Daikin Navigator WWV - Cooling Tower Control System; Cooling Tower Fan Staging Logic; Cooling Tower Bypass Valve Control

OPERATION
NAVIGATOR WWV/TWVDAIKIN APPLIED
34
Condenser Freeze Protection
To protect the condenser from freezing, the condenser pump will
start if the manual reset ow loss alarm is not active and either of
the following are true:
• LWT is equal to or less than the Cond Freeze set point for
at least three seconds AND LWT sensor fault isn’t active
• EWT is equal to or less than the Cond Freeze set point
minus 0.6°C for at least three seconds AND EWT sensor
fault isn’t active
Freeze protection will end when manual reset ow loss alarm is
active or all of the following are true:
• LWT is at least 1.11°C (2°F) above the Cond Freeze set
point or LWT sensor fault is active
• EWT is at least 1.11°C (2°F) above the Cond Freeze set
point or EWT sensor fault is active
• Pump has been running for at least 15 minutes
Condenser Pump Selection
Condenser pump selection, staging, auto control, starts and run
hours function in the same way as for the evaporator section
beginning on page 33.
Cooling Tower Control
WWV cooling tower control includes the capability to control 1 or
2 fan stages, a bypass valve, and a fan VFD.
Cooling Tower Fan Staging
Tower fan staging is enabled when the Tower Control set point is
set to a CP (controlled parameter) of either Condenser EWT or
Condenser LWT based on the Tower Control set point. A stage
timer should start when the condenser pump starts or when the
fan stage is changed.
The rst stage should turn on when the following conditions are
met:
• Stage timer > Tower Fan Stage On Delay set point
• CP > Stage 1 On Temperature set point
• Bypass valve position > Stage On Position/Speed set point
(if Valve/VFD Control Conguration = Valve Stage)
• VFD Speed > Stage On Position/Speed set point (if Valve/
VFD Control Conguration = VFD Stage or Valve SP/VFD
Stage)
The second fan stage can turn on when the following conditions
are met:
• Number of Tower Fan Stages = 2
• Stage timer > Stage On Delay set point
• CP > Stage 2 On Temperature set point
• Bypass valve position > Stage On Position/Speed set point
(if Valve/VFD Control Conguration = Valve Stage)
• VFD Speed > Stage On Position/Speed set point (if Valve/
VFD Control Conguration = VFD Stage or Valve SP/VFD
Stage)
The second fan stage should turn o󰀨 when the following
conditions are met:
• Stage timer > Tower Fan Stage O󰀨 Delay set point
• CP < Stage 2 On Temperature set point – Stage O󰀨
Di󰀨erential set point
• Bypass valve position < Stage O󰀨 Position/Speed set point
(if Valve/VFD Control Conguration = Valve Stage)
• VFD Speed < Stage O󰀨 Position/Speed set point (if Valve/
VFD Control Conguration = VFD Stage OR Valve SP/VFD
Stage)
The rst fan stage should turn o󰀨 when the following conditions
are met:
• Stage timer > Tower Fan Stage O󰀨 Delay set point
• CP < Stage 1 On Temperature set point – Stage O󰀨
Di󰀨erential set point
• Bypass valve position < Stage O󰀨 Position/Speed set point
(if Valve/VFD Control Conguration = Valve Stage)
• VFD Speed < Stage O󰀨 Position/Speed set point (if Valve/
VFD Control Conguration = VFD Stage OR Valve SP/VFD
Stage)
The fan stage should also be set to 0 when condenser pump
state is not Run.
Cooling Tower Bypass Valve
When the Valve/VFD Control Conguration set point is set to
None or VFD Stage, bypass valve position should always be set
to 0%.
If the Valve/VFD Control Conguration set point is set to Valve
Set Point, Valve SP/VFD Stage, or Valve Stage, the bypass valve
should be controlled as described in the following mode sections.
As the calculated position varies from 0 to 100%, the voltage
signal for the Bypass Valve Position output should vary based on
the Valve Type set point:
• If ‘NC to tower’ then 0 to 100% = 0 to 10 VDC
• If ‘NO to tower’ then 0 to 100% = 10 to 0 VDC
For both valve control modes, when active a valve position
is calculated and limited to a range from the Minimum Valve
Position set point to the Maximum Valve Position set point.
Valve Set Point Mode
This mode is enabled when the Valve/VFD Control set point is set
to Valve Setpoint or Valve SP/VFD Stage. When the condenser
state becomes Run, the valve position will be controlled to a
position limited to a range from the Minimum Valve Position
set point to the Maximum Valve Position set point. In this mode
the valve position is calculated by a PID loop to control the
condenser EWT or LWT (as selected by the Tower Control set
point) to the Valve/VFD Set Point.
Valve Stage Mode
This mode is enabled when the Valve/VFD Control set point is
set to Valve Stage. When the condenser state becomes Run, the
valve position will be controlled to a position limited to a range
from the Valve Minimum Position set point to the Valve Maximum