.Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.Economizers.Subsequences.Limits.Common .Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.Economizers.Subsequences.Limits.CommonThis block models the multi zone VAV AHU minimum outdoor air control with a single common damper for minimum outdoor air and economizer functions based on outdoor airflow measurement, designed in line with the Section 5.16.6 of the ASHRAE Guideline 36, May 2020.
The controller is enabled when the supply fan is proven on
(u1SupFan=true) and the AHU operation mode
Buildings.Controls.OBC.ASHRAE.G36.Types.OperationModes equals
occupied. Otherwise the damper position limits are set
to their corresponding maximum and minimum physical or at
commissioning fixed limits. The state machine chart below
illustrates listed conditions:
The controller sets the outdoor and return damper position
limits so that the outdoor airflow rate VOut_flow
stays equal or above the minimum outdoor air setpoint
VOutMinSet_flow. The fraction of the controller output
signal between yMin and uRetDam_min is
linearly mapped to the outdoor air damper minimal position
yOutDam_min while the fraction of the controller
output between uRetDam_min and yMax is
linearly mapped to the return air damper maximum position
yRetDam_max. Thus the dampers are not interlocked.
The following control charts show the input/output structure and an expected damper position limits for a well configured controller.
The expected damper position limits vs. the control loop signal are as follows:
0 to 0.0 and
1 to 1.0.yMin to 0.