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(Configuration
SERV
LOSP) + 2.0° F (1.1º C) then re-
move a stage of capacity.
NOTE: The freeze set point is 34 F (1.1 C) for fresh water
systems (Configuration
SERV
point is Brine Freeze Set Point (Configuration
LOSP), for Medium Temperature Brine systems (Configu-
ration
SERV
FLUD=2).
Override #2: Circuit A Low Saturated Suction Temperature
in Cooling
Override #3: Circuit B Low Saturated Suction Temperature
in Cooling
Override #4: Circuit C Low Saturated Suction Temperature
in Cooling — These overrides attempt to avoid the low suction
temperature alarms. This override is active only when more
than one compressor in a circuit is ON. If the Saturated Suction
Temperature is less than Brine Freeze Set Point (Configura-
tion
SERV
LOSP) –18.0 F (–10 C) for 90 seconds, or the
Saturated Suction Temperature is less than –4 F (–20 C), a
compressor in the affected circuit will be turned off.
Override #5: Low Temperature Cooling — This override re-
moves one stage of capacity when the difference between the
Control Point (Run Status
Water Temperature (Run Status
predetermined limit and the rate of change of the water is 0 or
still decreasing.
Override #6: Low Temperature Cooling — This override re-
moves two stages of capacity when the Entering Water
Temperature (Run Status
Control Point (Run Status
Override #7: Ramp Loading — If the unit is configured for
ramp loading (Configuration
the difference between the Leaving Water Temperature and the
Control Point is greater than 4º F (2.2º C) and the rate of
change of the leaving water is greater than Cool Ramp Loading
Rate (Setpoints
COOL
CRMP) then no capacity stage
increase will be made. Operating mode 5 (MD05) will be in
effect.
Override #8: Service Manual Test Override — The manual
test consists in adding a stage of capacity every 30 seconds, un-
til the control enables all of the requested compressors and
Minimum Load Control selected in the ComfortLink™ display
Service Test menu. All safeties and higher priority overrides
are monitored and acted upon.
Override # 9: Demand Limit — This override mode is active
when a command to limit the capacity is received. If the
current unit capacity is greater than the active capacity limit
value, a stage is removed. If the current capacity is lower than
the capacity limit value, the control will not add a stage that
will result in the new capacity being greater then the capacity
limit value. Operating mode 4 (MD04) will be in effect.
Override #10: Cooler Interlock Override — This override
prohibits compressor operation until the Cooler Interlock
(Inputs
GEN.I
LOCK) is closed.
Override #11: High Temperature Cooling — This override
algorithm runs once when the unit is switched to ON. If the dif-
ference between the Leaving Water Temperature (Run Status
VIEW
LWT) and the Control Point (Run Status
VIEW
CTPT) exceeds a calculated value and the rate of
change of the water temperature is greater than –0.1º F/min, a
stage will be added.
Override #12: High Temperature Cooling — This override
runs only when Minimum Load Control is Enabled (Configu-
ration
UNIT
HGBP = 1, 2 or 3). This override will add a
stage of capacity if the next stage is Minimum Load Control,
when the difference between the Leaving Water Temperature
(Run Status
VIEW
LWT) and the Control Point (Run
Status
VIEW
CTPT) exceeds a calculated value and the
rate of change of the water temperature is greater than a fixed
value.
FLUD=1). The freeze set
SERV
VIEW
CTPT) and the Leaving
VIEW
LWT) reaches a
VIEW
EWT) is less than the
VIEW
CTPT.)
OPTN
RL.S=ENBL) and if
Override #13: Minimum On/Off and Off/On Time Delay —
Whenever a capacity step change has been made, either with
Minimum Load Control or a compressor, the control will re-
main at this capacity stage for the next 90 seconds. During this
time, no capacity control algorithm calculations will be made.
If the capacity step is a compressor, an additional 90-second
delay is added to the previous hold time (see Override #22).
This override allows the system to stabilize before another
capacity stage is added or removed. If a condition of a higher
priority override occurs, the higher priority override will take
precedence.
Override #14: Slow Change Override — This override pre-
vents compressor stage changes when the leaving temperature
is close to the control point and slowly moving towards the
control point.
Override #15: System Manager Capacity Control — If a
Chillervisor module is controlling the unit and the Chillervisor
module is controlling multiple chillers, the unit will add a stage
to attempt to load to the demand limited value.
Override #16: Circuit A High Pressure Override
Override #17: Circuit B High Pressure Override
Override #18: Circuit C High Pressure Override — This over-
ride attempts to avoid a high pressure failure. The algorithm is
run every 4 seconds. At least one compressor must be on in the
circuit. If the Saturated Condensing Temperature for the circuit
is above the High Pressure Threshold (Configuration
SERV
HP.TH) then a compressor for that circuit will
be removed. If Minimum Load Control was enabled for
High Ambient (Configuration
Minimum Control Valve will be energized.
Override #19: Standby Mode — This override algorithm will
not allow a compressor to run if the unit is in Standby mode,
(Run Status
VIEW
Override #22: Minimum On Time Delay — In addition to
Override #13 Minimum On/Off and Off/On Time Delay, for
compressor capacity changes, an additional 90-second delay
will be added to Override #13 delay. No compressor will be
deenergized until 3 minutes have elapsed since the last com-
pressor has been turned ON. When this override is active, the
capacity control algorithm calculations will be performed, but
no capacity reduction will be made until the timer has expired.
A control with higher precedence will override the Minimum
On Time Delay.
Override #23: Circuit A Low Saturated Suction
Temperature in Cooling
Override #24: Circuit B Low Saturated Suction
Temperature in Cooling
Override #25: Circuit C Low Saturated Suction
Temperature in Cooling — If the circuit is operating in an
area close to the operational limit of the compressor, the circuit
capacity will remain at the same point or unload to raise the sat-
urated suction temperature. This algorithm will be active if at
least one compressor in the circuit is on and one of the follow-
ing conditions is true:
1. Saturated Suction Temperature is less than Brine Freeze
(Configuration
2. Saturated Suction Temperature is less than Brine Freeze
(Configuration
proach (Leaving Water Temperature – Saturated Suction
Temperature) is greater than 15º F (8.3º C) and the Circuit
Superheat (Return Gas Temperature – Saturated Suction
Temperature) is greater than 15º F (8.3º C).
NOTE: The freeze set point is 34 F (1.1 C) for fresh
water systems (Configuration
freeze set point is Brine Freeze Set Point (Configuration
SERV
LOSP), for Medium Temperature Brine
systems (Configuration
23
UNIT
HGBP=3), then the
HC.ST=2).
SERV
LOSP) – 6º F (3.3º C).
SERV
LOSP) and the circuit ap-
SERV
FLUD=1). The
SERV
FLUD=2).
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