140.925-IOM (APR 2019)
Page 22
XLP3 EVAPORATIVE CONDENSERS
OPERATION
Remote Reset:
Connection of between terminals 5 and 6 latches
triac output in alarm state after set point is exceeded. Opening
the connection will reset the output to non-alarm state.
NOTICE
If the VCOS trips, turn off, then lock and tag out the
electrical supply to the fan motor(s). Adjust the set point
screw an additional 1/4 turn clockwise, and push in the
manual reset button. Start up the fan motor(s) to
determine if the start-up will cause the VCOS to trip.
Repeat this adjustment process until the VCOS no longer
trips when the unit is operated. Make sure to lock out and
tag out the electrical supply to the fan motor(s) before
entering the unit or re-setting the switch, each time an
adjustment to the VCOS is made. After the final adjustment
has been made, start and stop the fan motor(s) two more
times to ensure that the VCOS is properly set.
Figure 20 — Electronic VCOS with Alarm Contact is shown
FAN CONTROL
EC Fan System Fan Control
All EC fan motors are controlled simultaneously by a single 20mA
analog signal where 4mA is 0% speed and 20mA is 100% speed.
NOTICE
With evaporative cooling, a 15 second fan motor delay
will not be noticed when staging up.
Independent Fan Control (Optional)
Independent fan control is standard on all XLP3 Condensers that
are equipped with Belt Drive Fan System. In an operating forced
draft unit with independent fan capabilities and no partitions, idle
fans tend to windmill in the reverse direction. A windmilling fan
poses no threat to the system while turning freely, but can create
a large shock load when the fan motor is suddenly powered up.
Proper staging of fans when starting from a windmilling condi-
tion will prevent excessive stresses on the drive system. There
are two control strategy options:
•
VFD:
The recommended control option is to use a variable
frequency drive to control all of the motors. VFDs regulate
motor speed electronically and start motors with reduced
voltage and frequency. The result is a gentle motor start,
and therefore reduced stress.
•
No VFD
•
Staging Up:
Turn all motors off for 15 seconds.
Following the 15 second delay, bring all required fans
onlinse. Allow for a 1 second time delay between fan
stages to reduce staging current.
•
Staging Down:
Turn off the fan motor. No need for
delays.
NOTICE
For a unit with a VFD, with a switching frequency of 2.5
kHz, the line lead length cannot exceed 100 feet. If the
switching frequency is higher that 2.5 kHz and/or the line
lead length exceeds 100 feet, a dV/dT output filter is
recommended to protect the motor. Since the switching
frequency and maximum line length requirements vary
between VFD and motor suppliers, contact your local
Frick Representative to determine if a dV/dT filter is
required.
Variable Frequency Drive Operation
• Applications utilizing variable frequency drives (VFDs) for
fan motor control must use inverter duty motors built in
compliance with NEMA standard MG-1, Part 31.
• Operation of the unit at a speed which resonates with
components of the drive system or support structure may
result in vibrations which could damage the components
or structure, and/or create objectionable noise. Therefore,
these resonant speed ranges should be identified at start-
up and locked out to prevent operation of the motor at
these resonant speeds. The “Resonant Speed Identification
Procedure” must be conducted on page 22.
• Please refer to the manufacturer’s variable frequency drive
recommended start-up procedure for further information
or consult with your local Frick Representative for any VFD
applications.
NOTICE
The minimum turndown ratio for units with a belt drive is
10:1 (or 6 hz). Units with the oil pump do not have a
minimum speed.
Resonant Speed Identification Procedure
There are several characteristic frequencies at which vibration
levels may resonate with unit structural components. These
include fan speed, motor speed, bearing frequency, and blade
pass frequency. Within the overall operating speed range of a
unit, it is not unusual for one or more of these characteristic
frequencies to excite the structural components over relatively
small speed ranges and create an increase in vibration levels.
If the vibration levels are excessive at these resonant speeds,
they need to be locked out to prevent the VFD from operating
the motor at these speeds. The following procedure describes
how to identify the lockout speed ranges:
• Ensure the VFD that controls the fan motor is off, and the
power to the motor circuit is locked out.
• Attach the accelerometer (provided by others) onto the
box beam as shown in Figure 21. The accelerometer should
be placed on the top of the bearing support channel, near
the fan side bearing, as shown.