32
OM 200MICRO
The number of cooling tower stages is decreased only when the valve position drops below the
minimum position set point and the temperature and time requirements described above for fan
staging down are met. The valve then modulates open as the temperature starts to rise after the fan
stage is turned off.
When the chiller is commanded to start, and either type of valve control is selected, the bypass valve
is positioned to anticipate the heat rejection needed at the time of startup. When condenser flow has
not been confirmed, but the chiller is in the start requested state, the valve position is based on the
minimum position, maximum position and Oat set points. If the optional outdoor air temperature
sensor is not installed, the valve position is determined solely by the minimum and maximum position
set points. If the maximum and minimum positions are set to the same value, the valve will always be
set to that fixed position prior to start-up.
Menu 20, Tower Valve Control
Item
Screen
Line
Display
Field
Range
Extended Name
None
Valve Set Point
1
Valve Control=None
1
Stage Set Point
Cooling Tower Bypass Ctrl Type
Valve Spt=65.0°F
1
40-99.5°F
Bypass Valve Control Set Point
2
Value Deadb=2.0°F
2
1.0-10.0°F
Bypass Valve Control Dead Band
Min Position=20%
1
0-50%
For Calculating Valve Position
1
3
Max Positon=80%
2
50-100%
For Calculating Valve Position
NC to Tower
1
Valve Type=NC
1
NO to Tower
Bypass Valve Default Position
Mod Limit=7.5°F
1
4.0-25.0°F
Bypass Valve Modulation Limit
2
Sample time=15Sec
2
15Sec-15Min
Ent Cond Temp Integration Time
Max Change=4%
1
1-20%
Max Allowable Valve Pos Change
2
3
PA Time=15Min
2
1.0-60 Min
Proj Ahead Calculation Window
Min Start Pos=0%
1
0-100%
Min Valve Position at Startup
1
Max Start Position=100%
2
0-100%
Max Valve Position at Startup
Min Pos At=60°F
1
0-99.5°F
OAT for Minimum Position
3
2
Max Pos At=90°F
2
0-99.5°F
OAT for Maximum Position
Valve Control=
A value must be selected telling the MicroTech which type of control will be used for
the tower valve. If none is selected, the remaining values are not required for tower control.
Valve Spt=
This value is the water temperature the MicroTech will maintain by modulating the
tower valve.
Valve Deadb=
This value is the control dead band that is used in the MicroTech when calculating
control actions.
Min Position=
This value is used in calculating when the valve position will change. The default
values should be adequate for most applications.
Max Position=
This value is used in calculating when the valve position will change. The default
values should be adequate for most applications.
Valve Type=
This value indicates the type of output
(increasing or decreasing voltage)
supplied
to the control valve controller. If the valve requires an 0-10 Vdc to open select the 'N/C' valve.
The 'N/O' selection would provide a 0 Vdc for valve to be open and a 10 Vdc for the valve to be
fully closed.
Mod Limit=
This value is used in MicroTech calculations and can increase or decrease the
controller sensitivity.
Sample Time=
This value determines how frequently the MicroTech looks at the water
temperature entering the condenser.
Max Change=
The value limits the amount the valve position can change at one time.
PA Time=
This value will reduce control point overshoot and produce quicker response to load
variations.
