CHAPTER 5. ENGINEERING ANALYSIS

TABLE OF CONTENTS

5.1 INTRODUCTION

........................................................................................................... 5-1 5.2 TECHNOL OGIES UNABLE TO BE INCLUDED IN THE ENGINEERING ANAL YSIS

...................................................................................................................... 5 -2 5 .3 PRODUCT CLASSES ANAL YZED

.............................................................................. 5-4 5.4 EFFICIENCY LEVELS

................................................................................................... 5-5 5.4.1 Baseline Units

........................................................................................................... ....... 5-5 5.4.2 Incremental Efficiency Levels

......................................................................................... 5-6 5.5 METHODOLOGY OVERVIEW

.................................................................................... 5-9 5.5.1 AHAM Data Request

..................................................................................................... 5-1 0 5.5.2 Manufacturer Interviews

................................................................................................ 5- 10 5.5.3 Product Teardowns

........................................................................................................ 5-11 5.5.3.1 Selection of Units

......................................................................................... 5-11 5.5.3.2 Generation of Bill of Materials

.................................................................... 5-11 5.5.3.3 Cost Structure of the Spreadsheet Models

................................................... 5-12 5.5.4 Review of Previous Technical Support Documents

...................................................... 5-13 5.5.5 Product Testing

.......................................................................................................... .... 5-13 5.6 ANAL YSIS AND RESULTS

........................................................................................ 5-14 5.6.1 Cooking Products

......................................................................................................... .. 5-14 5.6.1.1 AHAM Data

................................................................................................. 5-14 5.6.1.2 Review of Past TSDs

................................................................................... 5-17 5.6.1.3 Product Testing and Teardowns

................................................................... 5-24

LIST OF TABLES Table 5.4.1 1996 TSD Baseline Energy Factors for Cooking Products

................................. 5-6 Table 5.4.2 Efficiency Levels for Residential Gas Cooktops

................................................. 5-7 Table 5.4.3 Efficiency Levels for Residential Electric Cooktops

........................................... 5-7 Table 5.4.4 Efficiency Levels for Residential Gas Ovens

...................................................... 5-8 Table 5.4.5 Efficiency Levels for Residential Electric Ovens

................................................ 5-9 Table 5.4.6 Efficiency Levels for Residential Microwave Ovens

.......................................... 5-9 Table 5.5.1 Engineering Analysis Methods

.......................................................................... 5-10 Table 5.5.2 Major Manufacturing Processes

........................................................................ 5-13 Table 5.6.1 Gas Cooktop Manufacturing Cost and Efficiency Increments

.......................... 5-18 Table 5.6.2 Electric Coil Cooktop Manufacturing Cost and Efficiency Increments

............ 5-19 Table 5.6.3 Electric Smooth Cooktop Manufacturi ng Cost and Efficiency Increments

....... 5-19 Table 5.6.4 Gas Standard Oven Manufacturi ng Cost and Efficiency Increments

................ 5-20 Table 5.6.5 Gas Self-Cleaning Oven Manufactur ing Cost and Efficiency Increments

........ 5-21 Table 5.6.6 Electric Standard Oven Manufacturing Cost and Efficiency Increments

.......... 5-21

5-iTable 5.6.7 Electric Self-Cleaning OvenManufacturing Cost and Efficiency Increments

.......................................................................................................... 5-22 Table 5.6.8 Slopes and Intercepts for Oven Energy Factor versus Cavity Volume Relationship

....................................................................................................... 5-23 Table 5.6.9 Microwave Oven Manufacturing Cost and Efficiency Increments

................... 5-24 Table 5.6.10 Microwave Oven Features (Table 1 of 4)

.......................................................... 5-25 Table 5.6.11 Microwave Oven Features (Table 2 of 4)

.......................................................... 5-25 Table 5.6.12 Microwave Oven Features (Table 3 of 4)

.......................................................... 5-25 Table 5.6.13 Microwave Oven Features (Table 4 of 4)

.......................................................... 5-26 Table 5.6.14 Microwave Oven Input, Output, and Cooking Efficiency (1 of 4)

.................... 5-28 Table 5.6.15 Microwave Oven Input, Output, and Cooking Efficiency (2 of 4)

.................... 5-28 Table 5.6.16 Microwave Oven Input, Output, and Cooking Efficiency (3 of 4)

.................... 5-28 Table 5.6.17 Microwave Oven Input, Output, and Cooking Efficiency (4 of 4)

.................... 5-28 Table 5.6.18 Microwave Oven Rated versus Measured Output for AHAM and DOE Tests

................................................................................................................... 5-30 Table 5.6.19 Key Differences Between IEC Standard 705 and IEC Standard 60705

............ 5-33 Table 5.6.20 IEC Standard 705 versus IEC Standard 60705 Test Results

............................. 5-34 Table 5.6.21 IEC Standard 705 versus IEC Standard 60705-2006 Test Results, Without Rounding

............................................................................................................ 5-37

LIST OF FIGURES Figure 5.5.1 Manufacturing Cost Assessment Stages

............................................................ 5-12 Figure 5.6.1 AHAM Microwave Oven Efficiency versus Rated Output Power

.................... 5-16 Figure 5.6.2 AHAM Microwave Oven Efficiency versus Oven Cavity Volume

.................. 5-17 Figure 5.6.3 DOE and AHAM Microwave Oven Effi ciency versus Rated Output Power

.... 5-29 Figure 5.6.4 DOE and AHAM Microwave Oven Efficiency versus Measured Output Power

................................................................................................................. 5-31 Figure 5.6.5 DOE Non-Rounded versus Rounded Test-to-Test Efficiency Variation Measured U sing IEC Standard 60705

................................................................ 5-35 Figure 5.6.6 DOE Non-Rounded versus Rounde d Efficiency Measured Using IEC Standard 60705

.................................................................................................. 5-36

5-iiCHAPTER 5. ENGINEERING ANALYSIS

5.1 INTRODUCTION After conducting the screening analysis, the U.S. Department of Energy (DOE) performed an engineering analysis based on th e remaining design options. The engineering analysis consists of estimating the energy a nd water consumption and costs of products at various levels of increased effi ciency. This section provides an overview of the engineering analysis (section 5.1), considers technologies that are unable to analyzed for this rulemaking (section 5.2), discusses proposed product cla sses (section 5.3), estab lishes baseline unit specifications (section 5.4.1), discusses incrementa l efficiency levels (section 5.4.2), explains the methodology used during data gathering (5.5) and di scusses the analysis a nd results (section 5.6) As described in section 1.3 of chapter 1 of this technical su pport document (TSD), DOE is continuing the energy conservation standards ru lemaking for commercial clothes washers and microwave oven standby power, and analyses rela ted to these products will be published in subsequent TSDs. As a result, this chapter pr esents results for resi dential cooking products, including microwave oven energy factor. The primary inputs to the engine ering analysis are baseline information from the market and technology assessment (chapter 3 of the TS D) and technology options from the screening analysis (chapter 4.) Additional inputs include cost and energy efficiency data, which DOE received from the Association of Home App liance Manufacturers (AHAM), obtained from the previous rulemaking analysis, and qualified and supplemented through testing, teardown analysis and manufacturer interviews. The primary output of the engineering analys is is a set of costefficiency curves. In the subsequent markups analysis (chapter 7), DOE determined customer ( i.e. product purchaser) prices by applying distribution markups , sales tax and contractor markups. After applying these markups, they serv e as the input to the building energy-use and end-use load characterization (c hapter 6) and the life-cycle cost (LCC) and payback period (PBP) analyses (chapter 8). DOE typically structures its engineering analysis around one of three methodologies. These are: (1) the design-option approach, wh ich calculates the incremental costs of adding specific design options to a baseline model; (2) the efficiency-level approach, which calculates the relative costs of achieving increases in ener gy efficiency levels, without regard to the particular design options used to achieve such increases; and/or (3) the reverse engineering or cost-assessment approach, which involves a “b ottom-up” manufacturing cost assessment based on a detailed bill of materials (BOM) derived from teardowns of the product being analyzed. Deciding which methodology to use for the engin eering analysis depends on the product, the design options under study, and any histor ical data that DOE can draw on.

5-15.2 TECHNOLOGIES UNABLE TO BE INCLUDED IN THE ENGINEERING ANALYSIS In performing the engineering analysis, DOE did not consider for analysis certain technologies that met the screeni ng criteria but were unable to be evaluated for one or more of the following reasons: (1) data are not available to evaluate consumer usage of a product incorporating the technology and, therefore, the test procedure conditions and methods may not be applicable; (2) data are not available to evaluate the energy efficiency characteristics of the technology; and (3) available data suggest that the efficiency benefits of the technology are negligible. In the first two cases, DOE is unabl e to adequately assess how these technologies impact annual energy consumption. For technologies that lack consumer us age details, including operating conditions, duration, and frequency, DOE believes that the ex isting test procedures may specify conditions and methods that are not representa tive of actual usage. DOE furthe r believes that even if data were available to amend the test procedures, su ch changes could be ex tensive enough to require total revision, which in turn could warrant the creation of a separate product class for that technology in the event that the test pr ocedure changes indi cated unique utility. Furthermore, certain technologies cannot be measured according to the conditions and methods specified in the existing test procedure. In other cases, available data suggest that so me of the design options would result in such small energy savings as to be negligible. Becau se DOE intends to focus on the technologies with measurable impact on efficiency, design options with negligible energy savings have been eliminated from further consideration.

 Several technologies are availabl e for cooktops that allow the burners or heating elements to automatically adjust in response to cooki ng-state setpoints, such as cooking vessel temperature. These include thermostatically controlled gas cooktop burners as well as electronic controls for electri c cooktops. However, DOE is unaware of any data to quantify the energy efficiency e ffects of such technologies. Fu rther, efficiency benefits of these design options can only be realized under variable burner or element conditions. Because the cooktop test procedure does not account for consumer usage patterns, the energy savings of these technologies cannot be adequately measured. Therefore, DOE did not consider these design options for further analysis.

 Similarly, DOE is unaware of any data that indicates a measurable energy efficiency impact of insulation in gas and electric coil cooktops, so DOE did not analyze this design option for these product classes.

 Induction cooktops require ferromagnetic cookwar e in order to transfer energy to the food contents. While the test block specified in the DOE test procedure is aluminum and thus is unable to measure the efficiency of induction cooktops, the National Bureau of Standards (NBS), now called National Institute of Standards and Technology (NIST),

5-2proposed an alternate method of measuring the energy consumption of such cooktops by simply attaching a ferromagnetic material to th e bottom of the test block. Data obtained by this method suggested an efficiency improvement over baseline electric smooth cooktops. However, this test method has not been rigorously validated for incorporation into the DOE test procedure and therefore, due to the unresolved nature of the NIST data, DOE eliminated induction elements fo r electric smooth cooktops from further consideration.

 Some electric cooktops and microwave ovens with electronic controls consume standby power, but the efficiency metrics ( i.e. , energy factor (EF)) do not incorporate such power in their calculation. Even though DOE consider s the consumer usage of these products to be well-defined, the current test procedur e does not measure standby power. Thus DOE is unable to quantify the impact on energy sa vings of low-standby-lo ss electronic controls for these products and did not consider th ese design options during the analysis.

 The only currently available gas ovens that DOE is aware of that incorporate radiant burners do so for broiling, which is a secondary cooking function that is not the focus of the DOE efficiency measurement; energy efficiency is instead measured during the primary bake function. Thus the energy bene fits are not captured by the test procedure under these conditions. Accordingly, DOE elim inated radiant burners in gas ovens from further analysis.

 While there are several residential steam ovens currently on the market, DOE believes that the existing test procedure may speci fy conditions and methods that are not representative of actual usage. DOE further believes that even if data were available to amend the test procedure, such changes could be extensive en ough to require total revision, which in turn could warrant the creat ion of a separate produc t class in the event that the test procedure changes indicated unique utility. Thus, DOE did not consider steam cooking in the analysis.

 For added insulation in microwave ovens, th is technology will not improve the EF, since during the short duration of the DOE test procedure as we ll as during typical usage, the microwave oven cavity walls do not measurably h eat up. Thus, the energy savings of this design option would be so small as to not be measurable.

 Cooking sensors, which terminate the operation of a microwave oven based upon inferred cooking state, appear to promote shorter c ook times and thus lower energy consumption. Due to the lack of consumer usage detail s, including operating conditions, duration, and frequency of use, DOE believes that the existing test procedure may specify conditions and methods that are not representative of act ual usage. Thus, DOE did not consider this design option for further analysis.

 According to AHAM, dual magnetrons in microwave ovens do not improve energy efficiency due to the added losses associatedwith two magnetron heaters. In addition, AHAM stated that the additional cost of dual magnetrons could not be economically

5-3justified. DOE does not have any efficiency data on dual magnetrons by which to evaluate this design option. Therefore, it did not consider dual magnetrons for further analysis.

 AHAM stated that virtually no residential solo-function microwav e oven still uses a ceramic stirrer. Almost all microwave ove ns use polypropylene or mica film stirrers, which have lower losses than ceramic stirre rs. According to AHAM, this design option has already been optimized so there is no oppor tunity for efficiency improvements. The stirrer cover, however, may be made of ceramic when there are browning elements that generate too much heat for a plastic cover. These covers absorb some microwave energy but are needed to prevent f ood splatter inside the wave guide. Eliminating the ceramic cover would adversely affect consumer utili ty by requiring cleaning of the stirrer or by reducing the life of the stirrer. Therefore, DOE’s analysis did not consider eliminating or improving the ceramic stirrer cover.

 According to AHAM, losses associated with th e wave guide are typi cally less than 0.5 percent of the overall energy consumption. DOEis not aware of any data demonstrating efficiency improvements associated with wave guide improvement, so DOE did not analyze this design option.

5.3 PRODUCT CLASSES ANALYZED DOE separated residential cooking products into product classes. Because DOE considered a separate energy conservation stan dard for each product class, the criteria for separation into different classes ar e (1) type of energy used (natur al gas or electricity), and (2) capacity or other performance-relate d features such as those that provide utility to the consumer, or others deemed appropriate by the Secretary that would justify the estab lishment of a separate energy conservation standar d. (42 U.S.C. 6295 (q)) For cooking products, DOE analyzed product classes based on the energy source ( i.e. , gas or electric) and the cooking method ( i.e. cooktops, ovens, and microwave ovens.) These distinctions yielded five cooking product classes: (1) gas cook tops; (2) electric cooktops; (3) gas ovens; (4) electric ovens; and (5) microwave ovens. DOE’s product classes are based on the list of product classes defined by DOE in its 1996 Technical Support Document for Residential Cooking Products (1996 TSD), which was released as part of the previous standards rulemaking. 1 Gas and electric ranges aare not listed below as produc t classes. Because ranges consist of both a cooktop and oven, any potenti al cooktop and oven standards will apply to the individual components of the range . As a result, product classes for ranges are not necessary.
For gas cooktops , DOE’s analyzed product class is:

aDOE defines a “conventional range” under EPCA as “a class of kitchen ranges and ovens which is a household cooking appliance consisting of a conventional cooking top and one or more conventional ovens.” (10 CFR 430.2)

5-4 Conventional burners.
For electric cooktops , DOE’s 1996 TSD determined that the ease of cleaning smooth elements provides enhanced consumer utility over coil elements. Because smooth elements typically use more energy than coil elements , DOE analyzed the following product classes for electric cooktops:

 Low or high wattage open (coil) elements; and

 Smooth elements.
For electric ovens , the 1996 TSD determined that the type of oven-cleaning system is a utility feature that affects performance. DOE found that standard ovens and ovens using a catalytic continuous-cleaning process use roughly the same amount of energy. Self-cleaning ovens use a pyrolytic process that provides enhan ced consumer utility with lower overall energy consumption as compared to either standard orcatalytically lined ovens . Thus, DOE analyzed the following product classes for electric ovens:

 Standard oven with or wit hout a catalytic line; and

 Self-cleaning oven.
For gas ovens , DOE analyzed the following produc t classes based upon the same reasoning as electric ovens:

 Standard oven with or wit hout a catalytic line; and

 Self-cleaning oven.

For microwave ovens , DOE analyzed no further class breakdown. This product class can encompass microwave ovens with and with out browning elements, but does not include microwave ovens that incorporate convection systems (combination ovens). DOE did not conduct an analysis of combination microwave ovens due to the inability of the test procedure to measure the performance of the convection compone nt and thus a lack of data evaluating the energy efficiency or energy efficiency char acteristics of microwave ovens incoporating convection systems.

5.4 EFFICIENCY LEVELS

5.4.1 Baseline Units
DOE selected baseline units as reference points for each product class, against which DOE measured changes resulting from energy cons ervation standards. The baseline unit in each product class represents the basic ch aracteristics of equipm ent in that class. Typically, a baseline unit is a unit that just meets current required energy conservation standards and provides basic consumer utility.

5-5DOE used the baseline units in the engine ering analysis and th e life-cycle-cost and payback-period analysis. To determine energy savings and changes in price, DOE compared each higher energy efficiency or lower energy effi ciency design option with the baseline unit. The identification of baseline units required es tablishing the baseline efficiency level. For residential cooking products (except for the pr escriptive standard for gas cooking products), there are no existing minimum energy conservation standards, as previous analyses ( i.e. , from the 1996 TSD) failed to determine economic justif ication for them. The DOE test procedure uses EF to rate the efficiency of cooking products. The EF for these products is the ratio of the annual useful cooking energy outpu t of the cooking appliance ( i.e. the energy conveyed to the item being heated) to its total annual energy c onsumption. In accordance with the 1996 TSD on residential cooking products, DOE has selected the baseline EFs listed in Table 5.4.1 for the product classes DOE is using in this rulemaking. Table 5.4.1 1996 TSD Baseline Energy Factors for Cooking Products

Product Class Baseline from 1996 TSD EF Gas Conventional Burner Cooktop 0.156 Electric Open (Coil) Element Cooktop 0.737 Electric Smooth Element Cooktop 0.742 Gas Standard Oven 0.030 Gas Self-Clean Oven 0.054 Electric Standard Oven 0.107 Electric Self-Cl ean Oven 0.096 Microwave Oven 0.557

5.4.2 Incremental Efficiency Levels For the majority of the product classes pres ented in section 5.3, DOE analyzed several efficiency levels and obtained incremental co st data at each of these levels. Table 5.4.2 through Table 5.4.6 provide efficiency leve ls and the reference source of each level for each of the products under consideration. The maximum levels identified in these tables are based on data developed from the design-option analysis in the previous rulemaking.
Table 5.4.2 presents the efficiency levels analyzed for residential gas cooktops . The baseline and higher efficiency levels are based on the analysis performed in 1996 for the previous rulemaking. Since the 1996 TSD took a design-option approach to the analysis, each efficiency level is associated with a particular desi gn option or combination of design options. Two higher efficiency levels for gas cooktops were included in the 1996 TSD that are not considered here due to the elim ination of design options. In the current analysis, reflective surfaces were screened out due to impacts on co nsumer utility, and thermostatically controlled burners were not analyzed due to the inability of the DOE test procedure to adequately represent usage patterns and therefore energy efficiency characteristics. The combination of design options that produces the maximu m technologically feasible EF is designated as “max-tech.”

5-6DOE has structured the analysis for standi ng pilot igntion systems as a design option associated with the baseline configuration because DOE has determined that cooktops incorporating such ignition systems do not provide unique utility for reasons stated in section 3.3 of chapter 3 of this TSD. The first standards efficiency level correspond s to the elimination of standing pilot lights. Table 5.4.2 Efficiency Levels fo r Residential Gas Cooktops

Level Efficiency Level Source Conventional Burners Cooking Efficiency EF Baseline 1996 TSD Baseline (with standing pilots) 0.399 0.156 1 1996 TSD (without standing pilots) 0.399 0.399 2 Max-Tech (1996 TSD) 0.420 0.420 The 1996 TSD analyzed two efficiency levels for electric coil cooktops and three levels for electric smooth cooktops . Since the 1996 TSD took a design-option approach to the analysis, each efficiency level is associated w ith a particular design option or combination of design options. In the current analysis, however , reflective surfaces were screened out as a design option for electric coil cooktops due to impacts on consumer utility, and induction elements were not analyzed for electric smooth cooktops because the available efficiency data, while suggestive of energy savings, cannot be valid ated by the existing DOE test procedure. In addition, radiant elements for smooth electric co oktops, which were included in the 1996 TSD, were not considered as a design option for this rulemaking because manufacturer data provided to DOE for the 1996 TSD indicated that this technology does not o ffer an efficiency improvement over the baseline according to the DOEtest procedure. Therefore, only a single efficiency level beyond the baseline was anal yzed for both electric coil and smooth cooktops, and by default this level becomes the max-tech, as shown in Table 5.4.3
. Table 5.4.3 Efficiency Levels for Residential Electric Cooktops

Level Efficiency Level Source Open (Coil) Elements Smooth Elements Cooking Efficiency EF Cooking Efficiency EF Baseline 1996 TSD Baseline 0.737 0.737 0.742 0.742 1 1996 TSD 0.769 (Max-Tech) 0.769 0.753 (Max-Tech) 0.753 Efficiency levels for gas ovens , as shown in Table 5.4.4, are based on the 1996 TSD. Since the 1996 TSD took a design-option approach to the analysis, each efficiency level is associated with a particular de sign option or combination of de sign options. The oven separator design option from the 1996 TSD was screened out in the current analys is due to consumer safety and utility issues, as we ll as a lack of practicability to design and manufacture. Lowstandby-loss electronic controls we re added as design options for both standard and self-cleaning gas ovens, but were not included as efficiency levels because DOE does not have efficiency or cost increment information on them. The baseline efficiency level for gas standard ovens assumes that th e product is equipped with standing pilot lights, and the first standard s efficiency level corresponds to the elimination of standing pilot lights based on the same reas on as for gas cooktops. However, because the cleaning cycle of gas self-cleaning ovens requi res electrical energy use, the existing energy

5-7conservation standard in effect requires that such ovens currently be equipped with a nonstanding pilot ignition system because such an i gnition system is disallowed if there is an electrical cord provided on the pr oduct. Therefore, the baseline efficiency level for gas selfcleaning ovens assumes they lack a standing pilot light. Further, the first standards efficiency level is not based on elimination of a standing pilot, but ratheron the addition of the forced convection design option. Electronic spark ignition lowers the standby power consumption as well as the cooking efficiency of standard gas ovens, and since th e standard gas oven EF rating includes standby power, the use of electronic spark ignition results in an overall reduction in energy consumption. Electric spark ignition has the same functionality as hot surface i gnition sources and is therefore listed as an alternate efficiency level to the hot surface (glo-bar) design option. Table 5.4.4 Efficiency Levels for Residential Gas Ovens

Level Efficiency Level Source Standard Oven Self-Cleaning Oven Cooking Efficiency EF Cooking Efficiency EF Baseline 1996 TSD Baseline (with standing pilot light) 0.059 0.0298 0.071 0.0540

1 1996 TSD 0.058 (Glo-bar ignition) 0.0536 0.088 0.0625 2 1996 TSD 0.061 0.0566 0.088 0.0627 3 1996 TSD 0.062 0.0572 0.089 (Max-Tech) 0.0632 4 1996 TSD 0.065 0.0593

- - 5 1996 TSD 0.065 0.0596

- - 6 1996 TSD/Current Analysis 0.066 (Max-Tech) 0.0600

- - 1a (1) 1996 TSD (with electronic spark ignition) 0.058 0.0583

- - (1) Note: Standard levels 1 and 1a correspond to designs that are utilized for the same purpose--eliminate the need for a standing pilot--but the technologies for each design are different. Standard level 1 is a hot surface ignition device while standard level 1a is a spark ignition device Efficiency levels for electric ovens , shown in Table 5.4.5, are primarily based on the 1996 TSD. The oven separator design option from the 1996 TSD was screened out in the current analysis due to consumer safety and utility issues, as well as a l ack of practicabil ity to design and manufacture. The bi-radiant oven was screened ou t due to a lack of tech nological feasibility and practicability to manufacture, as well as impacts on consum er utility. Low-standby-loss electronic controls were added as design options for both standard and self-cleaning electric ovens in this analysis, but were not included as efficiency levels because, even though the test procedure accounts for the energy consumption of electronic controls, DOE does not have incremental efficiency or cost information on them.

5-8Table 5.4.5 Efficiency Levels for Residential Electric Ovens
Level Efficiency Level Source Standard Oven Self-Cleaning Oven Cooking Efficiency EF Cooking Efficiency EF Baseline 1996 TSD Baseline 0.122 0.1066 0.138 0.1099 1 1996 TSD/Current Analysis 0.128 0.1113 0.138 0.1102 2 1996 TSD/Current Analysis 0.134 0.1163 0.142 (Max-Tech) 0.1123 3 1996 TSD/Current Analysis 0.137 0.1181

- - 4 1996 TSD/Current Analysis 0.140 0.1206

- - 5 1996 TSD/Current Analysis 0.141 (Max-Tech) 0.1209

- - For microwave oven energy factor, Table 5.4.6 lists the efficiency levels that were retained from the 1996 TSD, even though recent AHAM-supplied data suggests slightly different baseline and maximum-available e fficiencies of a representative sample of current models. For example, the minimum efficiency among the microwave ovens recently tested by AHAM was 54.8 percent, while the maximum efficiency wa s 61.8 percent, compared to 55.7 percent and 60.2 percent, respectively, from the 1996 TSD. However, it was noted that the standard deviation in efficiency measurements for any given microwave oven ranged from 0.2 to 1.2 absolute percentage points. To attempt to id entify microwave oven design options associated with efficiency levels, DOE performed a reverse- engineering analysis on a representative sample of microwave ovens. DOE did not find any addi tional design options beyond those that were identified in the advance no tice of proposed rulemaking (ANOPR). DOE also performed efficiency testing on the sample of microwave ovens, which validated data submitted by AHAM. Results from both AHAM and DOE efficiency testing showed no identifiable correlation between cooking efficiency and either cavity vol ume or rated output power. As part of the reverse-engineering analysis, DOE also ev aluated microwave oven magnetrons, magnetron power supplies, and fan motors (identified as design options in chapter 3 of this TSD), and determined that efficiencies for these design optio ns have changed little since the 1996 analysis. For these reasons, it was determined by DOE that the efficiency levels from the 1996 TSD were still representative of the state of current mi crowave oven technology to the extent that the DOE test procedure can capture performance. Further discussion of the AHA M test data and DOE testing and analysis is provided in section 5.6.1.1. Table 5.4.6 Efficiency Levels fo r Residential Microwave Ovens

Level Efficiency Level Source Efficiency Level (EF) Baseline 1996 TSD Baseline 0.557 1 1996 TSD 0.586 2 1996 TSD 0.588 3 1996 TSD 0.597 4 1996 TSD Max-Tech 0.602

5.5 METHODOLOGY OVERVIEW DOE typically uses data submitted by AHAM as the primary source of cost information for the engineering analysis. AHAM generally provides DOE with aggregated incremental

5-9manufacturing cost data from it member compan ies, whereupon DOE conducts an independent review of the AHAM data using several methods and data sources. To gain a better understanding of the data submitted by member compan ies and to be able to relate the costs of improving efficiency to discrete (or system) technologies, DOE typically conducts interviews with manufacturers of resident ial cooking products. For this rulemaking, however, with general support from interested parties, DOE reviewedthe previous TSD and compared cost and performance information to AHAM data and other published data. For microwave ovens specifically, DOE performed deta iled product teardowns on a sample of models spanning a range of efficiencies and product features. Table 5.5.1 below shows the methods DOE used for the engineering analysis. Table 5.5.1 Engineering Analysis Methods

Method Products AHAM Data Microwave Ovens Only Review of Past TSD All Cooking Products Product Teardown Microwave Ovens Only Product Testing Microwave Ovens Only Manufacturer Interviews All Cooking Products

5.5.1 AHAM Data Request In support of this rulemaking effort, DOE requested incremental cost data from AHAM for each of the product categories. The requested data would represent the average incremental production cost to improve a baseline unit to a sp ecified efficiency level. In addition, DOE requested shipments, shipment-weighted average e fficiency, and market share efficiency data. As discussed above, AHAM did notprovide cost information, agreeing with DOE that the previous analysis from the 1996 TSD, updated to reflect current manufacturing costs, would be appropriate for this rulemaking. AHAM did, howev er, provide efficiency data for a sample of microwave ovens, as discussed in section 5.6.1. Data provided to DOE by AHAM are contained in appendix 5A.

5.5.2 Manufacturer Interviews
To better understand cost variances due to the variability in baseline units, design strategies, and cost structures that may ex ist among manufacturers, DOE supplemented the estimated cost data with information obtained through follow-up manufacturer interviews. These confidential interviews provide d a deeper understanding of th e various combinations of technologies used to increase pr oduct efficiency, and their asso ciated manufacturing costs. Sample questions asked during the follow-up inte rviews, which were also conducted in support of the manufacturer impact analysis , are contained in appendix 13B. During the interviews, DOE also gathered information about the capital expenditures required to increase the efficiency of the ba seline units to various efficiency levels ( i.e. ,
5-10conversion capital expenditures by efficiency or energy-use level). The interviews provided information about the size and the nature of the capital investments. DOE also requested information about the depreciation method used to expense the conversion capital.

5.5.3 Product Teardowns Other than obtaining detailed manufacturing co sts directly from a ma nufacturer, the most accurate method for determining the production cost of a piece of equipmen t is to disassemble the equipment piece-by-piece and estimate the materi al and labor cost of each component using a process commonly called a physical teardown. A supplementary method, called a catalog teardown, uses published manufactur er catalogs and supplementary component data to estimate the major physical differences between a piec e of equipment that has been physically disassembled and another piece of similar equi pment. DOE only performed physical teardown analysis on microwave ovens. The teardown me thodology is described in detail in section 5.5.3.1 through section 5.5.3.3.

5.5.3.1 Selection of Units During the process of selecting units for t eardown, DOE considers three main questions:

 What efficiency levels should be captured in the t eardown analysis?

 Are there units on the market th at capture all potential effici ency levels and design options?

 Which of the available units are most representative? In responding to the preceding questions, DOEadopts the following criteria for selecting units for the t eardown analysis:

 The selected products should span the full range of efficiency levels for each product class under consideration;

 Within each product class, if possible, the se lected products should come from the same manufacturer and be within the same product series;

 The selected products should prim arily come from manufacturers with large market share in that product class, although the highest effici ency products were chosen irrespective of manufacturer; and

 The selected products should have non-efficiency-related features that are the same as, or similar to, features of other products in the sa me class and at the same efficiency level.

5.5.3.2 Generation of Bill of Materials The end result of each teardown is typically a structured bill of ma terials (BOM). The process is discussed here in the context of the general methodology used for teardown analysis, although it should be noted a more limited approach was used for microwave ovens due to the substantial uniformity in design and construc tion among the sample units. Structured BOMs describe each equipment part and its relationship to the other part s, in the estimated order of

5-11assembly. The BOMs describe each fabrication a nd assembly operation in detail, including the type of equipment needed ( e.g. , stamping presses, injection molding machines, spot-welders, etc.) and the process cycle times. The resultis a thorough and explicit model of the production process. The BOMs incorporate all materials, components, and fasteners, classi fied as either raw materials or purchased parts and assemblies. Th e classification into raw materials or purchased parts is based on DOE’s previous industry expe rience, recent informati on in trade publications, and discussions with high- and low-volume original equipment manufacturers (OEMs). For purchased parts, the purchase price is an estimate based on volume-variable price quotations and detailed disc ussions with suppliers. For fabricatedparts, the price of intermediate materials ( e.g. , tube, sheet metal) and the cost of transforming them into finished parts are an estimate based on current industry pricing.
The cost of raw materials is determined us ing data sources such as American Metals Market for prices for copper, steel and aluminum, for example. 2 DOE research suggests that the price of steel drastica lly increased in 2005, and the price of copper has increased significantly since 2004. Because DOE is using a 5-year average in material prices, these price increases are normalized, which better represen ts long-term material prices.

5.5.3.3 Cost Structure of the Spreadsheet Models The manufacturing cost assessment methodology used is a detailed, component-focused technique for rigorously calculati ng the manufacturing cost of a pr oduct (direct materials, direct labor and some overhead costs.) Figure 5.5.1 shows the three major steps in generating the manufacturing cost.

Figure 5.5.1 Manufacturing Cost Assessment Stages The first step in the manufacturing cost a ssessment is the creation of a complete and structured BOM from the disassembly of the units selected for teardown. The units are dismantled, and each part is characterized acco rding to weight, manufacturing processes used, dimensions, material, and quantity. The BOM in corporates all materials, components, and fasteners with estimates of raw material costs and purchased part costs. Assumptions on the sourcing of parts and in-house fa brication are based on industry experience, information in trade publications, and discussions with manufacturers. Interviews and plant visits are also conducted with manufacturers to ensure accuracy on methodology and pricing.

5-12Following the development of a detailed BOM, the major manufacturing processes are identified and developed for the spreadsheet m odel. These processes are listed in Table 5.5.2. Table 5.5.2 Major Manufacturing Processes

Fabrication Finishing Assembly/Joining Quality Control Fixturing Washing Adhesive Bonding Inspecting & Testing Stamping/Pressing Powder Coating Spot Welding Brake Forming De-burring Seam Welding Cutting and Shearing Polishing Insulating Fabrication process cycle times are estimatedand entered into the BOM. For this analysis, $24.00 per hour was used as the average fully-burdened labor rate based on typical annual wages and benefits of industry employees. In the final step of the cost assessment, assembly times and associated direct labor costs are estimated. Once the cost estimate for each teardown unit is finalized, a detailed summary is preparedfor relevant components, subassemblies and processes. The BOM thus details all aspects of unit costs. Design options used in units subject to tear down are noted in the summary sheet of each cost model and are cost-estimated individually. Thus, various implementations of design options can be accommodated, ranging from assemblies that ar e entirely purchased to units that are made entirely from raw materials. Hybrid assemblies, consisting of purchased parts and parts made on site are thus also accommodated.

5.5.4 Review of Previous Technical Support Documents DOE reviewed previous rulemaking TSDs to assess their applicability to the current standard setting process for cooking products. These previous rulemaking technical support documents served as a source for design options , baseline efficiency levels, and energy consumption analysis, in addition to other source s. DOE utilized the 1996 TSD as a source for baseline unit efficiency as well as design options and incremental cost and efficiency data. This approach for cooking products was generall y supported by intere sted parties.

5.5.5 Product Testing DOE conducted product testing on microwave ovens to develop a better understanding of the potential efficiency improvements a ssociated with various design options.

5-135.6 ANALYSIS AND RESULTS

5.6.1 Cooking Products

5.6.1.1 AHAM Data Conventional Cooking Products AHAM did not provide DOE with cost-efficiency data for conventional cooking products ( i.e. , cooking products other than microwave ovens), in part because it stated that its members indicated that there have been no technology breakthroughs since the last rulemaking and that its members were not able to adequately assess many of the design options. In concurrence with interested parties, DOE believes that the efficien cy characteristics of gas and electric cooktops and ovens from the 1996 TSD are still valid. Ther efore, the efficiency data provided in the 1996 TSD are also presumed to still be valid. Furthe rmore, DOE believes that the cost of the design options investigated in the 1996 TSD are also va lid once adjusted to reflect changes in the producer price index (PPI). The data from the 1996 TSD are detailed in section 5.6.1.2.
Microwave Ovens
In contrast to conventional cooking products, microwave ovens were presumed to have incorporated improved technology since 1996. Th erefore, AHAM provided data on microwave oven efficiency (and standby power) for a sample of microwave ovens currently available in the U.S. market. 3 Microwave oven efficiency was tested according to DOE’s test procedure, which utilizes the International Electrotechni cal Commission (IEC) Standard 705-1988 and Amendment 2-1993, Methods for measuring the performanc e of microwave ovens for household and similar purposes . Standby power was tested in accordance with IEC Standard 62301-2005, Household electrical appliances – Measurement of standby power

. The microwave oven test procedure specifi ed in IEC Standard 705-1998 and Amendment 2-1993 calls for heating a glass container contai ning one liter of water at full power until the water temperature is raised by a specified am ount. The starting temperature of the water T 1 in degrees Celsius ( ° C) is given as:

T 1 = T 0 – (10 ± 1 ° C) where,

T 0 = the ambient temperature, specified as 20 ± 2 ° C The water is heated by the operation of the microwave oven until the final water temperature T 2 in ° C is:

T 2 = T 0 ± 1 ° C The microwave power output P in W is then calculated from:

5-14P = (4.187 m w (T 2 – T 1 ) + 0.88 m c (T 2 – T 0 ))/t where,

m w = the mass of the water in grams (g)
m c = the mass of the container in g t = the heating time in seconds (s) The time to heat the water load, power input P INin W, and the total energy consumption E M in watt-hours (Wh) of the microwave oven during the test period are also recorded. This test is repeated three times, unless the power output value resulting from the second test is within 1.5 percent of the value obtained from the first test. The two or three values of P are averaged for further calculations. Cooking efficiency Eff MO is then obtained using:
Eff MO = P/P IN For the remainder of the calculations, the te st procedure specified in 10 CFR 430 subpart B appendix I is utilized. Note th at in the following calculations, all temperatures are expressed in degrees Fahrenheit. The mi crowave oven test energy output E T in Wh (kilo-joules (kJ)) b is calculated as:

E T = C P M W (T 2 – T 1 ) + C C M C (T 2 – T 0 ))/K e where,

M W = the measured mass of the test water load in pounds (lb), (g) M C = the measured mass of the test container before filling with test water load in lb (g) T 1 = the initial test water load temperature in ° F ( ° C) T 2 = the final test water load temperature in ° F ( ° C) T 0 = the measured ambient room temperature in ° F ( ° C) C C = 0.210 British thermal units (BTU)/lb- ° F (0.88 kJ/kilogram (kg)- ° C), specific heat of the test container C P = 1.0 BTU/lb- ° F (4.187 kJ/kg- ° C), specific heat of water K e = 3,412 BTU/kWh (3,600 kJ/kWh), conve rsion factor of kWh to BTU. The two or three values for test energy output are averaged and the microwave oven annual energy consumption E MO is calculated in kWh per year from:

E MO = (E M x O M )/E T where,

E M = the test energy consumption in Wh (kJ)

b Note that in order to correctly utilize the equation as specified in the test procedure to produce either watt-hours for standard units or kJ for metric units, additional factors must be applied. For standard units, E T must be multiplied by 1000. For metric units, E T must be divided by 3600.

5-15O M = 79.8 kWh (287,280 kJ) per year, the microw ave oven annual useful cooking-energy output Finally, the microwave oven energy factor R MO (equivalent to EF) is calculated from:

R MO = O M/E MO EF is the metric for microwave ovens on which the DOE efficiency standard is based, while AHAM provided test data in terms of cooking efficiency in their data submittal for this rulemaking. From the above equations, it can be observed that there ar e several contributing factors that can lead to significant test-to-test variations in measuredEF and efficiency. First, the tolerances on the temperature specifications are s ubstantial relative to the absolute values. The range of allowable temperatures for ambient, starting, and final temperatures can lead to acceptable test load temperature rises ranging from 4–16 ° C. Since the heating time is on the order of only a few tens of seconds, power and energy output calculations are difficult to measure consistently test-to-test. In addition, the efficiency calc ulation assumes that input power is constant for the duration of the test, which may not be the case. These factors make the existing test procedure diffi cult to conduct with accuracy and repeatability. In the recent testing for this analysis, although AHAM only tested 21 units from 9 manufacturers, the units were se lected to represent a broad spectrum of models available in the marketplace with varying cap acities and features. Figure 5.6.1 and Figure 5.6.2 display the AHAM microwave oven efficiency data.

50% 55% 60% 65%Efficiency

600 700 800 900 1000 1100 1200 1300 1400 Rated Output Power (W) Figure 5.6.1 AHAM Microwave Oven Effi ciency versus Rated Output Power 4

5-16Figure 5.6.1 illustrates a small variation in e fficiency across all rated output powers, approximately ±3.5 absolute percentage points from the average efficiency. There is a lack of a correlation between microwave oven rated output power and microwave oven efficiency. Figure 5.6.2 illustrates the relationship between micr owave oven efficiency and microwave oven volume. Similarly, there is no correlation be tween microwave oven efficiency and volume. Figure 5.6.1 and Figure 5.6.2 confirm DOE’s appro ach of creating a single product class for microwave ovens irrespective of rated output power or cavity volum e, and demonstrate that there is no basis to specify an efficiency standard th at is a function of eith er rated output power or cavity volume.

50% 55% 60% 65%Efficiency

0.0 0.5 1.0 1.5 2.0 2.5 Microwave Oven Volume (ft^3) Figure 5.6.2 AHAM Microwave Oven Effi ciency versus Oven Cavity Volume 5

5.6.1.2 Review of Past TSDs After consulting with AHAM and various interested parties and suppliers, DOE determined that the design options for cooking pr oducts other than microwaves have not changed significantly since the 19 96 TSD analysis. Also, no industry-a ggregated manufacturing cost data were supplied to DOE in the ANOPR phase of th is rulemaking. Therefore, DOE decided to update the 1996 TSD analysis using the PPI to sc ale incremental manufacturing cost data for gas and electric cooktops, and gas a nd electric standard and self-cl eaning ovens. For gas cooktops and ovens, the PPI for gas household cooking equi pment was utilized. Similarly, the PPI for electric household cooking equipment was us ed for electric cooktops and ovens. Comparison of current microwave oven effici ency data with analogous data from the 1996 TSD shows that the range of efficiency leve ls based on EF analyzed in the 1996 TSD are

5-17still valid, although AHAM indicated in comments pr ovided along with its data submittal for this rulemaking that certain design options used to ac hieve those levels have already been optimized. 6 But as noted in section 5.4.2, the range of efficiency levels from the 1996 TSD is still representative of the perform ance of current microwave oven models. Therefore, for the purposes of this analysis, the same efficiency le vels are used. As with the conventional cooking products, the incremental manufacturing cost data from the 1996 TSD was scaled by the PPI forelectric household cooking equipment, which includes microwave ovens, to obtain the costefficiency relationship. Cooktop Test Procedure DOE’s cooktop test procedure is based on meas uring the amount of energy required to raise an aluminum block test load from room te mperature to a specified temperature above room temperature at full input heating rate, then operating the burner or element a fixed time longer at a reduced input heating rate. The size of the test block depends on the burner or element size, and the test is repeated for each burner or element. Annual energy consumption is calculated from the average cooking efficiency of the burners or elem ents. Cooktops are rated using EF, which is the ratio of the annual useful cooking-energy outpu t of the cooktop to its total annual energy consumption. The annual energy consumption incl udes the energy input during the time the load is being heated, plus the en ergy consumed by any standing pilot during standby hours for a gas cooktop. Therefore, design options that raise the cooking efficien cy of a gas or electric cooktop and/or reduce the energy consumption of a pilo t on a gas cooktop can decrease the total annual energy consumption and therefore improve EF. Gas Cooktops Table 5.6.1 describes the design options and de sign option combinati ons that result in increased EF of gas cooktops. The design options and efficiency levels analyzed are those presented in the 1996 engineering analysis, with several design options (reflective surfaces and thermostatically controlled burne rs) eliminated in this analys is as described in section 5.4.2. Table 5.6.1 Gas Cooktop Manufacturing Cost and Efficiency Increments

Level Efficiency Level Description Cooking Efficiency EF Delta Manufacturer Cost from Baseline (2006$)
Baseline Baseline 39.9% 0.156

- 1 Baseline + Electronic Ignition 39.9% 0.399 $12.06
2 1 + Sealed Burners 41.8% 0.420 $32.06 Notes: Baseline: Cooktop cooking efficiency = 39.9%, four conventional 9,000 BTU/hr burners, two 117 BTU/hr standing pilot lights (1) Electronic Ignition: Standing pilot lights eliminated, cooking efficiency increase = 0.0% (2) Sealed Burners: Cooking efficiency increase = 4.8% (relative percent)

5-18Electric Coil Cooktops Table 5.6.2 describes the design option that results in incr eased cooking efficiency of electric open (coil) cooktops. The design optio n and efficiency levels analyzed are those presented in the 1996 engineering analysis, wi th one design option (r eflective surfaces) eliminated in this analysis as described in section 5.4.2. Table 5.6.2 Electric Coil Cooktop Manufactu ring Cost and Efficiency Increments

Level Efficiency Level Description Cooking Efficiency EF Delta Manufacturer Cost from Baseline (2006$)
Baseline Baseline 73.7% 0.737

- 1 Baseline + Improved Contact Conductance 76.9% 0.769 $2.28
Notes: Baseline: Cooktop cooking efficiency = 73.7%, two 6-inch 1,250 W and two 8-inch 2,100 W elements (1 ) Improved Contact Conductance: Cooking e fficiency increase = 4.3% (relative percent) Electric Smooth Cooktops Table 5.6.3 describes the design options that result in increased cooking efficiency of electric smooth cooktops. The design options an d efficiency levels anal yzed are those presented in the 1996 engineering analysis, wi th one design option (induction element) eliminated in this analysis as described in section 5.4.2. Another design option (radiant element) discussed in the 1996 engineering analysis was notincluded in this analysis because it exhibited a lower efficiency than the baseline cooktop. Table 5.6.3 Electric Smooth Cooktop Manufacturing Cost and Efficiency Increments

Level Efficiency Level Description Cooking Efficiency EF Delta Manufacturer Cost from Baseline (2006$)
Baseline Baseline 74.2% 0.742

- 1 Baseline + Halogen Lamp Element 75.3% 0.753 $89.09 Notes: Baseline: Cooktop cooking efficiency = 74.2%, two 6-inch 1,500 W and two 8-inch 2,000 W solid disk elements (1) Halog en Element: Cooking efficiency increase = 1.5% (relative percent), two small 1,200 W and two large 1,800 W circular lamps
Conventional Oven Test Procedure DOE’s oven test procedure is based on meas uring the amount of energy required to raise an aluminum block test load from room temp erature to a specified temperature above room temperature. Ovens are rated using EF, which is the ratio of the annual useful cooking-energy output of the oven (energy conveyed to the item being heated) to its total annual energy consumption. The annual energy consumption incl udes the energy input during the time the load is being heated plus the energy consumed by ot her features such as a clock, standing pilot, electronic ignition system, and/or self-cleaning cycles. Theref ore, design options that raise the

5-19cooking efficiency of the oven and/or reduce the energy consumption of features not related to heating food can decrease the total annual energy consumpti on and therefore improve EF.
Gas Ovens Table 5.6.4 describes the design options and de sign option combinati ons that result in increased EF of gas standard ovens. The design op tions and efficiency levels analyzed are those presented in the 1996 engineering analysis, with one design option (o ven separator) eliminated in this analysis as de scribed in section 5.4.2. Table 5.6.4 Gas Standard Oven Manufacturing Cost and Efficiency Increments

Level Efficiency Level Description Cooking Efficiency EF Delta Manufacturer Cost from Baseline (2006$)
Baseline Baseline 5.9% 0.0298

- 1 Baseline + Electric Glo-bar Ignition 5.8% 0.0536 $12.06 2 1 + Improved Insulation 6.1% 0.0566 $15.64 3 2 + Improved Door Seals 6.2% 0.0572 $16.72
4 3 + Forced Convection 6.5% 0.0593 $38.86 5 4 + Reduced Vent Rate 6.5% 0.0596 $40.48
6 5+ Reduced Conduction Losses 6.6% 0.0600 $44.11 1a Baseline + Electronic Spark Ignition 5.8% 0.0583 $15.00 Notes: Baseline: Cooking efficiency = 5.92%, 2 inches of 1.09 lb/cubic foot insulation, standing pilot light ignition = 175 BTU/hr (1) Baseline + Electric Glo-Bar Ignition: Cooking efficiency decrease = 0.152 (absolute percentage points), added electricity consumption = 176 Wh (2) 1 + Improved Insulation: Cooking effici ency increase = 4.9% (relative percent) (3) 2 + Improved Door Seals: Cooking effici ency increase = 1.0% (relative percent) (4) 3 + Forced Convection: Cooking e fficiency increase = 4.8% (relative pe rcent), added electricity consumption = 15 Wh (5) 4 + Reduced Vent Rate: Cooking effici ency increase = 0.5% (relative percent) (6) 5 + Reduced Conduction Losses: Cooking efficiency increase = 0.05 (absolute percentage points) (1a) Baseline + Electronic Spark Ignition: Cooking efficiency decrease = 0.09 (absolute percentage points), added electricity consumption = 0.0 Wh. Standard levels 1 and 1a correspond to designs that are utilized for the same purpose--eliminate the need for a standing pilot--but the technolo gies for each design are different. Standard level 1 is a hot surface ignition device while standard level 1a is a spark ignition device Table 5.6.5 describes the design options and de sign option combinati ons that result in increased EF of gas self-cleaning ovens. The de sign options and efficiency levels analyzed are those presented in the 1996 engineering anal ysis, with one design option (oven separator) eliminated in this analysis as described in section 5.4.2.

5-20Table 5.6.5 Gas Self-Cleaning Oven Manufacturing Cost and Efficiency Increments

Level Efficiency Level Description Cooking Efficiency EF Delta Manufacturer Cost from Baseline (2006$)
Baseline Baseline 7.1% 0.0540

- 1 Baseline + Forced Convection 8.8% 0.0625 $11.01 2 1 + Reduced Conduction Losses 8.8% 0.0627 $15.38 3 2 + Improved Door Seals 8.9% 0.0632 $16.60 Notes: Baseline: Cooking efficiency = 7.13%, clock power = 3.6 W, 2 inches of 1.90lb/cubic foot insulation, electronic ignition = 176 Wh, self-cleaning energy consumption = 43,158 BTU (1) Baseline + Forced Convection: C ooking efficiency increase = 23% (rel ative percent), added electricity consumption (during cooking and cleaning cycles) = 15 Wh (2) 1 + Reduced Conduction Losses: Cooking efficiency increase = 0.05 (absolute percentage points) (3) 2 + Improved Door Seals: Cooking effici ency increase = 1.0% (relative percent)
Electric Ovens Table 5.6.6 describes the design options and de sign option combinati ons that result in increased EF of electric standard ovens. The de sign options and efficiency levels analyzed are those presented in the 1996 engi neering analysis, with several design options (bi-radiant oven and oven separator) eliminated in this analysis as descri bed in section 5.4.2.
Table 5.6.6 Electric Standard Oven Manufactu ring Cost and Efficiency Increments

Level Efficiency Level Description Cooking Efficiency EF Delta Manufacturer Cost from Baseline, (2006$)
Baseline Baseline 12.2% 0.1066

- 1 Baseline + Reduced Vent Rate 12.8% 0.1113 $1.63
2 1 + Improved Insulation 13.4% 0.1163 $4.84 3 2 + Improved Door Seals 13.7% 0.1181 $8.53
4 3 + Forced Convection 14.0% 0.1206 $48.14 5 4 + Reduced Conduction Losses 14.1% 0.1209 $51.69 Notes: Baseline: Cooking efficiency = 12.15%, clock power = 3.9 W, 2 inches of 1.09 lb/cubic foot insulation (1 ) Baseline + Reduced Vent Rate: Cooking efficiency increase = 0.62% (absolute percentage points) (2) 1 + Improved Insulation: Cooking efficiency increase = 0.52% (relative percent) (3) 2 + Improved Door Seals: Cooking efficiency increase = 0.24 (absolute percentage points) (4) 3 + Forced Convection: Cooking e fficiency increase = 0.33 (absolute pe rcentage points), added electricity consumption = 15 Wh (5) 4 + Reduced Conduction Losses: Cooking efficiency increase = 0.05 (absolute percentage points) Table 5.6.7 describes the design options and de sign option combinati ons that result in increased EF of electric self-cleaning ovens. Th e design options and efficiency levels analyzed are those presented in the 1996 e ngineering analysis, with severa l design options (bi-radiant oven and oven separator) eliminated in this analysis as descri bed in section 5.4.2.

5-21Table 5.6.7 Electric Self-Cleaning Oven Manufac turing Cost and Efficiency Increments

Level Efficiency Level Description Cooking Efficiency EF Delta Manufacturer Cost from Baseline, (2006$)
Baseline Baseline 13.8% 0.1099

- 1 Baseline + Reduced Conduction Losses 13.8% 0.1102 $4.37
2 1 + Forced Convection 14.2% 0.1123 $43.98 Notes:Baseline: Cooking efficiency = 13.79%, clock power = 3.8 W, 2 inches of 1.09 lb/cubic foot insulation, selfcleaning energy consumption = 5,286 Wh (1) Baseline + Reduced Conduction Losses: Cooking effici ency increase = 0.05 (absolute percentage points) (2) 1 + Forced Convection: Cooking e fficiency increase = 0.33 (absolute pe rcentage points), added electricity consumption = 15 Wh Conventional Oven Energy Use versus Volume The oven cost-efficiency relati onships detailed above are pr edicated upon baseline ovens with a cavity volume of 3.9 ft 3 . It is well documented, however, th at efficiency scales with oven cavity volume. This variation between efficiency, and thus EF , and oven volume results from the fact that larger ovens have higher thermal masses and larger vent rates than smaller ovens. Since the test procedure for establishing EF is a tr ansient test with a fixed test load, the increased energy consumption due to the increased mass of larger units yields a lower EF. The 1980 DOE engineering analysis for residential appliances 7 established a relationship between oven volume and EF from data compiled by the National Bureau of Standards (which was renamed to the National Institute of Standards and Technology (NIST)). Using these data, linear equations were derived for both electric and gas ovens. No dist inction was found to exist between standard and self-cleaning ovens for either gas or electric ovens. Intercepts fo r a particular baseline model or oven design were chosen so that the equations pass through the desired EF corresponding to a particular volume. Values from the 1996 TSD for the slopes and intercepts for gas and electric ovens are listed in Table 5.6.8. The 1996 TSD did not analyze data at every efficiency level, and higher efficiency levels are not included in Table 5.6.8 because certain design options have been eliminated in the current analysis. DOE believes the slopes and intercep ts of these equations from the 1996 TSD to still be valid.

5-22Table 5.6.8 Slopes and Intercepts for Oven Energy Factor versus Cavity Volume Relationship
Energy Efficiency Level Electric Gas Slope = -0.0157 Slope = -0.0073 Standard Self-Clean Standard Self-Clean Baseline

- 0.1632 0.0865 0.0865 1 0.1752

- 0.0895

- 2 0.1802

- - - 3 0.1822

- 0.0935

- Note: EF = (Slope x Volume) + Intercept where Volume is expressed in cubic feet. Conventional Oven Standby Power In the ANOPR, DOE stated it would consider additional design optio ns that would result in a lowering of the energy consumption of non-cooking features ( e.g. standby power) for conventional ovens during the notice of proposed rulemaking (NOPR) phase. However, no data were received on standby power for any of these products, so no additional analysis was performed.
Microwave Ovens Table 5.6.9 describes the design options and de sign option combinati ons that result in increased EF of microwave ovens. The design opti ons and efficiency levels analyzed are those presented in the 1996 engineering analysis, with incremental manu facturing costs scaled by the PPI for electric household cooking equipment. For the NOPR, DOE sought input from interested parties on the approach of analyzing additional de sign options that would result in a lowering of the energy consumption of non-cooking features ( e.g. standby power), even though the test procedure currently does not account for such usage in EF. DOE is separately considering an updated test procedure to incorporate a measurement of standby and off mode power, as well as energy conservation standards for microwave ov en standby and off mode power consumption.

5-23Table 5.6.9 Microwave Oven Manufacturing Cost and Efficiency Increments

Level Efficiency Level Description Cooking Efficiency EF Delta Manufacturer Cost from Baseline (2006$)
Baseline Baseline 55.7% 0.557

- 1 Baseline + More Efficient Power Supply 58.6% 0.586 $8.68
2 1 + More Efficient Fan 58.8% 0.588 $17.95 3 2 + More Efficient Magnetron 59.7% 0.597 $32.53
4 3 + Reflective Surfaces 60.2% 0.602 $51.11 Notes: Baseline: Cooking efficiency = 55.7% (1 ) Efficient Power Supply: Cooking efficiency increase = 2.9 (absolute percentage points) (2) Efficient Fan: Cooking efficiency increase = 0.23 (absolute percentage points) (3) Efficient Magnetron: Cooking efficiency increase = 0.90 (absolute percentage points) (4) Reflective Surfaces: Cooking efficiency in crease = 0.50 (absolute percentage points)

5.6.1.3 Product Testing and Teardowns Microwave Oven Efficiency DOE conducted product testing and tear down analysis for microwave ovens to supplement AHAM-supplied data, to validate th e approach of updating the 1996 TSD analysis, and to examine the microwave oven test procedur e for potential updates. In order to identify design options, circuit designs, a nd display options, DOE disassembled a representative sample of 32 units to gain an in-depth understandi ng of common microwave oven design elements, components, and manufacturing practices. DOE also evaluated the IEC microwave oven test standard which is referenced by the currentDOE test procedure (IEC Standard 705) in comparison to the current IEC test standard (IEC Standard 60705-2006, Household microwave ovens – Methods for measuring performance (IEC Standard 60705).)

Test Units DOE conducted a market survey of microwave oven models and their associated features to identify the primary differentiators among comme rcially-available units, and to then select a representative range of test units which incorporate these features. DOE selected 32 microwave ovens based on parameters that could be identifi ed from product literature . These included: 1) rated output power in W; 2) rated cavity volume in ft 3 ; 3) display type; 4) the presence or absence of a cooking sensor; and 5) magnetron pow er supply technology. For the latter, certain models were advertised as incorporating “invert er technology” that allows variable power output for different user-selectable cooking -level settings. The key parameters for each of the test units are presented in Table 5.6.10 thr ough Table 5.6.13. In some cases, several units were selected from a single manufacturer that appeared to have similar construction, rated power, and volume, but differed in ancillary features such as the type of display or the presence of a cooking sensor.

5-24Such similarities are noted in the tables. Nome nclature for the display entries are described in the following paragraphs. Table 5.6.10 Microwave Oven Features (Table 1 of 4) DOE Unit Number DOE1 DOE2 DOE3 DOE4 DOE5 DOE6 DOE7 DOE8 Rated Output Power (W) Stated Volume (ft 3 ) 700 700 700 700 0.7 0.7 0.7 0.7 800

1 800 1 800 0.8 800 0.8 Cooking Sensor Inverter Power Supply - - - -

- - - - Y

- -

- -

- -

- Type Characters # of LEDs for backlighting
SizeDisplay LED LED LED LED #, 1 x 4 #, 1 x 4 #, 1 x 4 #, 1 x 4

N/A N/A N/A N/A 1.50" x 0.43" 1.50" x 0.43" 1.45" x 0.70" 1.90" x 0.83" VFD A, 1 x 7

N/A 2.25" x 0.75" LED #, 1 x 4

N/A 1.50" x 0.80" LCD #, 1 x 4 None 1.87" x 0.83" LCD #, 1 x 4 None 1.87" x 0.83" Unit is Similar to

---- - DOE5

- - Table 5.6.11 Microwave Oven Features (Table 2 of 4) DOE Unit Number DOE9 DOE10 DOE11 DOE12 DOE13 DOE14 DOE15 DOE1 6
Stated Volume (ft 3 ) Rated Output Power (W) 900 0.9 1000 1000 1000 1.1 1.1 1 1000 0 1100 1.1 1100 1.1 1100 1.8 Cooking Sensor Inverter Power Supply -

- - - -

- - - -

- -

- Y

- Y

- Type Characters # of LEDs for backlighting
SizeDisplay LED #, 1 x 4

N/A 2.00" x 0.65" LED LED LED #, 1 x 4 #, 1 x 4 #, 1 x 4

N/A N/A N/A 1.85" x 1.10" 1.75" x 0.85" 1.75" x 0.70" VFD #, 1 x 4

N/A 2.20" x 0.65" LED #, 1 x 4

N/A 2.00" x 0.65" LCD A, 1 x 6 5 2.53" x 0.95" VFD A, 1 x 7

N/A 2.25" x 0.75" Unit is Similar to

- --- - - DOE14

- Table 5.6.12 Microwave Oven Features (Table 3 of 4) DOE Unit Number DOE17 DOE18 DOE19 DOE20 DOE21 DOE22 DOE23 DOE2 4 Rated Output Power (W) Stated Volume (ft 3 ) 1100 1100 1100 1100 1 1.4 1 1.3 1100 1.1 1100

1 1150 1.4 1200 2.2 Cooking Sensor Inverter Power Supply - - - -

- - - - -

- -

- Y

- Y Y Type Characters # of LEDs for backli g htin g SizeDisplay LCD LCD LCD LED #, 1 x 4 A, 1 x 5 #, 1 x 4 #, 1 x 4 3 4 None N/A 1.83" x 0.80" 2.03" x 0.81" 1.87" x 0.83" 1.50" x 0.80" LED #, 1 x 4

N/ A 1.47" x 0.80" LCD #, 1 x 4 3 2.00" x 0.83" VFD A, 1 x 7

N/ A 2.25" x 0.75" LCD A, 1 x 6 10 2.05" x

1.10" Unit is Similar to - - DOE17 -

- DOE17 DOE16 DOE3 0

5-25Table 5.6.13 Microwave Oven Features (Table 4 of 4) DOE Unit Number DOE25 DOE26 DOE27 DOE28 DOE29 DOE30 DOE31 DOE3 2 Rated Output Power (W) Stated Volume (ft 3 ) 1200 1200 1200 1200 1.2 2.2 1.2 2 1200 2 1250 2.2 1300 1.2 1300 1.2
Inverter Power Supply Cooking Sensor - Y Y Y - Y - - Y

- Y Y Y Y Y Y Type Characters # of LEDs for backlighting
SizeDisplay LCD LCD LCD LCD #, 1 x 4 A, 1 x 6 A, 1 x 7 D, 2 x 8 5 10 4 6 1.85" x 0.83" 2.05" x 1.10" 2.03" x 0.78" 2.45" x 1.17" LCD A, 1 x 7 4 2.03" x 0.78" LCD A, 1 x 6 4 2.05" x

1.10" LCD #, 1 x 4

10 1.75" x 0.80" LCD A, 1 x 6 10 2.05" x

1.10" Unit is Similar to DOE17 DOE30 DOE25 -

- DOE31

- DOE3 1 The range of rated output powers and cavity volumes were determined on the basis of manufacturer specifications. Rate d output power, which is a measur e of the power transferred to the food load at the full-scale cooking setti ng, ranged from 700 to 1,300 W. Cavity volumes, which typically roughly scale wi th output power, ranged from rated values of 0.7 to 2.2 ft 3

. Three different display tec hnologies were observed to be incorporated in the sample units: 1) LED; 2) LCD; and 3) VFD. (Details of each technology are di scussed later in this section in the context of standby power.) The display format for each microwave oven was characterized as either numeric (#), alphanumeric (A), or dot matrix (D). Whereas numeric displays can only show time, al phanumeric displays can also di splay letters (though usually in simplified format). Dot matrix displays can show various fonts, letters, and symbols via matrices of pixels, making them the most flexible disp lay technology. Since display power consumption is a function of not only the type of technology usedbut the overall size and number of digits in the display as well, the dimensions of each disp lay were measured and the number of rows and columns of digits were record ed. Finally, some LCDs use LEDs for backlighting, allowing a microwave oven user to read the disp lay both at night and in daylight. All 32 microwave ovens in the DOE sample we re subjected to efficiency testing via the current DOE test procedure, which is based by reference on IEC Standard 705, which has been superseded by IEC Standard 60705. c DOE subsequently subjected 12 of the 32 microwave ovens to additional cooking efficiency testing per IEC Standard 60705 to investigate the differences between the two test standards. DOE conducted additional testing of an inverterbased microwave oven to assess the impact of oper ating such a system at various power levels. Lastly, DOE considered possible improvementopportunities for the current cooking test procedure.

General Construction All microwave ovens examined by DOE contain a metal cavity that is mechanically attached to the front and rear ch assis frames. Each of these pieces had been formed by stamping, joined, and then the assembly is painted. To this frame, a bottom panel is attached. This bottom

c Current IEC standards may be obtained from www.iec.ch . However, IEC does not make obsolete standards available.

5-26panel covers the turntable moto r and also acts as an electr ical ground for the magnetron power supply and the magnetron. The inner cavity occupies , on average, about 70 percent of the width and height of the microwave oven. The remaining space is used for cooling channels, the magnetron, the magnetron power supply, the cooli ng fan, the microwave oven controller, and other miscellaneous components.
All of the microwave ovens examined have a doo r that is hinged on the left side of the unit. Beneath the right edge of the door, a latch mechanism with three switches ensures that the microwave oven cannot operate its magnetron without the door being closed. To the right of the door, the user interface frame typically features a foil-based button array under a flexible plastic cover, along with the display. The display may be either attached directly to the user interface frame or integrated into the main control boar d for the microwave oven. The main control board typically consists of a single-sided printed circui t board (PCB) which features a small alternating current to direct current (AC- DC) power supply, several relays, and control logic. All power coming into the microwave oven is filtered throu gh a separate power filtration board to which the power cord is attached.
In addition to the aforemen tioned components, baseline microwave ovens contain a magnetron power supply featuring a microwave ove n transformer, a high voltage diode, and a high-voltage aluminum electrolytic capacitor. The user interf ace for these microwave baseline ovens is a simple LCD or LED display. A si ngle-speed fan keeps the magnetron and microwave oven transformer cool during operation, while a turntable may rotate the food load inside the cavity while the microwave oven is operating. A single incandescent light bulb (20 W and higher) typically provides cavity illumination during operation and when the door is open. More sophisticated microwave ovens may contain cooking sensors, larger and multicolored displays with more complex graphics, an d/or inverter-based magnetron power supplies. Cooking sensors and displays will be discussed in more detail below in sections regarding standby power.
Because the microwave field is not unifor m inside microwave oven cavities (creating “hot” spots), manufacturers have developed various methods to improve cooking uniformity. Within the DOE sample, mode stirrers and turntables for the food were the only methods observed, although DOE is aware of other approaches that could be taken, such as utilizing dual magnetrons and associated wave guides. Mode stir rers temporally change the distribution of the microwave energy delivered to the cavity and thus cause the “hot” spots to move around the cavity. However, only one unit in the DOE sa mple (designated “DOE16”) contains a mode stirrer. Most manufacturers have shifted away from this appro ach in favor of turntables. Turntable motors were observed in all microw ave ovens sampled by DOE. By rotating the food through the “hot” spots, turntables help improve cooking uniformity. Both a turntable and mode stirrer require a motor, as does the blower, whic h provides cooling air to remove the significant heat dissipated by the magne tron and its power supply.

5-27Efficiency Testing Using the Current DOE Test Procedure DOE conducted efficiency tests on all sa mpled units using the current DOE test procedure, which references IEC Standard 705. As can be seen in Table 5.6.14 through Table 5.6.17, the DOE test results noted similar cooking efficiencies and input and output powers as the results submitted by AHAM, which were presented in section 5.6.1.1. Table 5.6.14 Microwave Oven Input, Output, and Cooking Efficiency (1 of 4) DOE Unit Number DOE1 DOE2 DOE3 DOE4 DOE5 DOE6 DOE7 DOE8 Stated Volume ( ft 3 ) Measured In p ut Power ( W ) 0.7 0.7 0.7 0.7 1,192.8 1,129.8 1,121.9 996.8 1.0 1.0 0.8 1,374.6 1,314.9 1,356.7 0.8 1,374.0 Rated Output Power (W) Measured Output Power (W) 700.0 700.0 700.0 700.0 686.1 654.8 627.0 593.8 800.0 800.0 800.0 818.5 767.6 781.7 800.0 786.7 Energy Factor 57.5% 58.0% 55.9% 59.6% 59.5% 58.4% 57.6% 57.3% Table 5.6.15 Microwave Oven Input, Output, and Cooking Efficiency (2 of 4) DOE Unit Number DOE9 DOE10 DOE11 DOE12 DOE13 DOE14 DOE15 DOE16 Stated Volume ( ft 3 ) Measured In p ut Power ( W ) 0.9 1,602.4 1.1 1.1 1.0 0.0 1,769.9 1,701.8 1,713.0 1,736.4 1.1 1.1 1,886.2 1,876.3 1.8 1,566.7 Rated Output Power (W) Measured Output Power (W) 900.0 964.6 1,000.0 1,000.0 1,000.0 1,000.0 1,007.8 1,010.3 1,013.6 1,024.5 1,100.0 1,100.0 1,145.9 1,105.3 1,100.0 949.7 Energy Factor 60.2% 56.9% 59.4% 59.2% 59.0% 60.8% 58.9% 60.6% Table 5.6.16 Microwave Oven Input, Output, and Cooking Efficiency (3 of 4) DOE Unit Number DOE17 DOE18 DOE19 DOE20 DOE21 DOE22 DOE23 DOE24 Stated Volume ( ft 3 ) Measured In p ut Power ( W ) 1.0 1.4 1.0 1.3 1.1 1.0 1,829.8 1,882.2 1,815.7 1,774.3 1,851.8 1,823.1 1.4 1,626.8 2.2 1,926.2 Rated Output Power (W) Measured Output Power (W) 1,100.0 1,100.0 1,100.0 1,100.0 1,100.0 1,100.0 1,046.7 1,114.0 1,057.3 1,072.5 1,134.0 1,038.2 1,150.0 966.7 1,200.0 1,130.8 Energy Factor 57.2% 59.2% 58.2% 60.4% 61.2% 56.9% 59.4% 58.7% Table 5.6.17 Microwave Oven Input, Output, and Cooking Efficiency (4 of 4) DOE Unit Number DOE25 DOE26 DOE27 DOE28 DOE29 DOE30 DOE31 DOE32 Stated Volume ( ft 3 ) Measured In p ut Power ( W ) 1.2 2.2 1.2 2.0 2.0 1,871.2 1,925.1 1,812.7 1,904.5 1,904.5 2.2 1,919.8 1.2 1,917.1 1.2 1,928.2 Rated Output Power (W) Measured Output Power (W) 1,200.0 1,200.0 1,200.0 1,200.0 1,200.0 1,147.7 1,116.6 1,114.4 1,149.4 1,137.9 1,250.0 1,105.4 1,300.0 1,121.9 1,300.0 1,119.0 Energy Factor 61.3% 58.0% 61.5% 60.4% 59.7% 57.6% 58.5% 58.0% Both DOE’s and AHAM’s microwave oven samp les contained units with manufacturerrated output powers ranging from 700 to 1,300 W. DOE-tested efficiencies varied from 56 to 61 percent. These measured efficiencies were similar to the results submitted by AHAM to DOE (see section 5.6.1.1), which noted cooking e fficiencies of 55 to 62 percent.

5-2862%

61%

60%

59%

58%

57%

56%

55%

54%

Figure 5.6.3Efficiency (EF)

600 700 800 900 1,000 1,100 1,200 1,300 Rated Output Power (W) AHAM Standard MOT AHAM Inverter Drive DOE Standard MOT DOE Inverter Drive

DOE and AHAM Microwave Oven Efficiency versus Rated Output Power DOE is unaware of the specific microwave ovens that AHAM tested. However, it is possible to infer some model features on the basi s of identified characteristics, such as rated output power. The models identified in Figure 5. 6.3 as “AHAM Inverter” units were inferred as such because all of the microwave ovens that DOEis aware of on the market that have a rated output power at or in excess of 1,250 W feature an inverter driving the magnetron. DOE was unable to ascertain if any additi onal inverter units at lower out put powers are contained within the AHAM data submittal. DOE noted that none of its microwave ovens with inverter-based magnetron power supplies achieved as high an effi ciency as comparable microwave ovens with standard magnetron power supplies and high output powers. AHAM commented in its data submittal that inverter-based pow er supplies are 2 percent more efficient than standard power supplies (82 versus 84 percent, respectively). 8 Yet, collectively, the DOE and the inferred AHAM inverter units have lower cooking efficien cies than the highest-e fficiency non-inverter units. Thus, while it is possible that invertersystems are more efficient than the simple microwave oven transformers they can replace, the overall efficiencies of inverter-based microwave ovens on the market do not presen tly demonstrate a corresponding efficiency improvement. In considering the issue of inverter versus non-inverter power supply efficiencies, DOE observed that besides being much more comple x, the inverter power supplies examined by DOE also feature large aluminum heat sinks and plastic tunnels to direct air flow over key components. The data sheets for th e rectifiers and insulated-gate bipolar transistors used in the inverter power supplies note maximum heat dissipation requirements in excess of 400 W. During its teardown analysis, DOE al so noted that inverter power s upplies in its test sample use 50 percent heavier fan motors, indicating a greater need for heat removal from such systems and

5-29thus implying lower efficiencies, since energy is lost through heat dissipation from the power supply. However, regardless of the type of magn etron power supply used, al most all units in the AHAM and DOE samples meet the baseline effi ciency of 55.7 percent for microwave ovens proposed in section 5.4.1. DOE then investigated whether there was a correlation betw een microwave oven efficiency and measured output pow er. Typically, rated output pow ers in the test samples were observed to be within 50 W of measured output power, as shown in Table 5.6.18. Table 5.6.18 Microwave Oven Rated versus Measured Output for AHAM and DOE Tests

Unit # Rated Output

( W ) Measured Output (W) Deviation from Rated Output
DOE4 DOE3 DOE2 AHAM10 DOE1 AHAM11 700 700 700 700 700 700 594 627 655 671 686 699 -15.2% -10.4% -6.5% -4.2% -2.0% -0.1% AHAM1 DOE6 DOE7 DOE8 AHAM16 DOE5 800 800 800 800 800 800 743 768 782 787 795 818 -7.1% -4.1% -2.3% -1.7% -0.7% 2.3% DOE9 900 965 7.2% AHAM22 950 907 -4.5% AHAM20 AHAM12 AHAM4 AHAM5 AHAM14 AHAM19 DOE10 DOE11 DOE12 AHAM3 DOE13 AHAM15 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000 930 967 971 973 986 999 1,008 1,010 1,014 1,015 1,025 1,028 -7.0% -3.3% -2.9% -2.7% -1.4% -0.1% 0.8% 1.0% 1.4% 1.5% 2.5% 2.8% Unit # Inverter Rated Output

(W ) Measured Output (W) Deviation from Rated

Out p ut DOE16 DOE22 DOE17 DOE19 AHAM21 DOE20 DOE15 DOE18 AHAM13 DOE21 DOE14 1,100 1,100 1,100 1,100 1,100 1,100 1,100 1,100 1,100 1,100 1,100 950 1,038 1,047 1,057 1,060 1,073 1,105 1,114 1,119 1,134 1,146 -13.7% -5.6% -4.8% -3.9% -3.7% -2.5% 0.5% 1.3% 1.7% 3.1% 4.2% DOE23 1,150 967 -15.9% DOE27 DOE26 DOE24 DOE29 AHAM2 DOE25 DOE28 AHAM17 AHAM6 Y Y 1,200 1,200 1,200 1,200 1,200 1,200 1,200 1,200 1,200 1,114 1,117 1,131 1,138 1,145 1,148 1,149 1,152 1,205 -7.1% -7.0% -5.8% -5.2% -4.6% -4.4% -4.2% -4.0% 0.4% DOE30 AHAM8 AHAM9 Y Y Y 1,250 1,250 1,250 1,105 1,142 1,166 -11.6% -8.6% -6.7% DOE32 DOE31 AHAM7 Y Y Y 1,300 1,300 1,300 1,119 1,122 1,173 -13.9% -13.7% -9.8% The measured output for the AHAM data av eraged 2.8 percent less than rated output power, with a range in deviation fr om rated output of +3.1 percent to -9.8 percent). Most units had a measured output lower than their rated output. As ment ioned previously, the AHAM data sample did not identify whether an microwav e oven had an inverter power supply for the magnetron. Thus, the presence of an inverter in the AHAM data set is solely inferred by the DOE market survey. Output power measurements within the DOE sample followed a similar pattern to the data submitted by AHAM, though with a greate r proportion of units having measured output

5-30power below rated output power. The divergen ce ranged from a high of about 7 percent above rated output power to a low of about 16 percen t below rated output power, with the average divergence being about -5 percen t. The results for rated output power shown in Figure 5.6.3 and Figure 5.6.4 indicate that the DOE efficiency data as a function of measured output power exhibits largely similar charac teristics as the AHAM data su bmittal, and neither shows an identifiable correlation.

54% 55% 56% 57% 58% 59% 60% 61% 62%Efficiency (EF) AHAM Standard MOT AHAM Inverter Drive DOE Standard MOT DOE Inverter Drive

600 700 800 900 1,000 1,100 1,200 1,300 Measured Output Power (W) Figure 5.6.4 DOE and AHAM Microwave Oven Efficiency versus Measured Output Pow er
The m aximum measured output power of approximately 1,200 W represents the practical limit of residential microwave ovens currently on the market, since at even the highest measured efficiency, input power is approaching the amperage limits of residential electrical circuits. For example, the maximum input power measured by DOE in its test sample was approximately 1,925 W, while two microwave ovens in the AHAM data submittal exceeded 2,000 W of input power during cooking efficiency tests. For a standard 120 volts AC (VAC) circuit, these input powers would correspond to 16.0 and 16.7 ampere s (A), respectively. Higher output powers may thus only be achievable with microwave ovens that have even highe r efficiencies or by a transition to 240 VAC circuits for microwav e ovens. Higher input and output powers are common for commercial microwave ovens, but these products require higher line voltages. Impacts of Design Options on Cooking Efficiency DOE identified the following design options pr esent in its sample of microwave ovens and observed the following impacts associated with each design option on cooking efficiency:

5-31• Cooking sensors. There was no identifiable relationship between th e absence or presence of a cooking sensor and the measured efficiency. The only clear impact of some cooking sensors was on the standby power consumption.

• Improved fan efficiency. The units subjected to reverse-engineering all appeared to incorporate fans of similar type and construction, i.e . single-speed shaded-pole-motors (SPMs) with plastic blades and presumably sim ilar efficiency characteristics. Therefore, no impacts could be quantified for the effect of improved fan efficiency on microwave oven efficiency.

• Improved magnetron efficiency. Despite th e range of magnetron manufacturers and models, there was notable consistency of rated magnetron efficiency among the data sheets that DOE was able to ob tain. All data sheets indi cated a conversion efficiency range of 71 to 72 percent. Therefore, no re lationship between microwave oven efficiency and magnetron efficiency could be evaluate d, nor did DOE have a means of evaluating the efficiency of those magnetrons for whic h data sheets were unavailable, since the magnetrons could not be tested by DOE in isolation.

• Improved microwave oven transformer power supply efficiency. Among the units torn down, only the inverter-type microwave ovens had an identifiably different efficiency performance characteristic th an the microwave ovens with standard power supplies, and the data indicate that overall efficiency is not improved by inverter power supplies. All standard microwave oven transformers appear to be similar in construction and, hence, no data was available to evaluate the effect of incremental improvements in conventional microwave oven transformers. Furthermore, DOE did not have the means of evaluating the efficiency of the microwave oven power s upplies alone, since they could not be tested by DOE in isolation.

• Low-standby-loss electronic controls. By definition, these technologies impact only standby power consumption rather than cooking efficiency.

• Modified wave guide. This design option described in the market and technology assessment (chapter 3 of the TSD), wherein special coatings are applied to the wave guide interior surfaces, was not observed in the DOE test units. However, two different orientations of the wave gui de were noted, and an attempt was made to identify any impact that wave guide orie ntation would have on measur ed efficiency. No such relationship was found. For more detailed descriptions of each of th ese design options, see ch apter 3 of the TSD. Based on this analysis, DOE believes that the e fficiency improvements associated with these design options has changed little since the 1996 TSD analysis.

5-32Comparison of IEC Test Procedures for Measuring Efficiency The existing DOE microwave oven test proce dure references IEC Standard 705, but this IEC test procedure has been declared obsolete by th e IEC. The current IEC test procedure is IEC Standard 60705. Because there are key differe nces between these two IEC procedures, the impact of which on efficiency measurements were not known to DOE, and because manufacturers which do conduct effi ciency testing are likely to be using the current version, a test series was conducted on a sub-sample of the microwave ovens to compare efficiency measurements made using both IEC test procedures. The general methodology for each test procedur e is largely the same, and consists of heating 1 kg of water in a boros ilicate container from about 10 ° C below room temperature to room temperature, using the maximum power setting on the microwave oven. The input power over the duration of the test, and thus energy consumed during th e test, are compared to the energy absorbed by the test load to obtain the efficiency measurement. DOE conducted tests per IEC Standard 60705 on 12 selected microwave ovens from its original 32 unit sample with a representative rang e of output power, effici ency, and test-to-test variation observed in the DOE testing, whic h utilizes IEC Standard 705. The table below summarizes key differences noted between the testprocedures that can potentially impact the final energy efficiency calculation. Table 5.6.19 Key Differences Between IEC Standard 705 and IEC Standard 60705 IEC Standard 705-1988 and Amendment 2-1993 IEC Standard 60705-2006 Ambient Temp.,T 0 = 20 ± 2 ° C Starting Water Temp., T 1 = T 0– (10 ± 1 ° C) Final Water Temp., T 2 = T 0 ± 1 ° C Ambient Temp.,T 0 = 20 ± 5 ° C Starting Water Temp., T 1 = 10 ± 1 ° C Final Water Temp., T 2 = 20 ± 2 ° C Electrical Input Energy neglects the magnetron filament heat-up time, the measurement starting when the input current reaches 90 percent of its final value. Measurement of Electrical Input Energy includes the energy consumed during the magnetron filament heat-up time.
No mention of rounding off efficiency or output power calculations Efficiency is rounded off to the nearest whole number, while output power is rounded off to the nearest 50 W Temperature measurement accurate within 0.25 ° C and linearity better than 1 percent. Time measurement accurate w ithin 0.25 seconds. No specifications for accuracy of temperature and time measurements.

It can be noted that, for the efficiency measurement, IEC Standard 60705 includes the energy consumed during the magnetron filament h eat-up time, while IEC Standard 705 excludes filament heat-up time. Thus, the IEC Standard 60705 efficiency measurement can be considered more accurately as an overall microwave oven e fficiency measurement, while the IEC Standard 705 efficiency measurement can be considered stri ctly a cooking efficiency measurement. Table 5.6.20 shows the results for the test procedure comparison. Per the IEC Standard 60705 test

5-33procedure, DOE rounded the measured output of each test to the closest 50 W and then averaged the rounded values.
Table 5.6.20 IEC Standard 705 versus IEC Standard 60705 Test Results

Test Unit # Rated Power Output (W) Efficiency (%) IEC Standard 705-1998 and Amendment 2-1993 Measured

Power Output (W) Test-to-Test Efficiency Range (%) Efficiency (%) IEC Standard 60705-2006 (rounded) Measured Power Output (W) Test-to-Test Efficiency Range (%) DOE1 700 686 57.5 1.46 650 55.3 3.57 DOE6 DOE5 800 800 743 58.4 0.06 795 59.5 0.4 733 57.0 3.45 733 58.7 3.33 DOE9 900 965 60.2 0.48 917 58.3 5.00 DOE22 DOE19 DOE15 DOE21 1,100 1,100 1,100 1,100 1,038 56.9 0.71 1,057 58.2 0.47 1,073 58.9 0.77 1,105 61.2 0.21 1,000 55.0 3.57 1,017 56.7 3.45 1,083 58.0 3.39 1,083 59.3 1.67 DOE27 DOE29 1,200 1,200 1,114 61.5 1.07 1,131 59.7 0.92 1,067 59.3 1.67 1,100 58.0 0.00 DOE30 1,250 1,142 57.6 0.67 1,050 55.3 1.79 DOE32 1,300 1,119 58.0 1.24 1,083 57.0 5.17
There is a consistent decrease in efficiency of about 1 to 2 percent from IEC Standard 705 to IEC Standard 60705 for all of the microwave ovens. This largely-c onsistent decrease in the calculated efficiency for IEC Standard 60705 was due in significant part to the requirement that the measured input energy include the ener gy consumed during the magnetron filament heatup time, whereas IEC Standard 705 specifies that the measurement of energy input begins when the current reaches 90 percent of its maximum value. Therefore, IEC Standard 60705 factors in a higher energy consumption to the efficiency calculation than IEC Standard 705 does. Another significant difference between test procedures is the specifications for accuracy of the test instrumentation. IEC Standard 705 specifies that temperature measurements be accurate within 0.25 °C, with linear ity better than 1 percent, as well as that time measurements be accurate within 0.25 seconds. In contrast, IEC Standard 60705 does not provide any accuracy requirements for these measurements. Using a st andard thermocouple, which typically has an accuracy no better than 0.5 °C, or a less accurate time measurement equipment could create significant test-to-test variation in efficiency results. The variation of test-to-test efficiency re sults per IEC Standard 60705 for an individual microwave oven ranged from 0 to 5 percent of th e average value, which was much greater than the comparable variation for IEC Standard 705, whos e test-to-test variation in efficiency results ranged from 0 to 1.5 percent for the same sub-sa mple of microwave ovens . This larger range associated with IEC Standard 60705 is believed to be attributable to the effects of the procedure’s requirement to round the power output to th e nearest 50 W and the efficiency to the nearest whole number afte r each individual test, pr ior to averaging.

5-34The prescribed rounding under IEC Standard60705 would make it more difficult to achieve an overall efficiency increase via improvements in minor components such as fan/turntable motors and oven light bulbs, which each consume less than 20 W. For any component efficiency improvements to have a m easurable effect after rounding the power output and efficiency calculations, power consumption woul d have to be reduced by at least 25 W. To demonstrate the effect of rounding more clearly, the raw data from the IEC Standard 60705 testing were used to calcula te efficiency in the same ma nner as for IEC Standard 705; i.e., no rounding was performed on output power or efficiency from the individual tests prior to averaging. As shown in Figure 5.6.5 , the test-to-test variation in efficiency for the rounded data is on average four times higher th an that of the non-rounded data. The effect of rounding output power and efficiency also causes a significant change in the calculated efficiency, as seen in Figure 5.6.6. The rounded efficiencies varied from the non-rounded values by as much as 0.75 percentage points.

6 IEC Standard 60705 Non-Rounded Test-to-Test Results Range IEC Standard 60705 Rounded Test-to-Test Results Range

5

4

3

2

1

0 1 6 5 9 22 19 15 21 27 29 30 32 DOE Test Unit #Test-to-Test Range (%)

Figure 5.6.5 DOE Non-Rounded versus Rounded Test-to-Test Efficiency Variation Measured Using IEC Standard 60705

5-35Efficiency (%) IEC Standard 60705 Non-Rounded Efficiency 60 IEC Standard 60705 Rounded Efficiency

59

58

57

56

55

54 1 6 5 9 22 19 15 21 27 29 30 32 DOE Test Unit # Figure 5.6.6 DOE Non-Rounded versus Rounded Efficiency Measured Using IEC Standard 60705

The non-rounded data obtained via IEC Sta ndard 60705 still show a consistent 1 to 2 percentage point decrease in efficiency for all of the units tested as compared to the IEC Standard 705 tests, which DOE believes to be attr ibutable to the differences in the energy input measurement. As with the rounded IEC Sta ndard 60705 results, the non-rounded data for IEC Standard 60705 also show more te st-to-test variation for a given unit (0 to 2.1 percentage points) than the variations test-to-test during the IEC St andard 705 testing (0 to 1.5 percentage points). This remaining increment in test-to-test variati on was likely due to the more lenient tolerances on the prescribed ambient and final test load temp eratures. The IEC Standard 60705 test procedure specifies ambient temperature as 20 ± 5 °C, as compared to 20 ± 2 °C for the IEC Standard 705 test procedure. For the final test load te mperature, IEC Standard 60705 specifies 20 ± 2 °C, while IEC Standard 705 specifies it as ambient temperature ± 1 °C.

5-36Table 5.6.21 IEC Standard 705 versus IEC St andard 60705-2006 Test Results, Without Rounding

Test Unit # Rated Power Output (W) Efficiency (%) IEC Standard 705-1998 and Amendment 2-1993

Measured

Power Output (W) Test-to-Test Efficiency Range (%) Efficiency (%) IEC Standard 60705-2006 (no rounding)

Measured Power Output (W) Test-to-Test Efficiency Range (%) DOE1 700 686 57.5 1.46 659 56.1 0.56 DOE6 DOE5 800 800 743 58.4 0.06 795 59.5 0.4 740 57.2 0.96 722 58.0 0.70 DOE9 900 965 60.2 0.48 925 59.0 1.66 DOE22 DOE19 DOE15 DOE21 1,100 1,100 1,100 1,100 1,038 56.9 0.71 1,057 58.2 0.47 1,073 58.9 0.77 1,105 61.2 0.21 1,012 55.6 0.50 1,023 56.8 0.20 1,075 57.5 0.53 1,087 59.4 0.76 DOE27 DOE29 1,200 1,200 1,114 61.5 1.07 1,131 59.7 0.92 1,061 59.3 1.05 1,112 58.4 0.87 DOE30 1,250 1,142 57.6 0.67 1,074 56.0 0.82 DOE32 1,300 1,119 58.0 1.24 1,087 56.4 2.14 Based on observations and analysis of test re sults, DOE believes that IEC Standard 705 is more likely to produce consistent test results than IEC Standard 60705 be cause the measurement requirements in IEC Standard 705 are more stri ngent. Therefore, DOE believes that IEC Standard 705 should be retained as the ba sis for the DOE cooking efficiency tests.

5-37REFERENCES

1 U.S. Department of Energy (DOE). 1996. Technical Support Document for Residential Cooking Products. Washington, DC. Available online at http://www.eere.energy.gov/buildings/appliance_stan dards/residential/cooking_products_0998_r.html

2 American Metals Market. Available online at http://www.amm.com/

.
3 Association of Home Appliance Manufacturers (AHAM). 2006. AHAM Test Data on Microwave Ovens . October 23, 2006. Docket N o. EE-2006-STD-0127, Comment Number 17.

4 Ibid

.
5 Ibid

.

6 Ibid

.

7 U.S. Department of Energy (DOE). 1980. Engineering Analysis . Washington, DC, DOE/CS-1066, June 1980.

8 AHAM. 2006. Op. cit

.

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