FB_BA_AHU_1st_10

Template of an air conditioning system.

The main components of the template are:

Plant control and start program
Supply air temperature sequence control
Room temperature cascade control
Summer night cooling
Pressure control of the supply and extract air fan
Thermal air treatment using air heaters, coolers and energy recovery by means of plate heat exchangers
External and exhaust air damper with spring return actuator and end position monitor
External and extract air filters with analog differential pressure monitoring

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

Block diagram

Plant diagram

Switch-on sequence of the aggregates of the plant

Within PlantCmd, a step sequence controller sequentially controls the switching on and off of the aggregates one after the other. When switching from aggregate to aggregate, predefined delay times and feedback from the aggregates are taken into account.

The order of the aggregates is determined by the ordinal number of the individual elements of the bidirectional array arrAggregate.

Step	Stages of plant start-up	Aggregate	Function blocks
00	E_BA_AC_PlantStep01.eOff	Plant Off
01	E_BA_AC_PlantStep01.eErc	Energy recovery	Erc
02	E_BA_AC_PlantStep01.ePreRinse	Prerinsing of the hot water air heater	PreHtr
03	E_BA_AC_PlantStep01.eDamperOuA	Outside air damper	OuADmp
04	E_BA_AC_PlantStep01.eFanSupplyAir	Supply air fan	SuAFan
05	E_BA_AC_PlantStep01.eDamperExhA	Exhaust air damper	ExhADmp
06	E_BA_AC_PlantStep01.eFanExtractAir	Extract air fan	ExtAFan
07	E_BA_AC_PlantStep01.eCooler	Cold water air cooler	Col
08	E_BA_AC_PlantStep01.eOn	Room supply air cascade, plant On	TCasCtrl

If the plant has reached step 08 E_BA_AC_PlantStep01.eOn, the supply air temperature sequence control TSeqLink is enabled when the cascade control TCasCtrl is switched on.

Starting up the plant in cold weather

When the system is switched on in cold weather, the step sequence control of the PlantCmd command includes the plant step PreRinse of the preheater E_BA_AC_PlantStep01.ePreRinse. In this step, the return temperature control of the hot water air heater is activated. This procedure is intended to prevent the freezing of the hot water air heater during the plant start-up.

Fault shutdown

The plant switches off at:

Fire alarm
Frost alarm
NOTICE
Fan faults (feedback monitoring, thermoelectric overload, maintenance switch)
Incorrect position of the outside and exhaust air damper.
Filter blockages

The following table lists the event-capable objects of the template that can trigger relevant PlantLock faults. The parameterization of these events can be found in FB_init.

Function block	eEnPlantLock	Function block	bPrioMedium
TSuA.MV	E_BA_LockPriority.eMedium	PlantLock	x
FiltOuAMonit.DstMainAlarm	E_BA_LockPriority.eMedium		x
OuADmp.MonitOpen.Dst	E_BA_LockPriority.eMedium		x
SuAFan.Dst	E_BA_LockPriority.eMedium		x
SuAFan.ThOvrld	E_BA_LockPriority.eMedium		x
SuAFan.MntnSwi	E_BA_LockPriority.eMedium		x
SuADiffPrssMonit.Dst	E_BA_LockPriority.eMedium		x
ExhADmp.MonitOpen.Dst	E_BA_LockPriority.eMedium		x
ExtAFan.Dst	E_BA_LockPriority.eMedium		x
ExtAFan.ThOvrld	E_BA_LockPriority.eMedium		x
ExtAFan.MntnSwi	E_BA_LockPriority.eMedium		x
ExtADiffPrssMonit.Dst	E_BA_LockPriority.eMedium		x
PreHtr.TRt.MV	E_BA_LockPriority.eMedium		x
PreHtr.TFrost.MV	E_BA_LockPriority.eMedium		x
PreHtr.FrostThermostat.Input	E_BA_LockPriority.eMedium		x
PreHtr.Pu.Dst	E_BA_LockPriority.eMedium		x

The parameterization of the lock priority of the event-enabled objects can be found in the FB_init of this template.

Temperature control

In this plant template a simple room air supply air cascade is realized as control strategy.

The setpoints for the plant are generated in the templates SpTRm / TCasCtrl and forwarded to the sequence controllers within the templates PreHtr, Col and Erc.

Sequence control

The number of sequence controllers in the control sequence varies and depends on the number of aggregates in the ventilation system. The PID sequence controllers, which contribute to increasing the supply air temperature, are arranged on the left of the control sequence. The controllers of the aggregates that cool down the supply air temperature are located on the right.
Several heating or cooling aggregates can be integrated into the control sequence.
Only one PID controller is active at any one time in the sequence control. All others remain at the value of their maximum or minimum control value.

The sequence control TSeqLink is enabled when bOn is received from the cascade control TCasCtrl.
The start sequence controller with which the plant starts up is determined depending on the weather temperature Site.stGeneralSettings.fTWth or the operation mode OpMod.

The stTSeqLink data structure is used to transmit the plant enable and the number of the start controller to the sequence controllers of the PreHtr air heater, Col air cooler and Erc energy recovery unit.
The ventilation system in the sequence diagram is equipped with an air heater, an energy recovery unit and an air cooler.
All aggregates are integrated into a sequence controller for continuous control of the supply air temperature TSuA at very low outdoor temperatures in winter through to high outdoor temperatures in summer.

The sequence on the left starts with the control range of the PreHtr air heater. At low outside temperatures, the output of the air heater is increased until the supply air temperature TSuA has reached its setpoint.

If the outside temperature TOuA rises, the sequence controller TSuACtrl of the PreHtr air heater reduces its actuating variable until it reaches the lower limit of its control range.

If the setpoint of the supply air temperature TCasCtrl is still not reached, the sequence controller TSuACtrl of the air heater PreHtr switches to the sequence controller TSuACtrl of the energy recovery Erc.
The behavior of the energy recovery Erc depends on the ratio of the weather temperature Site.stGeneralSettings.fTWth and the extract air temperature TExtA.

If the weather temperature Site.stGeneralSettings.fTWth is lower than the extract air temperature TExtA, energy recovery recovers heat energy from the extract air and transfers it to the outside air. The red characteristic curve is then activated in the control sequence.

The control direction of the sequence controller TSuACtrl is therefore indirect (heating mode).

In summer, the extract air temperature is often lower than the weather temperature. The energy flow of the energy recovery Erc is then inverted. The heat from the outside air is transferred to the exhaust air TExhA and the supply air temperature is reduced as a result. In this operating case, the sequence follows the blue characteristic curve. The control direction of the sequence controller TSuACtrl is therefore direct (cooling mode).

At high outside temperatures, if the recovery capacity of the Erc is not sufficient to cool the outside air OuA down far enough, the sequence controller TSuACtrl of the energy recovery Erc switches on to the sequence controller TSuACtrl of the cooler Col. This increases the capacity of the cooler until the setpoint of the supply air temperature is reached.

Filter monitoring

The outside and extract air filters are monitored via the function blocks FiltOuAMonit and FiltExtAMonit with the analog differential pressure sensors DiffPrssOuAFilt / DiffPrssExtAFilt. The filter monitors are enabled when bOn is received from the cascade control TCasCtrl.

Night cooling

Night cooling can be controlled via the function block SumNgtCol.

Syntax

FUNCTION_BLOCK FB_BA_AHU_1st_10 EXTENDS FB_BA_View
VAR_INPUT CONSTANT    
  TOuA                    : FB_BA_SensorAnalog;
  TExhA                   : FB_BA_SensorAnalog;
  TSuA                    : FB_BA_SensorAnalog;
  TExtA                   : FB_BA_SensorAnalog;
  TRm                     : FB_BA_SensorAnalog;

  DiffPrssOuAFilt         : FB_BA_SensorAnalog;
  FiltOuAMonit            : FB_BA_Hys_21;
  DiffPrssExtAFilt        : FB_BA_SensorAnalog;
  FiltExtAMonit           : FB_BA_Hys_21;

  OuADmp                  : FB_BA_AC_Dmp2P;
  SuAPrss                 : FB_BA_SensorAnalog;
  SuADiffPrss             : FB_BA_SensorAnalog;
  SuAFan                  : FB_BA_AC_FanCtl;
  SuADiffPrssMonit        : FB_BA_FdbAnalog;

  ExhADmp                 : FB_BA_AC_Dmp2P;
  ExtAPrss                : FB_BA_SensorAnalog;
  ExtADiffPrss            : FB_BA_SensorAnalog;
  ExtAFan                 : FB_BA_AC_FanCtl;
  ExtADiffPrssMonit       : FB_BA_FdbAnalog;

  PreHtr                  : FB_BA_AC_PreHtr;
  Erc                     : FB_BA_AC_ErcPl_02;
  Col                     : FB_BA_AC_ColT_02;

  SpTRm                   : FB_BA_Scale_04_Y2_3;
  TCasCtrl                : FB_BA_AC_TCasCtrl_01;

  SumNgtCol               : FB_BA_AC_SumNgtCol;
  OpMod                   : FB_BA_AC_OpMod1St;
  EnPrio                  : FB_BA_AC_EnPrio;

  PlantLock               : FB_BA_PlantLock;

  PlantCmd                : FB_BA_AC_PlantCmd_AHU_1st_10;

  TSeqLink                : FB_BA_AC_SeqT;
  stTSeqLink              : ST_BA_SeqLink;

  arrAggregate            : ARRAY [1..BA_Param.nMaxAggregate] OF ST_BA_Aggregate;
END_VAR

VAR_INPUT CONSTANT

Name	Type	Description
TOuA	FB_BA_SensorAnalog	Represents the outside air temperature
TExhA	FB_BA_SensorAnalog	Represents the exhaust air temperature
TSuA	FB_BA_SensorAnalog	Represents the supply air temperature
TExtA	FB_BA_SensorAnalog	Represents the extract air temperature
TRm	FB_BA_SensorAnalog	Represents the room temperature
DiffPrssOuAFilt	FB_BA_SensorAnalog	Analog differential pressure via the outside air filter
FiltOuAMonit	FB_BA_Hys_21	Analog monitoring of the outside air filter. The filter monitoring uses the analog differential pressure DiffPrssOuAFilt and can trigger both a pre-alarm and a main alarm.
DiffPrssExtAFilt	FB_BA_SensorAnalog	Analog differential pressure via the extract air filter
FiltExtAMonit	FB_BA_Hys_21	Analog monitoring of the extract air filter. Filter monitoring uses the analog differential pressure FiltExtAMonit and can trigger both a pre-alarm and a main alarm.
OuADmp	FB_BA_AC_Dmp2P	Activation of the outside air damper with a spring return actuator and end position monitor.
SuAPrss	FB_BA_SensorAnalog	Supply air pressure
SuADiffPrss	FB_BA_SensorAnalog	Differential pressure via the supply air fan
SuAFan	FB_BA_AC_FanCtl	Activation and control of the speed-controlled supply air fan.
SuADiffPrssMonit	FB_BA_FdbAnalog	Analog differential pressure monitoring via the supply air fan. Differential pressure monitoring uses the SuADiffPrss analog differential pressure sensor and can trigger a plant shutdown alarm.
ExhADmp	FB_BA_AC_Dmp2P	Control of the exhaust air damper with a spring return actuator and end position monitor.
ExtAPrss	FB_BA_SensorAnalog	Extract air pressure. The extract air pressure is the controlled variable of the pressure controller of the extract air fan ExtAFan.
ExtADiffPrss	FB_BA_SensorAnalog	Differential pressure via the extract air fan
ExtAFan	FB_BA_AC_FanCtl	Control and regulation of the speed-controlled extract air fan.
ExtADiffPrssMonit	FB_BA_FdbAnalog	Analog differential pressure monitoring via the extract air fan. Differential pressure monitoring uses the analog differential pressure sensor ExtADiffPrss and can trigger a plant shutdown alarm.
PreHtr	FB_BA_AC_PreHtr	Activation and control of a hot water air heater. The function block is regarded as an aggregate and is part of the temperature sequence control of this plant due to its implemented sequence controller.
Erc	FB_BA_AC_ErcPl_02	Activation and control of a plate heat exchanger for the energy recovery of a ventilation system. The function block is considered as an aggregate and is part of the temperature sequence control of this plant due to its implemented sequence controller.
Col	FB_BA_AC_ColT_02	Activation and control of a temperature-controlled cold water air cooler. The function block is considered as an aggregate and is part of the temperature sequence control of this plant due to its implemented sequence controller.
SpTRm	FB_BA_Scale_04_Y2_3	Setpoint program for supply air temperature control with a supply air temperature setpoint, including summer/winter compensation via a characteristic curve.
TCasCtrl	FB_BA_AC_TCasCtrl_01	Room temperature control by means of room-supply air cascade. It consists of a master controller for setpoint calculation for heating, cooling and energy recovery.
SumNgtCol	FB_BA_AC_SumNgtCol	Night cooling control
OpMod	FB_BA_AC_OpMod1St	The function block is used to switch on the plant. It represents the choice of plant operation mode, a timer program and a plant selector switch.
EnPrio	FB_BA_AC_EnPrio	Defines the plant release for controlling the step sequence control of a plant and the release of the priorities "Safety", "Critcial" and "Program" based on the plant operation mode OpMod. These releases are transferred to PlantCmd.
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 plant. These relevant faults trigger the operation mode Fault E_BA_AC_OpMod01.eAlarm in the operation mode program OpMod. As a result, the air conditioning system is shut down. A list of the faults that shut down the plant can be found under Fault shutdowns.
PlantCmd	FB_BA_AC_PlantCmd_AHU_1st_10	The function block represents the plant command of the aggregates and functions of this air conditioning system. The integrated step sequence controller fixes the order in which the individual aggregates of the plant are switched on or off sequentially one after the other.
TSeqLink	FB_BA_AC_SeqT	Represents the start and control of the supply air temperature sequence control.
stTSeqLink	ST_BA_SeqLink	Data and command structure between the individual sequence controllers of the temperature control sequence PreHtr, Col, Erc and the supply air temperature sequence control TSeqLink.
arrAggregates	ST_BA_Aggregate	The array contains a bidirectional data and command structure for each aggregate. When the step sequence controller is switched up or down, the switching command determined for each aggregate is transferred via the bidirectional communication structure arrAggregate. Feedback from the aggregates for switching the step sequence control up or down is transmitted to the plant control unit via the communication structure.

Requirements

Development environment	Necessary function
TwinCAT from v3.1.4024.56	TF8040 \| TwinCAT Building Automation from V5.8.0.0