## 626O9&/ L/~



## Electric Oven and Cooktop Data Analysis

Preparedfor Association of Home Appliance Manufacturers July 15, 1994

Arthur D.Little, Inc. Acorn Park Cambridge, Massachusetts 02140-2390 

# v //

Anr I ''t.



## Electric Oven and Cooktop Data 

## Analysis·

Prepared for Association of Home Appliance 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 ofthe Modified (Reduced) Range Energy Usage
........ 4 3.0 Review ofDOE Baseline Efficiency Assumptions forElectric Ovens and Cooktops ................................................ 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 ofForced 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 ofReflective Coating on Oven Utility
............. : 11 4.2.2 Impact ofReflective 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 ofthe 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 ofSurface Contact Resistance on Range-Top Efficiency 24 5.1.2 Conductance Analysis
................... ........... 25 5.2 Impact ofContact Conductance on Coil Efficiency

- Testing ......... 26 Appendix A
.............................................. A-1 Appendix B
................... .... ....................... B-l Table of Contents
1.0 Background


### . ,," .................................................................................. .. 2.0 Review ofBaseline DOEAnnual Energy Consumption for Electric Ovens and Cooktops '
........................................... . 2.1 Implications ofthe Modified (Reduced) Range Energy Usage
....... . 3.0 Review ofDOE 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 ofForced 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 ofReflective Coating on Oven Utility
............. : 11 4.2.2 Impact ofReflective Coatings on Oven Efficiency
.......... 12 4.2.3 Reflective SurfaceEfficiency 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 DoorSeal for StandardElectric 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 ofthe OvenWindow 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 ofSurface ContactResistance on Range-Top Efficiency
. 24 5.1.2 Conductance Analysis
.............................. 25 5.2 Impact ofContact Conductance on CoilEfficiency

- Testing.
. . . . . . .. 26 

# - Appendix A A-I Appendix B B-1

### 1.0 Background The objective ofthis study is to develop technical information forthe Association of Home Appliance Manufacturers (AHAM) relative to DOE rule making forelectric ovens and cooktops. AHAM will incorporate these data into their response to DOE. The DOE has recommended a series ofdesign options to improve the efficiency of electric ovens and cooktops. These recommendations were discussed in the March 4, 1994 Notice ofProposed Rulemaking (10 CFR Part 430). The proposed efficiency levels for electric ovens would have adramatic effect on both product price and functionality. The proposed electric oven design options are: Electric Oven, Non-Self-Cleaning
0 Baseline 1 0 +Remove DoorWindow 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 DoorWindow 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 forelectric ovens by DOE. I. .. ," , "..'l''"."'--:" 1.0 Background The objective ofthis study is to develop technicaI infonnation for the Association of Home Appliance Manufacturers (AHAM) relative to DOErule making for electric ovens and cooktops. AHAM will incorporate these data into their response to DOE. The DOE has recommended a series ofdesign options to improve the efficiency of electric ovens and cooktops. These recommendations were discussed in the March 4, 1994 Notice ofProposed 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:

ElectricCooktop, 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 

### DOEhas selected level 2 forelectric cooktops. Our findings are reported as follows: 2.0 Review ofBaseline DOE Annual Energy Consumption forElectric Ovens and Cooktops 3.0 Review ofBaseline DOE Efficiency Assumptions forElectric 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 ElectricOvens 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 onrecent metered studies are presented in Table 1. Table 1: DOE ElectricOven 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 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 ofBaseline DOEAnnual Energy Consumption for Electric Ovens and Cooktops 3.0 Review ofBaseline 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 Consumptionfor 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 DOEand a modified set ofenergy usage data based onrecent 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 toearlier assumptions) annual usage based on a review ofstudies that examined range electric energy requirements. Using the five metered studies from this review DOE determined an average consumption of605.1 kWh/yr which they used to develop theirenergy usage profile. This average range energy was then partitioned into oven and cooktop usages based on several factors including sales ofrange 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 of617 kWh/yr. The DOE energy values were based in part on metered studies that were morethan 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 bythe DOE. The modified set ofelectric range energy is recommended. The modified energy valuespresented inTable 1were obtained by: * Averaging the results of3recent metered studies (1988 through 1992) presented in Table 2 * Partitioning therange 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 forEstimating End UseEnergies", Prepared for Siena Pacific Power Co., 1988 (3) "Description ofElectric Energy use in Single-Family Residences inthe Pacific Northwest: 1986-1992"; Bonneville Power Administration, Dec 1992 (ELCAP) The first two studies were cited by DOE (Appendix A; v2 ofTSD) 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 earlierassumptions) annual ,:!sage based on a review ofstudies that examined range electric energy requirements. Using the five metered studies from 

### this review DOE detennined an average consumption of605.1 kWh/yr which they used to develop theirenergy usage profile. This average range energy was then partitioned into oven and cooktop usageS based on several factors including sales 'ofrange 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 of617 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 longerrelevant. The declining energy usage associated with electric ranges is noted by the DOE. The modified set ofelectric range energy is recommended. The modified energy values presented in Table 1were obtained by:
• Averaging the results of3recent 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) "IntegratingEIP and HE55 Infonnation for Estimating End UseEnergies", Prepared for SienaPacific PowerCo., 1988 (3)
.

### "Description ofElectric 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 ofTSD) butthe 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 Summarizingthese 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 ofthe Modified (Reduced) Range Energy Usage 

### The substantial reduction (25%) inrange 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 ofthese appliances. Examining the DOE generated paybacks in light ofthe 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 forthe Level 4 design options forthe 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 'EQii lr ii. _"mpU -N t Table 2: 1988Through 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 ofthe Modified (Reduced) Range Energy Usage 

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

### DOE assumptions has a significant impact onconsumerpaybackperthe DOE Cost Analysis Assumptions. Product paybacks per DOE assumptions are increased by 25% given the lower energy consumption ofthese appliances. Examining the DOE generated paybacks in light ofthe reduced energy usage for the electric coil element stretches the level 2 paybackto 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

.. perTable 2 data 

### The paybackfor 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: Paybackfor Electric Oven Options

Electric Oven Self-clean ElectricOven - . Standard

.. per Table 2 data

### Based on these results, the self-clean oven level 3and 4 options exceed halfofthe projected life ofthe product. The.design option review presented in Sections 4 and 5ofthis report will use DOE generated values ofenergy consumed to facilitate comparisons between the findings presented by DOE andthe results ofthis 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 inthis section should beused as a guide in revising downward the energy usage ofelectric ovens and cooktops. 3.0 Review of DOE Baseline EfficiencyAssumptionsfor Electric Ovens and Cooktops 

### The DOE test procedure for determining cooking efficiency is a keytechnical parameter in the evaluation ofoven performance (i.e., energy factor). DOE's assumption forbaseline efficiency are in general high as compared to the efficiency test data developed byfour major range manufacturers. In addition, these average values ofefficiency (used as baseline) do not reflect the variability in product efficiency that results in today's manufacturing ofranges, ovens, and cooktops. Baseline efficiency levels should be established that accounts forthe majority ofthe units produced. 3.1 Efficiency Testing Fourmanufacturers pulled several ranges offtheir 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 ofthe manufacturers' tests are presented in Table 5as the average value calculated from total sample population. Cooktop sample size represents testing of several elements oneach range. Based on these results, the self-clean oven level 3 and 4 options exceed halfofthe projected life ofthe product. ' ' The,design option reviewpresented in Sections 

### 4 and 

### 5 ofthis report will use DOE generated values ofenergy consumed to facilitate comparisons between the findings presented by DOE and the results ofthis study. 

### In the**electri~** oven analyses, oven cooking energy andself-cleanenergy consumption were considered (clock energy consumption was not included). However, for future evaluation, the DOE should adapt more current energy usage data and theinformation provided inthis section should be used as a guide in revising qownwm;d the energy usage ofelectric ovens andl cooktol's. 3.0 Review of DOE Baseline EfficiencyAssumptionsfor Electric Ovens and Cooktops ' The DOEtest procedure for determining cookingeffiCiency is a key technical parameterin the evaluation ofoven performance (i.e., energy factor). DOE's assumption for baseline efficiency

## ale in general high as compared to the efficiency test datadeveloped by four majorrange manufacturerS. In addition,**thes~** average values ofefficiency (used as baseline) do not reflect the variability in product efficiency**~t** results in today's manufacturingofranges, ovens, a,nd cooktops. Baseline efficiency levels should beestablishedthat accounts·for the majority ofthe units produced: ' 3.1 EfficiencyTesting Fourmanufacturers pulled several ranges offtheir assembly line and conducted the 

### DOE efficiency testfor:

• Coil Cooktops • SmoothCooktops • Standard Oven • Self-Clean Oven • Self-Clean-Convection Oven (3 manufacturers provided data) The self-clean convection oven data onefficiency will be introduced in this**s~tion** and its implication on design viability (payback) 

### will**~** discussed in a later section. , Results ofthe manufacturers' tests are presentedin "rable 5 as the average,value' calculated from total sample population. Cooktop'sample size representS testing'of severalelements on eachrange.Table 5: DOE EfficiencyTest 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 ofproduction 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 EfficiencyTest Data and Baseline DOE Assumotions

,OOKtOp

- La011 .1-3. I I470-/o0 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 Accountfor 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 inbaseline data is critical ifit is expected that in the future all units shipped must meet an efficiency target. Using the average test value would result in halfthe 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% ofthe range product coming offthe 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 EfficiencyTest Resultsfor Electric Cooktop Elements and Ovens

# ========~:I

These average efficiency numbers ofproduction 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 ManufacturerGenerated EfficiencyTest Data and Baseline DOE Assumptions

.

## ~~~------~--~----~----~---

3.2 Modification in Baseline Numbersto Accountfor ManufactUring Variability While the average efficiency numbers developed by the manufacturers are in relatively close agreement with the DOEbaseline, thebaseline average results do not reflect normal product variability. This change in baseline data is critical ifit is expected thatinthe future all units shipped must meet an efficiency target. Using the average test value would result in halfthe units failing. A modified baseline efficiency level is recommended. Using the manufacturerdatabase, modified baseline efficiencynumbers are presented in Table 7. These modified baseline efficiencies would allow approximately 82% ofthe range product coming offthe 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 ofthe individual options relative to the oven utility, oven efficiency/energy savings, and simple payback. Forthese 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 aconservative examination ofpayback for the several design options. Using these high DOE usage assumptions, the paybacks calculated forthe various options usually exceeded half ofthe product projected life. These consumption values were not restated to. the modified results presented in Section 2 ofthis 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 setat 2.1. This matched the lower end ofthe DOE assumptions forcostmultipliers (Appendix A). 4.1 Forced Convection Design Option DOE hasrecommended that forced convection be adopted as partofthe electric standard oven and electric self-clean oven level4efficiency improvements. Based on ourevaluation ofavailable data, information provided bythe manufacturers, and oven thermal analysis, this option does not meet consumer payback requirements and it changes the utility ofthe oven. 4.1.1 ImpactofForced Convectionon Oven Utility If full-time forced convection ovens are mandated, consumers will have to change a lifetime ofcooking habits based on recipes and cooking procedures using conventional oven cooking. Favorite familyrecipes would be affected by time/temperature changes required forconvection cooking. Cooking quality, orthe quality ofthe food resulting fromthe cooking process, would change, depending on the cooking process used. This study assesses, through a literature review, the effects ofconvection ovens on cooking quality. A literature search was initiated using the key words "convection oven". Six research papers were retrieved from two peerreviewed scientificjournals. Two papers were submitted from university sponsored research. Each paper was reviewed forconvection 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 ofthe individual options relative to the oven utility, oven efficiency/energy savings, and simple payback. Forthese 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 conservativeexamination ofpayback for the**seve~** design options. Using these high DOE usage assumptions, the paybacks calculated for the various options usually exceeded halfofthe product projected life. These consumption values were not restated to,the modified results presented in Section 2 ofthis 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 ofthe, DOE assumptions for cost multipliers (Appendix A). ' ' 4.1 Forced Convection Design Option DOE has,recommended that forced convection be adopted as part ofthe electric standard oven and electric self-clean oven level 4 efficiency improvements. Based on ourevaluation ofavailable data. information provided bythe manufacturers. and oven thennal analysis, this option does not meet consumerpaybackrequirements and it changes the utility ofthe oven. 4.1.1 Impact ofForced Convection

# on Oven Utility· Iffull-time forced convection ovens are mandated, consumers will have to change a lifetime ofcookinghabits based on recipes and cookingprocedures using conventional oven cooking. Favorite family recipes would be affected by time/temperature changes required for convection cooking;" Cooking quality, orthe quality'ofthe food resulting from the cooking process, would change, depen:ding on the Cooking process used. ' This study assesses, through a literature review,'the effects ofconvection ovens on cooking quality. A literature search was initiated using the key words "convection oven". Six research papers were retrieved from two peerreviewed scientificjournals. Two'papers were submitted from university sponsored research. Eachpaper was reviewed for convection oven/cooking quality data.

### ResearchPapersReviewed 1. "Sensory quality and energy use for baking ofmolasses 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 forscrambled eggs and beefpatties heated in institutional microwave and convection ovens" Cremer, M.L., J. Food Science, Volume 47, 1982, p. 871-874. 3. "Comparison ofdrying kinetics offoods 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 beefroasts after infrared and convection heat processing" Unklesbay, N., Davis, M.E., Krause, G. Journal ofFood Science, Volume 48, 1983, p. 864-904. 5. "Temperatures ofspaghetti after heating in convection ovens at service locations in acommissary foodservice system." Cremer, M.L. Journal ofFood Science, Volume 43, 1978, p. 1062-1079. 6. "Nutrient retention ofportioned menu items after infrared and convection heat processing" Unklesbay, N., Davins, ME., Krause, G. Journal ofFood Science, Volume 48, 1983, p. 869-873. 7. "A study ofdesign 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 thepeer reviewedjournals, the findings were: * Cookies baked in a convection oven were significantly different fromthose baked in standard orinfrared 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 ofmolasses 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 beefpatties heated in institutional microwave and convection ovens" Cremer, M.L., J. Food Science, Volume 47, 1982, p. 871-874. 3. "Comparison ofdrying kinetics offoods 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 beefroasts after infrared and convection heat processing" Unklesbay, N., Davis, M.E., Krause, G. Journal ofFood Science, Volume48, 1983, p. 864-904. 5. "Temperatures ofspaghetti after heating in convection ovens at service Locations in a commissary foodservice system." Cremer, M.L. Journal ofFood Science, Volume 43, 1978, p. 1062-1079. 6. "Nutrient retention ofportioned menu items afterinfrared and convection heat processing" Unklesbay, N., Davins, M.E., Krause, G. Journal ofFood Science, Volume 48, 1983, p. 869-873. 7. "A study ofdesign 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., ThennodorCorporation. 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 peerreviewedjournals, the fmdings were:
• Cookies baked in a convection oven were significantly.different from those baked in standard orinfrared ovens. -
• More energy was used in the convection baking process.

### * Heating in a conventional oven ofready prepared or commissary type food yielded food ofhighersensory quality with lower energy input than food prepared in aconvection oven. * The effect ofinfrared and convective heatingupon nutrient retention was similar in portioned menu items. * In a convection oven, the rate ofmoisture 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 morethan cakes and beef when comparing convection and standard oven modes. 4.1.2 ForcedConvection ImpactonOven Efficiency 

### The addition offorced convection to a "standard" residential product has amarginal impact on efficiency, and these gains are farless than those assumed by DOE. Range manufacturers tested 14 self-clean ovens with convection and found thatthe average efficiency was 14.12% as compared to 13.79% fortheir test of20 self-clean ovens. 

### The impact ofthis option on overall energy savings is less than 8kWh/yr as compared to DOE's assumed savings of41 kWh/yr for self-clean ovens and 33 kWh/yr for astandard oven (using DOE's adjusted values for EAo 

### minus the clock energy consumption). Table 8presents a detailed comparison ofpotential energy savings oftheconvection 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 ofready prepared orcommissary type food yielded food ofhigher sensory quality with lower energy input than food prepared in a convection oven. '
• The effect,ofinfrared and convective heating upon nutrient retention was similar in portioned menu items.
• In a convection oven, the rate ofmoisture loss increases with highertemperature due to the greaterdriving forces for heat and mass transfer. Forproducts with low moisture coritent, the convection oven'is not advantageous'becausethe 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 beefwhen comparing, convection and standard oven modes. 4.1.2, ForcedConvection Impact

### on Oven Efficiency The addition offorced convection to a "standard" residentialproduct 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 of20 self-clean ovens. The impact ofthis option on overall energy'savings is les's than 8 kWhlyr

# as compared to DOE's assumed savings of41 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 ofpotentialenergy savings ofthe convection feature based on the DOEadjusted 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 ofthe manufacturers relative to efficiency improvements ofadding convection to standard residential ovens. Our analysis (see Appendix B for model description) showed that competing heat transfer effects limit the effectiveness ofthe 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 bythe internal heat transfer characteristics ofthe product (conduction limited). The current DOE test procedure featuring an aluminum block (highly conductive) cannot simulate the impact offorced convection on product quality and hence its use in forced convection testing is very limited. 4.1.3 Consumer PaybackAssociated with ForcedConvection 

### Examination ofthe consumer payback aspect ofadding forced convection showed that the payback associated with this option easily exceeds the halflife ofthe range and that paybacks of 100+ years are likely. For this analysis, a simple payback was used ofthe form Payback = incrementalprice increaseofthe convectionfeature Payback

-- energy savings associatedwith 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 manufacturingcostpremium 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 Ourthennal analysis supports the findings ofthe manufacturers relative to efficiency improvements ofadding convection to standardresidential ovens. Ouranalysis (see Appendix B for model description) showed that competing heat transfereffects limit the effectiveness ofthe convection option. Forthe residential oven geometry and convection configuration, the enhancements relative to increased heat transferto 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 ofthe product (conduction limited). The current DOEtest procedure featuring an aluminum block (highly conductive) cannot simulate the impact offorced convection on product quality and hence its use in forced convection testing is very limited. 4.1.3 ConsumerPaybackAssociated with'ForcedConvection Examination ofthe consumer payback aspect ofadding forced convection showed that the payback associated**~ith** this option easily exceeds the halflife ofthe range and that paybacks of 100+ years are likely. Forthis analysis, a simple payback was . used ofthe fonn 

### Payback = 

### incremental price increase ofthe convectionfeature energy savings associated with convection The incremental price increase associated withthe convection option was developed from manufacturers' data. Three range manufacturers with extensive experience 

### in , convection ovens provided cost premium data that was significantly higherthan the DOE assumptions. The average manufacturing**cost~remiums** for the convection option as provided bythe range manufacturers was: 

### Average manufacturing costpremiumfor convection 

### == $39.6110ven

### Using a multiplier of2.1 (see Appendix A) on manufacturing cost to achieve a sell -price results in an average price premium of: AverageIncrementalPrice for ConvectionFeature $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 notjustified 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 I .08/kWh $ .58 141.3 yr Self-clean Oven 81.95 --- Seffclean Oven_81_95$.l1/kWh $ .73 112.3 yr 

### 4.2 Reflective Surfaces forOven Cavity DOE has recommended that reflective surfaces be incorporated into the oven as an energy saving technique. Our analysis ofthis option suggests that: * Current oven utility is not maintainable using reflective surfaces. * Modest energy savings are possible. * Consumerpayback is long. * Major oven design modifications are likely in order to duplicate the current product life. 4.2.1 ImpactofReflectiveCoatingon Oven Utility The addition ofreflective walls to an existing oven design will change the cooking process and, as aresult, willimpact theutility ofthe 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 fromthe element that has its wave length set by the very hightemperatures ofthe bottom heating element.

_ , s g a

_ Using a multiplier of2:1(see· Appendix A) on manufacturing cost to achieve a sell -price results in an average price premium of:

. . . Average Incremental Pricefor 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 notjustified based on energy cost savings. Using the modified energy usage data would result in even longerpaybacks (Section 2.0).

. - . . Table 9: Forced Convection Payback

Standard Oven 81.95 Self-clean Oven 81.95
4.2 Reflective SurfacesforOven Cavity .DOE has recommendedthat reflective surfaces be incorporated into the oven as an energy saving technique. Our analysis ofthis 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 orderto duplicate the current product life. 4.2.1 ImpactofReflective Coating

### on Oven Utility The addition ofreflective walls to an existing oven design will change the cooking process and, as a result, will impact the utilityofthe 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 reflectiveaven will reflect radiant heat from the element that has its wave length set by.the very high temperatures ofthe bottom heating element.

### The characteristics ofthis reflected radiation is different than thethermal radiation emitted by the current cavity. The heat re-radiated from the walls is essentially oven setpoint temperature (far less than the element temperature) and this radiation has a longer wavelength as compared to the output ofthe 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 ofthe appliance possibly resulting in overbrowning offood surfaces and underdone interiors. Underdone interiors could affect food safety, since the interior ofthe food may not reach proper sterilization temperature. Additionally, the emissivity ofthereflective 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 ofthe product. In particular, the self-cleaning oven process damages the reflective walls. Currently, about 29% ofgas ranges and 58% ofelectric ovens are self-cleaning. There is no known cost effective material that will maintain reflective surfaces in aself-cleaning oven over its 19 year life. [1]l

### 21 4.2.2 ImpactofReflective Coatingson Oven Efficiency 

### Our thermal analysis ofthe impact ofreflective 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 oreven thin oil films eliminate the benefit ofa reflective surface. These effects are described in the balance ofthis section. 4.2.3 Reflective SurfaceEfficiency Analysis 

### The maximum oven efficiency improvement resulting from the use ofreflective 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 ofthe heat source energy being reflected offthe oven wall surfaces which keeps more ofthe energy within the oven cavity (less energy is absorbed by the surface) and increases the percentage ofuseful heat. The net effect is a slightly lower oven wall temperature.

[1] Battelle, et al., TechnicalInputto NAECA Rulemaking for Gas-Fired Ranges,GRI Interim Report No. GRI93/0319, July 1993. [2] Aronov, M., et al., AnalysisofDesignOptions forReducing theEnergy Consumptionof ResidentialGas Ovens, American Gas Association Laboratories Research Report, GRI Contract #5086-241-1220.

a m.4U.tuuWN aImUS The characteristics ofthis 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 longerwavelength as compared to the output ofthe 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. Theproposed reflective surface modification to residential oven products changes the cooking quality ofthe appliance possibly resulting in overbrowning offood surfaces and underdone interiors. Underdone interiors could affect food safety, since the
. interior ofthe food may not reach propersterilization temperature. Additionally, the emissivity ofthe reflective surface would not stay constant due to food spills, blueing from heat, and cleaning compounds. Reflective materials degrade afterthe first baking function and continue to degrade through the life oftheproduct. 

### In particular. the self-cleaning oven process damages the reflective walls. Currently. about 29% ofgas ranges and 58% ofelectric ovens are self-cleaning. There is no known costeffective material that will maintain reflective surfaces in a self-cleaning oven overits 

### 19 year life. [1][2] 4.2.2 ImpactofReflective Coatings

### on Oven Efficiency Our thermal analysis ofthe impact ofreflective 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 oreven thin oil films eliminate the benefit ofa reflective surface. These effects are described in the balance ofthis section. 4.2.3 Reflective Surface EfficiencyAnalysis The maximumovenefficiency improvement resulting from the use ofreflective surfaces onthe oven interior was determined to be less than .58 percentage points (e.g.• from 12.15% to 12.73%) using ouroven model (see Appendix B). The improvement in oven performanceresults from a larger portion"ofthe heat source energy being reflected offthe oven wall surfaces which keeps more ofthe energy within the oven cavity (less energy is absorbed by the surface) and increases the percentage ofuseful heat. The net effect is a slightly lower oven wall temperature. 

# - [1] Battelle, etal., Technical Input to NAECA Rulemakingfor Gas-FiredRanges, GR! Interim Repon No. GRI93/0319, July 1993. [2] Aronov, M.,et al.•Analysis of Design OptionsforReducing 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 orreflected. The energy thatis absorbed is re-radiated at a different wavelength. Thus, the emissivity isequal to the absorptivity ofthe 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 ofreflective surfaces, the emissivity ofthe oven interior is reduced to model the appropriate coating. The analysis ofreflective 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 tothe Baseline Oven Design (Emissivity for porcelain oven = .92) 

### LI E miss~~~~ty ~~~ ' - ''IP. 

### X O n * _r en_) 

## I .1 .58 .3 .32 .5 .17 .7 .0 8 

### Table 11 breaks down the actual energy savings forthe different surface emissivities analyzed. The annual energy savings isbased on adjusted DOE annual cooking energy output including self-cleaning energy when appropriate. Table 11: Breakdown of Savingsfor 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 testdatafor 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 .1mayjepresent the highest attainable energy savings for areflective surface. An emissivity of .1represents a polished, unoxidized, and oil free surface which will only exist on anew product. As soon as a consumer begins to cook in the oven an oil film will startto 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 orreflected. Theenergy that is absorbed is re-radiated at a different wavelength. Thus, the emissivity is equal to the absorptivity ofthe 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 ofreflective surfaces, the emissivity ofthe oven interior is reduced to model the appropriate coating. 

## The analysis ofreflective 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**  Relativetothe Baseline Oven Design (Emissivityfor 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 ofSavings 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 minusclock 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 onlyexist on a new product. As soon as a consumerbegins to cook in the oven an oil film will startto 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: Emissivitlesfor Various Types of Surfaces IIIIB.ill^'^NM ^^I^^Surfame Emlssvt Aluminum - polished .05 Aluminum - slightlyoxidized .15 Steel- polished .1 Steel
- slightlyoxidized .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
- slightlyoxidized .28 Zinc Coating
- badlyfurnished .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 ofthe best choices for areflective 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 ofthe oven. For the stainless steel cavity, the wall emissivity would be .5 (oxidized) after the first self-clean cycle; and the benefit ofthe surface would be reduced by about 60%. Chrome coatings are best suited for the standard oven which have temperatures of 600°F. The deposits ofeven thin coatings of oil from normal cooking use would quickly cause the deterioration ofthe reflective quality ofthe plating. An average cavity emissivity of about .45 for a chrome-plated oven in daily use would be very reasonable (assumes halfthe oven is still highly reflective [e=.1] and the other half is soiled [e=.82]). Again, about 60% ofthe energy savings benefit ofthe oven would be lost. Frequent cleaning ofthe 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 ConsumerPaybackAssociatedwithReflectiveSurfaces 

### The payback associated with the standard or self-clean oven with reflective interior surfaces was found to be greater than 8-years when using theenergy savings associated with a highly reflective cavity (ideal assumption). A 20+ year payback is realized ifthe oven surface reflectance is reduced to account for surface soil or surface oxidation that will occur oven the life ofthe product. - - -

OR -M. 9-

- - *I% a M--Jr.a- Table 12: Emlsslvltlesfor 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 5kWh. For self-cleaning ovens, one ofthe best choices for a reflective cavity would be stainless steel. Stainless steel would be suitable wall material for an oven that will see hundreds of900"F self-clean cleaning cycles overthe average 19-year life ofthe oven. For the stainless steel cavity, the wall emissivity would be .5 (oxidized) after the flfSt self-clean cycle; and the benefit ofthe surface would be reduced by about 60%. Chrome coatings are best suited for the standard oven which have temperatures of 600r. The deposits ofeven thin coatings ofoil from normal cooking use would quickly cause the deterioration ofthe reflective quality ofthe plating. An 

### average cavity emissivity ofabout .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% ofthe energy savings benefit ofthe oven would be lost. Frequent cleaning ofthe oven would improve the reflectivity cavity quality provided the user did not scratch ordamage the surface using typical cleaning pads and oven cleaning chemicals. 4.2.3 ConsumerPaybackAssociated with Reflective Surfaces 

### The payback associated with the standard orself-cle!n oven with reflective interior surfaces was found to be 

### greaterthan 8-years when using the energy savings associated with a highly reflective cavity (ideal assumption). A 20+ yearpayback is realized ifthe oven surface reflectance is reduced to account for surface soil or surface oxidation that will occur oven the life ofthe product.

### This design option payback period isexcessive, difficult to achieve in practice, and if implemented would alter the utility ofthe product. Paybacks calculated for this option are shown in Table 13 for both the "ideal" case and forreflective 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 areflective surface; it is substantially less expensive than a stainless steel cavity or liners. The price premium associated with chrome plating was taken as average ofArthur D. Little, DOE and manufacturers' estimates. 4.2.4 ReflectiveSurface IssuesRelativeto Manufacturing 

### Inthe 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 forthe reflective surface due to the stability ofthe protective oxide which forms on chrome, and electroplating for compatibility withexisting manufacturing operations for the oven cavity. Two general classes ofchrome plating are available: hard chrome and "decorative" chrome. The first,hard chrome, is used forengineering applications where wear and corrosion resistance are needed. Decorative chrome produces ahighly reflective surface, and would be the process ofchoice for the oven application. The overall process forachieving apolished surface using decorative chrome at minimum cost progresses through the following steps: * Mechanical polishing ofthe substrate * Copper plating (0.1 mil) * Mechanical buffing ofthe copper layer * Copper plating (flash) * Nickel plating (2 layers 0.2mil in thickness)

_M -. M _ -a This design option payback period is excessive, difficult to.achieve in practice, and if implemented would alter the utility ofthe product. Paybacks**calculat~d** for this option are shown in Table 13 for both the "ideal;' case and for reflective surfaces afterservice and aging has occurred.
.**'~able** 13: PaybackAssociated with Reflective Oven Surfaces**~~~~~~~~~~~~~**

self·Clean
'The payback analysis. was based on using chrome plating onthe oven cavity
.. While this technique may not be suitable fora 19-yearproduct life, it is probably··the least

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

than a stainless steel cavity orliners. The price premium associated with chrome !plating was taken as average ofArthur 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 ofthe protective oxide which forms on chrome, and electroplating for compatibility with existing manufacturing operations for the oven cavity. Two general classes ofchrome 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 ofchoice 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'ofthe substrate· Copperplating (0.1 mil) I Mechanical buffing ofthe copperlayer Copper plating (flash) Nickel plating (2 layers 0.2 mil in thickness)

### Chrome plating Typically, the decorative chrome plate is less than 50 millionths ofan inch. For a part in which only the interior needs plating, masking and stripping steps may be included to block offthe external surface. Cost ofthe plating can beestimated from the time in the bath, and the part loading per tank. For purposes ofthis calculation, tank time costs of$40 to $50 per hour (margins not included) and deposition ofV2 mil in 15 minutes have been assumed. The cost ofa part then depends on the parts per rack, and the rack capacity ofthe tank. Inthis calculation, 8parts per rack or 4 oven cavities and door pieces perrack were assumed. This leads to an oven cavity plating cost ofonly $2.50 to $3.00 without overheating and margins. Polishing ofthe steel surface and masking ofthe external surfaces introduces additional costs. For hand operations, the costs ofthese steps could exceed the cost ofthe plating. However, forlarge production volumes, robotic polishing and masking steps will significantly bring down costs. Forthis preliminary analysis, surface preparation costs equaled that ofplating, for a total cost of $5.00 to $6.00. Range manufacturers would have to make majorinvestments in an automated chrome plating line to achieve this low cost premium. Use ofplating 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 forreflective surface

- $11.55/oven This incremental pure estimate is about 3times ofthat assumed by the DOE ($3.06/unit retail). Another chrome plating estimate was provided by one ofthe major range companies which placed the manufacturing cost premium ofachrome plated oven over the standard product at $9.40/unit or acustomer price increase of $19.74/unit. The average ofthese 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 ofthe oven stresses the oven walls further promoting the cracking process. The effect ofcracks on the corrosion rate ofthe substrate due to oxidation, and food and cleaning chemicals must be determined.

a _ I_ w *Ul • Chrome plating Typically, the decorative chromeplateis less than 50 millionths ofan inch. For a part in which only the interior needs plating, masking and stripping steps may be included to block offthe external surface. Cost ofthe plating can be estimated from the time in the bath, and the part loading

.per tank. Forpurposes ofthis calculation, tank time costs of$40 to $50 perhour

(margins not included) and deposition of

### Yl mil in 15 minutes have been assumed. The cost ofa part then depends on the parts perrack, and the rack capacity ofthe tank. In this calculation, 8 parts per rack or4 oven cavities and door pieces perrack were assumed. This leads to an oven cavity plating cost oforily $2.50to $3.00 without overheating and margins. Polishing ofthe steel surface and masking ofthe external surfaces introduces additional costs. Forhand operations, the costs ofthese steps could exceed the cost ofthe plating. However, for large production volumes, robotic polishing and masking steps will significantly bring down costs. Forthis preliminary analysis, surface preparation costs equaled that ofplating, 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 costpremium. Use ofplating vendors coulddouble the cost. The preliminary chrome plating cost can be summarized as follows:
• Average plating and preparation cost .. $5.50/oven • Incremental consumerprice for reflective surface
... $11.55/oven This incremental pure estimate is about 3 times ofthat assumed by the DOE ($3.06/unit retail). Another chrome platingestimate was provided by one ofthe major range companies which placed the manufacturing cost premiumofa chrome plated oven overthe standard product at $9.40/unit ora customerprice increase of $19.741unit. The average ofthese three values is $11.45 [= (19.74 

### + 11.55 

### + 3.06)/3] which was used in the payback analysis. Significant materials issues relative toa 19-yearchrome cavity life are:
• Chrome deposits are brittle and can microcrack depending on the thickness and the applications. Thennal cycling ofthe oven stresses the oven walls further promoting the cracking process. The effect ofcracks onthe corrosion rate ofthe substrate due to oxidation, and food and cleaning chemicals must be determined.

### * Thermal cycling ofthe oven cavity stresses the deposit increasing the potential for loss ofadhesion. Quality control ofbath and operating parameters becomes critical to insure consistent adhesion ofthe deposit. * The cavity reflectivity will likely change over time. In addition, the manufacturers will likely have major investments including: * Oven design modifications since deposition ofbright chrome on the interior surface ofan 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 ofthe completed part.

- Polishing and buffing ofinterior 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 ofthe box.

- Atrade-offanalysis should be conducted regarding the cost benefits of masking the outside ofthe 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 ofsetting up an internal plating operation versus the use ofexternal plating shops. An internal chrome plating operation entails an investment in a waste treatment plant and precautions for working withchromic acid. 4.3 Improved Door Seal forStandard Electric Ovens 

### Based on efficiency and cost data provided by manufacturers this option has a very minor impact on oven efficiency and aprice premium that creates a payback in excess of 10 years. In addition,the door seal improvements may effect the cooking performance ofthe oven. The door seal allows both fresh air to enter the oven cavity (bottom seal) and it acts as apartial oven vent (upper door seal line). Modifications to the door seal could have anegative impact ofmoisture concentration in the cavity with a resulting negative impact on cooking perforrmnce.

-- I
_ - . • Thermal cycling ofthe oven cavity stresses the deposit increasing the potential for loss ofadhesion. Quality control ofbath and operating parameters becomes critical to insure consistent adhesion ofthe deposit.'
. . • The cavity reflectivity will likely change overtime. In addition, the manufacturers will likely have majorinvestments including:
• Oven designmodifications since deposition ofbright chrome on the interior surface ofan open welded box presents severalissues:

- Crevices along the weld line and coiners creates the potential for solution retention in recesses. Residual bath solutions cancontaminate subsequent plating bathes and cause corrosion ofthe completed part.

- Polishing and buffmg ofinterior surfaces with comers and right angles may require specializedequipment.

- Conformal anodes may be needed to obtain unifonn thickness and deposit properties on the inside ofthe box.
. . . - A trade.:offanalysis should be conducted regarding the cost benefits 9f masking the outside ofthe cavity from plating. Masking before plating and stripping the mask afterplating can contribute significant to cost.
• An appliance manufacturer has to considerthe cost benefits ofsetting up an internal plating operation versus the use ofexternal 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 dataprovided by manufacturers this option has a very minorimpact on oven efficiency and a price premiumthat creates a payback in excess of 10years. In addition, the door

## seal improvements may effectthe cooking performance ofthe oven. The door seal allows both fresh 

### air to enterthe oven cavity (bottom seal) and itacts as a partial oven vent (upperdoor seal line). Modifications to the door seal could have a negative impact ofmoisture concentration in the cavity with a resulting negative impact on cooking**perfo~ce.**4.3.1 ImprovedDoorSealEfficiency 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 Associatedwith 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 ofthe major range manufacturers. 4.3.2 PaybackAssociatedwithImprovedDoorSeal 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 ofadapting 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 ImprovedDoorSealEfficiency 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 .24percentage 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 comparingtheir perfonnance to standard oven performance. These tests were conducted by one ofthe majorrange manufacturers. 4.3.2 PaybackAssociatedwith ImprovedDoorSeal Usingthe energy savings shown above and the price added associated with incorporating a self-clean doorinto a standard oven, the payback was estimated in the range of 13 to 17 years. Table 15 presents the payback fmdings. Table 15: Paybackfor Standard Oven Door Seal Improvement**~~~**

Standard Oven
The incremental price ofadapting a self-clean door seal to a standard oven was detennined by:

• Averaging the manufacturing costestimated provided bythree majorrange 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 2inches, that is, increasing the insulation wrap around the oven from 2 to 4 inches. While a2-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 ofthe oven and range appliances. The current range product is designed around anumber ofkitchen 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 ofrange (i.e. appliance touching cabinet side walls andback wall) * Cooking cavity large enough to accommodate alarge turkey roaster pan and an oven that can cook multiple racks offood * Need to maintain cool coil cooktop surface ofrange (at30-inch level) * Need to have the oven as high as possible to minimize lifting products to and fromthe oven As aresult ofthese needs, the oven design has evolvedto the following: * 23-inch wideby 16-inch wide, by 18-inch deep cavity * 2inches ofinsulation around cavity * 3-inch side wall air wipe(needed for zero clearance) * Y'-inch clearance for construction/installation tolerance (e.g., 29 1⁄22-inchwide cabinet) *3-inch space clearance between the top ofthe oven insulation and range cooktop

surface (Note: 2 inches minimum needed forcold elements/bowls, and 1-inch air wide needed when all elements and oven are in use) * 22-inch space across back ofoven to provide air wipe cooling and electrical connections ofoven heating elements (bake and broil) 4.4 Increased Oven Insulation Design Option DOE 

### has recommended an increase in cavity insulation of2 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 ofthe oven and range appliances. The current range product is designed around a number ofkitchen 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 ofrange (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 offood Need to maintain cool coil cooktop surface ofrange (at 3D-inch level) Need to have the oven as high as possible to minimize lifting products to and from the oven As'aresult ofthese needs, the oven design has evolvedto the following:
• 23-inchwide by 16-inchwide, by IS-inchdeep cavity • 2 inches ofinsulation 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 ofthe 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 ofoven to provide air wipe cooling and electrical connections ofoven heating elements (bake and broil)

### Increasing the insulation (2 to 4 inches) thickness would either: * Increase the size ofthe overall cabinet * Reduce the oven cavity volume Both of these options would impact the utility ofthe appliance. Increasing the size ofthe range to accommodate the additional insulation would result in aproduct that could not be retrofitted into existing kitchens (range width increase from 30to 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 roofinsulation, and adding the extra oven floorinstallation would effectively eliminate the drawer space under the cavity. This is an important feature for today's ranges and it is a point ofproduct differentiation. Taking the approach ofreducing the cavity size to accommodate the additional insulation would have a large impact on cooking utility. Forexample, reducing the cavity width from 22to 23 inches to 18 t_9 

### inches would eliminate the possibility ofcooking large family dinne.g. 25 lb. turkey, In addition,the muchnarrower 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 ofracks ofproducts. 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 forIncreasedInsulation 

### 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 ofthis design may affect the utility ofthe 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 ofthe overall cabinet
• Reduce the oven cavity volume Both ofthese options would impact the utility ofthe appliance. Increasing the size ofthe range to accommodate the additional insulation would result in a product that could not be retrofitted into existing kitchens (range width increase from 30to 34 inches). In addition, the oven cavity would be lowered by two inches within the range to accommodatethe extratop 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 roofinsulation, and adding the extra oven floor installation wouldeffectively eliminate the drawer space under the cavity. This is an important feature for today's ranges and it isapoint ofproduct differentiation.
. Taking the approach ofreducing the cavity size to accorrunodate the additional insulation would have a large impact on cooking utility. Forexample, reducing the cavity width from 22 to 23 inches to 18 t 19 inches would eliminate the possibility ofcooking large family dinne e.g. 25 lb. turkey. Inaddition,the much narrower oven would impacttypical two-pan g ormance. Intwo-pan or sheet-baking performance, the clearance around the sheets orpans (18- by 13Y2-inch) is needed for uniform heating/cooking ofracks ofproducts. 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 EnergySavingsAnalysis forIncreasedInsulation Ouranalysis 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 ofthis design may affect the utility ofthe 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 energyconsumption (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, butreductions in material thickness are very limited. These limitations arebased on: * An average porcelain thickness is needed for adequate wall coverage. * Sheet metal thickness reductions are limited by the use ofalready 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 ofthe cavity. Sheet metalthickness 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 butthey would still require oven redesign (e.g., ribs, door shape) and new tooling. Theenergy 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 thickerinsulation 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 ovenefficiency, 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 ofalready

# thin materials (typical .024inches). Porcelain coverage is non-unifonn

### in the oven giventhe current manufactUring techniques and
.the average thickness is established to provide the minimum porcelain layer·for the most difficult to coat areas ofthe cavity. Sheet metal thickness is close to minimum given current tooling, existing part designs (e.g. draws) and assembly techniques. A majorrange manufacturer estimates that material weight reductions of Y2 lb are possiblebutthey 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 thanthe 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 1kWh/yr 4.5.1 Reductionin Thermal Mass Analysis 

### A 1⁄22to 1lb 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 CavityThermal Mass onAnnual Energy Consumption and Oven Efficiency

h lb .35% 1 1.08 12.14 13.95 1lb .700% 2 1.8 12.18 14.00 * 1lb represent much less than 10% ofthe oven cavityweight (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 ofa lower thermal mass is negligible at steady state conditions because the heat loss through the wall is dominated by the resistance ofthe insulation surrounding the oven cavity wall. 4.6 Elimination ofthe Oven Window Design Option Elimination ofthe current oven window by definition has a positive energy savings and a good payback. This option does change the utility ofthe 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% ofall 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 userwill have to open the door severaljimes to determine doneness. 4.6.1 EnergySavingsAnalysisforWindowElimination Our analysis indicates that the amount ofenergy saved relative to window elimination is about halfthat reported by DOE (5kWh/yr as compared to 10 kWh/yr). This decrease in oven efficiency is due to several dooropenings per cycle.
M%.%--. WPR M M.q~N Table 17: Potential Energy Saving due to Reduced Mass



# --

4.5.1 Reduction in ThermalMass 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 cavityThermal Mass on Annual Energy Consumption and Oven Efficiency

• 1 Ib represent much less than 10% ofthe 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 ofa lowerthennal mass is negligible at steady state conditions because the heat lossthrough the wall is dominated by the resistance ofthe insulation surrounding the oven cavity wall. 4.6 Elimination ofthe Oven Window Design Option Elimination ofthe current oven window by definition has a positive energy savings and a good payback. This option does change the utility ofthe oven, that is, consumers currentlyperceive a majorbenefit in the window option, and are willing to pay a premium for this feature. Roughly 70% of

### all units shipped include a window. The userwill 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. Ratherthan quickly inspecting through the

.window, the user will have to open the door severaJ.times to determine doneness.

4.6.1 EnergySavingsAnalysis for WindowElimination Our analysis indicates that the amount ofenergy saved relative to window elimination is about halfthat reported by DOE (5 kWhlyr as compared to 10 kWh/yr). This decrease in oven efficiency is due to several door openings percycle.

### Our analysis assumes three product examinations per cook cycle. For some products where proper finishing isdifficult, thenumber ofdoor openings may be greater. This suggests that theefficiency impact at best is a .25percentage point increase and notthe .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 Eliminatinga Door Window on a Self-Clean Electric Oven Energy Consumption

Y2 window 1.6% 4.7 5.0 12.30% 14.12% Nowindow 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 ofthe window saves approximately 9.7 kWh per year for a self-clean oven. However, these values assume no dooropening. To determine the effect ofdoor openings or energy savings, the actual energy saved per cycle must be calculated. The number ofcooking cycles can be estimated tobe 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 Btuto reach 305T'from 77°F * Only cooking energy was considered since the oven doorcannot be opened during self-clean Each cooking cycle used about .964kWh which results in approximately 30 watt hrs (102 Btus) saved percycle when the window is eliminated, To determine how much energy is lostby opening the oven door, all ofthe 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. __

_ . _ Ouranalysis assumes three product examinations per cook cycle. For some products .where proper finishing is difficult, the number ofdoor 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 energyrequirements 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: Effectsof Reducing or Eliminating a Door WIndow ona Self-Clean Electric Oven Energy Consumption

• Based on adjusted cooking energy output (Eco) and self-cleaning energy (EscJ when applicable The elimination ofthe window saves approximately 9.7 kWhperyear for a self-clean oven. However, these values assume no door opening. To determine the effect ofdoor openings orenergy savings, the actual energy saved percycle must be calculated. The numberofcooking cycles can be estimated to be about 264 by usingthe following infonnation:
. • Adjusted annual DOE cookingenergy for self-clean electric: 255 kWh
• 13.9% cookingefficiency
• The DOEestablished test method for heating an 8.5-1b aluminum block which requires about 457.5 Btu to reach 305"F from 77°F
• Only cookingenergy was considered since the oven door cannot beopened during self-clean
. Each cooking cycle used about .964 kWh which res\llts in approximately 30 watt 

### hrs (102 B,tus) saved percycle when the window is eliminated: To determine**h~w** much energy is lost by opening the oven door, all ofthe 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 EfficiencyWhen 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 of77.2% to 80.5%. The potential for achieving this large improvement was investigated as part ofthis 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 EffectofSurface ContactResistanceonRange-Top Efficiency The effect ofcontact 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 ofapproximately ±.005 inches. The degree ofcontact with the cooking surface varies with flatness and roughness ofthe cooking utensil (pot or pan). As part ofthis program, arange of "contact" conditions were considered on several tests boiling pasta. Findings include: * The steady state efficiency ofthe cooktop is 95.0%. * Increasing the contact pressure between the pot and coil by a factor ofnearly 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 EfficiencyWhen 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 of77.2% to 80.5%. The potential for achieving this large improvement was investigated as part ofthis 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 EffectofSurface ContactResistance on Range-Top Efficiency 

### The effect ofcontact resistance on range-top efficiency was evaluated by perfonning heat transfercalculations and conducting tests using the UnifonnTest Procedure for commercial range-tops. Residential range-tops are manufactured with a flatness ofapproximately ±.OO5 inches. The"degree ofcontact with the cooking surface varies with flatness and roughness ofthe cooking utensil (pot orpan). As part ofthis program. arange of "contact" conditions were considered on several tests boilingpasta. Fmdings include:
• The steady state efficiency ofthe cooktop is 95.0%. 

# - • Increasing the contactpressure**betw~en** 

### the pot and coil by a factor ofnearly four has 

### nO'impacton steady state efficiency.
• Ifthe 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 ofcontact resistance in range-top coils. Inthis 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 ofsteel 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 theburner pan under the heating element is small and not included. 2) Theburner transfers heat to the potby conduction only with the above assumed value for contact resistance. Data from G.E. shows strong correlation ofcontact pressure and heattransfer 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 afactor ofapproximately 50. The results of Situation 3above, the mostrealistic, also demonstrates thatradiation 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 ofcontact 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 Burnertemperature 14000P Pot emissivty .6 Range-top emissivity .9
. Contact resistance .002 hr. ft. °PlBtu The contactresistance was

## taken from the G.E. Handbook for contactbetweentwo milled surfaces ofsteel and aluminum. Three situations were modeled. l) The coil transfers heat to the pot by radiation exchange with the burnertop surface only. This assumes a non-conducting'medium between the coil and the, pot. Reflection and emission from the burnerpan underthe heating element"is small and not included. 2:) The burner transfers heat to the potby conduction only with the above assumed value for**con~ct resistanc~.**  Datafrom G.E.**s~ows** strong correlation ofcontact pressure and heat transferconductance.
. 3) The coil transfers heat by radiation and conduction with the above assumed valve for contact resistance. 11le,analyticalresults are given in·Table 21.' The model indicates that the conduction tltrough the gap dominates'radiation by a factor ofapproximately 50. Theresults of Situation 3 above, the most realistic, also demonstrates that radiation has a small influence compared to conduction. In addition, contactpressure is the dominate parameter in both contact resistance and forcing**th~** pot and coil"to confonnto each other.



# -Table 21: Analytical Heat Transfer Results 

### :ii 

### (Atfl

.. .

1 Radiation heat transfer only between coil 1.3 X104 top surface and pot .x10 2 Conduction heat transfer only via contact 75 resistance between coiland 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 atypical 8-inch coil top and tests were performed withthe coil on "high." New 12-inch diameter aluminum pots with lids and containing 20 Ibs. ofwater were used perthe 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, ofwater and the lid positioned normally. 2) Contact resistance was then increased by placing a weight ofapproximately 68 lbs. on the top ofthe lid, increasing the pressure on the coil by a factor of3.8. 3) The effect ofatighter lid produced in condition 2above was investigated by clamping the lid closed and running the test. The weight ofthe clamps were negligible. 4) A space was provided between the coil and the pot to evaluate the overall effect ofthe situation where the coil orpot 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 withthe coil are essentially the same regardless ofcontact pressure. An increase in contactpressure 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 HeatTransfer Results

2 3 Radiation heat transfer only between coil top surface and pot Conduction heattransfer only via contact resistance between coil and pot Conduction and radiation heat transfer between coil and pot 5.2 Impactof Contact Conductance on Coil Efficiency
- Testing1.13 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. ofwater were used perthe 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 waterto approximately 200°F. A thermocouple centered in the water was used to determine the energy transferred. Four different tests were completed. 1) 

### Abase test was completed with 20 lbsl ofwater and the lid positioned normally. 2) Contact resistance was then increased by placing a weight ofapproximately 68 Ibs. on the top ofthe lid, increasing the pressure on the coil by a factor of3.8. 3) The effect ofa tighter lid produced in condition 2 above was investigated by clamping the lid closed and I1:!.nning the test. The weight ofthe clamps were negligible. 4) A space was provided between the coil and the potto evaluate the overall effect ofthe situation where the coil orpot 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 ofcontactpressure. An increase in contactpressure 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 majormechanism 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 1with 68.5 lb. weight added 9 Conductance to95.0 94.7 Same case as 1with clamped lid 94.9 96.5 Impact on Efficiency if the Pot and Coil are Same case as 1with airspacing 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 1with 68.5 lb. weight added to lid 94.8 95.1 95.0 94.7 96.5 .Same case as 1with clamped lid Impact on Efficiency if 

## r----------------+------+---- ___ the Pot and Coil are Same case as 1with 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 forestimating manufacturing cost to retail cost had a netresult of producing a multiplier in the range of2.16 to 3.01. We used aconservative value of 2.1 in our analysis. This multiplier represents the various mark-ups that occur after manufacturing or ApproximateRetail Cost=(K)ManufacturingCost where K =Mark-up Factor 

### Table A-1 presents the DOE datarelative to estimated manufacturing costs and retail options forelectric 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 (2or 4) ARetail ACost

^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 of2.16 to 3.01. We used a conservative value of 2.1 in our analysis. This multiplierrepresents the various mark-ups that occur after manufacturing orApproximateRetail Cost 

### = (K) Manufacturing Cost where K 

### = Mark-up Factor 

### Table**A~1** 

### presents the DOE datarelative 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 ofinvestigating 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 ofthe TransientThermal 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 aphysical system. TTA is a FORTRAN program which is designed to solve differential equations which arise inheat 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 ofa physical system. TTA can model both transient and steady state behavior ofasystem. Oven Model Using TTA, athermal model ofan average residential oven (Figure 1)has been developed to analyze the impact ofvarious 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. Backinside 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 ofinvestigatmg 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,ofa physical system. TT A isaFORTRAN program which is designed to solve differential equations which ariseinheat 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 transfercoefficients, radiative view factors and emissivities, and geometry are input requiredto model the thennal behaviorofa pi:lysical system. 

### ITAcan model both transient and'steady

, ,state,behaviorofa system.

Oven Model Using 'IT A, a thennal model ofan average residential oven (Figure 1) has been developed to analyze the impact ofvarious 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 source15.5" 5.5"
15"

22"

Steel .029" Insulation2" 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 andtottom 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"

InsideWall 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 modelassumptions can be summarized as follows:
• Convection occurs between oven cavity air 

### and the heating element and walls. • Heating element radiates to oven walls, top andnottom 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 AnalysisOven 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: TransierrtThermal 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 inthe oven model:

'Table B-1: Wall Materials Properties US,ed In Baseline Oven DeSign to calculate Conduction HeatTransierparameters



# -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, ft 2/sec Tf = film temperature, F (average ofwall and oven air temperatures) h = convective heat transfer coefficient Btu/(hr ft 2 °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 ofc and m used in the oven model. Table B-2: Definitionsof Variables Used in Convection Calculations
X A

X Top .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: Grashofnumber:

### 2~(Tw- T)L 3 

### v2

where: 

### Pr

# =Prandtl number L 

### = characteristic length. ft g 

### = 32.2 ftfs2**~** 

### = lfTf. 

### IIR Tw = wall temperature. F T

# =oven temperature. F v = kinematic viscosity. ft2/sec Tf = film temperature. F (average ofwall and oven airtemperatures) 

## 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 ofthe wall to the oven air. Table B-2 details the values ofc 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 ofporcelain was assumed to be .92. The parameters for conduction, convection and radiation were determined to describe the interrelationships ofnodes 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 of80°F and an oven set point temperature of350°F. For steady state runs the heating element surface temperature was varied until the oven setpoint temperature was reached. The relative change inheat loss is an indication ofthe energy savings once the oven has reached steady state conditions. The model was run in atransient mode to determine the effects ofdesign options on heat up time. The percentage change in heat up timeis an indication ofthe 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 ofthese savings to total energy consumed in acooking cycle must be understood. The cooking cycle energy consumption is made ofthree components: energy required to preheat theoven, steady state heat losses and energy absorbed by the cooking food. To estimate the energy required for acooking 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 DOEtest 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 ofcooking cycles per year can be estimated tobe 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 heatup, a conventional electric oven, was operated to a350°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 atypical 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 ofporcelain waS assumed to be .92.
.

. . The parameters for conduction, convection and radiation were determined to describe the interrelationships ofnodes in the oven model and listed above. These values

.were used as inputs in TTA to solve the steady state aI,ld transient analyses.

. . All design'options were compared at ambient temperatures. of80°F and an oven set pointtemperature of350°F. Forsteady 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 ofthe energy savings once the oven has reached steady state conditions. The model was run in a transient modeto determine the effects ofdesign options on heat up time. The percentage change in'heat up time is.an indication ofthe 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 ofthese savings to total energy consumed in a cooking cycle must be understood. The cooking cycle energy consuIl}.ption is made ofthree 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 bythe DOE was utilized. The DOEestimates that approximately 293 kWh peryear (adjusted DOE vallues) are used for oven cooking in a home. Considering the DOEtest .procedure for heating an 8.5 lb aluminum block to**325~F** (requires

### 45i.5 Btus) and an oven cOoking efficiency of12.10% for a conventional electric oven,.the amount ofcooking cycles per year can be estimated to be approximately 264 (standard electric oven). ,The average per cycle energyconsumption is about 3781 Btus or 1108 watt-hrs
.

.To determine the approximate energy required for heat up, a conventional electric

oven,**w~** operated to a 350°F oven set pointtemperature. 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 oventhermal 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 fora Cooking Cycle

.:i~- C!: o'ing '' e:": ':%t
.... . t : : 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 ofHeat 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 ofHeatTransfer, 3rd Edition 3. Holman, J. P., Heat Tranfer, 5th Edition.



# -Engineering Sciences Fax Transmittal Form To: Brooke Stauffer AHAM RegulatoryAffairs From: David Mallory ARTHUR D. LUTrLE, INC. 20AcornPark, Room 20/533 Cambridge, MA02140-2390 Tel! Return FAX: 

### Fax No: 1-202-434.7400
Date: July 18, 1994 Pages(includingthisone): 1 617498-5856 617/498-7206 Message: Dear Mr. Stauffer 

### Iamsendingthe informationyou requestedfrom ArieneMarge onannual usefulcooking energyoutputforelectric ovensand cooktops, seeTable 1. Table 1Annual UsefulCooking EnergyOutput For ElectricOvensAnd Cooktops 

### DOEValues ModifiedValues Ovens 

# 1 35.5 kWh/yr 26.6kWhtyr 

### Cooktops 209.4 kWh/yr 157.0IWh/yr Themodifiedannual energyusagevaluesdetailed inADL's reportwhere based on recent metered studiesthat indicatedthe adjusted DOEvalueswhere approximately25%toohigh. This ratiowasalsoappliedto theannualuseful cookingenergyoutputforelectricovensand cooktopstodetermine thevalues in Table 1. Ifyouanyquestionsonthe information, pleasedo nohesitatetocall.

Helpingcreate the right product ttherighttime 

## Artlur P LIle EngineeringScience. FaxTransmittal Form TO: BrookeStautter AHAM FIXNo: 1-202-434-7400 RegulatDryAffairs From: David Mallory

. Date:**~uly** 18.1994 ARTHUR D. U1TLE,INC.' 20Acom Park, Room201533 Cambridge, MA02140-2380 Pages (Includingthisone): 1 Tel: 617/498-5856 Return FAX: ·617/498-7'208 Message: DearMr. Stauffer: Iamsendingthe information yOU requestedfrom Arlene Margeot:'annual useful cooking energyoutputforelectricovensandcooktops, see Table 1. Table 1Annual Useful Cooking Energy Output For ElectricOvens And Cooktops 

### DOEValues ModifiedValue,s Ovens**3S.~** kWhlyr 26.6 kWhlyr Cooktops 209.4kWhlyr 157.0 WoIhJyr Themodified annualenergyusagevaJues detailed inADl's reportwhere based on recent meteredstudiesthat Indicatedthe,adjusted DOEvalues where approximately25%toohigh. ThIs ratio

### was alsoapptiedtotheannual usefulcookingenergyoutputforelectricovensand cooktopstodeterminethevalues in Table 1. ' Ifyou anyquestionsonthe information, pleasedonohesitatetocall.

Helpingcreatetherightproductat'the righttime 

## ArthIr 

## P 'Little