The following list includes all data points that can be read and written from a BACnet primary plant. The items ensure coordination between primary plant and the room. In addition, appropriate Desigo primary application is mentioned for the given room function.
Data point name | Description | Desigo primary application |
|---|---|---|
AhuDmd | The evaluated demand signal of the rooms to central air handling 1:Off | PXC {AHU80} |
NumAirDmd | Number of rooms with demand | None |
AQualDmd | The evaluated air quality signal of the rooms to central air handling | PXC {AHU80} |
SpHiTSu | Setpoint high for supply air temperature | PXC {AHU80} |
SpLoTSu | Setpoint low for supply air temperature | PXC {AHU80} |
Enable supply air supply
On the DXR2 room automation station a threshold can be defined for the minimum number of collected air demand messages from the rooms. The air demand to air supply is only enabled if the minimum number of air demand messages is reached. The threshold and hysteresis can be configured.
Description | Name | Default value |
|---|---|---|
Number of minimum air demand plant mode | AirDmdMin | 4 |
Hysteresis for number of minimum air demand plant mode | HysAirDmdMin | 2 |
Select supply air temperature
setpoints
Central air handling is designed for heating and cooling. The consumers in the rooms decided whether warm or cool air is to be supplied.
Heat and cooling demand is determined from the rooms, evaluated, and decided, depending on the number, whether heating or cooling must be transmitted to air handling. This occurs using a lower (heating) and upper (cooling) supply air temperature setpoint to which the central air handling unit is controlled. As illustrate in the following graph, demand (0...100 %) is determined via the grouping functions for higher supply-air temperature for heating and demand (0…100 %) for lower supply air temperature for cooling. The control setpoints for supply air temperature control in the air handling unit is derived from this.
The changeover condition air reports whether the supply air can be used from the air handling unit for heating or cooling to the individual rooms. The following operating modes are supported:
- Changeover condition (ChovrCndAir) = Heating
- Changeover condition (ChovrCndAir) = Cooling
- Changeover condition (ChovrCndAir) = Neither
- Changeover condition (ChovrCndAir) = Neutral
| ||||
YH | Heating valve positions |
| YC | Cooling valve positions |
Changeover condition heating
The supply air setpoint for heating resides, as depicted in the diagram, on the left side, and is determined dependent on demand 0...100% accordingly. Conclusion for the room: The air is warm so that the air volume can be increased for heating.
Changeover condition cooling
The supply air setpoint resides, as depicted in the diagram, on the right side, and is determined dependent on demand 0...100% accordingly. Derived for the room: The air is cold so that the air volume can be increased for cooling.
Neither changeover condition
Heating and cooling in the VAV application is blocked and the setpoints are set to a start setpoint for heating and cooling.
- High setpoint for supply air temperate (SpHiTSu) = Start value for cooling SttValC
- Low setpoint for supply air temperature (SpLoTSu) = Start value heating SttValH
Conclusion for the room: Neither heating nor cooling, the volume flow controller for room temperature is not enabled.
Changeover condition neutral
Heating and cooling in the VAV application is enabled and the setpoints are set to a start setpoint for heating and cooling.
- High setpoint for supply air temperate (SpHiTSu) = Start value for cooling SttValC
- Low setpoint for supply air temperature (SpLoTSu) = Start value heating SttValH
VAV evaluation for AirOptiControl
The following variants are available on the DXR2 to optimize fan speed on air handling units with speed-controlled fans:
- Speed optimization via damper positions.
The ten largest supply air and extract air damper positions are acquired and the average calculated. The resulting value is used for fan speed optimization of the AHU. - Speed optimization via air volume deviation.
The deviation signals from the supply air VAV controllers are acquired from the room segments. The air volume flow deviation is calculated as:
((air flow setpoint - measured air flow)/nominal air flow)) x 100[%]
The 10 largest deviations are evaluated and the average is used to optimize the fan stage.
The number of deviations is counted between 5...20% for monitoring. - Speed optimization via setpoint evaluation of volume flow. It is used is supply air damper positions and measured air flows are not known. The setpoints of the supply air and extract VAV boxes is added up and the AHU fan stage is used as of this value for optimized air flow.
Relief function
Relief function monitoring becomes active as soon as air supply is activated. It calculates air demand for the AHU to ensure sufficient control stability of static pressure in the AHU. A relief command is provided to the VAV controller in the group if room demand is too low; it reacts by increasing the air flow setpoint to increase air demand.
Description | Name | Default value |
|---|---|---|
Configurable min. number of air demand requests required for operational stability of the central AHU. 1...50 | AirDmdMax | 10 |
Hysteresis for number of maximum air demand plant mode 1...5 | HysAirDmdMax | 2 |
Can configure whether the relief function can be activated in each room with supply VAV for each VAV:
Description | Name | Default value |
|---|---|---|
Enable relief 0:No | EnRlf | 0:No |
Air volume flow relief | AirFlRlf | 50 [m3/h] |
Central override of VAV
Central functions can centrally override all VAV in a supply group. The following parameters can be used.
Description | Name | Default value |
|---|---|---|
Enable supply air VAV overridden value 0:No | EnVavSuOvrr | 0:No |
Supply air VAV overridden value | VavSuOvrr | 50 [m3/h] |
Enable extract air VAV overridden value 0:No | EnVavExOvrr | 0:No |
Extract air VAV overridden value | VavExOvrr | 50 [m3/h] |