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Economizer function in Xenta 121

Issue

Considerations to make when using the economizer function in a Xenta 121.

Environment

  • Xenta 121-FC
  • Xenta 121-HP
  • Vista Workstation
  • ZBuilder
  • LonMaker
  • NL220

Cause

The economizer / outside air damper function of the Xenta 121 requires that certain considerations be made in order for it to work properly. This includes the wiring and display of a mixed air temperature sensor.

Resolution

Some things to consider when using the economizer in Xenta 121:

  1. The Xenta 121 application requires that a mixed air temperature sensor be used when the economizer mode is set up. This is to keep the application from bringing in too much cold air and freezing a coil. It is not possible to bypass this requirement in the software, but installing a ~1.8K ohm resistor in place of the mixed air temperature sensor will fulfill this requirement.
  2. The control method for the economizer can either be selected as Space temperature controlling against cooling setpoint or Mixed air controlling against setpoint value. Even if the space temperature method is selected the application still requires a mixed air temp sensor for safety lockout purposes.
  3. By default, the mixed air temperature is not displayed on the front end even if it is being used by the economizer. In order to display the mixed air temperature, navigate to the SNVT menu while on the Configuration tab of ZBuilder. Check the box at the bottom that says nvoGenericTemp. When the cursor is hovered over the text a tool tip pops up and indicates that this is used for displaying the mixed air temp. Next, select the I/O Setup tab and the Mixed Air Temperature point will appear and can now be dragged to the desired point assignment.

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Revision #:
1 of 1
Last update:
‎2018-09-10 04:59 AM
Updated by: