Carrier 39E/ER - Manual

HEATING & COOLING
39E/ER
Fan Motors and Drives
Application Data
Fan Motors and Drives for Central Station Air-Handling Units
60 Hertz
INTRODUCTION
The same careful attention given to the selection of the
fan should be afforded to the selection of the fan motor
and drive. It is the purpose of this publication to define
the major factors involved in the selection procedures for
these most important components
Factory Installed or Field Supplied? — This
decision is a very basic and important one. Basic, in that it
needs to be made early, in the ordering phase of the job.
Important, in that the results of the motor and drive
selection directly affect the satisfactory performance and
economical operation of the equipment selected.
Limitations — Every fan has limitations relating to
maximum speed and shaft horsepower. Refer to Table 1
for maximum fan horsepower and fan speed limits on
standard 39E/ER air handlers.
Fixed or Variable? — Fixed drives are recommended
for all applications. However, variable pitch drives are
often specified because they permit fan speed (thus, sys­
tem air volume) to be easily field adjusted. Unfortunately,
this advantage is usually offset by balancing problems
inherent in their design that cause vibration and prema­
ture belt wear, especially in the higher horsepower drives.
For this reason, variable pilch drives with motors larger
than 25 hp are not recommended and are not available
from the factbrv.
NOTE: In the event that such a field-supplied drive
proves unsatisfactory, contact the drive supplier for any
additional technical assistance required
Service Factor — Almost all drives are subject to
occasional overload, consequently it is good engineering
practice to have ample capacity designed into the drive to
take care of these overloads. Although higher service
factors will extend the belt life, they will also increase the
drive loss, resulting in reduced energy efficiency. A
reasonable service factor for fans is considered to be
1.2 to 1.5.
Drive Loss — Proper allowance should be made so the
motor selected does not run overloaded. The major
factors in drive efficiency are the load on the belt and the
bending radius of the belt around the pulley. Belt tension,
operating temperature and drive alignment also con­
tribute to drive losses. Considering these factors, the
drive loss is generally between 2 to 6% of the maximum
fan brake horsepower. Using a 3% selection allowance is
reasonable.
Motor Speed — Generally, 1800-rpm motors are used
on 39E Series air handlers, All factory-supplied standard
drives are designed for 1800 rpm, except for some smaller
airfoil units that require 3600-rpm motors due to space
limitations. Larger motors in certain size units may
require an optional (L5) cabinet extension.
Table 2 gives a complete summary of standard motor
sizes, limitations, and speeds. Tables 3 dnd 4 give a com­
plete summary of space and sheave limitations of all fan
unit sizes with all NEMA standard motors.
Open Drip Proof (ODP) or Totally Enclosed
Fan-Cooled (TEFC) Motors(Fig. 1) — ODP motors
are recommended. Compared to TEFC motors, ODP
motors are less expensive, have a higher service factor
and are normally more readily available from vendor
stock.
The 39E/ ER motors are mounted in the unit airstream
and operate with cool air passing over the motor. This
provides additional cooling to windings and motor bear­
ings and increases the life of the motor, thereby reducing
the need for a TEFC motor.
The ODP motors have ventilation openings that allow
air over and around the motor windings to keep the
temperature as low as possible.
The TEFC motors utilize an internal fan to cool the
motor windings. They do not have any openings for venti­
lation air.
Totally enclosed air over (TEAO) motors rely on
strictly unit airflow to cool the motor windings. They do
not have an internal fan or openings for ventilation air.
Voltage — The nominal power system voltage will
normally be more than the motor nameplate voltage.
NEMA standards are as follows:
Nominal Power System
Voltage
208
240
480
600
Motor Nameplate
Voltage
200
230
460
575
Field-Installed Inverters — High-efficiency motors
are recommended whenever an inverter is field installed
to control fan speed. High-efficiency motors can handle
the extra heat generated much better than standard
motors. The projected life of the motor when controlled
by an inverter will be improved if a high-efficiency motor
is used.
Manufacturer reserves the right to discontinue, or change at any time, specifications or designs without notice and without incurring obligations.
Book 13 PC201 Catalog No 513-907 PrintedinUSA Form 39E-15XA Pg 1 4-89 Replaces: 39E-12XA
Tab 1b