JOHNSON CONTROLS
213
SECTION 7 - OPERATION
FORM 201.23-NM2
ISSUE DATE: 09/25/2020
7
Fan on and off control points will vary for standard
and optional optimized IPLV chillers. Unless controls
dictate all fans running due to high VSD ambient tem-
peratures, fans will sequence on when a compressor
runs and discharge pressure rises. During compressor
ramp up or ramp down when compressors are staged,
the current fan stage will be held.
The number of fans is factory programmable under the
password protected Unit Setup Mode.
Standard IPLV Fan Control
Fan staging ON and OFF points will be determined
by the ambient temperature. The fan stage will be
incremented, unless the 5 second timer between fan
stages is still timing when the discharge pressure rises
above the Fan ON Press. The fan stage is decremented,
unless the 5 second timer between fan stages is still
timing when the discharge pressure falls below the Fan
OFF Press. When a fan stage is incremented, the fan
delay timer is set to 5 seconds, and the Fan ON pres-
sure is ramped 20 psig over the original ON point back
to the original value over the next 20 seconds. When
a fan stage is decremented, the fan delay timer is set
to 5 seconds, and the Fan OFF pressure is ramped 20
PSIG below the original Fan OFF point, back to the
original value over the next 20 seconds. The ON and
OFF points will vary as ambient temperature changes.
Figure 58 on page 213 below shows the fan ON and
OFF points relative to ambient temperature.
Standard IPLV Fan Control
90
100
110
120
130
140
150
160
170
180
190
75 85 95 105 115 125
Ambient Air Temp (°F)
Discharge Pressure (PSIG)
Fan On Press
Fan Off Press
LD10633
FIGURE 58 - STANDARD IPLV FAN CONTROL
Optimized IPLV Fan Control
Fan staging ON and OFF points will be determined
by the ambient temperature. The fan stage will be
incremented, unless the 5 second timer between fan
stages is still timing when the discharge pressure rises
above the Fan ON Press. The fan stage is decremented,
unless the 5 second timer between fan stages is still
timing when the discharge pressure falls below the Fan
OFF Press. When a fan stage is incremented, the fan
delay timer is set to 5 seconds, and the Fan ON pres-
sure is ramped 20 PSIG over the original ON, point
back to the original value over the next 20 seconds.
When a fan stage is decremented, the fan delay timer is
set to 5 seconds, and the Fan OFF pressure is ramped
20 PSIG below the original Fan OFF point, back to the
original value over the next 20 seconds. The ON and
OFF points will vary as ambient temperature changes.
Figure 59 on page 213 below shows the fan ON and
OFF points relative to ambient temperature.
Optimized IPLV Fan Control
90
95
100
105
110
115
120
125
130
135
140
145
150
155
75 85 95 105 115 125
Ambient Air Temp (°F)
Discharge Pressure (PSIG)
Fan On Press
Fan Off Press
LD10634
FIGURE 59 - HIGH IPLV FAN CONTROL
High VSD Cabinet Ambient Temperature Fan
Operation
All condenser fans on all systems will run when the
chiller is off and enabled to run, if the VSD internal
ambient temperature is higher than 5°F below the VSD
Cabinet Ambient Temperature Cutout of 158°F (158°F
minus 5°F equals 153°F). When the fans turn on in this
situation, the fan outputs will cycle one at a time with
a 100 ms delay between fan starts. When the VSD in-
ternal ambient falls below the “Restart Temperature”
(158°F Cutout minus 10°F equals 148°F), the fans will
all be turned off without a delay.
VSD TEMPERATURE CONTROL, OPERATION
OF THE COOLANT PUMP, AND VSD CABINET
COOLING FANS
The Coolant pump and VSD Cabinet Cooling Fans will
run to cool the VSD whenever any of the following
conditions are met:
• VSD Comp IGBT Baseplate Temperature on a 2
or 4 compressor unit is greater than 10°F (5.6°C)
below the cutout (Cutout 218°F [103.3°C] mi-
nus 10°F [5.6°C] equals 208°F [97.8°C]). When
the VSD internal ambient falls below the restart
temperature (Cutout 218°F [103.3°C] minus 15°F
[8.3°C] equals 203°F [95°C]), the fans and pump
will turned o without a time delay.
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