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CHAPTER 5. ENGINEERING ANALYSIS

TABLE OF CONTENTS

5.1 INTRODUCTION ........................................................................................................... 5-1

5.2 PRODUCT CLASSES ANALYZED.............................................................................. 5-2

5.3 EFFICIENCY LEVELS................................................................................................... 5-2

5.3.1 Baseline Efficiency Levels .............................................................................................. 5-3

5.3.2 Incremental Efficiency Levels......................................................................................... 5-3

5.4 METHODOLOGY OVERVIEW.................................................................................... 5-5

5.4.1 Manufacturer Interviews.................................................................................................. 5-5

5.4.2 Product Testing ................................................................................................................ 5-6

5.4.3 Product Teardowns .......................................................................................................... 5-7

5.4.3.1 Selection of Units........................................................................................... 5-7

5.4.3.2 Generation of Bill of Materials...................................................................... 5-7

5.4.3.3 Cost Structure of the Spreadsheet Models..................................................... 5-8

5.4.3.4 Cost Model and Definitions........................................................................... 5-9

5.4.3.5 Cost Model Assumptions............................................................................. 5-10

5.5 ANALYSIS AND RESULTS........................................................................................ 5-10

5.5.1 Manufacturer Interviews................................................................................................ 5-10

5.5.1.1 Product Classes............................................................................................ 5-11

5.5.1.2 Design Features of Current Baseline Products ............................................ 5-12

5.5.1.3 Potential Incremental Efficiency Levels...................................................... 5-12

5.5.1.4 Design Options Required to Improve Efficiency......................................... 5-12

5.5.1.5 Impact on Consumer Utility......................................................................... 5-13

5.5.1.6 Installation and Repair Costs as a Function of Efficiency........................... 5-13

5.5.2 Product Testing .............................................................................................................. 5-13

5.5.2.1 Product Selection ......................................................................................... 5-13

5.5.2.2 Test Approach and Results .......................................................................... 5-14

5.5.3 Product Teardowns ........................................................................................................ 5-15

5.5.4 Modeled Performance.................................................................................................... 5-16

5.5.4.1 Air Flow Optimization................................................................................. 5-16

5.5.4.2 Additional Component Improvements......................................................... 5-19

5.5.4.3 Design Options Not Specifically Considered .............................................. 5-21

5.5.5 Combined Tested and Modeled Performance................................................................ 5-22

5.5.6 Cost Estimates................................................................................................................ 5-26

LIST OF TABLES

Table 5.3.2.1 Portable AC Efficiency Level Equation Coefficients............................................ 5-5

Table 5.4.3.1 Major Manufacturing Processes ............................................................................ 5-9

Table 5.5.5.1 Portable AC Efficiency Level Equation Coefficients.......................................... 5-25

Table 5.5.6.1 Incremental Portable AC Manufacturer Production Costs .................................. 5-26
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LIST OF FIGURES

Figure 5.3.2.1 Efficiency Level Curves by Cooling Capacity..................................................... 5-5

Figure 5.4.3.1 Manufacturing Cost Assessment Stages............................................................... 5-8

Figure 5.5.2.1 Measured Cooling Capacity and EERcm............................................................. 5-15

Figure 5.5.4.1 R-410A Compressor Performance Characteristics............................................. 5-20

Figure 5.5.5.1 Modeled Cooling Efficiency versus Cooling Capacity at Each Efficiency 

Level by Unit ..................................................................................................... 5-23

Figure 5.5.5.2 Modeled Power Consumption versus Cooling Capacity at Each Efficiency 

Level by Unit ..................................................................................................... 5-24

Figure 5.5.5.3 Linear Trends Between Power Consumption and Cooling Capacity by 

Efficiency Level................................................................................................. 5-25

Figure 5.5.5.4 Efficiency Level Curves by Cooling Capacity................................................... 5-26
5-1

CHAPTER 5. ENGINEERING ANALYSIS

5.1 INTRODUCTION

After conducting the screening analysis, the U.S. Department of Energy (DOE) 

performed an engineering analysis based on the remaining design options. The engineering 

analysis consists of estimating the energy consumption and costs of portable air conditioners 

(AC) at various levels of increased efficiency. This section provides an overview of the 

engineering analysis (section 5.1), discusses product classes (section 5.2), establishes baseline 

and incremental efficiency levels (section 5.3), explains the methodology used during data 

gathering (section 5.4) and discusses the analysis and results (section 5.5).

The primary inputs to the engineering analysis are baseline information from the market 

and technology assessment (chapter 3 of this preliminary technical support document (TSD)) and 

technology options from the screening analysis (chapter 4 of this preliminary TSD). Additional 

inputs were determined through teardown analysis and manufacturer interviews. The primary 

output of the engineering analysis is a cost-efficiency curve. In the subsequent markups analysis 

(chapter 6 of this preliminary TSD), DOE determined customer (i.e., product purchaser) prices 

by applying distribution markups, sales tax and contractor markups. After applying these 

markups, the cost-efficiency curve serves as the input to the building energy-use and end-use 

load characterization (chapter 7 of this preliminary TSD), and the life-cycle cost (LCC) and 

payback period (PBP) analyses (chapter 8 of this preliminary TSD). 

DOE typically structures its engineering analysis around one of three methodologies.

These are: (1) the design-option approach, which 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 energy 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 “bottom-up” manufacturing cost assessment based 

on a detailed bill of materials (BOM) derived from teardowns of the product or equipment being 

analyzed. Deciding which methodology to use for the engineering analysis depends on the 

covered product, the design options under study, and any historical data that DOE can draw on.
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DOE used a hybrid approach of the design-option and reverse-engineering approaches for 

this analysis. This approach involved physically disassembling commercially available products, 

reviewing publicly available cost information, and modeling equipment cost. From this 

information, DOE estimated the manufacturer production costs (MPCs) for a range of products 

currently available on the market. DOE then considered the steps manufacturers would likely 

take to improve product efficiencies. In its analysis, DOE determined that manufacturers would 

likely rely on certain design options to reach higher efficiencies. From this information, DOE 

estimated the cost and efficiency impacts of incorporating specific design options at each 

efficiency level. This preliminary TSD chapter further describes the process DOE followed to 

establish its cost-efficiency relationship for portable ACs.

5.2 PRODUCT CLASSES ANALYZED

Because portable air conditioners are not currently covered by the Energy Policy and 

Conservation Act (ECPA) of 1975, Pub. L. 94-163 (42 United States Code (U.S.C.) 6291–6309), 

there are no existing product classes for these products. DOE may divide covered products into 

product classes by the type of energy used or by capacity or other performance-related features 

that affect efficiency. Different energy conservation standards may apply to different product 

classes. (42 U.S.C. 6295(q))

DOE considered two product characteristics for potentially establishing multiple portable 

AC product classes: duct configuration and capacity. As discussed in chapter 3 of this 

preliminary TSD, DOE only conducted this preliminary analysis on single-duct and dual-duct 

portable ACs. DOE is not considering spot coolers in this analysis. Also as discussed in chapter 3 

of this preliminary TSD, duct configuration (i.e., the presence of a condenser inlet air duct from 

the unconditioned space) has an impact on portable AC efficiency; however, DOE is not aware 

of any unique consumer utility associated with duct configuration. DOE determined that duct 

configuration, therefore, does not require separate product classes.

Portable AC efficiencies also typically increase for products with higher capacities. From 

its test and modeled data, DOE observed a consistent trend relating efficiency to capacity across 

the range of analyzed capacities. DOE relied on this trend to determine appropriate efficiencies 

for its analysis instead of separating portable ACs into different product classes by capacity. 

Therefore, for this preliminary analysis, DOE analyzed a single portable AC product class.

5.3 EFFICIENCY LEVELS

DOE developed representative efficiency levels using a combination of test and modeled 

portable AC performance data. Each efficiency level corresponds to a particular set of design 

options, primarily based on duct configuration.
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5.3.1 Baseline Efficiency Levels

Typically, a baseline unit is a unit that just meets current energy conservation standards 

and provides basic consumer utility. Because there are no existing energy conservation standards 

for portable ACs, DOE observed whether units tested with lower efficiencies incorporated 

similar design options or features, and considered these features when defining a baseline 

configuration. 

As discussed further in section 5.5.2, based on testing conducted in support of DOE’s test 

procedure notice of proposed rulemaking (NOPR) issued on February 12, 2015 (February 2015 

Test procedure NOPR),aand the notice of data availability (NODA) published in the Federal 

Register on May 9, 2014 (May 2014 NODA, 79 FR 26639), DOE observed that the air flow

pattern through a portable AC has a significant effect on measured cooling capacity and cooling 

energy efficiency ratio (EERcm). Cooling capacity describes the net amount of heat the portable 

AC is able to remove from the conditioned space, in British thermal units per hour (Btu/h). 

EERcm is equal to the cooling capacity divided by the overall power draw of the unit while in 

cooling mode, in Btu per watt-hour (Btu/Wh). For units that draw air from the conditioned space 

over the condenser and then exhaust it outside of the conditioned space, an equivalent amount of 

infiltration air must enter the conditioned space due to the net negative pressure differential that 

is created between the conditioned and unconditioned spaces. Because the proposed test 

conditions specify that infiltration air would be at a higher temperature than the conditioned air, 

the infiltration air offsets a portion or all of the cooling capacity for each portable AC. The 

greater the amount of infiltration air, the lower the cooling capacity will be.

Based on the measured condenser exhaust air flow rates and the corresponding calculated 

magnitudes of the infiltration air heating effect, DOE determined that single-duct units (i.e., units 

that draw all of the condenser intake air from within the conditioned space and exhaust to the 

unconditioned space via a duct) would represent the baseline efficiency level for portable ACs.

Section 5.5.5 provides additional detail on the EERcm-cooling capacity relationship DOE 

developed for the baseline efficiency level.

5.3.2 Incremental Efficiency Levels

DOE developed incremental efficiency levels based on the design options manufacturers 

would likely use to improve portable AC efficiency. As discussed in sections 5.3.1 and 5.5.2, the 

presence of infiltration air has a large impact on unit performance. DOE expects that when 

improving efficiencies beyond the single-duct baseline, manufacturers would first make 

improvements to incrementally reduce the amount of infiltration air.

The first efficiency level beyond the baseline, Efficiency Level 1, represents the first 

improvement a manufacturer would make for a single-duct unit. This efficiency level assumes 

 

a The test procedure is available at: 

http://www1.eere.energy.gov/buildings/appliance_standards/product.aspx/productid/79. 
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manufacturers would convert single-duct units to dual-duct, but that the units would still have a 

significant quantity of infiltration air. At Efficiency Level 1, infiltration air flow was selected to 

equal half of the total air flow over the condenser (i.e., half of the condenser air flow is from the 

conditioned space, and the other half is from the unconditioned space via the condenser inlet 

duct). This amount of infiltration air flow is approximately equal to the average observed for 

dual-duct units in DOE’s test sample.

Efficiency Level 2 represents dual-duct units with reduced infiltration air flow. Out of its 

test sample, DOE observed that all dual-duct units drew in a certain amount of infiltration air. 

The best-performing units in the test sample had infiltration air flows equal to approximately 25 

percent of the total condenser air flow. Units meeting Efficiency Level 2 would have infiltration 

air flows similar to the 25 percent observed in testing.

Efficiency Level 3 represents ideal dual-duct performance. At this level, the dual-duct 

products would intake all of the condenser air from the unconditioned space via the condenser 

inlet duct, resulting in no infiltration air. DOE notes that it did not observe this air flow

configuration for any products in its test sample, but included it in this analysis because DOE 

tentatively concludes it is technically feasible and results in a significant increase in efficiency.

Efficiency Level 4 is the max-tech level as determined by DOE. This level combines the 

ideal dual-duct air flow configuration described for Efficiency Level 3 with additional design 

option changes to improve efficiency. Although DOE did not observe any portable ACs with 

these additional design options, DOE regards each of them as options that manufacturers would 

be likely to consider incorporating to achieve the highest possible efficiencies. At Efficiency 

Level 4, units would incorporate more efficient compressors and blower motors, larger heat 

exchangers, and low-standby-power electronic controls. Similar to Efficiency Level 3, DOE did 

not test any portable ACs performing at Efficiency Level 4, but estimated the potential 

performance improvements for products incorporating these design changes based on available 

information and modeling described in section 5.5.4.

DOE relied on its investigative testing and modeled data to determine product EERcm and 

cooling capacity at each of the efficiency levels. These data resulted in a range of product 

efficiencies for each efficiency level depending on the individual product cooling capacities. 

DOE evaluated the relationships between cooling capacity and EERcm at each efficiency level 

configuration, and developed the following equation to describe the representative EERcm for a 

given cooling capacity at each efficiency level:

EERcm =

Cooling Capacity

(A × Cooling Capacity + B)

Table 5.3.2.1 below provides the coefficients A, in Wh/Btu, and B, in watts (W), for each 

analyzed efficiency level that would be used to determine EERcm in Btu/Wh. Figure 5.3.2.1 plots 

each efficiency level curve for cooling capacities from 0 to 10,000 Btu/h.
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Table 5.3.2.1 Portable AC Efficiency Level Equation Coefficients 

Efficiency Level A Coefficient

(Wh/Btu)

B Coefficient

(W)

Baseline 0.113 855.5

EL1 0.1201 685.4

EL2 0.1222 566.3

EL3 0.1256 426.9

EL4 0.1205 355.1

Figure 5.3.2.1 Efficiency Level Curves by Cooling Capacity

Section 5.5.5 provides additional detail describing how DOE developed the relationships 

between EERcm and cooling capacity at each efficiency level. 

5.4 METHODOLOGY OVERVIEW

DOE relied on multiple sources of information for this engineering analysis. These 

sources include manufacturer interviews, internal product testing, and product teardowns.

5.4.1 Manufacturer Interviews

DOE understands that there is variability among manufacturers in product offerings, 

design strategies, and cost structures. To better understand and explain these variances, DOE 
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conducted manufacturer interviews as part of this analysis. These confidential interviews 

provided a deeper understanding of the various combinations of technologies used to increase 

portable AC efficiency, and their associated manufacturing costs. Sample questions for the 

engineering analysis that were sent to manufacturers participating in these interviews are 

contained in appendix 5-A of this preliminary TSD.

5.4.2 Product Testing

DOE does not currently cover portable ACs and, therefore, does not compile a list of 

portable AC performance data. There is also little publicly available data on portable AC

performance from other sources. Where data is available, often the test basis is unknown or not 

directly applicable to this analysis (e.g., the California Energy Commission (CEC) requires 

reporting of spot cooler performance based on American National Standards Institute 

(ANSI)/American Society of Heating, Refrigerating, and Air-Conditioning Engineers 

(ASHRAE) Standard 128-2001 “Method of Rating Unitary Spot Air Conditioners”

(ANSI/ASHRAE 128-2001); however, more recent industry standards, including 

ANSI/Association of Home Appliance Manufacturers (AHAM) PAC-1-2009 “Portable Air 

Conditioners”b(AHAM PAC-1-2009), Canadian Standards Association (CSA) C370-2013 

“Cooling Performance of Portable Air Conditioners” (CSA 370-13)

c

, and the 2011 updated 

version of ANSI/ASHRAE Standard 128, ANSI/ASHRAE Standard 128-2011 “Method of 

Rating Unitary Spot Air Conditioners” (ANSI/ASHRAE Standard 128-2011) all require a 

substantially lower indoor ambient testing temperature).

To address this lack of portable AC performance data, DOE conducted its own 

investigative testing. As discussed in the February 2015 Test Procedure NOPR, DOE conducted 

testing according to an air enthalpy method (similar to current industry test methods) and a 

calorimeter method (similar to the method used for room ACs).Specifically, DOE conducted the 

testing to:

 Investigate and determine the most representative test methodology for portable 

ACs;

 Establish efficiency trends for products over a range of capacities;

 Develop a better understanding of the design options and product features 

currently available on the market; 

 Develop a better understanding of the operational characteristics of portable ACs.

 

b ANSI/AHAM test procedures are available for purchase online at: www.aham.org. 

c CSA standards are available for purchase online at: http://shop.csa.ca/. 
5-7

5.4.3 Product Teardowns

Other than obtaining detailed manufacturing costs directly from a manufacturer, the most 

accurate method for determining the production cost of a product is to disassemble representative

units piece-by-piece and estimate the material, labor, and overhead costs associated with each 

component using a process commonly called a physical teardown. DOE performed physical 

teardown analysis on portable ACs from a range of manufacturers. The teardown methodology is 

explained in the following sections.

5.4.3.1 Selection of Units

DOE generally adopts the following criteria for selecting units for teardown analysis:

 The selected products should span the full range of efficiency levels for each product class 

under consideration;

 Within each product class, the selected products should, if possible, come from the same 

manufacturer and belong to the same product platform;

 The selected products should, if possible, come from manufacturers with large market shares

in that product class, although the highest efficiency products are 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 same class and at the same efficiency level.

5.4.3.2 Generation of Bill of Materials

The end result of each teardown is a structured BOM, which describes each product part

and its relationship to the other parts, in the estimated order of assembly. The BOMs describe 

each fabrication and assembly operation in detail, including the type of value—added equipment 

needed (e.g., stamping presses, injection molding machines, spot-welders, etc.) and the estimated

cycle times associated with each conversion step. The result is a thorough and explicit model of 

the production process.

Materials in the BOM are divided between raw materials that require conversion steps to 

be made ready for assembly, while purchased parts are typically delivered ready for installation.

The classification into raw materials or purchased parts is based on DOE’s previous industry 

experience, recent information in trade publications, and discussions with original equipment 

manufacturers (OEMs). For purchased parts, the purchase price is based on volume-variable 

price quotations and detailed discussions with suppliers.

For parts fabricated in-house, the prices of the underlying “raw” metals (e.g., tube, sheet 

metal) are estimated on the basis of 5-year averages to smooth out spikes in demand. Other 

“raw” materials such as plastic resins, insulation materials, etc. are estimated on a current-market 
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basis. The costs of raw materials are based on manufacturer interviews, quotes from suppliers, 

secondary research, and by subscriptions to publications including the American Metals Marketd

(AMM). Past price quotes are indexed using applicable Bureau of Labor Statistics producer price 

index tables as well as AMM monthly data. 

5.4.3.3 Cost Structure of the Spreadsheet Models

The manufacturing cost assessment methodology used is a detailed, component-focused 

technique for rigorously calculating the manufacturing cost of a product (direct materials, direct 

labor and some overhead costs). Figure 5.4.3.1 shows the three major steps in generating the 

manufacturing cost.

Figure 5.4.3.1 Manufacturing Cost Assessment Stages

The first step in the manufacturing cost assessment was the creation of a complete and 

structured BOM from the disassembly of the units selected for teardown. The units were 

dismantled, and each part was characterized according to weight, manufacturing processes used, 

dimensions, material, and quantity. The BOM incorporates all materials, components, and 

fasteners with estimates of raw material costs and purchased part costs. Assumptions on the 

sourcing of parts and in-house fabrication were based on industry experience, information in 

trade publications, and discussions with manufacturers. Interviews and plant visits were 

conducted with manufacturers to ensure accuracy on methodology and pricing.

Following the development of a detailed BOM, the major manufacturing processes were 

identified and developed for the spreadsheet model. Some of these processes are listed in Table 

5.4.3.1.

 

d For information on American Metals Market, please visit: www.amm.com.
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Table 5.4.3.1 Major Manufacturing Processes

Fabrication Finishing Assembly/Joining Quality Control

Fixturing

Stamping/Pressing

Brake Forming

Cutting and Shearing

Insulating

Turret Punch

Tube Forming

Enameling

Washing

Powder Coating

De-burring

Polishing

Refrigerant Charging

Adhesive Bonding

Spot Welding

Seam Welding

Packaging

Inspecting & Testing

Fabrication process cycle times for each part made in-house were estimated and entered 

into the BOM. Based on estimated assembly and fabrication time requirements, the labor content 

of each appliance could be estimated. For this analysis, DOE estimated labor costs based on 

typical annual wages and benefits of industry employees.

Cycle requirements for fabrication steps were similarly aggregated by fabrication 

machine type while accounting for dedicated vs. non-dedicated machinery and/or change-over 

times (die swaps in a press, for example). Once the cost estimate for each teardown unit was 

finalized, a detailed summary was prepared for relevant components, subassemblies and 

processes. The BOM thus details all aspects of unit costs: material, labor, and overhead. 

Design options used in units subject to teardown 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 are 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.

5.4.3.4 Cost Model and Definitions

The cost model is based on production activities and divides factory costs into the 

following categories:

 Materials: Purchased parts (i.e., motors, valves, etc.), raw materials, (i.e., cold rolled 

steel, copper tube, etc.), and indirect materials that are used for processing and 

fabrication.

 Labor: Fabrication, assembly, indirect, and supervisor labor. Fabrication and assembly 

labor cost are burdened with benefits and supervisory costs.

 Overhead: Equipment, tooling, and building depreciation, as well as utilities, equipment 

and tooling maintenance, insurance, and property taxes.

Cost Definitions

Because there are many different accounting systems and methods to monitor costs, DOE 

defined the above terms as follows:
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 Direct material: Purchased parts (out-sourced) plus manufactured parts (made in-house 

from raw materials).

 Indirect material: Material used during manufacturing (e.g., welding rods, adhesives).

 Fabrication labor: Labor associated with in-house piece manufacturing.

 Assembly labor: Labor associated with final assembly.

 Supervisory labor: Labor associated with fabrication and assembly basis. Assigned on a 

span basis (x number of employees per supervisor) that depends on the industry.

 Indirect labor: Labor costs that scale with fabrication and assembly labor. These included 

the cost of technicians, manufacturing engineering support, stocking, etc. that are 

proportional to all other labor. 

 Equipment depreciation: Money allocated to pay for initial equipment installation and 

replacement as the production equipment is amortized. All depreciation is assigned in a 

linear fashion and affected equipment life depends on the type of equipment.

 Tooling depreciation: Cost for initial tooling (including non-recurring engineering and 

debugging of the tools) and tooling replacement as it wears out or is rendered obsolete.

 Building depreciation: Money allocated to pay for the building space and the conveyors 

that feed and/or make up the assembly line.

 Utilities: Electricity, gas, telephones, etc.

 Maintenance: Annual money spent on maintaining tooling and equipment.

 Insurance: Appropriated as a function of unit cost.

 Property Tax: Appropriated as a function of unit cost.

5.4.3.5 Cost Model Assumptions

As discussed in the previous section, assumptions about manufacturer practices and cost 

structure played an important role in estimating the final product cost. In converting physical 

information about the product into cost information, DOE reconstructed manufacturing processes 

for each component using internal expertise and knowledge of the methods used by the industry.

Site visits allowed DOE to confirm its cost model assumptions through direct observation of the 

manufacturing plant, as well as through manufacturer interviews, reviews of current Bureau of 

Labor Statistics data, etc.

5.5 ANALYSIS AND RESULTS

5.5.1 Manufacturer Interviews

DOE conducted interviews with portable AC manufacturers to develop a better 

understanding of current product features and the technologies used to improve energy 

efficiency. The manufacturers interviewed represent a wide range of U.S. market share and 

included both domestic and international companies that sell portable ACs in the United States. 

During these interviews, DOE asked manufacturers questions about the following topics related 

to the engineering analysis:
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 Product classes

 Design features of current baseline products

 Proposed incremental efficiency levels

 Design options required to meet each efficiency level

 Performance at reduced ambient temperatures

 Impacts on consumer utility

 Installation and repair costs as a function of efficiency

The discussion helped DOE understand what proposed design options have already been 

implemented and what additional design options DOE should consider. 

The discussion below represents a consolidation of the manufacturer responses.

5.5.1.1 Product Classes

Because DOE does not currently cover portable ACs, there are no existing product class 

divisions within this product type. During manufacturer interviews, DOE requested feedback on 

potential product classes that would separate single-duct and dual-duct units each into multiple 

product classes based on capacity, from less than 8,000 Btu/h to greater than 14,000 Btu/h. DOE 

established the potential capacity bins for product classes based on the range of available 

capacities listed in publicly available data. DOE notes that these capacities correspond to existing 

industry test methods, and would not be comparable to cooling capacities as determined 

according to the method proposed in the February 2015 Test Procedure NOPR.

Manufacturers generally responded in support of product classes that separate single-duct 

and dual-duct configurations for testing and standards. They indicated that each configuration 

would have different efficiencies due to differing air conditions flowing over the condenser and 

other design choices impacting portability and noise.

However, manufacturers stated that there is no significant consumer utility associated 

with a single-duct configuration compared with a dual-duct configuration. Manufacturers 

indicated that dual-duct and single-duct portable ACs of similar rated capacities typically have 

the same overall power, utilizing similar compressors, chassis sizes and fan speeds. 

While there may be no utility associated with the different product configurations,

manufacturers indicated that single-duct units tend to be more popular due to a lower cost than 

the dual-duct configuration and because they were the first configuration introduced to the 

market. Also, two ducts take up more space and can be cumbersome for consumers who are 

unfamiliar with the installation and presence of multiple ducts. However, manufacturers also 

indicated that single-duct units may have higher rates of returns due to consumer dissatisfaction

with their cooling performance.

Manufacturers also indicated that the listed product classes, which were in 2,000 Btu/h 

intervals, may be too granular, and there should be fewer capacity bins for each duct 

configuration. DOE also received feedback that it should align product classes with room ACs so 
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there is a direct comparison between the two similar products. This would be helpful to 

consumers who make purchasing decisions based on capacity rather than efficiency rating.

5.5.1.2 Design Features of Current Baseline Products

DOE discussed with manufacturers the features of baseline products. Because of the lack 

of a consistent test method, manufacturers indicated that it is difficult to compare efficiencies 

and capacities between products from different manufacturers. However, manufacturers 

indicated that baseline portable ACs typically include the same components as units at higher 

efficiencies, perhaps with smaller heat exchangers or less efficient compressors.

5.5.1.3 Potential Incremental Efficiency Levels

DOE asked manufacturers to comment on suitable efficiency levels for the potential

portable AC product classes. Manufacturers were asked to comment on the appropriateness of 

each incremental efficiency level and the max-tech levels. DOE based the incremental efficiency 

levels in the interview guide on publicly available efficiency and capacity information. 

Accordingly, the efficiency levels do not correspond to efficiencies that would be measured by 

the method proposed in the February 2015 Test Procedure NOPR. However, the information 

provided by manufacturers helped DOE understand the range of efficiencies that may be 

achieved as measured according to existing industry test methods.

In general, manufacturers did not object to the efficiency levels DOE selected for 

analysis; however, there was some concern that larger increments in efficiency between levels 

could be difficult to achieve. Additionally, manufacturers expressed concern that not all products 

are currently rated using the same test method. Accordingly, certain efficiency levels may be too 

high or low depending on the rating conditions. Also, some manufacturers were concerned about 

meeting the maximum efficiency levels with current materials and components. They suggested

that higher efficiency products are currently being investigated, but the necessary changes are not 

completely understood at this time. 

5.5.1.4 Design Options Required to Improve Efficiency

DOE asked manufacturers to describe the changes associated with each efficiency level 

relative to the baseline units in each product class. From the reverse-engineering analysis and 

experience with room ACs and dehumidifiers, DOE predicted the key design options would be

increased compressor efficiency and heat exchanger sizes. DOE highlighted these options during 

discussions with manufacturers to determine the necessary design options to meet incremental

efficiency levels. 

Manufacturers generally agreed that the primary changes required to meet higher 

efficiency levels are likely more efficient compressors and motors. They indicated that larger 

heat exchangers and higher air flow rates with larger ducting components would increase 

efficiency, but size and noise limitations associated with portability would limit the extent of 
5-13

these design options. Manufacturers also stated that the costs associated with these design 

options would be significant. Manufacturers confirmed that microchannel heat exchangers, 

variable-speed compressors, and other advanced technologies to improve efficiency are not 

currently being implemented in portable ACs. Manufacturers stated that they would likely utilize 

improved compressor efficiencies and larger heat exchangers to improve portable AC 

efficiencies before incorporating these design options.

5.5.1.5 Impact on Consumer Utility

DOE asked manufacturers how these design option changes may impact consumer utility. 

Manufacturers indicated that overall performance would not be impacted; however, larger fans 

may increase the fan operating noise, and larger components and cases would increase the 

overall unit weight and decrease portability. Also, in addition to the general cost of parts 

associated with the design options, increasing the number of ducts would increase the packaging

size, adding to the shipping cost.

5.5.1.6 Installation and Repair Costs as a Function of Efficiency

Manufacturers indicated that single-duct units are more portable than dual-duct units, and 

are therefore easier to install and move from one room to another. Otherwise, manufacturers did 

not indicate that product lifetimes or installation and repair costs would vary significantly with 

improvements in efficiency.

5.5.2 Product Testing

DOE conducted investigative testing on portable ACs in support of the May 2014 NODA 

and February 2015 Test Procedure NOPR to determine the appropriate methodology to be 

included in a future DOE portable AC test procedure. 29 FR 26639 (May 9, 2014). DOE utilized 

the results of this investigative testing to support this preliminary engineering analysis. The 

following sections detail the testing process, from product selection through data analysis.

5.5.2.1 Product Selection

DOE’s test sample included 24 portable ACs. DOE selected units covering a range of 

manufacturer-rated capacities (5,000 to 14,000 Btu/h) and energy efficiency ratios (EERs, 7.0 to 

12 Btu/Wh) from a range of manufacturers. Because DOE does not currently regulate portable 

ACs, the rated capacities and EERs do not necessarily reflect performance under the conditions 

proposed in the February 2015 Test Procedure NOPR; however, they provided a basis for DOE 

to differentiate between units available on the market. DOE’s test sample also covered the two 

major product configurations: 17 single-duct units and 7 dual-duct units. DOE notes that one of 

the dual-duct units shipped with a conversion kit to enable testing in single-duct configuration. 

DOE tested this unit in both single-duct and dual-duct configurations.
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5.5.2.2 Test Approach and Results

DOE first performed testing in accordance with AHAM PAC-1-2009 to determine 

baseline performance according to industry standards. This baseline performance was then used 

to evaluate the suitability of the current industry standards through comparisons with modified or 

alternate test approaches.

As discussed and presented in the May 2014 NODA, DOE further investigated heat 

transfer effects not currently captured in available portable AC test procedures, through 

additional testing according to a room calorimeter approach adapted from ANSI/ASHRAE 

Standard 16-1983 (RA 99), “Method of Testing for Rating Room Air Conditioners and Packaged 

Terminal Air Conditioners” (ANSI/ASHRAE Standard 16-1983). DOE conducted that testing on 

a representative sample of four single-duct and two dual-duct units. For this preliminary analysis, 

DOE conducted similar calorimeter testing on an additional 18 test units not covered by the May 

2014 NODA. The calorimeter testing used two test chambers, one maintained at the indoor 

conditions, 80 degrees Fahrenheit (°F) dry-bulb temperature and 67 F wet-bulb temperature,

and the other maintained at the outdoor conditions, 95 F dry-bulb temperature and 75 F wetbulb temperature, specified in AHAM PAC-1-2009. Rather than installing the test unit in the 

wall between the indoor and outdoor test rooms, as for a room AC, the portable AC under test

was located within the indoor test room with the condenser duct(s) interfacing with the outdoor 

test room by means of the manufacturer-supplied or manufacturer-recommended mounting 

fixture.

DOE then considered a modified test approach that followed the procedure outlined in 

AHAM PAC-1-2009, but included calculations to account for any heat effect due to infiltration 

air. DOE found that infiltration air heat input caused a significant reduction in cooling capacity 

and efficiency when compared with the results from the nominal AHAM PAC-1-2009 test 

procedure.

In the February 2015 Test Procedure NOPR, DOE concluded that the AHAM PAC-1 test 

approach should be the basis of a DOE test procedure for portable ACs to ensure representative 

test results, minimize additional test burden, and align with current industry practices. Therefore, 

DOE proposed referencing the newly-released version of the PAC-1 standard, AHAM PAC-1-

2014e with additional provisions and clarifications to determine representative performance.

Figure 5.5.2.1 presents the measured cooling capacity and EERcm of its test sample consistent 

with the approach proposed in the February 2015 Test Procedure NOPR. As can be seen from 

the lower measured cooling capacities compared to the manufacturer-rated values, the inclusion 

of infiltration air heating results in a significant reduction in net cooling.

 

e As noted in the February 2015 Test Procedure NOPR, DOE’s testing and analysis in support of the test procedure 

rulemaking was completed prior to the publication of AHAM PAC-1-2014. After careful examination, DOE 

concluded that the differences between the 2009 and 2014 versions of the test standard would not significantly affect 

testing results, and, therefore, DOE proposed a test procedure that would reference certain provisions of the current 

version of the standard (AHAM PAC-1-2014). 
5-15

Figure 5.5.2.1 Measured Cooling Capacity and EERcm

In the February 2015 Test Procedure NOPR, DOE also proposed test procedures to 

determine heating capacity and efficiency in heating mode, energy consumption in off-cycle

mode, and energy consumption in various standby modes and off mode. In addition, DOE also 

proposed an overall combined EER (CEER), which combines unit performance in each of these 

available modes. However, because cooling is the primary function of DOE expects that 

manufacturers would likely focus on improving efficiency in this mode to achieve higher 

CEERs. Accordingly, DOE focused on performance in cooling mode for this engineering 

analysis. Later rulemaking stages would consider portable AC performance based on CEER.

As detailed in the following sections, DOE utilized test data when conducting teardowns 

and modeling to correlate efficiency gains with certain design options for the units in the test 

sample. 

5.5.3 Product Teardowns

After completing the investigative testing described in the previous section, DOE 

conducted teardowns on 23 units in its sample that were available at the end of the test series. 

The teardown units spanned the range of product efficiencies and features available on the 

market from multiple manufacturers. DOE relied on the portable AC teardowns to supplement 

the information gained through manufacturer interviews and to investigate how product 

construction related to performance observed during testing. Specifically, the teardowns allowed 

DOE to identify design features for improving efficiency and to develop corresponding 

manufacturing costs for products at different efficiency levels.

DOE observed all portable ACs in the teardown sample had similar construction. All 

units were housed in a plastic case with either a plastic or metal internal structure. The units
5-16

typically featured distinct upper and lower internal sections to separate the evaporator and 

condenser and their associated components. The top section included the evaporator, evaporator 

blower, and filter, while the bottom section included the condenser, compressor, and condenser 

blower assembly, including an air filter. For the single-duct units, the duct was connected at one 

end to the condenser exhaust port on the back of the case and at the other end to the window 

mounting bracket for exhausting the air outside of the conditioned space. Dual-duct units 

similarly attached the duct to the back of the case at the condenser exhaust, but also included a 

second duct attached at the condenser air inlet. Both ducts were connected to the window 

mounting bracket. For all units, the accordion-style collapsible plastic coil ducts were almost 

identical, with slight variations in diameter and construction (i.e., some ducts included a wire 

support while others were entirely plastic).

The units were constructed such that any condensate formed on the evaporator in the 

upper chamber would drip over the condenser, allowing some or all condensate to evaporate

before the remainder is collected in a small internal reservoir at the bottom of the unit. All units 

either implemented a slinger wheel or pump in the internal reservoir to circulate any collected 

condensate back on to the condenser where it would be evaporated and removed from the case in 

the condenser exhaust air stream. All units included a condensate drain outlet to allow manual

draining of any condensate collected in the internal reservoir that exceeds the amount that could 

be re-evaporated. 

All units featured rotary R-410A compressors secured to the base of the unit’s internal 

case platform. DOE observed that all blowers used permanent split capacitor (PSC) motors. The 

evaporator and condenser within each unit had similar dimensions and number of tube passes, 

and were connected via capillary tubes. The copper tubing exiting the evaporator and entering 

the compressor was typically insulated, though the thickness and length of insulation varied 

among units. All of the units in DOE’s test and teardown sample featured electronic controls, 

although DOE believes other units available on the market may use electromechanical controls.

5.5.4 Modeled Performance

Although DOE tested and tore down a large sample of units from different manufacturers 

at varying capacities and efficiencies, the sample did not cover the entire range of efficiency 

levels and design options that are technically feasible. To fill in the gaps in the teardown sample 

and to estimate the maximum efficiencies possible as measured by the method proposed in the 

February 2015 Test Procedure NOPR, DOE numerically modeled unit performance with various 

design option configurations.

5.5.4.1 Air Flow Optimization

DOE’s test and teardown sample included both single-duct and dual-duct units covering a 

range of rated capacities and efficiencies. As discussed in the February 2015 Test Procedure 

NOPR, DOE determined that infiltration air has the most significant impact on performance 

when compared with other heat transfer components. DOE also found that air infiltration has the 
5-17

largest impact on single-duct unit performance, due to infiltration air flow equaling condenser 

inlet flow rates. Accordingly, single-duct units typically had lower measured efficiencies and 

capacities compared to dual-duct units. Therefore, DOE considered single-duct units as the 

current baseline configuration. 

DOE expects that manufacturers would rely on adjusting the air flow configuration to 

improve the performance of units that produce significant infiltration air flow. DOE identified 

this as the least expensive design option available to increase both cooling capacity and 

efficiency, and therefore the most likely to be implemented. Other design options to improve 

efficiency (e.g., increasing heat exchanger size or improving compressor and motor efficiencies) 

have smaller impacts on performance at higher costs. Therefore, DOE first considered 

incremental improvements to the air flow configuration to estimate the feasible improvements in 

efficiency for all units in the test and teardown sample.

Efficiency Level 1

The first incremental change in the air flow design corresponds to Efficiency Level 1. 

This change involves moving to a dual-duct configuration that draws 50 percent of the condenser 

inlet from the conditioned space, and in turn, has an equivalent amount of infiltration air. DOE 

notes that dual-duct units in its test sample drew between 37 and 72 percent of condenser inlet air 

from the conditioned space. This first incremental improvement represents an improvement to an 

average performing dual-duct unit currently available on the market.

To determine the resulting impact on efficiency and capacity, DOE first reduced the 

infiltration air latent and sensible heat contribution by 50 percent. The method proposed in the 

February 2015 Test Procedure NOPR determines the infiltration air heating effect via a direct 

calculation, so DOE was able to account for this change with no additional modeling. 

However, changing the condenser air source and internal air flow pattern leading to the 

condenser has additional effects on unit performance beyond reducing infiltration air flow. While 

a single-duct unit draws all condenser inlet air from the conditioned space, a dual duct unit with 

50 percent infiltration air draws half of the condenser inlet air from the conditioned space and the 

other half from the outdoor conditions. As a result, the average condenser inlet air conditions

change from 80 °F dry-bulb temperature and 51-percent relative humidity to 87.5 °F dry-bulb 

temperature and 45.5-percent relative humidity (the average of the indoor and outdoor test 

conditions). The increase in dry-bulb temperature and reduction in relative humidity result in less 

effective heat transfer from the condenser to the air stream, decreasing cooling capacity and 

efficiency. 

To calculate the impact of the updated condenser air flow conditions on cooling capacity

and efficiency, DOE performed energy modeling utilizing the MarkN program developed for use 

in its most recent room AC energy conservation standards direct final rule. 76 FR 22454 (Apr. 

21, 2011). The MarkN program was itself an update of an adaptation to the Oak Ridge National 

Laboratory Mark III Heat Pump program for modeling room AC cooling performance. This 

program was originally used in support of the 1997 room AC final rule. 62 FR 50122 (Sept. 24, 
5-18

1997). The 1997 final rule and 2011 TSDfprovide further details regarding the use of these 

programs in support of the room AC energy conservation standards rulemakings. 

DOE first used the numerical model to simulate unit performance for models in the test 

and teardown sample. The model inputs include product component specifications and the 

ambient operating conditions. DOE obtained component information from the product 

teardowns, including heat exchanger construction (number of rows, tube passes, tube spacing, fin 

spacing, etc.), refrigerant tubing (lengths and diameters of inlet/outlet tubes and capillary tubes), 

and compressor specifications. 

DOE calibrated the model results for multiple units in the teardown sample using 

available test data. DOE then modeled additional scenarios, changing only the condenser inlet air

conditions. DOE developed a relationship between the condenser inlet air conditions and the 

resulting cooling capacity based on these simulations. This relationship was used to estimate the 

reduction in overall cooling capacity when condenser inlet conditions were adjusted for a 

combination of indoor and outdoor air.

DOE also used the MarkN model results to estimate the change in compressor power at 

the adjusted condenser inlet air conditions. Compressors draw more power at higher condenser 

inlet air temperatures because of the higher operating temperature and pressure of the refrigerant 

in the condenser. DOE used the model results to develop a relationship for compressor power 

consumption based on condenser inlet conditions. The calculated efficiency results at each 

efficiency level account for the changes in compressor power draw at the different condenser 

inlet air conditions.

In addition to variations in compressor power draw, DOE also considered the increase in 

blower motor power required when moving from a single-duct to dual-duct configuration. DOE 

assumed that introducing an additional duct would require a 10-percent increase in blower motor 

power to overcome the added external static pressure associated with the additional duct. 

Efficiency Levels 2 and 3

Efficiency Levels 2 and 3 also represent dual-duct performance, but with incrementally 

less condenser inlet air drawn from within the conditioned space. Efficiency Level 2 represents 

25-percent condenser inlet air from the conditioned space, and Efficiency Level 3 assumes that 

no condenser inlet air is drawn from the conditioned space. At Efficiency Level 3, there would 

be no pressure differential between the indoor and outdoor spaces, resulting in no infiltration air. 

At these efficiency levels, DOE considered the same impacts on performance as for Efficiency 

Level 1: air infiltration heat, compressor power, and blower motor power. However, DOE also 

 

f The TSD in support of the 2011 room AC direct final rule is available online at: 

www.regulations.gov/#!documentDetail;D=EERE-2007-BT-STD-0010-0053.
5-19

assumed that blower motor power would increase by 5 percent at these efficiency levels to 

accommodate the additional air flow through the condenser inlet duct. 

5.5.4.2 Additional Component Improvements

As discussed above, DOE also identified other design options that could be utilized to 

increase portable AC efficiency beyond improving the air flow configuration, including 

increasing heat exchanger area and improving compressor and fan motor efficiencies. DOE 

incorporated these changes to estimate performance at the max-tech Efficiency Level 4.

Increased Heat Exchanger Area

DOE is aware that increasing the heat transfer area of the evaporator and condenser coils 

may improve portable AC performance. At the max-tech efficiency level, DOE considered the 

efficiency improvements that would be associated with larger coils. From manufacturer 

interviews, DOE learned that portable AC case sizes and weights are already approaching the 

limits of acceptable portability for consumers. Significantly larger case sizes or greater weights 

would limit the ability for consumers to move units from room to room or to carry the unit up or 

down stairs. Accordingly, DOE considered a 10-percent increase in coil cross-sectional area in 

estimating the potential efficiency improvement associated with larger coils. At this coil size, 

product cases and weights would not change significantly from those currently available on the 

market. Based on manufacturer interviews, DOE expects that manufacturers would increase coil 

cross-sectional area to improve heat transfer rather than increasing heat exchanger depth or 

increasing fin density because it results in a relatively larger efficiency improvement.

To estimate the effect of larger heat exchangers on efficiency, DOE again modeled unit 

performance using the MarkN model. DOE began with the model inputs for the optimized dualduct configuration (i.e., condenser inlet air at the outdoor conditions) and adjusted the heat 

exchanger parameters for a 10-percent larger cross-sectional heat transfer area. DOE also 

modeled the other potential heat exchanger design options, increasing coil depth and increasing 

fin density, and confirmed that increasing cross-sectional area resulted in the largest efficiency 

gains.

Improved Compressor Efficiency

To determine appropriate ranges of compressor efficiencies, DOE utilized information 

gathered in the preliminary engineering analysis for dehumidifiers.g79 FR 29380 (May 22, 

2014). As shown in Figure 5.5.4.1, compressors are available at rated EERs ranging from 

roughly 8.5 to 10.5 Btu/Wh. DOE notes that this range represents a limited number of 

compressors based on a survey of the market, not necessarily those observed during teardowns. 

 

g The preliminary engineering analysis for dehumidifiers is available in the preliminary TSD for this rulemaking, 

found at http://www.regulations.gov/#!documentDetail;D=EERE-2012-BT-STD-0027-0015. 
5-20

DOE expects the range presented in Figure 5.5.4.1 to be representative of compressors available 

to portable AC manufacturers.

Figure 5.5.4.1 R-410A Compressor Performance Characteristics

At Efficiency Level 4, DOE assumed the compressor in each optimized dual-duct unit at 

Efficiency Level 3 would be replaced with a compressor at an EER of 10.5 Btu/Wh. The 

efficiency improvement associated with this design change varied from unit to unit depending on 

the efficiency of the compressor currently used. The overall average compressor efficiency 

observed for units in DOE’s teardown sample, and therefore the average compressor efficiency 

at Efficiency Level 3, was 9.8 Btu/Wh.

Improved Blower Motor Efficiency

DOE is aware that efficiency gains may be possible through improvements to the 

portable AC blower motor. DOE noted that all units in its teardown sample used PSC fan motors. 

Permanent-magnet motors would provide slightly higher motor efficiencies compared to PSC 

motors (DOE estimates them to be 80-percent efficient compared to 60 percent for PSC motors), 

but the improvements to overall efficiency would be relatively small due to the smaller portion 

of energy consumed by the blower motor compared to the compressor. In interviews with DOE, 

manufacturers stated that they likely would not rely on changes to the blower to improve product 

efficiency due to the small efficiency gains and high cost. However, to consider the maximum 

efficiency possible for portable ACs, DOE considered this change to the blower motor.

Low-Standby-Power Electronic Controls

7.5

8

8.5

9

9.5

10

10.5

11

0 5000 10000 15000 20000

Rated Compressor EER (Btu/h/W)

Rated Compressor Capacity (Btu/h)
5-21

For this preliminary engineering analysis, DOE considered portable AC performance in 

terms of EERcm and cooling capacity. In the February 2015 Test Procedure NOPR, DOE 

proposed an overall CEER that would also incorporate energy consumption in other modes, such 

as heating mode, standby mode, off mode, and off-cycle mode. DOE conducted this preliminary 

analysis only based on EERcm, which does not account for operation outside of cooling mode. 

However, DOE still incorporated a change to low-standby-power electronic controls at the maxtech efficiency level because the downstream analyses for this preliminary analysis account for 

performance in the other non-cooling modes.

5.5.4.3 Design Options Not Specifically Considered

DOE observed that manufacturers typically implement the design options discussed 

above to improve portable AC capacity and efficiency. Additionally, while many of the 

technology options identified in chapter 3 of this preliminary TSD may produce energy savings 

in certain real-world situations, DOE did not further consider them in this analysis because there 

was not sufficient information available on the specific efficiency gains or the DOE test 

procedure would not capture those potential improvements. DOE considered the following 

design options in this engineering analysis, but does not expect manufacturers to rely on these 

features to meet higher efficiency levels.

Add Subcooler to Condenser Coil

DOE is aware that subcooling the refrigerant exiting the condenser may improve product 

efficiencies by increasing the amount of heat rejected by the condenser. However, based on 

product testing, DOE expects that any beneficial refrigerant subcooling already occurs within 

existing condensers. DOE observed that refrigerant temperatures exiting the condenser were well 

below the refrigerant condensing temperature. DOE expects that the use of condensate spray on

the condenser contributes to the subcooling without the need for an additional heat exchanger.

Increased Heat-Transfer Coefficients

In the market and technology assessment, chapter 3 of this preliminary TSD, DOE 

identified technologies that would improve heat transfer coefficients in portable AC heat 

exchangers. In its teardown sample, DOE observed that units already incorporate many of the 

design options that would improve heat transfer coefficients, such as slit fins, grooved refrigerant 

tubes, and condensate spray over the condenser. DOE also identified microchannel heat 

exchangers as a potential means to improve heat-transfer coefficients. As discussed in chapter 3, 

DOE expects the efficiency gains to be limited with a microchannel heat exchanger, but they 

may reduce the necessary refrigerant charge and condenser size.

Because portable ACs already include many design options to improve heat transfer in 

the evaporator and condenser, and because it lacks information on the potential efficiency gains 

with microchannel heat exchangers, DOE did not specifically consider these design options in 

further improving portable AC efficiencies.

Improved Duct Connections
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In the market and technology assessment, DOE identified improved duct connections to 

the portable AC case and mounting bracket as a technology option to potentially improve 

portable AC performance by reducing air leakage. DOE did not observe any units in the test 

sample that provided additional sealing in the duct connections. DOE also lacks information 

regarding leakage rates and potential savings associated with reducing condenser air leakage to 

the room. Therefore, DOE did not further consider the improvements associated with improved 

duct connections in this preliminary analysis.

Improved Product Case Insulation

In the market and technology assessment, DOE identified insulation as a component to 

potentially improve portable AC performance. DOE found that the cases had little or no 

insulation, and based on the February 2015 Test Procedure NOPR, the case heat transfer is 

included in the overall cooling capacity. Therefore, DOE identified case insulation as a potential 

improvement to efficiency. However, DOE observed that the average case surface temperature 

for products in its test sample was 82 °F. DOE expects that adding insulation to the product case 

would result in little or no improvement compared to existing product cases. Additionally, as 

noted above, there is little room in the case to add additional components. Adding insulation 

would likely increase the overall case dimensions.

Part-Load Technology Improvements

In the market and technology assessment, DOE identified variable-speed compressors 

and thermostatic or electronic expansion valves to potentially improve portable AC performance. 

However, DOE notes that these design options would typically improve portable AC 

performance under varying conditions. The technologies would help to optimize the refrigeration 

system performance to the specific indoor and outdoor conditions. Because the test procedure 

proposed in the February 2015 Test Procedure NOPR would be conducted under constant 

ambient conditions, incorporating these design options would have no measurable impact on 

performance. Accordingly, DOE did not further consider these design options in this preliminary 

engineering analysis.

5.5.5 Combined Tested and Modeled Performance

Based on the design options considered at each efficiency level, DOE estimated the 

performance of units beyond its test sample. The test sample units served as the starting points 

for the incremental improvements at each efficiency level, so DOE could estimate the potential 

performance improvements for specific units. Figure 5.5.5.1 presents efficiency and cooling 

results for each unit in DOE’s test sample, with the appropriate design options applied for each 

efficiency level. At higher efficiency levels, unit performance increased in both EERcm and 

cooling capacity. 
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Figure 5.5.5.1 Modeled Cooling Efficiency versus Cooling Capacity at Each Efficiency 

Level by Unit

Because a unit’s cooling capacity factors into the calculation of EERcm, DOE also 

considered how a unit’s power consumption changed at each efficiency level. Figure 5.5.5.2

presents the calculated power consumption versus cooling capacity for each unit at each 

efficiency level.
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Figure 5.5.5.2 Modeled Power Consumption versus Cooling Capacity at Each Efficiency 

Level by Unit

Figure 5.5.5.2 shows that the air flow configurations associated with Efficiency Levels 1 

through 3 increase cooling efficiency by increasing cooling capacity. Power consumption for 

these efficiency levels increases compared to the baseline because of the increased compressor 

and blower motor power consumption, as discussed in section 5.5.4.1. At Efficiency Level 4, 

cooling capacity increases slightly with the larger heat exchangers, and power consumption 

decreases with improvements to the compressor and blower motor efficiencies.

From this plot, DOE observed that a linear relationship provided the best-fit trend to the 

data points corresponding to units within the same efficiency level. This established the

relationship between power draw and cooling capacity. Figure 5.5.5.3 shows the individual data 

points broken down by efficiency level and includes the linear trend for each efficiency level.
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Figure 5.5.5.3 Linear Trends Between Power Consumption and Cooling Capacity by 

Efficiency Level

DOE used these linear equations to develop curves relating EERcm to cooling capacity. 

As discussed in section 5.3.2, the resulting curves are based on the following equation with the 

coefficients provided in Table 5.5.5.1.

EERcm =

Cooling Capacity

Power =

Cooling Capacity

(A × Cooling Capacity + B)

Table 5.5.5.1 Portable AC Efficiency Level Equation Coefficients 

Efficiency Level A Coefficient

(Wh/Btu)

B Coefficient

(W)

Baseline 0.113 855.5

EL1 0.1201 685.4

EL2 0.1222 566.3

EL3 0.1256 426.9

EL4 0.1205 355.1
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Figure 5.5.5.4 Efficiency Level Curves by Cooling Capacity

5.5.6 Cost Estimates

As described in section 5.4.3, DOE developed estimates of MPCs for each unit in the 

teardown sample. The incremental costs provided below in Table 5.5.6.1 represent the additional 

costs manufacturers would incur by producing models at each efficiency level compared to the 

baseline.

Table 5.5.6.1 Incremental Portable AC Manufacturer Production Costs 

Efficiency Level Incremental MPC

(2013$)

Baseline $ -

EL1 $ 4.09

EL2 $ 4.67

EL3 $ 5.26

EL4 $ 47.76

As discussed in section 5.5.4, Efficiency Levels 1 through 3 represent changes to the air 

flow configuration. The small incremental costs at these efficiency levels represent the cost for 

an additional duct and larger blower motor. At Efficiency Level 4, the incremental MPC is 

significantly higher due to the high-cost design options incorporated at this level, including 

larger heat exchangers (and the additional cost of a larger case and internal components) and 

more efficient compressors and blower motors.