.Buildings.Obsolete.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.VAV.Economizers.Subsequences.Limits

Information

This 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 ASHRAE Guidline 36 (G36), PART 5.N.6.c.

The controller is enabled when the supply fan is proven on (uSupFan=true), the AHU operation mode Buildings.Obsolete.Controls.OBC.ASHRAE.G36_PR1.Types.OperationModes equals occupied, and the freeze protection stage Buildings.Obsolete.Controls.OBC.ASHRAE.G36_PR1.Types.FreezeProtectionStages is stage1 or lower. 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 uRetDamMin is linearly mapped to the outdoor air damper minimal position yOutDamPosMin while the fraction of the controller output between uRetDamMin and yMax is linearly mapped to the return air damper maximum position yRetDamPosMax. 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:

Revisions

• July 10, 2020, by Antoine Gautier:
  Changed default value of integral time for minimum outdoor air control. Set yMin to 0.
  This is for #2019.
• March 14, 2020, by Jianjun Hu:
  Replaced mulAnd by logic and block to avoid vector-valued calculation.
  This is for #1829.
• July 17, 2017, by Michael Wetter:
  Replaced block that checks for equality of real values within a tolerance by two inequality checks.
• June 06, 2017, by Milica Grahovac:
  First implementation.