CascadeExtractSupplyAirX2Setpt

CascadeExtractSupplyAirX2Setpt (FB)

FUNCTION_BLOCK CascadeExtractSupplyAirX2Setpt

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 system with active cooling

Representation

Function description

General

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

CascadeExtractSupplyAirTemperature

This function block is used to generate the supply air setpoint temperature of a ventilation system from

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

2) Current actual temperature (exhaust 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 ‘Fast heating’ and ‘Free night cooling’ are taken into account when forming the supply air setpoint temperature. The formation of the supply air setpoint temperature takes place with a time delay (tDelayControl) after the release/locking of the controller (xEn = TRUE). The cascade controller is enabled if the following conditions described below are fulfilled simultaneously: 1) The special operating mode Fast heating is locked (xFastHeatEn = FALSE). 2) The special operating mode Free night cooling is locked (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-up delay (time duration = tDelayControl) has ended. In all other situations the cascade controller is locked.

Control

The current actual temperature rActTemp is, with the cascade controller 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) an offset temperature is generated in the cascade controller. In heating mode (rActTemp < rSetPtTemp) this produces a positive offset temperature in the range 0.0 - rMaxRelativeSUP K. In cooling mode ( rActTemp > rSetPtTemp ) thus a negative offset temperature 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 rMinSUPTemp or rMaxSUPTemp . At the output rMinSUPTemp the calculated minimum supply air setpoint temperature is continuously shown (rActTemp + rMinRelativeSUP, absolutely limited to rMinSUP or rMaxSUP) . At the output rMaxSUPTemp the calculated maximum supply air setpoint temperature is continuously shown (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 carried out 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 ‘Fast 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 of (rSetPtTemp + 1) and rSetPtTempCool) Maximum value - output signal of the cascade controller: rMaxSUPTemP - (maximum 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 enabling of the cascade controller for active cooling occurs if the following conditions described below are all fulfilled simultaneously: 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 switch-on delay (duration = tDelayControl) has ended. 5) The input xEnCool is enabled (xEnCool = TRUE). In all other situations the cascade controller for active cooling is disabled.

Control

The current actual temperature rActTemp is, with the cascade controller for active cooling operation 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 heating mode (rActTemp < current setpoint temperature) this produces a positive offset temperature in the range 0.0 - Minimum value - output signal of the cascade controller for active cooling operation K. In cooling mode (rActTemp > current setpoint temperature) this produces a negative offset temperature 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 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 carried out according to the following function table.

Release cascade controller for active cooling operation	rActTemp within limit	Supply air setpoint temperature	Notes
FALSE	X	Maximum value of (rSetPtTemp + 1) and rSetPtTempCool	Controller locked
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	rActX	REAL	9
Input	rSetPtminHum	REAL	40
Input	rSetPtmaxHum	REAL	70
Input	rSetPtTemp	REAL	21
Input	rSUPTemp	REAL	20
Output	rSetPtSUPxHumidify	REAL
Output	rSetPtSUPxDehumidify	REAL
Output	rMinSUPX	REAL
Output	rMaxSUPX	REAL
Output	rSetPtxHumidify	REAL
Output	rSetPtxDehumimdify	REAL
Output	xEnHum	BOOL
Output	xEnDehum	BOOL
Input Const	rPI_Tn	REAL	400
Input Const	rPI_Kp	REAL	1.4
Input Const	rMaxHumSUP	REAL	80
Input Const	rMinHumSUP	REAL	30
Input Const	tDelayControl	TIME	TIME#5m0s0ms
Input Const	rP	REAL	980.0
Input Const	rManValueDehum	REAL
Input Const	eManModeNDehum	eManNum	eManNum.Auto
Input Const	rManValueHum	REAL
Input Const	eManModeNHum	eManNum	eManNum.Auto