190
JOHNSON CONTROLS
FORM 201.21-NM1 (1223)
CONDENSOR FAN CONTROL (CON'T)
Fan on and o 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 pressure
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 origi-
nal value over the next 20 seconds. The ON and OFF
points will vary as ambient temperature changes. FIG.
35 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
FIG. 35 - STANDARD IPLV FAN CONTROL
Optimized IPLV Fan Control
Fan staging on and o 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 pressure 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. FIG. 36 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
FIG. 36 - HIGH IPLV FAN CONTROL
High VSD Cabinet Ambient Temperature
Fan Operation
All condenser fans on all systems will run when the
chiller is o 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
- 5°F = 153 °F). When the fans turn on in this situa-
tion, the fan outputs will cycle one at a time with a 100
ms delay between fan starts. When the VSD internal
ambient falls below the “Restart Temperature” (158°F
Cutout - 10°F = 148 °F), the fans will all be turned o
without a delay.
OPERATION
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