iWorx® MPU2
505-009, Effective: June 30, 2015
25
© 2015 Taco Electronic Solutions, Inc.
Cooling with Modulated Output (Valve or Variable Speed Circulator)
The calculated cooling loop setpoint is derived from the cooling setpoint and the loop proportional gain.
CalcCoolingLoopSp = CalcCoolingSp- ½(Kp)
The cooling output is modulated by a P+I control loop based on the cooling loop setpoint and the space temperature.
The P+I control loop will modulate the output to maintain a constant space temperature. As the temperature increases
above the cooling loop setpoint, the cooling output will be modulated open. The cooling output will be modulated closed
as the temperature decreases below the cooling loop setpoint. When unoccupied mode is entered, the cooling loop
setpoint is set up through a separate unoccupied cooling setpoint.
To prevent the integral component from becoming too large, there is anti-wind up reset protection. This protection
clamps the integral value when all of the components add up to more than 100% or less than 0%. The following equa-
tions are used for P+I control:
Kp = Proportional Gain
Ki = Integral Gain
Error = CoolingLoopSp - SpaceTemp
Cooling with Stages and Modulation
The controller can combine its staged and modulated modes. In the combined mode of operation, the modulated out-
put is considered to be one of the stages. The stage to be associated with modulation is selected in the
Staged Cooling
configuration page.
Modulation starts when the selected stage would normally start (i.e., if stage 2 is selected as the modulating stage, it
starts if stage 1 has been active for the
Staging Interval
and the temperature is still above the cooling control band).
If the modulating stage is not the last stage, subsequent stages are activated once the
Stage Threshold
percentage
has been met by the modulating output and has remained there for the duration of the
Staging Interval
.
In order to maintain a smooth total cooling output, the modulating output responds to subsequent stages activating or
deactivating. It does so by clearing its interval output when a subsequent stage is activated:
I= 0
Modulating Output = K_p × Error
It forces its interval output to the
Staging Interval
whenever a subsequent stage is deactivated. This feature prevents
large jumps in overall cooling output.
I = Staging Threshold
Modulating Output= (K_p × Error) + I
