CHAPTER 4. SCREENING ANALYSIS 

TABLE OF CONTENTS 

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

4.2 SCREENED-OUT TECHNOLOGIES............................................................................ 4-2
 

4.2.1 High-Efficiency Expansion Valves...................................................................... 4-2
 

4.2.2 Condenser Fan Motor Controllers ....................................................................... 4-2
 

4.2.3 Liquid-Suction Heat Exchangers ......................................................................... 4-2
 

4.2.4 Defrost Cycle Controls ........................................................................................ 4-3
 

4.2.5 Defrost Mechanisms ............................................................................................ 4-3
 

4.3 REMAINING TECHNOLOGIES ................................................................................... 4-3
 
 

 

CHAPTER 4. SCREENING ANALYSIS
 

4.1 INTRODUCTION 

This chapter addresses the screening analysis that the U.S. Department of Energy 

(DOE) conducted in support of the ongoing energy conservation standards rulemakings 

for residential central air conditioners and heat pumps. This rulemaking is mandated by 

the National Appliance Energy Conservation Act of 1987 (NAECA), and is effective for 

products manufactured five years after the date of publication of a final rule establishing 

energy conservation standards. 

In the market and technology assessment (chapter 3), DOE presented an initial list 

of technologies that can reduce the energy consumption of central air conditioners and 

heat pumps. The goal of the screening analysis is to screen out technologies that will not 

be considered further in the rulemaking analyses. Some of the technologies considered in 

chapter 3 can reduce annual energy consumption under real-world conditions, but may 

not increase the seasonal energy efficiency ratio (SEER) or heating seasonal performance 

factor (HSPF) as calculated using the DOE test procedure. DOE removed from 

consideration those technologies that do not increase SEER or HSPF. DOE evaluated the 

remaining technologies using the screening criteria set forth in the Energy Policy and 

Conservation Act (EPCA). (42 U.S.C. 6311–6317) 

Section 325(o) EPCA establishes criteria for prescribing new or amended 

standards that are designed to achieve the maximum improvement in energy efficiency. 

Further, EPCA directs the Secretary of Energy to determine whether a standard is 

technologically feasible and economically justified. (42 U.S.C. 6295(o)(2)(A), as 

directed by 42 U.S.C. 6316(a)(1)–(3)) EPCA also establishes guidelines for determining 

whether a standard is economically justified. (42 U.S.C. 6295(o)(2)(B)) In view of the 

EPCA requirements for determining whether a standard is technologically feasible and 

economically justified, DOE applies the following set of screening criteria to determine 

which design options are unsuitable for further consideration in the rulemaking (Title 10 of 

the Code of Federal Regulations, Part 430, Subpart C, Appendix A at 4(a)(4) and 5(b)): 

Technological feasibility. Technologies incorporated in products or in working 

prototypes will be considered technologically feasible. 

Practicability to manufacture, install, and service. If mass production of a 

technology in products and reliable installation and servicing of the technology could 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 be considered practicable to manufacture, 

install, and service. 

Adverse impacts on product utility or product availability. If DOE 

determines that a technology has significant adverse impact on the utility of the product 

to significant subgroups of consumers, or result in the unavailability of any covered 

product type with performance characteristics (including reliability), features, sizes, 

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capacities, and volumes that are substantially the same as products generally available in 

the United States at the time, it will not be considered further. 

Adverse impacts on health or safety. If DOE determines that a technology will 

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

In sum, if DOE determines that a particular technology, or combination of 

technologies, fail to meet one or more of the four criteria, it will be screened out. Section 

4.2 below documents the reasons for eliminating any technology. 

4.2 SCREENED-OUT TECHNOLOGIES 

As stated above, technologies that do not increase SEER or HSPF are not 

considered beneficial in the context of this rulemaking. Therefore, DOE removed the 

following technologies from consideration: higher efficiency expansion valves, 

condenser fan motor controllers, liquid-suction heat exchangers (LSHXs), defrost cycle 

controls, and defrost mechanisms. 

4.2.1 High-Efficiency Expansion Valves 

In actual operating conditions, high-efficiency expansion valves such as electronic 

expansion valves (EEVs) can reduce the annual energy consumption of central air 

conditioners and heat pumps by adapting to varying loads and ambient conditions. 

However, because each test within the DOE test procedure is a steady-state test (i.e., tests 

are conducted at a single, specified temperature and relative humidity), there is no 

opportunity for high-efficiency expansion valves to reduce SEER or HSPF. 

Consequently, DOE did not consider high-efficiency expansion valves as a design option 

in the engineering analysis. 

4.2.2 Condenser Fan Motor Controllers 

Under actual operating conditions, condenser fan motor controllers can adapt 

condenser operation to changing ambient temperatures and thereby reduce annual energy 

consumption of central air conditioners and heat pumps. However, because each test 

within the DOE test procedure is a steady-state test (i.e., tests are conducted at a single, 

specified temperature and relative humidity), there is no opportunity to account for the 

effect of a condenser fan motor controller on SEER or HSPF. Consequently, DOE did 

not consider condenser fan motor controllers as a design option in the engineering 

analysis. 

4.2.3 Liquid-Suction Heat Exchangers 

An LSHX is a heat exchanger that serves to cool liquid refrigerant entering the 

expansion valve by utilizing some of the gaseous refrigerant from the evaporator coil. 

The purpose of this is to sub-cool the incoming liquid through superheating of the suction 

vapor. In general, LSHXs are installed in refrigeration systems to ensure proper system 

operation and can potentially improve system performance under actual field operating 

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conditions. However, the performance of an LSHX is dependent upon a number of 

factors, including refrigerant type, operating temperature, and ambient conditions, and 

thus DOE does not have enough information to suggest that an LSHX would consistently 

increase SEER or HSPF as rated using the DOE test procedure. Consequently, DOE did 

not consider LSHXs as a design option in the engineering analysis. 

4.2.4 Defrost Cycle Controls 

A defrost cycle control system is set up to adapt from previous defrost cycles to 

attain improved defrost system operation at various outdoor temperature conditions. This 

technology can save energy annually by using a computer to run the defroster at the 

optimum time and optimum temperature based on the ambient temperature range. 

However, this system adds efficiency because it helps account for outdoor temperature 

variation. The static nature of the DOE test procedure ambient conditions does not allow 

for increases in SEER or HSPF due to implementation of such a system. As a result, DOE 

did not consider defrost cycle controls as a design option in the engineering analysis. 

4.2.5 Defrost Mechanisms 

Several mechanisms exist which may be used to aid in defrosting heat pump heat 

exchanger coils. One of these is the “frost-less” heat pump coil, which adds an 

accumulator to the heat pump cycle, trapping heat from the condenser liquid and using it 

to increase the temperature of the outdoor coil by several degrees. This reduces the 

buildup of frost on the coil, but is only effective within a small range of ambient 

temperatures at and above the freezing point of water. Additionally, such systems 

increase compressor work, and thus do not appear to have any positive benefit on rated 

SEER or HSPF values as measured using the DOE test procedure. 

A second defrost mechanism which currently exists is hot-water defrosting. This 

system uses an additional circuit of valves and tubing which allows for some of the 

refrigerant to be used to heat water, which is then stored and used to defrost the coil by 

being sent through additional tubing around the coil. However, such a system would 

make no impact on the values of SEER or HSPF determined using the DOE test 

procedure. Consequently, DOE did not consider either of these defrost mechanisms as 

design options in the engineering analysis. DOE is not aware of any defrost mechanisms 

other than frost-less heat pumps or hot-water defrost that are currently in use on the 

market or in development that could have a potential benefit to rated SEER or HSPF. 

4.3 REMAINING TECHNOLOGIES 

After eliminating those technologies that do not increase SEER and do not meet 

the four screening criteria described in Section 4.1, DOE is considering the following 

technologies: 

• higher efficiency fan motors 

• higher efficiency fan blades 

4-3 
 

• improved evaporator coils 

• improved condenser coils 

• higher efficiency compressors 

• microchannel heat exchangers 

• flat-tube heat exchangers 

4-4