4-i

CHAPTER 4. SCREENING ANALYSIS

TABLE OF CONTENTS

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

4.2 TECHNOLOGY OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

4.3 EMERGING TECHNOLOGIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

4.3.1 Electro-Hydrodynamic Enhanced Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . 4-2

4.3.2 Copper Rotor Motor with Improved Efficiency . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4.3.3 Non-HFC/HCFC Refrigerants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

4.3.3.1 Ammonia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4.3.3.2 Carbon Dioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

4.3.3.3 Hydrocarbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

4.4 COMMERCIAL TECHNOLOGIES THAT CAN ENHANCE EER . . . . . . . . . . . . . . 4-8

4.4.1 Evaporator Coil Area (Keeping Coil Rows the Same) . . . . . . . . . . . . . . . . . . . 4-9

4.4.2 Condenser Coil Area (Keeping Coil Rows the Same) . . . . . . . . . . . . . . . . . . . . 4-9

4.4.3 Coil Rows (Keeping Coil Heat Transfer Performance the Same) . . . . . . . . . . 4-10

4.4.4 Coil Rows (Keeping Face Area the Same) . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10

4.4.5 Microchannel Heat Exchangers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11

4.4.6 Deep Coil Heat Exchangers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12

4.4.7 Low Pressure-Loss Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12

4.4.8 High-Efficiency Fan Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12

4.4.9 High-Efficiency Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

4.4.10 Air-Foil Centrifugal Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

4.4.11 Backward-Curved Centrifugal Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14

4.4.12 Synchronous (Toothed) Belt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-14

4.4.13 Direct Drive Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15

4.4.14 High-Efficiency Propeller Condenser Fans and Motors . . . . . . . . . . . . . . . . . 4-15

4.4.15 Condenser Fan Diameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16

4.4.16 Evaporator Fan Diameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-16

4.4.17 Elimination of Air Leakage Paths within Unit . . . . . . . . . . . . . . . . . . . . . . . . 4-16

4.5 SCREENING PROCESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

LIST OF TABLES

Table 4.5.1 Design Options Not Viable for Consideration in the Engineering Analysis . . 4-18

Table 4.5.2 Design Options Viable for Consideration in the Engineering Analysis . . . . . 4-19
a

 Although the Process Rule specifically applies only to new or revised energy conservation standards for consumer

products, the Department applies its procedures to new or revised standards for industrial equipment as well. 

4-1

CHAPTER 4. SCREENING ANALYSIS

4.1 INTRODUCTION

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

the Act) establishes energy-efficiency standards and test procedures for certain commercial,

unitary, air cooled air conditioners and air source heat pumps rated at or greater than 65,000

Btu/h, but less than 240,000 Btu/h. (42 U.S.C. 6313(a)(1) and (2) Further, the Act provides

criteria for prescribing new or amended standards which will achieve the maximum

improvement in energy efficiency, which the Secretary of Energy determines is technologically

feasible and economically justified. (42 U.S.C. 6313(a)(6)(A)) It also establishes guidelines for

determining whether a standard is economically justified. (42 U.S.C. 6313(a)(6)(B))

In view of the EPCA requirements for determining whether a standard is technologically

feasible and economically justified, 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 the DOE in the consideration and promulgation of

new or revised product efficiency standards under EPCA.a

 These procedures elaborate on the

statutory criteria provided in 42 U.S.C. 6313 and in part eliminate problematic design options

early in the process of revising an energy efficiency standard. Under the guidelines, before

publishing an advance notice of proposed rulemaking (ANOPR), DOE eliminates from

consideration design options that present unacceptable problems with respect to the following

four factors:

• technological feasibility;

• practicability to manufacture, install and service;

• adverse impacts on equipment utility to consumers or availability; and

• adverse impacts on health or safety.

The Department will not consider a technology that does not meet any one of the above

guidelines. 10 CFR Part 430, subpart C, appendix A, at paragraph 5(b)(1)-(4). Also, the

Department understands that there are potential energy savings associated with technologies and

techniques that can improve the net annual energy performance of a system, but which generally

reduce the energy efficiency ratio (EER) of commercial unitary air-conditioning equipment, or

have no effect on EER. Because the energy-efficiency standards for commercial unitary airconditioning equipment in 42 U.S.C. 6313(a)(1)(C) and (2)(A) are measured and expressed in

terms of EER, the Department will not consider those technologies at this time.
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This screening analysis evaluates commercial unitary air conditioning and heat pump

technologies as possible design options that, in view of the above guidelines, would improve

energy efficiency and be technologically feasible and practicable to manufacture, install and

service, have no adverse impact on utility or availability to consumers, and have no adverse

impact on health or safety. If a particular design option meets all four criteria, DOE will

evaluate the design option further for its effect on energy efficiency performance and reveal the

results of that evaluation when it publishes a Notice of Proposed Rulemaking (NOPR) in

connection with these products.

4.2 TECHNOLOGY OPTIONS

For the commercial unitary equipment covered under this rulemaking, there is a rather

long list of design options that can enhance the equipment’s energy efficiency. Design options

fall into one of two categories based on their development status and impact on the equipment’s

EER:

• Emerging technologies

• Commercial technologies that enhance EER

4.3 EMERGING TECHNOLOGIES

Emerging technologies are those technologies that are currently unavailable on the

commercial market but are being examined in the laboratory as possible means to enhance

efficiency. The following technologies within this category are further described below:

• Electro-hydrodynamic enhanced heat transfer,

• Copper rotor motor with improved efficiency, and

• Non-hydrofluorocarbon/hydrochlorofluorocarbon (HFC/HCFC) refrigerants (e.g.,

ammonia, carbon dioxide, and hydrocarbons).

4.3.1 Electro-Hydrodynamic Enhanced Heat Transfer

Electro-hydrodynamic enhancement (EHD) of heat transfer is the result of applying a

high-voltage electrostatic potential field across a heat transfer fluid, such as a refrigerant or

refrigerant mixture. The applied field destabilizes the thermal boundary layer, thereby producing

better mixing of the bulk fluid flow and increasing the net heat transfer coefficient. This

procedure appears to be more effective when applied to phase change processes (e.g., boiling

and condensation). The Department had initial studies done with several refrigerants, including

R-123, R-134a, an R-11/Ethanol mixture, and R-404A. For R-134a, EHD provided dramatic

improvements in heat transfer, especially at lower refrigerant qualities (more liquid and less

vapor). This technology may allow manufacturers to produce highly compact heat exchangers
4-3

with less complicated surfaces without sacrificing heat transfer efficiency. Experiments to

analyze the heat transfer coefficient for R-123 in pool boiling showed an increment from a

baseline of about 1.5 kilowatts per square meter Kelvin (kW/m2K) to about 8.5 kW/m2K at an

applied potential of 1800 volts. This phenomenon is typically used to electronically control the

capacity of a heat exchanger by raising the applied voltage to increase the heat transfer. This can

lead to improved efficiencies by using smaller capacity equipment, most of the time without

EHD, and then utilizing the EHD effect during peak loads. Another potential application is to

use continuous EHD enhancement with smaller, less costly heat exchangers. The EHD effect

would offset the loss of heat transfer capacity experienced with the smaller heat exchangers. 

Similarly, EHD can replace, or work in conjunction with, enhanced surface heat exchangers. To

use EHD, an electrical voltage (from a few volts to thousands of volts) is applied to the heat

transfer device. However, because the heat transfer fluids are typically dielectric (of low

electrical conductivity), even high voltages produce very little current. This low current helps

keep the power (voltage times current) and the associated energy penalty low. The required

electronics also represent an increased material cost. More significantly, applying the

electronics would require a more complicated manufacturing process.1

Because electro-hydrodynamic heat transfer is in the research stage, the Department

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. 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 consumers or equipment

availability, or any adverse impacts on consumers' health or safety. Therefore, DOE will not

consider electro-hydrodynamic heat transfer as a design option for improving the energy

efficiency of commercial unitary air cooled air conditioners and air source heat pumps.

4.3.2 Copper Rotor Motor with Improved Efficiency

Making the critical components of an induction motor's rotor (e.g., conductor bars and

end rings) out of copper instead of aluminum improves the energy efficiency of the motor. The

greater conductivity of copper results in lower resistance heating losses in the rotor and thus

lower losses in the motor. In fact, for the case of similar motor rotors, copper rotors can reduce

the electric motor total energy losses by between 15 percent and 23 percent. Further

improvements in the design and fabrication of copper motors, such as optimization of the steel

laminations, could further increase the efficiency of copper motors over aluminum motors.2

 

However, the die casting process for aluminum rotors is well-established, contrary to the

die casting for copper. Copper melts at higher temperatures than aluminum, resulting in higher

thermal stresses in the die mold, which in turn cause cracks to appear in the mold after short

periods of operation. These technical barriers have impeded the manufacture of the copper cast

rotor.3

 Because of these technological issues, the Department believes that it would not be

practicable to manufacture, install and service copper rotor motors for use in commercial unitary

air cooled air conditioners and air source heat pumps on the scale necessary to serve the relevant

market at the time of the standard’s effective date. Also, because copper rotor motors are in the
4-4

research stage of development, it is not possible to assess whether this technology will have any

adverse impacts on equipment utility to consumers or equipment availability, or any adverse

impacts on consumers’ health or safety. Therefore, DOE will not consider copper rotor motor

technology as a design option for improving the energy efficiency of commercial unitary air

cooled air conditioners and air source heat pumps.

4.3.3 Non-HFC/HCFC Refrigerants

Three non-HFC/HCFC refrigerants, ammonia (NH3), carbon dioxide (CO2), and various

hydrocarbons (such as propane and isobutane), are technologically feasible replacements for

HFC and HCFC refrigerants used in commercial unitary air-conditioning equipment rated at or

greater than 65,000 Btu/h, but less than 240,000 Btu/h. Due to the impending phaseout of

HFC/HCFC-based refrigerants, the Department examined each of these three refrigerants as a

possible alternative for this rulemaking. Although these alternative refrigerants are technically

feasible for use in commercial unitary air-conditioning equipment, they do not necessarily

improve energy efficiency.

Typically, the refrigerant, and the design of the air-conditioning system that uses it, must

be examined on a case-by-case basis to determine the actual energy efficiency of that system. 

However, “cycle efficiency” is one metric that can be used to estimate the relative benefit of one

refrigerant compared to other refrigerants. (See Chapter 19, “Refrigerants,” in the 2001

ASHRAE Handbook – Fundamentals.4

) An ideal cycle efficiency is related to the

thermodynamic efficiency of an air conditioner and it is calculated based on (1) the refrigerant

properties at each state of the thermodynamic cycle, and (2) the net energy that must be removed

or added to the refrigerant to complete the cycle. Of these three refrigerants, only ammonia has

an ideal cycle efficiency above those of the HFC refrigerants currently being used for the

commercial unitary air-conditioning equipment covered under this rulemaking. While a

comparison between the efficiencies of hydrocarbon refrigerants and hydrofluorocarbon

refrigerants provides mixed results, in every case CO2 is the least efficient of the alternative

refrigerants under consideration. Also see the Alliance for Responsible Atmospheric Policy

Report, and the section concerning replacement refrigerants for commercial unitary air

conditioners at http://www.arap.org/adlittle/summary.html (March 2004) and Section 1 of the

report at http://www.arap.org/adlittle/1.html. (March 2004).

In addition to technological feasibility and energy efficiency concerns, the Department

investigated: (1) the practicability to manufacture, install, and service commercial unitary air

conditioners that would potentially use ammonia, carbon dioxide, or hydrocarbons; (2) possible

adverse impacts on equipment utility and availability to consumers; and (3) potential adverse

impacts on health and safety.
4-5

4.3.3.1 Ammonia

Ammonia is currently used in large industrial refrigeration systems (e.g., cold storage

warehouses) and some laboratory refrigeration systems, and although its use in commercial

unitary air-conditioning systems is technologically feasible, ammonia presents significant

problems in commercial unitary air-conditioning systems used to cool buildings. Problems

include adverse effects on safety and health, as well as on the manufacturing, installation and

service of commercial unitary air-conditioning equipment rated at or greater than 65,000 Btu/h,

but less than 240,000 Btu/h. It is not likely that the combined effect of all these problems will be

overcome before the effective date of an energy efficiency standard.

Large industrial refrigeration systems (as opposed to air-conditioning systems) almost

exclusively use ammonia. It is a hazardous substance and service personnel are specially

trained, certified, and equipped to work around it. Any transition to the use of ammonia in

smaller air-conditioning systems would require significant re-training and re-certification of air

conditioning service personnel, more so than a change to any HFC-based alternatives. Although

it is technologically feasible to train such service personnel, it is unlikely that there would be a

sufficient number of them available with the level of expertise needed to work with ammoniabased air-conditioning systems by the effective date of an energy efficiency standard.

In the presence of any amount of water, ammonia exhibits no tolerance to some materials

commonly used in the manufacture of air-conditioning equipment. Ammonia is highly corrosive

to the copper tubing used in air-conditioning equipment, and would require changing to a

different tubing material (e.g., galvanized carbon steel or stainless steel) and method of

manufacture of heat-exchanger coils. Further, the higher tensile strength of stainless steel might

require new machinery and possibly new manufacturing methods to produce coils in the volume

needed to meet demand. Ammonia can also be corrosive to copper wiring and other components

used in hermetic compressor motors and would, therefore, require development of entirely new

lines of compressors apart from those currently being manufactured for commercial unitary airconditioning equipment. This is already true for existing ammonia-based refrigeration

equipment, such as food freezers, where large open compressors, or in some cases semi-hermetic

compressors, are used. One manufacturer recently designed a small hermetic scroll compressor

for ammonia in which all of the copper in the motor has been replaced with aluminum, but other

examples of this are not known. See http://www.mycomj.co.jp/eindex/mycorole.html (March

2004).

Furthermore, because there are few, if any, examples of compression-based ammonia airconditioning systems in the size ranges covered by the rulemaking, any transition to ammoniabased systems would require massive changes in the design and manufacture of the compressors

and other components. It is unlikely that such changes would occur by the effective date of an

energy-efficiency standard even if no other issues were present with the use of ammonia.

Safety is perhaps the most significant issue with ammonia. Ammonia used in

compression-based refrigeration systems is anhydrous (without water) and has very high purity
4-6

(>98 percent). It is flammable in concentrations of 16 to 25 percent with air, and presents a

potential fire hazard in the event of a leak. The Environmental Protection Agency (EPA)

classifies ammonia in this form as an extremely hazardous substance. The U.S. Occupational

Safety and Health Administration (OSHA) classifies ammonia as a material that is hazardous to

occupant and worker safety. The American National Standards Institute (ANSI)/American

Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 34-

2001, Designation and Classification of Refrigerants,5

 lists ammonia in Safety Group B2 because

it is highly toxic, even in low concentrations with air. Further, ANSI/ASHRAE Standard 15-

2001, Safety Code for Mechanical Refrigeration,6

 limits the amount of ammonia in any

refrigeration equipment. The National Institute for Occupational Safety and Health (NIOSH)

sets the level of exposure for a normal person to ammonia (1⁄2 hour without a respirator and no

lasting effects) at 500 parts per million (ppm). The NIOSH considers exposure to 2400 ppm of

ammonia for 30 minutes as life threatening. Local safety codes may be more restrictive. An

ammonia leak inside a building, including any potential use in commercial unitary air

conditioning systems, can adversely effect human health.

For all the reasons outlined above, the Department has screened out the use of ammonia

as an alternative refrigerant for this rulemaking.

4.3.3.2 Carbon Dioxide

Carbon dioxide naturally exists in the atmosphere, and it does not have the toxicity or

flammability issues that are associated with ammonia or hydrocarbons as refrigerants. In recent

years, CO2 has received significant interest due to its good environmental properties. The main

focus of this interest has been in automotive air conditioners, where large refrigerant emissions

may occur.

Carbon dioxide was used as a refrigerant prior to the mid 1950s. The use of CO2 in large

commercial unitary air-conditioning systems is technologically feasible; however, it presents

several problems. The critical temperature of CO2 is 87.8 /F; therefore heat rejection occurs

above the critical point in a typical comfort cooling application. This means that CO2 does not

operate in a typical vapor compression cycle realized by the conventional refrigerants, but in a

transcritical cycle. This transcritical cycle offers a lower efficiency than the vapor compression

cycle due to the significant irreversibilities in the throttling and CO2-to-air heat rejection. 

Although some of these irreversibilities could be minimized by new heat exchanger designs and

work-producing expansion devices, the recovery of heat transfer and throttling irreversibilities

can only be accomplished with limited effectiveness. Consequently, it may be expected that the

potential for high system efficiency using CO2 is lower than that for refrigerants realizing the

conventional vapor compression cycle.7

Commercial unitary air-conditioning systems that would potentially use CO2 as a

refrigerant would need to withstand pressures that are much higher than those employing

hydrofluorocarbon-based refrigerants. This would require development of new designs for

compressors, heat exchangers, service equipment, and other critical components, which are much
4-7

more durable than the conventional designs for these devices. Furthermore, the high pressure

makes handling and servicing a CO2-based system more difficult and would require specially

trained personnel. The combination of these problems makes it unlikely that CO2-based

commercial unitary air-conditioning systems could be manufactured, installed, and serviced to

the extent necessary to serve the relevant market by the effective date of a new energy-efficiency

standard. For these reasons, the Department has screened out the use of CO2 as an alternative

refrigerant for this rulemaking. 

4.3.3.3 Hydrocarbons

Hydrocarbons, such as isobutane, propane, propylene and ethane, are technologically

feasible for use as refrigerants. However, due to safety concerns, their use has been limited to

industrial applications, laboratory applications, and small capacity systems such as refrigerators. 

Industrial refrigeration applications generally refer to complex customized appliances used in the

chemical, pharmaceutical, petrochemical, and manufacturing industries. Industrial refrigeration

applications do not include air conditioning, which pipes refrigerated air directly into occupied

areas, because hydrocarbon refrigerants are highly flammable gases, even in small

concentrations of 1 to 10 percent in solution with air.

The ANSI/ASHRAE Standard 34-2001 classifies hydrocarbons “A3,” highly flammable. 

The National Fire Protection Association (NFPA), National Electrical Code Handbook, Article

500-5(a)(4), classifies propane as Class I Group D and describes it, in part, as a flammable gas

mixed with air that may burn or explode. Also, building codes in some states and local

jurisdictions regulate the use of hydrocarbons as potential refrigerants, including prohibiting the

use of hydrocarbons in automobile air conditioners. It follows that these regulations reduce

direct risk to human health and safety from the use of hydrocarbons in these applications by

restricting access to areas near those systems.

Flammability is the major liability of hydrocarbons. It makes manufacturing, transport,

storage, installation, and service of unitary equipment more difficult. Commercial unitary airconditioning equipment that uses a hydrocarbon refrigerant would likely need to include safety

features to protect against the possibility of fire and explosion. New designs would have to be

developed and new sensing/control capabilities to be implemented to mitigate the flammability

risks.8

 Trained personnel would need to follow special safe handling and installation procedures.

Because of the above concerns, the availability of hydrocarbon refrigerants for consumer

use is limited, and this situation is unlikely to change by the effective date of an energy

efficiency standard. For all these reasons, the Department has screened out hydrocarbons as

alternative refrigerants for improving the energy efficiency of commercial unitary air cooled air

conditioners and air-source heat pumps.

In summary, because of these technological issues with the ammonia, carbon dioxide,

and hydrocarbons, DOE will not consider these three alternative refrigerants as design options

for improving the energy efficiency of commercial unitary air cooled air conditioners and air
4-8

source heat pumps. 

4.4 COMMERCIAL TECHNOLOGIES THAT CAN ENHANCE EER

There are a number of technologies or design options which are currently commercially

available for commercial unitary air cooled air conditioners and air source heat pumps and

related equipment and which DOE proposes to consider to improve the EER (nominal full load)

rating. A typical example is improving compressor efficiency at the nominal rating conditions. 

Technologies within this category are:

• Evaporator Coil Area (Keeping Coil Rows the Same),

• Condenser Coil Area (Keeping Coil Rows the Same),

• Coil Rows (Keeping Coil Heat Transfer Performance the Same),

• Coil Rows (Keeping Face Area the Same),

• Microchannel Heat Exchangers,

• Deep Coil Heat Exchangers,

• Low Pressure-Loss Filters,

• High-Efficiency Fan Motors,

• High-Efficiency Compressors,

• Backward-Curved Centrifugal Fans,

• Air-Foil Centrifugal Fans,

• Synchronous (Toothed) Belts,

• Direct-Drive Fans,

• High-Efficiency Propeller Condenser Fans,

• Condenser Fan Diameters,

• Evaporator Fan Diameters, and

• Elimination of Air Leakage Paths Within Unit.
4-9

4.4.1 Evaporator Coil Area (Keeping Coil Rows the Same)

Increasing the evaporator coil area provides for a greater heat exchange area between the

cold refrigerant and the supply air. This increases the heat transfer effectiveness of the coil and

the overall efficiency of the air conditioning system. Increasing the evaporator coil area

increases the average temperature of refrigerant in the coil and reduces the temperature

difference between the refrigerant and the supply air. However, increasing the evaporator coil

area also tends to reduce the latent heat removal capability of the evaporator coil.

As a result of its technology options screening assessment, the Department finds that

manufacturers already incorporate a wide variation in evaporator coil area in certain commercial

unitary air cooled air conditioners and air source heat pumps. The wide variation in evaporator

coil area in units currently on the market suggests that further increases in coil area by

manufacturers would be technologically feasible. Further, evaporator coils are currently used in

all commercial unitary air-cooled air conditioners and air source heat pumps, thus demonstrating

that they are practical to manufacture, install and service. Evaporator coils are a necessary

component in commercial unitary equipment, and there are a number of coil manufacturers who

supply such products to manufacturers. Since evaporator coils are a necessary component of

existing equipment and suppliers are numerous, the Department anticipates no adverse impacts

on product utility to consumers or product availability from an increase in the evaporator coil

area. Finally, the fact that commercial unitary equipment currently uses evaporator coils is

evidence that adverse impacts on consumers' health or safety from increasing evaporator coil

area are unlikely. Therefore, the Department believes this design option is viable for

consideration in the engineering analysis.

4.4.2 Condenser Coil Area (Keeping Coil Rows the Same)

Increasing the condenser coil area provides for a greater heat exchange area between the

hot refrigerant vapor leaving the compressor and the outside air. A greater area where the heat

exchange occurs reduces the temperature of the liquid refrigerant entering the expansion device. 

This increases the specific refrigeration capacity of the refrigerant and the efficiency of the entire

system. In general, increasing the condenser coil face area provides for higher system

efficiency, at the expense of more materials and often greater total system size. 

As a result of this technology options screening assessment, the Department finds that

manufacturers already incorporate a wide variation in condenser coil area in certain commercial

unitary air-cooled air conditioners and air-source heat pumps. The wide variation in condenser

coil area in units currently on the market suggests that further increases in coil area by

manufacturers would be technologically feasible. Further, condenser coils are currently used in

all commercial unitary air-cooled air conditioners and air-source heat pumps, thus demonstrating

that they are practical to manufacture, install and service. Condenser coils are a necessary

component in commercial unitary equipment, and there are a number of coil manufacturers who

supply such products to manufacturers. Since condenser coils are a necessary component of
4-10

existing equipment and suppliers are numerous, the Department anticipates no adverse impacts

on product utility to consumers or product availability from an increase in the condenser coil

area. Finally, the fact that commercial unitary equipment currently uses condenser coils is

evidence that adverse impacts on health or safety to consumers from increasing condenser coil

area are unlikely. Therefore, the Department believes this design option is viable for

consideration in the engineering analysis.

4.4.3 Coil Rows (Keeping Coil Heat Transfer Performance the Same)

Decreasing the number of coil rows (in the evaporator or condenser) decreases the static

pressure drop over the coil, resulting in less work for the supply fan. However, as the number of

rows decreases, the heat exchange capacity of the coil decreases. This option is typically

combined with other design options that increase capacity, such as increasing the coil face area,

to maintain the desired rate of heat transfer across the coil surface. The difficulty here is

primarily finding space for the additional coil area. 

Notwithstanding the possibility of fewer rows of coils and corresponding decreases in

heat exchange capacity, the Department finds that manufacturers already reduce the number of

rows of coils in combination with other design options to maintain constant heat transfer in

certain commercial unitary air-cooled air conditioners and air-source heat pumps. The wide

variation in the number of rows of coils in units currently on the market suggests that changes in

the number of rows of coils in particular designs would be not only technologically feasible, but

also practical to manufacture, install and service. Coils are a necessary component in

commercial unitary equipment and there are a number of coil manufacturers who supply such

products to unitary equipment manufacturers. Since coils are a necessary component of existing

equipment and since suppliers are numerous, the Department anticipates no adverse impacts on

product utility to consumers or product availability. Finally, the fact that coils are currently used

in commercial unitary equipment is evidence that adverse impacts on health or safety to

consumers from changing the number of rows of coils are unlikely. Therefore, the Department

believes this design option is viable for consideration in the engineering analysis.

4.4.4 Coil Rows (Keeping Face Area the Same)

Increasing the number of coil rows increases the heat exchange capacity of a coil, but

also results in an increase in the static pressure drop over the coil, causing the fan to work

harder. In addition, most of the heat exchange in a multi-row coil takes place in the first rows in

contact with the incoming air, with each subsequent row providing less heat exchange than the

preceding row. There are diminishing returns from adding more coil rows. However, this may

be the only viable option to increasing heat transfer rates in systems with space constraints. 

Another concern for unitary package equipment used in a commercial building is that the supply

fan also operates for heating and for ventilation whenever the building is occupied. Therefore,

the supply fan typically operates many more hours than the cooling system. This presents a

problem for design options that increase supply fan energy because an increase in overall energy

use would result in a reduction in the EER.
4-11

Notwithstanding possible diminishing returns to improvements in EER as well as

increases in fan energy use, the Department finds that manufacturers already increase the number

of rows of heat exchanger coils while keeping the face area constant, combined with other design

options to maintain constant heat transfer, in certain commercial unitary air-cooled air

conditioners and air-source heat pumps. The wide variation in the number of rows of coils in

units currently on the market suggests that changes in the number of rows of coils in particular

designs would be not only technologically feasible, but also practical to manufacture, install and

service. Coils are a necessary component in commercial unitary equipment, and there are a

number of coil manufacturers who supply such products to unitary equipment manufacturers. 

Since coils are a necessary component of existing equipment and suppliers are numerous, the

Department anticipates no adverse impacts on product utility to consumers or product

availability. Finally, the fact that coils are currently used in commercial unitary equipment is

evidence that adverse impacts on health or safety to consumers from changing the number of

rows of coils are unlikely. Therefore, the Department believes this design option is viable for

consideration in the engineering analysis.

4.4.5 Microchannel Heat Exchangers

Microchannel heat exchangers, unlike a conventional coil tube with an attached plate fin,

have a rectangular aluminum cross-section containing several small channels through which

refrigerant passes. Aluminum fins are brazed between the rectangular tubes. All components

are aluminum. Microchannel designs provide more heat transfer per unit of face area than a

conventional coil design, while creating a lower pressure drop than a similarly performing

conventional coil. The small size and lower air-side pressure drop that results from

microchannel heat exchangers provide opportunities to reduce the size and weight of the heat

exchanger. That is why they are used in automobile air conditioners. However, the

microchannel heat exchanger has not penetrated building air conditioning markets, where size

and weight constraints are not as critical. In particular, the microchannel construction hinders

condensate removal, which makes its application for evaporator coils in unitary air conditioners

(and in heat pumps, both coils) difficult. However, this limitation would not prevent it from

being used for the condenser coils, where no condensate removal is required.

The Department finds that microchannel heat exchangers are already incorporated in

certain types of air conditioners. The wide variation in condenser coil area in units currently on

the market suggests that further changes in coil area by manufacturers would be technologically

feasible. Further, microchannel heat exchangers are being used in greater numbers of air

conditioners, thus demonstrating that they are practical to manufacture, install and service. Since

condenser coils are a necessary component of existing equipment and suppliers are numerous,

the Department anticipates no adverse impacts on product utility to consumers or product

availability from the use of microchannel heat exchangers in those condenser coils. Finally, the

fact that condenser coils are currently used in commercial unitary equipment is evidence that

adverse impacts on health or safety to consumers from changing the condenser coil area are

unlikely. Therefore, the Department believes this design option is viable for consideration in the

engineering analysis.
4-12

4.4.6 Deep Coil Heat Exchangers

The deep coil design option changes the typical evaporator coil design to one that uses

more rows of coil tubing with fewer fins per inch. The goal of the deep coil design is to provide

the advantages of a multi-row coil, which are compactness, good heat transfer, and good

dehumidification capability, while minimizing the static pressure impact. 

The Department finds that deep coil heat exchangers are already incorporated in certain

commercial unitary air cooled air conditioners and air source heat pumps. Because this is a

design variation in typical evaporator coil design, the technological feasibility, and practicability

to manufacture, install and service these types of coils have already been discussed in Section

4.4.1. Therefore, the Department believes this design option is viable for consideration in the

engineering analysis.

4.4.7 Low Pressure-Loss Filters

The purpose of low pressure-loss filter designs is the reduction of total system fan power

requirements. This is principally achieved by increasing the total face area of the filter design,

including modifications to the filter rack as well as the use of pleated filters. This allows for a

reduction in the average air velocity over the filter face and subsequent reduction in fan power.

The Department finds manufacturers already incorporate low pressure-loss filters in

certain commercial unitary air-cooled air conditioners and air-source heat pumps. Widespread

application of this simple technique to reduce fan power makes it not only technologically

feasible, but also practical to manufacture, service and install. Thus, the Department anticipates

no adverse impacts on product utility to consumers or product availability. Finally, the fact that

filters are currently used in commercial unitary equipment is evidence that adverse impacts on

health or safety from improving the pressure loss in the filters are unlikely. Therefore, the

Department believes this design option is viable for consideration in the engineering analysis.

4.4.8 High-Efficiency Fan Motors

High-efficiency electric motors that drive supply fans and condenser fans can increase

efficiency and reduce overall energy use in commercial air conditioning equipment and heat

pumps. From an energy conservation standpoint, this is particularly important for supply fans

because they also provide commercial building ventilation and typically operate for several times

the total operating hours of the air conditioning compressor. Further, both condenser and supply

fan motor efficiency improvements can increase full- and part-load efficiency for unitary

equipment. Typical supply fan motors for unitary package equipment in this size range (65,000

Btu/h to 240,000 Btu/h cooling capacity) are between 1.5 and 5 horsepower (hp) in size, with

motor efficiencies regulated under EPCA. (42 U.S.C. 6311 et seq., as amended) However,

motor efficiencies of four percentage points higher than EPCA levels are available throughout

this size range, and their use results in increased overall system efficiency.9
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The Department finds that high-efficiency fan motors are readily available and are

already incorporated in certain commercial unitary air-cooled air conditioners and air-source

heat pumps. Widespread application of high-efficiency fan motors to increase the system

efficiency not only makes them technologically feasible, but also practical to manufacture,

service and install. Thus, the Department anticipates no adverse impacts on product utility to

consumers or product availability. Finally, the fact that motors are currently used in commercial

unitary equipment is evidence that adverse impacts on health or safety to consumers from

improving the motor efficiency are unlikely. Therefore, the Department believes this design

option is viable for consideration in the engineering analysis.

4.4.9 High-Efficiency Compressors

Motors drive compressors and fans in heating, ventilating and air conditioning (HVAC)

equipment. Because virtually all such compressors are hermetic designs, the overall compressor

efficiency includes motor-efficiency. Higher efficiency compressor designs are an ongoing

industry challenge, and there have been substantial gains in compressor efficiency, which

translate into more-efficient air conditioning systems. Any further gains in compressor

efficiency will be more difficult to achieve. Previous DOE reviews of improvements in

compressor efficiency suggest that compressor manufacturers anticipate no more than a three

percent improvement by 2007 in compressor efficiency, based on design changes.10

The Department finds that high-efficiency compressors are already incorporated in

certain commercial unitary air-cooled air conditioners and air-source heat pumps. Widespread

application of high-efficiency compressors to increase the system efficiency not only makes

them technologically feasible, but also practical to manufacture, service and install. Thus, the

Department anticipates no adverse impacts on product utility to consumers or product

availability. Finally, the fact that high-efficiency compressors are currently used in commercial

unitary equipment is evidence that adverse impacts on health or safety to consumers from further

improvements to the compressor efficiency are unlikely. Therefore, the Department believes this

design option is viable for consideration in the engineering analysis.

4.4.10 Air-Foil Centrifugal Fans

Air-foil centrifugal fans can operate at efficiencies near 90 percent, but because of the

need to shape each fan blade and the need for greater detail in the inlet scroll design, these fans

are more technically complicated than either backward-curved or forward-curved fans.11

Although this particular design feature of fan blade designs may be more complicated to

manufacture, as a result of this technology options screening assessment, the Department finds

that air-foil centrifugal fans can be incorporated in certain commercial unitary air-cooled air

conditioners and air-source heat pumps. Further, widespread application of this technology to

increase fan system efficiency not only makes it technologically feasible, but also practical to

manufacture, service and install. Thus, the Department anticipates no adverse impacts on

product utility to consumers or product availability. Finally, the fact that certain air conditioning
4-14

and ventilating applications currently use air-foil centrifugal fans is evidence adverse impacts on

health or safety to consumers from improving the fan efficiency are unlikely. Therefore, the

Department believes this design option is viable for consideration in the engineering analysis.

4.4.11 Backward-Curved Centrifugal Fans

A backward-curved centrifugal fan has the tips of its blades inclined away from the

direction of the airflow (backwards), enabling it to move air at higher pressures. The backwardcurved blade fan is most efficient when it is built with blades that are made in an air-foil shape.12

Backward-curved fan designs have typical efficiencies near 80 percent, compared to the 65-70

percent efficiency common for forward-curved fan designs used for supply air fans in most

unitary HVAC equipment. However, backward-curved fans are larger than forward-curved fans

providing the same pressure and air flow. In addition, the higher tip speed of the backwardcurved fans can increase fan noise. 

Even though issues with increased fan dimensions and noise exist, as a result of this

technology options screening assessment, the Department finds that backward-curved centrifugal

fans are available on the market and already incorporated in certain commercial unitary aircooled air conditioners and air-source heat pumps. Widespread application of this technology to

increase fan system efficiency not only makes it technologically feasible, but also practical to

manufacture, service and install. Thus, the Department anticipates no adverse impacts on

product utility to consumers or product availability. Finally, the fact that certain applications

currently use backward-curved centrifugal fans is evidence adverse impacts on health or safety

to consumers from improving the fan efficiency are unlikely. Therefore, the Department

believes this design option is viable for consideration in the engineering analysis.

4.4.12 Synchronous (Toothed) Belt

Synchronous belts (also called timing, positive-drive, or high-torque drive belts) are

toothed, require the installation of engaging toothed-drive sprockets, and can be applied to

supply-air fan drives. Synchronous belts offer about 98 percent efficiency and maintain that

high efficiency over a wide load range.12 The automotive industry uses them in various

applications. The HVAC equipment industry recognizes the higher efficiency of this type of

belt, but has elected not to use it in its equipment due to the additional complexity of design and

manufacturing. 

Although the synchronous belt design and manufacturing may be more complicated, as a

result of this technology options screening assessment, the Department finds that synchronous

belts could be incorporated in certain commercial unitary air-cooled air conditioners and airsource heat pumps. Since the automotive industry uses the synchronous belts, they are not only

technologically feasible but also practical to manufacture, install, and service. More widespread

application within the heating, ventilating, and air conditioning industry would likely encourage

simpler designs and standardize manufacturing practices. With additional suppliers of these

belts, the Department anticipates no adverse impacts on product utility to consumers or product
4-15

availability. Since the belts are currently used in competing industries, adverse impacts on

health or safety to consumers are unlikely. Therefore, the Department believes this design

option is viable for consideration in the engineering analysis.

4.4.13 Direct Drive Fans

In a direct-drive fan, the fan wheel connects directly to the motor. Direct drive fans

prevent the sharp reduction in efficiency caused by belt drive slippage. 

The Department finds that certain commercial unitary air-cooled air conditioners and airsource heat pumps already incorporate direct drive fans. Widespread application of this simple

technique to increase fan system efficiency not only makes it technologically feasible, but also

practical to manufacture, service and install. Thus, the Department anticipates no adverse

impacts on product utility to consumers or product availability. Finally, the fact that direct-drive

fans are currently used in certain applications is evidence that adverse impacts on health or

safety to consumers from wider use of direct drive fans are unlikely. Therefore, the Department

believes this design option is viable for consideration in the engineering analysis.

4.4.14 High-Efficiency Propeller Condenser Fans and Motors

The condenser section of a commercial unitary air conditioner typically uses a propeller

fan to provide high air flow rates for this typically low-pressure application. Because propeller

fans are inherently low-pressure devices, they achieve maximum efficiency results even in cases

of zero external pressure.13 Unitary air conditioning equipment designs that minimize pressure

drop across the outdoor condensing coil can maximize fan efficiency. In addition, commercial

HVAC equipment typically uses multiple propeller-type, fractional-horsepower-motor fans, and

there is significant potential for increasing the efficiency of these small fan motors. Currently,

there is a wide range of energy-efficiency levels for such small motors on the market, and there

are no energy-efficiency standards. Use of advanced motor technologies, such as electronic

commutation and copper rotors, can improve the efficiency of a condenser fan from a range of

40-60 percent to a range of 85-90 percent.14 

The Department finds that high-efficiency propeller condenser fans and high-efficiency

motors are already incorporated in certain commercial unitary air-cooled air conditioners and airsource heat pumps. Widespread application of high-efficiency fans and motors to increase fan

system efficiency not only makes them technologically feasible, but also practical to

manufacture, service and install. Finally, the fact that condenser fans are currently used in

commercial unitary equipment is evidence that adverse impacts on health or safety to consumers

from improving the efficiencies of these components are unlikely. Therefore, the Department

believes this design option is viable for consideration in the engineering analysis.
4-16

4.4.15 Condenser Fan Diameters

Increasing condenser fan diameters would increase the amount of air passing through the

condenser coils per unit of fan energy, thereby increasing the fan system efficiency. Generally,

the biggest problem is finding space for these larger fan units within an already spaceconstrained cabinet.

Even with possible space constraints, the Department finds that increased diameters for

condenser fans are already incorporated in certain commercial unitary air-cooled air conditioners

and air-source heat pumps. Widespread application of this simple technique to increase fan

system efficiency not only makes it technologically feasible, but also practical to manufacture,

service and install as long as space is available. Finally, the fact that evaporator fans are

currently used in commercial unitary equipment is evidence that adverse impacts on health or

safety to consumers from increasing the fan diameter are unlikely. Therefore, the Department

believes this design option is viable for consideration in the engineering analysis.

4.4.16 Evaporator Fan Diameters

Increasing evaporator fan diameters would increase the amount of air passing through the

evaporator coils per unit of fan energy, thereby increasing the efficiency of the fan system. 

Generally, the biggest problem is finding space for these larger fan units within an already spaceconstrained cabinet.

Although there are possible space constraints, the Department finds that increased

diameters for evaporator fans are already incorporated in certain commercial unitary air-cooled

air conditioners and air-source heat pumps. Widespread application of this simple technique to

increase fan system efficiency not only makes it technologically feasible, but also practical to

manufacture, service and install as long as space is available. Finally, the fact that evaporator

fans are currently used in commercial unitary equipment is evidence that adverse impacts on

health or safety to consumers from increasing the fan diameter are unlikely. Therefore, the

Department believes this design option is viable for consideration in the engineering analysis.

4.4.17 Elimination of Air Leakage Paths within Unit

The Department’s engineering analysis of through-the-wall air conditioners found small

air leakage paths between the evaporator and condenser sections which, because of the pressure

differentials, can result in air passing between these sections and loss of efficiency. It appears

that eliminating these air leakage paths in through-the-wall air conditioners, through design or

manufacturing changes, is one of the more cost-effective ways to improve the efficiency of these

units. If similar air leakage paths occur regularly in commercial unitary air conditioners, design

or manufacturing changes to eliminate these leaks may represent a cost-effective way to increase

EER and annual energy performance.

The Department finds that where significant air leakage paths occur in certain unitary air
4-17

conditioners and heat pumps, design and manufacturing practices to reduce the air leakage exist

and are already incorporated in certain commercial unitary air-cooled air conditioners and airsource heat pumps. These practices are, therefore, technologically feasible. Also, because these

practices are widely applicable across different sizes of commercial unitary air conditioning

equipment, they are also practical and cost-effective ways to increase EER and would not have

any adverse impacts on product utility to consumers or on product availability. Finally, the fact

that these design practices are currently used in commercial unitary equipment is evidence that

adverse impacts on health or safety to consumers from eliminating more air leakage paths are

unlikely. Therefore, the Department believes this design option is viable for consideration in the

engineering analysis.

4.5 SCREENING PROCESS

For the purpose of this rulemaking, the Department screened out certain technologies as

design options. These technologies and the principal rationale for screening them out are

summarized in Table 4.5.1.
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Table 4.5.1 Design Options Not Viable for Consideration in the Engineering Analysis

EMERGING TECHNOLOGIES

Electro-Hydrodynamic Enhanced Heat Transfer — This is currently in the design stage.

Practical use of this technology is unlikely in the time frame established in the final rule.

Copper Rotor Motor with Improved Efficiency — Given current manufacturing issues and

small existing product volume for this technology, it is highly unlikely that enough copper

rotor motors will be available in the market in the time frame established in the final rule.

Non-Hydro-Fluorocarbon/Hydro-Chlorofluorocarbon (HFC/HCFC) Refrigerants (e.g.,

Ammonia, Hydrocarbons, CO2) — Long-running safety concerns with ammonia and

hydrocarbons are likely to preclude their use in any commercial systems developed within the

next few years in the United States. High pressures and low critical temperatures make design

of commercially viable CO2 air conditioning systems unlikely to occur in time for the final

rule.
4-19

While many of the technologies discussed in this report show promise, only certain

design options can improve the EER (nominal full-load) rating under DOE’s test procedures and,

therefore, are viable for consideration in the engineering analysis. These technologies are listed

in Table 4.5.2. 

Table 4.5.2 Design Options Viable for Consideration in the Engineering Analysis

COMMERCIAL TECHNOLOGIES THAT CAN ENHANCE EER

(1) Evaporator Coil Area (Keeping Coil Rows the Same)

(2) Condenser Coil Area (Keeping Coil Rows the Same)

(3) Coil Rows (Keeping Coil Heat Transfer Performance the Same)

(4) Coil Rows (Keeping Face Area the Same)

(5) Microchannel Heat Exchangers

(6) Deep Coil Heat Exchangers

(7) Low Pressure Loss Filters

(8) High-Efficiency Fan Motors

(9) High-Efficiency Compressors

(10) Air-Foil Centrifugal Fans

(11) Backward-Curved Centrifugal Fans

(12) Synchronous (Toothed) Belts

(13) Direct Drive Fans

(14) High-Efficiency Propeller Condenser Fans

(15) Condenser Fan Diameters

(16) Evaporator Fan Diameters

(17) Elimination of Air Leakage Paths Within Unit
4-20

1. Air-Conditioning and Refrigeration Institute. June 2, 2002. Electrohydrodynamic Heat

Transfer [Online]. Available URL: http://www.ari.org/rt/tu/1996/9601b.html

2. Cowie J. and E. Brush. June 4, 2002. Electrical Energy Efficiency Results of Die-Cast

Copper Rotors, Copper Development Association, Inc. [Online Report]. Available URL: 

http://www.copper-motor-rotor.org/pdf/eeresults.pdf

3. Copper Development Association, Incorporated. June 1, 2002. Application of High

Temperature Mold Materials To Die Cast the Copper Motor [Online Report]. Available

URL: http://www.copper-motor-rotor.org/pdf/project_description.pdf

4. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

(ASHRAE) 2001. Refrigerants, Chapter 19, ASHRAE Handbook of Fundamentals,

Atlanta, Georgia.

5. American National Standards Institute/American Society of Heating, Refrigerating and

Air-Conditioning Engineers, Inc. (ANSI/ASHRAE). 2001. Standard 34-2001,

Designation and Classification of Refrigerants, ASHRAE, Atlanta, Georgia.

6. American National Standards Institute/American Society of Heating, Refrigerating and

Air-Conditioning Engineers, Inc. (ANSI/ASHRAE). 2001. Standard 15-2001, Safety

Code for Mechanical Refrigeration, ASHRAE, Atlanta, Georgia.

7. Zhao Y., M.M. Ohade, and Radermacher R. June 5, 2002. Microchannels Heat

Exchangers with Carbon Dioxide: Final Report September 2001 [Online Report]. 

Center for Environmental Energy Engineering, University of Maryland, College Park,

Maryland. Available URL: 

http://www.arti-21cr.org/research/completed/finalreports/10020-final.pdf

8. Keller, F.J., Liang, H., Farzad, M., 1997. “Assessment of Propane as a Refrigerant in

Residential Air-Conditioning and Heat Pump Applications.” ASHRAE/NIST

Refrigerants Conference; Refrigerants for the 21st Century. October 6-7, 1997,

Gaithersburg, MD.

9. United States Department of Energy. July 2, 2002. How to buy a premium energy

efficient motor, Federal Energy Management Program, Energy Efficiency and Renewable

Energy Network [Online Report]. Available URL: 

http://www.eren.doe.gov/femp/procurement/pdfs/motors.pdf

10. United States Department of Energy. July 2, 2002. CAC TSD Technical Support

Document: Energy Efficiency Standards for Consumer Products: Residential Central

Air Conditioners and Heat Pumps, October 2000, Energy Efficiency and Renewable

Energy Network [Online Report]. Available URL:

REFERENCES
4-21

http://www.eren.doe.gov/buildings/codes_standards/reports/cac_hp_tsd/index.html

11. United States Department of Energy. June 3, 2002. Energy Tips: Replace V-Belts with

Cogged or Synchronous Belt Drives. Office of Industrial Technologies [Online Report]. 

Available URL: http://www.oit.doe.gov/bestpractices/pdfs/motor3.pdf

12. United States Army. June 4, 2002. Maintenance of Mechanical And Electrical

Equipment At Command, Control, Communications, Computers, Intelligence,

Surveillance, And Reconnaissance (C4isr) Facilities, HQUSACE/OCE Army Technical

Manuals [Online Report]. Available URL:

http://www.usace.army.mil/inet/usace-docs/armytm/tm5-692-2/chap14VOL-2.pdf

13. American Society of Heating, Refrigerating, and Air Conditioning Engineers

Incorporated. 2000. 2000 ASHRAE AVAC Applications, Atlanta, Georgia

14. Arthur D. Little, Incorporated. April 6, 2003. Opportunities for Energy Savings in the

Residential and Commercial Sectors with High-Efficiency Electric Motors [Online]

Available URL

http://www.eere.energy.gov/buildings/documents/pdfs/doemotor2_2_00.pdf