BAC_AC_StartTH_01

Functional description

The template BAC_AC_StartTH_01 is responsible for step-by-step startup of an air-conditioning plant with 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_StartTH_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-rinse heater
PLTSTP_AC_DMP	opening Damper
PLTSTP_AC_FANSUA	supply air fan on
PLTSTP_AC_FANEXTA	extract air fan on
PLTSTP_AC_ENTEMPCTRL	enabling temperature control, (sequence link)
PLTSTP_AC_ENHUMCTRL	enable humidity , (sequence link)
PLTSTP_AC_ENLMTMONIT	enabling limit monitoring
PLTSTP_AC_ON	On

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 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 take into account the overrun time of the fans during system shutdown.
SuAFanDlyOn	FB_BACnetAVSetpoint	AV object for entering a value for the start-up 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 start-up delay of the exhaust air fan when the air-conditioning plant is switched on
TSeqCtrlDlyOn	FB_BACnetAVSetpoint	AV object for entering a value for delayed temperature control enable
TSeqCtrlDlyOff	FB_BACnetAVSetpoint	AV object for entering a value for delayed temperature control disable
HSeqCtrlDlyOn	FB_BACnetAVSetpoint	AV object for entering a value for delayed humidity 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 prerinsing the heating coil.
SttPlt	FB_BA_StepCtrl12	The function block SttPlt is the core of the plant start program. The function block is generally enabled at the input bEn. If bEn = FALSE, all outputs of the function block are forced to FALSE. Step 1: prerinsing of the heating coil PLTSTP_AC_PRERI At the input bEvt01 the startup of the air-conditioning plant is first started with the prerinsing of the heating coil. Step 2: opening the outside and exhaust air damper PLTSTP_AC_DMP If the prerinsing process is completed or not required due to high outside temperatures, the input bEvt02 is set. This triggers the next startup step, the opening of the dampers. The condition for switching to the Open damper step is formed by the function block FdbPreri. Step 3: Starting the supply air fan PLTSTP_AC_FANSUA The limit switch of the outdoor air damper is connected to the input bEvt03. 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. Thus the program jumps to the next step without delay. Step 4: starting the exhaust air fan PLTSTP_AC_FANEXTA The limit switch of the exhaust air damper is connected to the input bEvt04. If the damper is open, step 4 of the exhaust air fan startup process is triggered. The startup of the exhaust 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. Thus the program jumps to the next step without delay. Step 5: Enable supply air sequence control temperature PLTSTP_AC_ENTEMPCTRL The input bEvt05 is constantly TRUE. Thus the enable of the supply air sequence control is only delayed by the value of udiDlyOn05. Step 6: enable supply air sequence control humidity PLTSTP_AC_ENHUMCTRL The input bEvt06 is constantly TRUE. Thus, the enable of the supply air sequence control is only delayed by the value of udiDlyOn06. Step 7: enable sensor limit value monitoring PLTSTP_AC_ENLMTMONIT The input bEvt07 is constantly TRUE. Thus the enable of the supply air sequence control is only delayed by the value of udiDlyOn07. Step 8: indicates that the ventilation system is in full operation PLTSTP_AC_ON The input bEvt08 is constantly TRUE. Thus, the enable of the supply air sequence control is only delayed by the value of udiDlyOn07. When the air-conditioning plant is shut down, the humidity control (step 6) is switched off first and then, with a time delay, the temperature control (step 5). The switch-off delay of the temperature control prevents condensation of residual moisture in the air ducts and, as a result, the response of a hygrostat when the plant is switched off. To bridge a overrun time of the fans, the closing of the dampers during shutdown of the plant is delayed by the timer DmpDlyCls.
SttPltEn	FB_BA_MMUX_B04	The multiplexer SttPltEn generates the general enable for the startup 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. This briefly resets the plant startup function block SttPlt. The start program is thus 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 the 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 SttPltis skipped in these operation modes. The prerinsing process is reported as completed. For normal plant operation, the opening of the dampers is triggered under the following conditions: 1. bMixADmpAvail = TRUE (A mixed air system is present. Startup operation is realized by means of mixed air system) 2. bPreriRdy = TRUE (The prerinsing process is completed) 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