BAC_AC_CasCtrlH_02
Functional description
The template is the master controller for a room or return air/supply air cascade humidity control.
The purpose of the master control is to maintain the room humidity within the comfort zone between an upper and lower set value.
The BACnet loop object PID_Humf is used to control the lower room humidity limit. It calculates the supply air humidity set value for humidification.
The BACnet loop object PID_Dehumf is used to control the upper room humidity limit. It calculates the supply air humidity set value for dehumidification.
Both controllers receive the room humidity set values from the upstream set value template.
The set values for the room humidity and the set values for the supply air humidity calculated by the loop objects are specified in g/kg, i.e. as absolute humidity.
The parameters YMin, YMax, gain and integral time for the two loop objects are continuously synchronised by the PID_Sync. Due to the difference between lower and upper set value, the characteristic output curves of the two PI controllers always show a parallel offset. An overlap of the supply air set values for humidification and dehumidification is thus avoided.
It is important to ensure that rSpRmHumf is always less than or equal to rSpRmDehumf. This is done in the upstream set value template.
Interface
Plant diagram
Block diagram
VAR_INPUT
rRmX : REAL;
rSpRmHumf : Real;
rSpRmDehumf : Real;
udiPltStp : REAL;
udiOpMod : REAL;
rRmX: Actual value of absolute room humidity in g/kg
rSpRmHumf: Lower room set value (humidification) in g/kg
rSpRmDehumf: Upper room set value (dehumidification) in g/kg
udiPltStp: Stages of the air-conditioning plant startup. See also BAC_AC_StartTH_01.
udiOpMod: Plant operation mode. See also BAC_AC_OpMod_01.
VAR_OUTPUT
rY_Hum : REAL;
rY_DeHum : REAL;
rY_Hum: Supply air set value humidification g/kg
rY_DeHum: Supply air set value dehumidification g/kg
VAR CONSTANT
PLT_NUM : BYTE := 1;
PLT_NUM: all alarms and events of all plant components within a controller are included in a global alarm and event list. The assignment of events and alarms to a plant is defined by the assignment of a PLT_NUM plant number.
The recording and processing of an alarm from an aggregate or a device takes place within the templates by means of the alarm function block FB_BA_Alarm.
The evaluation of the alarms of a plant, e.g. for the generation of a collective message or for plant shutdown in case of relevant faults, takes place within the template BAC_PltAlm_01 by means of the function block FB_BA_AlarmPlt.
The evaluation of different plant events within the templates of a plant, takes place within the template BAC_PltComnMsg_01 by means of the function block FB_BA_ComnMsg.
Important! The assignment and evaluation of the alarms and events of a plant can only be done correctly if all templates of a plant have the same plant number!
The plant number can be assigned in the Project Builder in the parameter menu for the templates or via a column in the Excel import.
Program description
Instance | Type | Task |
|---|---|---|
X | The AV object is referenced to the actual value input of the BACnet loop objects | |
W_Humf | The AV object is referenced to the setpoint input of the BACnet loop object PID_Humf | |
W_Dehumf | The AV object is referenced to the setpoint input of the BACnet loop object PID_Dehumf | |
En | The BV object is used for display and activation of the controller enable in the MCL or in a local operator display. | |
>=, AND | The result of this network is the enable of the two PID master controllers PID_Humf/PID_Dehumf. The enable depends on the plant operation mode udiOpMod and the plant steps udiPltStp during startup of the ventilation system. | |
PID_Humf | Master controller humidification | |
PID_Dehumf | Master controller dehumidification | |
rtrigSync | R_TRIG | Upon receipt of the controller enable bEn, the two master controllers are synchronized with the input setpoints W_Humf_rPrVal / W_Dehumf_rPrVal triggered by a rising edge and rtrigSync. |
Y_Humf | Supply air setpoint humidification. The AV object is referenced to the control value output of the BACnet loop object PID_Humf | |
Y_Dehumf | Supply air setpoint dehumidification. The AV object is referenced to the control value output of the BACnet loop object PID_Dehumf | |
TLogY_Humf | Trend logging of the supply air setpoint for heating Y_Humf | |
TLogY_Dehumf | Trend logging of the supply air setpoint for heating Y_Humf | |
PID_Sync | The function block synchronizes the parameters for the two master controllers PID_Humf/PID_Dehumf | |
tonDlySp | TON | Network for output of setpoints to the outputs of the template |
Version history
Version number | Comments |
|---|---|
1.0.0.1 | First release |