Applications Guide Tracer Graphical Programming - Trane

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Writing the discharge air control program
Figure 170: Dehumidify or humidify?
Writing the discharge air control
program
The discharge air control program must accomplish the same tasks as it
did in Chapter 7. Those tasks include the following:
• Discharge air setpoint calculation
• Cooling valve control
• Heating valve control
• Dehumidification
• Humidification
Much of the programming remains the same; however, the addition of
pre-cool and warm-up modes, as well as consideration of the SCC profile,
require some changes to the programming. Start with the program you
created in Chapter 7.
The first module calculates the discharge air setpoint based on the effective
space setpoint. See “Calculating the discharge air setpoint” on
page 165 for more information. This part of the program is unaffected by
the additional modes and the profile considerations.
Whether to humidify or dehumidify
The decision to humidify or dehumidify requires a minor modification.
Can you identify the necessary changes? (Hint: Take a look at the SCC
profile variables. Where do the outdoor air temperature and the space relative
humidity come from?)
Because the outdoor air temperature and the space relative humidity are
now communicated from the building automation system, replace the
Outdoor Air Temp input block with a Network Variable Input block. And
change the Network Variable Input block assigned to nviPercent01 to
nviSpaceRH in the SCC profile (Figure 170).
Network variable
input
Network variable input
CNT-APG001-EN 205