6.1-i APPENDIX 6.1. TECHNICAL DESCRIPTION OF THE REVERSE ENGINEERING COST ESTIMATION METHODOLOGY
TABLE OF CONTENTS
6.1.1 INTRODUCTION

.................................................. 6.1-1 6.1.2 TEAR-DOWNS

.................................................... 6.1-1 6.1.2.1 General Tear-Down Practice

..................................... 6.1-1 6.1.2.2 Specific Product Class Features

................................... 6.1-2 6.1.2.3 Weight Confirmation of Tear-down Results

......................... 6.1-2 6.1.2.4 Final Confirmation of Tear-down Results

.......................... 6.1-2 6.1.2.5 General Tear-down Practice of “Hypothetical” Units

.................. 6.1-3 6.1.3 CREATING THE TEAR-DOWN BILL OF MATERIALS

................... 6.1-4 6.1.4 ADDITIONAL PRODUCTION COST DATA

............................. 6.1-5 6.1.4.1 Labor and Factory Overhead

..................................... 6.1-5 6.1.4.2 Depreciation

.................................................. 6.1-5 6.1.4.3 Parts and Materials

............................................ 6.1-6 6.1.5 STRUCTURE OF THE COST MODELS

................................. 6.1-8 6.1.5.1 Main Cost Model

............................................. 6.1-8 6.1.6 SENSITIVITY ANALYSIS RESULTS

................................. 6.1-12
LIST OF TABLES Table 6.1.2.1 Specific Features for Each Product Class

........................... 6.1-2
LIST OF FIGURES Figure 6.1.3.1 Bill of Materials Sample

........................................ 6.6-5 Figure 6.1.5.1 Cost Model Structure

........................................... 6.6-8 Figure 6.1.5.2 Sample of Global Controls Sheet

.................................. 6.6-9 Figure 6.1.5.3 Subassembly Breakdown

........................................ 6.6-9 Figure 6.1.5.4 Site Table Spreadsheet

......................................... 6.6-10 Figure 6.1.5.5 Components Sheet

............................................ 6.6-10 Figure 6.1.5.6 In-house Fabrication Process

.................................... 6.6-11 Figure 6.1.5.7 Raw Materials Sheet

.......................................... 6.6-11 Figure 6.1.6.1 Standard Deviati ons of Manufacturing Costs

....................... 6.6-136.1-1 APPENDIX 6.1. TECHNICAL DESCRIPTION OF THE REVERSE ENGINEERING COST ESTIMATION METHODOLOGY
6.1.1 INTRODUCTION The manufacturing cost estimation methodology—"reverse engineering"—is a detailed, component-focused, activity-based technique for rigorously estimating the manufacturing cost of a product. It considers direct materials, direct labor, and plant overhead costs. This appendix describes the technical aspects of the approach as applied to residential furnaces and boilers. Refer to Chapter 6 of the Technical Support Document (TSD) for more information on assumptions and context.

6.1.2 TEAR-DOWNS The first step in the reverse engineering process was to perform tear-downs on equipment samples that are typical of today's furnaces and boilers. A tear-down is a thorough disassembly of the equipment followed by a detailed inspection of the parts and subassemblies. The level of resources allocated to different product classes and the unit selection process are described in Chapter 6.
6.1.2.1 General Tear-Down Practice Representative minimum, medium, and high-efficiency units were disassembled for many product classes, as discussed in Chapter 6. The Department made every attempt to perform the disassembly in reverse of the actual assembly process; the bill of materials (BOM) reflects the order of these operations. From observations of industry practices, DOE assumed that major sub-assemblies arrive pre-assembled at the final assembly line. There were a few cases where individual manufacturer practices differed from industrywide practices, but the cost impact of these differences is within the tolerances of the analysis. First, sub-assembly allocation practices varies between manufacturers—for example, some stage sub-assemblies elsewhere and then add them to the final assembly line, while others build all assemblies directly on the final assembly line. A reasonable middle ground was taken, and the extremes assessed; assembly times varied on the order of minutes, well within the tolerances of the analysis. Second, manufacturing out-sourcing practices vary between manufacturers. A similar middle ground was taken, and extreme points evaluated; these variations again fell within the tolerances of the analysis.6.1-2 6.1.2.2 Specific Product Class FeaturesEach product class presented some specific features that differ from the general teardown practice that the Department performed. Specific features for each product class are indicated in Table 6.1.2.1. Table 6.1.2.1 Specific Features for Each Product Class

Product Class Variation Gas Furnace Clamshell and tubular constructions evaluated separately and averaged. Gas Boiler Cast iron heat exchangers are in-sourced at a sister plant for one major manufacturer. The Department assumed the transfer price would be equivalent to the open market value, and a high level of automation is applicable. Oil Furnace None Oil Boiler Based on bills of materials of gas boilers and oil furnaces. Mobile Home Furnaces None Weatherized (Packaged) Furnaces A/C coil model used rather than furnace/boiler model. This is fully described in the Technical Support Document for the Residential Air-Conditioning Rulemaking. 1 6.1.2.3 Weight Confirmation of Tear-down Results The Department confirmed the cost and wei ght predictions using a number of methods. Initially, DOE compared shipping weight predicti ons with published shipping weights. Since cost and weight tend to be highly correlated in manufactured goods, the ability to accurately predict weight is usually an important indication of the accuracy of the cost model. However, DOE discovered that at least one equipment manufacturer had published erroneous weight data. Since it could not verify all the published weight s, DOE could not place confidence in the weight verification.
6.1.2.4 Final Confirmation of Tear-down Results For further confirmation of tear-down results, DOE solicited feedback and comments on the cost analysis directly from the manufacturers of units that were torn down. As a disinterested third party, DOE modeled their factory conditions and assumed production volumes, and calibrated the model assumptions and results for their particular units. Final results, as discussed in Chapter 6 of this TSD, were generated using a set of industry-wide aggregate assumptions to avoid disclosure of company-specific sensitive cost data.6.1-3 6.1.2.5 General Tear-down Practice of “Hypothetical” Units Although DOE had detailed information on a number of units physically torn down, it needed many more samples to span a broad range of efficiency levels in each of the product classes. To cost these samples, DOE created “hypothetical” units. For these units, DOE started from a calibrated tear-down BOM, and then modi fied the BOM to obtain the desired efficiency level. Typically, for any change in efficiency level, there are numerous paths to take and a variety of hardware changes that can be made to obtain a particular efficiency level. According to existing literature, three options appear to be the most promising for gas furnaces—increased heat exchanger area, improved heat transfer coefficient, and derating (see discussion in Chapter 6). Aside from the two design options selected for non-weatherized gas furnaces, a few others were considered for other product classes. These include: 1. Electronic ignition for boilers. 2. Two-stage Modulation. Efficiency gains ascribed to modulation varied from 0 percent to 2.5 percent, dependent on unit and operating conditions. A conservative 1 percent gain was applied. 3. Insulation. For weatherized furnaces only, additional insulation can improve AFUE ratings. In addition, design options that affect fueland electricity consumption were costed. These include: 1. Two-stage Modulation—Uses a two-speed combustion air fan, a dual flow rate gas valve, a multi-speed blower, and associated electronic controls. 2. Continuous Modulation—Uses a continuously variable combustion air fan and gas valve, a multi-speed blower, and associated sensors and controls. 3. Interrupted Ignition (Oil-Fired equipment only)—Uses interrupted firing of the burner rather than continuous, and associated controls. 4. Fan Atomized Burner (Oil-Fired equipment only) with modulation—Uses a fan and ECM motor to atomize the oil. Prototypes exist; conservative costs have been used to reflect the relatively undeveloped nature of this technology. For each hypothetical tear-down, DOE modified the BOM hardware to reflect applicable design options from the list above, costed each design option path, and averaged the results.6.1-4 6.1.3 CREATING THE TEAR-DOWN BILL OF MATERIALS The Department used the tear-down process to create a complete and structured BOM for each torn-down and hypothetical unit. In the process of completely dismantling each piece of the unit, DOE characterized every part according to weight, dimensions, material, quantity, and the manufacturing processes used to fabricate and assemble it. The BOMs incorporate all materials, components, and fasteners with estimates of raw materials and purchased parts and sub-assemblies. The Department based its sourcing assumptions on previous industry experience, recent information in trade publications, and discussions with high- and low-volume originalequipment manufacturers (OEMs). To augment its understanding of the industry's manufacturing practices, DOE also visited several manufacturing plants. These visits focused on observing and characterizing current manufacturing practices. Figure 6.1.3.1 illustrates a small section of a structured bill of materials. It shows:



### C Serial Number: Assigned during disassembly.



### C Part Number: Assigned during disassembly.



### C Description: A description of the part. Subassemblies are grouped.



### C Quantity: Number of parts assembled in a given step for a given subassembly.



### C Extended Quantity : Flat bill-of-materials.



### C V : This entry denotes whether a part is a purchased component or fabricated in-house.



### C Material : Material type or component number



### C OD, Length, Width, Depth, Thickness: Physical parameters that describe the finished part.



### C Extended Weight: Final weight of the part, in grams.



### C Extended Material Cost : Final material cost of the part (calculated), accounting for scrap losses but excluding required assembly, painting, fabrication, or joining costs.



### C Extended Assembly Time: The manual labor (in seconds) required to handle all parts and assemble them into the unit.6.1-5 Figure 6.1.3.1 Bill of Materials Sample

6.1.4 ADDITIONAL PRODUCTION COST DATA The tear-down process and the development of the structured BOMs provided the starting points for estimating production costs, but DOE still needed information on manufacturing operations, part and material prices, wages, plant equipment amortization, and plant overhead. Chapter 6 describes the assumptions and data sources. This section briefly describes the processes DOE used to gather the data and how it used them. 6.1.4.1 Labor and Factory Overhead The Department obtained information on equipment and tooling costs, typical process cycle times, and materials used for fabrication from the proprietary TIAX manufacturing databases. Plant equipment suppliers provided details concerning equipment capabilities and processing parameters (cycle times, scrap rates, etc.). Fabrication cycle rates are directly entered into the cost model and depend on part complexity and processes used. 6.1.4.2 Depreciation Depreciation, or amortization, is the accounting process by which capital costs are allocated to production volume. Amortization occurs over the whole period of time that it takes to produce a product, so that at the end of that time, all capital costs are accounted for in the full cost of producing the product. For example, if a manufacturer produces one million furnaces over ten years and amortizes a $10 million investment over the same ten years, each furnace produced during that time would include $10 in amortization charges. The methodology DOE used to allocate depreciation depended on whether it is assumed that the plant machinery is dedicated or non-dedicated to the production of the sample product. Dedicated machinery is tied solely to the production of the sample product. During times when a piece of dedicated machinery is not needed for that product, it sits idle. The entire capital cost of6.1-6 a piece of dedicated machinery is amortized across the annual volume of the sample product. Conversely, non-dedicated machinery may be used to produce another product when it is not needed for the sample product. Only a fraction of the capital cost of non-dedicated machinery is allocated to the sample product, based on the time the machinery was used to produce the sample product. For example, a non-dedicated press that was used 55 percent of the time to produce the sample product would allocate 55 percent of its depreciation charges to the sample product and 45 percent to the other products with which it is associated. A dedicated press, on the other hand, would allocate 100 percent of its depreciation to the sample product, even if its utilization was 55 percent, since the press is not used for any other production. The Department assumed that all fabrication machinery is non-dedicated, unless it is part of an assembly line (welding, or bending, directly on the line). Due to the seasonal nature of the furnace and boiler business, some manufacturers have off-season uses for their fabrication machinery (e.g., to make air conditioners). The Department also allocated labor to operate a piece of machinery based on whether the machinery is dedicated or non-dedicated. As equipment utilization rates approach 100 percent, the costs associated with dedicated versus non-dedicated equipment costs become equal. However, few dedicated pieces of equipment ever achieve 100 percent utilization due to lack of demand, capacity mismatches between process steps, scheduled downtime, etc. Thus, non-dedicated equipment results in lower overall costs per part, as depreciation, maintenance, and other costs are only assessed on the basis of how much time each part uses a piece of equipment. As equipment types vary, so do the manufacturing equipment and labor requirement s. Depreciation charges therefore also vary across equipment types.
6.1.4.3 Parts and Materials Cost estimates for raw materials and purchased components were drawn from TIAX manufacturing databases and supplemented with information obtained from manufacturer and supplier sources. The Department adjusted the cost estimates as appropriate to include price discounts typically seen in the industry as the result of high-volume purchases. As purchased components make up much of the unit costs, DOE paid special attention to establishing accurate OEM-level price data. Through manufacturer submissions, industry literature, and active research, DOE was able to ascertain the exact specifications for the majority of components used in the units under investigation. For the relatively few purchased components DOE could not identify, it substituted parts from comparable equipment. For example, a manufacturer's technical data sheet may report that a sample furnace uses a certain type of motor supplied by a particular company, but may not state the precise size or part number. In the cases when distributors could not positively identify the part, industry experts would compare the known attributes of similar units (such as horse power, voltage, etc.) with6.1-7 those of the sample equipment. The Department would then select a specific motor size and type based on an interpolation of the available data. The Department then consulted with local distributors, wholesalers, parts suppliers, and OEMs to determine high-volume pricing. The Department applied a discount to the prices received from each of those sources based on their place in the distribution chain. These discounts were based on markup data and DOE’s previous experience in the industry. The manydifferent data sources and the large purchased parts list also allowed DOE to do some crosschecking of price data and discounts. The Department selected those that, most likely reflected actual prices to OEMs. The discounts on each component are a function of the total dollar volume of a typical OEM's account with a typicalsupplier. Since DOE is modeled high volume OEMs who deal with one supplier for each component, this resulted in substantial discounts relative to retail or wholesale prices. In addition, OEM manufacturers commented on assumed OEM pricing, as detailed in section 6.1.2.4 of this appendix.

6.1.5 STRUCTURE OF THE COST MODELS Once the Department had collected all of the information required to estimate production costs for each sample, DOE used Excel spreadsheet models to perform the required calculations. In addition, DOE used Boothroyd-Dewhurst, Inc. (BDI) Design for Assembly software to calculate assembly times, and BDI’s Concurrent Costing software to estimate casting and machining processes. 2Figure 6.1.5.1 illustrates the structure and relationship of the spreadsheets and software used to make the estimates.6.1-8 Global Controls Sheet Materials Sheet

Components Sheet Processes

Sheet

BOM Sheets (1 per teardown)

BDI Design For Assembly BDI Concurrent

Costing Assy Time Part Data

Cast, Machined Part Cost Data Cost Data Global Variables

Site Table

Sheet Mfg Site Dependent Variables (labor rate, etc.)

Purchased Part Costs Equipment Cost, Cycle Times Material Costs

VBA Macros, Portability file data transfer Figure 6.1.5.1 Cost Model Structure

6.1.5.1 Main Cost Model The main model serves to hold data and perform the calculations that determine the production cost of the final assembled equipment. It contains a number of worksheets that perform different functions.

Global Controls Sheet. This worksheet sets parameters such as production volume and wages; it also displays the cost results by sub-assembly. The basic parameters (e.g., days available per year) of the Global Controls sheet are linked to multiple BOM sheets, one for each tear-down. A sample section of those controls is shown in Figure 6.1.5.2. Shaded fields are also varied in the sensitivity analysis.6.1-9 Designed Fabrication Work Days per Year: 240

Designed Assembly Wo rk Days per Year: 240 Runtime per Shift (hrs): 8 Equipment Uptime (%): 90% Designed Assembly Worker Downtime (%): 20% A uxiliary Equipment + Installation Cost: 60% Building Depreciati on Life (Years): 25 Tooling Depreciation (Years): 7 Ratio of Walkways to Fabrication + Storage: 20% Yearly Maintenance Ratio (as % of Equipment Cost) 4% Utility Cost (% of factory cost) 3.0%

Invest. Relativity Factor (%) 1

Avg Depreciation Life (%) 1 Freight Factor: 3% Freight Cost($/cu ft): $1.66 Benefits 40% Building Cost ($/sf) 120 Figure 6.1.5.2 Sample of Global Controls Sheet The Global Controls sheet also shows costs broken down by sub-assembly and cost category. The results are shown in tables 6.1.5.2 and 6.1.5.3. Figure 6.1.5.3 features costs by major sub-assembly and cost type. Cost breakdowns to this fine level allowed DOE to zero in on the differences between equipment across efficiency levels and facilitated the calibration and industry review processes.

XX% AFUE Material Labor Overhead Blower Casing Circulator Electrical/Controls Exterior Components Fuel Control Heat Exchanger Inducer Packaging Total Grand Total 

### Y Y Class

Figure 6.1.5.3 Subassembly Breakdown
Site Table Sheet.Variables that vary from manufacturing site to manufacturing site were isolated on the Site Table sheet. These include labor rates, purchasing power (effective production volumes for components shared across many product families), and a number of other variables. (see Figure 6.1.5.4). After individual manufacturer data was gathered, an industry average were generated, along with two sub-group averages—large and small manufacturers. To avoid disclosure of manufacturing site-specific information, the industry average column was6.1-10 Industry Avg Small Mfg. Large Mfg. Mfg A Mfg B Mfg C ... Assembly Factor assy shifts / day Design vs. Actual Capacity Ratio Direct Labor Rate fab shifts / day Ind:Dir Labor Ratio Mana g ement Span ( people/mana g er) Pa yDifference Mana g er to Line worker Production Volume Purchasing Power rework rate (all repaired) Lot size (days of inventory) JIT ratio Figure 6.1.5.4 Site Table Spreadsheet

Component ID Comp Class Name C omp SubClass

Name Name Manufacturer Part Number C os t Model ID Number Q1 Q1000 Q10000 Q100000 Q1000000 TotQty1 CompCost1 1 0 0 Dummy 2 Electronic PCB Control Board, Damper 3 Electronic PCB Control Board, Mfg A 4 Electronic PCB Control Board, Mfg B 5 Mechanical Motor Blower Motor 6 Mechanical Motor Blower Motor 7 Mechanical Motor Blower Motor 8 Mechanical Fan Blower Wheel 9 Mechanical Fan Blower Wheel 10 Mechanical Fan Blower Wheel 11 Mechanical Pump Circulator with gaskets 12 Mechanical Motor Blower Motor 13 Mechanical Motor Blower Motor 14 Electronic Switch Dual Pressure Switch SubAssy 15 Mechanical Fan Blower Wheel 16 Mechanical Fan Blower Wheel 17 Fuel System Valve Gas valve 18 Fuel System Valve Gas Valve Assy 19 Fuel System Valve Gas Valve Assy 20 ... ... ... Figure 6.1.5.5 Components Sheet used to generate all numbers in this TSD. The ranges found from individual manufacturers were used in the sensitivity analysis.

Components Sheet. The Components sheet contains two types of data: major purchased components unique to each model; and minor, common purchased components used by every model. Major Purchased Components . The Components sheet represents the output of the TIAX manufacturing component database, which logs multiple quotations at a variety of production volumes to build a production volume versus cost curve. These outputs are shown in the Q1 to Q1000000 columns in Figure 6.1.5.5. Depending on quantity per model and production volumes, the component cost is fed to the BOM sheet through the CompCostX column, which queries the result by unit number. These tables determine at least 45 percent of total cost.

Minor, Common Purchased Components . These include items such as connectors, wire, fasteners, board transformers, and other smaller parts that OEMs are likely to purchase from outside suppliers. From the TIAX manufacturing component database, DOE gathered price quotations from multiple sources (suppliers, distributors, prior experience) in quantities6.1-11 Process

ID Class Name S ub C lass Name Machine Name Capacity C apacity Units C apacity Rate C apacity Rate Units C ycle Time (minutes) Depreciation Life (Years) Q1 C apital Cost ($) 1 None None Dummy Process 2 Material Handling Convey Conveyor 3 Material Removal Tube Tube Cut 4 Deformation Forming Tube Tube Bend 5 Deformation Forming Tube Roll Form 6 Deformation Forming Tube Tube Coil 7 Sheet Metal Stamp Large Press 8 Sheet Metal Stamp Med Press 9 Sheet Metal Stamp Sm Press 10 Sheet Metal Bend Press Brake 11 Sheet Metal Blank Blanking 12 Sheet Metal Stamp Turret Punch 13 Material Removal Machine Machining Center 14 Casting Plastic Injection Mold 15 Casting Metal Sand Cast 16 Casting Metal Investment Cast 17 Finishing Powder Coat Paint 18 Material Removal Stamp Plasma 19 Assembly Adhesive Adhesive Bonding 20 Assembly Weld Seam Welding 21 ... ... ... Figure 6.1.5.6 In-house Fabrication Process

Class Name SubClass Name Material Full Name Physical Form Name Density (g/cc) Q1 Q1000 Q10000 Q100000 Q1000000 TotWt1 (g) MatCost1 ($/g) Polymer Thermoplastic ABS Pellet 1.06 Metal Commodity Metal Aluminum Sheet 2.70 Metal Commodity Metal Alumized Steel Sheet 7.87 Metal Commodity Metal Aluminum Tube Tube 2.70 Polymer Commodity Metal Strap Band N/A N/A

... ... ... ...... Figure 6.1.5.7 Raw Materials Sheet throughout the price versus volume curve. In the same fashion as for major purchased components, minor component costs are passed to the BOM sheets. Figure 6.1.5.6 shows modeled fabrication processes; material cost in these cases is determined by the part weight times a cost per gram as detailed on the Raw Materials sheet, Figure 6.1.5.7. For out-sourced parts, DOE applied a vendor profit markup of 1.2. The Department assumed that even in cases of a sister company manufacturing sub-components, this markup will capture the transfer pri ce and the profit of the sister unit.

Bill-of-Materials Sheet.The Bill-of-Materials sheet (as illustrated in Figure 6.1.3.1 and discussed in section 6.1.3) serves as a structured assembly tree, summarizes fabrication and assembly tool data, and calculates production costs based on the price of the part or material and the labor and machinery required to fabricate or assemble it. The BOM sheet also adjusts many other costs in response to changes in physical parameters. For example, the model adjusts baseline sheet metal sizes to incorporate different enclosure sizes. Also, the size of the fiberglass insulation is a function of the sheet metal it has to cover and the efficiency level of the unit (insulation is thicker at higher efficiencies). Many fastener quantities and labor costs are also a function of the sheet metal walls they have to secure. The result is that every unit cost estimate is unique, using the initial BOM as a starting point.6.1-12 Labor, parts, materials, and depreciation cost s are aggregated by sub-assembly and linked back to the Global Controls page.
Processes Sheet. This sheet, from the TIAX manufacturing database, is a list of process costs for all the plant machinery involved in the production of furnaces and boilers. An implicit assumption is that the plant equipment required to produce lower-efficiency samples is also able to produce higher-efficiency samples without any modification. The process data show installed equipment costs, equipment capacity, depreciation life, whether equipment is dedicated, cycle times, labor requirements per station, consumables costs, etc. The installed costs include price quotations for the equipment plus markups to account for installation labor and auxiliary equipment (e.g., electrical service to the equipment).
6.1.6 SENSITIVITY ANALYSIS RESULTS Chapter 6 of the TSD described the Monte Carlo analysis process. The results are presented in Figure 6.1.6.1 in the form of standard deviation values. These results are used as an input for the LCC analysis. Confidence intervals are easily calculated using standard deviation values.6.1-13 Material Labor Overhead Shipping Total
Non-weatherized Gas-fired Furnaces Baseline $5 $3 $2 $1 $6 80% AFUE $4 $2 $1 $1 $5 81% - 83% AFUE $5 $3 $2 $1 $6 Non-condensing Furnaces with Modulation $8 $3 $2 $1 $9 90% AFUE $3 $3 $4 $1 $6 92% AFUE $10 $3 $6 $1 $12 92% with Modulation $15 $3 $6 $1 $16 96% AFUE $35 $3 $6 $1 $36
Weatherized Gas-fired Furnaces
Mobile Home Furnaces 75% AFUE $5 $2 $1 $1 $5 80% AFUE $6 $2 $1 $1 $6 90% AFUE $30 $10 $3 $1 $32
Oil-fired Furnaces Baseline $6 $10 $6 $1 $14 Other Options $10 $10 $6 $1 $15
Gas Boilers Baseline $4 $4 $3 $1 $7 81% - 84% AFUE $4 $4 $3 $1 $6 Gas Boiler with Modulation $10 $4 $3 $1 $11 88% AFUE $30 $10 $3 $1 $32 91% AFUE $75 $15 $5 $1 $77 99% AFUE $100 $20 $10 $1 $102
Oil-fired Boilers Baseline $10 $4 $3 $1 $11 81%-86% AFUE $10 $4 $3 $1 $11 Oil Boiler with Other Options $10 $10 $6 $1 $15 90% AFUE $75 $15 $5 $1 $77 95% AFUE $100 $20 $10 $1 $102 Same as Non-weatherized

Figure 6.1.6.1 Standard Deviations of Manufacturing Costs6.1-14 REFERENCES
1. U.S. Department of Energy-Office of Building Research and Standards, Technical Support Document: Energy Efficiency Standards for Consumer Products: Residential Central Air Conditioners and Heat Pumps , 2000, U.S. Department of Energy. Washington, DC. <http://www.eere.energy.gov/buildings/appliance_standards/residential/ac_central.html> 2. Boothroyd Dewhurst, Design for Manufacture and Assembly ( DFMA), (Last accessed December 17, 2000, <http://www.dfma.com/software/dfaben.html>