CHAPTER 4. SCREENING ANALYSIS

TABLE OF CONTENTS

4.1 INTRODUCTION ........................................................................................................... 4-1

4.2 SCREENED-OUT TECHNOLOGY OPTIONS ............................................................. 4-1

4.2.1 Electro-hydrodynamic enhanced heat transfer ..................................................... 4-2

4.2.2 Alternative refrigerants ........................................................................................ 4-2

4.2.3 Sub-coolers .......................................................................................................... 4-3

4.3 REMAINING DESIGN OPTIONS ................................................................................. 4-3

LIST OF TABLES

Table 4.3.1 Retained Design Options for Small, Large, and Very Large Air-Cooled 

CUAC and CUHP .......................................................................................... 4-3

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CHAPTER 4. SCREENING ANALYSIS

4.1 INTRODUCTION

This chapter details the screening analysis conducted by the U.S. Department of Energy 

(DOE) of the technology options identified in the market and technology assessment (chapter 3 

of this technical support document (TSD)) for 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 air-cooled commercial unitary heat pumps, CUHP). In the market and 

technology assessment, DOE presented an initial list of technologies that can be used to increase 

the efficiency of the considered equipment. The goal of the screening analysis is to identify any 

technology options that will be eliminated from further consideration in the rulemaking analyses.

The candidate technology options are assessed based on DOE’s analysis as well as inputs 

from interested parties including manufacturers, trade organizations, and energy efficiency 

advocates. Technology options that are judged to be viable approaches for improving efficiency

are retained as inputs to the subsequent engineering analysis, and are designated as design 

options. Technology options that are not incorporated in commercial equipment or in working 

prototypes, or that fail to meet certain criteria, as to practicability to manufacture, install and 

service, as to impacts on product utility or availability, or as to health or safety will be eliminated 

from consideration. The rationale for either screening out or retaining each technology option is 

detailed in the following sections.

4.2 SCREENED-OUT TECHNOLOGY OPTIONS

The following section details the specific technology options that were screened out prior 

to the engineering analysis, along with the rationale for elimination.

The technologies identified in the market and technology assessment were evaluated 

pursuant to the criteria set out in the Energy Policy and Conservation Act (EPCA). (42 United 

States Code (U.S.C.) 6291-6317) DOE consulted with industry, technical experts, and other 

interested parties in developing a list of design options. DOE then applied the following set of 

screening criteria to determine which design options are unsuitable for further consideration in 

the rulemaking: 

(1) Technological feasibility. If it is determined that a technology has not been 

incorporated in commercial equipment or in working prototypes, then that technology will not be 

considered further.

(2) Practicability to manufacture, install, and service. If it is determined that mass 

production of a technology in commercial equipment and reliable installation and servicing of 

the technology could not be achieved on the scale necessary to serve the relevant market at the 

time of the effective date of the standard, then that technology will not be considered further. 

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(3) Impacts on product utility to consumers. If a technology is determined to have 

significant adverse impact on the utility of the equipment to significant subgroups of consumers, 

or results in the unavailability of any covered equipment type with performance characteristics 

(including reliability), features, size, capacities, and volumes that are substantially the same as 

equipment generally available in the United States at the time, it will not be considered further. 

(4) Safety of technologies. If it is determined that a technology will have significant 

adverse impacts on health or safety, it will not be considered further. 

After reviewing the technology options to increase the efficiency of the covered 

equipment against the screening criteria, DOE eliminated the following technology options from 

consideration in its rulemaking analysis. 

4.2.1 Electro-hydrodynamic enhanced heat transfer

Electro-hydrodynamic enhancement of heat transfer, which increases the net heat transfer 

coefficient by applying a high-voltage electrostatic potential field across a heat transfer fluid to 

destabilize the thermal boundary layer and incite fluid mixing, is still in the research stage. 

Although the technique has been shown to improve heat transfer in laboratory testing, DOE is 

not aware of any commercially available equipment or working prototypes that use electrohydrodynamic heat transfer. As a result, DOE does not believe at this time that this option meets 

the screening criterion of technological feasibility. In addition, DOE notes that this technology 

has not been adequately demonstrated for commercial deployment and, as a result, does not meet 

the criterion of practicability to install and service on a scale necessary to serve the relevant 

market at the time of the compliance date of a new standard. For these reasons, DOE did not 

consider electro-hydrodynamic heat transfer further analysis. 

4.2.2 Alternative refrigerants

DOE considered ammonia, carbon dioxide, and various hydrocarbons (such as propane 

and isobutane) as alternative refrigerants to those that are currently in use, such as R-410A. DOE 

notes that safety concerns need to be taken into consideration when using ammonia and 

hydrocarbons in air-conditioning systems. The Environmental Protection Agency (EPA) created 

the Significant New Alternatives Policy (SNAP) Program to evaluate alternatives to ozonedepleting substances. Substitutes are reviewed on the basis of ozone depletion potential, global 

warming potential, toxicity, flammability, and exposure potential. DOE notes that ammonia (in 

vapor compression cycles), carbon dioxide, and hydrocarbons have been approved or are being 

considered under SNAP for certain uses, but these or other low GWP alternatives are not yet 

listed as acceptable substitutes for this equipment.a DOE is also not aware of any other more 

efficient refrigerant options that are SNAP-approved. Because these alternative refrigerants have 

not yet been approved for this equipment, DOE screened out ammonia, carbon dioxide, and 

a On July 9, 2014, EPA proposed to list certain hydrocarbons and R-32 for residential self-contained A/C appliances 

as acceptable subject to use conditions to address safety concerns (See 79 FR 38811). EPA is also evaluating new 

refrigerants for other A/C applications, including commercial A/C. Additional information regarding EPA’s SNAP 

Program is available online at: http://www.epa.gov/ozone/snap/. 

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hydrocarbons as alternative refrigerants for improving the energy efficiency of small, large, and 

very large air-cooled CUAC and CUHP. 

4.2.3 Sub-coolers

A sub-cooler is a device located between the condenser coil outlet and the expansion 

device inlet used to further cool the refrigerant exiting the condenser in order to achieve a higher 

cooling/heating capacity for a unit. DOE notes that air-cooled CUAC and CUHP typically subcool the refrigerant in the condensing coil (i.e., providing additional decrease in the temperature 

of the refrigerant). DOE also notes that additional mechanical sub-cooling from smaller, 

secondary vapor-compression circuits has not been incorporated in commercial equipment or in 

working prototypes. As a result, DOE does not believe sub-cooling meets the criterion of 

technological feasibility and did not consider it for further analysis. 

4.3 REMAINING DESIGN OPTIONS

Table 4.3.1 lists the technology options that were retained by DOE and subsequently 

designated as design options. Each of these technologies will be evaluated (consistent with 

equipment available on the market) further in the subsequent engineering analysis. 

Table 4.3.1 Retained Design Options for Small, Large, and Very Large Air-Cooled 

CUAC and CUHP

Condenser and evaporator fan and fan motor improvements:

• Larger fan diameters

• More efficient fan blades (e.g., air foil centrifugal evaporator fans, 

backward-cured centrifugal evaporator fans, high efficiency 

propeller condenser fans) 

• High efficiency motors (e.g., copper rotor motor, high efficiency 

induction, permanent magnet, electronically commutated) 

• Variable speed fans/motors

Larger heat exchangers

Microchannel heat exchangers

Compressor Improvements

• High efficiency compressors

• Multiple compressor staging 

• Multiple- or variable-capacity compressors

Thermostatic expansion valves

Electronic expansion valves

Reduced indoor fan belt loss

• Synchronous (toothed) belts 

• Direct-drive fans

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