Applications Guide Tracer Graphical Programming - Trane

®
Chapter 8 Constant-volume AHU with warm-up, pre-cool, and communications
Adding the pre-cool and warm-up decisions
The heat/cool mode and night heat/cool decisions are the same as those in
Chapter 7. See “Adding night heat/cool” on page 184 for more information.
However, the mode and setpoints program must incorporate additional
decisions to accommodate pre-cool and warm-up modes. These decisions
arespecifiedinthesequenceofoperationandsummarizedhere:
Enter pre-cool when all of the following are true:
• The unit is occupied (including occupied, occupied standby, and occupied
bypass modes).
• The unit is in cooling mode.
• The space temperature is at least 3°F above the effective cooling setpoint.
Exit pre-cool mode when the space temperature falls to within 2°F of the
effective cooling setpoint.
Enter warm-up mode when all of the following are true:
• The unit is occupied (including occupied, occupied standby, and occupied
bypass modes).
• The unit is in heating mode.
• The space temperature is at least 3°F below the effective heating setpoint.
Exit warm-up mode when the space temperature rises to within 2°F of
the effective heating setpoint.
Implement these decisions in graphical programming using the night
heat/cool decision as a model. Note that you must base the decision for
each mode on a value that is offset by 3°F from the effective cooling and
heating setpoints (Figure 176 on page 215).
• Use Add and Subtract blocks to calculate the setpoints for each Deadband
block.
• Configure the Deadband block for pre-cool as greater than, but configure
the Deadband block for warm-up as less than.
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