626O9&/ L/~

Electric Oven and

Cooktop Data

Analysis

Prepared for

Association of Home Appli

Manufacturers

July 15, 1994

Arthur D. Little, Inc.

Acorn Park

Cambridge, Massachusetts

02140-2390

v //

Anr

EE-RM-94-230 COMMENT 61A

I ''t. 

Electric Oven and 

Cooktop Data 

Analysis· 

Prepared for 

Association of Home Applia

Manufacturers 

July. 15, 1994 

Arthur D. Little, Inc. 

Acorn Park 

Cambridge, Massachusetts 

02140-2390 
Table of Contents

1.0 Background .............................................. 1

2.0 Review of Baseline DOE Annual Energy Consumption for Electric Ovens

and Cooktops ......... ................................. 2

2.1 Implications of the Modified (Reduced) Range Energy Usage ........ 4

3.0 Review of DOE Baseline Efficiency Assumptions for Electric Ovens and

C ooktops ................................................ 5

3.1 Efficiency Testing ...................................... 5

3.2 Modification in Baseline Numbers to Account for Manufacturing

Variability ............................................ 6

4.0 Electric Oven Design Option Review ............................. 7

4.1 Forced Convection Design Option ........................... 7

4.1.1 Impact of Forced Convection on Oven Utility ............. 7

4.1.2 Forced Convection Impact on Oven Efficiency ............. 9

4.1.3 Consumer Payback Associated with Forced Convection ....... 10

4.2 Reflective Surfaces for Oven Cavity .......................... 11

4.2.1 Impact of Reflective Coating on Oven Utility ............. : 11

4.2.2 Impact of Reflective Coatings on Oven Efficiency .......... 12

4.2.3 Reflective Surface Efficiency Analysis . .... ............. 12

4.2.3 Consumer Payback Associated with Reflective Surfaces ..... 14

4.2.4 Reflective Surface Issues Relative to Manufacturing ......... 15

4.3 Improved Door Seal for Standard Electric Ovens ................. 17

4.3.1 Improved Door Seal Efficiency ........................ 18

4.3.2 Payback Associated with Improved Door Seal ............. 18

4.4 Increased Oven Insulation Design Option ...................... 19

4.4.1 Energy Savings Analysis for Increased Insulation ........... 20

4.5 Thermal Mass Design Option .............................. 21

4.5.1 Reduction in Thermal Mass Analysis ................... 22

4.6 Elimination of the Oven Window Design Option ................. 22

4.6.1 Energy Savings Analysis for Window Elimination .......... 22

5.0 Coil Cooktop Design Option Review ............................ 24

5.1 Improved Contact Conductance Design Option for Electric Coil Cooktop 24

5.1.1 Effect of Surface Contact Resistance on Range-Top Efficiency 24

5.1.2 Conductance Analysis ................... ........... 25

5.2 Impact of Contact Conductance on Coil Efficiency - Testing ......... 26

Appendix A .............................................. A-1

Appendix B ................... .... ....................... B-l

Table of Contents 

1.0 Background . ,," .................................................................................. .. 

2.0 Review of Baseline DOE Annual Energy Consumption for Electric Ovens 

and Cooktops ' ........................................... . 

2.1 Implications of the Modified (Reduced) Range Energy Usage ....... . 

3.0 Review of DOE Baseline Efficiency Assumptions for Electric Ovens and 

Cooktops ............................................... . 

3.1 Efficiency Testing ..................................... . 

3.2 Modification in Baseline Numbers to Account for Manufacturing 

V . b'li ' arta 1 ty ........................................... . 

1 

2 

4 

5 

5 

6 

4.0 Electric Oven Design Option Review .......................... " 7 

4.1 Forced" Convection Design Option ........................... 7 

4.1.1 Impact of Forced Convection on Oven Utility ............. 7 

4.1.2 Forced Convection Impact on Oven Efficiency ........... " 9 

4.1.3 Consumer Payback Associated with Forced Convection . . . . . .. 10 

4.2 Reflective Surfaces for Oven Cavity . . . . . . . . . . . . . . . . . . . . . . . . .. 11 

4.2.1 Impact of Reflective Coating on Oven Utility ............. : 11 

4.2.2 Impact of Reflective Coatings on Oven Efficiency .......... 12 

4.2.3 Reflective Surface Efficiency Analysis .................. 12 

4.2.3 Consumer Payback Associated with Reflective Surfaces ...... 14 

4.2.4 Reflective Surface Issues Relative to Manufacturing . . . . . . . .. 15 

4.3 Improved Door Seal for Standard Electric Ovens . . . . . . . . . . . . . . . .. 17 

4.3.1 Improved Door Seal Efficiency. . . . . . . . . . . . . . . . . . . . . . .. 18 

4.3.2 Payback Associated with Improved Door Seal ............. 18 

4.4 Increased Oven Insulation Design Option ...................... 19 

4.4.1 Energy Savings Analysis for Increased Insulation . . . . . . . . . .. 20 

4.5 Thermal Mass Design Option .............................. 21 

4.5.1 Reduction in Thennal Mass Analysis ................... 22 

4.6 Elimination of the Oven Window Design Option ................. 22 

4.6.1 Energy Savings Analysis for Window Elimination .......... 22 

5.0 Coil Cooktop Design Option Review ............................ 24 

5.1 Improved Contact Conductance Design Option for Electric Coil Cooktop 24 

5.1.1 Effect of Surface Contact Resistance on Range-Top Efficiency . 24 

5.1.2 Conductance Analysis .............................. 25 

5.2 Impact of Contact Conductance on Coil Efficiency - Testing. . . . . . . .. 26 

- Appendix A A-I 

Appendix B B-1 
1.0 Background

The objective of this study is to develop technical information for the Association of

Home Appliance Manufacturers (AHAM) relative to DOE rule making for electric

ovens and cooktops. AHAM will incorporate these data into their response to DOE.

The DOE has recommended a series of design options to improve the efficiency of

electric ovens and cooktops. These recommendations were discussed in the March 4,

1994 Notice of Proposed Rulemaking (10 CFR Part 430). The proposed efficiency

levels for electric ovens would have a dramatic effect on both product price and

functionality.

The proposed electric oven design options are:

Electric Oven, Non-Self-Cleaning

0 Baseline

1 0 + Remove Door Window

2 1 + Improved Door Seals

3 2 + Reduced Vent Rate

1 4 3 + Reflective Surfaces

2 5 4 + Added Insulation

6 5 + Forced Convection

3,4 7 6 + Reduced Thermal Mass

8 7 + Improved Insulation

9 8 + Bi-Radiant Oven

10 9 + Oven Separator

5 11 10 + Reduced Conductive Losses

Electric Oven, Self-Cleaning

1 '0 Baseline

1 0+ Remove Door Window

2 2 1 + Reflective Surfaces

3 3 2 + Forced Convection

4 3 + Added Insulation

4 5 4 + Reduced Thermal Mass

6 5 + Bi-Radiant Oven

7 6 + Oven Separator

5 8 7 + Reduced Conductive Losses

Level 4 has been selected for electric ovens by DOE.

I. .. ," , "..'l''"."'--:"

1.0 Background 

The objective of this study is to develop technicaI infonnation for the Association of 

Home Appliance Manufacturers (AHAM) relative to DOE rule making for electric 

ovens and cooktops. AHAM will incorporate these data into their response to DOE. 

The DOE has recommended a series of design options to improve the efficiency of 

electric ovens and cooktops. These recommendations were discussed in the March 4, 

1994 Notice of Proposed Rulemaking (10 CFR Part 430). The proposed efficiency 

levels for electric oyens would have a dramatic effect on·ooth product price and 

functionality . 

The proposed electric oven design options are: 

Electric Oven, Non-Self-Cleanlng 

:.::':',. ,'. 

Electric Oven, SeH-Cleanlng 

Level 4 has been selected for electric ovens by DOE. 
Electric cooktop design options are:

Electric Cooktop, Smooth Element

1, 2, 3 0 Baseline: Solid Disk Element

4 1 0 + Halogen Lamp Element

5 2 0 + Induction Element

3 0 + Radiant Element

DOE has selected level 2 for electric cooktops.

Our findings are reported as follows:

2.0 Review of Baseline DOE Annual Energy Consumption for Electric Ovens and

Cooktops

3.0 Review of Baseline DOE Efficiency Assumptions for Electric Ovens and

Cooktops

4.0 Electric Oven Design Option Review

5.0 Coil Cooktop Design Option Review

2.0 Review of Baseline DOE Annual Energy Consumption for Electric Ovens

and Cooktops

DOE's annual energy consumption for electric ranges and ovens are approximately

25% too high. The baseline annual energy usage used by the DOE and a modified

set of energy usage data based on recent metered studies are presented in Table 1.

Table 1: DOE Electric Oven and Cooktop Data

u · In II ~~~~~~I

* Includes clock energy consumption

Electric Oven*

- Standard 327.4 . 245.6

- Self-clean 346.7 260.0

Electric Cooktop

- Coil Elements 271.1 203.3

- Smooth 293.7 220.3 , ~~~~~~~~~~~~~~~~~~~~

I

1

Electric cooktop design options are: 

Electric Cooktop, Coli Element 

o Baseline: Coil Element 

2 o + Improved Contact Conductance 

3, 4, 5 2 1 + Reflective Surfaces 

Electric Cooktop, Smooth Element. 

DOE has selected level 2 for electric cooktops. 

Our findings are reported as follows: 

2.0 Review of Baseline DOE Annual Energy Consumption for Electric Ovens and 

Cooktops 

3.0 Review of Baseline DOE Efficiency Assumptions for Electric Ovens and 

Cooktops 

4.0 Electric Oven Design Option Review 

5.0 Coil Cooktop Design Option Review 

2.0 Review of Baseline DOE Annual Energy Consumption for Electric Ovens 

and Cooktops 

DOE's annual energy consumption for electric ranges and ovens are approximately 

25% too high. The baseline annual energy usage used by the DOE and a modified 

set of energy usage data based on recent metered studies are presented in Table 1. . ._0. 

Table 1: DOE Electric Oven and Cooktop Data 

- Coil Elements 

- Smooth 

• Includes clock energy consumption 

327.4 

346.7 

271.1 

293.7 

- 245.6 

260.0 

203.3 

220.3 
DOE's values represent adjusted (compared to earlier assumptions) annual usage

based on a review of studies that examined range electric energy requirements.

Using the five metered studies from this review DOE determined an average

consumption of 605.1 kWh/yr which they used to develop their energy usage profile.

This average range energy was then partitioned into oven and cooktop usages based

on several factors including sales of range type (self-clean versus standard). For

example, the standard oven with a coil cooktop uses 598 kWh/yr and the self-clean

oven plus coil cooktop produced a usage value of 617 kWh/yr. The DOE energy

values were based in part on metered studies that were more than 13 years old. (note:

product life assumed by DOE is 19 years). These older studies have very high

electric usage and are no longer relevant. The declining energy usage associated with

electric ranges is noted by the DOE. The modified set of electric range energy is

recommended.

The modified energy values presented in Table 1 were obtained by:

* Averaging the results of 3 recent metered studies (1988 through 1992) presented

in Table 2

* Partitioning the range value into oven and cooktop using DOE's approach

The recent range metered studies used to generate Table 2 were:

(1) "Residential Energy Usage Comparison Project", EPRI Report CU-6952

(2) "Integrating EIP and HE55 Information for Estimating End Use Energies",

Prepared for Siena Pacific Power Co., 1988

(3) "Description of Electric Energy use in Single-Family Residences in the Pacific

Northwest: 1986-1992"; Bonneville Power Administration, Dec 1992 (ELCAP)

The first two studies were cited by DOE (Appendix A; v2 of TSD) but the

Bonneville Power study is omitted. This extensive study examined the range energy

use at 318 sites. Electric range energy usage results from the Bonneville study were:

* Mean: 472 kWh/yr

* Median: 403 kWh/yr

* Standard Deviation: 251 kWh/yr

* Skewness: 1.114

Summarizing these most recent studies, we find that the average range energy use is

449 kWh/yr (Table 2).

DOE's values represent adjusted (compared to earlier assumptions) annual ,:!sage 

based on a review of studies that examined range electric energy requirements. 

Using the five metered studies from this review DOE detennined an average 

consumption of 605.1 kWh/yr which they used to develop their energy usage profile. 

This average range energy was then partitioned into oven and cooktop usageS based 

on several factors including sales 'of range type (self-clean versus standard). For 

exmnple, the standard oven with a coil cooktop uses 598 kWh/yr and the self-clean 

oven plus coil cooktop produced a usage value of 617 kWh/yr. The DOE 'energy 

values were based in part on metered studies that were more than 13 years old. (note: 

product life assumed by DOE is 19 years). These older studies have very high 

electric usage and are no longer relevant. The declining energy usage associated with 

electric ranges is noted by the DOE. The modified set of electric range energy is 

recommended. 

The modified energy values presented in Table 1 were obtained by: 

• Averaging the results of 3 recent metered studies (1988 through 1992) presented 

in Table 2 

• Partitioning the range value into oven and cooktop using DOE's approach 

The recent range metered studies used to generate Table 2 were: 

(1) "Residential Energy Usage Comparison Project", EPRI Report CU-695~ 

(2) "Integrating EIP and HE55 Infonnation for Estimating End Use Energies", 

Prepared for Siena Pacific Power Co., 1988 

(3) . "Description of Electric Energy use in Single-Family ResidenCes in the Pacific 

Northwest: 1986-1992"; Bonneville Power Administration, bec 1992 (ELCAP) 

The first two studies were cited by DOE (Appendix A; v2 of TSD) but the 

Bo'nneville Power study is omitted. This extensive study examined the range energy' 

use at 318 sites. Electric range energy usage results from the Bonneville study were: 

• Mean: . 472 kWhlyr . 

• . Median: 403 kWh/yr 

• Standard Deviation: 251 kWhlyr , 

• Skewness: 1.114 

Summarizing these most recent studies, we find that the average ,range energy use is 

449 kWh/yr (Table 2). 
Table 2: 1988 Through 1992 Metered Study Summaries

This new average range value (449 kWh/yr) was modified to individual oven and

cooktop usage by assuming the same energy split between cooktop and oven that

DOE used (e.g., standard oven - 245.6 kWh/yr=327.4'(449/605)).

2.1 Implications of the Modified (Reduced) Range Energy Usage

The substantial reduction (25%) in range energy as compared to the DOE

assumptions has a significant impact on consumer payback per the DOE Cost

Analysis Assumptions. Product paybacks per DOE assumptions are increased by

25% given the lower energy consumption of these appliances.

Examining the DOE generated paybacks in light of the reduced energy usage for the

electric coil element stretches the level 2 payback to 6.5 years as shown in Table 3.

Table 3: Electric Coll Cooktop Payback

* per Table 2 data

The payback for the Level 4 design options for the electric self-clean oven is 11.5

years and the standard electric oven with level 4 options is 6.12 years as shown in

Table 4.

Table 4: Payback for Electric Oven Options

Electric Oven DOE N/A , 7.1 7.8 9.2

Self-clean Modified- N/A 8.9 9.8 11.5

Electric Oven -. Doe N/A 3.7 4.9 4.9

Standard Modified* N/A 4.6 6.1 6.1

* per Table 2 data

R W,.Ull= q ' II 1"iA

(1) So Cal Edison 390

(2) Siena 484

(3) Bonneville 472

Average 449 kWh/yr

I^^ ^ ^ ^ ^ ^ v ;; ^ g^j:j -t «N

lr 'EQii _"mpU ii. -N

 t

Table 2: 1988 Through 1992 Metered Study Summaries 

This new average range value (449 kWh/yr) was modified to individual oven and 

cooktop usage by assuming the same energy split between cooktop and oven that 

DOE used (e.g., standard oven - 245.6 kWhlyr=327.4i449/605». 

2.1 Implications of the Modified (Reduced) Range Energy Usage 

The substantial reduction (25%) in range energy as compared to th~ DOE 

assumptions has a significant impact on consumer payback per the DOE Cost 

Analysis Assumptions. Product paybacks per DOE assumptions are increased by 

25% given the lower energy consumption of these appliances. 

Examining the DOE generated paybacks in light of the reduced energy usage for the 

electric coil element stretches the level 2 payback to 6.5 years as shown in Table 3. 

Table 3: Electric Coli Cooktop Payback 

Payback (yr) per DOE's Assumptions 

with mn.I'1,t .. ." energy 

usage" 6.5 12.3 12.3 12.3 

.. per Table 2 data 

The payback for the Level 4 design options for the electric self-clean oven is 11.5 

years and the standard electric oven with level 4 options is 6.12 years as shown in 

Table 4. 

Table 4: Payback for Electric Oven Options 

Electric Oven 

Self-clean 

Electric Oven - . 

Standard 

.. per Table 2 data 
Based on these results, the self-clean oven level 3 and 4 options exceed half of the

projected life of the product.

The. design option review presented in Sections 4 and 5 of this report will use DOE

generated values of energy consumed to facilitate comparisons between the findings

presented by DOE and the results of this study. In the electric oven analyses, oven

cooking energy and self-clean energy consumption were considered (clock energy

consumption was not included). However, for future evaluation, the DOE should

adapt more current energy usage data and the information provided in this section

should be used as a guide in revising downward the energy usage of electric ovens

and cooktops.

3.0 Review of DOE Baseline Efficiency Assumptions for Electric Ovens and

Cooktops

The DOE test procedure for determining cooking efficiency is a key technical

parameter in the evaluation of oven performance (i.e., energy factor). DOE's

assumption for baseline efficiency are in general high as compared to the efficiency

test data developed by four major range manufacturers. In addition, these average

values of efficiency (used as baseline) do not reflect the variability in product

efficiency that results in today's manufacturing of ranges, ovens, and cooktops.

Baseline efficiency levels should be established that accounts for the majority of the

units produced.

3.1 Efficiency Testing

Four manufacturers pulled several ranges off their assembly line and conducted the

DOE efficiency test for:

* Coil Cooktops

* Smooth Cooktops

* Standard Oven

* Self-Clean Oven

* Self-Clean-Convection Oven (3 manufacturers provided data)

The self-clean convection oven data on efficiency will be introduced in this section

and its implication on design viability (payback) will be discussed in a later section.

Results of the manufacturers' tests are presented in Table 5 as the average value

calculated from total sample population. Cooktop sample size represents testing of

several elements on each range.

Based on these results, the self-clean oven level 3 and 4 options exceed half of the 

projected life of the product. ' ' 

The, design option review presented in Sections 4 and 5 of this report will use DOE 

generated values of energy consumed to facilitate comparisons between the findings 

presented by DOE and the results of this study. In the electri~ oven analyses, oven 

cooking energy and self-clean energy consumption were considered (clock energy 

consumption was not included). However, for future evaluation, the DOE should 

adapt more current energy usage data and the information provided in this section 

should be used as a guide in revising qownwm;d the energy usage of electric ovens 

andl cooktol's. 

3.0 Review of DOE Baseline Efficiency Assumptions for Electric Ovens and 

Cooktops ' 

The DOE test procedure for determining cooking effiCiency is a key technical 

parameter in the evaluation of oven performance (i.e., energy factor). DOE's 

assumption for baseline efficiency ale in general high as compared to the efficiency 

test data developed by four major range manufacturerS. In addition, thes~ average 

values of efficiency (used as baseline) do not reflect the variability in product 

efficiency ~t results in today's manufacturing of ranges, ovens, a,nd cooktops. 

Baseline efficiency levels should be established that accounts· for the majority of the 

units produced: ' 

3.1 Efficiency Testing 

Four manufacturers pulled several ranges off their assembly line and conducted the 

DOE efficiency test for: 

• Coil Cooktops 

• Smooth Cooktops 

• Standard Oven 

• Self-Clean Oven 

• Self-Clean-Convection Oven (3 manufacturers provided data) 

The self-clean convection oven data on efficiency will be introduced in this s~tion 

and its implication on design viability (payback) will ~ discussed in a later section. , 

Results of the manufacturers' tests are presented in "rable 5 as the average, value' 

calculated from total sample population. Cooktop'sample size representS testing' of 

several elements on each range. 
Table 5: DOE Efficiency Test Results for Electric Cooktop Elements and Ovens

Cooktop - Coil 68 73.74%

Cooktop- Smooth 68 74.17%

Standard Oven 18 12.15%

Self-Clean Oven 20 13.795

Convection Self-Clean 14 14.12%

These average efficiency numbers of production oven and cooktops compare

reasonably well with DOE baseline efficiency numbers as shown in Table 6. The

only large difference is in the coil cooktop results.

Table 6: Comparison Between Manufacturer Generated Efficiency Test Data and Baseline DOE

Assumotions

,OOKtOp - La011 .1-3. I I470-/o 0

Cooktop - Smooth 74.17% 71.3%

Standard Oven 12.15% 12.1%

Self-Clean Oven 13.79% 13.9%

Convection Self-Clean 14.12% NA

3.2 Modification in Baseline Numbers to Account for Manufacturing Variability

While the average efficiency numbers developed by the manufacturers are in

relatively close agreement with the DOE baseline, the baseline average results do not

reflect normal product variability. This change in baseline data is critical if it is

expected that in the future all units shipped must meet an efficiency target. Using

the average test value would result in half the units failing. A modified baseline

efficiency level is recommended. Using the manufacturer data base, modified

baseline efficiency numbers are presented in Table 7. These modified baseline

efficiencies would allow approximately 82% of the range product coming off the

assembly line to meet baseline assumptions.

Table 7: Recommend Baseline Efficiencies

Cooktop - Coil 73.74% 4.29% / 69.45%

Cooktop- Smooth 73.14% 2.79% 70.38%

Standard Oven 12.15% .83% 11.3%

Self-Clean Oven 13.78% 1.15% 12.63%

11% ._ IM11% tO

Table 5: DOE Efficiency Test Results for Electric Cooktop Elements and Ovens 

========~:I 

These average efficiency numbers of production oven and cooktops compare 

reasonably well with DOE baseline efficiency numbers as shown in Table 6. The 

only large difference is in the coil cooktop results. -, . ..~.--

Table 6: Comparfson Between Manufacturer Generated Efficiency Test Data and Baseline DOE 

Assumptions . 

~~~------~--~----~----~---

3.2 Modification in Baseline Numbers to Account for ManufactUring Variability 

While the average efficiency numbers developed by the manufacturers are in 

relatively close agreement with the DOE baseline, the baseline average results do not 

reflect normal product variability. This change in baseline data is critical if it is 

expected that in the future all units shipped must meet an efficiency target. Using 

the average test value would result in half the units failing. A modified baseline 

efficiency level is recommended. Using the manufacturer data base, modified 

baseline efficiency numbers are presented in Table 7. These modified baseline 

efficiencies would allow approximately 82% of the range product coming off the 

assembly line to meet baseline assumptions. 

Table 7: Recommend Baseline EffiCiencies 

~IIIIIIIII!II~IIII!I!!IIIIIIIIIIIIIIIIII! 
4.0 Electric Oven Design Option Review

The oven design alternatives reviewed in the following subsections describe the

impact of the individual options relative to the oven utility, oven efficiency/energy

savings, and simple payback. For these analyses, energy savings were based on the

annual total cooking energy consumption (Eco) as well as the self-clean energy

consumption (Esc)presented by DOE. These values do not include clock energy and,

provide a conservative examination of payback for the several design options. Using

these high DOE usage assumptions, the paybacks calculated for the various options

usually exceeded half of the product projected life. These consumption values were

not restated to. the modified results presented in Section 2 of this study given that

DOE has not yet had the opportunity to review these findings. The multiplier used to

develop the retail cost premium from the manufacturing cost estimates was set at 2.1.

This matched the lower end of the DOE assumptions for cost multipliers (Appendix

A).

4.1 Forced Convection Design Option

DOE has recommended that forced convection be adopted as part of the electric

standard oven and electric self-clean oven level 4 efficiency improvements. Based on

our evaluation of available data, information provided by the manufacturers, and oven

thermal analysis, this option does not meet consumer payback requirements and it

changes the utility of the oven.

4.1.1 Impact of Forced Convection on Oven Utility

If full-time forced convection ovens are mandated, consumers will have to change a

lifetime of cooking habits based on recipes and cooking procedures using

conventional oven cooking. Favorite family recipes would be affected by

time/temperature changes required for convection cooking. Cooking quality, or the

quality of the food resulting from the cooking process, would change, depending on

the cooking process used.

This study assesses, through a literature review, the effects of convection ovens on

cooking quality. A literature search was initiated using the key words "convection

oven". Six research papers were retrieved from two peer reviewed scientific journals.

Two papers were submitted from university sponsored research. Each paper was

reviewed for convection oven/cooking quality data.

a . _ _

4;0 Electric Oven O.sign Option Review 

The oven design alternatives reviewed in the following subsections describe the 

impact of the individual options relative to the oven utility, oven efficiency/energy 

savings, and simple payback. For these analyses, energy savings were based on the 

annual total cooking energy consumption (Eco) as well as the self-clean energy 

consumption (Esc)presented by DOE. ,These values do not include clock energy and. 

provide a conservative examination of payback for the seve~ design options. Using 

these high DOE usage assumptions, the paybacks calculated for the various options 

usually exceeded half of the product projected life. These consumption values were 

not restated to, the modified results presented in Section 2 of this study given that 

DOE has not yet had ,the opportunity to review these findings. The multiplier used to 

develop the retail cost premium from the manufacturing cost estimates was set at 2.1. 

This matched the lower ,end of the, DOE assumptions for cost multipliers (Appendix 

A). ' ' 

4.1 Forced Convection Design Option 

DOE has ,recommended that forced convection be adopted as part of the electric 

standard oven and electric self-clean oven level 4 efficiency improvements. Based on 

our evaluation of available data. information provided by the manufacturers. and oven 

thennal analysis, this option does not meet consumer payback requirements and it 

changes the utility of the oven. 

4.1.1 Impact of Forced Convection on Oven Utility· 

If full-time forced convection ovens are mandated, consumers will have to change a 

lifetime of cooking habits based on recipes and cooking procedures using 

conventional oven cooking. Favorite family recipes would be affected by 

time/temperature changes required for convection cooking;" Cooking quality, or the 

quality' of the food resulting from the cooking process, would change, depen:ding on 

the Cooking process used. ' 

This study assesses, through a literature review,' the effects of convection ovens on 

cooking quality. A literature search was initiated using the key words "convection 

oven". Six research papers were retrieved from two peer reviewed scientific journals. 

Two' papers were submitted from university sponsored research. Each paper was 

reviewed for convection oven/cooking quality data. 
Research Papers Reviewed

1. "Sensory quality and energy use for baking of molasses cookies prepared with

bleached and unbleached flour and baked in infrared, forced air convection, and

conventional deck ovens" J. Heist & M.L. Cresser, J. Food Science, Vol. 55, No.

4, 1990, p. 1095-1100.

2. "Sensory quality and energy use for scrambled eggs and beef patties heated in

institutional microwave and convection ovens" Cremer, M.L., J. Food Science,

Volume 47, 1982, p. 871-874.

3. "Comparison of drying kinetics of foods using a fan-assisted convection oven, a

microwave oven and a combined microwave/convection oven" Al-Duri, B. and

Mcintyre, S., J. Food Engineering, Volume 15, 1992, p. 139-155.

4. "Nutrient retention in pork, turkey breast and corned beef roasts after infrared

and convection heat processing" Unklesbay, N., Davis, M.E., Krause, G. Journal

of Food Science, Volume 48, 1983, p. 864-904.

5. "Temperatures of spaghetti after heating in convection ovens at service locations

in a commissary foodservice system." Cremer, M.L. Journal of Food Science,

Volume 43, 1978, p. 1062-1079.

6. "Nutrient retention of portioned menu items after infrared and convection heat

processing" Unklesbay, N., Davins, ME., Krause, G. Journal of Food Science,

Volume 48, 1983, p. 869-873.

7. "A study of design approaches to convection cooking" Lovingwood, R.P.,

DeMerchant, E.A., Himes, L.J., Virginia Polytechnic Institute and State

University, Walsh, C.M., and Kirkley, S.L., Thermodor Corporation.

8. "Oven performance in convection versus. radiant mode" Lovingwood, R.P., De

Merchant, E.A., and Himes, L.J., Virginia Polytechnic Institute & State

University, Blacksburg, VA.

From the peer reviewed journals, the findings were:

* Cookies baked in a convection oven were significantly different from those baked

in standard or infrared ovens.

* More energy was used in the convection baking process.

4 .1.e., ^ N I adl^

Research Papers Reviewed 

1. "Sensory quality and energy use for baking of molasses cookies prepared with 

bleached and unbleached flour and baked in infrared, forced air convection, and 

conventional deck ovens" 1. Heist & M.L. Cresser, 1. Food Science, Vol. 55, No. 

4, 1990, p. 1095-1100. 

2. "Sensory quality and energy use for scrambled eggs and beef patties heated in 

institutional microwave and convection ovens" Cremer, M.L., J. Food Science, 

Volume 47, 1982, p. 871-874. 

3. "Comparison of drying kinetics of foods using a fan-assisted convection oven, a 

microwave oven and a combined microwave/convection oven" AI-Duri .. B. and 

Mcintyre, S., J. Food Engineering, Volume 15, 1992, p. 139-155. 

4. "Nutrient retention in pork, turkey breast and corned beef roasts after infrared 

and convection heat processing" Unklesbay, N., Davis, M.E., Krause, G. Journal 

of Food Science, Volume 48, 1983, p. 864-904. 

5. "Temperatures of spaghetti after heating in convection ovens at service Locations 

in a commissary food service system." Cremer, M.L. Journal of Food Science, 

Volume 43, 1978, p. 1062-1079. 

6. "Nutrient retention of portioned menu items after infrared and convection heat 

processing" Unkles bay, N., Davins, M.E., Krause, G. Journal of Food Science, 

Volume 48, 1983, p. 869-873. 

7. "A study of design approaches to convection cooking" Lovingwood, R.P.,· 

DeMerchant, E.A., Himes, L.J., Virginia Polytechnic Institute and State 

University, Walsh, C.M., and Kirkley, S.L., Thennodor Corporation. 

8. "Oven perfonnance in convection versus. radiant mode" Lovingwood, R.P., De 

Merchant, E.A., and Himes, L.J., Virginia Polytechnic Institute & State 

University, Blacksburg, VA. . 

From the peer reviewed journals, the fmdings were: 

• Cookies baked in a convection oven were significantly. different from those baked 

in standard or infrared ovens. -

• More energy was used in the convection baking process. 
* Heating in a conventional oven of ready prepared or commissary type food

yielded food of higher sensory quality with lower energy input than food

prepared in a convection oven.

* The effect of infrared and convective heating upon nutrient retention was similar

in portioned menu items.

* In a convection oven, the rate of moisture loss increases with higher temperature

due to the greater driving forces for heat and mass transfer. For products with

low moisture content, the convection oven is not advantageous because the

diffusion process is slow.

From the university sponsored research, the findings were:

* Food prepared by convection was identifiable (lumped layer cake with crack in

center; cookies with variation in browning across the top; meats with crunchier

exterior).

* Cookies and chicken varied more than cakes and beef when comparing

convection and standard oven modes.

4.1.2 Forced Convection Impact on Oven Efficiency

The addition of forced convection to a "standard" residential product has a marginal

impact on efficiency, and these gains are far less than those assumed by DOE.

Range manufacturers tested 14 self-clean ovens with convection and found that the

average efficiency was 14.12% as compared to 13.79% for their test of 20 self-clean

ovens.

The impact of this option on overall energy savings is less than 8 kWh/yr as

compared to DOE's assumed savings of 41 kWh/yr for self-clean ovens and 33

kWh/yr for a standard oven (using DOE's adjusted values for EAo minus the clock

energy consumption).

Table 8 presents a detailed comparison of potential energy savings of the convection

feature based on the DOE adjusted baseline energy use. Using the modified oven

energy data presented earlier would show an even smaller savings.

- _ __ ^ - _

• Heating in a conventional oven of ready prepared or commissary type food 

yielded food of higher sensory quality with lower energy input than food 

prepared in a convection oven. ' 

• The effect ,of infrared and convective heating upon nutrient retention was similar 

in portioned menu items. 

• In a convection oven, the rate of moisture loss increases with higher temperature 

due to the greater driving forces for heat and mass transfer. For products with 

low moisture coritent, the convection oven 'is not advantageous 'because the 

diffusion process is slow. 

From the university sponsored research, the 'findings were: 

• Food prepared by convection was identifiable (lumped layer cake with crack in 

center; cookies with variation in browning across the top; meats with crunchier 

exterior). 

• Cookies and chicken varied more than cakes and beef when comparing, 

convection and standard oven modes. 

4.1.2, Forced Convection Impact on Oven Efficiency 

The addition of forced convection to a "standard" residential product has a marginal, 

impact on efficiency, and these gains are far less than those assumed by DOE. 

Range manufacturers tested '14 self-clean ovens with convection and found that the, 

average efficiency was 14.12% as compared to 13.79% for their test of 20 self-clean 

ovens. 

The impact of this option on overall energy'savings is les's than 8 kWhlyr as 

compared to DOE's assumed savings of 41 kWhlyr for self-cle~ ovens and 33 

kWhiyr for a standard oven (using DOE's adjusted values for EAO minus the clock 

energy consumption). 

Table 8 presents a detailed comparison of potential energy savings of the convection 

feature based on the DOE adjusted baseline energy use. Using the modified oven 

energy data presented earlier would, show an even smaller savings. ' 
Table 8: Energy Saved Using a Convection Option

to · _·~~~~~~~~

Self-clean Oven .33% pdints 313 kWh 7.3 kWh* 41 kWh/yr

Standard Ovens .33% points 293 kWh 7.7 kWh 33 kWh/yr

* Assumed for standard ovens based on self-clean tests

** Example: Savings = 313 - 313 (13.79/14.12) = 7.3 kWh/yr

Our thermal analysis supports the findings of the manufacturers relative to efficiency

improvements of adding convection to standard residential ovens. Our analysis (see

Appendix B for model description) showed that competing heat transfer effects limit

the effectiveness of the convection option. For the residential oven geometry and

convection configuration, the enhancements relative to increased heat transfer to the

product is nearly balanced by greater oven cavity and door losses. The opportunity

to increase surface heat transfer to the food product is limited by the internal heat

transfer characteristics of the product (conduction limited). The current DOE test

procedure featuring an aluminum block (highly conductive) cannot simulate the

impact of forced convection on product quality and hence its use in forced convection

testing is very limited.

4.1.3 Consumer Payback Associated with Forced Convection

Examination of the consumer payback aspect of adding forced convection showed

that the payback associated with this option easily exceeds the half life of the range

and that paybacks of 100+ years are likely. For this analysis, a simple payback was

used of the form

Payback = incremental price increase of the convection feature Payback -- energy savings associated with convection

The incremental price increase associated with the convection option was developed

from manufacturers' data. Three range manufacturers with extensive experience in

convection ovens provided cost premium data that was significantly higher than the

DOE assumptions. The average manufacturing costpremiums for the convection

option as provided by the range manufacturers was:

Average manufacturing cost premium for convection = $39.61/oven

I itasdtC ¶a [anEtn

4% W% 9 :A&IW%

Table 8: Energy Saved Using a Convection Option 

* Assumed for standard ovens based on self-clean tests 

** Example: Savings == 313 - 313 (13.79/14.12) == 7.3 kWhlyr 

Our thennal analysis supports the findings of the manufacturers relative to efficiency 

improvements of adding convection to standard residential ovens. Our analysis (see 

Appendix B for model description) showed that competing heat transfer effects limit 

the effectiveness of the convection option. For the residential oven geometry and 

convection configuration, the enhancements relative to increased heat transfer to the 

product is nearly balanced by greater oven cavity and door losses. The opportunity 

to increase surface heat' transfer to the food prOduct is limited by the internal heat 

transfer characteristics of the product (conduction limited). The current DOE test 

procedure featuring an aluminum block (highly conductive) cannot simulate the 

impact of forced convection on product quality and hence its use in forced convection 

testing is very limited. 

4.1.3 Consumer Payback Associated with' Forced Convection 

Examination of the consumer payback aspect of adding forced convection showed 

that the payback associated ~ith this option easily exceeds the half life of the range 

and that paybacks of 100+ years are likely. For this analysis, a simple payback was 

used of the fonn 

Payback = incremental price increase of the convection feature 

energy savings associated with convection 

The incremental price increase associated with the convection option was developed 

from manufacturers' data. Three range manufacturers with extensive experience in , 

convection ovens provided cost premium data that was significantly higher than the 

DOE assumptions. The average manufacturing cost~remiums for the convection 

option as provided by the range manufacturers was: 

Average manufacturing cost premium for convection == $39.6110ven 
Using a multiplier of 2.1 (see Appendix A) on manufacturing cost to achieve a sell

-price results in an average price premium of:

Average Incremental Price for Convection Feature $81.95/oven

Potential payback for this option are presented in Table 9 and they range from 106 to

141 years. These paybacks are extremely long and demonstrate that the forced

convection option is not justified based on energy cost savings. Using the modified

energy usage data would result in even longer paybacks (Section 2.0).

Table 9: Forced Convection Payback

IStandard Oven I $.1/kWh $ .77 106.4 yr

Io O 8195h .08/kWh I $ .58 141.3 yr Self-clean Oven 81.95 --- Seffclean Oven_81_95$.l1/kWh $ .73 112.3 yr

4.2 Reflective Surfaces for Oven Cavity

DOE has recommended that reflective surfaces be incorporated into the oven as an

energy saving technique. Our analysis of this option suggests that:

* Current oven utility is not maintainable using reflective surfaces.

* Modest energy savings are possible.

* Consumer payback is long.

* Major oven design modifications are likely in order to duplicate the current

product life.

4.2.1 Impact of Reflective Coating on Oven Utility

The addition of reflective walls to an existing oven design will change the cooking

process and, as a result, will impact the utility of the oven. A reflective oven cavity

will convey very different thermal radiation to the food as compared to the current

highly emissive cavity designs. A highly reflective Qven will reflect radiant heat

from the element that has its wave length set by the very high temperatures of the

bottom heating element.

_ , s g a _

Using a multiplier of 2: 1 (see· Appendix A) on manufacturing cost to achieve a sell 

-price results in an average price premium of: 

. . . 

Average Incremental Price for Convection Feature::; $81.95/oven 

Potential payback for this option are presented in Table 9 and they range from 106 to 

141 years. These paybacks are extremely long and demonstrate that the forced 

convection option is not justified based on energy cost savings. Using the modified 

energy usage data would result in even longer paybacks (Section 2.0). . - . . 

Table 9: Forced Convection Payback 

Standard Oven 81.95 

Self-clean Oven 81.95 

4.2 Reflective Surfaces for Oven Cavity 

.DOE has recommended that reflective surfaces be incorporated into the oven as an 

energy saving technique. Our analysis of this option suggests that: 

• Current oven utility is not maintainable using reflective surfaces. 

• Modest ·energy savings are possible. 

• Consumer .payback is long. 

• Major oven design modifications are likely in order to duplicate the current 

product life. 

4.2.1 Impact of Reflective Coating on Oven Utility 

The addition of reflective walls to an existing oven design will change the cooking 

process and, as a result, will impact the utility of the oven. A reflective oven cavity 

will convey very different thennal radiation to the food as compared to the current 

highly emissive cavity designs. A highly reflective aven will reflect radiant heat 

from the element that has its wave length set by. the very high temperatures of the 

bottom heating element. 
The characteristics of this reflected radiation is different than the thermal radiation

emitted by the current cavity. The heat re-radiated from the walls is essentially oven

set point temperature (far less than the element temperature) and this radiation has a

longer wavelength as compared to the output of the heating element. The difference

in the wavelength between the reflective cavity and the current design will have a

large effect on surface browning and food quality.

The proposed reflective surface modification to residential oven products changes the

cooking quality of the appliance possibly resulting in overbrowning of food surfaces

and underdone interiors. Underdone interiors could affect food safety, since the

interior of the food may not reach proper sterilization temperature. Additionally, the

emissivity of the reflective surface would not stay constant due to food spills, blueing

from heat, and cleaning compounds. Reflective materials degrade after the first

baking function and continue to degrade through the life of the product. In

particular, the self-cleaning oven process damages the reflective walls. Currently,

about 29% of gas ranges and 58% of electric ovens are self-cleaning. There is no

known cost effective material that will maintain reflective surfaces in a self-cleaning

oven over its 19 year life. [1]l

21

4.2.2 Impact of Reflective Coatings on Oven Efficiency

Our thermal analysis of the impact of reflective surfaces indicates that energy savings

are not significant when compared to today's highly emissive oven designs. The

small energy reduction is attributed to a slightly lower oven wall temperature as

compared to porcelain coated products. These effects produce lower wall/cabinet

losses. In addition, we found that surface oxidation or even thin oil films eliminate

the benefit of a reflective surface. These effects are described in the balance of this

section.

4.2.3 Reflective Surface Efficiency Analysis

The maximum oven efficiency improvement resulting from the use of reflective

surfaces on the oven interior was determined to be less than .58 percentage points

(e.g., from 12.15% to 12.73%) using our oven model (see Appendix B). The

improvement in oven performance results from a larger portion of the heat source

energy being reflected off the oven wall surfaces which keeps more of the energy

within the oven cavity (less energy is absorbed by the surface) and increases the

percentage of useful heat. The net effect is a slightly lower oven wall temperature.

[1] Battelle, et al., Technical Input to NAECA Rulemaking for Gas-Fired Ranges, GRI Interim Report No. GRI93/0319, July 1993.

[2] Aronov, M., et al., Analysis of Design Options for Reducing the Energy Consumption of Residential Gas

Ovens, American Gas Association Laboratories Research Report, GRI Contract #5086-241-1220.

a m.4U.tuuWN aImUS

The characteristics of this reflected radiation is different than the thenna! radiation 

emitted by the current cavity. The heat re-radiated from the walls is essentially oven 

set point temperature (far less than the element temperature) andthis radiation has a 

longer wavelength as compared to the output of the heating element. The difference 

in the wavelength between the reflective cavity and the current design will have a 

large effect on surface browning and food quality. 

The proposed reflective surface modification to residential oven products changes the 

cooking quality of the appliance possibly resulting in overbrowning of food surfaces 

and underdone interiors. Underdone interiors could affect food safety, since the . 

interior of the food may not reach proper sterilization temperature. Additionally, the 

emissivity of the reflective surface would not stay constant due to food spills, blueing 

from heat, and cleaning compounds. Reflective materials degrade after the first 

baking function and continue to degrade through the life of the product. In 

particular. the self-cleaning oven process damages the reflective walls. Currently. 

about 29% of gas ranges and 58% of electric ovens are self-cleaning. There is no 

known cost effective material that will maintain reflective surfaces in a self-cleaning 

oven over its 19 year life. [1][2] 

4.2.2 Impact of Reflective Coatings on Oven Efficiency 

Our thermal analysis of the impact of reflective surfaces indicates that energy savings 

are not significant when compared to today's highly emissive oven designs. The 

small energy reduction is attributed to a slightly lower" oven wall temperature as 

compared to porcelain coated products. These effects produce lower wall/cabinet 

losses. In addition. we found that surface oxidation or even thin oil films eliminate 

the benefit of a reflective surface. These effects are described in the balance of this 

section. 

4.2.3 Reflective Surface Efficiency Analysis 

The maximum oven efficiency improvement resulting from the use of reflective 

surfaces on the oven interior was determined to be less than .58 percentage points 

(e.g .• from 12.15% to 12.73%) using our oven model (see Appendix B). The 

improvement in oven performance results from a larger portion" of the heat source 

energy being reflected off the oven wall surfaces which keeps more of the energy 

within the oven cavity (less energy is absorbed by the surface) and increases the 

percentage of useful heat. The net effect is a slightly lower oven wall temperature. 

- [1] Battelle, et al., Technical Input to NAECA Rulemaking for Gas-Fired Ranges, GR! Interim Repon No. GRI93/0319, July 1993. 

[2] Aronov, M., et al .• Analysis of Design Options for Reducing the Energy Consumption of Residential Gas 

Ovens, American Gas Association Laboratories Research Report, GR! Contract #5086-241-1220. 
In most situations, radiation energy is either absorbed or reflected. The energy that is

absorbed is re-radiated at a different wavelength. Thus, the emissivity is equal to the

absorptivity of the surface. A highly absorptive surface will have a high emissivity

and a highly reflective surface will have a low emissivity. Therefore, to analyze the

effect of reflective surfaces, the emissivity of the oven interior is reduced to model

the appropriate coating.

The analysis of reflective surfaces focused on steady state and transient heating

improvements. Emissivity values of .1, .3, .5 and .7 were examined to determine

savings in oven efficiency. Table 10 summarizes these heat loss reductions.

Table 10: Heat Loss Reductions for Reflective Coatings Relative to the Baseline Oven

Design (Emissivity for porcelain oven = .92)

LI E miss~~~~ty ~~~ * ' - ''IP. _r X O n en_) I

.1 .58

.3 .32

.5 .17

.7 .08

Table 11 breaks down the actual energy savings for the different surface emissivities

analyzed. The annual energy savings is based on adjusted DOE annual cooking

energy output including self-cleaning energy when appropriate.

Table 11: Breakdown of Savings for Reflective Oven Surfaces

.5 4.03 3.81 12.32% 13.96% |

.3 7.48 7.10 12.47% 14.11%

.1 13.29 12.63 12.73% 14.37%

* Using manufactures test data for efficiency; baseline self-clean efficiency = 13.79%; baseline standard

oven efficiency = 12.15%

* Based on adjusted DOE energy usage values (EAo minus clock energy consumption)

The savings associated with an emissivity of .1 mayjepresent the highest attainable

energy savings for a reflective surface. An emissivity of .1 represents a polished,

unoxidized, and oil free surface which will only exist on a new product. As soon as

a consumer begins to cook in the oven an oil film will start to develop, the surface

will oxidize and the energy savings will quickly decrease. Table 12 illustrates how a

degradation in surface finish will affect emissitivies.

In most s.ituations, radiation energy is either absorbed or reflected. The energy that is 

absorbed is re-radiated at a different wavelength. Thus, the emissivity is equal to the 

absorptivity of the surface. A highly absorptive surface will have a high emissivity 

and a highly reflective surface will have a low emissivity. Therefore, to analyze the 

effect of reflective surfaces, the emissivity of the oven interior is reduced to model 

the appropriate coating. 

The analysis of reflective surfaces focused on steady state and transient heating 

improvements. Emissivity values of .1, .3, .5 and .7 were examined to detennine 

savings in oven efficiency. Table 10 summarizes these heat loss reductions. 

Table 10:' Heat Loss Reductions for Reflecti~e ~oatlngs Relative to the Baseline Oven 

Design (Emissivity for porcelain oven = .92) . 

.1 . 58 

.3 .32 

.5 .17 

.7 .08 

Table 11 breaks down the actual energy savings for the different surface emissivities 

analyzed. The annual energy savings is based on adjusted DOE annual cooking 

energy output including self-cleaning energy when appropriate. 

. Table 11: Breakdown of Savings for Re~lective Oven Surfaces .. 

* Using manufactures test data for efficiency; baseline self-clean effiCiency = 13.79%; baseline standard 

oven efficiency = 12.15% 

** Based on adjusted DOE energy usage values (EAO minus clock energy consumption) 

The savings associated with an emissivity of .1 may.[epresent the highest attainable 

. energy' savings for a reflective surface. An emissivity of .1 represents a polished, 

unoxidized, and oil free surface which will only exist on a new product. As soon as 

a consumer begins to cook in the oven an oil film will start to develop, the surface 

will oxidize and the energy savings will quickly decrease. Table 12 illustriltes how a 

degradation in surface finish will affect- emissitivies. . 
Table 12: Emissivitles for Various Types of Surfaces

IIIIB.ill^'^NM ^^I^^Surfame Emlssvt

Aluminum - polished .05

Aluminum - slightly oxidized .15

Steel- polished .1

Steel - slightly oxidized .2

Stainless Steel - polished .19-.25

Stainless Steel - slightly oxidized .53

Nickel - polished (Chrome like) .06

Nickel - oxidized .49

Zinc Coating - very bright .14

Zinc Coating - slightly oxidized .28

Zinc Coating - badly furnished .53

Oil Film on Surface ( on polished surface) .82

Based on the information in Table 12, we would expect highly reflective wall

surfaces in an oven to quickly erode which will raise emissivities values closer to

.5-.8. As a result, we would expect the annual energy savings to be below 5 kWh.

For self-cleaning ovens, one of the best choices for a reflective cavity would be

stainless steel. Stainless steel would be suitable wall material for an oven that will

see hundreds of 900'F self-clean cleaning cycles over the average 19-year life of the

oven.

For the stainless steel cavity, the wall emissivity would be .5 (oxidized) after the first

self-clean cycle; and the benefit of the surface would be reduced by about 60%.

Chrome coatings are best suited for the standard oven which have temperatures of

600°F. The deposits of even thin coatings of oil from normal cooking use would

quickly cause the deterioration of the reflective quality of the plating. An average

cavity emissivity of about .45 for a chrome-plated oven in daily use would be very

reasonable (assumes half the oven is still highly reflective [e=.1] and the other half is

soiled [e=.82]). Again, about 60% of the energy savings benefit of the oven would

be lost. Frequent cleaning of the oven would improve the reflectivity cavity quality

provided the user did not scratch or damage the surface using typical cleaning pads

and oven cleaning chemicals.

4.2.3 Consumer Payback Associated with Reflective Surfaces

The payback associated with the standard or self-clean oven with reflective interior

surfaces was found to be greater than 8-years when using the energy savings

associated with a highly reflective cavity (ideal assumption). A 20+ year payback is

realized if the oven surface reflectance is reduced to account for surface soil or

surface oxidation that will occur oven the life of the product.

OR -M. 9- - - *I% a M--Jr. a -

Table 12: Emlsslvltles for Various Types of Surfaces 

Aluminum - polished 

Aluminum - slightly oxidized 

- polished 

Steel - slightly oxidized 

Stainless Steel - polished 

Stainless Steel - slightly oxidized 

Nickel- rome like) 

Nickel - oxidized 

- very bright 

.05 

.15 

.1 

.2 

.19-.25 

.53 

.06 

.49 

.14 

.28 

.53 

Based on the infonnation in Table 12, we would expect highly reflective wall 

surfaces in an oven to quickly erode which will raise emissivities values closer to 

.5-.8. As a result, we would expect the annual energy savings to be below 5 kWh. 

For self-cleaning ovens, one of the best choices for a reflective cavity would be 

stainless steel. Stainless steel would be suitable wall material for an oven that will 

see hundreds of 900"F self-clean cleaning cycles over the average 19-year life of the 

oven. 

For the stainless steel cavity, the wall emissivity would be .5 (oxidized) after the flfSt 

self-clean cycle; and the benefit of the surface would be reduced by about 60%. 

Chrome coatings are best suited for the standard oven which have temperatures of 

600r. The deposits of even thin coatings of oil from normal cooking use would 

quickly cause the deterioration of the reflective quality of the plating. An average 

cavity emissivity of about .45 for a chrome-plated oven in daily use would be very 

reasonable (assumes half the oven is still highly reflective [£=.1] and the other half is 

soiled [£=.82]). Again, about 60% of the energy savings benefit of the oven would 

be lost. Frequent cleaning of the oven would improve the reflectivity cavity quality 

provided the user did not scratch or damage the surface using typical cleaning pads 

and oven cleaning chemicals. 

4.2.3 Consumer Payback Associated with Reflective Surfaces 

The payback associated with the standard or self-cle!n oven with reflective interior 

surfaces was found to be greater than 8-years when using the energy savings 

associated with a highly reflective cavity (ideal assumption). A 20+ year payback is 

realized if the oven surface reflectance is reduced to account for surface soil or 

surface oxidation that will occur oven the life of the product. 
This design option payback period is excessive, difficult to achieve in practice, and if

implemented would alter the utility of the product. Paybacks calculated for this

option are shown in Table 13 for both the "ideal" case and for reflective surfaces

after service and aging has occurred.

liable 13: Payback Associated with Reflective Oven Surfaces

$.08/kWh $11.45/oven 13.29 10.76 yr 4.03 35.51 yr

Standard Oven $.10/kWh $11.45/oven 13.29 8.62 yr 4.03 28.41 yr

Sel - Cn $.08/kWh $11.45/oven 12.63 11.33 yr 3.81 37.57 yr

L'' I $.10/kWh $11.45/oven 12.63 9.07 yr 3.81 30.05 yr

The payback analysis was based on using chrome plating on the oven cavity. While

this technique may not be suitable for a 19-year product life, it is probably the least

expensive method for obtaining a reflective surface; it is substantially less expensive

than a stainless steel cavity or liners. The price premium associated with chrome

plating was taken as average of Arthur D. Little, DOE and manufacturers' estimates.

4.2.4 Reflective Surface Issues Relative to Manufacturing

In the following paragraphs preliminary costs to manufacture electroplated chrome

surfaces for ovens are developed and issues relative to achieving 20-year life with

such surfaces are discussed.

We have selected electroplated chrome for the reflective surface due to the stability

of the protective oxide which forms on chrome, and electroplating for compatibility

with existing manufacturing operations for the oven cavity.

Two general classes of chrome plating are available: hard chrome and "decorative"

chrome. The first, hard chrome, is used for engineering applications where wear and

corrosion resistance are needed. Decorative chrome produces a highly reflective

surface, and would be the process of choice for the oven application. The overall

process for achieving a polished surface using decorative chrome at minimum cost

progresses through the following steps:

* Mechanical polishing of the substrate

* Copper plating (0.1 mil)

* Mechanical buffing of the copper layer

* Copper plating (flash)

* Nickel plating (2 layers 0.2 mil in thickness)

_M -. M _ -a

This design option payback period is excessive, difficult to .achieve in practice, and if 

implemented would alter the utility of the product. Paybacks calculat~d for this 

option are shown in Table 13 for both the "ideal;' case and for reflective surfaces 

after service and aging has occurred. . 

'~able 13: Payback Associated with Reflective Oven Surfaces 

~~~~~~~~~~~~~ 

self·Clean 

'The payback analysis. was based on using chrome plating on the oven cavity .. While 

this technique may not be suitable fora 19-year product life, it is probably·· the least 

. c~xpensive method for obtaining a reflective surface; it is substantially less expensive 

than a stainless steel cavity or liners. The price premium associated with chrome 

!plating was taken as average of Arthur D. Little, OOE and manufacturers' estimates. 

,4.2.4 Reflective Surface Issues Relative to Manufacturing 

In the following paragraphs preliminary costs to manufacture electroplated chrome 

surfaces for ovens are developed and issues relative to achieving 20-year life with 

such surfaces are discussed. 

We have selected electroplated chrome for the reflective surface due to the stability 

of the protective oxide which forms on chrome, and electroplating for compatibility 

with existing manufacturing operations for the oven cavity. 

Two general classes of chrome plating are available: hard chrome and "decorative" 

chrome. The first, hard chrome, is used for engineering applications where wear and 

corrosion resistance are needed. Decorative chrome produces a highly reflective 

surface, and would be the process of choice for the oven application. The overall 

process for achieving a polished surface using decorative chrome at minimum cost 

progresses through the following steps: 

• 

• 

• 

• 

• 

Mechanical polishing' of the substrate· 

Copper plating (0.1 mil) I 

Mechanical buffing of the copper layer 

Copper plating (flash) 

Nickel plating (2 layers 0.2 mil in thickness) 
Chrome plating

Typically, the decorative chrome plate is less than 50 millionths of an inch. For a

part in which only the interior needs plating, masking and stripping steps may be

included to block off the external surface.

Cost of the plating can be estimated from the time in the bath, and the part loading

per tank. For purposes of this calculation, tank time costs of $40 to $50 per hour

(margins not included) and deposition of V2 mil in 15 minutes have been assumed.

The cost of a part then depends on the parts per rack, and the rack capacity of the

tank. In this calculation, 8 parts per rack or 4 oven cavities and door pieces per rack

were assumed. This leads to an oven cavity plating cost of only $2.50 to $3.00

without overheating and margins.

Polishing of the steel surface and masking of the external surfaces introduces

additional costs. For hand operations, the costs of these steps could exceed the cost

of the plating. However, for large production volumes, robotic polishing and

masking steps will significantly bring down costs. For this preliminary analysis,

surface preparation costs equaled that of plating, for a total cost of $5.00 to $6.00.

Range manufacturers would have to make major investments in an automated chrome

plating line to achieve this low cost premium. Use of plating vendors could double

the cost.

The preliminary chrome plating cost can be summarized as follows:

* Average plating and preparation cost - $5.50/oven

* Incremental consumer price for reflective surface - $11.55/oven

This incremental pure estimate is about 3 times of that assumed by the DOE

($3.06/unit retail). Another chrome plating estimate was provided by one of the

major range companies which placed the manufacturing cost premium of a chrome

plated oven over the standard product at $9.40/unit or a customer price increase of

$19.74/unit. The average of these three values is $11.45 [= (19.74 + 11.55 + 3.06)/3]

which was used in the payback analysis.

Significant materials issues relative to a 19-year chrome cavity life are:

* Chrome deposits are brittle and can microcrack depending on the thickness and

the applications. Thermal cycling of the oven stresses the oven walls further

promoting the cracking process. The effect of cracks on the corrosion rate of the

substrate due to oxidation, and food and cleaning chemicals must be determined.

a I_ _ *Ulw 

• Chrome plating 

Typically, the decorative chrome plate is less than 50 millionths of an inch. For a 

part in which only the interior needs plating, masking and stripping steps may be 

included to block off the external surface. 

Cost of the plating can be estimated from the time in the bath, and the part loading 

. per tank. For purposes of this calculation, tank time costs of $40 to $50 per hour 

(margins not included) and deposition of Yl mil in 15 minutes have been assumed. 

The cost of a part then depends on the parts per rack, and the rack capacity of the 

tank. In this calculation, 8 parts per rack or 4 oven cavities and door pieces per rack 

were assumed. This leads to an oven cavity plating cost of orily $2.50 to $3.00 

without overheating and margins. 

Polishing of the steel surface and masking of the external surfaces introduces 

additional costs. For hand operations, the costs of these steps could exceed the cost 

of the plating. However, for large production volumes, robotic polishing and 

masking steps will significantly bring down costs. For this preliminary analysis, 

surface preparation costs equaled that of plating, for a total cost of $5.00 to $6.00. 

Range manufacturers would have to make major investments in an automated chrome 

plating line to achieve this low cost premium. Use of plating vendors could double 

the cost. 

The preliminary chrome plating cost can be summarized as follows: 

• Average plating and preparation cost .. $5.50/oven 

• Incremental consumer price for reflective surface ... $11.55/oven 

This incremental pure estimate is about 3 times of that assumed by the DOE 

($3.06/unit retail). Another chrome plating estimate was provided by one of the 

major range companies which placed the manufacturing cost premium of a chrome 

plated oven over the standard product at $9.40/unit or a customer price increase of 

$ 19.741unit. The average of these three values is $11.45 [= (19.74 + 11.55 + 3.06)/3] 

which was used in the payback analysis. 

Significant materials issues relative to a 19-year chrome cavity life are: 

• Chrome deposits are brittle and can microcrack depending on the thickness and 

the applications. Thennal cycling of the oven stresses the oven walls further 

promoting the cracking process. The effect of cracks on the corrosion rate of the 

substrate due to oxidation, and food and cleaning chemicals must be determined. 
* Thermal cycling of the oven cavity stresses the deposit increasing the potential

for loss of adhesion. Quality control of bath and operating parameters becomes

critical to insure consistent adhesion of the deposit.

* The cavity reflectivity will likely change over time.

In addition, the manufacturers will likely have major investments including:

* Oven design modifications since deposition of bright chrome on the interior

surface of an open welded box presents several issues:

-Crevices along the weld line and comers creates the potential for solution

retention in recesses. Residual bath solutions can contaminate subsequent

plating bathes and cause corrosion of the completed part.

- Polishing and buffing of interior surfaces with corners and right angles may

require specialized equipment.

- Conformal anodes may be needed to obtain uniform thickness and deposit

properties on the inside of the box.

- A trade-off analysis should be conducted regarding the cost benefits of

masking the outside of the cavity from plating. Masking before plating and

stripping the mask after plating can contribute significant to cost.

· An appliance manufacturer has to consider the cost benefits of setting up an

internal plating operation versus the use of external plating shops. An internal

chrome plating operation entails an investment in a waste treatment plant and

precautions for working with chromic acid.

4.3 Improved Door Seal for Standard Electric Ovens

Based on efficiency and cost data provided by manufacturers this option has a very

minor impact on oven efficiency and a price premium that creates a payback in

excess of 10 years. In addition, the door seal improvements may effect the cooking

performance of the oven. The door seal allows both fresh air to enter the oven cavity

(bottom seal) and it acts as a partial oven vent (upper door seal line). Modifications

to the door seal could have a negative impact of moisture concentration in the cavity

with a resulting negative impact on cooking perforrmnce.

-- _ I - .

• Thermal cycling of the oven cavity stresses the deposit increasing the potential 

for loss of adhesion. Quality control of bath and operating parameters becomes 

critical to insure consistent adhesion of the deposit.' . . 

• The cavity reflectivity will likely change over time. 

In addition, the manufacturers will likely have major investments including: 

• Oven design modifications since deposition of bright chrome on the interior 

surface of an open welded box presents several issues: 

- Crevices along the weld line and coiners creates the potential for solution 

retention in recesses. Residual bath solutions can contaminate subsequent 

plating bathes and cause corrosion of the completed part. 

- Polishing and buffmg of interior surfaces with comers and right angles may 

require specialized equipment. 

- Conformal anodes may be needed to obtain unifonn thickness and deposit 

properties on the inside of the box. . . . 

- A trade.:off analysis should be conducted regarding the cost benefits 9f 

masking the outside of the cavity from plating. Masking before plating and 

stripping the mask after plating can contribute significant to cost. 

• An appliance manufacturer has to consider the cost benefits of setting up an 

internal plating operation versus the use of external plating shops .. An internal 

'chrome plating operation entails an investment in a waste treatment plant -and 

precautions for working with chromic acid. 

4.3 Improved Door Seal for Standard Electric Ovens 

Based on efficiency and cost data provided by manufacturers this option has a very 

minor impact on oven efficiency and a price premium that creates a payback in 

excess of 10 years. In addition, the door seal improvements may effect the cooking 

performance of the oven. The door seal allows both fresh air to enter the oven cavity 

(bottom seal) and it acts as a partial oven vent (upper door seal line). Modifications 

to the door seal could have a negative impact of moisture concentration in the cavity 

with a resulting negative impact on cooking perfo~ce. 
4.3.1 Improved Door Seal Efficiency

The oven efficiency was found to increase by .24 percentage points (i.e., baseline

efficiency increased 12.15% to 12.39%) when the standard oven gasket was replaced

with the improved gasket system. As shown below in Table 14, this door seal

improvement results in 5.68 kWh being saved.

Table 14: Energy Saving Associated with an Improved Door Seal

Standard Oven with . Standard Oven withal .24%* 293 kWh/yr 5.68 kWh/yr new Door Seal

*Would raise baseline efficiency of 12.15 to 12.39%

The .24 percentage points improvement to oven efficiency was determined by

conducting efficiency tests on 5 standard ranges modified with the improved seals

(self-clean type gasket) and comparing their performance to standard oven

performance. These tests were conducted by one of the major range manufacturers.

4.3.2 Payback Associated with Improved Door Seal

Using the energy savings shown above and the price added associated with

incorporating a self-clean door into a standard oven, the payback was estimated in the

range of 13 to 17 years. Table 15 presents the payback findings.

Table 15: Payback for Standard Oven Door Seal Improvement

I*Standard*Oven 774$ .08/kWh $.45/yr 17.2 yr

Stndr Ov$ .1/kWh $.57/yr 13.58 yr

The incremental price of adapting a self-clean door seal to a standard oven was

determined by:

* Averaging the manufacturing cost estimated provided by three major range

manufacturers.

(Average $3.69/door seal system)

* Multiplying the average manufacturer cost increment by 2.1 (i.e., price = 2.1 *

3.69)

Modifications to a standard oven for a self-clean seal include mounting brackets, door

liner (2 pieces), and the new gasket.

49 .%. -- 6W% M& 1.-

4.3.1 Improved Door Seal Efficiency 

The oven efficiency was found to increase by .24 percentage points (i.e., baseline 

efficiency increased 12.15% to 12.39%) when the standard oven gasket was replaced 

with the improved gasket system. As shown below in Table 14, this door seal 

improvement results in 5.68 kWh being saved. 

Table 14: Energy Saving Associated with an Improved Door Seal 

Standard Oven with 

new Door Seal 

• Would raise baseline efficiency of 12.15 to 12.39% 

The .24 percentage points improvement to oven efficiency was detennined by 

conducting efficiency tests on 5 standard ranges modified with the improved seals 

(self-clean type gasket) and comparing their perfonnance to standard oven 

performance. These tests were conducted by one of the major range manufacturers. 

4.3.2 Payback Associated with Improved Door Seal 

Using the energy savings shown above and the price added associated with 

incorporating a self-clean door into a standard oven, the payback was estimated in the 

range of 13 to 17 years. Table 15 presents the payback fmdings. 

Table 15: Payback for Standard Oven Door Seal Improvement 

~~~ 

Standard Oven 

The incremental price of adapting a self-clean door seal to a standard oven was 

detennined by: 

• Averaging the manufacturing cost estimated provided by three major range 

manufacturers. 

(Average $3.69/door seal system) 

• MUltiplying the average manufacturer cost increment - by 2.1 (i.e., price = 2.1 * 

3.69) 

Modifications to a standard oven for a self-clean seal include mounting brackets, door 

liner (2 pieces), and the new gasket. 
4.4 Increased Oven Insulation Design Option

DOE has recommended an increase in cavity insulation of 2 inches, that is, increasing

the insulation wrap around the oven from 2 to 4 inches. While a 2-inch increase

insulation will have a large impact (1.4 percentage points on a 12.15% baseline) on

the oven energy usage it will have a negative effect on the utility of the oven and

range appliances. The current range product is designed around a number of kitchen

constraints which include:

* 30-inch installed width (standard for U.S. kitchens)

* 30-inch countertop height (standard for U.S. kitchens)

* 24-inch deep countertop dimension (standard for U.S. kitchens)

* Zero clearance installation of range (i.e. appliance touching cabinet side walls

and back wall)

* Cooking cavity large enough to accommodate a large turkey roaster pan and an

oven that can cook multiple racks of food

* Need to maintain cool coil cooktop surface of range (at 30-inch level)

* Need to have the oven as high as possible to minimize lifting products to and

from the oven

As a result of these needs, the oven design has evolved to the following:

* 23-inch wide by 16-inch wide, by 18-inch deep cavity

* 2 inches of insulation around cavity

* 3-inch side wall air wipe(needed for zero clearance)

* Y'-inch clearance for construction/installation tolerance (e.g., 29 1⁄22-inch wide

cabinet)

*3-inch space clearance between the top of the oven insulation and range cooktop

surface (Note: 2 inches minimum needed for cold elements/bowls, and 1-inch air

wide needed when all elements and oven are in use)

* 22-inch space across back of oven to provide air wipe cooling and electrical

connections of oven heating elements (bake and broil)

4.4 Increased Oven Insulation Design Option 

DOE has recommended an increase in cavity insulation of 2 inches, that is, increasing 

the insulation wrap around the oven from 2 to 4 inches. While a 2-inch increase 

insulation will have a large impact (1.4 percentage points on a 12.15% baseline) on 

the oven energy usage it will have a negative effect on the utility of the oven and 

range appliances. The current range product is designed around a number of kitchen 

constraints which include: . 

• 

• 

• 

• 

• 

.. 

• 

30-inch installed width (standard for u.s. kitchens) 

30-inch countertop height (standard for U.S. kitch~ns) 

, , 

24-inch deep countertop dimension (standard for U.S .. kitchens) 

Zero clearance installation of range (Le. appliance touching cabinet side walls 

and back wall) 

Cooking cavity large enough to accommodate a large turkey roaster pan and an 

oven that can cook multiple racks of food 

Need to maintain cool coil cooktop surface of range (at 3D-inch level) 

Need to have the oven as high as possible to minimize lifting products to and 

from the oven 

As 'a result of these needs, the oven design has evolved to the following: 

• 23-inch wide by 16-inch wide, by IS-inch deep cavity 

• 2 inches of insulation around cavity 

• ~-inch side wall.air wipe(needed for zero clearance) 

• Vz-inch clearance for construction/installation tolerance (e.g., 29 ~-inch wide 

cabinet) . 

• . 3-inch space clearance between the top of the oven insulation and range cooktop 

surface (Note: 2 inches minimum needed for co'il elementslbowls, and I-inch air 

wide needed when all elements and oven are in use) 

• 2~-inch space across back of oven to provide air wipe cooling and electrical 

connections of oven heating elements (bake and broil) 
Increasing the insulation (2 to 4 inches) thickness would either:

* Increase the size of the overall cabinet

* Reduce the oven cavity volume

Both of these options would impact the utility of the appliance.

Increasing the size of the range to accommodate the additional insulation would

result in a product that could not be retrofitted into existing kitchens (range width

increase from 30 to 34 inches). In addition, the oven cavity would be lowered by

two inches within the range to accommodate the extra top insulation (need 3-inch

space between cooktop and oven insulation liner) thereby making the oven access

more difficult as users would have to lift products from lower elevations. This

additional lifting would be very difficult on the elderly and those who are physically

challenged. Finally, lowering the cavity for the additional roof insulation, and adding

the extra oven floor installation would effectively eliminate the drawer space under

the cavity. This is an important feature for today's ranges and it is a point of product

differentiation.

Taking the approach of reducing the cavity size to accommodate the additional

insulation would have a large impact on cooking utility. For example, reducing the

cavity width from 22 to 23 inches to 18 t_9 inches would eliminate the possibility

of cooking large family dinne.g. 25 lb. turkey, In addition, the much narrower

oven would impact typical two-pan bakormance. In two-pan or sheet-baking

performance, the clearance around the sheets or pans (18- by 132-inch) is needed for

uniform heating/cooking of racks of products. Typical two-pan baking includes

cookies, two large cakes, 4 nine-inch round cakes, pies, and roast with vegetables.

Finally, some current cookware could not be suitable for reduced oven space.

4.4.1 Energy Savings Analysis for Increased Insulation

Our analysis using the oven model agrees with the DOE finding that thicker

insulation (up to 4 inches) can achieve a 1.4 percentage point increase in oven

efficiency, but implementation of this design may affect the utility of the appliance.

Table 16 illustrates the annual energy savings and oven efficiency improvements for

both standard and self-clean electric ovens.

, _U.......% aO M.uN_

Increasing the insulation (2 to 4 inches) thickness would either: 

• Increase the size of the overall cabinet 

• Reduce the oven cavity volume 

Both of these options would impact the utility of the appliance. 

Increasing the size of the range to accommodate the additional insulation would 

result in a product that could not be retrofitted into existing kitchens (range width 

increase from 30 to 34 inches). In addition, the oven cavity would be lowered by 

two inches within the range to accommodate the extra top insulation (need 3-inch 

space between cooktop and oven insulation liner) thereby making the oven access 

more difficult as users would have to lift products from lower elevations. This 

additional lifting would be very difficult on the elderly and those who are physically 

challenged. Finally, lowering the cavity for the additional roof insulation, and adding 

the extra oven floor installation would effectively eliminate the drawer space under 

the cavity. This is an important feature for today's ranges and it isa point of product 

differentiation. . 

Taking the approach of reducing the cavity size to accorrunodate the additional 

insulation would have a large impact on cooking utility. For example, reducing the 

cavity width from 22 to 23 inches to 18 t 19 inches would eliminate the possibility 

of cooking large family dinne e.g. 25 lb. turkey. In addition, the much narrower 

oven would impact typical two-pan g ormance. In two-pan or sheet-baking 

performance, the clearance around the sheets or pans (18- by 13Y2-inch) is needed for 

uniform heating/cooking of racks of products. Typical two-pan baking includes 

cookies, two large cakes, 4 nine-inch round cakes, pies, and roast with vegetables. 

Finally, some current cookware could not be suitable for reduced oven space. 

4.4.1 Energy Savings Analysis for Increased Insulation 

Our analysis using the oven model agrees with the DOE finding that thicker 

insulation (up to 4 inches) can achieve a 1.4 percentage point increase in oven 

efficiency, but implementation of this design may affect the utility of the appliance. 

Table 16 illustrates the annual energy savings and oven efficiency improvements for 

both standard and self-clean electric ovens. 

-
Table 16: Improvement in Oven Efficiency Associated with Added Insulation

Baseline Oven 12.10% 13.90% (2' thick) ,

Added 1 32 InlAdded 10.4% 30.5 35 5 13.5% 15.5% Insulation

Based on annual adjusted cooking energy output (Eco) and. self-clean energy consumption (Esc)

when applicable

To complete the analysis, the baseline oven information was modified to reflect a

thicker insulation with the same thermal conductivity. The analysis indicates that a

thicker insulation reduces steady state heat losses, lowering the oven's energy

consumption. The model also indicates that changes in energy required to heat the

oven cavity are negligible.

4.5 Thermal Mass Design Option

Decreasing the thermal mass will improve the oven efficiency, but reductions in

material thickness are very limited. These limitations are based on:

* An average porcelain thickness is needed for adequate wall coverage.

* Sheet metal thickness reductions are limited by the use of already thin materials

(typical .024 inches).

Porcelain coverage is non-uniform in the oven given the current manufacturing

techniques and the average thickness is established to provide the minimum porcelain

layer for the most difficult to coat areas of the cavity. Sheet metal thickness is close

to minimum given current tooling, existing part designs (e.g. draws) and assembly

techniques. A major range manufacturer estimates that material weight reductions of

1⁄2V lb are possible but they would still require oven redesign (e.g., ribs, door shape)

and new tooling.

The energy savings associated with a VY lb reduction in cavity thermal mass is far

less than the assumptions made by DOE. The energy savings are presented in Table

17. -

Insulation 

Based on annual adjusted cooking energy output (Eco) and. self-clean energy consumption (ESC> 

when applicable 

To compiete the analysis, the baseline oven information was modified to reflect a 

thicker insulation with the same thermal conductivity. The analysis indicates that a 

thicker insulation reduces steady state heat losses, lowering the oven's ~nergy 

consumption. The model also indicates that changes in energy required to ·heat the 

oven cavity are negligible. 

4.5 Thermal Mass Design Option 

Decreasing the thennal mass will improve the oven efficiency, but reductions in 

. material thickness are very limited. These limitations are based on: 

• An average porcelain thickness is needed for adequate wall coverage. 

• Sheet metal thickness reductions are limited by the use of already thin materials 

(typical .024 inches). 

Porcelain coverage is non-unifonn in the oven given the current manufactUring 

techniques and . the average thickness is established to provide the minimum porcelain 

layer· for the most difficult to coat areas of the cavity. Sheet metal thickness is close 

to minimum given current tooling, existing part designs (e.g. draws) and assembly 

techniques. A major range manufacturer estimates that material weight reductions of 

Y2 lb are possible but they would still require oven redesign (e.g., ribs, door shape) 

and new· tooling. . 

The energy savings associated with a ¥lIb reduction in cavity thermal mass is far 

less than the assumptions made by DOE. The energy savings are presented in Table 

.17. • 
Table 17: Potential Energy Saving due to Reduced Mass

Self-Clean 6.4 kWh/yr 1.09 kWh/yr

Standard 6.3 kWh/yr 1 kWh/yr

4.5.1 Reduction in Thermal Mass Analysis

A 1⁄22 to 1 lb reduction in oven cavity thermal mass will reduce oven energy

consumption by 0.35% to 0.70%. Table 18 illustrates the effect on adjusted annual

energy consumption and oven efficiency.

Table 18: The Effect of Reducing Oven Cavity Thermal Mass on Annual Energy

Consumption and Oven Efficiency

h lb .35% 1 1.08 12.14 13.95

1 lb .700% 2 1.8 12.18 14.00

* 1 lb represent much less than 10% of the oven cavity weight (sheet metal and porcelain only)

' Based on annual adjusted cooking energy output (Eco) and self-cleaning energy (Esc) when applicable

The reduced thermal mass decreases the energy required to heat the oven cavity from

ambient temperatures. The effect of a lower thermal mass is negligible at steady

state conditions because the heat loss through the wall is dominated by the resistance

of the insulation surrounding the oven cavity wall.

4.6 Elimination of the Oven Window Design Option

Elimination of the current oven window by definition has a positive energy savings

and a good payback. This option does change the utility of the oven, that is,

consumers currently perceive a major benefit in the window option, and are willing

to pay a premium for this feature. Roughly 70% of all units shipped include a

window. The user will have to change their behavior when using the oven without a

window. In particular, baking will require more user attention as the baked product

(e.g., cake or cookies) nears completion. Rather than quickly inspecting through the

window, the user will have to open the door severaljimes to determine doneness.

4.6.1 Energy Savings Analysis for Window Elimination

Our analysis indicates that the amount of energy saved relative to window

elimination is about half that reported by DOE (5 kWh/yr as compared to 10

kWh/yr). This decrease in oven efficiency is due to several door openings per cycle.

M% .%- -. WPR M M.q~N

Table 17: Potential Energy Saving due to Reduced Mass 

--

4.5.1 Reduction in Thermal Mass Analysis 

A Yz to I lb reduction in oven cavity thennal mass will reduce oven energy 

consumption by 0.35% to 0.70%. Table 18 illustrates the effect on adjusted annual 

energy consumption and oven efficiency. 

Table 18: The Effect of Reducing Oven cavity Thermal Mass on Annual Energy 

Consumption and Oven Efficiency 

• 1 Ib represent much less than 10% of the oven cavity weight (sheet metal and porcelain only) 

•• Based on annual adjusted cooking energy output (Eco). and self-cleaning energy (Esc) when applicable 

The reduced thennal mass decreases the energy required to heat the oven cavity from 

ambient temperatures. The effect of a lower thennal mass is negligible at steady 

state conditions because the heat loss through the wall is dominated by the resistance 

of the insulation surrounding the oven cavity wall. 

4.6 Elimination of the Oven Window Design Option 

Elimination of the current oven window by definition has a positive energy savings 

and a good payback. This option does change the utility of the oven, that is, 

consumers currently perceive a major benefit in the window option, and are willing 

to pay a premium for this feature. Roughly 70% of all units shipped include a 

window. The user will have to change their behavior when using the oven without a 

window. In particular, baking will require more user attention as the baked product 

(e.g., cake or cookies) nears completion. Rather than quickly inspecting through the 

. window, the user will have to open the door severaJ.times to determine doneness. 

4.6.1 Energy Savings Analysis for Window Elimination 

Our analysis indicates that the amount of energy saved relative to window 

elimination is about half that reported by DOE (5 kWhlyr as compared to 10 

kWh/yr). This decrease in oven efficiency is due to several door openings per cycle. 
Our analysis assumes three product examinations per cook cycle. For some products

where proper finishing is difficult, the number of door openings may be greater.

This suggests that the efficiency impact at best is a .25 percentage point increase and

not the .48% to .55% projected by DOE.

Eliminating an oven door window reduces the input energy requirements for. cooking

by approximately 3% as determined through modelling the oven. This reduction in

energy consumption increases the oven efficiency from 12.10% to 12.47% for

standard electric oven and from 13.9% to 14.33% for a self-clean electric (Table 19).

Table 19: Effects of Reducing or Eliminating a Door Window on a Self-Clean Electric

Oven Energy Consumption

Y2 window 1.6% 4.7 5.0 12.30% 14.12%

No window 3.1% 9.1 9.7 12.49% 14.35%

* Based on adjusted cooking energy output (Eco) and self-cleaning energy (Esc) when applicable

The elimination of the window saves approximately 9.7 kWh per year for a self-clean

oven. However, these values assume no door opening.

To determine the effect of door openings or energy savings, the actual energy saved

per cycle must be calculated. The number of cooking cycles can be estimated to be

about 264 by using the following information:

* Adjusted annual DOE cooking energy for self-clean electric: 255 kWh

* 13.9% cooking efficiency

* The DOE established test method for heating an 8.5-lb aluminum block which

requires about 457.5 Btu to reach 305T' from 77°F

* Only cooking energy was considered since the oven door cannot be opened

during self-clean

Each cooking cycle used about .964 kWh which results in approximately 30 watt hrs

(102 Btus) saved per cycle when the window is eliminated,

To determine how much energy is lost by opening the oven door, all of the oven air

is assumed to be replaced by ambient air. This results in about 16 Btu heat loss per

door opening for the model oven.

_ . _

Our analysis assumes three product examinations per cook cycle. For some products 

.where proper finishing is difficult, the number of door openings may be greater. 

ntis suggests that the efficiency impact·at best is a .25 percentage point increase and 

not the .48% to .55% projected by DOE. . 

Eliminating an oven door window reduces ·the input energy requirements for. cooking 

. by approximately 3% as determined through modelling the oven. This reduction in 

energy consumption increases the oven efficiency from 12.10% to 12.47% for 

standard electric oven and from 13.9% to 14.33% for a self-clean electric (Table 19). 

Table 19: Effects of Reducing or Eliminating a Door WIndow on a Self-Clean Electric 

Oven Energy Consumption 

• Based on adjusted cooking energy output (Eco) and self-cleaning energy (EscJ when applicable 

The elimination of the window saves approximately 9.7 kWh per year for a self-clean 

oven. However, these values assume no door opening. 

To determine the effect of door openings or energy savings, the actual energy saved 

per cycle must be calculated. The number of cooking cycles can be estimated to be 

about 264 by using the following infonnation: . 

• Adjusted annual DOE cooking energy for self-clean electric: 255 kWh 

• 13.9% cooking efficiency 

• The DOE established test method for heating an 8.5-1b aluminum block which 

requires about 457.5 Btu to reach 305"F from 77°F 

• Only cooking energy was considered since the oven door cannot be opened 

during self-clean . 

Each cooking cycle used about .964 kWh which res\llts in approximately 30 watt hrs 

(102 B,tus) saved per cycle when the window is eliminated: 

To determine h~w much energy is lost by opening the oven door, all of the oven air 

is assumed to be replaced by ambient air. This results in about 16 Btu heat loss per 

door opening for the model oven. 
Table 20 shows that the actual annual energy savings for a self-clean oven may be

reduced to about 7.0 kWh when 3 door openings occur per cooking cycle because the

window is eliminated.

Table 20: Actual Annual Energy Savings and Oven Efficiency When the Door Window Is

Eliminated and 3 Extra Door Openings Occur

-No window 5.0 9.7 .014 264 3.7 6.0 12.15% 1417%

5.0 Coil Cooktop Design Option Review

5.1 Improved Contact Conductance Design Option for Electric Coil Cooktop

DOE has recommended that improved contact conductance for electric cooktops

would increase the coil cooktop efficiency from DOE's baseline of 77.2% to 80.5%.

The potential for achieving this large improvement was investigated as part of this

program. Findings indicate that little real efficiency improvement is possible.

These test findings were based on cooking experiments (using the Uniform Test

Procedure) and not the DOE block test which is not suitable for measuring this

effect.

5.1.1 Effect of Surface Contact Resistance on Range-Top Efficiency

The effect of contact resistance on range-top efficiency was evaluated by performing

heat transfer calculations and conducting tests using the Uniform Test Procedure for

commercial range-tops.

Residential range-tops are manufactured with a flatness of approximately ±.005

inches. The degree of contact with the cooking surface varies with flatness and

roughness of the cooking utensil (pot or pan). As part of this program, a range of

"contact" conditions were considered on several tests boiling pasta. Findings include:

* The steady state efficiency of the cooktop is 95.0%.

* Increasing the contact pressure between the pot and coil by a factor of nearly

four has no impact- on steady state efficiency.

* If the pot/coil interface is not flat (e.g., small gap of .01 inches), the efficiency

drops to below 70%.

4 _^-.L.. W% a !bAl

Table 20 shows that the actual annual energy savings for a self-clean oven may be 

reduced to about 7.0 kWh when 3 door openings occur per cooking cycle because the 

window is eliminated. 

Table 20: Actual Annual Energy Savings and Oven Efficiency When the Door WIndow Is 

Eliminated and 3 Extra Door Openings Occur 

5.0 Coil Cooktop Design Option Review 

5.1 Improved Contact Conductance Design Option for Electric Coil Cooktop 

DOE has recommended that improved contact conductance for electric cooktops 

would increase the coil cooktop efficiency from DOE's baseline of 77.2% to 80.5%. 

The potential for achieving this large improvement was investigated as part of this 

program. Findings indicate that little real efficiency improvement is possible. 

These test findings were based on cooking experiments (using the Unifonn Test 

Procedure) and not the DOE block test which is not suitable for measuring this 

effect. 

5.1.1 Effect of Surface Contact Resistance on Range-Top Efficiency 

The effect of contact resistance on range-top efficiency was evaluated by perfonning 

heat transfer calculations and conducting tests using the Unifonn Test Procedure for 

commercial range-tops. 

Residential range-tops are manufactured with a flatness of approximately ±.OO5 

inches. The" degree of contact with the cooking surface varies with flatness and 

roughness of the cooking utensil (pot or pan). As part of this program. a range of 

"contact" conditions were considered on several tests boiling pasta. Fmdings include: 

• The steady state efficiency of the cooktop is 95.0%. 

- • Increasing the contact pressure betw~en the pot and coil by a factor of nearly 

four has nO'impact on steady state efficiency. 

• If the pot/coil interface is not flat (e.g., small gap of .01 inches), the efficiency 

drops to below 70%. 
5.1.2 Conductance Analysis

A simple heat transfer model was used to estimate the importance of contact

resistance in range-top coils. In this analysis, an aluminum pot containing boiling

water was considered with the following assumed values:

Pot thickness .125 in.

Inside pot surface temperature 212'F

Burner temperature 1400°F

Pot emissivty .6

Range-top emissivity .9

Contact resistance .002 hr. ft. °F/Btu

The contact resistance was taken from the G.E. Handbook for contact between two

milled surfaces of steel and aluminum. Three situations were modeled.

I) The coil transfers heat to the pot by radiation exchange with the burner top

surface only. This assumes a non-conducting medium between the coil and the

pot. Reflection and emission from the burner pan under the heating element is

small and not included.

2) The burner transfers heat to the pot by conduction only with the above assumed

value for contact resistance. Data from G.E. shows strong correlation of contact

pressure and heat transfer conductance.

3) The coil transfers heat by radiation and conduction with the above assumed valve

for contact resistance.

The analytical results are given in Table 21. The model indicates that the conduction

through the gap dominates radiation by a factor of approximately 50. The results of

Situation 3 above, the most realistic, also demonstrates that radiation has a small

influence compared to conduction. In addition, contact pressure is the dominate

parameter in both contact resistance and forcing the pot and coil to conform to each

other.

It _ _ .

5.1.2 Conductance 'Analysis 

A simple heat transfer model was used to estimate the importance of contact 

resistance in range-top coils. [n this analysis, aD aluminum. pot containing boiling 

water was considered with the following assumed values: 

Pot thickness .125 in. 

Inside pot surface temperature 212°P 

Burner temperature 14000

P 

Pot emissivty .6 

Range-top emissivity .9 . 

Contact resistance .002 hr. ft. °PlBtu 

The contact resistance was taken from the G.E. Handbook for contact between two 

milled surfaces of steel and aluminum. Three situations were modeled. 

l) The coil transfers heat to the pot by radiation exchange with the burner top 

surface only. This assumes a non-conducting'medium between the coil and the, 

pot. Reflection and emission from the burner pan under the heating element "is 

small and not included. 

2:) The burner transfers heat to the pot by conduction only with the above assumed 

value for con~ct resistanc~. Data from G .E. s~ows strong correlation of contact 

pressure and heat transfer conductance. . 

3) The coil transfers heat by radiation and conduction with the above assumed valve 

for contact resistance. 

11le,analytical results are given in· Table 21.' The model indicates that the conduction 

tltrough the gap dominates' radiation by a factor of approximately 50. The results of 

Situation 3 above, the most realistic, also demonstrates that radiation has a small 

influence compared to conduction. In addition, contact pressure is the dominate 

parameter in both contact resistance and forcing th~ pot and coil" to confonn to each 

other. 

-
Table 21: Analytical Heat Transfer Results

:ii (Atfl .. .

1 Radiation heat transfer only between coil 1.3 X 104

top surface and pot .x10

2 Conduction heat transfer only via contact 75

resistance between coil and pot

3 Conduction and radiation heat transfer 105

between coil and pot

5.2 Impact of Contact Conductance on Coil Efficiency - Testing

The experimental investigation involved an efficiency test on a residential range-top

and used the proposed uniform test procedure (UTP) for commercial range-tops.

The range-top coil element tested was a typical 8-inch coil top and tests were

performed with the coil on "high." New 12-inch diameter aluminum pots with lids

and containing 20 Ibs. of water were used per the UTP specification. The system

was stabilized by heating one pot for 30 minutes. Next,. a test pot was placed on the

burner with the water initially at room temperature (approximately 70F). A watt

hour meter measured the electrical energy required to raise the water to

approximately 200°F. A thermocouple centered in the water was used to determine

the energy transferred. Four different tests were completed.

1) A base test was completed with 20 lbs, of water and the lid positioned normally.

2) Contact resistance was then increased by placing a weight of approximately 68

lbs. on the top of the lid, increasing the pressure on the coil by a factor of 3.8.

3) The effect of a tighter lid produced in condition 2 above was investigated by

clamping the lid closed and running the test. The weight of the clamps were

negligible.

4) A space was provided between the coil and the pot to evaluate the overall effect

of the situation where the coil or pot was not flat.

All four tests outlined above were completed twice and the results are shown in

Table 22.

As indicated, efficiency results for the pot in contact with the coil are essentially the

same regardless of contact pressure. An increase in contact pressure by a factor of

almost 4 had no noticeable effect. As demonstrated in the analytical results,

conduction via physical contact with the pot is the major mechanism for heat transfer.

a u~mqWE !JXu

Table 21: Analytical Heat Transfer Results 

2 

3 

Radiation heat transfer only between coil 

top surface and pot 

Conduction heat transfer only via contact 

resistance between coil and pot 

Conduction and radiation heat transfer 

between coil and pot 

5.2 Impact of Contact Conductance on Coil Efficiency - Testing 

1.13 X 104 

5.75 X 105 

5.85 X 105 

The experimental investigation involved an efficiency test on a residential range-top 

and used the proposed uniform test procedure (UTP) for commercial range-tops. 

The range-top coil element tested was a typical 8-inch coil top and tests were 

performed with the coil on "high." New 12-inch diameter alwninum pots with lids 

and containing 20 lbs. of water were used per the UTP specification. The system 

was stabilized by heating one pot for 30 minutes. Next" a test pot was placed on the 

burner with the water initially at room temperature (approximately 70"F). A watt 

hour meter measured the electrical energy required to raise the water to 

approximately 200°F. A thermocouple centered in the water was used to determine 

the energy transferred. Four different tests were completed. 

1) A base test was completed with 20 lbsl of water and the lid positioned normally. 

2) Contact resistance was then increased by placing a weight of approximately 68 

Ibs. on the top of the lid, increasing the pressure on the coil by a factor of 3.8. 

3) The effect of a tighter lid produced in condition 2 above was investigated by 

clamping the lid closed and I1:!.nning the test. The weight of the clamps were 

negligible. 

4) A space was provided between the coil and the pot to evaluate the overall effect 

of the situation where the coil or pot was not flat. 

All four tests outlined above were completed twice and the results are shown in 

Table 22. 

- As indicated, efficiency results for the pot in contact with the coil are essentially the 

same regardless of contact pressure. An increase in contact pressure by a factor of 

almost 4 had no noticeable effect. As demonstrated in the analytical results, 

conduction via physical contact with the pot is the major mechanism for heat transfer . 

• 
Table 22: Range-Top Efficiency Using UTP Protocol

;.. X ,*^.* *w^.,<:.**^ 'Stest~ IX fIM

Impact on Efficiency 14-quart pot with 20 Ib. water and lid 94.8 95.1

of Increased Same case as 1 with 68.5 lb. weight added 9

Conductance to95.0 94.7

Same case as 1 with clamped lid 94.9 96.5 Impact on Efficiency if

the Pot and Coil are Same case as 1 with air spacing between

Not in Good Contact - pot and burner

Small Gap Test 1: .057 in.

Test 2: .013 in.

_ . ._ _

Table 22: Range-Top Efficiency Using UTP Protocol 

Impact on Efficiency 

of Increased 

Conductance 

14-quart pot with 20 ·Ib. water and lid 

Same case as 1 with 68.5 lb. weight added 

to lid 

94.8 95.1 

95.0 94.7 

.Same case as 1 with clamped lid 96.5 

Impact on Efficiency if r----------------+------+----___ the Pot and Coil are Same case as 1 with air spacing between 

Not in Good Contact - pot and bumer . 

Small Gap Test 1: .057 in. 61.2 66.0 

Test 2: .013 in. 
Appendix A

Estimation of Manufacturing Cost to Retail Pricing Multiplier

The DOE analysis for estimating manufacturing cost to retail cost had a net result of

producing a multiplier in the range of 2.16 to 3.01. We used a conservative value of

2.1 in our analysis. This multiplier represents the various mark-ups that occur after

manufacturing or

Approximate Retail Cost = (K) Manufacturing Cost

where K = Mark-up Factor

Table A-1 presents the DOE data relative to estimated manufacturing costs and retail

options for electric oven and cooktop designs.

Table A-1: Manufacturing Cost Multiplier

Coil Element 2 $2.28. $4.79 2.1

Standard Oven 4 $19.11 $41.30 2.16

Self-Clean Oven 4 $18.44 $55.51 3.01

* = difference between level (2 or 4)

A Retail

A Cost

^Am -»> - , 1 SN *-n _W

Appendix A 

Estimation of Manufacturing Cost to Retail Pricing Multiplier 

The DOE analysis for estimating manufacturing cost to retail cost had a net result of 

producing a multiplier in the range of 2.16 to 3.01. We used a conservative value of 

2.1 in our analysis. This multiplier represents the various mark-ups that occur after 

manufacturing or 

Approximate Retail Cost = (K) Manufacturing Cost 

where K = Mark-up Factor 

Table A~1 presents the DOE data relative to estimated manufacturing costs and retail 

options for electric oven and cooktop designs. 

Table A-1: Manufacturing Cost Multiplier 

• £\ = difference between level (2 or 4) 

-K= A Retail 

11 Cost 

-
Appendix B

Oven Analysis

An oven analysis was conducted using Arthur D. Little's Transient Thermal Analysis

program and an oven model capable of investigating design changes. Modifications

such as eliminating the viewing window, reflective interior surfaces, improved

insulation and convection cooking were analyzed using this process to identify

changes in cooking energy requirements and cooking efficiency.

Description of the Transient Thermal Analysis Program

Arthur D. Little developed the Transient Thermal Analysis Program (TTA) for the Jet

Propulsion Laboratory in August 1963 [Reference 1]. This program numerically

solves the equations which are used to describe the thermal behavior of a physical

system. TTA is a FORTRAN program which is designed to solve differential

equations which arise in heat transfer problems involving conduction, radiation and

convection. TTA uses a finite difference solver with a Newton - Raphson iterative

process to solve the radiation terms.

Thermal characteristics, such as conductivities, convective heat transfer coefficients,

radiative view factors and emissivities, and geometry are input required to model the

thermal behavior of a physical system. TTA can model both transient and steady

state behavior of a system.

Oven Model

Using TTA, a thermal model of an average residential oven (Figure 1) has been

developed to analyze the impact of various energy saving design recommendations

made in the DOE Energy Conservation Program for Consumer Products: Proposed

Rule dated March 4, 1994. The baseline model consists of 10 nodes (Figure 2):

1. Ambient air

2. Oven cavity air

3. Top inside wall

4. Bottom inside wall

5. Right inside wall

6. Back inside wall

7. Left inside wall

8. Door - front- inside wall

9. Glass - front inside wall

10. Heat source

Appendix B 

Oven Analysis 

An oven analysis was conducted using Arthur D. Little's Transient Thennal Analysis 

program and an oven model capable of investigatmg design changes. Modifications' 

such as eliminating the viewing window, reflective interior surfaces, improved 

insulation and convection cooking were analyzed using this process to identify 

changes in cooking energy'requirements and cooking efficiency. 

Description of the Transient Thermal At:lalysis Program 

Arthur D. Little developed the Transient Thermal Analysis Program ('ITA) for the Jet 

Propulsion Laboratory in August 1963 [Referen~ I]. This program numencally 

solves the equations which are used to describe the thermal behavior, of a physical 

system. TT A isa FORTRAN program which is designed to solve differential 

equations which arise in heat transfer problems involving conduction, radiation and 

convection. ITA uses a finite difference solver with a Newton' - Raphson iterative 

process to solve the radiation terms. 

Thennal characteristics, such as conductivities, convective heat transfer coefficients, 

radiative view factors and emissivities, and geometry are input required to model the 

thennal behavior of a pi:lysical system. ITA can model both transient and' steady 

, ,state ,behavior of a system. 

Oven Model 

Using 'IT A, a thennal model of an average residential oven (Figure 1) has been 

developed to analyze the impact of various energy saving design recommendations 

made in the DOE Energy Conservation Program for Consumer Products: Proposed 

Rulie dated March 4, 1994. The baseline model consists of 10 nodes (Figure 2): 

1. Ambient air 

2. Oven cavity air 

3. Top inside wall 

4. Bottom inside wall 

5. Right inside wall 

6. Back inside wall 

7. Left inside wall 

8. Door - front- inside wall 

9. Glass - front inside wall 

10. Heat source 
15.5" 5.5"

15"

22"

Steel .029" Insulation 2" Glass .065" Air .5"

Porcelain .00675" Steel Glass .065"

Inside Wall Inside Wall

Figure B-1: Average Residential Oven Characteristics

The relationships between nodes and critical model assumptions can be summarized

as follows:

* Convection occurs between oven cavity air and the heating element and walls.

* Heating element radiates to oven walls, top and tottom surfaces.

* Conduction/convection occurs between the walls and the ambient air.

* Ambient air is at a fixed temperature.

* Heating element source is at a fixed temperature.

Am -_ n -- , W^% 0J B M

15.5" 5.5" 

Steel.029" 

Porcelain .00675" 

Inside Wall 

22" 

~Insulation 2" 

of • Steel 

Rgure 8-1: Average Residential Oven Characteristics 

Glass .065" 

Inside Wall 

.5" 

Glass .065" 

The relationships between nodes and critical model assumptions can be summarized 

as follows: 

• Convection occurs between oven cavity air and the heating element and walls. 

• Heating element radiates to oven walls, top and nottom surfaces. 

• Conduction/convection occurs between the walls and the ambient air. 

• Ambient air is at a fixed temperature. 

• Heating element source is at a fixed temperature. 
*

-8

3

7

/0I.I ___ : . . . * . / ---. i .--- ------------------ ------------- ". "" , 9 ..

4i -

10 -' , , ' * .. 

Rgure B-2: Transient Thermal Analysis Oven Model

These relationships were used to write the equations to describe the heat transfer

between nodes. To write these equations, conduction, convection, radiation and heat

generation coefficients were defined. Table B-1 lists thermal conductivities that were

assumed for the conduction calculations in the oven model:

Table B-1: Wall Materials Properties Used In Baseline Oven Design to Calculate

Conduction Heat Transfer Parameters

rorcela i4i .uo o .o I 1oU

Sheet Metal: .028- 25.0 490

Insulation 2 . .021 1.09

Glass .062 .70 165 Inuato 2 0110

3 

7 

6 

10 

4 

.. -.. ------_ ...................... _ ............................ -_ ................ --_ .. ---_ ........ -_ .......... -_ .. .. . ', .... : 

, 

.. ''' " , . " .,' , /" , , , 

.... , .. ,'" :_, , " ,," .. ~ .... ~."....... ,,-,' ... -' 

" ~ 

'" ... '--;-'-+-- 8 

.. ' ... ","'i 

r---"";""-+-5 

---,---+- 9 

....................... -_..... -_ ............... -_ ............... --- _ ... __ .... -------- _ ... _--------... ---... -..... -----

Figure B-2: Transierrt Thermal Analysis Oven Model 

These relationships were used to write the equations to describe the heat transfer 

between nodes. To write these equations, conduction, convection, radiation and heat 

generation coefficients were defined. Table B-1 lists thennal conductivities that were 

assumed for the conduction calculations in the oven model: 

'Table B-1: Wall Materials Properties US,ed In Baseline Oven DeSign to calculate 

Conduction Heat Transierparameters 

-
The basic equations used to calculate the convective heat transfer coefficients

included:

NM QwhcL C(GrPr)M K

Gr - Grashof number 2(Tw- T)L v 2

where:

Pr = Prandtl number

L = characteristic length, ft

g = 32.2 ft/s2

= 1/Tf, 1/R

Tw = wall temperature, F

T = oven temperature, F

v = kinematic viscosity, ft2/sec

Tf = film temperature, F (average of wall and oven air temperatures)

h = convective heat transfer coefficient Btu/(hr ft2 °F)

k = thermal conductivity Btu/(hr - ft °F)

The variables c and m are dependent on the orientation of the wall to the oven air.

Table B-2 details the values of c and m used in the oven model.

Table B-2: Definitions of Variables Used in Convection Calculations

X A XTop .14 .333 .27 .25

Bottom .77 .25 .14 .333

Sides .555 .25 .555 .25

Back .555 .25 .555 .25

Front - Wall .555 .25 .555 .25

Front - Glass .555 .25 .555 .25

Heating Element .53 .25 -

_ _ _ ,

• 

The basic equations used to calculate the convective heat transfer coefficients 

included: 

hcL M NJl : C(GrPr) K 

Gr: Grashof number: 2~ (Tw- T) L 3 

v2 

where: 

Pr = Prandtl number 

L = characteristic length. ft 

g = 32.2 ftfs2 

~ = lfTf. IIR 

T w = wall temperature. F 

T = oven temperature. F 

v = kinematic viscosity. ft2/sec 

Tf = film temperature. F (average of wall and oven air temperatures) 

he = convective heat transfer coefficient Btul(hr rt2 oF) . 

k = thennal conductivity Btul(hr - ft oF) 

The variables c and m are dependent on the orientation of the wall to the oven air. 

Table B-2 details the values of c and m used in the oven model. 

Table 8-2: Definitions of Variables Used In Convection calculations 
The main parameters required for the radiation terms include the surface emissivity

and the surface view factors. The view factors which describe the interaction of

radiation energy between two surfaces were calculated from data presented in

References 2 and 3. The emissivity of porcelain was assumed to be .92.

The parameters for conduction, convection and radiation were determined to describe

the interrelationships of nodes in the oven model and listed above. These values

were used as inputs in TTA to solve the steady state and transient analyses.

All design options were compared at ambient temperatures of 80°F and an oven set

point temperature of 350°F. For steady state runs the heating element surface

temperature was varied until the oven set point temperature was reached. The

relative change in heat loss is an indication of the energy savings once the oven has

reached steady state conditions.

The model was run in a transient mode to determine the effects of design options on

heat up time. The percentage change in heat up time is an indication of the reduction

in heat required to reach the set point temperature. In these runs, the heat source

temperature was varied for each design option to maintain a constant heat input rate.

To transform the steady state energy loss savings and the reduction in heat up time

into actual annual energy savings, the relationship between each of these savings to

total energy consumed in a cooking cycle must be understood. The cooking cycle

energy consumption is made of three components: energy required to preheat theoven, steady state heat losses and energy absorbed by the cooking food. To estimate

the energy required for a cooking cycle, information published by the DOE was

utilized. The DOE estimates that approximately 293 kWh per year (adjusted DOE

values) are used for oven cooking in a home. Considering the DOE test procedure

for heating an 8.5 lb aluminum block to 325°F (requires 457.5 Btus) and an oven

cooking efficiency of 12.10% for a conventional electric oven, the amount of cooking

cycles per year can be estimated to be approximately 264 (standard electric oven).

,The average per cycle energy consumption is about 3781 Btus or 1108 watt-hrs.

To determine the approximate energy required for heat up, a conventional electric

oven, was operated to a 350°F oven set point temperature. A watt-hr meter was used

to record input power during the heat up period. The heat up time was determined to

be under 7 minutes with approximately 890 Btus required to heat the oven thermal

mass.

Table B-3 illustrates the energy breakdown for a typical electric oven. This

information is used to help calculate annual cooking energy savings from oven

efficiency improvements identified in steady state and transient oven model analyses.

The main parameters required for the radiation terms include the surface emissivity 

and the surface view factors. The view factors which describe the interaction of 

radiation energy between two surfaces were. calculated from data presented in 

References 2 and 3. The emissivity of porcelain waS assumed to be .92. . 

. . 

The parameters for conduction, convection and radiation were determined to describe 

the interrelationships of nodes in the oven model and listed above. These values 

. were used as inputs in TT A to solve the steady state aI,ld transient analyses. 

. . 

All design' options were compared at ambient temperatures. of 80°F and an oven set 

point temperature of 350°F. For steady state runs the heating element surface . 

temperature. was varied until the oven set point temperature was reached .. The 

relative change in heat loss is an indication of the energy savings once the oven has 

reached steady state conditions. 

The model was run in a transient mode to determine the effects of design options on 

heat up time. The percentage change in' heat up time is.an indication of the reduction 

i~ heat required to reach the set point temperature. In these runs, the heat source. 

temperature was varied for each design option to maintain a constant heat input rate. 

To transform the steady 'state energy loss savings and the reduction in heat up time· 

into actual annual energy savings~ the relationship between each of these savings to 

total energy consumed in a cooking cycle must be understood. The cooking cycle 

energy consuIl}.ption is made of three components: energy required to preheat the' 

oven, steady state heat .losses and energy absorbed by the cooking food. To estimate 

the energy required for' a cooking cycle. infonnation published by the DOE was 

utilized. The DOE estimates that approximately 293 kWh per year (adjusted DOE 

vallues) are used for oven cooking in a home. Considering the DOE test .procedure 

for heating an 8.5 lb aluminum block to 325~F (requires 45i.5 Btus) and an oven 

cOoking efficiency of 12.10% for a conventional electric oven, .the amount of cooking 

cycles per year can be estimated to be approximately 264 (standard electric oven). 

,The average per cycle energy consumption is about 3781 Btus or 11 08 watt-hrs . 

. To determine the approximate energy required for heat up, a conventional electric 

oven, w~ operated to a 350°F oven set point temperature. A watt~hr meter was used 

to record input power during the heat up period. The heat up time was detennined to 

be under 7 minutes with approximately 890 Btus required to heat the oven thermal 

mass. 

Table B-3 illustrates the energy breakdown for a typical electric oven. This 

information is used to help calculate annual cooking energy savings from oven 

efficiency improvements identified in steady state and transient oven model analyses. 
Table B-3: Breakdown of Energy Requirements for a Cooking Cycle

.:i~- . C!: o'ing '' ':%t t e:": : : .... 

Energy, Btus 890 2433 458 3781

Percentage 123.5% 64.4% 12.1% 100%

References:

1. Arthur D. Little, Inc., 'Description of a Transient Thermal Analysis Program,' report to Jet Propulsion

Laboratory, February 1967.

2. Kreish, Frank, Principles of Heat Transfer, 3rd Edition

3. Holman, J. P., Heat Tranfer, 5th Edition.

- -. * _ . _

Table B-3: Breakdown of Energy Requirements for a Cooking Cycle 

References: 

1. Arthur D. Little, Inc., "Description of a Transient Thermal Analysis Program: report to Jet Propulsion 

Laboratory, February 1967. 

2. Kreish, Frank, Principles of Heat Transfer, 3rd Edition 

3. Holman, J. P., Heat Tranfer, 5th Edition. 

-
Engineering Sciences

Fax Transmittal Form

To: Brooke Stauffer

AHAM

Regulatory Affairs

From: David Mallory

ARTHUR D. LUTrLE, INC.

20 Acorn Park, Room 20/533

Cambridge, MA 02140-2390

Tel!

Return FAX:

Fax No: 1-202-434.7400

Date: July 18, 1994

Pages (including this one): 1

617498-5856

617/498-7206

Message:

Dear Mr. Stauffer

I am sending the information you requested from Ariene Marge on annual useful cooking

energy output for electric ovens and cooktops, see Table 1.

Table 1 Annual Useful Cooking Energy Output For Electric Ovens And Cooktops

DOE Values Modified Values

Ovens 1 35.5 kWh/yr 26.6 kWhtyr

Cooktops 209.4 kWh/yr 157.0 IWh/yr

The modified annual energy usage values detailed in ADL's report where based on recent

metered studies that indicated the adjusted DOE values where approximately 25% too high.

This ratio was also applied to the annual useful cooking energy output for electric ovens and

cooktops to determine the values in Table 1.

If you any questions on the information, please do no hesitate to call.

Helping create the right product t the right time

Artlur P LIle

Engineering Science. 

Fax Transmittal Form 

TO: Brooke Stautter 

AHAM 

FIX No: 1-202-434-7400 

RegulatDry Affairs 

From: David Mallory . Date: ~uly 18.1994 

ARTHUR D. U1TLE, INC.' 

20 Acom Park, Room 201533 

Cambridge, MA 02140-2380 

Pages (Including this one): 1 

Tel: 617/498-5856 

Return FAX: ·617/498-7'208 

Message: 

Dear Mr. Stauffer: 

I am sending the information yOU requested from Arlene Marge ot:' annual useful cooking 

energy output for electric ovens and cooktops, see Table 1. 

Table 1 Annual Useful Cooking Energy Output For Electric Ovens And Cooktops 

DOE Values Modified Value,s 

Ovens 3S.~ kWhlyr 26.6 kWhlyr 

Cooktops 209.4 kWhlyr 157.0 WoIhJyr 

The modified annual energy usage vaJues detailed in ADl's report where based on recent 

metered studies that Indicated the, adjusted DOE values where approximately 25% too high. 

ThIs ratio was also apptied to the annual useful cooking energy output for electric ovens and 

cooktops to determine the values in Table 1. ' 

If you any questions on the information, please do no hesitate to call. 

Helping create the right product at 'the right time 

ArthIr P 'Little