Issue
When using the economizer (outside air damper) function in the Xenta 121, specific setup considerations are required to ensure proper operation and avoid equipment damage.
Environment
- Xenta 121-FC
- Xenta 121-HP
- Vista Workstation
- ZBuilder
Cause
The economizer function relies on a mixed air temperature sensor to prevent excessive intake of cold air, which could freeze the coil. The application logic enforces this requirement and does not allow bypassing it through software configuration.
Resolution
Sensor Requirement
- A mixed air temperature sensor is mandatory when economizer mode is enabled.
- If a physical sensor is not available, a ~1.8K ohm resistor can be installed in its place to satisfy the software requirement.
Control Methods
- The economizer can operate in one of two modes:
- Space Temperature Control – regulates based on cooling setpoint.
- Mixed Air Temperature Control – regulates based on mixed air setpoint.
- Note: Even when using space temperature control, the mixed air temperature sensor is still required for safety lockout.
Displaying Mixed Air Temperature
By default, the mixed air temperature is not shown on the front end. To display it:
- Open ZBuilder and go to the Configuration tab.
- Navigate to the SNVT menu.
- Check the box labeled nvoGenericTemp.
- A tooltip will confirm this is for displaying mixed air temperature.
- A tooltip will confirm this is for displaying mixed air temperature.
- Switch to the I/O Setup tab.
- The Mixed Air Temperature point will now be visible and can be assigned to the desired location.
