FB_BA_AC_PreHtr

The template represents the open-loop and closed-loop control of a hot water air heater.

The main tasks of the template are:

Control of the supply air temperature (TSuACtrl).
Control of the return temperature (TRtCtrl).
Frost monitoring on the air side with frost protection thermostat (FrostThermostat).
Frost monitoring air side with analog frost protection sensor (TFrost).
Enable the heater pump (Pu).
Control of the heater valve (Vlv).
Collecting and evaluating safety-relevant faults using the PlantLock
To be part of the step sequence control of an air conditioning system, see Aggregates

A maximum choice of control signals from the temperature sequence controller TSuACtrl and the frost protection functions TFrostPrtcCtrlAir / TRtCtrl prevent the hot water air heater from icing up.

	The initialization of the template takes place within the method FB_Init.

Principle diagram 01

The principle diagram shows the intended use of the template with the plant elements involved.

Principle diagram 02

The diagram shows the integration of the template within a plant.

Block diagram

Syntax

FUNCTION_BLOCK FB_BA_AC_PreHtr EXTENDS FB_BA_View
VAR_INPUT
  fSpTSuA                 : REAL;
  fTSuA                   : REAL;
  bSyncTSuACtrl           : BOOL;
  fSyncTSuACtrl           : REAL;
  bDehumf                 : BOOL;
  bSkipPreRinse           : BOOL;
  fTWth                   : REAL;
  bTWthLowLimit           : BOOL;
  bResetDehumf            : BOOL;
END_VAR
VAR_OUTPUT
  bCmd                    : BOOL;
  fPresentValue           : REAL;
  bFrost                  : BOOL;
  bPreRinseReady          : BOOL;
  bActiveSeqCtrl          : BOOL;
END_VAR
VAR_IN_OUT
  stTSeqLink              : ST_BA_SeqLink;
  stAggregate             : ST_BA_Aggregate;
END_VAR
VAR_INPUT CONSTANT PERSISTENT
  {attribute 'parameterCategory' := 'Behaviour'}
  fHysPuOn                : REAL := 5.0;
  {attribute 'parameterCategory' := 'Behaviour'}
  fHysPuOff               : REAL := 1.0;
END_VAR
VAR_INPUT CONSTANT
  TFl                     : FB_BA_SensorAnalog;
  TRt                     : FB_BA_SensorAnalog;
  TSuACtrl                : FB_BA_AC_PreHtrTSuACtrl;
  TRtCtrl                 : FB_BA_AC_TRtCtrl;
  TFrost                  : FB_BA_SensorAnalog;
  TFrostPrtcCtrlAir       : FB_BA_PID_Sp;
  FrostThermostat         : FB_BA_SensorBinary;
  Vlv                     : FB_BA_Vlv;
  Pu                      : FB_BA_Pu1st;
  PlantLock               : FB_BA_PlantLock;
  Aggregate               : FB_BA_Aggregate;
END_VAR
VAR
  bPrioSfty               : BOOL;
  bPrioCrit               : BOOL;
  PrioSwiVal              : FB_BA_PrioSwi_B04;

  HysPu                   : FB_BA_Swi2P;
  SyncTSuACtrl            : FB_BA_RFTrig;
  SyncSeqCtrlIsActive     : FB_BA_RFTrig;
  PrioSwiSync             : FB_BA_PrioSwi_R04;
END_VAR

Inputs

Name	Type	Description
fSpTSuA	REAL	Setpoint of the supply air temperature
fTSuA	REAL	Measured value of the supply air temperature
bSyncTSuACtrl	BOOL	Input for synchronization of the supply air sequence controller in the function block TSuACtrl.
fSyncTSuACtrl	REAL	Synchronization value for the supply air sequence controller in the function block TSuACtrl.
bDehumf	BOOL	Input dehumidification mode active. This state has an effect on the sequence control in the supply air temperature control TSuACtrl template.
bSkipPreRinse	BOOL	Input to skip the pre-rinse process in the function block TRtCtrl.
fTWth	REAL	Measured value weather temperature
bTWthLowLimit	BOOL	The variable indicates that the outside temperature has fallen below the lower limit value. The following actions are triggered when the outside temperature falls below a critical value: Heater pump activation, forced pump operation Enabling the return temperature control in the function block TRtCtrl During plant start-up, pre-rinse mode is active in the function block TRtCtrl
bResetDehumf	BOOL	Input to reset the dehumidification mode in the template TSuACtrl.

Outputs

Name	Type	Description
bCmd	BOOL	Current switching status of the single-stage pump.
fPresentValue	REAL	Current control value of the heater valve.
bFrost	BOOL	Frost protection active display. The message is triggered either by the frost protection thermostat FrostThermostat or by falling below the lower limit value of the analog frost protection sensor TFrost. The signal Frost protection active triggers the plant operation mode Frost protection in the template FB_BA_AC_OpMod1St_Prio.
bPreRinseReady	BOOL	Display, pre-rinse process has reached set temperature. This signal is used as a switching condition for the step sequence control of a ventilation system.
bActiveSeqCtrl	BOOL	Indicates that the sequence controller TSuACtrl is the active one in the sequence control.

Inputs/outputs

Name	Type	Description
stSeqLink	ST_BA_SeqLink	The data and command structure is the link between the supply air temperature sequence controller Ctrl and the supply air temperature sequence controller TSeqLink of an air conditioning system.
stAggregate	ST_BA_Aggregate	Bidirectional aggregate structure via which the enables and switching values are transmitted to the evaluation function block of the step sequence control Aggregate. The aggregate structure transmits the recorded feedback signals up and down to the central plant control.

Inputs CONSTANT PERSISTENT

Name	Type	Description
fHysPuOn	REAL	Upper switching point of the hysteresis to switch on the pump.
fHysPuOff	REAL	Lower switching point of the hysteresis to switch off the pump.

Inputs CONSTANT

Name	Type	Description
TFl	FB_BA_SensorAnalog	The function block represents the flow temperature sensor.
TRt	FB_BA_SensorAnalog	The function block represents the return temperature sensor.
TSuACtrl	FB_BA_AC_PreHtrTSuACtrl	The function block represents the supply air temperature control of a preheater and is part of the temperature sequence control of an air conditioning system. The control signal is forwarded to the heater valve Vlv via a maximum selection.
TRtCtrl	FB_BA_AC_TRtCtrl	The function block represents the open-loop and closed-loop control of the return temperature of a hot water air heater. The control signal is forwarded to the heater valve Vlv via a maximum selection.
TFrost	FB_BA_SensorAnalog	The function block represents a frost protection sensor on the air side.
TFrostPrtcCtrlAir	FB_BA_PID_Sp	The function block represents the analog frost protection monitoring on the air side of the preheater. The control signal is forwarded to the heater valve Vlv via a maximum selection.
FrostThermostat	FB_BA_SensorBinary	The function block represents a frost protection thermostat.
Vlv	FB_BA_Vlv	The function block represents the heater valve.
Pu	FB_BA_Pu1st	The function block represents the heater pump.
PlantLock	FB_BA_PlantLock	When the function block is called, the relevant faults of the event-enabled objects are collected and output at this and lower levels of the template. These relevant faults cause specific switching actions via the variables bPrioSfty and bPrioCrit in the template. The event-enabled objects of the template that trigger faults with bPrioCrit are listed below. TRt.MV, TFrost.MV, FrostThermostat.Input, Pu.Dst The parameterization of the lock priority of the event-enabled objects can be found in the FB_init of this template.
Aggregates	FB_BA_Aggregate	The aggregate function block represents a receive block of a step sequence controller. Within the function block, the aggregate structure stAggregate is evaluated and integrated into the template using the inputs and outputs.

Variables

Name	Type	Description
bPrioSfty	BOOL	The variable is an evaluation of the "Safety" lock priority of the event-enabled objects of the project structure and causes targeted switching actions in the template when a relevant fault is triggered.
bPrioCrit	BOOL	The variable is an evaluation of the "Critical" lock priority of the event-enabled objects in the project structure and causes targeted switching actions in the template when a relevant fault is triggered.
PrioSwiVal	FB_BA_PrioSwi_B04	The priority switch uses the command structure stCmd to determine the enable conditions for the supply air temperature control TSuACtrl and for the pre-rinse process of the return air temperature control TRtCtrl.
HysPu	FB_BA_Swi2P	The two-position switch switches the heater pump on and off depending on the valve position fPresentValue and the switching point of the hysteresis fHysPuOn/fHysPuOff.
SyncTSuACtrl	FB_BA_RFTrig	A rising edge at the input bValue of the function block synchronizes the supply air temperature control TSuACtrl to the value of fSyncTSuACtrl.
SyncSeqCtrlIsActive	FB_BA_RFTrig	The variable TSuACtrl.bSeqActv indicates that the sequence control is active. This rising edge triggers a pulse at the input bValue of the function block SyncSeqCtrlIsActive. If the sequence controller of the preheater is the active one in the sequence control bActiveSeqCtrl and the lower limit of the outside temperature bTWthLowLimit is active, the pulse of SyncSeqCtrlIsActive triggers a synchronization of the supply air temperature controller TSuACtrl to the value of the valve position Vlv.fMdlt.
PrioSwiSync	FB_BA_PrioSwi_R04	The priority switch prioritizes the synchronization of the supply air temperature control TSuACtrl.

Requirements

Development environment	Necessary function
TwinCAT from v3.1.4024.35	TF8040 \| TwinCAT Building Automation from V5.0.0.0