Applications Guide Tracer Graphical Programming - Trane

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Writing the cooling tower fan module
Figure 76: Sump heater module completed
Writing the cooling tower fan module
Review the portion of the sequence of operation concerning the cooling
tower fan.
If condenser water flow is established and if the condenser water temperature
rises 2.5°F above the setpoint, start the fan at low speed.
Switch the fan to high speed if the condenser water temperature rises
to 5.0°F above the setpoint. Turn off the fan when the condenser supply
water temperature falls below the setpoint minus 2.5°F. A minimum
30-second delay is required between starting the fan at low
speed and switching to high speed.
The following important points may be drawn from the above sequence.
• Condenser water flow is a prerequisite to starting the fan.
• This part of the sequence involves a concept known as staging. Multipledeadbandsmaybeusedtocontrolthefanstages.
• The fan must remain at low speed for 30 seconds prior to transitioning
to high speed. You need to incorporate time-based control.
Adding the input blocks
Two inputs (hardware) and one variable are required for control of the
cooling tower fan.
• Flow Status
• Supply Temp
• Supply Temp Setpoint
To add the input blocks:
1. Place an Input (Hardware) block in the design space and assign the
binary input, Flow Status to it.
2. Create a Wireless write block, name it SupplyTemp, and connect it to
the Supply Temp input block.
3. Place the SupplyTemp wireless read block in the design space.
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