Applications Guide Tracer Graphical Programming - Trane

®
Chapter 8 Constant-volume AHU with warm-up, pre-cool, and communications
Controlling the cooling valve
How do the additional modes and profile considerations change control of
the cooling valve? Examine the sequence of operation with regard to the
cooling valve. The changes for this chapter are shown in italics.
Modulate the cooling valve to maintain the discharge air temperature at
the discharge air cooling setpoint when all ofthefollowingaretrue:
• The supply fan is on.
• The air handler is in cooling mode.
• The economizer function is not enabled.
Or when all ofthefollowingaretrue:
• The supply fan is on.
• The air handler is in cooling mode (including pre-cool).
• The economizer function is enabled.
• The outdoor air damper is open at least 90%.
Modulate the cooling valve to maintain the space relative humidity at the
space relative humidity setpoint when all ofthefollowingaretrue:
• The supply fan is on.
• The air handler is in cooling mode.
• Dehumidification is enabled.
Open the cooling valve completely when all of the following are true:
• The supply fan is on.
• The air handler is in cooling mode.
• The pre-cool mode is active.
• Economizing is not allowed, or the outdoor air damper is open at least
90%.
Close the cooling valve when any of the following is true:
• The air handler is in heating mode.
• The supply fan is off.
• The discharge air temperature sensor is failed.
Incorporatepre-coolmodeintothedecisiontoenablethecoolingvalve.
Add another And block and complete the logic to determine whether the
cooling valve is enabled or if it should open completely (Figure 171 on
page 207).
206 CNT-APG001-EN