McQuay WSC Operating Manual page 32

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
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.
d) SP4. Select STAGE UP TIME from 1 to 60 minutes. The default value of 2 minutes is
e) SP5. Select STAGE DOWN TIME from 1 to 60 minutes. The default value of 5 minutes
f) If TEMP is selected in SP1, use
g) If LIFT is selected in SP1, use
2) VALVE SETPOINT Screen
a) SP1, Select NC or NO depending if valve is closed to tower with no control power or open
b) If TEMP was selected for fan control above, use
32
lift expressed in psi.
More than one fan can be used per stage through the use of relays.
probably a good starting point. The value may need to be adjusted later depending on
actual system operation.
is probably a good starting point. The value may need to be adjusted later depending on
actual system operation.
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.
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.
to tower with no control power.
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) SP8, Set MINIMUM VALVE POSITION when EWT is at or below SP9. Default is
0%.
vi) SP9, Set the EWT at which the valve position is set to allow the fans to stage up
(SP8). Default is 60°F.
vii) SP10, Set the initial valve position when EWT is at or above SP11. Default is 100%.
SP11, Set the EWT at which initial valve position is set to SP8. Default is 90°F.
viii) SP12, Set the minimum position to which the valve can go. Default is 10%.
ix) SP13, Set the maximum position to which the valve can go. Default is 100%.
x) SP14, Set the control gain for error. Default is 25.
xi) SP15, Set the control gain for slope. Default is 25.
OM Centrif Micro ΙΙ-5