FB_BA_AC_TRtCtrl

The template is used for open-loop and closed-loop control of the return temperature of a hot water air heater.

To prevent frost damage, the heating coil of the ventilation system is first preheated with warm water when the outside temperature is low.

To do this, the flip-flop rsPreRinseActive is first set in the template FB_BA_AC_TRtCtrl. The return temperature controller Ctrl receives the pre-rinse setpoint from the setpoint curve PreRinseSp via the selector. To prevent the heating coil from overheating during preheating, the pre-rinse setpoint is varied by the characteristic curve PreRinseSp depending on the outside temperature. When the desired return temperature is reached, the hysteresis module PreRinseHys switches on. The flip-flop rsPreRinseReady is then set.

The system start program FB_BA_AC_PlantCmd_AHU_1st_10 is informed via the output bPreRinseReady that it can continue with the next step, e.g. Opening the outdoor air damper.

The flip-flop rsPreRinseActive remains set so that the pre-rinse setpoint is still present at the return temperature controller.

If the system start program has switched on the fans and enabled the supply air temperature control in its subsequent steps, the flip-flop rsPreRinseActive is reset using the input bSeqActive. The pre-rinse process is now complete. For permanent frost protection operation of the heating coil during system operation and system standstill, the return temperature controller receives the reduced setpoint of the AV object SpTRtW. The output bQ of the function block PreRinseDelay becomes TRUE if the pre-rinse process is started and the pre-rinse setpoint is not reached after a delay time has elapsed. The fault is reported using the BV object PreRinseDst.

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

Block diagram

Syntax

FUNCTION_BLOCK FB_BA_ActuatorAnalog EXTENDS FB_BA_View
VAR_INPUT
  bEnPreRinse               : BOOL;
  fTRt                      : REAL;
  bTWthLowLimit             : BOOL;
  fTWth                     : REAL;
  bSkipPreRinse             : BOOL; 
  bSeqActive                : BOOL;
END_VAR
VAR_OUTPUT
  fY                        : REAL;
  bPreRinseActive           : BOOL;
  bPreRinseReady            : BOOL;
  bPreRinseDstb             : BOOL;
END_VAR
VAR_INPUT CONSTANT
  SpTRtW                    : FB_BA_AV_Op;
  PreRinseDelay             : FB_BA_DlyOn;
  PreRinseDst               : FB_BA_BV;
  PreRinseSp                : FB_BA_Scale_02;
  Ctrl                      : FB_BA_Loop;
END_VAR
VAR
  rtrigPreRinse             : R_TRIG;
  rsPreRinseReady           : RS;
  rsPreRinseActive          : RS;
  PreRinseHys               : FB_BA_Swi2P;
END_VAR

Inputs

Name	Type	Description
bEnPreRinse	BOOL	Enabling the pre-rinse process.
fTRt	REAL	Measured value of the return temperature of the hot water air heater.
bTWthLowLimit	BOOL	The variable indicates that the outside temperature has fallen below the lower limit value. This state is used to enable the return temperature controller Ctrl.
fTWth	REAL	Current value of the outside temperature.
bSkipPreRinse	BOOL	Input for skipping the pre-rinse process.
bSeqActive	BOOL	This input is used to inform the controller that the supply air temperature control of the ventilation has gone into operation or that the supply air temperature sequence controller has been enabled.

Outputs

Name	Type	Description
fY	REAL	Control value output of the return temperature controller Ctrl.
bPreRinseActive	BOOL	Display, pre-rinse process active.
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, see sample FB_BA_AC_PlantCmd_AHU_1st_10.
bPreRinseDstb	BOOL	Display, pre-rinse process faulty.

Inputs CONSTANT

Name	Type	Description
SpTRtW	FB_BA_AV_Op	The analog value object is used to enter the return temperature setpoint when there is a risk of frost or low outside temperatures.
PreRinseDelay	FB_BA_DlyOn	The template represents a start-up delay and triggers the message "Pre-rinse process faulty" at the object PreRinseDst if the result of the pre-rinse hysteresis PreRinseHys is not achieved.
PreRinseDst	FB_BA_BV	The binary object displays the message "Pre-rinse process faulty".
PreRinseSp	FB_BA_Scale_02	Template for calculating the pre-rinse setpoint as a function of the outside temperature fTWth for return temperature control during system start-up.
Ctrl	FB_BA_Loop	PID controller for controlling the return temperature of the heating coil.

Variables

Name	Type	Description
rtrigPreRinse	R_TRIG	rtrigPreRinse activates the pre-rinse at the RS flip-flop rsPreRinseActive by a rising edge at input CLK.
rsPreRinseReady	RS	Setting the RS flip-flop indicates that the pre-rinse process has reached its set temperature.
rsPreRinseActive	RS	The pre-rinse process is activated by setting the RS flip-flop.
PreRinseHys	FB_BA_Swi2P	The result of the pre-rinse hysteresis PreRinseHys indicates that the pre-rinse process has reached its set temperature.

Requirements

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