[Ahu24] Air handling unit, supply air temperature and supply air humidity control, pressure control

Plant example Ahu24 has speed-controlled fans, chilled water cooling coil, hot water heating coil, hot water reheating coil, energy recovery with a run-around coil, humidifier and shutoff dampers.

Functions

Supply air temperature control
Supply air humidity control
Pressure control

Plant diagram

Components

Fans, speed-controlled
Shutoff dampers
Energy recovery with run-around coil
Hot water heating coil
Chilled water cooling coil
Hot water reheating coil
Humidifier

Components and functions

Components and functions of the plant example:

Component	Function	BACnet object
	Fire detection contact Switches the plant to: Off	[BI] Fire detection contact
	Manual operating mode selection Switches the plant to: Auto \| Off \| On	[MCnfVal] Manual operating mode selection
	Scheduler program Switches the plant to: Off \| On	[MSchedule] Scheduler
	Present operating mode Reports the present operating mode: Off \| On Plant operating modes and control sequence	[MCalcVal] Present operating mode
	Reason for present operating mode Reports the reason for the present operating mode: Exception \| Operating mode switch \| Manual operating mode selection \| Scheduler \| Switching action operating	[MCalcVal] Reason for present operating mode
	Temperature control basic setpoints (1) Setpoints for upper (cooling setpoint) and lower (heating setpoint) extract air temperature Function diagram for temperature control basic setpoints (1)	[ACnfVal] Setpoint for cooling [ACnfVal] Setpoint for heating
	Seasonal temperature compensation (2) Corrects the high and low extract air temperature setpoint per the outside temperature. Function diagram for seasonal temperature compensation (2)	[BCalcVal] Seasonal temperature compensation > [ACalcVal] Present setpoint high for supply air temperature > [ACalcVal] Present setpoint low for supply air temperature
	Humidity control basic setpoints (1) Setpoints for upper (dehumidification setpoint) and lower (humidification setpoint) supply air humidity	> [ACnfVal] Setpoint for dehumidification > [ACnfVal] Setpoint for humidification
	Exhaust air differential pressure sensor Measures the differential pressure between duct and environment.	[AI] Extract air pressure (Located in extract air fan)
	Monitor negative pressure At too low a pressure, switches the plant to: Off
	Flow monitoring extract air The plant is switched to off if the differential pressure does not build after switching on the fan. Monitors the dampers and the fan.	> [BCalcVal] Flow monitoring
	Supply air differential pressure sensor Measures the differential pressure between duct and environment.	> [AI] Supply air pressure (Located in Supply air fan)
	Monitor positive pressure At too high a pressure, switches the plant to: Off
	Flow monitoring supply air The plant is switched to off if the differential pressure does not build after switching on the fan. Monitors the dampers and the fan.	> [BCalcVal] Flow monitoring
	Extract air temperature sensor Measures extract air temperature.	> [AI] Extract air temperature
	Extract air humidity sensor Measures the extract air humidity.	> [AI] Extract air humidity
	Supply air temperature sensor Measures the supply air temperature.	> [AI] Supply air temperature
	Supply air humidity sensor Measures supply air humidity.	> [AI] Supply air humidity
	Humidity detector Limits the maximum relative supply air humidity.	> [BI] Humidity detector (Located in Humidifier)
	Supply air fan	Supply air fan (Folder)
	Pressure controller Controls the supply air pressure. Function diagram for supply air pressure control	> [Controller] Pressure controller
	Supply air pressure setpoint Determines the setpoint for supply air pressure.	> [ACnfVal] Setpoint supply air pressure
	Command Switches on/off the fan as needed.	> [BO] Command
	Speed Controls the fan speed between 0 and 100 [%].	> [AO] Speed
	Maintenance switch Switches off the fan and the plant. The fan outputs are blocked locally at a high priority (Prio 2).	> [BI] Maintenance switch
	Fault message Fault messages, e.g. from the external motor control (variable speed drives). Switches off the fan and the plant.	> [BI] Fault
	Volume flow calculation Measures and calculates the volume flow.	Volume flow calculation (Folder)
	Differential pressure sensor for volume flow calculation Measures the differential pressure at one of the measuring points prepared on the fan for the volume flow measurement.	> [AI] Differential pressure for air volume flow calculation
	Displays the volume flow.	> [ACalcVal] Air volume flow
	Reheating coil	Reheating coils (Folder)
	Reports hot water demand to heat distribution.	> [BCalcVal] Hot water demand
	Pump	Pump (Folder)
	Pump command Switches on/off the pump as needed.	> [BO] Command
	Pump run when the outside air temperature is low Pump always operates at low outside temperatures (frost protection).
	Kick function (pump kick) Prevents the pump from seizing during long idle periods. [KICKFNCT] Kick function
	Valve	Valve (Folder)
	Temperature controller Controls the supply air temperature. Function diagram for supply air temperature control	> [Controller] Temperature controller
	Valve position Controls the valve position: 0...100 [%]	> [AO] Position
	Humidifier	Humidifier (Folder)
	Humidity controller Controls supply air humidity (humidification).	> [Controller] Humidity controller
	Command Switches on/off the humidifier as needed.	> [BO] Command
	Control Control the humidifier: 0 and 100 [%]	> [AO] Modulating
	Fault message Reports fault messages of the external humidifier fault.	> [BI] Fault
	Cooling coil	Cooling coil (Folder)
	Reports chilled water demand to cooling distribution.	> [BCalcVal] Chilled water demand
	Valve	Valve (Folder)
	Temperature controller Controls the supply air temperature. Function diagram for supply air temperature control	> [Controller] Temperature controller
	Humidity controller Controls supply air humidity (dehumidification). Function diagram humidity control	> [Controller] Humidity controller
	Valve position Controls the valve position: 0...100 [%]	> [AO] Position
	Heating coil	Heating coil (Folder)
	Reports hot water demand to heat distribution.	> [BCalcVal] Hot water demand
	Frost protection Prevents the hot water heating coil from freezing. The frost protection controller opens the valve (modulated) at a declining return temperature, e.g. below 10 [°C]. If the frost protection monitor triggers: The plant switches off. The valve fully opens (100%) and the pump is also switched on. Both at high priority (Prio 4).	> [BI] Frost protection monitor > [Controller] Frost protection controller
	Purge optimization Purges the heating coil with hot water at cold outside temperature prior to switching on fans. Duration and valve opening are optimized using function [PURGE] purge optimization. [PURGE] Purge optimization	> [BCalcVal] Startup purge active
	Return temperature sensor Measures the return temperature. The last purge optimization is prematurely canceled when exceeding a specific limit value, e.g. 30 [°C] during purge optimization. Supports frost protection. The reaction is the same as the one initiated for triggering the frost protection monitor, when dropping below a specific limit value, e.g. 4 [°C].	> [AI] Return temperature
	Pump	Pump (Folder)
	Pump command Switches on/off the pump as needed.	> [BO] Command
	Pump run when the outside air temperature is low Pump always operates at low outside temperatures (frost protection).
	Kick function (pump kick) Prevents the pump from seizing during long idle periods. [KICKFNCT] Kick function
	Valve	Valve (Folder)
	Temperature controller Controls the supply air temperature. Function diagram for supply air temperature control	> [Controller] Temperature controller
	Valve position Controls the valve position: 0...100 [%]	> [AO] Position
	Extract air filter	Extract air filter (Folder)
	Maintenance message after reaching the limit value for differential pressure. This requires a volume flow measurement. The present maintenance limits are derived from the smaller of the two values: Theoretical differential pressure for a clean filter from the filter characteristic curve plus the offset (typically 100 [Pa]) Measured differential pressure multiplied by a factor (typically factor = 3) Number 1 is the determinative value at average and large volume flows. Number 2 is the determinative value at smaller volume flows.	> [AI] Differential pressure > [ACalcVal] Present maintenance limit > [BCalcVal] Maintenance indication > [ACnfVal] Maintenance limit offset > [ACnfVal] Maintenance limit factor
	Extract air fan	Extract air fan (Folder)
	Pressure controller Controls extract air pressure. Function diagram for extract air pressure control	> [Controller] Pressure controller
	Setpoint extract air pressure Determines the extract air pressure setpoint.	> [ACnfVal] Setpoint extract air pressure
	Command Switches on/off the fan as needed.	> [BO] Command
	Speed Controls the fan speed between 0 and 100 [%].	> [AO] Speed
	Maintenance switch Switches off the fan and the plant. The fan outputs are blocked locally at a high priority (Prio 2).	> [BI] Maintenance switch
	Fault message Fault messages, e.g. from the external motor control (variable speed drives). Switches off the fan and the plant.	> [BI] Fault
	Volume flow calculation Measures and calculates the volume flow.	Volume flow calculation (Folder)
	Differential pressure sensor for volume flow calculation Measures the differential pressure at one of the measuring points prepared on the fan for the volume flow measurement.	> [AI] Differential pressure for air volume flow calculation
	Displays the volume flow.	> [ACalcVal] Air volume flow
	Energy recovery (Run-around coil system) Reuses sensible energy from extract air for supply air by transferring heat. Changeover heating/cooling: Determines whether it can be heated or cooled using extract air: Energy recovery can be used to heat if the extract air temperature is higher than the outside temperature. Energy recovery can be used to cool if the extract air temperature is lower than the outside temperature.	Energy recovery (Folder)
	Anti-icing protection The temperature sensor measures the glycol temperature after energy recovery. The anti-icing protection controller holds the glycol temperature sufficiently high by increasing the bypass rate. Prevents freezing of any condensation and icing on the exchanger surface.	> [AI] Glycol temperature > [Controller] Anti-icing protection controller
	Efficiency The thermal efficiency of heat recovery is calculated based on outside, extract, and supply air temperature after heat recovery.	> [AI] Supply air temperature after heat recovery > [ACalcVal] Efficiency
	Pump speed optimization Limits the pump speed in the function of the extract air volume flow.	> [BCalcVal] Pump modulating limitation active
	Valve	Valve (Folder)
	Temperature controller Controls the supply air temperature. Function diagram for supply air temperature control	> [Controller] Temperature controller
	Valve position Controls the valve position: 0...100 [%]	> [AO] Position
	Pump	Pump (Folder)
	Temperature controller Controls the supply air temperature. Function diagram for supply air temperature control	> [Controller] Temperature controller
	Pump command Switches on/off the pump as needed.	> [BO] Command
	Control Controls the pump: 0 and 100 [%]	> [AO] Modulating
	Reports pump faults. Switches off the plant at a very low outside temperature, e.g. -15 [°C].	> [BI] Fault
	Outside air filter	Outside air filter (Folder)
	Maintenance message after exceeding the limit value for differential pressure. This requires a volume flow measurement. The present maintenance limits are derived from the smaller of the two values: Theoretical differential pressure for a clean filter from the filter characteristic curve plus the offset (typically 100 [Pa]) Measured differential pressure multiplied by a factor (typically factor = 3) Number 1 is the determinative value at average and large volume flows. Number 2 is the determinative value at smaller volume flows.	> [AI] Differential pressure > [ACalcVal] Present maintenance limit > [BCalcVal] Maintenance indication > [ACnfVal] Maintenance limit offset > [ACnfVal] Maintenance limit factor
	Outside air damper	Outside air damper (Folder)
	Command Opens and closes the outside air damper. Adjustable damper runtime in the program.	> [BO] Command
	Exhaust air damper	Exhaust air damper (Folder)
	Command Opens and closes the exhaust air damper. Adjustable damper runtime in the program.	> [BO] Command
	Sensor for outside temperature Measures outside temperature.	> [AI] Outside air temperature
	Outside air humidity Measures outside air humidity.	> [AI] Outside air humidity

Functions and diagrams

Overview

Supply air temperature control with seasonal temperature compensation:

Key

1	Basic setpoints for temperature control
SpH	Setpoint for heating
SpC	Setpoint for cooling
2	Seasonal temperature compensation
HiCorr	High correction value
LoCorr	Low correction value
3	Present supply air temperature setpoints
PrSpLoTSu	Present setpoint low for supply air temperature
PrSpHiTSu	Present setpoint high for supply air temperature
4	Supply air temperature control
Erc	Energy recovery
Hcl	Heating coil
Ccl	Cooling coil
ReHcl	Reheating coil
Actg =1	Control action for the rotary heat exchanger is heating.
Actg =0	Control action for the rotary heat exchanger is cooling.
Pu'Mdlt	Pump, modulating control
Vlv-Pos	Valve position
TCtr	Temperature controller

Plant example Ahu24 is used as supply air temperature control.

Ahu24 can be adapted to the following applications with just a few modifications:

Extract air/supply air temperature cascade control
Room/supply air temperature cascade control
Pure room temperature control

Temperature control basic setpoints (1)

Basic setpoints, that, for example, are operated by the operator:

BACnet objects

Name	Description	Object type	Default value
SpC	Setpoint for cooling	ACnfVal	21 [°C]
SpH	Setpoint for heating	ACnfVal	20 [°C]

This plant example deals with basic setpoints for temperature control of the supply air setpoints.

Seasonal temperature compensation (2)

Seasonal temperature compensation corrects the high and low supply air temperature setpoint per the outside temperature.

The correction begins on the outside temperature start point [TOa...SttPnt] and ends with the outside temperature end point [TOa...EndPnt]. [Sp…CorrEndPnt] determines the height of the correction.

Key

PrSpShftHi	Output of the function seasonal temperature compensation
CHAR_LIN	Function block
TOa	Outside air temperature
SpHiCorrEndPnt	High correction value at the outside temperature end point
TOaHiEndPnt	Outside air temperature high for end point
TOaHiSttPnt	Outside air temperature high for start point
PrSpShftLo	Output of the function seasonal temperature compensation
SpLoCorrEndPnt	Low correction value at the outside temperature end point
TOaLoEndPnt	Outside temperature up to which the temperature compensation increases the low setpoint.
TOaLoSttPnt	Outside temperature at which the temperature compensation increases the low setpoint.

BACnet objects

Name	Description	Object type	Default value
SsnCmpT	Seasonal temperature compensation The seasonal temperature compensation is active if a correction is not equal to zero.	BCalcVal	Inactive

Name

Description

Object type

Default value

SsnCmpT

Seasonal temperature compensation

The seasonal temperature compensation is active if a correction is not equal to zero.

BCalcVal

Inactive

Set values on function block CHAR_LIN

Name	Description	Default value
TOaHiSttPnt	Outside air temperature high for start point (X1 on CHAR_LIN) Outside temperature at which the temperature compensation increases the high setpoint.	30 [°C]
TOaHiEndPnt	Outside air temperature high for end point (X2 on CHAR_LIN) Outside temperature up to which the temperature compensation increases the high setpoint.	34 [°C]
SpHiCorrEndPnt	High correction value at the outside temperature end point = > Height of the correction (Y2 on CHAR_LIN)	-2 [K]
TOaLoSttPnt	Outside air temperature low for start point (X1 on CHAR_LIN) Outside temperature at which the temperature compensation increases the low setpoint.	-10 [°C]
TOaLoEndPnt	Outside air temperature low for end point (X2 on CHAR_LIN) Outside temperature up to which the temperature compensation increases the low setpoint.	-15 [°C]
SpLoCorrEndPnt	Low correction value at the outside temperature end point = > Height of the correction (Y2 on CHAR_LIN)	2 [K]

Combination of basic setpoints (1) and seasonal temperature compensation (2) and (3)

Key

SpTSu	Setpoint for supply air temperature
PrSpShftLo	Output of the function seasonal temperature compensation
SpC	Setpoint for cooling
SpH	Setpoint for heating
PrSpLoTSu	Present setpoint low for supply air temperature
PrSpHiTSu	Present setpoint high for supply air temperature
PrSpShftHi	Output of the function seasonal temperature compensation
PrSpHiTSu	Present setpoint high for supply air temperature

BACnet objects

Name	Description	Object type	Default value
PrSpHiTSu	Present setpoint high for supply air temperature The present setpoint high for supply air temperature for cooling operation as corrected by the seasonal temperature compensation	ACalcVal	21 [°C]
PrSpLoTSu	Present setpoint low for supply air temperature The present setpoint low for supply air temperature for heating operation as corrected by the seasonal temperature compensation	ACalcVal	20 [°C]

Name

Description

Object type

Default value

PrSpHiTSu

Present setpoint high for supply air temperature

The present setpoint high for supply air temperature for cooling operation as corrected by the seasonal temperature compensation

ACalcVal

21 [°C]

PrSpLoTSu

Present setpoint low for supply air temperature

The present setpoint low for supply air temperature for heating operation as corrected by the seasonal temperature compensation

ACalcVal

20 [°C]

Supply air temperature control (4)

Key

Vlv'Pos, Spd	Valve position, speed
Actg =1	Control action for the rotary heat exchanger is heating.
Actg =0	Control action for the rotary heat exchanger is cooling.
ReHcl'Vlv'Pos	Reheating coil valve position
Hcl'Vlv'Pos	Heating coil valve position
Erc'Pu'Mdlt	Modulating control of energy recovery pump
Erc'Vlv'Pos	Energy recovery bypass valve position
Ccl'Vlv'Pos	Cooling coil valve position
PrSpLoTSu	Present setpoint low for supply air temperature
PrSpHiTSu	Present setpoint high for supply air temperature
TSu	Supply air temperature

BACnet objects

Name	Description	Object type	Default value
ReHcl'Vlv'TCtr	Temperature controller air reheating coil Controls the supply air temperature.	Controller	N/A
ReHcl'Vlv'TCtr	The temperature controller acts as a PI controller (PID with derivative action time Tv=0) and compares the temperature setpoint [PrSpLoTSu] against the supply air temperature [TSu] and calculates the valve position [ReHcl'Vlv'Pos] on the output. The following controller variables are preset: - Controller gain: 5 [%/K] - Integral action time Tn: 180 [s] The controller is locked in the following cases: - High outside air temperature (it is also released at a high outside air temperature even in the case of dehumidification)
Hcl'Vlv'TCtr	Temperature controller for heating coil Controls the supply air temperature.	Controller	N/A
Hcl'Vlv'TCtr	The temperature controller acts as a PI controller (PID with derivative action time Tv=0) and compares the temperature setpoint [SpTSu] against the supply air temperature [TSu] and calculates the valve position [Hcl'Vlv'Pos] on the output. The following controller variables are preset: - Controller gain: 5 [%/K] - Integral action time Tn: 180 [s] The controller is locked in the following cases: - High outside temperature - Dehumidification
HCl'FrPrtCtl	Frost protection heating coil Supports frost protection.	Controller	N/A
HCl'FrPrtCtl	The temperature controller acts as a PI controller (PID with derivative action time Tv=0) and compares the temperature setpoint of 10 [°C] against the return air temperature [Hcl'TRt] and calculates the valve position [Hcl'Vlv'Pos] on the output. The following controller variables are preset: - Controller gain: 5 [%/K] - Integral action time Tn: 180 [s]
Erc'Pu'TCtr	Temperature controller for energy recovery pump Controls the supply air temperature.	Controller	N/A
Erc'Pu'TCtr	Conditions for heating are fulfilled: The temperature controller acts as a PI controller (PID with derivative action time Tv=0) and compares the temperature setpoint (average of [PrSpHiTSu] and [PrSpLoTSu]) against the supply air temperature [TSu] and calculates the speed [Erc'Spd] on the output. The following controller variables are preset: - Controller gain: 5 [%/K] - Integral action time Tn: 180 [s] Conditions for cooling are fulfilled: The temperature controller acts as a PI controller (PID with derivative action time Tv=0) and compares the temperature setpoint (average of [PrSpHiTSu] and [PrSpLoTSu]) against the supply air temperature [TSu] and calculates the modulating control for the pump [Erc'Pu'Mdlt] on the output. The pump speed is limited in the function of the extract air volume flow. The volume flow volumes for the limitation are set specific to the project. Behavior at plant startup: Ramp-up at low outside temperature and if purge optimization [PURGE] occurred: Energy recovery is started at 100% and the temperature controller-heating coil immediately assumes temperature control. Ramp-up if no purge optimization [PURGE] occurred: Temperature controller-energy recovery is normally enabled and assumes temperature control.
Erc'Vlv'TCtr	Temperature controller for energy recovery bypass valve Controls the supply air temperature.	Controller	N/A
Erc'Vlv'TCtr	Conditions for heating are fulfilled: The temperature controller acts as a PI controller (PID with derivative action time Tv=0) and compares the temperature setpoint (average of [PrSpHiTSu] and [PrSpLoTSu]) against the supply air temperature [TSu] and calculates the speed [Erc'Spd] on the output. The following controller variables are preset: - Controller gain: 5 [%/K] - Integral action time Tn: 180 [s] Conditions for cooling are fulfilled: The temperature controller acts as a PI controller (PID with derivative action time Tv=0) and compares the temperature setpoint (average of [PrSpHiTSu] and [PrSpLoTSu]) against the supply air temperature [TSu] and calculates the modulating control for the pump [Erc'Pu'Mdlt] on the output. Behavior at plant startup: Ramp-up at low outside temperature and if purge optimization [PURGE] occurred: Energy recovery is started at 100% and the temperature controller-heating coil immediately assumes temperature control. Ramp-up if no purge optimization [PURGE] occurred: Temperature controller-energy recovery is normally enabled and assumes temperature control.
Ccl'TCtr	Temperature controller for cooling coil Controls the supply air temperature.	Controller	N/A
Ccl'TCtr	The temperature controller acts as a PI controller (PID with derivative action time Tv=0) and compares the temperature setpoint [PrSpHiTSu] against the supply air temperature [TSu] and calculates the valve position [Ccl'Vlv'Pos] on the output. The following controller variables are preset: - Controller gain: 5 [%/K] - Integral action time Tn: 180 [s] The controller is locked in the following cases: - Low outside temperature

Icing protection on energy recovery with run-around coil

Holds the glycol temperature sufficiently high by increasing the bypass rate.

Prevents freezing of any condensation and thus icing on the exchanger surface.

BACnet objects

Name	Description	Object type	Default value
Erc'lcPrtCtr	Anti-icing protection controller Prevents icing on the exchanger surface.	Controller	N/A
The anti-icing protection controller acts as a PI controller (PID with derivative action time Tv=0) and compares the temperature setpoint set on input [Sp] against the glycol temperature [Erc'TGly] and calculates value [YCtrMax] on the output on BACnet object Erc'Vlv'TCtr (temperature controller valve for energy recovery). The following controller variables are preset: - Controller gain: 10 [%/K] - Integral action time Tn: 120 [s]

Name

Description

Object type

Default value

Erc'lcPrtCtr

Anti-icing protection controller

Prevents icing on the exchanger surface.

Controller

N/A

The anti-icing protection controller acts as a PI controller (PID with derivative action time Tv=0) and compares the temperature setpoint set on input [Sp] against the glycol temperature [Erc'TGly] and calculates value [YCtrMax] on the output on BACnet object Erc'Vlv'TCtr (temperature controller valve for energy recovery).

The following controller variables are preset:
- Controller gain: 10 [%/K]
- Integral action time Tn: 120 [s]

Supply air humidity control:

Key

1	Basic setpoints humidity control
SpHum	Setpoint for humidification
SpDhu	Setpoint for dehumidification
2	Supply air humidity control
Erc	Energy recovery
Hcl	Heating coil
Ccl	Cooling coil
Hum	Humidifier
ReHcl	Reheating coil
Actg =0	Control action for the rotary heat exchanger is cooling.
Actg =1	Control action for the rotary heat exchanger is heating.
Vlv-Pos	Valve position
Mdlt	Modulating
TCtr	Temperature controller
HuCtr	Humidity controller

Plant example Ahu24 is used as supply air humidity control.

Humidity control basic setpoints (1)

Basic setpoints, that, for example, are operated by the operator:

BACnet objects

Name	Description	Object type	Default value
SpDhu	Setpoint for dehumidification	ACnfVal	60 [%RH]
SpHum	Setpoint for humidification	ACnfVal	45 [%RH]

This plant example deals with basic setpoints for humidity control of the supply air setpoints.

Supply air humidity control (2)

Key

Vlv'Pos, Mdlt	Valve position, modulating control
Hum'Mdlt	Modulating control of the humidifier
Ccl'Vlv'Pos	Cooling coil valve position
SpHum	Setpoint for humidification
SpDhu	Setpoint for dehumidification
HuSu	Supply air humidity

BACnet objects

Name	Description	Object type	Default value
Hum'HuCtr	Humidity controller-humidifier Controls supply air humidity.	Controller	N/A
Hum'HuCtr	The humidity controller acts as a PI controller (PID derivative actions time Tv=0) and compares the setpoint for humidification [SpHum] against the supply air humidity [HuSu] and calculates the modulating control [Hum'Mdlt] on the output. The following controller variables are preset: - Controller gain: 1 [%/g/kg] - Integral action time Tn: 180 [s]
Ccl'Vlv'HuCtr	Humidity controller cooling coils Controls supply air humidity.	Controller	N/A
Ccl'Vlv'HuCtr	The humidity controller acts as a PI controller (PID with derivative action time Tv=0) and compares the humidity setpoint [SpDHu] against the supply air humidity [HuSu] and calculates the valve position [Ccl'Vlv'Pos] on the output. It is supplied as a minimum controller output [YCtrMin] to the temperature controller (Ccl'Vlv'TCtr). The following controller variables are preset: - Controller gain: 1 [%/g/kg] - Integral action time Tn: 180 [s]

Supply air pressure control

Controls the supply air pressure using the supply air fan.

Key

Spd, PrVal	Speed, Present value
SpdMax	Maximum speed
SpdMin	Minimum speed
SpP	Pressure setpoint
P	Pressure

BACnet objects

Name	Description	Object type	Default value
FanSu'PCtr	Pressure controller for supply air fan Controls the supply air pressure.	Controller	N/A
The pressure controller acts as a PI controller (PID with derivative action time Tv=0) and compares the setpoint for supply air pressure [SpPSu] against the supply air pressure [PSu] and calculates the fan speed [Spd] on the output. The following controller variables are preset: - Controller gain: 0.2 [%/Pa] - Integral action time Tn: 60 [s]

Name

Description

Object type

Default value

FanSu'PCtr

Pressure controller for supply air fan

Controls the supply air pressure.

Controller

N/A

The pressure controller acts as a PI controller (PID with derivative action time Tv=0) and compares the setpoint for supply air pressure [SpPSu] against the supply air pressure [PSu] and calculates the fan speed [Spd] on the output.

The following controller variables are preset:
- Controller gain: 0.2 [%/Pa]
- Integral action time Tn: 60 [s]

Extract air pressure controller

Controls the extract air pressure using an extract air fan.

Key

Spd, PrVal	Speed, Present value
SpdMax	Maximum speed
SpdMin	Minimum speed
SpP	Pressure setpoint
P	Pressure

BACnet objects

Name	Description	Object type	Default value
FanEx'PCtr	Pressure controller for extract air fan Controls extract air pressure.	Controller	N/A
The pressure controller acts as a PI controller (PID with derivative action time Tv=0) and compares the setpoint for extract air pressure [SpPEx] against the extract air pressure [PEx] and calculates the fan speed [Spd] on the output. The following controller variables are preset: - Controller gain: 0.2 [%/Pa] - Integral action time Tn: 60 [s]

Name

Description

Object type

Default value

FanEx'PCtr

Pressure controller for extract air fan

Controls extract air pressure.

Controller

N/A

The pressure controller acts as a PI controller (PID with derivative action time Tv=0) and compares the setpoint for extract air pressure [SpPEx] against the extract air pressure [PEx] and calculates the fan speed [Spd] on the output.

The following controller variables are preset:
- Controller gain: 0.2 [%/Pa]
- Integral action time Tn: 60 [s]

Plant operating modes and control sequence

Plant operating modes:

Off (1)
On (2)

The operating modes are reported on [MCalcVal] object 'Present operating mode'.

At the same time, the reason for the present operating mode is reported to another [MCalcVal] object:

Exception (1)
Manual operating mode selection (2), resulting from an active (not equal to Auto) manual operating mode selection
Scheduler (3), resulting from an active scheduler
Switching action is performed (4) and is the result of a transition state on the plant (e.g. longer switch-off due to a delay to dry out the cooler)

The components for control are connected to function block CMDSEQ_B and are also acquired by this function block. See table below.
[CMDSEQ_B] Command sequence for binary

There is a normal mode and exception mode.

Normal operation

Sources for normal mode:

[MCnfVal] Manual operating mode selection
[MSchedule] Scheduler

In normal mode, the components are controlled at priority 15 per the operating mode, sequence, and function in function block CMDSEQ_B. The set timeouts and/or delays are considered.

Exception mode

Sources for exception mode:

Fire detection contact
Faults in the components, e.g. fault contact, frost protection monitor, maintenance switch
Faulty monitoring signals, e.g. flow monitoring

In exception mode, all outputs are switched off directly at priority 5 and the present operating mode is set to 'Off'. This is reported to function block CMDSEQ_B on input [RpdOff] and the components are switched off immediately as of the function block at priority 15.

The set timeouts and/or delays are not considered.

Special case frost protection:

In this case, outputs [AO] valve position and [BO] pump command are switched on by the heating coil at priority 4.

Special case maintenance switch:

In this case, outputs [AO] speed and [BO] command are switched off by the fans at priority 2.

Components, sequence, and function in CMDSEQ_B

Plant operating mode	Component
	Hcl	DmpOa	DmpEh	Erc	FanSu	FanEx	ReHcl	Ccl	Hum
Off	Off	Off	Off	Off	Off	Off	Off	Off	Off
On	On	On	On	On	On	On	On	On	On

Sequences
Start sequence	1	2	2	3	3	3	3	3	3
Start function	Feedback or Timeout	AND (Group with next aggregate)	Feedback	AND (Group with next aggregate)	AND (Group with next aggregate)	AND (Group with next aggregate)	AND (Group with next aggregate)	AND (Group with next aggregate)	AND (Group with next aggregate)
Start delay	5m	-	-	-	-	-	-	-	-

Stop sequence	3	3	3	2	2	2	2	1	1
Stop function	AND (Group with next aggregate)	AND (Group with next aggregate)	AND (Group with next aggregate)	Delay	AND (Group with next aggregate)	AND (Group with next aggregate)	AND (Group with next aggregate)	Feedback or Timeout	AND (Group with next aggregate)
Stop delay	-	-	-	1m	-	-	-	5m	-

Start sequence

The heating coil switches on.
It is further switched if an operating message from the heating coil arrives on the input pin of CMDSEQ_B or, at the latest after 5 minutes (function Feedback or Timeout). The ramp-up purge generates the operating message.
The shutoff dampers switch on (function AND).
In this plant example, the shutoff dampers do not have an end switch. The operating message (closed, open) is formed via commands and set runtimes for the applicable damper. It is still switched if the message (open) is on both dampers.
The fans, energy recovery, air cooling coil, the reheater, and the humidifier switch on at the same time (function AND, Group with next aggregate).

Stop sequence

The humidifier and cooling coil switch off at the same time (function AND, Group with next aggregate).
It is further switched if an operating message (Off) from both components arrives on the input pin of CMDSEQ_B or, at the latest after 5 minutes (function Feedback or Timeout).
When switching off the corresponding components (humidifier and cooling coil), the operating message (On) is maintained up to 5 minutes. The component can dry out if it was operating. If the component is not operating, its operating message is immediately set to Off without a delay to the stop sequence.
The fans, energy recovery, and reheater switch off at the same time (function AND, Group with next aggregate). It waits for 1 minute (function delay).
The shutoff dampers close and the heater switches off (function AND, Group with next aggregate).

Start-up control and alarm handling

Start-up control (nested chart SttUpAlmHdl)

The following functionality is available for an automatic startup of the plant, e.g. after a loss of power and return of power:

Fixed switch-on delay (can be set on input pin [DlySttUp])
The plant remains off to ensure communications are reliable and cross-check references are triggered. 'Exception' is reported as the reason for the present operating mode.
Automatic acknowledge (2x) of possible pending alarms during a fixed switch-on delay.
Additional adjustable delay for staged plant ramp-up (can be set on input pin [DlyOn])

Alarm handling (nested chart SttUpAlmHdl)

The state of events on the plant is acquired by BACnet object 'Plant state'. The state is mapped on function block CMN_EVT.
[CMN_EVT] Common event

The following functions are available:

Automatic acknowledge (2x) after startup
Alarm acknowledgement with a value object
Alarm indication:
- For pending alarms On
- For unprocessed alarms flashing
Ability to connect the acknowledge button [BI]
Ability to connect to an alarm indication [BO], e.g. an alarm lamp through an output block [BO]
Ability to connect to other alarm handling functions on other plants, e.g. acknowledge button and alarm indication for multiple plants in the same control cabinet

Startup function and alarm handling for flat plants

I/O data points

Name	Description	Type	Signal / connection	State text	Engineering unit
FireDetCont	Fire detection contact Alarm function: Extended (Notification class 7) Reference value: Tripped Time deviation: 0 [s]	BI	NC contact	Normal \| Tripped	N/A
FanEh'PEx	Extract air fan extract air pressure	AI	0...10 [V]	N/A	0...500 [Pa]
FanSu'Psu	Supply air fan supply air pressure	AI	0...10 [V]	N/A	0...500 [Pa]
TEx	Extract air temperature	AI	LG-Ni1000	N/A	0...50 [°C]
HuEx	Extract air humidity	AI	0...10 [V]	N/A	0...1000 [%RH]
TSu	Supply air temperature	AI	LG-Ni1000	N/A	0...50 [°C]
HuSu	Supply air humidity	AI	0...10 [V]	N/A	0...1000 [%RH]
Hum'HuDet	Humidifier humidity detector	BI	NC contact	Normal \| Tripped	N/A
FanSu'Spd	Supply air fan speed	AO	0...10 [V]	N/A	0...100 [%]
FanSu'Cmd	Supply air fan command	BO	NO contact	Off \| On	N/A
FanSu'MntnSwi	Supply air fan maintenance switch Alarm function: Basic (Notification class 8) Reference value: Maintenance Time deviation: 0 [s]	BI	NO contact	Normal \| Maintenance	N/A
FanSu'Flt	Supply air fan fault Alarm function: Basic (Notification class 8) Reference value: Tripped Time deviation: 0 [s]	BI	NO contact	Normal \| Tripped	N/A
FanSu'AirFlCalc'DiffP	Supply air fan air volume flow calculation Differential pressure	AI	0...10 [V]	N/A	0...1000 [Pa]
ReHcl'Vlv'Pos	Reheating coil valve position	AO	0...10 [V]	N/A	0...1000 [%]
ReHcl'Pu'Cmd	Reheater heating coil pump command	BO	NO contact	Off \| On	N/A
Hum'Cmd	Humidifier command	BO	NO contact	Off \| On	N/A
Hum'Mdlt	Humidifier modulating control	AO	0...10 [V]	N/A	0...1000 [%]
Hum'Flt	Humidifier fault message	BI	NO contact	Normal \| Tripped	N/A
Ccl'Vlv'Pos	Cooling coil valve position	AO	0...10 [V]	N/A	0...1000 [%]
Hcl'TRt	Heating coil return temperature	AI	LG-Ni1000	N/A	0...100 [°C]
Hcl'Vlv'Pos	Heating coil fan position	AO	0...10 [V]	N/A	0...100 [%]
Hcl'Pu'Cmd	Heating coil pump command	BO	NO contact	Off \| On	N/A
Hcl'FrPrtMon	Frost protection monitor Alarm function: Extended (Notification class 7) Reference value: Tripped Time deviation: 0 [s]	BI	NC contact	Normal \| Tripped	N/A
FilEx'DiffP	Extract air filter differential pressure	AI	0...10 [V]	N/A	0...500 [Pa]
FanEx'Spd	Exhaust air fan speed	AO	0...10 [V]	N/A	0...100 [%]
FanEx'Cmd	Exhaust air fan command	BO	NO contact	Off \| On	N/A
FanEx'MntnSwi	Exhaust air fan maintenance switch Alarm function: Basic (Notification class 8) Reference value: Maintenance Time deviation: 0 [s]	BI	NO contact	Normal \| Maintenance	N/A
FanEx'Flt	Exhaust air fan fault Alarm function: Basic (Notification class 8) Reference value: Tripped Time deviation: 0 [s]	BI	NO contact	Normal \| Tripped	N/A
FanSu'AirFlCalc'DiffP	Extract air fan air volume flow calculation differential pressure	AI	0...10 [V]	N/A	0...1000 [Pa]
Erc'Vlv'Pos	Energy recovery valve position	AO	0...10 [V]	N/A	0...100 [%]
Erc'Pu'Cmd	Energy recovery pump command	BO	NO contact	Off \| On	N/A
Erc'Pu'Mdlt	Energy recovery pump modulating control	AO	0...10 [V]	N/A	0...100 [%]
Erc'Pu'Flt	Energy recovery pump fault Alarm function: Extended (Notification class 7) Reference value: Tripped Time deviation: 0 [s]	BI	NO contact	Normal \| Tripped	N/A
Erc'TGly	Energy recovery glycol temperature	AI	LG-Ni1000	N/A	-20...50 [°C]
Erc'TSuAfErc	Energy recovery supply air temperature after energy recovery	AI	LG-Ni1000	N/A	0...50 [°C]
FilOa'DiffP	Outside air filter differential pressure	AI	0...10 [V]	N/A	0...500 [Pa]
DmpOa'Cmd	Outside air damper command	BO	NO contact	Close \| Open	N/A
DmpEh'Cmd	Exhaust air damper command	BO	NO contact	Close \| Open	N/A
TOa	Outside temperature	AI	LG-Ni1000	N/A	-70...70 [°C]
HuOa	Outside air humidity	AI	0...10 [V]	N/A	0...1000 [%RH]

[Ahu24] Air handling unit, supply air temperature and supply air humidity control, pressure control

See also