46
OMM 1008-1
c)
If LIFT was selected for fan control, use:
i)
SP3, Set the VALVE TARGET (setpoint), usually 30 psi below the minimum fan stage setpoint
established in TOWER SP15. This keeps full flow through the tower until the last fan is staged off.
ii)
SP5, Set VALVE DEADBAND, the default of 6 psi is a recommended initial setting.
iii)
SP12, Set the minimum position to which the valve can go. Default is 10%.
iv)
SP13, Set the maximum position to which the valve can go. Default is 100%.
v)
SP14, Set the control gain for error. Default is 25.
vi)
SP15, Set the control gain for slope. Default is 25.
NOTE: Setpoints 14 and 15 are site specific dealing with system fluid mass, component size and other factors
affecting the reaction of the system to control inputs. These setpoints should be set by personnel experienced
with setting up this type of control.
Figure 22, Bypass Valve Positions
Initial Valve Position
Max Start Position
Set Point (90%)
Min Start Position
Set Point (10%)
Max Position
@ Setpoint
(90°F)
Min Position
@ Setpoint
(65°F)
See
Figure 8
on page 8 for fan staging and bypass valve field wiring connection points.
3. Tower staging with bypass valve controlled by fan stage (VALVE STAGE)
This mode is similar to #2 above except that the bypass valve setpoint changes to be set at the same point of
whatever fan stage is active rather than just maintaining a single minimum condenser EWT. In this mode the
valve controls between fan stages and tries to maintain the fan stage setting in effect. When it is max open or
max closed (staging up or down) and the temperature (or lift) moves to the next fan stage, the valve will go
the opposite max setting. This mode reduces fan cycling.
This mode is programmed the same as Mode #2 above except that in SETPOINT, TOWER, SP2, VALVE
STAGE is selected instead of VALVE SP and:
•
SP6, Set the valve position (% open) above which the first fan can stage on (fan stage ON temperature
and STAGE UP TIMER must also be satisfied). Default is 80%.
•
SP7, Set the valve position (% closed) below which the first fan can stage off (the fan stage temperature
and STAGE DOWN TIMER must also be satisfied). Default is 20%.
4. Fan VFD, no bypass valve (VFD STAGE)
The fan VFD mode assumes the tower is driven by one large
fan. Set up is as above except in SETPOINT, TOWER, SP2, VALVE/VFD is selected.
