FB_HVACCirculationPump

Application

This function block serves to control pumps in HVAC systems.

VAR_INPUT

eDataSecurityType     : E_HVACDataSecurityType;
bSetDefault           : BOOL;
bEnable               : BOOL;
bAuto                 : BOOL;
eCtrlModeActuator     : E_HVACActuatorMode; 
rOutsideTemp          : REAL;
rValvePosition        : REAL;
bFeedbPump            : BOOL;
bPumpProtec           : BOOL;
bAntiBlocking         : BOOL;
bManSwitch            : BOOL;
bCtrlVoltage          : BOOL;
bReset                : BOOL;               

eDataSecurityType:if eDataSecurityType:= eHVACDataSecurityType_Persistent, the persistent VAR_IN_OUT variables of the function block are stored in the flash of the computer if a value changes. For this to work, the function block FB_HVACPersistentDataHandling must be instanced once in the main program, which is called cyclically. Otherwise the instanced FB is not released internally.

A change of value can be initiated by the building management system, a local operating device or via a write access from TwinCAT. When the computer is restarted, the saved data are automatically read back from the flash into the RAM.

Application example: Example_PERSISTENT.zip

If eDataSecurityType:= eHVACDataSecurityType_Idle the persistently declared variables are not saved in a fail-safe manner.

bSetDefault: If the variable is TRUE, the default values of the VAR_IN_OUT variables are adopted.

bEnable: the function block is enabled if bEnable = TRUE.

bAuto: input for the request from the automatic program. The request is overridden by eCtrlModeActuator.

eCtrlModeActuator: Enum that defines the operation mode.

rOutsideTemp: input for transmitting the outside temperature value.

rValvePosition: if there is a control valve in the hydraulic circuit of the pump, the position of the control valve must be applied here.

bFeedbPump: this input is for displaying the operating message in a visualization system and for monitoring the pump function.

bPumpProtec: a pump error message is connected to the input bPumpProtec. There is a pump error if the input bPumpProtec is FALSE. The output bPump becomes FALSE in the event of a fault. The pump can only be restarted after an acknowledgment on the input bReset.

bAntiBlocking: input for transferring the anti-blocking request, i.e. if TRUE the request is active.

bManSwitch: if the pump has a manual/emergency switch in the control cabinet, this can be connected to the input bManSwitch; the status of the manual/emergency switch will then be monitored. If bManSwitch = FALSE, then output bPump is disabled. The output bPump can only be switched on if bManSwitch = TRUE (quiescent current principle).

bCtrlVoltage: in order to suppress a torrent of messages, the error message from bPumpProtec is only acquired if the input bCtrlVoltage is TRUE.

bReset: acknowledge input in the event of a fault.

VAR_OUTPUT

bPump                 : BOOL;      
byState               : BYTE;                
bStateManSwitch       : BOOL;
bReqOutsideTemp       : BOOL;           
bReqValve             : BOOL;           
eStateModeActuator    : E_HVACActuatorMode;         
bErrorPumpProtec      : BOOL;
bErrorPumpFeedb       : BOOL;                 
bErrorGeneral         : BOOL;                
byError               : BYTE;                
bInvalidParameter     : BOOL;

bPump: output variable for controlling a pump.

byState: output of the pump state as byte.
byState.0 := bEnable
byState.1 := bPump
byState.2 := bReqOutsideTemp
byState.3 := bReqValve
byState.4 := bAntiblocking
byState.5 := bFeedbPump
byState.6 := NOT bManSwitch
byState.7 := bCtrlVoltage

bStateManSwitch: status message of the manual/emergency switch. A TRUE signals that the manual/emergency operating level is activated.

bReqOutsideTemp: if the condition to request the pump depending on the outside temperature is TRUE, the output variable bReqOutsideTemp becomes TRUE.

bReqValve: if the condition for requesting the pump depending on the valve position is reached, the variable bReqValve becomes TRUE.

eStateModeActuator: indicates in which operation mode the actuator is.

bErrorPumpProtec: error from the pump.

bErrorPumpFeedb: if the input bFeedbPump does not go TRUE within the time of tFeedbPumpDelay (tFeedbPumpDelay must be > t#0s) after setting the output bPump, this is recognized as a fault and this output is set to TRUE and the output bPump to FALSE. The error message must be acknowledged with bReset.

bErrorGeneral: there is a general error.

byError: output of the errors as byte.
byError.1 := bInvalidParameter
byError.2 := bErrorGeneral
byError.3 := bErrorPumpProtec
byError.4 := bErrorPumpFeedb

bInvalidParameter: TRUE if an error occurs during the plausibility check. The message must be acknowledged with bReset.

VAR_IN_OUT

tStopDelay           : TIME;
tFeedbPumpDelay      : TIME;
rOutsideTempLimit    : REAL;
rValvePositionLimit  : REAL;
eReqOutsideTemp      : E_HVACReqOutsideTemp;     
eReqValve            : E_HVACReqValve;

tStopDelay: the time tStopDelay [s] delays the switching off of the pump after the switch-on conditions are no longer fulfilled. The variable is saved persistently. Preset to 0 s.

tFeedbPumpDelay: the monitoring function of the pump feedback message [s] is only active if tFeedbPumpDelay is > t#0s. If tFeedbPumpDelay = t#0s the monitoring function is deactivated (0s..3600s). The variable is saved persistently. Preset to 0 s.

rOutsideTempLimit: value [°C] above or below which the pump is switched on or off depending on the outside temperature (-60 °C..60 °C). The variable is saved persistently. Preset to 10 °C.

rValvePositionLimit: threshold value for the position of a control valve associated with a pump, from which the pump should switch on automatically, e.g. heater pump (0%..100%). The variable is saved persistently. Preset to 3%.

eReqOutsideTemp: depending on the outside temperature, the pump can be compulsorily switched on, e.g. for frost protection purposes when the temperature limit value rOutsideTempLimit is undershot. The prerequisite is that bEnable = TRUE and that the pump is in automatic mode. The variable is saved persistently.

eReqValve: depending on the position of the valve associated with the pump, the pump can be switched on when the threshold value rValvePositionLimit is exceeded. The ENUM activates the switch-on via the valve position. In addition, the ENUM determines whether the temperature-dependent and valve position-dependent switch-on conditions are ORed or ANDed together.

The table below shows a summary of all possible combinations:

By means of various combinations of the two variables, eReqOutsideTemp and eReqValve, this function block can be adapted to the requirements of a heating circuit, an air heater, an air cooler or a feed pump.