1、 DEPARTMENT OF THE AIR FORCE HEADQUARTERS AIR FORCE CIVIL ENGINEER SUPPORT AGENCY 18 SEP 2013 APPROVED FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED FROM: AFCEC/DD 139 Barnes Drive Suite 1 Tyndall AFB FL 32403-5319 SUBJECT: Engineering Technical Letter (ETL) 13-6: Energy-Efficient Motors and Adjustable
2、-Speed Drives 1. Purpose. This ETL provides users with application, selection, installation, energy analysis, and repair guidance for energy-efficient motors and adjustable-speed drives (ASD) and supersedes Air Force pamphlet (AFPAM) 32-1192, Energy-Efficient Motors and Adjustable-Speed Drives, date
3、d 1 August 2000. The recommendations in this ETL assure a reliable motor system when upgrading to energy-efficient motors or ASDs. Detailed guidance is provided regarding energy efficiency analysis so potential savings from a particular design can be estimated. ASD design options are described in de
4、tail to ensure that ASD installations do not degrade electrical systems. This ETL supplements Unified Facilities Criteria (UFC) 3-520-01, Interior Electrical Systems. For general criteria and requirements, refer to UFC 3-520-01, Interior Electrical Systems; Air Force manual (AFMAN) interservice publ
5、ication (IP) 32-1083_IP, Facilities Engineering - Electrical Interior Facilities; and AFMAN 32-1082_IP, Facilities Engineering - Electrical Exterior Facilities. Note: Use of the name or mark of a specific manufacturer, commercial product, commodity, or service in this ETL does not imply endorsement
6、by the Air Force. 2. Application. Compliance with this ETL is recommended for energy-efficient motors and ASDs in interior and exterior electrical systems that are the responsibility of the base civil engineer at all facilities and bases. The guidance regarding ASDs also applies to standard-efficien
7、cy motors. 2.1. Authority: Air Force policy directive (AFPD) 32-10, Installations and Facilities UFC 3-520-01, Interior Electrical Systems 2.2. Effective Date: Immediately 2.3. Intended Users: AFCEC/CF Major command (MAJCOM) engineers MAJCOM functional managers Base civil engineers (BCE) Base mainte
8、nance organizations Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 2.4. Coordination: MAJCOM electrical engineers AFCEC/CN AFCEC/CFT 3. Acronyms and Glossary. See Attachment 1, Acronyms and Glossary. 4. References. See Attachment 2, References. 5.
9、 Scope. 5.1. This ETL provides guidance and recommendations regarding energy-efficient motors and ASDs. The guidance addresses energy efficiency analysis and equipment design options. 5.2. This ETL relies on existing industry information and analysis tools. MotorMaster+, a software program for motor
10、 analysis, is discussed in detail because of its wide industry acceptance and ease of use. ASD Calculator for ASD analysis is also discussed. 5.3. Electrical protection associated with energy-efficient motors and ASDs is described in detail because of the unique protection needs associated with this
11、 equipment. 6. Energy Efficiency Criteria and Energy Efficiency Analysis. 6.1. Federal Requirements for Energy Efficiency. 6.1.1. The Energy Independence and Security Act of 2007 (EISA07) requires the Air Force to reduce facility energy intensity (energy consumption per gross square foot), using fis
12、cal year 2003 as the base year, as follows: Fiscal Year Percentage Reduction 2006 2 2007 4 2008 9 2009 12 2010 15 2011 18 2012 21 2013 24 2014 27 2015 30 6.1.2. Code of Federal Regulations, Title 10, Part 434 (10 CFR 434), Energy Provided by IHSNot for ResaleNo reproduction or networking permitted w
13、ithout license from IHS-,-,-3 Code for New Federal Commercial and Multi-Family High Rise Residential Buildings. This regulation establishes performance standards for the design of new federal commercial and multifamily high-rise buildings. Some of the guidelines are relevant to retrofits. 10 CFR 434
14、.401 specifies minimum acceptable full-load motor efficiencies for single-speed polyphase motors that are expected to operate more than 1000 hours per year. 6.1.3. 10 CFR 436, Federal Energy Management and Planning Programs. This regulation establishes procedures for determining the life-cycle cost-
15、effectiveness of energy conservation measures and for prioritizing energy conservation measures in retrofits of existing federal buildings. 6.2. Guidance for Energy Efficiency Analysis. 6.2.1. Electric motor systems that operate continuously or for many hours a year consume electricity that costs ma
16、ny times the price of the motor. This makes less-efficient motors excellent targets for replacement. If the driven load operates at less than full load for a majority of the time, installing ASDs will reduce energy consumption and save operating costs. 6.2.2. Fan motors in air handlers can account f
17、or 20 percent or more of energy usage in a commercial-type building. Energy costs of air distribution systems can be significantly decreased by converting constant-volume systems to variable air volume (VAV) systems or by increasing the efficiency of existing VAV systems. 6.2.3. Good candidates for
18、VAV conversion are constant-volume systems with dual ducts or terminal reheat that use backward-inclined or airfoil fans. On existing VAV systems, convert airflow control from inlet vanes or outlet dampers to ASD control. Figure 1 shows the relative power consumption using outlet dampers, inlet vane
19、s, or ASD control. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4 Figure 1. Variable Air Volume Systems Versus Power Output 6.2.4. In many cases, energy savings can be realized simply by replacing older motors with newer energy-efficient motors. H
20、owever, further savings can often be obtained by evaluating system needs and making an additional minor design change. For example, an exhaust system might be oversized. By using a smaller fan (and motor), a savings of 30 percent to 50 percent might be possible. By installing an ASD, a savings of 50
21、 percent to over 80 percent might be possible. Energy efficiency improvement should be considered at the system level, not just the component (motor) level. 6.2.5. Paragraph 7 provides specific guidance regarding energy savings analyses for motor upgrades and installations. Paragraph 8 provides guid
22、ance for energy savings analyses for the application of ASDs. 7. Energy-Efficient Motors. 7.1. Energy-Efficient Motor Design. 7.1.1. Introduction. 7.1.1.1. When converting electrical energy into mechanical energy, motors have several losses: electrical losses, iron (core) losses, mechanical (frictio
23、n and windage) losses, and stray losses, dependent on design and manufacturing. Energy-efficient motors reduce energy losses through improved design, better materials, and improved manufacturing techniques. With proper installation, energy-efficient motors can run cooler and consequently have higher
24、 effective service factors, longer bearing and insulation life, and less vibration. Energy-efficient motors tend to last 020406080100120020406080100Percent Air FlowPercentPowerConsumptionASDInlet VanesOutlet DamperProvided by IHSNot for ResaleNo reproduction or networking permitted without license f
25、rom IHS-,-,-5 longer and may require less maintenance. By running cooler, bearing grease lasts longer, lengthening the required time before re-greasing. Lower operating temperatures also equate to longer-lasting insulation; insulation life usually doubles for each 18 F (10 C) reduction in operating
26、temperature. Figure 2. Energy-Efficient Motor 7.1.1.2. Energy-efficient motors are manufactured using the same frame as a standard T-frame motor but have the following differences: Higher quality and thinner steel laminations in the stator More copper in the windings Optimized air gap between the ro
27、tor and stator Reduced fan losses Closer matching tolerances Greater length 7.1.1.3. An energy-efficient motor produces the same shaft output power (horsepower) but uses less input power (kilowatts kW) than a standard-efficiency motor. Energy-efficient motors must have nominal full-load efficiencies
28、 that meet or exceed National Electrical Manufacturers Association (NEMA) performance standards. 7.1.1.4. There are several opportunities for selecting an energy-efficient motor for a particular installation, including when purchasing a motor for a new application, considering rewinding of a failed
29、motor, or evaluating the retrofit of an operable but inefficient motor to save energy. Energy-efficient motors should be considered for the following applications: For all new installations When major modifications are made to existing facilities or processes For all new purchases of equipment packa
30、ges that contain electric motors, such as air conditioners, compressors, and filtration systems When purchasing spares or replacing failed motors In place of rewinding standard efficiency motors Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-6 To re
31、place grossly oversized and under-loaded motors When an energy analysis indicates sufficient savings for an application 7.1.2. NEMA Motor Standards. 7.1.2.1. NEMA MG 1, Motors and Generators, establishes standards for the construction and performance of motors. This document is the principal referen
32、ce for motor design, construction, and performance. 7.1.2.2. NEMA has assigned Design classifications that establish operating specifications for different motor types. The Design letter indicates the motors torque characteristics and is an important motor selection consideration. Most induction mot
33、ors are Design B, with Design A being the second-most common type. Table 1 lists the key characteristics of NEMA Designs B, C, and D motors. The Design A motor is a variation of the Design B motor and has a higher starting current and starting torque. Provided by IHSNot for ResaleNo reproduction or
34、networking permitted without license from IHS-,-,-7 Table 1. NEMA Polyphase Motor Designs NEMA Design Starting Current Starting Torque Breakdown Torque Percent Slip B Medium Medium High 5% maximum Design B Applications: Normal starting torque for fans, blowers, rotary pumps, unloaded compressors, so
35、me conveyors, metal-cutting machine tools, miscellaneous machinery. Slight speed change when changing load. C Medium High Medium 5% maximum Design C Applications: High-inertia starts, such as large centrifugal blowers, fly wheels, and crusher drums. Loaded starts, such as piston pumps, compressors,
36、and conveyors. Slight speed change when changing load. D Medium Extra High Low 5% or more Design D Applications: Very high inertia and loaded starts. Considerable variation in load speed. 7.1.2.3. NEMA released specifications for a Design E motor in the October 1994 update to NEMA MG 1. The letter “
37、E” was assigned because it is the next design to be standardized following the Design D motor, not because “E” stands for “efficiency.” Nonetheless, the Design E specification has minimum efficiency values as one of its design requirements, specified in MG 1, Table 12-11. The Design E efficiency req
38、uirements are more stringent than for other motors designated as energy efficient. The Design E motor was specified to satisfy international standards developed by the International Electrotechnical Commission (IEC). IEC has a standard that is slightly less restrictive on torque and starting current
39、 than the Design B motor. This IEC standard allows designs to be optimized for higher efficiency. Design E motors can be used instead of Design A and B motors, with the following considerations: 7.1.2.3.1. For most moderate- to high-usage applications appropriate for a Design A or B motor, the Desig
40、n E motor is usually a better choice for energy efficiency. However, there are slight performance differences between the designs. Design E locked rotor torque requirements are different from Design B. They are required to be somewhat higher than Provided by IHSNot for ResaleNo reproduction or netwo
41、rking permitted without license from IHS-,-,-8 Design B levels for many motors under 20 horsepower and some motors over 200 horsepower, but are allowed to be lower for most motors from 20 horsepower to 200 horsepower. This means that a Design E replacement motor for an existing Design B motor should
42、 be carefully evaluated to ensure it has sufficient torque to start when connected to its load. 7.1.2.3.2. Except for very small motors (under 3 horsepower), Design E motors are allowed to have considerably higher locked rotor (starting) current than Design B motors. (Note that Design A motors still
43、 have no upper limit for their locked rotor current.) In the first 10 milliseconds of starting, any motors current can exceed the nominal locked rotor current. This momentary current spike is called “inrush” current and is likely to be highest of all in Design E motors. High inrush current can cause
44、 false trips by instantaneous trip units. As part of a Design E motor installation, the electrical protection should be reviewed to confirm that the motor will be able to start and accelerate to its full-load speed without tripping the associated electrical protection. In some cases, it might be nec
45、essary to replace the motor starter as part of the motor replacement. 7.1.2.3.3. Although the NEMA standard allows the same slip (up to 5 percent) for Designs A, B, and E motors, the range of actual slip of Design E motors is likely to be lower than for Designs A and B. This lower slip should be fac
46、tored into savings calculations in retrofit situations for variable torque (such as pump and fan) applications. 7.1.3. Motor Efficiency Overview. 7.1.3.1. A standard motor is designed to ensure its temperature rise requirements are satisfied in a cost-effective manner, with motor efficiency being a
47、secondary consideration. To be considered energy efficient, a motor must meet performance criteria published by NEMA. An energy-efficient motor has a nominal full-load efficiency rating that meets or exceeds the efficiency specified in NEMA MG 1, Table 12-10. Manufacturers also sell motors with effi
48、ciencies significantly higher than the NEMA standard and use many terms to describe their most efficient motors, including adjectives such as high, super, premium, and extra, but there is no NEMA standard for any terminology other than energy efficient. These additional terms can create confusion wh
49、en comparing motors; for this reason, always consult the nominal efficiency rating and the minimum efficiency rating. The nominal efficiency rating is the average efficiency of many motors of duplicate design. Even within a group of duplicate design motors there is some variation in actual efficiencies due to variations in motor materials and
