CascadeExtractSupplyAirTemp2Setpt

CascadeExtractSupplyAirTemp2Setpt (FB)

FUNCTION_BLOCK CascadeExtractSupplyAirTemp2Setpt

Short description

Formation of two supply air setpoint temperatures using two cascade controllers (PI controllers) Additional functions: Limitation of the supply air setpoint temperatures Typical application: Supply air temperature control in a ventilation unit with active cooling\

Representation

Function description

General

This function block corresponds to the block ‘CascadeExtractSupplyAirTemperature’, which here is extended by an additional cascade controller to form a separate supply air setpoint temperature for the cooler in active cooling operation.\

CascadeExtractSupplyAirTemperature

This function block is used to form the supply air setpoint temperature of a ventilation unit from \

1. Current setpoint temperature (exhaust air or room temperature) in °C\

2) Current actual temperature (exhaust air or room temperature) in °C taking into account the relative (*rMinSUPTemp* and *rMaxSUPTemp*) and absolute (**rMinSUP** and **rMaxSUP**) limits. In addition, the special operating modes ‘Rapid heating’ and ‘Free night cooling’ are taken into account when forming the supply air setpoint temperature. The formation of the supply air setpoint temperature is time-delayed (**tDelayControl**) after the enabling / disabling of the controller (*xEn* = TRUE). The cascade controller is enabled if the following conditions described below are simultaneously met: 1) The special operating mode *Rapid heating* is disabled (*xFastHeatEn* = FALSE). 2) The special operating mode *Free night cooling* is disabled (*xFNCEn* = FALSE). 3) The current actual temperature *rActTemp* does not violate its absolute limits (+5.0 - +50.0 °C). 4) The control is enabled (*xEn* = TRUE) and the start delay (duration = **tDelayControl**) has ended. In all other situations the cascade controller is disabled.\

Control

The current actual temperature rActTemp is, when the cascade controller is enabled (PI controller, xEn = TRUE, expiry of the time duration tDelayControl, no limit violation at the input rActTemp ) continuously compared with the current setpoint temperature rSetPtTemp and depending on the magnitude / sign of the difference or depending on the controller settings ( rPI_Kp or rPI_Tn ) a offset temperature is generated in the cascade controller. In the heating case ( rActTemp < rSetPtTemp ) a positive offset temperature thus arises in the range 0.0 - rMaxRelativeSUP K. In the cooling case ( rActTemp > rSetPtTemp ) a negative offset temperature thus arises in the range 0.0 - rMinRelativeSUP K. In the fully regulated state ( rActTemp = rSetPtTemp ) the offset temperature does not change. This offset temperature is then added to the current setpoint temperature and, if necessary, limited to the calculated limits &#xNAN;rMinSUPTemp or rMaxSUPTemp limited. At the output rMinSUPTemp the calculated minimum supply air setpoint temperature is continuously displayed ( rActTemp + rMinRelativeSUP, absolutely limited to rMinSUP or rMaxSUP ) . At the output rMaxSUPTemp the calculated maximum supply air setpoint temperature is continuously displayed ( rActTemp + rMaxRelativeSUP, absolutely limited to rMinSUP or rMaxSUP ). The current actual temperature rActTemp is monitored for compliance with limits. On every limit violation ( rActTemp < +5.0 °C or rActTemp > +50.0 °C ) the cascade controller is deactivated.\

Selection of the supply air setpoint temperature

The selection of the supply air setpoint temperature is made according to the following function table.\

xFastHeatEn	xFNCEn	rActTemp within limit	xEn	Supply air setpoint temperature	Notes
TRUE	X	X	X	rMaxSUP	Special operating mode ‘Rapid heating’
FALSE	TRUE	X	X	rMinSUP	Special operating mode ‘Free night cooling’
FALSE	FALSE	FALSE	X	rSetPtTemp	Limit violation actual temperature
FALSE	FALSE	X	FALSE	rSetPtTemp	Locking of the control
FALSE	FALSE	TRUE	TRUE	rSetPtTemp + Offset temperature	Normal operation

Legend: X = any\

Formation of the current supply air setpoint temperature rSetPtSUPTemp

The current supply air setpoint temperature rSetPtSUPTemp is formed from the supply air setpoint temperature, extended by a manual override module.\

Supply air setpoint temperature	eManModeN	rSetPtSUPTemp	Notes
X	eMANNUM.Auto	Supply air setpoint temperature	Manual override module in automatic
X	eMANNUM.Man	rManValue	Manual override module in manual operation

Legend: X = any\

Cascade controller for active cooling operation (PI controller)

This cascade controller is used to form the supply air setpoint temperature for a cooling device from \

1. Current setpoint temperature (maximum value of ( rSetPtTemp + 1) and rSetPtTempCool )\

2) Current actual temperature (exhaust air or room temperature) in °C taking into account the following limits: Minimum value - output signal of the cascade controller: *rMinSUPTemP* - (maximum value of (*rSetPtTemp* + 1) and *rSetPtTempCool*) Maximum value - output signal of the cascade controller: *rMaxSUPTemP* - (maximum value of (*rSetPtTemp* + 1) and *rSetPtTempCool*) The formation of the supply air setpoint temperature takes place after enabling / disabling of the main cascade controller, provided the input *xEnCool* is active (= TRUE). The cascade controller for active cooling operation is enabled if the following conditions described below are simultaneously met: 1) The special operating mode *Rapid heating* is disabled (*xFastHeatEn* = FALSE). 2) The special operating mode *Free night cooling* is disabled (*xFNCEn* = FALSE). 3) The current actual temperature *rActTemp* does not violate its absolute limits (+5.0 - +50.0 °C). 4) The control is enabled (*xEn* = TRUE) and the start delay (duration = **tDelayControl**) has ended. 5) The input *xEnCool* is enabled (*xEnCool* = TRUE). In all other situations the cascade controller for active cooling operation is disabled.\

Control

The current actual temperature rActTemp is, when the cascade controller for active cooling operation is enabled, continuously compared with the current setpoint temperature (maximum value of ( rSetPtTemp + 1) and rSetPtTempCool ) and depending on the magnitude / sign of the difference or depending on the controller settings ( rPI_Kp or rPI_Tn ) an offset temperature for active cooling operation is generated in the cascade controller. In the heating case ( rActTemp < current setpoint temperature ) a positive offset temperature thus arises in the range 0.0 - Minimum value - output signal of the cascade controller for active cooling operation K. In the cooling case ( rActTemp > current setpoint temperature ) a negative offset temperature thus arises in the range 0.0 - Maximum value - output signal of the cascade controller for active cooling operation K. In the fully regulated state ( rActTemp = current setpoint temperature ) the offset temperature does not change. This offset temperature is then added to the current setpoint temperature and, if necessary, limited to the calculated limits &#xNAN;rMinSUPTemp or rMaxSUPTemp limited. The current actual temperature rActTemp is monitored for compliance with limits. On every limit violation ( rActTemp < +5.0 °C or rActTemp > +50.0 °C ) the cascade controller is deactivated.\

Selection of the supply air setpoint temperature

The selection of the supply air setpoint temperature is made according to the following function table.\

Enable cascade controller for active cooling operation	rActTemp within limit	Supply air setpoint temperature	Notes
FALSE	X	Maximum value of ( rSetPtTemp + 1) and rSetPtTempCool	Controller disabled
X	FALSE	Maximum value of ( rSetPtTemp + 1) and rSetPtTempCool	Limit violation
TRUE	TRUE	Current setpoint temperature + offset temperature	Normal operation

Legend: X = any\

Formation of the current supply air setpoint temperature rSetPtSUPTempCool

The current supply air setpoint temperature rSetPtSUPTempCool is formed from the supply air setpoint temperature, extended by a manual override module.\

Supply air setpoint temperature	eManModeNCool	rSetPtSUPTempCool	Notes
X	eMANNUM.Auto	Supply air setpoint temperature	Manual override module in automatic
X	eMANNUM.Man	rManValueCool	Manual override module in manual operation

Legend: X = any\

CODESYS

InOut:

Scope	Name	Type	Initial
Input	xEn	BOOL
Input	rActTemp	REAL	0
Input	rSetPtTemp	REAL	21
Input	rSetPtTempCool	REAL	24
Input	xEnCool	BOOL
Input	xFastHeatEn	BOOL	FALSE
Input	xFNCEn	BOOL	FALSE
Output	rSetPtSUPTemp	REAL
Output	rSetPtSUPTempCool	REAL
Output	rMinSUPTemp	REAL
Output	rMaxSUPTemp	REAL
Input Const	rPI_Tn	REAL	600
Input Const	rPI_Kp	REAL	1
Input Const	rMaxSUP	REAL	26
Input Const	rMaxRelativeSUP	REAL	6
Input Const	rMinSUP	REAL	16
Input Const	rMinRelativeSUP	REAL	-8
Input Const	tDelayControl	TIME	TIME#5m0s0ms
Input Const	rManValueCool	REAL
Input Const	eManModeNCool	eManNum	eManNum.Auto
Input Const	rManValue	REAL
Input Const	eManModeN	eManNum	eManNum.Auto