In HVAC Applications

Electric motors In HVAC applications

Discussion:

Premium efficiency motors operating at a nominal 1800 rpm with class f insulation are readily available but can cost more than lower efficiency class b insulation motors. If the motor is needed immediately, an uninformed purchaser might buy the cheaper motor rather than the premium efficiency motor even though the utility may pay the initial cost difference and the improved efficiency will pay the cost difference many times over during the life of the new motor.

If the failed motor is “inverter rated” or operates at a nominal speed other than 1800 rpm, it may be difficult to quickly acquire a premium efficiency replacement.

Premium efficiency motors typically operate at a slightly higher rpm than less efficient motors (perhaps 1780 vs. 1750 rpm) so if accommodations are not made, the driven equipment (fan, pump, etc.) Will turn faster and create more flow/pressure thus increasing energy consumption. The purchaser should try to closely match full load motor speeds or adjustments should be made at the time of replacement. This is not an issue if variable frequency drives (vfds) are used.

Motor & VFD procurement strategy: try to purchase only 1800-rpm premium efficiency motors. Specify VFDs that are compatible with standard motors rather than “inverter rated” motors. Take the time to match motor speeds or make speed adjustments to driven equipment.

Yes, this takes time, planning and communication but it can save thousands of dollars during the life of a motor. Motormaster+ is an excellent tool for developing a motor procurement strategy and for determining rpm, efficiency and approximate cost of most motors.

http://www1.eere.energy.gov/manufacturing/tech_deployment/software_motor master.html Instructions for the new construction designer

1. The owner wants motor driven systems that use “off the shelf” premium efficiency motors so when the motor fails, an appropriate replacement can be found in local stock. In order to make this possible, we specify Variable Frequency Drives that are compatible with standard motors. If the designer creates a need for an unusual motor (900 RPM, metric, inverter rated, etc.) It will not be replaced in kind when it fails. 2. Endeavor to use NEMA rated 1800 RPM motors with Class F insulation when appropriately matched to the driven equipment. Do not select motor speeds requiring V-belt drive reduction ratios greater than 6 to 1. 3. The type of control for every motor shall be identified on the drawings. 4. Motor bearings shall be factory lubricated, for motors less than 1/3 HP. Sleeve bearings will only be permitted for fractional HP motors and where specifically recommended by the equipment manufacturer as the better type of bearing for the application. Ceramic bearings may be cost justified. 5. Vertical shaft motors for special application shall be equipped with suitable thrust bearings. 6. Shaded pole-type motors are not acceptable except for motors less than 1/8 HP. 7. Motors shall typically be open drip-proof construction. Totally enclosed or explosion proof types shall be provided where conditions dictate. 8. Voltage ratings for motors shall be as follows:  Less than 1/2 HP and 1/2 HP sizes for intermittent light duty, such as sump pumps, door operators, unit heaters, etc.,: 120 volt  Fractional HP motors in “above ceiling” terminal devices may be 120 or 277 volt single phase.  Motors 1/2 HP and larger: continuous operation 460, 460/230/208, 3 phase. Connect to 460 volt source when available.  Motors less than 5 HP in variable speed applications may be 277 volt or less when wire runs longer than 50 feet are necessary between the ASD and motor.  Motors over 150 hp: coordinate with THE OWNER. 9. Motors shall be sized to operate between 70% and 95% of full motor load when running at full speed. If a larger future load is anticipated, size and position the motor mounting pad to accommodate the larger anticipated motor frame size. 10.Avoid exposing motors to the weather. Install motors in penthouses or other suitable enclosures. Motors mounted in equipment exposed to the weather shall be of the totally enclosed type, even though a weatherproof enclosure is provided. HVAC electric motor specification

Part 1

1.01 General

A. Scope

1. These standards apply to the selection and installation of electric motors used in hvac applications. Coordinate all requirements and references with other divisions.

B. Related documents

1. Division 15: adjustable speed drives.

2. Division 16: motor controls (including disconnects) power factor correction and identification.

C. Codes, regulations, and standards

1. Motors shall conform to NEMA. Standards for each specific purpose and application.

A. Meet or exceed prevailing energy code.

B. Motor shall be listed and labeled by a recognized laboratory such as UL or ETL.

Part 2

2.01 Products

A. Motors 3 HP and larger shall meet the following nominal efficiency requirements:

B. Motors shall be rated for "continuous duty," with class f insulation and the service factor shall be 1.15 for three-phase motors and 1.35 for single-phase motors.

C. Every motor shall have its unique serial number clearly engraved or stamped on a non-corrosive metal nameplate at the factory. This nameplate shall be permanently attached to the motor with metal fasteners.

End of section