BAC_AC_StartT_01

Functional description

The template BAC_AC_StartT_01 is responsible for step-by-step startup of an air-conditioning plant without humidification and dehumidification.

The steps during plant startup are described through the variable udiPltStp. The steps are transferred to all units of the plant, so that each unit is integrated in the startup procedure of the air-conditioning plant.

Interface

BAC_AC_StartT_01 1:

System diagram

Block diagram

The following plant steps are described via the variable udiPltStp:

udiPltStp
PLTSTP_AC_OFF	Off
PLTSTP_AC_PRERI	pre-rincing heater
PLTSTP_AC_DMP	opening damper
PLTSTP_AC_FANSUA	supply air fan on
PLTSTP_AC_FANEXTA	extract air fan on
PLTSTP_AC_ENTEMPCTRL	ennabling temperature control, (sequence linker)
PLTSTP_AC_ENLMTMONIT	limit monitoring
PLTSTP_AC_ON	plant On (started)

VAR_INPUT

udiOpMod        : UDINT; 
bExhADmpOpn     : BOOL; 
bOuADmpOpn      : BOOL;
bPreriRdy       : BOOL; 
bMixADmpAvail   : BOOL;

udiOpMod: Plant operation mode. See also BAC_AC_OpMod_01

bOuADmpOpn: Feedback outside air damper open

bExhADmpOpn: Feedback exhaust air damper open

bPreriRdy: Prerinsing at heating coil complete

bMixADmpAvail: Mixed air system for startup process available

VAR_OUTPUT

udiPltStp       : UDINT;
bWhtTLmtCrit    : BOOL;

udiPltStp: Output of the current system startup steps

bWhtTLmtCrit: The outside temperature is below a critical value, so that prerinsing of the heating coil is required on startup of the air-conditioning plant. The pumps for the preheater and the reheater are switched on. The ramp function for the the mixed air dampers is activated on plant startup.

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
DmpDlyCls	FB_BACnetAVSetpoint	AV object delays closing of the dampers during shutdown of the air-conditioning plant, to consider the overrun time of the fans during system shutdown.
SuAFanDlyOn	FB_BACnetAVSetpoint	AV object for entering a value for the switch-on delay of the supply air fan when the air-conditioning plant is switched on
ExtAFanDlyOn	FB_BACnetAVSetpoint	AV object for entering a value for the switch-on delay of the outlet air fan when the air-conditioning plant is switched on
TSeqCtrlDlyOn	FB_BACnetAVSetpoint	AV object for entering a value for delayed control enable
LmtMonitDlyOn	FB_BACnetAVSetpoint	AV object for entering a value for delayed enable of the temperature sensor limit value monitoring
WthT_LmtCrit	FB_BACnetAVSetpoint	AV object for entering an outside temperature value at which the air-conditioning plant should start with prerinsing the heating coil.
SttPlt	FB_BA_StepCtrl12	The function block SttPlt is the core of the system start program. Input bEn is used for a general enable of the function block. If bEn is FALSE, all outputs of the function block are also FALSE. Step 1: Prerinsing of the heating coil PLTSTP_AC_PRERI At input bEvt01, startup of the air-conditioning plant initially starts with prerinsing of the heating coil. Step 2: Opening the outside and exhaust air damper PLTSTP_AC_DMP The input bEvt02 is set when the prerinsing process is complete or is not required, due to high external temperatures. This triggers the next startup step, opening of the dampers. The condition for advancing to the open dampers step is formed by the function block FdbPreri. Step 3: Start supply air fan PLTSTP_AC_FANSUA At input bEvt03 the limit switch for the outside air damper is connected. If the damper is open, step 3 of the supply air fan startup process is triggered. The startup of the supply air fan can be delayed at input udiDlyOn03. In smoke extraction mode the value for the fan startup delay is set to zero by the upstream selector. The program then moves to the next step without delay. Step 4: Start outlet air fan PLTSTP_AC_FANEXTA At input bEvt04 the limit switch for the exhaust air damper is connected. If the damper is open, step 4 of the exhaust air fan startup process is triggered. The startup of the outlet air fan can be delayed at input udiDlyOn04. In smoke extraction mode the value for the fan startup delay is set to zero by the upstream selector. The program then moves to the next step without delay. Step 5: Enable supply air sequence control temperature PLTSTP_AC_ENTEMPCTRL The input bEvt05 is constantly TRUE. This means that enable of the supply air sequence control is only delayed by the value of udiDlyOn05. Step 6: Enable sensor limit value monitoring PLTSTP_AC_ENLMTMONIT The input bEvt06 is constantly TRUE. This means that enable of the supply air sequence control is only delayed by the value of udiDlyOn06. Step 7: Indicates that the ventilation system is fully operational PLTSTP_AC_ON The input bEvt07 is constantly TRUE. This means that enable of the supply air sequence control is only delayed by the value of udiDlyOn06. During shutdown of the air-conditioning plant, the step sequence from step 7 to step 3 takes place without delay. Closing of the dampers after the fans are switched off is delayed by the timer DmpDlyCls. Step 1, prerinsing of the heating coil, is skipped.
SttPltEn	FB_BA_MMUX_B04	The multiplexer SttPltEn generates the general enable for the start-up program, depending on the plant operation modes. If the plant operation mode changes during operation, the variable SttPltEn_Rebt at the comparison output becomes TRUE. As a result, the plant startup function block SttPlt is temporarily reset. The start program is set to a defined state and restarted according to the new operation mode.
SttPltEvt01	FB_BA_MMUX_B24	The multiplexer SttPltEvt01 generates the enable for starting the prerinsing process, depending on the plant operation modes
FdbPreri	FB_BA_MMUX_B08	The multiplexer FdbPreri generates the enable for opening the dampers. In operation modes OPMOD_AC_SMEXTTPRG, OPMOD_AC_SMEXTTSUA, OPMOD_AC_SMEXTTEXHA, OPMOD_AC_NGTCOL and OPMOD_AC_OVRHTGPRTC, TRUE is output at output bVal. Step 1 of the plant startup function block SttPlt is skipped in these operation modes. The prerinsing process is reported as complete. For normal plant operation, opening of the dampers is triggered under the following conditions: 1. bMixADmpAvail = TRUE (A mixed-air system is present. The startup mode is realised via the mixed-air system) 2. bPreriRdy = TRUE (The prerinsing process is complete) 3. The outside temperature is uncritical. The output of function block WthT_LmtCritFnct is FALSE.
WthT_LmtCritFnct	FB_BA_Swi2P	The function block WthT_LmtCritFnct is a two-point switch. It sets the output variable bWthTLmtCrit to TRUE or FALSE, depending on the outside temperature. The switching point for the two-point switch is specified via the AV object WhtT_LmtCrit.
PltStpPrio	FB_BA_PrioSwi_UDI12	The priority switch PltStpPrio evaluates the current steps during the startup process and relays them via the variable udiVal to the BACnet MV object PltStp for display at the management level.
PltStp	FB_BACnetMVDisplay	The BACnet MV object indicates the current step during the startup process.

Version history

Version number	Comments
1.0.0.1	First release