Applications Guide Tracer Graphical Programming - Trane

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Writing the discharge air control program
Figure 113: Determining whether to economize
Close the outdoor air damper completely when any of the following is
true:
• The unit is in unoccupied mode.
• The outdoor air temperature falls below the low setpoint for the outdoor
air temperature.
• The supply fan is off.
• The sensor for the mixed air temperature is failed.
Determining whether to economize
Because the control of the outdoor air damper is potentially complex, you
may simplify the program by separating the decision to economize from
the actual control of the damper.
Complete the first part of this program, as shown in Figure 113, to determine
some factors important to control of the outside air damper.
• Use a Deadband block to check the outside air temperature against
thelowoutsideairtemperaturesetpoint.Youwillusethisinformation
later in the program.
• Use a second Deadband block to check the outside air temperature
against the economizer changeover, or outside air temperature, setpoint.
Combine the economizer enable setting and the heat/cool mode
with the result of this deadband to determine whether conditions
warrant economizer operation.
• Use a Network Configuration Input (nci) block to access the outdoor
air temperature setpoint associated with the DAC profile.
CNT-APG001-EN 121