.Buildings.Obsolete.Controls.OBC.ASHRAE.G36_PR1.AHUs.SingleZone.VAV.Economizers.Subsequences.Enable

Information

This is a single zone VAV AHU economizer enable/disable sequence based on ASHRAE G36 PART 5.5 and PART 5.A.17. Additional conditions included in the sequence are:

• Buildings.Obsolete.Controls.OBC.ASHRAE.G36_PR1.Types.FreezeProtectionStages (PART 5.9),
• Supply fan status TSupFan (PART 5.4.d),
• Buildings.Obsolete.Controls.OBC.ASHRAE.G36_PR1.Types.ZoneStates (PART 5.3.b).

The economizer is disabled whenever the outdoor air conditions exceed the economizer high limit cutoff setpoint plus the hysteresis low limit parameter (TOutHigLimCutLow or hOutHigLimCutLow) as shown in the figure. And the economizer is enabled whenever the outdoor air conditions are below the economizer high limit cutoff setpoint plus the hysteresis high limit parameter (TOutHigLimCutHig or hOutHigLimCutHig). This sequence allows for all device types listed in ASHRAE 90.1-2013 and Title 24-2013.

In addition, the economizer is disabled without a delay whenever any of the following is true:

• supply fan is off,
• zone state is heating,
• freeze protection stage is not 0.

The following state machine chart illustrates the transitions between enabling and disabling:

Revisions

• July 30, 2019, by Kun Zhang:
  Added the option to allow fixed plus differential dry bulb temperature cutoff.
• July 06, 2017, by Milica Grahovac:
  First implementation.