Applications Guide Tracer Graphical Programming - Trane

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Chapter 7 Constant-volume AHU example
Figure 162: Night heat/cool decision
Adding night heat/cool
Consider the following important points about night heat/cool mode from
the sequence of operation.
• The air-handling unit must be unoccupied.
• The supply fan starts if the space temperature falls below the unoccupied
heating setpoint or the space temperature rises above the unoccupied
cooling setpoint.
• The supply fan stops if the space temperature rises above the unoccupied
heating setpoint or the space temperature falls below the unoccupied
cooling setpoint.
• When in night heat/cool mode and heating, the outdoor air damper
remains closed.
• When in night heat/cool mode and cooling, the outdoor air damper
modulates if the outside air temperature is less than the economizer
changeover setpoint and the economizer is enabled.
Implement the night heat/cool mode decision as shown in Figure 162.
• Use the Deadband blocks to turn the night heat/cool mode on and off.
(A deadband value of 4°F is used in this example.)
• Use the Night Heat/Cool variable to allow for implementation of night
heat/cool mode in other programs.
• Use an And block to make sure that the air-handling unit is unoccupied
before entering night heat/cool mode.
The mode and setpoints program (Figure 163 on page 185) completes the
constant volume air-handling unit. Compile and download the program.
184 CNT-APG001-EN