BAC_AC_SeqT_01

Functional description

The template BAC_AC_SeqT_01 is responsible for starting the supply air temperature sequence control of an air-conditioning plant.

On startup of the air-conditioning plant the system determines whether to start with the heating, cooling or heat recovery sequence. The start sequence is selected depending on the plant operation mode and the outside temperature.

Only one element of the sequence can be in control. When the output of a controlling sequence element reaches Y Min or Y Max, the control is transferred to the next sequence controller that is ready for switch-on.

Interface

BAC_AC_SeqT_01 1:

System diagram

Block diagram

Linking of the global sequence link structure g_stSeqLinkT[PLT_NUM]

g_stSeqLinkT[PLT_NUM]

Order of the sequences

The order of the control sequence is specified by the globally defined variables. If necessary, the sequence order can be adjusted slightly.

For example if energy recovery is to take place upstream of the mixed air system.

Globally defined sequence numbers of the sequence controllers:

SEQNUM_T_REHTR	1	Sequenznummer Nacherhitzer//Sequence number reheater
SEQNUM_T_PREHTR	2	Sequenznummer Vorerhitzer//Sequence number preheater
SEQNUM_T_MIX	3	Sequenznummer Mischluft//Sequence number mixed air
SEQNUM_T_ERC	4	Sequenznummer Energierückgewinnung//Sequence number energy recovery
SEQNUM_T_COL	5	Sequenznummer Kühler//Sequence number cooler
SEQNUM_T_OFF	6	kein Sequenzregler aktiv//no sequence controller active

VAR_INPUT

udiOpMod    : UDINT; 
udiPltStp   : UDINT; 
rSuAT       : REAL;

udiOpMod: Plant operation mode. See also BAC_AC_OpMod_01

udiPltStp: Steps during startup of the air-conditioning plant. See also BAC_AC_StartT_01

rSuAT: Measured value supply air temperature

VAR_OUTPUT

bSumLmt     : BOOL; 
bWinLmt     : BOOL;

bSumLmt: Summer mode

bWinLmt: Winter mode

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!

Within a ventilation system with sequence controller the plant number indicates which field from the global data structure g_stSeqLinkT[PLT_NUM] is used as link between the individual sequence controllers and the corresponding control function blockFB_BA_SeqLink.

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
WthTLmtSum	FB_BACnetAVSetpoint	AV object for input of an outside temperature value from which the air-conditioning plant starts in the cooling sequence.
WthTLmtWin	FB_BACnetAVSetpoint	AV object for input of an outside temperature value from which the air-conditioning plant starts in the heating sequence.
SttSeqT	FB_BA_PrioSwi_USI08	The priority switch is used to select the start sequence. Prio 1: bEN01 In overheating protection mode (OPMOD_AC_OVRHTGPRTC), the system invariably starts with the cooling sequence ( SEQNUM_T_COL). Prio 2: bEN02 In cooling protection mode (OPMOD_AC_COLDWNPRTC), the system invariably starts with the heating sequence ( SEQNUM_T_PREHTR). Prio 4: bEN04 The upstream function block WthTLmtWinHys checks whether the actual outside temperature is below the critical value of AV object WthTLmtSum. If this is the case, the air-conditioning plant starts with the control sequence of the preheater. (SEQNUM_T_PREHTR) Prio 5: bEN05 The upstream function block WthTLmtSumHys checks whether the actual outside temperature is above the value of AV object WthTLmtSum. If this is the case, the air-conditioning plant starts with the control sequence of the cooler. (SEQNUM_T_COL) Prio 8: bEN08 In the transitional periods between winter and summer, the inputs of bEn04 and bEn05 are FALSE on account of the weather. In this case priority 8 applies at the priority switch. It means that the air-conditioning plant starts in the energy recovery sequence (SEQNUM_T_ERC).
SeqLinkT	FB_BA_SeqLink	The function block SeqLinkT is the core of the template BAC_AC_SeqT_01. The sequence linker is linked with all supply air controllers of the sequence via the global data structure g_stSeqLinkT[PLT_NUM] . It is the central control element, and responsible for switching between the sequence controllers and starting of the control sequence. The sequence linker is enabled at input bEn via the steps during startup of the ventilation system, if udiPltStp is >= the global constant PLTSTP_AC_ENTEMPCTRL .
CurSeqT	FB_BACnetMVDisplay	The MV object indicates the currently active sequence controller.

Version history

Version number	Comments
1.0.1	First release