and 7 .3.4 present the average annual energy consumption by efficiency level for both product classes.7-4 Table 7.3.3 Microwave Ovens and Countertop Combination Ovens: Annual Energy
Consumption by Standby Power Level
Efficiency

Level Standby Energy Use
(W) (kWh/year)

Baseline 4 .00 34.75

1 2 .00 17.38

2 1.5 0 13.03

3 1 .00 8.69

4 0.02 0.17

Table 7.3.4 Over the Range Combination Ovens: Annual Energy Consumption by
Standby Power Level
Efficiency

Level Standby Energy Use
(W) (kWh/year)

Baseline 4.50 39.10

1 3.70 32.15

2 2.70 23.46

3 2.20 19.11

4 0.04 0.35

7.3.2 Variability of Annual Energy Consumption

Figures 7.3.1 and 7 .3.2 show the range of average annual energy consumption by efficiency level for both product classes. Because variation among households in active use of

microwave ovens has a small effect on th e number of standby hours, the range in standby energy use is very small.7-5 0 5 10 15 20 25 30 35 40

Level 0 Level 1 Level 2 Level 3 Level 4Annual Energy Use (kWh)

Efficiency Level Microwave and MWO

- Combo CT Average Annual Energy Use Average; Median; Box 25%

- 75%; Whisker 5%

- 95%

median

average

Figure 7.3.2 Range of Annual Energy Use for Microwave Ovens
and Countertop Combination Ovens

0 5 10 15 20 25 30 35 40 45

Level 0 Level 1 Level 2 Level 3 Level 4Annual Energy Use (kWh)

Efficiency Level Combination Oven

- OTR Average Annual Energy Use

Average; Median; Box 25%

- 75%; Whisker 5%

- 95%

median

average

Figure 7.3.3 Range of Annual Energy Use for Over the Range

Combination Ovens7-6 REFERENCES

1. U.S. Department of Energy: Energy Information Administration, Residential Energy Consumption Survey: 2005 Public Use Data Files . 2008: Washington, DC. http://www.eia.doe.gov/emeu/ recs/recspubuse05/pubuse05.html

2. U.S. Department of Energy

- Energy Efficiency & Renewable Energy, Technical Support Document: Energy Efficiency Program for Consumer Products and Commercial and Industrial Equipment, Residential Dishwashers, Dehumidifier s, and Cooking Products,

and Commercial Clothes Washers , 2008. Washington, DC.