CHAPTER 4. SCREENING ANALYSIS

TABLE OF CONTENTS

4.1 INTRODUCTION

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4.2 SCREENED-OUT TECHNOLOGIES

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4.2.1 High-Efficiency Expa nsion Valves

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4.2.2 Condenser Fan Motor Controllers

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4.2.3 Liquid-Suction Heat Exchangers

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4.2.4 Defrost Cycle Controls

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4.2.5 Defrost Mechanisms

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4.3 REMAINING TECHNOLOGIES

................................................................................... 4-3CHAPTER 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 cond itioners 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 (c hapter 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 analys es. Some of the technologies considered in chapter 3 can reduce annual energy consum ption 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 cr iteria set forth in the Energy Policy and Conservation Act (EPCA). (42 U.S.C. 6311–6317)

Section 325(o) EPCA esta blishes 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, Subp art 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 relia ble 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 w ill be considered practicable to manufacture, install, and service.

Adverse impacts on product utility or pro duct availability. If DOE determines that a technology has significan t adverse impact on the utility of the product to significant subgroups of consumers, or result in the unavaila bility of any covered product type with performance characteristics (including reliability), features, sizes,

4-1capacities, 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 th is rulemaking. Therefore, DOE removed the following technologies from consideration: higher efficiency expansion valves,

condenser fan motor controllers , liquid-suction heat exchange rs (LSHXs), defrost cycle controls, and defrost mechanisms.

4.2.1 High-Efficiency Expansion Valves

In actual operating conditions, high-efficiency expansion va lves such as electronic expansion valves (EEVs) can reduce the a nnual 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 temp erature 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, condens er fan motor controllers can adapt condenser operation to changing ambient te mperatures 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 inco ming liquid through superheating of the suction vapor. In general, LSHXs are installed in re frigeration systems to ensure proper system operation and can potentially improve system performance under actual field operating

4-2conditions. However, the performance of an LSHX is dependent upon a number of factors, including refrigerant type, operatin g 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 usin g 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 am bient conditions does not allow for increases in SEER or HSPF due to impleme ntation 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 co il 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 pum ps or hot-water defrost that are currently in use on the market or in development that could have a potential benefit to ra ted SEER or HSPF.

4.3 REMAINING TECHNOLOGIES

After eliminating those tec hnologies that do not increase SEER and do not meet the four screening criteria described in S ection 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

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