[Ahu23] Air handling unit, temperature and humidity cascade control, pressure control
Plant example Ahu23 has speed-controlled fans, chilled water cooling coil, hot water heating coil, energy recovery with a rotary heat exchanger, a humidifier, shutoff dampers, and fire dampers.
Functions
- Temperature control with extract air/supply air temperature cascade control
- Humidity control with extract air/supply air cascade control
- Pressure control
Plant diagram
Components
- Fans, speed-controlled
- Shutoff dampers and fire dampers
- Energy recovery with rotary heat exchanger
- Hot water heating coil
- Chilled water cooling coil
- Hot water reheating coil
- Humidifier
Components and functions of the plant example:
Component | Function | BACnet object |
|---|---|---|
| Fire detection contact Switches the plant to: Off | [BI] Fire detection contact |
| Operating mode switch Switches the plant to: Auto | Off | On | [MI] Operating mode switch |
| 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 | [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 and lower 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. | [BCalcVal] Seasonal temperature compensation |
| Temperature cascade control (3) (Extract air/supply air temperature cascade) Calculates the high and low supply air setpoint per the extract air temperature. |
> [ACalcVal] Present setpoint high for room temperature > [ACalcVal] Present setpoint low for room temperature > [ACalcVal] Present setpoint high for supply air temperature > [ACalcVal] Present setpoint low for supply air temperature > [ACnfVal] Gain > [ICnfVal] Integral action time Tn > [ACnfVal] Minimum supply air temperature setpoint > [ACnfVal] Maximum supply air temperature setpoint |
| Humidity control basic setpoints (1) Setpoints for upper and lower extract air humidity | > [ACnfVal] Setpoint for dehumidification > [ACnfVal] Setpoint for humidification |
| Humidity cascade control (3) (Extract air/supply air humidity cascade) Calculates the high and low supply air setpoint per the extract air humidity. |
> [ACalcVal] Present setpoint high for room humidity > [ACalcVal] Present setpoint low for room humidity > [ACalcVal] Present setpoint high for supply air humidity > [ACalcVal] Present setpoint low for supply air humidity > [ACnfVal] Gain > [ICnfVal] Integral action time Tn > [ACnfVal] Minimum setpoint for supply air humidity > [ACnfVal] Maximum setpoint for supply air humidity |
| Supply air fire dampers Opens and closes the fire damper group in the supply air. Monitors the position open. Adjustable damper runtime in the program. |
> [BO] Command > [BI] Feedback open > [BCalcVal] Position monitoring |
| Extract air fire dampers Opens and closes the fire damper group in the extract air. Monitors the position open. Adjustable damper runtime in the program. |
> [BO] Command > [BI] Feedback open > [BCalcVal] Position monitoring |
| Smoke detector Switches the plant to: Off The smoke detector contacts are switched in series. | > [BI] Smoke detector |
| Exhaust air differential pressure sensor Measures the differential pressure between duct and environment. | [AI] Extract air pressure (Located in |
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 |
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 |
| Supply air fan |
|
Pressure controller Controls the supply air pressure. | > [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 | |
| Reheating coil |
|
Reports hot water demand to heat distribution. | > [BCalcVal] Hot water demand | |
Pump |
| |
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. |
| |
Valve |
| |
Temperature controller Controls the supply air temperature. | > [Controller] Temperature controller | |
Valve position Controls the valve position: 0...100 [%] | > [AO] Position | |
| Humidifier |
> [BI] Fault |
Humidity controller Controls supply air humidity (humidification). | > [Controller] Humidity controller | |
Protects against too high relative supply air humidity by reducing the humidifier power. The humidity detector triggers less frequently when reducing the power. | > [Controller] Limitation 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. | > [Controller] Humidity controller | |
| Cooling coil |
|
Reports chilled water demand to cooling distribution. | > [BCalcVal] Chilled water demand | |
Valve |
| |
Temperature controller Controls the supply air temperature. | > [Controller] Temperature controller | |
Humidity controller Controls supply air humidity (dehumidification). | > [Controller] Humidity controller | |
Valve position Controls the valve position: 0...100 [%] | > [AO] Position | |
| Heating coil
|
|
Reports hot water demand to heat distribution. | > [BCalcVal] Hot water demand | |
Frost protection Prevents the hot water heating coil from freezing. If the frost protection monitor triggers:
| > [BI] Frost protection monitor | |
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. | > [BCalcVal] Startup purge active | |
Pump |
| |
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. |
| |
Valve |
| |
Temperature controller Controls the supply air temperature. | > [Controller] Temperature controller | |
Valve position Controls the valve position: 0...100 [%] | > [AO] Position | |
| Extract air filter |
|
Maintenance message after reaching the limit value for operating hours. | > [BCalcVal] Operating state > [ICalcVal] Operating hours > [ICnfVal] Maintenance limit > [BCalcVal] Maintenance indication > [BCnfVal] Reset operating hours | |
| Energy recovery (Rotary heat exchanger) Reuses sensitive and, to some extent, latent energy from extract air for the supply air through the transfer of heat and, to some extent, humidity. Changeover heating/cooling: Determines whether it can be heated or cooled using extract air:
|
|
Temperature controller Controls the supply air temperature. The supply air setpoint is the result of the average of the high setpoint for supply air temperature and the low setpoint for supply air temperature. | > [Controller] Temperature controller | |
Speed Controls the speed of the rotary heat exchanger: 0…100 [%] | > [AO] Speed | |
Anti-icing protection The temperature sensor measures the exhaust air temperature after energy recovery. The anti-icing protection controller holds the exhaust air temperature sufficiently high by lowering the power (speed). Prevents freezing of any condensation and icing on the exchanger surface. | > [AI] Exhaust air temperature after energy recovery > [Controller] Anti-icing protection controller | |
Reports faults from external energy recovery control. | > [BI] Fault | |
| Outside air filter |
|
Maintenance message after reaching the limit value for operating hours. | > [BCalcVal] Operating state > [ICalcVal] Operating hours > [ICnfVal] Maintenance limit > [BCalcVal] Maintenance indication > [BCnfVal] Reset operating hours | |
| Exhaust air fan |
|
Pressure controller Controls extract air pressure. | > [Controller] Pressure controller
| |
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: 0...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 | |
| Outside air damper |
|
Command Opens and closes the outside air damper. Adjustable damper runtime in the program. | > [BO] Command | |
| Exhaust air damper |
|
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 |
Temperature control (
Overview
Extract air/supply air temperature cascade 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 | Temperature cascade control |
PrSpLoTSu | Present setpoint low for supply air temperature |
PrSpHiTSu | Present setpoint high for supply air temperature |
PrSpLoT | Present setpoint low for room temperature |
PrSpHiT | Present setpoint high for room temperature |
4 | Supply air temperature control |
Spd | Speed |
VlvPos | Valve position |
TCtr | Temperature controller |
Plant example Ahu23 is used as extract air/supply air temperature cascade control.
Ahu23 can be adapted to the following applications with just a few modifications:
- Room/supply air temperature cascade control
- Pure supply air temperature 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 | 24 [°C] |
SpH | Setpoint for heating | ACnfVal | 21 [°C] |
This plant example deals with basic setpoints for temperature control of the extract air setpoints.
Seasonal temperature compensation (2)
Seasonal temperature compensation corrects the high and low extract 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 |
SpHiCorrEndPnt | High correction value at the outside air end point |
TOaHiEndPnt | Outside air temperature high for end point |
TOa | Outside air temperature |
TOaHiSttPnt | Outside air temperature high for start point |
PrSpShftLo | Output of the function seasonal temperature compensation |
SpLoCorrEndPnt | Low correction value at the outside air 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 |
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. | 26 [°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. | 32 [°C] |
SpHiCorrEndPnt | High correction value at the outside temperature end point = > Height of the correction (Y2 on CHAR_LIN) | 3 [K] |
TOaLoSttPnt | Outside air temperature low for start point (X1 on CHAR_LIN) Outside temperature at which the temperature compensation increases the low setpoint. | 26 [°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. | 32 [°C] |
SpLoCorrEndPnt | Low correction value at the outside temperature end point = > Height of the correction (Y2 on CHAR_LIN) | 1 [K] |
Combination of basic setpoints (1) and seasonal temperature compensation (2)
Key
SpTR | Room temperature setpoint or extract air temperature setpoint |
PrSpHiT | Present setpoint high for room temperature |
PrSpShftHi | Output of the function seasonal temperature compensation |
PrSpLoT | Present setpoint low for room temperature |
PrSpShftLo | Output of the function seasonal temperature compensation |
TOa | Outside air temperature |
BACnet objects
Name | Description | Object type | Default value |
|---|---|---|---|
PrSpHiT | Present setpoint high for room temperature The present setpoint high room temperature or extract air setpoint for cooling operation as corrected by the seasonal temperature compensation | ACalcVal | 23 [°C] |
PrSpLoT | Present setpoint low for room temperature The present setpoint low room temperature or extract air setpoint for heating operation as corrected by the seasonal temperature compensation | ACalcVal | 22 [°C] |
The comfort area for the room is defined using the two basic setpoints for the room or extract air temperature; both of which are compensated to account for outside temperature.
Temperature cascade control (3)
Extract/supply air temperature cascade control calculates the high and low supply air temperature setpoint as per the extract air temperature.
Function block CAS_CTR calculates the following setpoints:
- [PrSpHiTSu] Present setpoint high for supply air temperature
- [PrSpLoTSu] Present setpoint low for supply air temperature
The supply air setpoints [PrSpLoTSu] and [PrSpHiTSu] are limited on the low side by the minimum supply air temperature setpoint [SpTSuMin] and by the maximum supply air temperature setpoint [SpTSuMax] on the high side.
If the room or extract air temperature [TR] exceeds the present setpoint high for the room temperature [PrSpHiT], the present setpoint high for supply air [PrSpHiTSu] is continuously reduced until the minimum setpoint low for supply air [SpTSuMin] is reached.
If the room or extract air temperature [TR] drops below the present setpoint low for room temperature [PrSpLoT], the present setpoint low for supply air [PrSpLoTSu] is continuously increased until the maximum setpoint for supply air [SpTSuMax] is reached.
Setpoints are forwarded to the components responsible for supply air temperature control (4).
The setpoint for energy recovery with rotary heat exchanger is calculated using the average of [PrSpHiTSu] and [PrSpLoTSu].
Key
TSu | Supply air temperature |
SpTSuMax | Maximum supply air temperature setpoint |
PrSpLoTSu | Present setpoint low for supply air temperature |
PrSpHiTSu | Present setpoint high for supply air temperature |
SpTSuMin | Minimum supply air temperature setpoint |
PrSpLoT | Present setpoint low for room temperature |
PrSpHiT | Present setpoint high for room temperature |
TR | Room temperature (or extract air temperature TEx) |
BACnet objects
Name | Description | Object type | Default value |
|---|---|---|---|
PrSpHiT | Present setpoint high for room temperature The present setpoint high room temperature or extract air setpoint for cooling operation as corrected by the seasonal temperature compensation | ACalcVal | 23 [°C] |
PrSpLoT | Present setpoint low for room temperature The present setpoint low room temperature or extract air setpoint for heating operation as corrected by the seasonal temperature compensation | ACalcVal | 22 [°C] |
PrSpHiTSu | Present setpoint high for supply air temperature Calculated supply air setpoint for cooling | ACalcVal | 18 [°C] |
PrSpLoTSu | Present setpoint low for supply air temperature Calculated supply air setpoint for heating | ACalcVal | 18 [°C] |
SpTSuMax | Maximum supply air temperature setpoint Limits supply air on the high side. | ACnfVal | 32 [°C] |
SpTSuMin | Minimum supply air temperature setpoint Limits supply air on the low side. | ACnfVal | 15 [°C] |
Gain | Gain Gain factor for the cascade controller | ACnfVal | 3 [K/K] |
Tn | Integral action time Tn Integral action time for the cascade controller | ICnfVal | 1200 [s] |
Supply air temperature control (4)
Key
Vlv'Pos, Spd | 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'Spd | Speed of energy recovery with rotary heat exchanger speed |
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 |
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: The controller is locked in the following cases: | |||
Hcl'Vlv'TCtr | Temperature controller for heating coil Controls the supply air temperature. | Controller | N/A |
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: The controller is locked in the following cases: | |||
Erc'TCtr | Temperature controller for energy recovery Controls the supply air temperature. | Controller | N/A |
Conditions for heating are fulfilled: The following controller variables are preset: Conditions for cooling are fulfilled: The following controller variables are preset: Behavior at plant startup: Ramp-up at low outside temperature and if purge optimization [PURGE] occurred: Ramp-up if no purge optimization [PURGE] occurred: | |||
Ccl'TCtr | Temperature controller for cooling coil Controls the supply air temperature. | Controller | N/A |
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: The controller is locked in the following cases: | |||
Icing protection on energy recovery with rotary heat exchangers
Holds the exhaust air temperature sufficiently high by lowering the power (speed).
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 exhaust air temperature after energy recovery [TEhAfErc] and calculates value [YCtrMax] on the output on BACnet object Erc'TCtr (temperature controller for energy recovery). The following controller variables are preset: | |||
Extract air / supply air cascade control:
Key
1 | Basic setpoints humidity control |
SpHu | Setpoint for humidity |
SpDhu | Setpoint for dehumidification |
3 | Humidity cascade control |
PrSpLoHuSu | Present setpoint low for supply air humidity |
PrSpHiHuSu | Present setpoint high for supply air humidity |
PrSpLoHu | Present setpoint low for room humidity |
PrSpHiHu | Present setpoint high for room humidity |
4 | Supply air humidity control |
Vlv-Pos | Positioning |
Mdlt | Modulating control |
Plant example Ahu23 is used as extract air/supply air humidity cascade 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 | 40 [%RH] |
This plant example deals with basic setpoints for humidity control of the extract air setpoints.
Humidity cascade control (3)
Humidity cascade control of the extract air-supply air calculates the high and low supply air temperature setpoint as per the extract air humidity.
Function block CAS_CTR calculates the following setpoints:
- [PrSpHiHuSu] Present supply air humidity high in [g/kg]
- [PrSpLoHuSu] Present supply air humidity low in [g/kg]
The supply air humidity setpoints [PrSpLoHuSu] and [PrSpHiHuSu] are limited on the low side by the minimum supply air humidity setpoint [SpHuSuMin] in [g/kg] and on the high side by the maximum supply air humidity setpoint [SpHuSuMax] in [hg/kg].
If the extract air humidity [HuEx] exceeds the present high humidity setpoint [PrSpHiHu], the present high supply air humidity setpoint [PrSpHiHuSu] is continuously reduced until the minimum supply air humidity setpoint [SpHuSuMin] is achieved.
If the extract air humidity [HuEx] drops below the present low humidity setpoint [PrSpLoHu], the present low supply air humidity setpoint [PrSpLoHuSu] is increased continuously until the maximum supply air humidity setpoint [SpHuSuMax] is achieved.
Setpoints are forwarded to the components responsible for supply air humidity control (4).
Key
HuSu | Supply air humidity |
SpHuSuMax | Maximum setpoint for supply air humidity |
PrSpLoHuSu | Present setpoint low for supply air humidity |
PrSpHiHuSu | Present setpoint high for supply air humidity |
SpHuSuMin | Minimum setpoint for supply air humidity |
PrSpLoHu | Present setpoint low for room humidity |
PrSpHiHu | Present setpoint high for room humidity |
HuR | Room air humidity (Extract air humidity, HuEx) |
BACnet objects
Name | Description | Object type | Default value |
|---|---|---|---|
PrSpHiHu | Present setpoint high for room humidity | ACalcVal | [%RH] |
PrSpLoHu | Present setpoint low for room humidity | ACalcVal | [%RH] |
PrSpHiHuSu | Present setpoint high for supply air humidity Calculated supply air setpoint for dehumidification | ACalcVal | [g/kg] |
PrSpLoHuSu | Present setpoint low for supply air humidity Calculated supply air setpoint for humidification | ACalcVal | [g/kg] |
SpHuSuMax | Maximum setpoint for supply air humidity Limits supply air on the high side. | ACnfVal | [g/kg] |
SpHuSuMin | Minimum setpoint for supply air humidity Limits supply air on the low side. | ACnfVal | [g/kg] |
Gain | Gain Gain factor for the cascade controller | ACnfVal | 3 [K/K] |
Tn | Integral action time Tn Integral action time for the cascade controller | ICnfVal | 1200 [s] |
Supply air humidity control (4)
Key
Vlv'Pos, Mdlt | Position, modulating control |
Hum'Mdlt | Modulating control of the humidifier |
Ccl'Vlv'Pos | Cooling coil valve position |
PrSpLoHuSu | Present setpoint low for supply air humidity |
PrSpHiHuSu | Present setpoint high for supply air humidity |
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 |
The humidity controller acts as a PI controller (PID derivative actions time Tv=0) and compares the humidity setpoint [PrSpLoHuSu] against the supply air humidity [HuSu] converted as absolute humidity and calculates the modulating control [Hum‘Mdlt] on the output. The following controller variables are preset: | |||
Ccl'Vlv'HuCtr | Humidity controller cooling coils Controls supply air humidity. | Controller | N/A |
The humidity controller acts as a PI controller (PID derivative actions time Tv=0) and compares the humidity setpoint [PrSpHiHuSu] against the supply air humidity [HuSu] converted as absolute humidity 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: | |||
Limitation of the supply air humidity:
Limits the supply air humidity to a maximum value in [%RH].
Prevents the triggering of the humidity detector.
BACnet objects
Name | Description | Object type | Default value |
|---|---|---|---|
Hum'LmCtr | Limitation controller Prevents the triggering of the humidity detector. | Controller | N/A |
The limitation controller acts as a PI controller (PID with derivative action time Tv=0) and compares the humidity setpoint set on input [Sp] against the supply air humidity [HuSu] in [%RH] and calculates value [YCtrMax] on the output on BACnet object Hum'HuCtr (humidity controller humidifier). The following controller variables are preset: | |||
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: | |||
Extract air pressure controller
Controls the extract air pressure using an exhaust 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 |
|---|---|---|---|
FanEh'PCtr | Pressure controller for exhaust 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: | |||
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)
- Operating mode switch (2), resulting from an active (not equal to Auto) operating mode switch
- Manual operating mode selection (3), resulting from an active (not equal to Auto) manual operating mode selection
- Scheduler (4), resulting from an active scheduler
- Switching action is performed (5) 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:
- [MI] Operating mode switch
- [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
- Smoke detector
- Faults in the components, e.g. fault contact, frost protection monitor, maintenance switch
- Faulty monitoring signals, e.g. fire dampers not open, 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 + FdpsSu | DmpEh + FdpsEx | Erc | FanSu | FanEh | 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 at the same time (function AND).
- In this plant example, the shutoff dampers do not have an end switch. The operating message 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 for 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. It can dry out if it was operating. If it 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 and fire dampers close and the reheater switches off (function AND, Group with next aggregate).
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
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 |
OpModSwi | Operating mode switch | MI | N/A | Auto | Off | On | N/A |
Fdp’Ex‘Cmd | Extract air fire dampers command | BO | NO contact | Close | Open | N/A |
Fdp'Ex'FbOpnd | Extract air fire damper feedback open | BI | NO contact | Closed | Opened | N/A |
Fdp'Su'Cmd | Supply air fire damper command | BO | NO contact | Close | Open | N/A |
Fdp'Su'FbOpnd | Supply air fire damper feedback open | BI | NO contact | Closed | Opened | N/A |
SmkDet | Smoke detector | N/A | NC contact | Normal | Triggered | N/A |
Fa'Eh'PEx | Exhaust air fan extract air pressure | AI | 0...10 [V] | N/A | 0...500 [Pa] |
Fa'Su'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 | Triggered | 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 |
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 | Triggered | N/A |
Ccl'Vlv'Pos | Cooling coil valve position | AO | 0...10 [V] | N/A | 0...1000 [%] |
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 |
Erc'Spd | Energy recovery speed | AO | 0...10 [V] | N/A | 0...100 [%] |
Erc'Flt | Energy recovery fault Alarm function: Basic (Notification class 8) Reference value: Tripped Time deviation: 0 [s] | BI | NO contact | Normal | Tripped | N/A |
Erc'TEhAfErc | Energy recovery exhaust air temperature after heat exchanger | AI | LG-Ni1000 | N/A | 0...50 [°C] |
FanEh'Spd | Exhaust air fan speed | AO | 0...10 [V] | N/A | 0...100 [%] |
FanEh'Cmd | Exhaust air fan command | BO | NO contact | Off | On | N/A |
FanEh'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 |
FanEh'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 |
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] |