OMM 1008-1
45
2. Tower Fan Staging With Bypass Valve Controlling Minimum EWT (VALVE SP).
1)
TOWER SETPOINT Screen
a)
SP1. Select TEMP if control is based on condenser EWT or LIFT if based on compressor lift
expressed in pressure.
b)
SP2. Select Valve SP for control of bypass valve based on temperature or lift.
c)
SP3. Select one to four fan outputs depending on the number of fan stages to be used. More than one
fan can be used per stage through the use of relays.
d)
SP4. Select STAGE UP TIME from 1 to 60 minutes. The default value of 2 minutes is probably a
good starting point. The value may need to be adjusted later depending on actual system operation.
e)
SP5. Select STAGE DOWN TIME from 1 to 60 minutes. The default value of 5 minutes is probably
a good starting point. The value may need to be adjusted later depending on actual system operation.
f)
If TEMP is selected in SP1, use
i)
SP6. Select STAGE DIFFERENTIAL in degrees F, start with default of 3 degrees F.
ii)
SP8-11. Set the STAGE ON temperatures consistent with the temperature range over which the
condenser EWT is desired to operate. The default values of 70
°
F, 75
°
F, 80
°
F and 85
°
F are a good place to
start in climates with moderate wet bulb temperatures. The number of STAGE ON setpoints used must be the
same as SP3.
g)
If LIFT is selected in SP1, use
i)
SP7. Select STAGE DIFFERENTIAL in PSI. Start with default of 6 PSI.
ii)
SP12-15. Start with default setpoints. The number of STAGE ON setpoints used must be the
same as SP3.
2)
VALVE SETPOINT Screen
a)
SP1, Select NC or NO depending if valve is closed to tower with no control power or open to tower
with no control power.
b)
If TEMP was selected for fan control above, use
i)
SP2, Set the VALVE TARGET (setpoint), usually 5 degrees below the minimum fan stage
setpoint established in TOWER SP11. This keeps full flow through the tower until the last fan is staged off.
ii)
SP4, Set VALVE DEADBAND, the default of 2 degrees F is a good place to start.
iii)
SP8, Set MINIMUM VALVE POSITION when EWT is at or below SP9. Default is 0%.
iv)
SP9, Set the EWT at which the valve position will be at (SP8). Default is 60
°
F.
v)
SP10, Set the initial valve position when EWT is at or above SP11. Default is 100%.
vi)
SP11, Set the EWT at which initial valve position is set to SP10. Default is 90
°
F.
vii)
SP12, Set the minimum position to which the valve can go. Default is 10%.
viii)
SP13, Set the maximum position to which the valve can go. Default is 100%.
ix)
SP14, Set the control gain for error. Default is 25.
x)
SP15, Set the control gain for slope. Default is 25.
!
CAUTION
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 to avoid possible equipment damage.
