Figure 54 - Typical Vfd Enclosure Locations; Ycal0043 – 0066 Low Ambient Fan Control Option - York YCAL0019 Installation, Operation And Maintenance Manual

SECTION 8 – UNIT OPERATION
YCAL0043 – 0066 LOW AMBIENT FAN
CONTROL OPTION
General
The low ambient option consists of a VFD (Variable
Frequency Drive) for each system that controls the
speed of the first fan (Fan 1, Sys #1 or Fan 2, Sys # 2)
in the fan staging sequence. The VFD's are located in
an enclosure in the compressor/piping/heat exchanger
section on (2) compressor chillers. System # 1 VFD
is located on the bottom and System # 2 is on the top.
Single system chillers have the VFD installed on the
top of chiller above the compressor section. Examples
of the typical VFD location and enclosure mountings
are shown in Figures 54 and 55.
The VFD will control fan speed when only a single
fan is running on a system. As discharge pressure ris-
es, the fan speed will be increased from zero RPM to
full speed. As discharge pressure continues to rise, the
VFD will operate the fan at full speed and the second
fan will be brought ON in a system, if needed. When-
ever the second fan is brought ON, the inverter will
already be running the first fan at full speed.
If discharge pressure falls, the chiller microprocessor
will turn the second fan OFF by de-energizing the fan
contactor. If pressure continues to fall, VFD speed will
decrease in an effort to maintain discharge pressure.
Speed may drop to the point where the VFD turns the
fan completely OFF or virtually OFF with a continued
drop in pressure.
Dual System VFD Enclosure Locatio

FIGURE 54 - TYPICAL VFD ENCLOSURE LOCATIONS

196
The VFD control input signal is from the discharge
pressure transducer in the respective system. The
transducer signal feeds both the chiller microprocessor
board input and the VFD.
The VFD will control the fan speed not only in low
ambient conditions, but in all ambients based on dis-
charge pressure. Speed control of the respective sys-
tem will occur whenever high voltage power is applied
to the VFD power inputs through the 7M (Sys 1) or
10M (Sys 2) contactors. The chiller microprocessor
will energize the 7M and 10M contactors whenever
the respective system liquid line solenoid is energized.
The VFD controls the speed of the fan based on a
discharge pressure setpoint and a differential control
range. When a compressor starts in a system, the in-
verter is activated through the 7M (Sys 1) or 10 M (Sys
2) contactor, which is controlled from the respective
liquid line solenoid valve control signal. At discharge
pressures below 260 PSIG, the VFD will turn the fan
OFF or speed will be reduced to small movements in
fan rotation.
The VFD will ramp up the speed of the fan as pres-
sure rises above the low end of the speed control range.
Throughout the pressure control range, the VFD con-
trols the speed of the fan based on discharge pressure
in the range of approximately 260 to 292 PSIG. At
pressures above 260 PSIG, the VFD will run the sys-
tem fan at full speed.
LD11298
n
Single System VFD Enclosure Location
ISSUE DATE: 4/28/2017
The pressures indicated in this section
describing the VFD control will vary
from VFD to VFD. Expect tolerances
for the entire pressure range of con-
trol to potentially shift -0 PSIG/+24
PSIG.
JOHNSON CONTROLS
FORM 150.67-NM1
LD12080