Applications Guide Tracer Graphical Programming - Trane

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Writing the cooling tower fan module
Figure 79: Startthefanatlowspeed
Use an And block to account for both conditions necessary to start the fan
at low speed.
To start the fan at low speed:
1. Place a Deadband block in the design space and set it as Centered.
2. Place a Constant block in the design space and assign the value 5.0 to
it.
3. Connect the SupplyTemp wireless read block to the Input port of the
Deadband block.
4. Connect the Supply Temp Setpoint variable block to the Setpoint port
of the Deadband block.
5. Connect the 5.0 constant block to the Deadband port of the Deadband
block.
6. Place an And block in the design space.
7. Connect the Flow Status input block and the Deadband block to the
And block.
8. Connect the And block to the Fan Start/Stop/Low output block
(Figure 79).
Transitioning the fan to high speed
The transitioning the fan to high speed depends on two additional criteria.
• The condenser supply temperature is 5.0°F above the setpoint.
• The fan is on at low speed, and it has been on at low speed for at least
30 seconds.
Transitioning the fan based on supply temp
Apply a second deadband to activate the fan at high speed based on a
combined deadband and offset from the setpoint of 5.0°F. See Figure 80
on page 74 for more information about how the deadbands work together.
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