System Regulation - Honeywell EXCEL 5000 User Manual

EXAMPLES
74-5577–33 (US)
EN2B-0184 GE51 R0518 (Europe)
This application regulates a partial air conditioning system with mixed air dampers,
an air heater, and an air cooler. Setpoint management using the ZEB statement
followed by PID controllers regulates this system.
Description The following diagram illustrates system setup.
ZEB/Load reset mode is 1 (ZEB) to receive the mixed air damper setpoint.
With the controllers, it is especially important to ensure that the proportional ranges
of the controller are set correctly.
When crossing the particular heating, cooling, and zero energy ranges, the control
loop must cover the maximum positioning signal change of the controller. The
proportional ranges (Xp) of the controllers are as follows:
Heater controller Xp = Heating reset range
Cooler controller Xp = Cooling reset range
Damper controller Xp = (P13*(100% + 20%)/(100% - 20%)) + P13
(Where P13 is the mixed air reset range.)
With the controller for the mixed air dampers, there is also a minimum limitation of
the positioning signal to 20 percent to guarantee a minimum fraction of outdoor air.
In this example, the Y3, Y4, and Y5 outputs from ZEB provide the fresh air setpoints
for the heating, cooling, and zero energy cases (pure damper operation). These
outputs serve as reference variables for the PID controllers. The fresh air sensor
provides the controlled variable. On the controllers for the cooler and the dampers,
the controller inputs for the controlled variable and reference variables are
deliberately exchanged to reverse the effects of the controller.
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CARE CONTROL ICONS

System Regulation