Issue
Test and air balance procedure for balancing airflow
Product Line
TAC Vista, EcoStruxure Building Operation
Environment
- Building Operation Automation Server Premium
- TAC Xenta 102-AX
- TAC Xenta 102-AX Plug-in
Cause
Each 102-AX controller must be calibrated on-site to report accurate airflow readings. The LNS Plug-in provides this functionality, but it may not be immediately clear what the correct procedure is to perform a valid calibration.
Resolution
Check the firmware version of your 102-AX controllers in the plug-in, Node Configuration tab. It will be shown under Program Revision. If it's anything earlier than 2.1.6 then the calibration won't work properly. The airflow setpoint changes but the damper does not modulate to maintain setpoint in the calibration mode. Your options in that situation are to manually manipulate the damper to maintain airflow setpoint in order to facilitate calibration or upgrade the controllers firmware.
Also verify that the box is set to "Pressure Independent" mode on the Unit Parameters tab. Pressure dependent boxes do not use airflow sensors, and therefore cannot be calibrated.
To balance the 102-AX in Building Operation version 1.4 or higher where the LNS plug-in is no longer provided, review the article TAC Xenta 102-AX TGML plug-in for Building Operation
To calibrate airflow using the 102-AX LNS plug-in:
- Go to the Node Configuration Tab.
- Select "Set Default m & b." This is a good idea before each calibration attempt since incorrect calibration values can make it more difficult to perform a valid calibration.
(NOTE: The m & b values can be viewed under the Airflow Parameters Tab of the 102AX LNS plug-in...m = Velocity Pressure Gain & b = Velocity Pressure Offset) - Select "Start Calibration." At this point the airflow setpoint should go to the minimum. You can check the Cooling Minimum airflow setpoint on the Airflow Parameters tab.
- The damper now modulates to maintain the minimum cooling flow setpoint. Watch the VAV Reading (Low) and wait for it to hit the minimum flow setpoint and level out.
If the airflow is fluctuating a lot, it could be that the low setpoint is below the threshold the box can confidently supply. Or it could be bad placement of the flow sensor in a turbulent area of the duct. It can affect your calibration greatly if the value is fluctuating too much.
A relatively level reading will provide a good calibration. - When it levels out, measure the actual airflow with a highly accurate magnehelic hood. Enter the actual value into Reference (Low) and select "Continue."
- The damper now modulates to maintain the maximum cooling flow setpoint. Watch the VAV Reading (High) and wait for it to hit the maximum flow setpoint and level out.
- When it levels out, measure the actual airflow with a highly accurate magnehelic hood. Enter the actual value into Reference (High) and select "Finish."
- The new calibrated m & b values are shown. The gain (m) is shown in the format of multiplier/divisor. Divide the values to get a decimal format of the gain. The closer to 1 this value is, the less calibration was required. actually gains of 2 or more indicate probable airflow reading problems. It may be advisable to reset factory calibration values and try the calibration again.
- The box should now be displaying values very close to actual measured readings. Test the low and high flow during normal operation using the Status Tab,
- Right click on the Space Temp and override the space temperature to a value equal to or greater than the Occupied Cooling Setpoint plus half the Cooling Band to drive the airflow setpoint to the cooling maximum airflow setpoint (you can find the Occupied Cooling Setpoint and Cooling Band on the Operating Tab).
- With the space temperature already in override, left click the Space Temp to change the space temperature without taking it out of override, and set the space temperature to the Occupied Cooling Setpoint minus half the Cooling Band to drive the airflow setpoint to the cooling minimum airflow setpoint.
- With the space temperature in override, right clicking it will take it out of override.
