Applications Guide Tracer Graphical Programming - Trane

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Chapter 7 Constant-volume AHU example
Controlling the humidifier
Writing the alarms program
The alarms program indicates diagnostic conditions to the operator and
protects the equipment from potential harm when such a condition exists.
According to the sequence of operations, the following diagnostic conditions
require an alarm indication:
• Dirty filter
• Duct humidity high limit
• Exhaust fan failure
• Low outdoor air temperature
• Low (mixed air) temperature detection
• Sensor failure (including discharge air temperature, mixed air temperature,
outdoor air temperature, and space temperature)
• Supply fan failure
The following failures shutdown the air handler and require a manual
reset:
• Discharge air or mixed air temperature sensor failure
• Fan failure
• Low mixed air temperature
All alarms must be resettable at the operator display.
The requirements for the Alarms program are nearly identical to the
same program in the VAV air handler with one exception: The duct static
pressure high limit is no longer needed. The duct humidity high limit was
added. The high limit for the duct static pressure is not applicable to a
constant-volume AHU. The use of humidification requires the addition of
a duct humidity high limit. Set the program properties as shown in
Figure 152 on page 177.
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