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Appliance Standards guidance documents are accessible on the U.S. Department of Energy, Energy 

Efficiency & Renewable Energy web site at: 

http://www1.eere.energy.gov/guidance/default.aspx?pid=2&spid=1.

Guidance Type: Enforcement

Category: Commercial Equipment

Product: Small, Large, and Very Large, Air-Cooled, Water-Cooled, and Evaporatively-Cooled Commercial 

Package Air Conditioners and Heat Pumps, Water-Source Heat Pumps, Single Package Vertical Units, 

and Computer Room Air Conditioners

Product Sub-type: All

Guidance Version: DRAFT

Issued: June 29, 2015

Comment Period Ends: July 29, 2015

The following is a draft U.S. Department of Energy (DOE or the Department) document regarding how to 

evaluate whether small, large, and very large air-cooled, water-cooled, and evaporatively-cooled 

commercial package air conditioners and heat pumps, water-source heat pumps, single package vertical 

units, and computer room air conditioners offered for sale with a variety of high static indoor blower or

oversized motor to qualify for a related DOE enforcement policy. 

This draft document is seeking comment regarding the best way to effectuate an enforcement policy 

and is not an interpretation of DOE’s regulations.

Comments and suggestions should be provided in WordPerfect, Microsoft Word, PDF, or text file format 

by sending an email to ComHVACMotorGuidance@ee.doe.gov. Please also include the docket number

EERE-2015-BT-GUID-0011. At the end of the comment period, this draft document may be adopted or

revised.

During a negotiated rulemaking regarding Certification for Commercial Heating, Ventilation, AirConditioning, Water-Heating, and Refrigeration Equipment, DOE agreed to adopt an enforcement policy 

under which DOE would not test a model of HVAC equipment with a high-static indoor blower or oversized motor provided (1) the manufacturer offers an otherwise equivalent model that contains a 

“standard motor” and (2) the high static indoor blower/oversized motor has the same (or better) 

relative efficiency performance as the “standard motor”. Due to time constraints in the negotiation, the 

parties did not define how to compare the efficiencies of motors for the purposes of this policy, but the 

parties did talk through and agree to the concept broadly. Instead, the parties agreed DOE would issue 

guidance to resolve that issue after accepting additional comment on the details of the procedure.

DOE proposes the following approach to compare the efficiencies of a “standard motor” and a highstatic indoor blower/oversized motor (“oversized motor”):

Standard Motor Oversized Motor OK to substitute oversized motor? (DOE would 

not test a unit with the oversized motor.)

Subject to standards

Can be tested with DOE TP

Subject to standards

Can be tested with DOE TP

Yes, if relative efficiency of oversized motor is at 

least as good as performance of standard motor

Subject to standards Not subject to standards Yes, if relative efficiency of oversized motor is at 
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Can be tested with DOE TP Can be tested with DOE TP least as good as performance of standard motor

Not subject to standards

Can be tested with DOE TP

Subject to standards

Can be tested with DOE TP

Yes, if relative efficiency of oversized motor is at 

least as good as performance of standard motor

Not subject to standards

Can be tested with DOE TP

Not subject to standards

Can be tested with DOE TP

Yes, if relative efficiency of oversized motor is at 

least as good as performance of standard motor

Subject to standards

Can be tested with DOE TP

Not subject to standards

Cannot be tested with 

DOE TP but can be tested 

with industry method

Cannot substitute oversized motor

Not subject to standards

Can be tested with DOE TP

Not subject to standards

Cannot be tested with 

DOE TP but can be tested 

with industry method

Cannot substitute oversized motor

Not subject to standards

Cannot be tested with 

DOE TP but can be tested 

with industry method

Not subject to standards

Cannot be tested with 

DOE TP but can be tested 

with industry method

Yes, if relative efficiency of oversized motor is at 

least as good as performance of standard motor –

and both motors are tested using same industry 

method

No standard test method No standard test method Cannot substitute oversized motor

Motors with 

horsepower < 1 

Motors with 

horsepower < 1 

Cannot substitute oversized motor

Motors with 

horsepower < 1

Motors with 

horsepower ≥ 1

Cannot substitute oversized motor

Determining relative efficiency of the motor

Compare the percent losses of the standard motor to the percent losses of the oversized motor. The 

percent losses in a standard or oversized motor are determined by comparing each motor’s wattage 

losses to the wattage losses of a corresponding reference motor. Although DOE appreciates that a 

variety of motor sizes, construction, and purposes are used in HVAC equipment, the HVAC members of 

the Commercial Certification Working Group stated that it was unfamiliar with the standards tables for 

electric motors and recommended that DOE should adopt a relatively simple way for DOE to implement 

its enforcement policy with respect to motor substitution. Accordingly, DOE does not believe that the 

reference motors need to reflect such a level of granularity because the motors generally scale in a 

similar manner. 

The Federal standard levels for 4 pole, open frame, general purpose electric motors (subtype I) (see 10 

CFR 431.25(a)) would be used to scale the performance of the standard motor to an oversized motor 

whether the motors are subject to Federal standard levels or not. Use the following steps to determine 

if an oversized motor is a suitable substitute for the standard motor for the purposes of DOE’s 

enforcement policy.

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Note, that 10 CFR 429.71 requires manufacturers to retain documentation supporting its certifications of compliance. 

Accordingly, any manufacturer using this methodology is required to maintain documentation of how the standard and 

oversized motor’s losses were determined and the supporting calculations specified below to demonstrate that it had ensured 

the substituted motor is authorized under the enforcement policy.
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1. Using the tested efficiency of the standard motor, determine the wattage losses of the standard 

motor (Lossstd) with the following equation, where ηstd is the tested efficiency of the standard motor 

and hpstd is the horsepower of the standard motor: 

Lossstd = 746 ∗ hpstd ∗

1−ηstd

ηstd

2. Determine the appropriate reference motor efficiency corresponding to the standard motor

(standard motor reference efficiency, ηrs). Using the Federal standard levels for 4 pole, open frame, 

general purpose electric motors (subtype I) in 10 CFR 431.25(a), look up the efficiency level that 

corresponds to the standard motor’s horsepower. 

3. Using the standard reference motor efficiency, determine the percent losses of the standard 

reference motor (Lossrs) with the following equation, where ηrs is the standard reference motor 

efficiency and hprs is the horsepower of the standard reference motor (hprs is equivalent to the 

horsepower of the standard motor):

Lossrs = 746 ∗ hprs ∗

1−ηrs

ηrs

4. With the wattage losses for both the standard motor and the standard reference motor, calculate 

the percentage losses of the standard motor as follows:

%Loss = 100 ∗

(Lossrs−Lossstd)

Lossrs

5. Determine the appropriate reference motor efficiency corresponding to the oversized motor 

(oversized motor reference efficiency, ηro). Using the Federal standard levels for 4 pole, open frame, 

general purpose electric motors (subtype I) in 10 CFR 431.25(a), look up the efficiency level that 

corresponds to the oversized motor’s horsepower. 

6. Using the oversized reference motor efficiency, determine the percent losses of the oversized 

reference motor (Lossro) with the following equation, where ηro is the oversized reference motor 

efficiency and hpro is the horsepower of the oversized reference motor (hpro is equivalent to the 

horsepower of the oversized motor):

Lossro = 746 ∗ hpro ∗

1−ηro

ηro

7. With the wattage losses for the oversized reference motor (Lossro) and the percent losses of the 

standard motor (%Loss), determine the allowable losses in watts for the oversized motor. 

Allowable Losses = (1 − %Loss) ∗ Loss ro

8. From the allowable losses, the minimum efficiency for the oversized motor (ηo) can be calculated 

according to the following equation, where hpo is the horsepower for the oversized motor.

ηo = 100 ∗

(hpo∗746)

(hpo∗746+Allowable Losses)
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9. The oversized motor is an acceptable substitute for the standard motor if the tested efficiency of the 

oversized motor is greater than or equal to ηo.

Example: A basic model commercial air conditioner was rated with a 5hp motor that has an efficiency of 

91.7%. If a manufacturer wants to sell this basic model commercial air conditioner with a 10hp motor as 

well, what is the minimum efficiency required for the 10hp motor?

The standard motor for this basic model of commercial air conditioner is the 5hp with an efficiency of 

91.7%. The wattage losses of the standard motor are:

Lossstd = 746 ∗ hpstd ∗

1 − ηstd

ηstd

= 746 ∗ 5hp ∗

1 − 0.917

0.917 = 337.6W

The reference motor efficiency corresponding to the standard motor is determined by looking up the 

appropriate value based on the standard motor’s horsepower in the Federal standard levels for 4 pole, 

open frame, general purpose electric motors (subtype I) in 10 CFR 431.25(a) . The reference efficiency 

for 5hp motor is 89.5%. 10 CFR 431.25(a). The standard reference efficiency is used to calculate the 

wattage losses for the standard reference motor.

Lossrs = 746 ∗ hprs ∗

1 − ηrs

ηrs

= 746 ∗ 5hp ∗

1 − 0.895

0.895 = 437.6W

Using the wattage losses for the standard motor and standard reference motor, calculate the percent 

losses. 

%Loss = 100 ∗

(Lossrs − Lossstd)

Lossrs

= 100 ∗

(437.6 − 337.6)

437.6

= 22.8%

Therefore, if a manufacturer wants to use a 10hp oversized motor in this commercial air conditioner 

basic model then the oversized motor must have at least 22.8% fewer losses than the corresponding 

oversized reference motor. 

The efficiency of the oversized reference motor can be found by looking up the efficiency for a 10hp in 

the Federal standard levels for 4 pole, open frame, general purpose electric motors (subtype I) in 10 CFR 

431.25(a). The oversized reference motor efficiency for the 10hp motor is 91.7%. (10 CFR 431.25(a)) 

Calculate the oversized reference motor’s wattage losses from the efficiency of the oversized reference 

motor:

Lossro = 746 ∗ hpro ∗

1 − ηro

ηro

= 746 ∗ 10hp ∗

1 − 0.917

0.917 = 675.2W

Then determine the allowable losses in watts for the oversized motor.

Allowable Losses = (1 − %Loss) ∗ Loss ro = (1 − 0.228) ∗ 675.2W = 521.3 W

Finally, determine the acceptable minimum efficiency for the oversized motor. 

ηo = 100 ∗

(hpo ∗ 746)

(hpo ∗ 746 + Allowable Losses)

= 100 ∗

(10hp ∗ 746)

(10hp ∗ 746 + 521.3W)

= 93.5%
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In summary, a 10hp motor with a minimum efficiency of 93.5% is an acceptable substitute for a 5hp 

standard motor with 91.7% efficiency according to DOE’s propose enforcement policy. 

Acceptable 10hp motor efficiency ≥ ηo

93.5% > 91.7% ∴ substitution permitted