Applications Guide Tracer Graphical Programming - Trane

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® Chapter 7 Constant-volume AHU example Control The following parameters for the sequence of operation are presented according to the equipment that must be controlled. Supply fan Operate the supply fan continuously whenever the air handler is in occupied or night heat/cool mode. Turn the supply fan off whenever one of the following occurs: • The air handler is unoccupied. • The run/stop interlock is open. • The mixed air temperature is too cold, and the low limit detection is closed. • The supply fan status indicates a fan failure after a 1-minute delay. Note: Afailureduetolowmixedairtemperatureorfanfailure requires a manual reset. Also, the low limit switch may require a manual, hardware reset. Outdoor air damper When the economizer function is enabled and the outdoor air temperature is less than the economizer changeover setpoint, modulate the outdoor air damper between the adjustable minimum position and fully open to maintain the discharge air cooling setpoint. Modulate the outdoor air damper closed, overriding the minimum position, to maintain the mixed air temperature at or above the mixed air setpoint. If the economizer function is disabled or the air handler is in the heat mode, control the outdoor air damper to its minimum position. If the outdoor air temperature falls below a low outdoor air temperature limit, control the outdoor air damper to its closed position. In unoccupied mode, control the outdoor air damper to its closed position. Also, if the supply fan is off or the mixed air temperature sensor is failed, control the outdoor air damper to its closed position. Exhaust fan Coordinate exhaust fan operation with the unit supply fan and outdoor air damper position. Turn on the exhaust fan whenever the supply fan is on and the outdoor air damper is open beyond 30%. Keep the exhaust fan on until the outdoor air damper closes to below 20% open or the supply fan is turned off. Cooling valve Modulate the cooling valve to maintain the discharge air temperature at the discharge air setpoint. If the economizer function is enabled and the outdoor air damper is not open at least 90%, control the cooling valve to its closed position. Also, close the cooling valve if the air handler is in heat 148 CNT-APG001-EN
® Reviewing the sequence of operation mode, the supply fan is off, or the discharge air temperature sensor is failed. Heating valve Modulatetheheatingvalvetomaintainthedischargeairtemperatureat the discharge air setpoint. Close the heating valve if the air handler is in cool mode, the supply fan is off, or the discharge air temperature sensor is failed. Open the heating valve if the supply fan is off and the outdoor air temperature falls below the adjustable freeze avoidance setpoint. Humidification Enable humidification mode when the air handler is in occupied mode, the supply fan is on, and the outdoor air temperature falls below 55°F. Modulate the humidifier to maintain the space relative humidity setpoint. If the duct relative humidity exceeds 85%, turn off the humidifier to prevent condensation in the duct work and indicate an alarm. Dehumidification Enable dehumidification mode when the air handler is occupied, the supply fan is on, the outdoor air temperature is above 55°F, and the space relative humidity is above the space dehumidification setpoint. Modulate the cooling valve to maintain space relative humidity and the heating valve to maintain discharge air temperature. Alarms In addition to the alarm requirements mentioned above, indicate an alarm at the operator display and turn on the alarm output when any sensor fails. Alarms must be resettable at the operator display. Diagnostic conditions include the following: • 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, space temperature, and duct static pressure) • Supply fan failure The following failures shutdown the air handler and require a manual reset: • Discharge or mixed air temperature sensor failure • Fan failure • Low mixed air temperature CNT-APG001-EN 149
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Applications Guide Tracer Graphical
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CNT-APG001-EN ®
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® Special notifications and format
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® Contents Chapter 5 Cooling tower
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® Contents Chapter7 Constant-volum
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® Contents Summary-question answer
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® Figures Chapter3 Modifyingtheexh
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® Figures Figure 96: Input blocks
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® Figures Chapter 8 Constant-volum
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® Tables Chapter7 Constant-volumeA
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® Chapter 1 Using the Tracer Graph
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® Summary-question answers PROGRAM
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® Index dehumidification, 166-169,
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Applications Guide Tracer Graphical Programming - Trane

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