CHAPTER 4. SCREENING ANALYSIS

TABLE OF CONTENTS

Chapter 4. Screening Analysis......................................................................................................4­i
 

TABLE OF CONTENTS..............................................................................................................4­I
 

CHAPTER 4. SCREENING ANALYSIS .................................................................................. 4­1
 

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

4.2 TECHNOLOGIES THAT DO NOT ENHANCE EER AS MEASURED...................... 4­2
 

4.2.1 Variable Speed Compressors............................................................................... 4­2
 

4.2.2 Complex Control Boards ..................................................................................... 4­2
 

4.2.3 Corrosion Protection ............................................................................................ 4­3
 

4.2.4 Clutched Motor Fan ............................................................................................. 4­3
 

4.2.5 Thermal Expansion Valve.................................................................................... 4­3
 

4.3 SCREENED­OUT TECHNOLGIES............................................................................... 4­4
 

4.3.1 Scroll Compressors.............................................................................................. 4­4
 

4.3.2 Higher Efficiency Fan Motors............................................................................. 4­5
 

4.3.3 Microchannel Heat Exchangers........................................................................... 4­5
 

4.3.4 Material Treatment of Heat Exchangers.............................................................. 4­6
 

4.3.5 Improved Air Flow and Fan Design .................................................................... 4­7
 

4.3.6 Heat Pipes ............................................................................................................ 4­8
 

4.4 REMAINING TECHNOLOGIES ................................................................................... 4­8
 

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CHAPTER 4. SCREENING ANALYSIS
 

4.1 INTRODUCTION
 

This chapter details the screening analysis that the U.S. Department of Energy (DOE)

conducted in support of the ongoing energy conservation standards rulemakings for packaged

terminal air conditioners (PTACs) and packaged terminal heat pumps (PTHPs).

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

of technologies that can improve the energy efficiency of PTACs and PTHPs. The purpose of

the screening analysis is to evaluate the technologies that improve equipment efficiency to

determine which technologies to consider further and which to screen out. DOE consulted with a

range of parties, including industry, technical experts, and others to develop a list of technologies

for consideration. Some of these technologies can reduce annual energy consumption of

equipment in actual applications, but may not improve the energy­efficiency ratio (EER) and

coefficient of performance (COP) of PTACs and PTHPs as measured by the Air­Conditioning

and Refrigeration Institute (ARI) 310/380­2004 Standard for Packaged Terminal AirConditioners and Heat Pumps (ARI 310/380­2004) test procedure, which DOE has incorporated

by reference into its regulations at 10 Code of Federal Regulations (CFR) section 431.95. DOE

removed from consideration those technologies that do not increase EER and COP per the test

procedures. DOE evaluated the remaining technologies pursuant to the criteria set out in the

Energy Policy and Conservation Act (EPCA), as amended. (42 U.S.C. 6311­6317)

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

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)) Appendix A to subpart C of Title 10, Code of Federal Regulations,

Part 430 (10 CFR Part 430), “Procedures, Interpretations and Policies for Consideration of New

or Revised Energy Conservation Standards for Consumer Products” (the Process Rule), sets forth

procedures to guide DOE in its consideration and promulgation of new or revised equipment

energy conservation standards. These procedures elaborate on the statutory criteria provided in

42 U.S.C. 6295(o) and, in part, eliminate problematic technologies early in the process of

prescribing or amending an energy efficiency standard. In particular sections 4(b)(4) and 5(b) of

the Process Rule guide DOE in determining whether to eliminate from consideration any

technology that presents unacceptable problems with respect to the following criteria:

Technological feasibility. Technologies incorporated in commercial equipment or in

working prototypes will be considered technologically feasible.

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

in commercial equipment 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

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the standard, then that technology will be considered practicable to manufacture, install, and

service.

Impacts on equipment utility or equipment availability. If a technology is determined

to have significant adverse impact on the utility of the equipment to significant subgroups of

customers, or result in the unavailability of any covered equipment type with performance

characteristics (including reliability), features, sizes, 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.

Adverse impacts on health or safety. If it is determined 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 technology, or a combination of technologies, has

unacceptable impacts on the policies stated in section 5(b) of the Process Rule, it will be

eliminated from consideration. If a particular technology fails to meet one or more of the four

criteria, it will be screened out. Sections 4.2 and 4.3 document the reasons for eliminating any

technology.

4.2 TECHNOLOGIES THAT DO NOT ENHANCE EER AS MEASURED

DOE eliminated three technologies because they have no effect on or do not increase

EER or COP as measured by the test procedure since the test procedure measures steady­state

energy efficiency. However, these features (i.e., variable speed compressors, complex control

boards, and corrosion protection) can reduce the energy consumption of the PTAC or PTHP in

actual applications, since they affect the cyclic operation of the equipment. Although these

technologies were not considered in the analyses, DOE does not discourage their use by

manufacturers because of their potential to reduce annual energy consumption. For each

technology removed for this reason, DOE provided an explanation of why the technology does

not affect EER.

4.2.1 Variable Speed Compressors

Variable speed compressors can increase efficiency over a broad operating range, but

they do not inherently increase the maximum efficiency at the compressor rating point. Because

the ARI 310/380­2004 test procedure calls for steady­state conditions (i.e., no variability in

inputs), the speed of the compressor must remain constant. If the compressor is to maintain

constant speed, there is no opportunity for the compressor to increase the measured EER because

the power input and work output are constant. Therefore, DOE did not consider this technology

in the engineering analysis.

4.2.2 Complex Control Boards

Fan motor controllers can reduce the annual energy consumption of PTACs and PTHPs

by adjusting the air flow over the heat exchangers to changing indoor and outdoor conditions.

For example, the PTAC or PTHP might only need the evaporator fan motor to be on at half

speed while the condenser fan motor is at full speed to maintain an indoor air temperature.

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Because the ARI 310/380­2004 test procedure calls for steady state operating conditions during

the test (i.e., no variation in the indoor and outdoor temperatures), there is no opportunity for

varying the speed of the fan motors to impact the EER calculation. Consequently, DOE did not

consider this technology in the engineering analysis.

Digital energy management control interfaces can reduce annual energy consumption of

PTACs or PTHPs by optimizing the operation of the equipment under varying operating

conditions. For example, they may allow operation managers in hotels to remotely turn off or

change temperature setpoints of units throughout a building. Although this technology can

reduce peak energy demand and also reduce overall energy consumption throughout the year, it

does not increase the EER under the ARI 310/380­2004 test procedure because of the steady

state test conditions. Therefore, DOE did not consider this technology in the engineering

analysis.

Heat pump controllers can reduce annual energy consumption of PTHPs by adapting the

operation of the heat pump cycle and use of supplemental electric resistance to changing loads

and ambient conditions. Because the ARI 310/380­2004 test procedure calls for steady­state

conditions, there is no opportunity to account for the adaptive technology of the heat pump cycle

to increase EER. Therefore, DOE did not consider this technology in the engineering analysis.

4.2.3 Corrosion Protection

PTACs and PTHPs are designed to have partial exposure to the elements (i.e., a section

exposed to the outdoors). While corrosion protection materials used in PTACs and PTHPs may

reduce the efficiency of the heat exchangers somewhat, they also protect the equipment and

prolong its use when it is exposed to chemically harsh operating conditions. Although it is

beneficial for the unit to be corrosion protected, it does not improve the EER as per the ARI

310/380­2004 test procedure. Since corrosion protection only helps maintain performance and

does not affect the EER of PTACs and PTHPs, DOE did not consider this technology in the

engineering analysis.

4.2.4 Clutched Motor Fan

DOE did not consider clutched motor fan technology. In theory, these devices would

work with PTACs and PTHPs to reduce the load on a single fan motor used to drive both the

evaporator and the condenser fan blades when the refrigerating system is not operating by

disengaging the condenser fan. In this way, power input could be reduced during times when

only the indoor blower is running to recirculate air, or when electric resistance heating is being

provided. However, the measure of energy use and EER for PTACs in cooling mode is based on

full cooling operation, in which both the indoor blower and the condenser fan must operate.

Hence, including a clutched condenser fan would not provide measurable energy efficiency

benefits.

4.2.5 Thermal Expansion Valve

DOE did not consider thermal expansion valve (TXV) technology for PTACs or PTHPs.

TXVs are expansion devices that meter the flow of refrigerant from the condenser to the

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evaporator at a rate equivalent to the amount of refrigerant being boiled off in the evaporator.

Typically, TXVs are installed in central air conditioning applications where equipment is rated

with the seasonal energy efficiency ratio (SEER) metric and testing occurs at various operating

conditions and temperatures. In contrast, PTACs and PTHPs are measured using the EER

metric, with testing occurring at a constant temperature of 95 degrees F. Therefore, the energy

efficiency benefits of a TXV will not affect the EER rating of a PTAC because the orifice of the

TXV and the flow of refrigerant would remain constant during testing. Therefore, DOE does not

consider TXVs to be a technology for improving the EER of PTACs and PTHPs.

4.3 SCREENED­OUT TECHNOLGIES

This section describes the technologies that DOE eliminated for failure to meet one of the

following four factors: (1) technological feasibility; (2) practicability to manufacture, install, and

service; (3) impacts on equipment utility or equipment availability; and (4) adverse impacts on

health or safety. DOE eliminated scroll compressors, higher efficiency fan motors, microchannel

heat exchangers, material treatment of heat exchangers, improved air flow and fan design, and

heat pipes.

4.3.1 Scroll Compressors

Although scroll compressors are currently used in residential and commercial air

conditioning applications, they have not yet penetrated the PTAC and PTHP market. Scroll

compressors are more difficult to manufacture than rotary compressors, cost more to

manufacture, and are also physically larger than rotary compressors.

DOE determined that manufacturers typically produce scroll compressors with cooling

capacities of approximately 20,000 Btu/h or higher, and that the majority of equipment using

scroll compressors is typically rated at capacities higher that 40,000 Btu/h. Manufacturers also

produce scroll compressors with housings larger than those used for compressors found in

PTACs and PTHPs. DOE found that scroll compressors are typically built to be 16 inches or

higher in height and that capacity ratings do not impact scroll compressor heights significantly.

For example, DOE found that the height of a scroll compressor only decreases by approximately

1.5 inches when capacity decreases from 80,000 to 20,000 Btu/h. However, significant

improvements in efficiency, when compared to rotary compressors, are generally achieved with

higher capacity models. DOE also found that scroll compressors typically weigh 50 pounds or

more, compared with the 25 to 30 pounds for a PTAC/PTHP rotary compressor found in PTACs

and PTHPs.

Thus, cost, weight, and height hinder the incorporation of scroll compressors in PTACs

and PTHPs. For PTACs and PTHPs to use current market scroll compressors, the equipment’s

wall sleeve dimensions would have to increase and other components would have to be resized.

In addition, currently available scroll compressors are not rated for the relatively lower capacities

(i.e., fractional horsepower ratings) required for PTACs and PTHPs. Since it is not currently

practical to manufacture scroll compressors in the sizes necessary for use in PTACs and PTHPs,

DOE screened out scroll compressors as a design option for improving the energy efficiency of

PTACs and PTHPs in the engineering analysis.

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4.3.2 Higher Efficiency Fan Motors

Manufacturers of PTACs and PTHPs use high efficiency permanent split capacitor (PSC)

fan motors due to their modest cost, high efficiency, compact design, and durability. Developing

more efficient PSC motor designs applicable to PTACs and PTHPs is an ongoing industry

challenge, and there have been no substantial gains in efficiency in recent years. PSC

manufacturers can improve efficiency by increasing the surface area of rotors, although the

overall size of the PSC motor would increase. PTACs and PTHPs have size constraints that do

not allow an increase in motor size to a level which would have a significant impact on energy

efficiency. DOE believes any further gains in PSC fan motor efficiency will be difficult to

achieve due to the size constraints of the equipment and because the impact on the EER would

be low. Therefore, DOE believes that it would not be practicable to manufacture, install, and

service this technology on the scale necessary to serve the relevant market at the time of the

effective date of an amended standard.

Besides PSC­based fan motors, PTAC and PTHP original equipment manufacturers

(OEMs) can choose to implement electronically commutated permanent magnet (ECM) or

direct­current (DC) motors. Both ECM and DC fan motors typically uses a brushless permanent

magnet (BPM) design for economy and longevity. Such motors may offer higher efficiencies

than PSC­based fan motors, but size implementation and cost issues have so far precluded the

industry from adopting them in any but a handful of units. Additionally, because the PTAC and

PTHP industries have a relatively small number of annual shipments, manufacturers typically

have to choose their motors from existing motor lines, rather than having motors customized for

their specific needs. The type of motor and its power rating are typically indicative of its

efficiency. For example, shaded pole motors are generally the lowest efficiency motors that are

available, particularly at very low power levels. By contrast, the electronically commutated

motors (ECM) or brushless permanent magnet motors (BPMs) are typically the most efficient

motors for the low power levels.

DOE determined that the PTAC and PTHP industries have not adopted ECMs or similar

high efficiency motors due to size and weight constraints. The size limitation is particularly

problematic when given the installation limitations of the sleeve sizes for PTACs and PTHPs,

particularly for non­standard PTACs. Ultimately, DOE screened out high efficiency motors as a

viable design option. DOE found that high efficiency motors are not available in the full ranges

of sizes needed for the PTAC and PTHP industries making it unlikely that this technology option

could be readily applied to these products. Therefore, it would not be practical to manufacture,

install, and service this technology on the scale necessary to serve the relevant market at the time

of the effective date of an amended standard. DOE did not consider BPM­based motors as a

design option for improving the energy efficiency of PTACs and PTHPs.

4.3.3 Microchannel Heat Exchangers

DOE found that microchannel heat exchangers are already incorporated in certain types

of air conditioning equipment. Specifically, microchannel heat exchangers are presently used in

condensers of automobile air conditioners and have been demonstrated in field tests of

prototypes of commercial unitary air conditioners. Micro­channel heat exchangers have a

rectangular aluminum cross­section containing several small channels through which refrigerant

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passes. Aluminum fins with a corrugated shape are brazed at a 90­degree angle between the

rectangular tubes. Micro­channel heat exchanger designs provide more heat transfer per volume

of heat exchanger core, can provide more heat transfer per unit of face area, and have lower

airside pressure drop.

DOE determined that micro­channel heat exchangers have inherent problems with

performance and condensate removal when installed in PTAC equipment. In particular,

manufacturers observed that the smaller airflow passages between plate fins are subject to

clogging in installations where debris is present, which can affect both the heat exchanger and

fan motor performance. Additionally, for PTACs and PTHPs operating in cooling mode,

condensate buildup on the evaporator of the installation may result in icing, which is harder to

remove from small horizontal micro­channel heat exchanger passages than from the vertical fins

found in the currently used tube and fin heat exchangers.

For the reasons stated above, manufacturers have chosen not to install micro­channel heat

exchangers in PTAC and PTHP designs. DOE determined that this technology has not yet

penetrated the PTAC and PTHP industry and that design challenges still exist. At this time,

DOE believes microchannel heat exchangers are technologically infeasible in PTAC and PTHP

applications. DOE understands that manufacturers are conducting research into the use of microchannel heat exchangers in their PTACs and PTHP design at this time. However, DOE does not

have definite knowledge of whether their research efforts will be successful, of when mircochannel heat exchangers could appear in either prototypes or equipment designs, and what the

contribution to system performance would be. Because this technology is in the research stage

for the PTAC industry, it is also not possible to assess whether it will have any adverse impacts

on equipment utility to customers or equipment availability, or on customer health or safety.

DOE believes it would not be practicable to manufacture, install and service this

technology on the scale and in the timeframe necessary to serve the relevant market at the time

of the effective date of an amended standard. Also, because this technology is in the research

stage, it is not possible to assess whether it will have any adverse impacts on equipment utility to

customers or equipment availability, or any adverse impacts on customers' health or safety.

Therefore, DOE screened out microchannel heat exchanger as a design option for improving the

energy efficiency of PTACs and PTHPs.

4.3.4 Material Treatment of Heat Exchangers

Material treatment of heat exchangers significantly improves their efficiency by allowing

the condensate that forms on the fins to be repelled and drained efficiently. Using material

treatment of heat exchangers to enhance the heat transfer properties is currently a patented

technology and only used by one PTAC and PTHP manufacturer. Mass production of the

patented technology is not practical and can not be achieved on the scale necessary to serve the

PTAC and PTHP market at the time of the effective date of the standard because it is proprietary

to only one manufacturer. Therefore, DOE screened out material treatment of heat exchangers as

a design option for improving the energy efficiency of PTACs and PTHPs.

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4.3.5 Improved Air Flow and Fan Design

Insulation material is commonly used in air conditioning equipment because it reduces

heat transfer between component sections. PTAC and PTHP manufacturers already apply small

quantities of insulation between the indoor and outdoor section of the PTACs and PTHPs.

However, the primary purpose of this insulation is for soundproofing rather than for heat transfer

application. The volumetric constraints of PTACs and PTHPs severely restrict the amount of

insulation that can be added. Because only a small amount of insulation can be applied, the heat

transfer benefits are negligible and therefore do not improve efficiency.

While tangential fan systems may offer marginally better heat exchanger performance

(i.e. the same cooling effect at a higher average heat exchanger temperature), volumetric

restrictions preclude their use. Tangential fans require slightly larger fan motors than propeller

or “squirrel­wheel” fan designs and require the use of separate fan motors for each heat

exchanger. The marginal EER gain by a tangential fan may be negated by the extra heat

produced by the larger fan motors required for tangential blowers. Tangential fan designs also

require different fan plenum shapes, which can decrease the space that can be used to increase

the heat exchangers area. Increasing the heat exchanger area has significantly larger EER gain

than increasing fan efficiency.

Single­fan units limit the design to one fan axis, which limits the design to either

propeller or blower fans. Manufacturers already optimize propeller or blower fans to suit each

motor power rating by maximizing air flow while minimizing the material used. This

optimization allows for minimum possible fan shaft power to be delivered to the fan while

generating the required airflow. All PTACs and PTHPs units having single­fan designs use the

“slinger” design fans to improve efficiency by spraying collected condensate on the condenser

coil. Because PTACs and PTHPs have size constraints, the fan dimensions are also constrained,

which limits the improvement in efficiency. Also, more efficient fan designs are an ongoing

industry challenge, and there has not been a substantial gain in efficiency in recent years.

In some PTACs and PTHPs, manufacturers have designed the unit to have separate fan

motors (or dual­fan motor) for each heat exchanger so energy can be conserved under varying

operating conditions. Dual­fans in PTACs or PTHPs allow the OEM to optimize a fan blade and

motor for each heat exchanger. Dual­fan units can also address variable conditions better by

reducing the speed of or even switching off a fan motor. Because the ARI 310/380­2004 test

procedure calls for steady state test conditions, there is no opportunity for varying the operation

time of each motor and therefore both motors would need to be on. DOE understands that dualfan PTACs and PTHPs have motors that are equally power rated and that the sum of the energy

consumed by both motors is fairly equal to that of a single­fan PTAC or PTHP fan motor.

Although separate fan motors for each heat exchanger conserve energy in real world situation, it

does not improve EER under the ARI’s test procedures. For the technical reasons outlined

above, DOE screened out improved air flow and fan design as a design option for improving the

energy efficiency of PTACs and PTHPs.

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4.3.6 Heat Pipes

Under humid ambient conditions, using heat pipes to pre­treat the entering air from the

conditioned space can improve the evaporator heat exchangers performance. Heat pipes pre­cool

the entering air (i.e., remove some sensible heat and increase the relative humidity level), which

means the evaporator heat exchanger has to remove less heat from the air. By reducing the need

for heat removal by the evaporator heat exchanger, less work is required by the compressor and

energy is conserved. A draw back to heat pipes is that they partially block the airflow to the

evaporator heat exchanger, which actually decreases the performance of the evaporator heat

exchanger and therefore decreases the EER of the equipment. Although heat pipes have the

potential of reducing energy consumption in humid conditions, in standard conditions they have

the potential to decrease EER. Also, the use of heat pipes in PTAC and PTHP design is currently

patented technology and only used by one manufacturer of PTACs and PTHPs.

Because heat pipes have the potential to decrease EER in certain conditions, it is not

practical to implement them into PTAC and PTHP design. Also, mass production of the

patented technology is not practical and can not be achieved on the scale necessary to serve the

PTAC and PTHP market at the time of the effective date of the standard because it is proprietary

to only one manufacturer. Therefore, DOE screened out heat pipes as a design option for

improving the energy efficiency of PTACs and PTHPs.

4.4 REMAINING TECHNOLOGIES

After eliminating those technologies that have no effect or do not increase EER and

screening out those technologies that that do not meet the requirements of sections 4(a)(4) and

5(b) of the Process Rule, DOE is considering the technologies in the following list.

• Higher efficiency compressor.

• Increase heat exchanger area (extension of surface area or addition of coil rows).

• Re­circuiting heat exchanger coils.

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