CO2
CO2 Measurement
The CO2 measurement provides an additional factor in the VAV application’s algorithm, which takes it into calculations along with the temperature control loop. The CO2 measurements can be derived from three different sources:
Control Point VAV panel,
dedicated universal input, U4 (connected sensor),
network.
Automatic Detection
The VAV application has a mechanism to provide an automatic CO2 detection in case the selected source does not provide any value. First, the application checks for the Control Point VAV panel availability. If the value cannot be read from the panel, the algorithm checks the dedicated U4 input and if no sensor is connected, it proceeds to check the value from the network. In case all these steps fail to provide the measured CO2 level, the algorithm uses the SpaceCO2Setpoint (by default, 1000 ppm), which has no effect on the VAV operation.
Note
In case more than one CO2 source is connected and active (for example, the Control Point VAV panel and sensor connected to the U4 input), it is possible to indicate one of them as a leading one using the Input Selector slot (RoomCO2Selector component in the CO2Selector folder of the VAV application) or calculate an average using the CO2 Averaging slot (the same location).
In the Control Point VAV and iSMA Configurator, it is possible to adjust the range of the U4CO2SensorRange variable for the CO2 sensor connected to the U4 input, which by default is 2000 ppm.
CO2 Control Loop
The CO2 measurement in the VAV application algorithm activates the CO2 control loop. If the set CO2 level is exceeded and the CO2 control loop output is:
0-50%: the VAV application increases the airflow scaling the 0-50% CO2 control loop to 0-100% of airflow;
Example
The airflow is controlled in the range of 100-200 l/s. The temperature control loop output is 10%, which means the airflow should be set to 110 l/s. However, the CO2 control loop output is 50%, which forces the 200 l/s airflow.
When the CO2 measurement is available, the algorithm compares it with the temperature control loop output and always the higher value of the two impacts the airflow control.
50-100%: if the CO2 control loop output still rises in spite of the VAV increasing the airflow, the output in the range of 50-100% is forwarded to the AHUOutDoorDamper variable (scaled to 0-100%) for the air handling unit to increase the opening level of the fresh air damper.
CO2 control