CHAPTER 5. ENGINEERING ANALYSIS

TABLE OF CONTENTS

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

5.2 EQUIPMENT CLASSES ANALYZED.......................................................................... 5-1

5.3 ENERGY EFFICIENCY METRIC ................................................................................. 5-2

5.3.1 Cooling Efficiency Metric ................................................................................... 5-2

5.3.2 Heating Efficiency Metric .................................................................................... 5-5

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

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

5.4.2 Incremental Efficiency Levels ............................................................................. 5-7

5.5 METHODOLOGY OVERVIEW .................................................................................. 5-12

5.5.1 Manufacturer Interviews .................................................................................... 5-13

5.5.2 Equipment Teardown ......................................................................................... 5-13

5.5.2.1 Selection of Units ..................................................................................... 5-13

5.5.2.2 Generation of Bill of Materials ................................................................ 5-14

5.5.2.3 Cost Structure of the Spreadsheet Models ............................................... 5-14

5.5.3 Shipping Costs ................................................................................................... 5-15

5.5.4 Equipment Testing ............................................................................................. 5-16

5.6 ANALYSIS AND RESULTS ........................................................................................ 5-16

5.6.1 Manufacturer Interviews .................................................................................... 5-16

5.6.2 Equipment Testing ............................................................................................. 5-17

5.6.3 Equipment Teardown ......................................................................................... 5-20

5.6.4 Energy Modeling ............................................................................................... 5-28

5.6.4.1 Heat Exchanger Model ............................................................................. 5-29

5.6.4.2 Compressor Model ................................................................................... 5-32

5.6.4.3 Expansion Model ...................................................................................... 5-33

5.6.4.4 Fan Model ................................................................................................ 5-33

5.6.4.5 Refrigeration Cycle Model ....................................................................... 5-34

5.6.5 Design Option Analysis ..................................................................................... 5-34

5.6.5.1 7.5-ton Models ......................................................................................... 5-35

5.6.5.2 15-ton Models .......................................................................................... 5-38

5.6.5.3 30-ton Models .......................................................................................... 5-41

5.6.5.4 Design Option Summary .......................................................................... 5-45

5.6.6 Cost-Efficiency Results ..................................................................................... 5-48

REFERENCES .......................................................................................................................... 5-50

LIST OF TABLES

Table 5.2.1 Proposed Equipment Classes ......................................................................... 5-2

Table 5.4.1 Baseline Efficiency Levels ............................................................................ 5-6

Table 5.4.2 Incremental Efficiency Levels ..................................................................... 5-12

5-i 
Table 5.5.1 Major Manufacturing Processes .................................................................. 5-15

Table 5.6.1 Small Air-Cooled CUAC and CUHP Test Units ......................................... 5-18

Table 5.6.2 Large and Very Large Air-Cooled CUAC and CUHP Test Units ............... 5-19

Table 5.6.3 Test Results of Selected Small, Large and Very Large CUAC and 

CUHP units .................................................................................................. 5-20

Table 5.6.4 Heat Transfer and Pressure Drop Correlations ............................................ 5-32

Table 5.6.5 Design Options for 7.5-Ton CUAC Units ................................................... 5-37

Table 5.6.6 Design Option for 15-Ton CUAC Units ...................................................... 5-40

Table 5.6.7 Design Options for 30-Ton CUAC Units .................................................... 5-44

Table 5.6.8 Design Option Summary for Different Efficiency Levels ........................... 5-46

Table 5.6.9 Small Air-Cooled CUAC and CUHP Cost-Efficiency Relationships ......... 5-49

Table 5.6.10 Large Air-Cooled CUAC and CUHP Cost-Efficiency Relationships ......... 5-49

Table 5.6.11 Very Large Air-Cooled CUAC and CUHP Cost-Efficiency 

Relationships ................................................................................................ 5-49

LIST OF FIGURES

Figure 5.4.1 Relationship between EER and COP for Heat Pump, ≥65,000 Btu/h 

and <135,000 Btu/h Cooling Capacity, Electric Heat/No Heating 

Equipment Class ............................................................................................ 5-8

Figure 5.4.2 Relationship between EER and COP for Heat Pump, ≥135,000 Btu/h 

and <240,000 Btu/h Cooling Capacity, Electric Heat/No Heating 

Equipment Class ............................................................................................ 5-9

Figure 5.4.3 Relationship between EER and COP for Heat Pump, ≥240,000 Btu/h 

and <760,000 Btu/h Cooling Capacity, Electric Heat/No Heating 

Equipment Class ............................................................................................ 5-9

Figure 5.4.4 Relationship between IEER and COP for Heat Pump, ≥65,000 Btu/h 

and <135,000 Btu/h Cooling Capacity, Electric Heat/No Heating 

Equipment Class .......................................................................................... 5-10

Figure 5.4.5 Relationship between EER and COP for Heat Pump, ≥135,000 Btu/h 

and <240,000 Btu/h Cooling Capacity, Electric Heat/No Heating 

Equipment Class .......................................................................................... 5-10

Figure 5.4.6 Relationship between EER and COP for Heat Pump, ≥240,000 Btu/h 

and <760,000 Btu/h Cooling Capacity, Electric Heat/No Heating 

Equipment Class .......................................................................................... 5-11

Figure 5.5.1 Manufacturing Cost Assessment Stages ...................................................... 5-15

Figure 5.6.1 Baseline 7.5-Ton Air-Cooled CUAC Full Production Cost Distribution .... 5-21

Figure 5.6.2 Baseline 7.5-Ton Air-Cooled CUAC Materials Cost Distribution .............. 5-21

Figure 5.6.3 Baseline 15-Ton Air-Cooled CUAC Full Production Cost Distribution ..... 5-22

Figure 5.6.4 Baseline 15-Ton Air-Cooled CUAC Materials Cost Distribution ............... 5-22

Figure 5.6.5 Baseline 30-Ton Air-Cooled CUAC Full Production Cost Distribution ..... 5-23

Figure 5.6.6 Baseline 30-Ton Air-Cooled CUAC Materials Cost Distribution ............... 5-23

Figure 5.6.7 7.5-ton Indoor Coil Face Area * Number of Tube Rows versus IEER ....... 5-24

Figure 5.6.8 7.5-ton Indoor Coil Face Area * Number of Tube Rows versus IEER ....... 5-25

Figure 5.6.9 15-ton Indoor Coil Face Area * Number of Tube Rows versus IEER ........ 5-25

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Figure 5.6.10 15-ton Outdoor Coil Face Area * Number of Tube Rows versus IEER ...... 5-26

Figure 5.6.11 30-ton Indoor Coil Face Area * Number of Tube Rows versus IEER ........ 5-26

Figure 5.6.12 30-ton Indoor Coil Face Area * Number of Tube Rows versus IEER ........ 5-27

Figure 5.6.13 Manufacturing Cost for ~7.5-ton CUAC with Electric Resistance 

Heating or No Heating ................................................................................. 5-27

Figure 5.6.14 Manufacturing Cost for ~15-ton CUAC with Electric Resistance 

Heating or No Heating ................................................................................. 5-28

Figure 5.6.15 Manufacturing Cost for ~30-ton CUAC with Electric Resistance 

Heating or No Heating ................................................................................. 5-28

Figure 5.6.16 User Interface of CoilDesigner .................................................................... 5-30

Figure 5.6.17 Schematic of a Refrigeration Cycle Using a Dual Compressor 

Configuration ............................................................................................... 5-34

Figure 5.6.18 Model Validation for 7.5-Ton CUAC Units After Applying IEER 

Weighting Factors ........................................................................................ 5-35

Figure 5.6.19 Model Validation for 15-Ton CUAC Units After Applying IEER 

Weighting Factors ........................................................................................ 5-38

Figure 5.6.20 Model Validation for 30-Ton CUAC Units with Tube-Fin Condensers 

After Applying IEER Weighting Factors .................................................... 5-41

Figure 5.6.21 Model Validation for 30-Ton CUAC Units with Microchannel 

Condensers After Applying IEER Weighting Factors ................................. 5-42

Figure 5.6.22 7.5-Ton EERs at Different Load Conditions for Five Efficiency Levels .... 5-45

Figure 5.6.23 15-Ton EERs at Different Load Conditions for Five Efficiency Levels ..... 5-47

Figure 5.6.24 30-Ton EERs at Different Load Conditions for Five Efficiency Levels ..... 5-47

Figure 5.6.25 Indoor Coil Face Area * Tube Row Number ............................................... 5-48

Figure 5.6.26 Outdoor Coil Face Area * Tube Row Number ............................................ 5-48

5-iii
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 products at various levels of 

increased efficiency. This section provides an overview of the engineering analysis (section 5.1),

discusses proposed equipment classes (section 5.2), establishes baseline unit specifications 

(section 5.4.1), discusses incremental efficiency levels (section 5.4.2), explains the methodology 

used during data gathering (5.5) and discusses the analysis and results (section 5.6) 

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

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

options from the screening analysis (chapter 4) Additional inputs include laboratory testing and 

reverse-engineering of representative equipment, energy modeling, and manufacturer interviews. 

The primary output of the engineering analysis is a set of cost-efficiency curves. In the 

subsequent markups analysis (chapter 6), DOE determined customer (i.e., equipment purchaser) 

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

markups, they serve as the input to the building energy-use and end-use load characterization 

(chapter 7) and the life-cycle cost (LCC) and payback period (PBP) analyses (chapter 8).

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

These are: (1) the design-option approach, which calculates the incremental costs of adding 

specific design options to a baseline model that will improve its efficiency (i.e., lower its energy 

use); (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 provides 

“bottom-up” manufacturing cost assessments for achieving various levels of increased 

efficiency, based on teardown analyses (or physical teardowns) providing detailed data on costs 

for parts and material, labor, shipping/packaging, and investment for models that operate at 

particular efficiency levels. A supplementary method called a catalog teardown uses published 

manufacturer catalogs and supplementary component data to estimate the major physical 

differences between a piece of equipment that has been physically disassembled and another 

piece of similar equipment for which catalog data are available to determine the cost of the latter 

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

product, the design options under study, and any historical data that DOE can draw on. 

5.2 EQUIPMENT CLASSES ANALYZED

DOE separated small, large, and very large, air-cooled commercial package air 

conditioning and heating equipment (also referred to in this notice as small, large, and very large 

air-cooled commercial unitary air conditioners, CUAC, and small, large, and very large aircooled commercial unitary heat pumps, CUHP) into equipment classes. Because DOE 

formulated a separate energy conservation standard for each equipment class, the criteria for 

separation into different classes are (1) type of energy used (e.g., natural gas or electricity), and 

5-1 
(2) capacity or other performance-related features such as those that provide utility to the 

consumer, or others deemed appropriate by the Secretary that would justify the establishment of 

a separate energy conservation standard. 

For the reasons discussed in chapter 3 of this TSD, DOE has analyzed for the purposes of 

this final rule the equipment classes for small, large, and very large, air-cooled CUAC and 

CUHP, presented in Table 5.2.1. 

Table 5.2.1 Proposed Equipment Classes

Equipment 

Class Equipment Type Cooling Capacity SubCategory Heating Type

1 

Small Commercial Packaged 

Air-Conditioning and Heating 

Equipment (Air-Cooled)

≥65,000 Btu/h and 

<135,000 Btu/h

AC

Electric Resistance Heating or 

No Heating

2 All Other Types of Heating

3 

HP

Electric Resistance Heating or 

No Heating

4 All Other Types of Heating

5 

Large Commercial Packaged 

Air-Conditioning and Heating 

Equipment (Air-Cooled)

≥135,000 Btu/h and 

<240,000 Btu/h

AC

Electric Resistance Heating or 

No Heating

6 All Other Types of Heating

7 

HP

Electric Resistance Heating or 

No Heating

8 All Other Types of Heating

9 

Very Large Commercial 

Packaged Air-Conditioning 

and Heating Equipment (AirCooled)

≥240,000 Btu/h and 

<760,000 Btu/h

AC

Electric Resistance Heating or 

No Heating

10 All Other Types of Heating

11

HP

Electric Resistance Heating or 

No Heating

12 All Other Types of Heating

5.3 ENERGY EFFICIENCY METRIC

The current energy conservation standards for small, large, and very large air-cooled 

CUAC and CUHP are based on energy efficiency ratio (EER) for cooling efficiency and, for aircooled CUHP heating efficiency, coefficient of performance (COP). 10 CFR 431.97(b). 

5.3.1 Cooling Efficiency Metric

On February 1, 2013, DOE published a request for information and notice of document 

availability for small, large, and very large, air cooled CUAC and CUHP. 78 FR 7296. In the 

RFI, DOE noted that it was considering whether to replace the existing efficiency descriptor, 

EER, with a new energy-efficiency descriptor, the integrated energy efficiency ratio (IEER). 

As part of a final rule published on May 16, 2012, DOE amended the test procedure for 

this equipment to incorporate by reference the Air-Conditioning, Heating and Refrigeration 

Institute (AHRI) Standard 340/360–2007, “Performance Rating of Commercial and Industrial 

5-2 
Unitary Air-Conditioning and Heat Pump Equipment,” including addendum 1 in December 2010 

and addendum 2 in June 2011 (AHRI Standard 340/360–2007). 77 FR 28928. AHRI Standard 

340/360–2007 includes methods and procedures for testing and rating equipment with both the 

EER and IEER metrics. EER is the ratio of the cooling capacity (in Btu/h) to the power input (in 

watts), and provides a measure of the efficiency of equipment operating at full load (i.e., 100 

percent cooling capacity). IEER is a single number figure of merit expressing cooling part-load 

EER efficiency on the basis of weighted operation at various load capacities for the equipment. 

The IEER metric factors in the efficiency of operating at part-loads of 75 percent, 50 percent, 

and 25 percent of capacity as well as the efficiency at full load. This is accomplished by 

weighting the full- and part-load efficiencies with the average amount of time operating at each 

loading point. The IEER metric incorporates part load efficiencies measured with outside 

temperatures appropriate for the load levels, i.e. at lower temperatures for lower load levels. 

EPCA authorizes DOE to establish “energy conservation standards” that set either a

single performance standard or a single design requirement—not both. (42 U.S.C. 6311(18)) As 

such, DOE may prescribe an energy conservation standard based either on a single performancebased standard or design requirement. In the case of small, large, and very large air-cooled 

CUAC and CUHP, the American Society of Heating, Refrigerating, and Air-Conditioning 

Engineers (ASHRAE) Standard 90.1–2010, “Energy Standard for Buildings Except Low-Rise 

Residential Buildings” (ASHRAE Standard 90.1–2010) specifies two performance requirements: 

EER and IEERa

. In DOE’s view, with respect to modifying its energy conservation standard with 

a new performance standard, the statute limits its choices to either an improved EER or a new 

standard using IEER. DOE did not consider altering its energy conservation standard to be based 

on a single design requirement because performance-based standards will provide manufacturers 

with more flexibility in developing equipment that meets the standard levels rather than requiring 

a specific design. DOE notes that a change in metrics (i.e., from EER to IEER) would 

necessitate an initial DOE determination that the new requirement would not result in 

backsliding when compared to the current standards. (42 U.S.C. 6313(a)(6)(B)(iii)(I)) 

As part of the RFI, DOE conducted a review of the market to see if part-load 

performance is currently being used and accepted for rating CUAC and CUHP. On January 2, 

2009, the Environmental Protection Agency (EPA) issued a draft ENERGY STAR specification 

for Light Commercial Air Conditioners and Heat Pumps equipment, i.e., small and large aircooled CUAC and CUHP, which proposed to adopt IEER as part of the minimum energy 

efficiency criteria.b

 In a January 30, 2009 letter regarding EPA’s draft, AHRI supported this 

change. DOE also noted in the RFI that the Consortium for Energy Efficiency (CEE), an 

organization for energy efficiency advocates, has adopted IEER for its Tier 0, 1, and 2 

efficiencies for CUAC and CUHP, i.e., small, large, and very large air-, water-, and 

a The IEER requirements were first established in Addenda from the 2008 Supplement to Standard 90.1–2007, and 

became effective on January 1, 2010. See ASHRAE Addenda. 2008 Supplement. 

http://www.ashrae.org/File%20Library/docLib/Public/20090317_90_1_2007_supplement.pdf

b ENERGY STAR. Re: EPA Proposed Draft Energy Star Specification for Light Commercial HVAC 

Equipment. 

http://www.energystar.gov/ia/partners/prod_development/revisions/downloads/lhvac/AHRI_Comments_D1.pdf

5-3 

 
evaporatively-cooled air conditioners and air- and water-source heat pumps.

c

 78 FR 7296, 7299 

(Feb. 1, 2013). 

DOE also noted in the RFI that IEER has gained support through efforts such as DOE’s 

Commercial Building Energy Alliance (CBEA) technology transfer program, which sponsors the 

High Performance Rooftop Unit Challenge (RTU Challenge). This program provides a market 

mechanism that reduces barriers for manufacturers to procure greater than 18-IEER 10-ton 

equipment and encourages the private sector to commit to adopt energy-efficient equipment. A 

number of manufacturers are currently participating in the RTU Challenge, including Lennox, 

7AC Technologies, Rheem, Carrier, and McQuay. Of these participants, both Carrier and 

McQuay have already begun producing AHRI-certified equipment meeting or exceeding 18

IEER. In conjunction with manufacturer support, fourteen CBEA-member private entities,d such 

as Target Corp., Macy’s, Inc., McDonald’s Corp., and others, have also signaled their support 

and indicated their strong interest in potentially purchasing high-efficiency rooftop units, a sign 

of their confidence in the RTU Challenge and its ability to use IEER to accurately portray the 

energy use of air-cooled CUAC and CUHP in the field. 78 FR 7296, 7299 (Feb. 1, 2013). 

As part of the RFI, DOE conducted a market analysis to compare the two metrics based 

on publicly available ratings of existing equipment currently available in the market. DOE made 

a document available for comment that provided the methodology and results of the investigation 

of the relationship between IEER and EER for air-cooled CUAC and CUHP with cooling 

capacities between 65,000 Btu/hr and 760,000 Btu/hr (i.e., 5 and 63 tons).e In the RFI, DOE 

noted that if it decides to propose standards using the IEER metric, it would transition the 

existing Federal energy conservation standards that are based on the EER metric to the new 

IEER metric to determine baseline energy-efficiency levels to use in the analysis. 78 FR 7296, 

7299 (Feb. 1, 2013). 

EPCA requires that test procedures be reasonably designed to produce test results that

measure the energy efficiency of covered equipment during a representative average use cycle or 

period of use. (42 U.S.C. 6314(a)(2)) As discussed above, the IEER metric weights the 

efficiency of operating at different part loads and full load based on usage patterns, which 

provide a more representative measure of annual energy use than the EER metric. A 

manufacturer that was involved in the development of the IEER metric indicated that the usage 

patterns weights for the IEER metric were developed by analyzing equipment usage patterns of 

several buildings across the 17 ASHRAE Standard 90.1–2010 (appendix B) climate zones 

identified. (Docket ID: EERE–2013–BT–STD–0007–0018, Carrier, at p. 1) The weighting 

factors accounted the hours of operation where mechanical cooling was active. Id. As a result, 

the IEER metric provides a more accurate representation of the annual energy use for this 

equipment than the EER metric, which only considers full load energy use. For the reasons, DOE 

is proposing energy conservation standards based on the IEER metric. 

c Consortium for Energy Efficiency. CEE Commercial Unitary AC and HP Specification. 

http://www.cee1.org/files/CEE_CommHVAC_UnitarySpec2012.pdf

d U.S. Department of Energy. Building Technologies Program. High Performance Rooftop Unit Challenge Fact 

Sheet. http://apps1.eere.energy.gov/buildings/publications/pdfs/alliances/techspec_rtus.pdf e The document is available at: 

http://www1.eere.energy.gov/buildings/appliance_standards/product.aspx/productid/77. 

5-4 

 
5.3.2 Heating Efficiency Metric

AHRI Standard 340/360–2007 also specifies methods and procedures for testing and 

rating equipment heating efficiency for air-cooled CUHP based on the COP metric. The heating 

efficiency COP is the ratio of the heating capacity (in watts) to the power input (in watts).f AHRI 

Standard 340/360–2007 provides methods to rate the COP at both high temperature steady state 

heating conditions (47 degrees Fahrenheit (°F) dry bulb and 43 °F wet bulb) and low temperature 

steady state heating conditions (17 °F dry bulb and 15 °F wet bulb). The current energy 

conservation standards for small, large, and very large air-cooled CUHP heating efficiency are 

based on the COP metric rated at the high temperature steady state heating conditions. 10 CFR 

431.97(b) 

DOE is not aware of any test procedures that have been developed that measure part load 

performance in heating mode for small, large, and very large air-cooled CUHP. DOE is not 

aware of any data regarding the annual usage for CUHP under part-load heating conditions to 

determine whether part-load heating hours are significant and would warrant the development of 

a part-load heating metric. One manufacturer noted that CUHP typically operate in full load 

heating mode and cycle the auxiliary heat on and off because heat pump capacity alone is 

inadequate to meet the building load. In addition, DOE is unaware of data regarding usage 

patterns for CUHP to determine appropriate test conditions under part-load heating conditions. 

Because DOE is unaware of any test procedures or usage data regarding part-load performance 

in heating mode for CUHP that shows that part-load heating hours are significant, DOE is not 

considering amendments to the test procedure to measure part-load heating efficiency at this 

time. DOE is proposing standards for the heating efficiency based on the COP metric. 

5.4 EFFICIENCY LEVELS

5.4.1 Baseline Units

DOE selected baseline units as reference points for each equipment class, against which 

DOE measured changes resulting from energy conservation standards. The baseline unit in each 

equipment class represents the basic characteristics of equipment in that class. Typically, a 

baseline unit is a unit that just meets current required energy conservation standards and provides 

basic consumer utility. DOE used the baseline units in the engineering analysis and the lifecycle-cost and payback-period analysis. To determine energy savings and changes in price, DOE 

compared each higher energy efficiency design option with the baseline unit. 

As discussed in section 5.3.1, DOE is proposing to replace the current cooling 

performance energy efficiency descriptor (i.e., EER), with a new energy efficiency descriptor 

(i.e., IEER), and a single EER level can correspond to a range of IEERs. As a result, DOE must 

establish a baseline IEER for each equipment class. DOE is typically obligated either to adopt 

those standards developed by ASHRAE or to adopt levels more stringent than the ASHRAE 

levels if there is clear and convincing evidence in support of doing so. (42 U.S.C. 6313(a)(6)(A)) 

ASHRAE Standard 90.1–2010 specifies minimum efficiency requirements using both the EER 

and IEER metrics. As discussed in the RFI, DOE evaluated the relationship between EER and 

f Any supplementary resistance heat is excluded from the test. 

5-5 

 
IEER by considering models that are rated at the current DOE standard levels based on the EER 

metric for each equipment class. DOE then analyzed the distribution of corresponding rated 

IEER values for each equipment class. DOE notes that the lowest IEER values associated with 

the current DOE standards for EER generally correspond with the ASHRAE Standard 90.1–2010 

minimum efficiency requirements. 78 FR 7296, 7299 (Feb. 1, 2013); EERE-2013-BT-STD0007-0001. Based on this evaluation, because DOE is considering energy conservation standards 

based on the IEER metric, DOE is proposing to use the ASHRAE Standard 90.1–2010 minimum 

IEER requirements to characterize the baseline cooling efficiency for each equipment class.

DOE also notes that equipment is available on the market that is at or near the ASHRAE 

Standard 90.1–2010 minimum IEER requirements. As a result, DOE is not considering higher 

IEER levels for the baseline.

As discussed in section 5.3.2, DOE is considering heating efficiency standards for CUHP 

based on the COP metric. The Energy Policy Act of 2005, Public Law 109–58 (Aug. 8, 2005) 

(EPAct 2005) established minimum COP levels for small, large, and very large air-cooled 

CUHP, which DOE codified in a final rule on October 18, 2005. 70 FR 60407. DOE is proposing 

to use the COP standard levels to characterize the baseline heating efficiency for each equipment 

class.

The baseline efficiency levels for each equipment class are presented below in Table 

5.4.1. 

Table 5.4.1 Baseline Efficiency Levels

Equipment Type Heating Type Baseline 

Efficiency Level

Small Commercial Packaged 

AC and HP (Air-Cooled) – 

≥65,000 Btu/h and <135,000 

Btu/h Cooling Capacity

AC

Electric Resistance 

Heating or No Heating 11.4 IEER

All Other Types of 

Heating 11.2 IEER

HP

Electric Resistance 

Heating or No Heating

11.2 IEER

3.3 COP

All Other Types of 

Heating

11.0 IEER

3.3 COP

Large Commercial Packaged 

AC and HP (Air-Cooled) – 

≥135,000 Btu/h and <240,000 

Btu/h Cooling Capacity

AC

Electric Resistance 

Heating or No Heating 11.2 IEER

All Other Types of 

Heating 11.0 IEER

HP

Electric Resistance 

Heating or No Heating

10.7 IEER

3.2 COP

All Other Types of 

Heating

10.5 IEER

3.2 COP

Very Large Commercial 

Packaged AC and HP (AirCooled) – ≥240,000 Btu/h 

and <760,000 Btu/h Cooling 

Capacity

AC

Electric Resistance 

Heating or No Heating 10.1 IEER

All Other Types of 

Heating 9.9 IEER

HP

Electric Resistance 

Heating or No Heating

9.6 IEER

3.2 COP

All Other Types of 

Heating

9.4 IEER

3.2 COP

5-6 
5.4.2 Incremental Efficiency Levels

For the equipment classes presented in section 5.2, DOE analyzed several efficiency

levels and obtained incremental cost data at each of these levels. Table 5.4.2 presents the 

efficiency levels for each equipment class. 

As part of the NOPR analyses, DOE considered four efficiency levels beyond the 

baseline efficiency level for each equipment class. These levels were developed primarily based 

on a review of industry standards and available equipment. For efficiency level (EL) 1, DOE 

used the IEER levels specified in a draft of addendum CLg to ASHRAE Standard 90.1–2010 

(Draft Addendum CL). For the higher efficiency levels, DOE initially determined the levels for 

equipment classes of CUAC with electric resistance heating or no heating based on the range of 

efficiency levels associated with equipment listed in the AHRI certification databaseh

 and the 

California Energy Commission’s (CEC) databasei

. DOE evaluated the full range of capacities for 

the small, large, and very large equipment classes with specific focus on 7.5-ton, 15-ton, and 30-

ton as the representative cooling capacities (see section 5.6). DOE chose efficiency levels for 

CUAC with all other types of heating equal to the efficiency levels for equipment with electric 

resistance heating or no heating, minus the differences in the IEER specifications for these pairs 

of equipment classes prescribed in the Draft Addendum CL. DOE believes these decreases in 

IEER appropriately reflect the additional power required for furnace pressure drop. Similarly for 

the CUHP equipment classes, DOE developed cooling mode efficiency levels equal to the 

CUAC efficiency levels minus the difference in IEER specifications for these two equipment 

types prescribed in the Draft Addendum CL. DOE believes that these decreases in IEER are

representative of the efficiency differences that occur due to losses from the reversing valve and 

coil circuitry required in heat pumps. 

The maximum-available efficiency levels rely on the performance of recently introduced

models. DOE evaluated available equipment literature and energy use information on these 

maximum-available efficiency models and conducted energy modeling to determine the 

feasibility of achieving these efficiency levels. For the ≥65,000 Btu/h and <135,000 Btu/h 

capacity CUAC with electric resistance heating or no heating equipment classes, DOE noted 

based on its review of the AHRI certification and CEC equipment databases that the maximumavailable unit was rated at 20.9 IEER. However, sufficient information allowing correlation of 

incremental efficiency gains with specific design options and incremental manufacturing costs 

was not available to properly evaluate this unit. DOE also notes that a different manufacturer 

currently offers a 7.5-ton model rated at 19.9 IEER and a 10-ton model rated at 20.8 IEER. DOE 

notes that there is also uncertainty regarding the way the design differences contribute to the 

added efficiency of the 10-ton model, making it difficult to accurately estimate the incremental 

cost associated with this efficiency gain. As a result, DOE is proposing to use 19.9 IEER as the 

maximum-available efficiency level representative of this equipment class. DOE is not aware of 

g ASHRAE periodically updates specifications in its Standard 90.1through a public review process. The Draft 

Addendum CL, which was made available for public review in October 2012, was the latest available version at the 

time DOE conducted the analyses for today’s NOPR. DOE notes that ASHRAE has more recently finalized 

Addendum CL, with minor modifications to the IEER levels for large air-cooled CUAC and CUHP (i.e., cooling 

capacity of >=135,000 Btu/h and <240,000 Btu/h).

h Available online at: http://www.ahridirectory.org/ahridirectory/pages/home.aspx. i

Available online at: http://www.appliances.energy.ca.gov/Default.aspx. 

5-7 

 
data showing that energy efficiency can be increased beyond these levels. As a result, DOE is 

proposing to use the maximum-available efficiency levels as the max-tech levels for the NOPR 

analyses.

For the CUHP equipment classes, DOE is proposing heating efficiency levels based on 

the variation of COP with IEER. In the advanced notice of proposed rulemaking (ANOPR) that 

was published on July 29, 2004 (hereafter referred to as the July 2004 ANOPR), DOE proposed 

to address the energy efficiency of air-cooled CUHP by developing functions relating COP to 

EER. 69 FR 45460, 45468 (July 29, 2004). This method was also used by industry to establish 

minimum performance requirements for ASHRAE Standard 90.1–1999. Id. AHRI supplied the 

ASHRAE Standard 90.1–1999 committee with curves relating the COP as a function of EER. 

Using this information, the committee then set the minimum COP levels to the COP 

corresponding to the selected minimum EER level. Id. DOE stated in the RFI that since this 

method was generally accepted by industry and interested parties involved in the development of 

ASHRAE Standard 90.1–1999, it was considering a similar approach for this rulemaking. DOE 

indicated that if it transitions to IEER as the cooling mode energy efficiency descriptor, DOE 

may establish minimum COP levels based on the variation of COP with IEER. 78 FR 7296, 7301 

(Feb. 1, 2013). 

To determine COP efficiency levels, DOE evaluated AHRI and CEC data for small, 

large, and very large air-cooled CUHP units with electric resistance heat or no heat to analyze 

the relationship between COP and both IEER and EER. DOE developed linear relationships 

between EER and COP, and IEER and COP through regression. Figure 5.4.1 through Figure 

5.4.3 show the relationships between EER and COP. Figure 5.4.4 through Figure 5.4.6 show the 

relationships between IEER and COP. 

Figure 5.4.1 Relationship between EER and COP for Heat Pump, ≥65,000 Btu/h and 

<135,000 Btu/h Cooling Capacity, Electric Heat/No Heating Equipment Class 

5-8 
Figure 5.4.2 Relationship between EER and COP for Heat Pump, ≥135,000 Btu/h and 

<240,000 Btu/h Cooling Capacity, Electric Heat/No Heating Equipment Class

Figure 5.4.3 Relationship between EER and COP for Heat Pump, ≥240,000 Btu/h and 

<760,000 Btu/h Cooling Capacity, Electric Heat/No Heating Equipment Class 

5-9 
Figure 5.4.4 Relationship between IEER and COP for Heat Pump, ≥65,000 Btu/h and 

<135,000 Btu/h Cooling Capacity, Electric Heat/No Heating Equipment Class 

Figure 5.4.5 Relationship between EER and COP for Heat Pump, ≥135,000 Btu/h and 

<240,000 Btu/h Cooling Capacity, Electric Heat/No Heating Equipment Class 

5-10 
Figure 5.4.6 Relationship between EER and COP for Heat Pump, ≥240,000 Btu/h and 

<760,000 Btu/h Cooling Capacity, Electric Heat/No Heating Equipment Class 

DOE’s review of the data showed that the correlations between COP and IEER using 

linear regressions are no less strong than the correlations between COP and EER for each 

cooling capacity range. Based on this evaluation, DOE is proposing to use the functions relating 

COP to IEER based on AHRI and CEC data to establish COP efficiency levels. For each CUHP 

equipment class, DOE selected COP levels corresponding to each incremental IEER level. 

The efficiency levels for each equipment class are presented in Table 5.4.2. 

5-11 
Table 5.4.2 Incremental Efficiency Levels

Equipment Type Heating Type

Efficiency Levels

Baseline EL1 EL2 EL3 EL4 

(Max-Tech)

Small Commercial 

Packaged AC and HP 

(Air-Cooled) – ≥65,000 

Btu/h and <135,000 

Btu/h Cooling Capacity

AC

Electric Resistance 

Heating or No 

Heating

11.4 IEER 12.9 IEER 14 IEER 14.8 IEER 19.9 IEER

All Other Types of 

Heating 11.2 IEER 12.7 IEER 13.8 IEER 14.6 IEER 19.7 IEER

HP

Electric Resistance 

Heating or No 

Heating

11.2 IEER

3.3 COP

12.2 IEER

3.3 COP

13.3 IEER

3.4 COP

14.1 IEER

3.5 COP

19.2 IEER

3.7 COP

All Other Types of 

Heating

11.0 IEER

3.3 COP

12 IEER

3.3 COP

13.1 IEER

3.4 COP

13.9 IEER

3.4 COP

19.0 IEER

3.6 COP

Large Commercial 

Packaged AC and HP 

(Air-Cooled) – 

≥135,000 Btu/h and 

<240,000 Btu/h Cooling 

Capacity

AC

Electric Resistance 

Heating or No 

Heating

11.2 IEER 12.2 IEER 13.2 IEER 14.2 IEER 18.4 IEER

All Other Types of 

Heating 11.0 IEER 12.0 IEER 13.0 IEER 14.0 IEER 18.2 IEER

HP

Electric Resistance 

Heating or No 

Heating

10.7 IEER

3.2 COP

11.4 IEER

3.2 COP

12.4 IEER

3.3 COP

13.4 IEER

3.3 COP

17.6 IEER

3.3 COP

All Other Types of 

Heating

10.5 IEER

3.2 COP

11.2 IEER

3.2 COP

12.2 IEER

3.3 COP

13.2 IEER

3.3 COP

17.4 IEER

3.3 COP

Very Large Commercial 

Packaged AC and HP 

(Air-Cooled) – 

≥240,000 Btu/h and 

<760,000 Btu/h Cooling 

Capacity

AC

Electric Resistance 

Heating or No 

Heating

10.1 IEER 11.6 IEER 12.5 IEER 13.5 IEER 15.5 IEER

All Other Types of 

Heating 9.9 IEER 11.4 IEER 12.3 IEER 13.3 IEER 15.3 IEER

HP

Electric Resistance 

Heating or No 

Heating

9.6 IEER

3.2 COP

10.6 IEER

3.2 COP

11.5 IEER

3.2 COP

12.5 IEER

3.2 COP

14.5 IEER

3.2 COP

All Other Types of 

Heating

9.4 IEER

3.2 COP

10.4 IEER

3.2 COP

11.3 IEER

3.2 COP

12.3 IEER

3.2 COP

14.3 IEER

3.2 COP

5.5 METHODOLOGY OVERVIEW

In order to develop the cost-efficiency relationships for small, large, and very large, aircooled CUAC and CUHP, DOE conducted testing and performed detailed equipment teardowns 

and reverse-engineering analyses on a sample of models to develop a manufacturing cost model. 

In addition, DOE supplemented the teardown analysis by conducting catalog teardowns for 

equipment spanning the full range of capacities from all manufacturers selling equipment in the 

United States. DOE conducted energy modeling analyses to identify key design features required 

to achieve higher efficiency levels, consistent with equipment available on the market. The 

energy modeling was used in conjunction with the manufacturing cost model to determine the 

incremental costs associated with higher-efficiency equipment design to develop the cost5-12 
efficiency relationships. DOE also supplemented these analyses by conducting interviews with 

equipment manufacturers to gain a better understanding of the design options and costs 

associated with achieving higher efficiency levels.

5.5.1 Manufacturer Interviews

DOE conducted confidential interviews with manufacturers of small, large, and very 

large, air-cooled CUAC and CUHP to develop a deeper understanding of the various 

combinations of technologies used to increase equipment efficiency, and their associated 

manufacturing costs. Sample questions asked during the interviews, which were also conducted 

in support of the manufacturer impact analysis, are contained in appendix 5A. During the 

interviews, DOE also gathered information about the capital expenditures required to increase 

the efficiency of the baseline units to various efficiency levels (i.e., conversion capital 

expenditures by efficiency or energy-use level). The interviews provided information about the 

size and the nature of the capital investments. DOE also requested information about the 

depreciation method used to expense the conversion capital. 

5.5.2 Equipment Teardown

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

accurate method for determining the production cost of a piece of equipment is to disassemble 

the equipment piece-by-piece and estimate the material and labor cost of each component using a 

process commonly called a physical teardown. A supplementary method, called a catalog 

teardown, uses published manufacturer catalogs and supplementary component data to estimate 

the major physical differences between a piece of equipment that has been physically 

disassembled and another piece of similar equipment. DOE performed physical and catalog 

teardown analyses on equipment for this rulemaking. The teardown methodology is described in 

detail in section 5.5.2.1 through section 5.5.2.3.

5.5.2.1 Selection of Units

During the process of selecting units for teardown, DOE considers three main questions: 

• What efficiency levels should be captured in the teardown analysis?

• Are there units on the market that capture all potential efficiency levels and design 

options? 

• Which of the available units are most representative?

In responding to the preceding questions, DOE adopts the following criteria for selecting 

units for the teardown analysis: 

• The selected products should span the full range of efficiency levels for each equipment 

class under consideration;

• Within each equipment class, if possible, the selected products should come from the 

same manufacturer and be within the same equipment series;

5-13 
• The selected equipment should primarily come from manufacturers with large market 

share in that equipment class, although the highest efficiency equipment were chosen 

irrespective of manufacturer; and 

• The selected equipment should have non-efficiency-related features that are the same as, 

or similar to, features of other equipment in the same class and at the same efficiency

level. 

5.5.2.2 Generation of Bill of Materials

The end result of each teardown is typically a structured bill of materials (BOM). 

Structured BOMs describe each equipment 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 equipment needed (e.g., stamping presses, injection molding 

machines, spot-welders, etc.) and the process cycle times. The result is a thorough and explicit 

model of the production process. 

The BOMs incorporate all materials, components, and fasteners, classified as either raw 

materials or purchased parts and assemblies. The classification into raw materials or purchased 

parts is based on DOE’s previous industry experience, recent information in trade publications, 

and discussions with high- and low-volume original equipment manufacturers (OEMs). 

For purchased parts, the purchase price is an estimate based on volume-variable price 

quotations and detailed discussions with suppliers. For fabricated parts, the price of intermediate 

materials (e.g., tube, sheet metal) and the cost of transforming them into finished parts are an 

estimate based on current industry pricing. 

The cost of raw materials is determined using prices for copper, steel and aluminum from 

the American Metals Market.1

 The price of steel drastically increased in 2005, and the price of 

copper has increased steadily since 2004. Because DOE is using a 5-year average in material 

prices from 2009–2013, these price increases are normalized, which better represents long-term 

material prices.

5.5.2.3 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 5.4.1 shows the three major steps in generating the 

manufacturing cost.

5-14 
Figure 5.5.1 Manufacturing Cost Assessment Stages

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

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

dismantled, and each part is characterized 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 are based on industry experience, information in trade 

publications, and discussions with manufacturers. Interviews and plant visits are also conducted 

with manufacturers to ensure accuracy on methodology and pricing. 

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

identified and developed for the spreadsheet model. These processes are listed in Table 5.5.1.

Table 5.5.1 Major Manufacturing Processes

Fabrication Finishing Assembly/Joining Quality Control

Fixturing Washing Adhesive Bonding Inspecting & Testing

Stamping/Pressing Powder Coating Spot Welding

Turret Punching De-burring Seam Welding

Brake Forming Polishing Brazing

Cutting and Shearing

Tube Forming

Fabrication process cycle times are estimated and entered into the BOM. For this 

analysis, $24.00 per hour was used as the average fully-burdened labor rate based on typical 

annual wages and benefits of industry employees. In the final step of the cost assessment, 

assembly times and associated direct labor costs are estimated. Once the cost estimate for each 

teardown unit is finalized, a detailed summary is prepared for relevant components, 

subassemblies and processes. The BOM thus details all aspects of unit costs. 

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. 

5.5.3 Shipping Costs

In addition to the MPC, DOE also considered the cost to ship the unit from the 

manufacturing facility to the first point on the distribution chain. In calculating the shipping 

costs, DOE first gathered estimates of the costs to ship a full trailer of manufactured equipment 

an average distance in the United States. DOE then used the representative unit sizes to calculate 

5-15 
a volume for each unit. Along with the dimensions of a shipping trailer, DOE used this cost and 

volume information to develop an average shipping cost for each equipment class directly 

analyzed.

5.5.4 Equipment Testing

DOE conducted equipment testing to verify the energy use of equipment and to develop a 

better understanding of the potential efficiency improvements associated with various design 

options and to develop disaggregated efficiency data. The equipment testing also served to 

provide information about the refrigeration system operating conditions to support the energy 

modeling analyses.

5.6 ANALYSIS AND RESULTS

DOE conducted the engineering analyses using the reverse-engineering approach, 

analyzing three specific capacities to represent each of the three cooling capacity categories (i.e., 

small, large, and very large). Based on a review of manufacturer equipment offerings and 

interviews with manufacturers, DOE selected representative capacities of 90,000 Btu/h (7.5 

tonsj

) for the ≥65,000 to <135,000 Btu/h capacity range, 180,000 Btu/h (15 tons) for the 

≥135,000 to <240,000 Btu/h capacity range, and 360,000 Btu/h (30 tons) for the ≥240,000 to 

<760,000 Btu/h capacity range.k DOE noted in the July 2004 ANOPR that 7.5 tons and 15 tons 

represent capacity points with large shipment volumes in their respective capacity range. 69 FR 

45460, 45469 (July 29, 2004). These capacities are near the center of their respective equipment 

class capacity ranges. Additionally, as discussed in section 5.6.1, DOE interviewed several 

equipment manufacturers as part of the current rulemaking and found that the majority of 

manufacturers interviewed agreed that the 7.5-ton, 15-ton, and 30-ton capacities adequately 

represent the three equipment class capacity ranges.

5.6.1 Manufacturer Interviews 

As previously discussed in section 5.5.1, DOE conducted confidential interviews with 

CUAC and CUHP manufacturers. Sample questions are contained in appendix 12A. In general, 

manufacturers interviewed agreed with DOE’s proposed methodology of evaluating a 

representative size unit for each equipment class, specifically 7.5 ton to represent small capacity 

units, 15 ton to represent large capacity units, and 30 tons to represent very large capacity units. 

Manufacturers indicated that the three capacity sizes DOE proposed to investigate generally have 

high sales volume. Some manufacturers remarked that DOE should evaluate both air 

conditioning units and heat pump. 

During the interviews, manufacturers indicated that the IEER metric was relatively new 

and expressed concern over testing variability and the robustness of the metric. Regarding the 

proposed methodology for evaluating different efficiency levels, manufacturers remarked that 

DOE should evaluate different size and efficiency equipment from the same manufacturer(s) and 

j

Air conditioning cooling capacity may be denoted in tons. An air conditioning ton is equivalent to 12,000 Btu/h of 

cooling capacity (or 3.5 kilowatts of cooling capacity).

k An air conditioning ton is equivalent to 12,000 Btu/h of cooling capacity.

5-16 

 
product family. Manufacturers interviewed did not oppose DOE’s proposal to conduct a reverse 

engineering analysis.

From the manufacturers interviewed, DOE collected a general impression of commercial 

air-cooled air conditioning and heating equipment on the market. Interviewed manufacturers 

indicated that all of the equipment covered in this rulemaking currently use scroll compressors 

and R-410A refrigerant. However, manufacturers employ different design strategies in terms of 

compressor staging, indoor and outdoor fan selection, and heat exchanger design. Manufacturers 

interviewed noted that technologies like variable speed drives and compressor staging could be 

employed to achieve higher IEER, however, manufacturers did not quantify the improvement 

potential of these technologies. Manufacturers also commented that although increasing the size 

of the heat exchangers in a unit increases efficiency, this approach has diminishing returns (i.e., 

the size increase that achieves 5 percent improvement would have to be more than doubled to 

achieve 10 percent improvement). Additionally, manufacturers remarked that CUACs and 

CUHPs are limited in terms of footprint size because the units are often installed on existing 

rooftop curbs. A rooftop curb is a mounting platform that provides structural support, weight 

distribution, and a level installation surface and DOE understood from the manufacturers 

interviewed that changing the size of a rooftop curb can be costly. CUACs and CUHPs are 

generally shipped by freight truck, which also imposes a size limit. Regarding installation, 

maintenance, and repair costs, manufacturers thought that an increase in efficiency level would 

likely cause units to become more complex and therefore more expensive to install, maintain, 

and repair. 

5.6.2 Equipment Testing 

As discussed above, DOE conducted the engineering analyses specifically analyzing 

representative capacities of 7.5 tons, 15 tons, and 30 tons. DOE conducted a market survey of 

small, large, and very large air-cooled CUAC and CUHP models and their features. DOE 

selected four 7.5-ton, two 15-ton, and one 30-ton CUAC models for testing and reverse 

engineering. The models were selected to develop a representative sample of the market at 

different efficiency levels. DOE based the selection of units on the efficiency data available in 

the AHRI certification database and the CEC equipment database. Where feasible, DOE selected 

models for reverse engineering with low and high efficiencies from a given manufacturer that are 

built on the same platform (i.e., the same basic design and construction). DOE also selected one 

7.5-ton CUHP model to evaluate the design differences between CUAC units and CUHP units. 

Details of the key features of the tested units are presented in Table 5.6.1. 

5-17 
Table 5.6.1 Small Air-Cooled CUAC and CUHP Test Units

Feature

Test Unit Description

CUAC – Electric Resistance Heating or No Heating

CUHP – Electric 

Resistance 

Heating or No 

Heating

Test Unit 1 Test Unit 2 Test Unit 3 Test Unit 4 Test Unit 5

Rated Cooling Tons 7.5 7.5 7.5 7.5 7.5

Cooling Stages 1 2 1 2 2

Rated IEER 11.4 13.2 12.2 14.5 12.8

Rated EER 11.2 12.2 11.2 12.6 12.1

Rated COP - - - - 3.5

Compresso

r 

Quantity 1 2 1 2 2

# of 

Circuits 1 2 1 2 2 

Type Scroll Scroll Scroll Scroll Scroll

Outdoor 

Coil

Quantity 1 1 1 1 1

Type Fin-andtube

Fin-andtube Microchannel Microchannel Fin-and-tube

Face Area 

(ft.2) 20.5 25.1 16.91 20.66 25.1

Fin Pitch 17 17 23 23 17

Tube Rows 2 2 1 1 2

Outdoor 

Fan

Quantity 2 2 1 1 2

Motor 

Horsepower

0.25 0.25 0.7 0.75 0.25

Speeds 1 1 1 2 1

Indoor Coil

Quantity 1 1 1 1 1

Type Fin-andtube

Fin-andtube Fin-and-tube Fin-and-tube Fin-and-tube

Face Area 

(ft.2) 8.9 11.1 9.89 12.36 11.1

Fin Pitch 15 15 16 16 15

Tube Rows 3 4 4 4 4

Indoor Fan

# of Motors/ 

# of Fans 1/1 1/1 1/1 1/1 1/1

Drive Belt Belt Belt Direct Belt

Motor 

Horsepower

1.7 1.7 1 3.75 1.2

Speeds 1 1 3 Variable 

Speed 1 

5-18 
Table 5.6.2 Large and Very Large Air-Cooled CUAC and CUHP Test Units

Feature

Test Unit Description

CUAC – Electric Resistance Heating or No Heating

Test Unit 6 Test Unit 7 Test Unit 8

Rated Cooling Tons 15 15 30

Cooling Stages 2 2 2

Rated IEER 13.2 Not Listed 11.9

Rated EER 12.2 11.0 10.1

Compressor

Quantity 2 2 4

# of 

Circuits 2 2 2 

Type Scroll Scroll Scroll

Outdoor 

Coil

Quantity 2 2 1

Type Fin-and-tube Fin-and-tube Microchannel

Face Area 

(ft.2) 21.4 (each) 20.19 (each) 32.9

Fin Pitch 17 21 20

Tube Rows 2 2 1

Outdoor 

Fan

Quantity 3 3 2

Motor 

Horsepower

0.25 0.33 1 

Speeds 1 1 1

Indoor Coil

Quantity 1 1 1

Type Fin-and-tube Fin-and-tube Fin-and-tube

Face Area 

(ft.2) 22 16.34 31.7 

Fin Pitch 15 15 15

Tube Rows 4 3 4

Indoor Fan

# of Motors/ 

# of Fans 1/2 1/1 1/2

Drive Belt Belt Belt

Motor 

Horsepower

2.2 2 10

Speeds 1 1 1

Because DOE is considering energy conservation standards based on the IEER metric, 

DOE conducted testing on each unit according to the IEER test method specified in AHRI 

Standard 340/360–2007. Table 5.6.3 shows the test results of selected small, large and very large 

CUAC and CUHP units. The maximum deviation of tested and rated cooling capacity is 

observed to be -7.9 percent. The maximum deviations of tested EER and IEER compared to 

rated EER and IEER are -4.4 percent and 12.9 percent, respectively. 

5-19 
Table 5.6.3 Test Results of Selected Small, Large and Very Large CUAC and CUHP 

units

Parameter Test 

Unit 1

Test 

Unit 2

Test 

Unit 3

Test 

Unit 4

Test 

Unit 5

Test 

Unit 6

Test 

Unit 7

Test 

Unit 8

Type CUAC CUAC CUAC CUAC CUHP CUAC CUAC CUAC

Nominal 

Cooling 

Capacity [ton]

7.5 7.5 7.5 7.5 7.5 15 15 30

Rated IEER 11.4 13.2 12.2 14.5 12.8 13.2 13 11.9

Rated EER 11.2 12.2 11.2 12.6 12.1 12.2 11 10.1

Tested Cooling 

Capacity [ton] 7.8 7.4 7.2 7.6 7.6 14.8 14.9 27.6c

Tested IEER 12.9 14.0 13.2 15.4a 13.3 13.2 NAb 11.2c

Tested EER 11.5 12.4 11.6 12.4 11.6 11.9 10.5 10.0c

a Corrected through energy modeling at 75 percent load point.

b Tested for IPLV instead of IEER prior to this rulemaking.

c Corrected indoor blower air flow rate to meet minimum static pressure requirement.

5.6.3 Equipment Teardown 

As part of the reverse engineering analyses, DOE conducted physical teardowns on each 

test unitl

 to develop a manufacturing cost model and to evaluate and identify key details for 

design features (e.g., heat exchangers, compressors, fan and fan motors, control strategies, etc.) 

and the corresponding manufacturing cost of each test unit. Because DOE was only able to 

conduct testing and physical teardowns on a limited sample of equipment, DOE supplemented 

these data by conducting catalog teardowns on 346 models spanning the full range of capacities 

and efficiency levels from all manufacturers selling equipment in the United States. DOE based 

the catalog teardowns on information provided in equipment literature and experience from the 

physical teardowns. 

Based upon product teardowns (supplemented by the energy modeling and design option 

analysis discussed in sections 5.6.4 and 5.6.5), DOE developed the following baseline production 

cost distributions and materials costs distributions for typical small, large, and very large aircooled CUACs, shown in Figure 5.6.1 through Figure 5.6.6. Depending on the manufacturer and 

the production volume, the depreciation costs may vary from those shown in the figures, which 

assume a “green-field” site. Production cost distributions include raw material, purchased part, 

labor (assembly, fabrication, supervision, and indirect labor), depreciation (equipment, tooling, 

and building depreciation), and other overhead (indirect process, maintenance, utility, property 

tax, and insurance) costs. Material cost distributions are broken down by major assemblies (e.g., 

structural sheet metal, indoor/outdoor heat exchangers and fan assemblies, sealed system, 

controls). DOE notes that the refrigeration system, heat exchangers, and fan components account 

for over 69 percent of the material costs for this equipment. 

l

For test unit #8, DOE conducted a partial teardown, examining key components (heat exchangers, compressors, 

fans/motors, controls, etc.) and basic design construction without fully disassembling the unit.

5-20 

 
Figure 5.6.1 Baseline 7.5-Ton Air-Cooled CUAC Full Production Cost Distribution

Figure 5.6.2 Baseline 7.5-Ton Air-Cooled CUAC Materials Cost Distribution

5-21 
Figure 5.6.3 Baseline 15-Ton Air-Cooled CUAC Full Production Cost Distribution

Figure 5.6.4 Baseline 15-Ton Air-Cooled CUAC Materials Cost Distribution

5-22 
Figure 5.6.5 Baseline 30-Ton Air-Cooled CUAC Full Production Cost Distribution

Figure 5.6.6 Baseline 30-Ton Air-Cooled CUAC Materials Cost Distribution

5-23 
Based on the physical/catalog teardowns, DOE evaluated the relationship between heat 

transfer area and IEER for both the indoor and outdoor coils.m Figure 5.6.7 through Figure 5.6.12

show the coil face area multiplied by the number of tube row for indoor and outdoor coils, 

respectively, for 7.5-ton, 15-ton, and 30-ton units.n DOE observed that the increased heat transfer 

area generally correlated with higher IEER values.

Figure 5.6.7 7.5-ton Indoor Coil Face Area * Number of Tube Rows versus IEER 

m The following are examples of equipment literature DOE reviewed (does not include complete list of analyzed 

literature): 

(1) United Technologies Corporation. “Carrier 50TC Cooling Only/Electric Heat, Packaged Rooftop, 3 to 15 

Nominal Tons: Product Data.” Available online at: 

http://www.docs.hvacpartners.com/idc/groups/public/documents/techlit/50tc-19pd.pdf (Accessed on Sept. 12, 2013).

(2) Lennox International Inc. “Lennox Packaged Electric/Electric LCH Energence® Rooftop Units: Product 

Specifications.” Available online at: 

http://tech.lennoxintl.com/C03e7o14l/3rEpIb5d/ehb_lch_bbox_1306_210556_020.pdf (Accessed on Sept. 12, 2013).

(3) Ingersoll Rand. “Trane Product Catalog: Packaged Rooftop Air Conditioners, VoyagerTM Cooling and 

Gas/Electric, 12 1⁄2 - 25 Tons, 60Hz“ Available online at: 

http://www.trane.com/CPS/Uploads/UserFiles/DXUnitarySystems/Light%20Rooftops/RT-PRC028-

EN_08022013.pdf (Accessed on Sept. 12, 2013). n For the 7.5-ton and 15-ton units, DOE evaluated heat transfer area versus IEER for units with tube-and-fin heat 

exchangers (for both the outdoor and indoor coils) to provide a consistent evaluation of coil sizes. For 30-ton units, 

because the majority of units on the market used microchannel heat exchangers for the outdoor coil, DOE evaluated 

heat transfer area versus IEER for units with microchannel heat exchangers for the outdoor coils and tube-and-fin 

heat exchangers for the indoor coils.

5-24 

 
Figure 5.6.8 7.5-ton Indoor Coil Face Area * Number of Tube Rows versus IEER

Figure 5.6.9 15-ton Indoor Coil Face Area * Number of Tube Rows versus IEER 

5-25 
Figure 5.6.10 15-ton Outdoor Coil Face Area * Number of Tube Rows versus IEER

Figure 5.6.11 30-ton Indoor Coil Face Area * Number of Tube Rows versus IEER 

5-26 
Figure 5.6.12 30-ton Indoor Coil Face Area * Number of Tube Rows versus IEER 

DOE developed equipment manufacturing costs for each physical/catalog teardown unit. 

Figure 5.6.13 through Figure 5.6.15 present the manufacturing costs for the air-cooled CUACs 

with no heat or electric resistance heat with capacities of approximately 7.5 tons, 15 tons, and 30 

tons.o

 

Figure 5.6.13 Manufacturing Cost for ~7.5-ton CUAC with Electric Resistance Heating or 

No Heating 

o ~7.5 tons included 7.3 – 7.7 ton units, ~15 tons included 14.3 – 16.3 ton units, and ~30 tons included 27 – 30 ton 

units.

5-27 

 
Figure 5.6.14 Manufacturing Cost for ~15-ton CUAC with Electric Resistance Heating or 

No Heating 

Figure 5.6.15 Manufacturing Cost for ~30-ton CUAC with Electric Resistance Heating or 

No Heating 

The manufacturing cost model was used in subsequent analyses to determine the cost of 

small, large, and very large air-cooled CUAC designs incorporating series of design options to 

increase efficiency. The results of these analyses are discussed in section 5.6.6. 

5.6.4 Energy Modeling 

In the absence of industry-supplied data for each capacity or efficiency level, and because 

DOE was only able to conduct testing on a limited sample of equipment, DOE conducted energy 

modeling of the equipment obtained for reverse engineering analysis and of equipment designs 

5-28 
that incorporate energy-saving design options. Moreover, the energy modeling analysis provided 

the energy consumption of individual components (i.e., compressor, indoor and outdoor fans, 

and controls) to characterize component energy use at different efficiency levels, which served as 

input to the building energy-use and end-use load characterization analysis (chapter 7) and the 

LCC and PBP analyses (chapter 8). 

DOE conducted energy modeling using the modeling tools developed by the Center for 

Environmental Energy Engineering (CEEE) of the University of Maryland at College Park

(UMCP). The modeling tools include a detailed heat exchanger modeling program CoilDesigner 

and a refrigeration cycle modeling program VapCyc. A compressor database was also included 

in the refrigerant cycle modeling program. The refrigeration cycle modeling program integrates 

the compressor model, heat exchanger models and a built-in expansion model to complete a 

refrigeration cycle model to simulate the performance of an air conditioning or heat pump system 

at specific operating conditions. Based on the key design features identified during physical 

equipment teardowns, DOE used the energy modeling tools to generate detailed performance 

data (e.g., capacity and EER for all available capacity stages) and validated EER against the 

result obtained from laboratory testing at each IEER capacity level (25, 50, 75, and 100 percent). 

It should be noted that EERs at these capacity levels were calculated using interpolation or 

degradation, as prescribed in AHRI Standard 340/360–2007. With the validated energy models, 

DOE identified the key design features required for 7.5-ton, 15-ton, and 30-ton air-cooled CUAC 

units with electric resistance heating or no heating to achieve each efficiency level.

EER can be calculated through the modeling tools, but there is no direct output of IEER. 

The corresponding performance data at 100-percent, 75-percent, 50-percent, and 25-percent load 

levels were calculated separately, using interpolation and/or degradation adjustments from actual 

capacity stages as prescribed by AHRI Standard 340/360–2007, and then used these as input to 

calculate the IEER according to the equations set forth in the test standard. For part load 

conditions, iteration may be required depending on the configuration of the unit when the 

outdoor air temperature becomes a function of the loading profile. In this case, multiple iterations 

were performed in VapCyc to ensure the outdoor temperature matches the requirement given the 

specific loading profile. 

5.6.4.1 Heat Exchanger Model

Fin-and-tube heat exchangers are still commonly used for CUAC. Microchannel heat 

exchangers have been used for many years in the automotive industry due to their low weight 

and compact design. While challenges still exist for CUAC applications, there are products sold 

on the market that utilize microchannel heat exchangers for small, large, and very large capacity 

CUAC. Therefore, a heat exchanger model applicable for both fin-and-tube and microchannel 

heat exchangers become necessary for this rulemaking. 

The heat exchanger modeling tool CoilDesigner developed by CEEE at the University of 

Maryland College Park was employed for this rulemaking. This software program includes the 

modeling capability of a variety of heat exchangers: fin-and-tube, microchannel, flat-tube, wirefin tube, and tube-in-tube heat exchangers. Physical geometry parameters of the heat exchanger 

are needed as the input for modeling. For this rulemaking analysis, both fin-and-tube and 

microchannel heat exchangers have been modeled. For fin-and-tube heat exchangers, the 

5-29 
geometry input parameters include: number of tubes perpendicular to air flow, number of tube 

rows or banks parallel to air flow, tube length, tube outer diameter (OD), tube thickness, tube 

spacing perpendicular and parallel to air flow, fin type, fin pitch, and fin thickness. For 

microchannel heat exchangers, the geometry input parameters include: number of tubes 

perpendicular to air flow, tube length, tube height, tube width, tube vertical spacing, un-finned 

tube length, ports (i.e. microchannels) per tube, port type, fin type, fin pitch, and fin thickness. 

Different heat exchanger parameters can be defined through the user interface of CoilDesigner. 

The circuitry of the heat exchangers can also be designed through the user interface to represent 

the actual connections of refrigerant tubes. Figure 5.6.16 shows the user interface of 

CoilDesigner.

The modeling approach of CoilDesigner is to divide each heat exchanger tube into 

multiple segments, and each segment is treated as a mini heat exchanger. Refrigerant-side and 

air-side heat transfer and pressure drop calculations are performed in each segment of each tube. 

Users can define the number of segments needed to perform the calculation. In general, the 

accuracy of modeling results can be enhanced with a higher number of segments. However, the 

computation effort increases correspondingly, which essentially increases the modeling time. In 

this modeling work, the number of segments of each tube is defined as 10 in order to provide 

reasonably accurate results, but without a significant increase in the computation time. 

Figure 5.6.16 User Interface of CoilDesigner

Inlet conditions of refrigerant-side and air-side are needed as the input in order to perform 

the heat exchanger modeling. These conditions include: refrigerant mass flow rate, inlet 

refrigerant temperature and pressure, air volume flow rate, inlet air pressure, temperature and 

humidity. Outlet conditions are calculated by the heat exchanger model. The output parameters 

Tube segment Circuitry

5-30 
include the refrigerant-side and air-side exit temperatures and pressures, and the heat exchanger 

capacities, etc. CoilDesigner also has a number of heat transfer and pressure drop correlations 

that may be selected as shown in Table 5.6.4. In this modeling work, the heat transfer and 

pressure drop correlations selected were those that provided the best match to the laboratory 

testing results. The same correlations were used for units modeled at different capacities.

CoilDesigner can work as a standalone design tool for various types of heat exchangers, 

and it can also be integrated into a refrigeration cycle to perform cycle modeling. When 

CoilDesigner is integrated into a refrigeration cycle, no input on the refrigerant side parameters 

is needed because they are calculated internally as part of the refrigeration cycle modeling in 

VapCyc. In this case, only the input parameters from the air side are needed, which include the 

air pressure, volume flow rate, inlet air temperature and humidity for both the condenser and 

evaporator. 

5-31 
Table 5.6.4 Heat Transfer and Pressure Drop Correlations 

Fin-and-tube 

Evaporator 

Air-side Heat Transfer Refrigerant-side Heat Transfer

Wang-Hwang-Lin2 Two-phase Jung 

Radermacher5

Vapor Gnielinski4

Air-side Pressure Drop Refrigerant-side Pressure Drop

Wang-Hwang-Lin2 Two-phase Jung 

Radermacher6

Vapor Blasius7

Fin-and-tube 

Condenser 

Air-side Heat Transfer Refrigerant-side Heat Transfer

Wang-Hwang-Lin2

Liquid Gnielinski4

Two-phase Shah8

Vapor Gnielinski4

Air-side Pressure Drop Refrigerant-side Pressure Drop

Wang-Hwang-Lin2

Liquid Blasius7

Two-phase Homogeneous9

Vapor Blasius7

Microchannel 

Condenser 

Air-side Heat Transfer Refrigerant-side Heat Transfer

Chang-Wang3

Liquid Gnielinski4

Two-phase Shah8

Vapor Gnielinski4

Air-side Pressure Drop Refrigerant-side Pressure Drop

Chang-Wang3

Liquid Blasius7

Two-phase Chen

Vapor Blasius7

2

: Wang et al. (2002) 3: Wang et al. (1999)

4

: Gnielinski (1976) 5: Jung and Radermacher (1989a)

6

: Jung and Radermacher (1989b) 7: Incorpera and DeWitt (1996)

8

: Shah (1979) 9: Ould Didi et al. (2002)

5.6.4.2 Compressor Model

The compressor model utilizes the AHRI 10-coefficient model [1]10, as described in Eq. 

5.1: 

X = C1+C2·S+C3·D+C4·S2+C5·S·D+C6·D2+C7·S3+C8·D·S2+C9·S·D2+C10·D3 Eq. 5.1

where:

C = Equation coefficient, represents compressor performance

S = Suction dew point temperature, degrees Celsius (°C) 

D = Discharge dew point temperature, °C 

5-32 
X represents any of the following variables:

• Power input, kW 

• Mass flow rate, kg/s

• Current, A 

• Compressor efficiency

The coefficients for each compressor can be obtained from compressor manufacturers. 

The cycle modeling program also provides a database that includes a comprehensive list of 

compressor coefficients

5.6.4.3 Expansion Model

VapCyc uses an isenthalpic expansion model. The subcooling and superheating are 

specified as inputs through the user interface of VapCyc. As equipment manufacturers typically 

provide recommended ranges of subcooling and superheating to optimize system performance, 

values within the recommended ranges were used in this modeling work. The refrigeration cycle 

solves automatically to meet the specific subcooling and superheating requirements.

5.6.4.4 Fan Model

 Indoor and outdoor fan power consumption has a great impact on the IEER of a unit, 

particularly for high IEER units. In the case that a unit is tested in a laboratory, the indoor and 

outdoor fan power use is measured, and therefore, they are used directly for the EER and IEER 

calculation. If not tested, the fan power use is estimated from the manufacturer published 

performance data at the nominal air flow rate and minimum static pressure. 

For a given refrigeration cycle at full load condition, the fan power consumption can be 

calculated given the air flow rates and static pressure. In addition, as design options may include 

changes in heat exchanger designs and air flow, the fan power requirement also changes. In such 

cases, the air-side pressure drop increases or decreases with the variation of air velocity due to 

coil size change. The air-side pressure drop variation is converted to fan power consumption 

change, which follows the fan power curve for the given specifications of equipment 

manufacturers.

Fan power consumption at part load conditions is estimated to be a function of the full 

load power consumption, as described in Eq. 5.2. Typically, fan power consumption correlates to 

the cube of air flow rates according to Fan Laws. The superscript of 3 was replaced with 2.5 to 

better characterize the fan power estimate of fin-and-tube and microchannel heat exchangers. 

5-33 
Ppart load = Pfull load ∗ (

Airflowpart load

Airflowfull load

)2.5 Eq. 5.2 

5.6.4.5 Refrigeration Cycle Model

The cycle model utilizes the refrigeration cycle model VapCyc developed by CEEE at 

UMCP. The cycle model integrates the above-mentioned compressor model, heat exchanger 

models and expansion model to form a refrigeration cycle model. Figure 5.6.17 shows a 

screenshot of a refrigeration cycle from VapCyc using a dual-compressor configuration. VapCyc 

also provides the flexibility of various design options, including using multiple compressors and 

heat exchangers in parallel. This feature provides great flexibility in modeling large and very 

large CUAC equipment, which often have multiple compressors and refrigeration cycles. In 

addition to the parameters describing the compressors and heat exchangers, system parameters 

such as degree of superheat and subcooling are also required as input for the modeling. Initial 

values of condensing and evaporating temperatures are also needed to initiate the iterations for 

solving the cycle. The modeling program has a built-in refrigerant property routine that provides 

the properties needed for the evaluation. The iteration terminates when the convergence criteria 

have been satisfied. The performance data are then output to an Excel spreadsheet for further 

analysis.

Figure 5.6.17 Schematic of a Refrigeration Cycle Using a Dual Compressor Configuration 

5.6.5 Design Option Analysis

As discussed above, DOE selected 7.5-ton, 15-ton and 30-ton unit designs to be 

representative of their equipment classes. Models were developed for the range of efficiency 

levels considered for each equipment class, from the baseline efficiency to the max-tech

efficiency, based on designs consistent with equipment that is sold on the market. The energy 

models at each capacity level were validated against laboratory testing and/or manufacturer data 

at multiple efficiency levels. In some cases the models were developed to represent designs of 

specific equipment models that are available for sale or that were tested and reverseengineered—in other cases, the models represented modifications of these designs based on 

consideration of alternative design options. 

5-34 
5.6.5.1 7.5-ton Models

Five 7.5-ton units were purchased and tested according to AHRI Standard 340/360–2007. 

Among the five tested units, one unit was used to validate the model built in CoilDesigner and 

VapCyc. This air-conditioning unit has a nominal cooling capacity of 7.5 tons, and is rated at 

11.2 EER and 11.4 IEER. It features a single refrigerant circuit with a single scroll compressor, 

fin-and-tube indoor and outdoor heat exchangers. The compressor model number was identified 

during the tear down analysis after completing the performance testing in the laboratory. Indoor 

and outdoor heat exchanger specifications were collected for creating the coil models in 

CoilDesigner. The circuiting of both heat exchangers in CoilDesigner also follows exactly the 

actual heat exchanger geometry. 

Figure 5.6.18 shows the model validation results of the tested 7.5-ton unit at 100-percent, 

75-percent, 50-percent and 25-percent load conditions. The maximum deviation between the 

tested and modeling results are 4.8 percent, with the modeling results slightly lower than the 

tested results. The overall tested IEER is 12.87, and the modeled IEER is 12.27, which is 4.7 

percent lower than the tested IEER. The purpose of the model validation is to create models in 

CoilDesigner and VapCyc so that the models, with adjustment to parameters in CoilDesigner and 

VapCyc (e.g., heat transfer and pressure drop correlations, initial values, etc.), output 

performance data close to the actual tested data, and then used for design option analysis after 

validation. Therefore, all reported results were final outputs from CoilDesigner and VapCyc, and 

no further correction was made for the difference between modeled and tested results.

Figure 5.6.18 Model Validation for 7.5-Ton CUAC Units After Applying IEER Weighting 

Factors 

The validated models were used for subsequent design option analysis. Table 5.6.5 shows 

the specifications of the different efficiency levels for the 7.5-ton units. EL 1 and EL 2 are based 

on actual laboratory testing data, and the max-tech unit is based on the specifications of a unit 

available on the market with modeled IEER matched with published data. The remaining the 

5-35 
efficiency levels are based on modeling results. The baseline efficiency level features a single 

refrigerant circuit with a fixed speed scroll compressor, fin-and-tube condenser and evaporator. 

The air flow rates through the condenser and evaporator are also fixed. 

The design change from the baseline efficiency level to EL1 is the increase of condenser 

and evaporator coils face area. Increased coil face area enhances the heat transfer in the 

condenser and evaporator. Given the same air flow rate, the increased coil face area leads to a 

lower velocity of air flowing through the coils. This reduces the air side pressure drop, which 

lowers the fan power consumption and contributes to an improvement of IEER. 

The design improvement from EL 1 to EL 2 include the increase of condenser and 

evaporator coils face area, and also features a dual-compressor design with two separate 

refrigerant circuits. The dual-compressor design allows two stages of capacity at different load 

conditions. At the full load condition, both compressors are in operation to meet the capacity 

demand. While at part load conditions, only one compressor is operating, allowing the power 

saving which essentially enhances the IEER.

The main design improvement from EL 2 to EL 3 is the implementation of a variable 

speed indoor fan. The variable speed indoor fan provides the optimum air flow rates needed to 

maximize the performance while minimizing the fan power consumption. Two stages of air 

flows are also provided in the outdoor unit in order to minimize the fan power consumption at 

part load conditions. 

For the max tech efficiency level (i.e., EL 4), a single refrigerant circuit design is 

implemented to further improve IEER. The single refrigerant circuit design ensures the best 

utilization of heat exchanger heat transfer area during part load conditions, and therefore 

significantly enhances the overall system performance. The compressors were also selected with 

different capacities to deliver three stages of capacity: i.e., full load capacity at 100 percent load 

conditions, compressor with greater capacity running at 75 percent load condition, and 

compressor with lower capacity running at 50 percent and 25 percent load conditions. Larger 

condenser and evaporator coils are also utilized for the max tech unit compared to other 

efficiency levels. A variable speed indoor fan provides different air flow rates depending on 

various load conditions. The condenser fans also provides three stages of air flows to effectively 

dissipate the condenser heat to the ambient environment while keeping the fan power 

consumption at a minimal value. 

5-36 
Table 5.6.5 Design Options for 7.5-Ton CUAC Units

ID 

Airflow

OD 

Airflow

# Basis IEER Ref. 

Circuit

# of 

Comp. Type Stage Capacity ratio Speed Type

Face 

area 

[ft^2]

Fin 

pitch Rows Stage Type Fin pitch

Face 

area 

[ft^2]

Row Stage

Baseline Modeling 11.4 1 circuit 1 Scroll 1 100 Fixed Tube-fin 7.2 15 3 1 Tube-fin 17 16.6 2 1

EL1 Teardown / 

Testing 12.9 1 circuit 1 Scroll 1 100 Fixed Tube-fin 8.9 15 3 1 Tube-fin 17 20.5 2 1

EL2 Teardown / 

Testing 14.0 2 circuits 2 Scroll 2 50/50 Fixed Tube-fin 11.1 15 4 1 Tube-fin 17 25.1 2 1

EL3 Modeling 14.8 2 circuits 2 Scroll 2 50/50 Fixed Tube-fin 11.1 15 4 VS Tube-fin 17 25.1 2 2

EL4

Modeling with

Published 

Manuf. Data

19.9 1 circuit 2 Scroll 3 64/36 Fixed Tube-fin 17.5 15 4 VS Tube-fin 18 36.1 2 3

Efficiency Level Compressor Indoor Heat Exchanger Outdoor Heat Exchanger

5-37 
5.6.5.2 15-ton Models

Two 15-ton units were purchased and tested. One of the units was selected for validating 

the model in CoilDesigner and VapCyc in order to develop the design options for the 15-ton 

capacity level. This unit has a nominal cooling capacity of 15.0 tons, and is rated at 12.2 EER 

and 13.2 IEER. It features two separate refrigerant circuits with two scroll compressors, fin-andtube indoor and outdoor heat exchangers. The compressor model numbers were identified during 

the tear down analysis after completing the performance testing in the laboratory. Indoor and 

outdoor heat exchanger specifications were collected for creating the coil models in 

CoilDesigner. The circuiting of both heat exchangers in CoilDesigner also follows exactly the 

actual heat exchanger geometry

Figure 5.6.19 shows the model validation of the test 15-ton unit at 100-percent, 75-

percent, 50-percent and 25-percent load conditions. The maximum deviation between the tested 

and modeling results are 1.2 percent, with the modeling results slightly higher than the tested 

results. The overall tested IEER is 13.22, and the modeled IEER is 13.28, which is only 0.5 

percent higher than the tested IEER. This shows a very close match between the tested and 

modeled results. 

Figure 5.6.19 Model Validation for 15-Ton CUAC Units After Applying IEER Weighting 

Factors 

As a similar approach employed for the 7.5-ton units, the validated 15-ton models were 

used in the subsequent design option analysis. Table 5.6.6 shows the specifications of the 

different efficiency levels for the 15-ton units. EL 2 is based on actual laboratory testing data, 

and the max-tech unit is based on the specifications of a unit available on the market with 

modeled IEER matched with published data. All other efficiency levels are based on modeling 

results. 

Baseline efficiency level features a dual-refrigerant-circuit with one fixed speed scroll 

compressor in each refrigerant circuit. Both the condenser and evaporator utilize fin-and-tube 

5-38 
type heat exchangers. Fixed speed indoor and outdoor fans provide constant air flow rates 

through the condenser and evaporator coils. 

The design change from the baseline efficiency level to EL1 is the increase of condenser 

and evaporator coils face area. Increased coil face area enhances the heat transfer in the 

condenser and evaporator. Given the same air flow rate, the increased coil face area leads to 

lower velocity of air flowing through the coils. This reduces the air side pressure drop, which 

lowers the fan power consumption and contributes to the improvement of IEER. 

The design improvement from EL 1 to EL 2 includes the increase of condenser and 

evaporator coils face area, and the number of tube rows of the evaporator coil is also increased 

from 3 to 4. A more efficient indoor blower was also implemented in EL 2, which lowers power 

consumption, and therefore leads to a higher IEER compared to EL 1. 

The main design improvement from EL 2 to EL 3 is the implementation of a variable 

speed indoor fan. The variable speed indoor fan provides the optimum air flow rates needed to 

maximize the performance while minimizing the fan power consumption. Two stages of air 

flows are also implemented in the outdoor unit in order to minimize the fan power consumption 

at part load conditions. 

Similar to the max-tech unit of the 7.5-ton equipment class, a single refrigerant circuit 

design is implemented in the 15-ton max tech unit. The single refrigerant circuit design ensures 

the best utilization of heat exchanger heat transfer area during part load conditions, and therefore 

significantly enhances the system performance. The compressors were also selected with 

different capacities to deliver three stages of capacity: i.e., full load capacity at 100 percent load 

conditions, compressor with greater capacity running at 75 percent load condition, and 

compressor with lower capacity running at 50 percent and 25 percent load conditions. Larger 

condenser and evaporator coils are utilized for the max tech unit compared to other efficiency 

levels. A variable speed indoor fan provides different air flow rates depending on various load 

conditions. The condenser fans also provides three stages of air flows to effectively dissipate 

heat to the ambient environment while keeping the fan power consumption at a minimal value. 

5-39 
Table 5.6.6 Design Option for 15-Ton CUAC Units

ID 

Airflow

OD 

Airflow

# Basis IEER Ref. 

Circuit

# of 

Comp. Type Stage Capacity ratio Speed Type

Face 

area 

[ft^2]

Fin 

pitch Rows Stage Type Fin pitch

Face 

area 

[ft^2]

Row Stage

Baseline Modeling 11.2 2 circuits 2 Scroll 2 50/50 Fixed Tube-fin 16.2 15 3 1 Tube-fin 21 26.6 2 1

EL1 Modeling 12.2 2 circuits 2 Scroll 2 50/50 Fixed Tube-fin 24.5 15 3 1 Tube-fin 21 40.4 2 1

EL2 Testing 13.2 2 circuits 2 Scroll 2 50/50 Fixed Tube-fin 22.0 15 4 1 Tube-fin 17 42.8 2 1

EL3 Modeling 14.2 2 circuits 2 Scroll 2 55/45 Fixed Tube-fin 22.0 15 4 VS Tube-fin 17 42.8 2 2

EL4

Modeling with

Published 

Manuf. Data

18.4 1 circuit 2 Scroll 3 64/36 Fixed Tube-fin 26.4 15 4 VS Tube-fin 18 59.2 2 3

Efficiency Level Compressor Indoor Heat Exchanger Outdoor Heat Exchanger

5-40 
5.6.5.3 30-ton Models

One 30-ton unit was purchased and tested. This unit has a nominal cooling capacity of 30 

tons, and is rated with 10.1 EER and 11.9 IEER. It features two separate refrigerant circuits with 

two fixed speed scroll compressors in each circuit. It has fin-and-tube indoor and outdoor heat 

exchangers. Because the indoor coil has four rows of tubes, it is designed to have a front-back 

split for the two refrigerant circuits to account for better part load performance. During the 

literature research of the 30-ton units, it was found that most of the 30-ton units on the market 

feature microchannel condenser coils, and it was also identified that the tested unit also has an 

alternative option with a microchannel condenser coil at identical performance rating. Therefore, 

the tested unit with a fin-and-tube condenser coil was selected for validating the models in 

CoilDesigner and VapCyc as a first step, and then a microchannel condenser coil identified from 

the manufacturer specification sheet was employed to replace the fin-and-tube condenser coil to 

revalidate the models in CoilDesigner and VapCyc in order to develop the design options for 

different 30-ton capacity levels. The compressor model numbers were identified during the tear 

down analysis after completing the performance testing in the laboratory. 

Figure 5.6.20 shows the model validation of the test 15-ton unit at 100-percent, 75-

percent, 50-percent and 25-percent load conditions. The maximum deviation between the 

modeling and tested results are 3.3 percent, with the modeling EER slightly higher than the 

tested result. The difference between modeling IEER and test result is found to be -2.3 percent. 

Figure 5.6.20 Model Validation for 30-Ton CUAC Units with Tube-Fin Condensers After 

Applying IEER Weighting Factors 

As a second step of the model validation, the fin-and-tube condenser was replaced with a 

microchannel condenser in order to be representative of the technologies implemented in the 30-

ton units. The indoor coil remains the same as previously validated. 

By utilizing the microchannel condenser coils, the model was revalidated, and the results 

are shown in Figure 5.6.21. The maximum deviation between the modeling and tested EERs are -

5-41 
2.8 percent, with the modeling results slightly lower than the tested results. The difference 

between the modeling and tested IEER is -1.7 percent, with the modeling result slightly lower 

than the tested value. 

Figure 5.6.21 Model Validation for 30-Ton CUAC Units with Microchannel Condensers

After Applying IEER Weighting Factors 

Based on these validation analyses, DOE believes the energy models for each capacity is 

representative of the actual unit performance.

Table 5.6.7 shows the specifications of the different efficiency levels for the 30-ton units. 

A 30-ton unit was tested and used for the model validation, as elaborate previously. Because the 

efficiency of this tested unit does not match precisely with the desired IEER level, it is not 

directly used in this design matrix. As a result, all efficiency levels of the 30-ton units are based 

on modeling results. 

Baseline efficiency level features a dual-refrigerant-circuit with two fixed speed scroll 

compressors in each refrigerant circuit. It also has fin-and-tube evaporator and microchannel 

condenser coils. Fixed speed indoor and outdoor fans provide constant air flow rates through the 

condenser and evaporator.

The design change from the baseline efficiency level to EL1 includes the increase of 

condenser and evaporator coils face area, and the implementation of two stages of air flow in the 

condenser coils to reduce the condenser fan power consumption in part load conditions. Given 

the same air flow rate, the increased coil face area leads to lower velocity of air flowing through 

the coils. This reduces the air side pressure drop, which lowers the fan power consumption and 

contributes to the improvement of IEER.

The design improvement from EL 1 to EL 2 include the increase of condenser face area, 

and the number of outdoor fans also increases from 2 to 4 with smaller motors in each fan 

assembly in order to minimize the condenser fan power consumption. 

5-42 
The design improvement from EL 2 to EL 3 is the implementation of a variable speed 

indoor fan and increased number of compressor staging. The variable speed indoor fan provides 

the optimum air flow rates needed to maximize the performance while minimizing the fan power 

consumption. Increased compressor staging lowers the compressor power at part load conditions. 

Four stages of capacity provide refined performance, i.e., four, three, two and one compressors 

are in operation for 100 percent, 75 percent, 50 percent and 25 percent load conditions, 

respectively.

Both the 7.5-ton and 15-ton max tech units feature a single refrigerant circuit to 

maximize the coil surface area use during part load conditions for maximizing IEER. However, 

such a feature is not applicable in a 30-ton unit max tech unit due to potentially challenges of oil 

circulation in large refrigeration systems. Therefore, the 30-ton max tech unit features a dualrefrigerant circuit design. As noted above, the increased compressor staging at the max-tech level 

lowers the compressor power at part load conditions. 

Condenser coil size was further increased from EL 3 in order to effectively dissipate 

condenser heat to the ambient in order to lower overall system power consumption. A variable 

speed indoor fan provides different air flow rates depending on various load conditions. The 

condenser fans also provides four stages of air flows to effectively dissipate heat to the ambient 

environment while keeping the fan power consumption at a minimal value. 

Comparing to the max tech units of 7.5-ton and 15-ton units, the 30-ton max tech unit has 

a much lower IEER. As the capacity of a unit increases, the design of such a unit has to consider 

the physical size in order to account for convenience of delivery and installation. Therefore, 

instead of significantly increasing the size of the condenser and evaporator coils, the air flow 

rates through the condenser and evaporator are increased substantially. The increase of air flow 

rates results in high fan power consumption, which essentially lowers the limit of IEER that a 

unit can reach. This is the main reason that the 30-ton max tech unit has an IEER much lower 

than that of the 7.5-ton and 15-ton units. 

5-43 
Table 5.6.7 Design Options for 30-Ton CUAC Units

ID 

Airflow

OD 

Airflow

# Basis IEER Ref. 

Circuit

# of 

Comp. Type Stage Capacity ratio Speed Type

Face 

area 

[ft^2]

Fin 

pitch Rows Stage Type Fin pitch

Face 

area 

[ft^2]

Row Stage

Baseline Modeling 10.1 2 circuits 4 Scroll 2 25/25/

25/25/ Fixed Tube-fin 21.9 15 4 1 Microchannel 23 23.0 1 1

EL1 Modeling 11.6 2 circuits 4 Scroll 2 25/25/

25/25/ Fixed Tube-fin 31.3 15 4 1 Microchannel 23 32.9 1 2

EL2 Modeling 12.5 2 circuits 4 Scroll 2 25/25/

25/25/ Fixed Tube-fin 31.3 15 4 1 Microchannel 23 46.1 1 2

EL3 Modeling 13.5 2 circuits 4 Scroll 4 25/25/

25/25/ Fixed Tube-fin 31.3 15 4 VS Microchannel 23 46.1 1 2

EL4

Modeling with

Published 

Manuf. Data

15.5 2 circuits 4 Scroll 4 25/25/

25/25/ Fixed Tube-fin 31.6 15 4 VS Microchannel 23 68.4 1 4

Efficiency Level Compressor Indoor Heat Exchanger Outdoor Heat Exchanger

5-44 
5.6.5.4 Design Option Summary

Table 5.6.8 summarizes the detailed design options for the baseline efficiency and 

incremental efficiency levels.

Detailed performance data at different load conditions for 7.5-ton, 15-ton and 30-ton 

units are shown in Figure 5.6.22, Figure 5.6.23 and Figure 5.6.24, respectively. It can be seen 

that the max-tech unit (EL 4) has significantly higher EERs than other efficiency levels due to 

the best available technologies implemented (e.g., variable speed indoor blowers, staged outdoor 

air flows, capacity staging, larger coils, and single refrigerant circuit (7.5-ton and 15-ton), etc.). 

Moreover, the slope of EL 4 flattens out as capacity increases from 7.5-ton to 15-ton, and to 30-

ton. This is mainly due to the substantial increase of indoor and outdoor fan power, which takes a 

much higher percentage of the overall power consumption as the system capacity increases. 

Comparing 30-ton units to 15-ton and 7.5-ton units, physical size of the units do no increase 

proportionally to the increase of capacity. Larger fans are utilized to draw more air at a higher 

velocity flowing through the coils, which result in an increase of static pressure, and therefore a 

significant increase of fan power consumption. It can also be seen that as the ambient 

temperature decreases, EER increases with decreasing part load until 50 percent. The transition 

point is from 50-percent to 25-percent part load, where the EER decreases. This is due to the 

degradation coefficient applied at the last part load condition. 

Figure 5.6.22 7.5-Ton EERs at Different Load Conditions for Five Efficiency Levels

5-45 
Table 5.6.8 Design Option Summary for Different Efficiency Levels

Equipment 

Type Baseline EL 1 (TSL 1) EL 2 (TSL 2) EL 3 (TSL 3) EL 4 (TSL 4)

Small CUAC, 

CUHP

Single compressor

(1 stage), fixed 

indoor and outdoor 

air flow

Baseline + increased 

outdoor and indoor 

coil heat transfer 

areas

EL1 + Two

compressor stages, 

increased outdoor 

and indoor coil heat 

transfer areas 

EL 2 + variable air 

volume for indoor 

fan, two stages 

outdoor coil air flow

EL3 + Single 

refrigerant circuit (3 

compressor stages), 

increased outdoor 

and indoor coil heat 

transfer areas, three 

compressor and 

outdoor coil air flow 

stages

Large CUAC, 

CUHP

Two-compressors (2 

stages), fixed indoor 

and outdoor air flow 

Baseline + increased 

outdoor and indoor 

coil heat transfer 

areas

EL 1 + increased 

outdoor and indoor 

coil heat transfer 

areas

EL 2 + variable air 

volume for indoor 

fan, two stages 

outdoor coil air flow

EL 3 + Single 

refrigerant circuit (3 

compressor stages), 

increased outdoor 

and indoor coil heat 

transfer areas, three 

compressor and 

outdoor coil air flow 

stages

Very Large

CUAC, CUHP

Four-compressors (2 

stages), two 

refrigerant circuits, 

fixed indoor and 

outdoor coil air flow

Baseline + increased 

outdoor and indoor 

coil heat transfer 

areas, two stages 

outdoor coil air flow

EL 1 + increased 

outdoor and indoor 

coil heat transfer 

areas

EL 2 + 4 

compressor stages, 

variable air volume 

for indoor fan 

EL 3 + increased 

outdoor and indoor 

coil heat transfer 

areas, four stages 

outdoor coil air flow

Note: In addition to the listed design options, most of the efficiency level steps included incremental indoor and outdoor fan and fan motor efficiency 

improvements.

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Figure 5.6.23 15-Ton EERs at Different Load Conditions for Five Efficiency Levels

Figure 5.6.24 30-Ton EERs at Different Load Conditions for Five Efficiency Levels

Figure 5.6.25 and Figure 5.6.26 show the coil face area multiplied by the number of tube 

row for indoor and outdoor coils, respectively. The progression of efficiency levels correlates 

with the increase of heat transfer area. From Figure 5.6.26 it can be seen that the heat transfer 

area of the 30-ton units is even smaller than that of the 15-ton and 30-ton units. This is due to the 

fact that 30-ton units utilize microchannel condenser coils, and therefore, the heat transfer area is 

significantly less than other capacity levels.

5-47 
Figure 5.6.25 Indoor Coil Face Area * Tube Row Number

Figure 5.6.26 Outdoor Coil Face Area * Tube Row Number

5.6.6 Cost-Efficiency Results 

With the validated energy models, DOE expanded the modeling tasks with various 

system design options and identified the key design features (consistent with equipment available 

on the market) required for 7.5-ton, 15-ton, and 30-ton air-cooled CUAC units with electric 

resistance heating or no heating to achieve each efficiency level. DOE then used these design 

features developed by the energy modeling in conjunction with the manufacturing cost model to 

5-48 
determine the incremental manufacturing and shipping costs for each efficiency level for 7.5-ton, 

15-ton and 30-ton units. 

DOE developed the cost-efficiency results shown in Table 5.6.9 through Table 5.6.11 for 

each cooling capacity range. DOE notes that the incremental costs would be equivalent for each 

of the equipment classes within a given cooling capacity range (i.e., CUAC units with electric 

resistance heating or no heat, CUAC units with all other types of heating, CUHP units with 

electric resistance heating or no heat, CUHP units with all other types of heating).

Table 5.6.9 Small Air-Cooled CUAC and CUHP Cost-Efficiency Relationships

Efficiency Level Incremental Manufacturer 

Production Cost 

Incremental Shipping 

Cost

Baseline - -

EL1 $115.93 -

EL2 $583.47 -

EL3 $788.88 -

EL4 (Max-Tech) $1,277.04 $102.86

Table 5.6.10 Large Air-Cooled CUAC and CUHP Cost-Efficiency Relationships

Efficiency Level Incremental Manufacturer 

Production Cost

Incremental Shipping 

Cost

Baseline - -

EL1 $419.16 -

EL2 $792.76 $192.86

EL3 $1,236.98 $192.86

EL4 (Max-Tech) $1,554.26 $192.86

Table 5.6.11 Very Large Air-Cooled CUAC and CUHP Cost-Efficiency Relationships

Efficiency Level Incremental Manufacturer 

Production Cost

Incremental Shipping 

Cost

Baseline - -

EL1 $542.65 -

EL2 $1,296.41 -

EL3 $1,834.67 -

EL4 (Max-Tech) $2,753.32 $444.00

5-49 
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