Sequence of control sequences
The various heating and cooling aggregates must be controlled in the proper sequence. Below, we consider the concept using a complex VAV room application as an example.
The sequence can be set in temperature control (VavTRCtlC11, VavTRCtlH11, VavTCasCtlC11, VavTCasCtlH11) for each heating/cooling element (in the ConfigExtension). Parallel as well as serial fan mode can be set for Fnc and Fpb.
The sequence always starts in the middle between the heating and cooling sequence.
The devices are then controlled in the cooling or heating sequence depending on the actual value and setpoint. The next sequence element is immediately controlled if a device is currently unavailable (fault, out of service).
The first sequence element on the heating side is the radiator.
If the PID controller is off at 100%, the sequence coordinator releases the ceiling heating as the next element and then the heating coils. The VAV boxes are set to a minimum volume flow for air exchange to occur. The volume flow is continuously increased if the room continues to request heat even after the heating coil valve is fully open.
The PID controller recalls the sequence as per the control signals if the room temperature reaches or exceeds the setpoint. The devices for the cooling sequence are controlled if the temperature increases.
A change to the plant operating mode (PltOpMod) directly impacts the device setpoints.
Sequence
In addition to the sequence for each heating/cooling element, the following is also established in the ConfigExtension for the various device operating modes:
- What devices are used: Radiant surfaces / air handling
- Control type: Modulating / 2-point
Device operating mode | Radiant surfaces / air handling | Modulating / 2-point register | Modulating / 2-point radiant surfaces |
|---|---|---|---|
Comfort | X | X | X |
Pre-Comfort | X | X | X |
Economy | X | X | X |
Protection | X | X | X |
Warmup | X | X | X |
Cool down | X | X | X |
Free cooling | X |
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Control type
The control command from the AF (BACnet) is always standardized to 0...100%. The minimum and maximum can be limited at the output, and selected for control between modulating, 2-point, and 1...10 stage
The PID control parameters and hysteresis values are properties of the BACnet controller objects belonging to the temperature controller AFs.
Modulating control in a range of 0...100% (PID controller) |
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2-position control |
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Staged control (1...10 stages) | The output command in % is mapped to the number of stages. An example with 4 stages and min/max limitation is depicted below. |
