.Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.Economizers.Subsequences.Limits.SeparateWithAFMS

Information

Block that outputs the position limits of the return and outdoor air damper for units with a separated minimum outdoor air damper and airflow measurement. It is implemented according to Section 5.16.5 of the ASHRAE Guideline 36, May 2020.

Minimum outdoor air set point

Calculate the outdoor air set point with Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.

Minimum outdoor air control loop

Minimum outdoor air control loop is enabled when the supply fan is proven ON (u1SupFan=true) and in occupied mode, and disabled and output set to zero otherwise

The minimum outdoor airflow rate shall be maintained at the minimum outdoor air set point by a reverse-acting control loop whose output is 0% to 100%. From 0% to 50% loop output, the minimum outdoor air damper is opened from 0% (minOutDamPhy_min) to 100% (minOutDamPhy_max).

Return air damper

• Return air damper minimum outdoor air control is enabled when the minimum outdoor air damper is fully open and the economizer outdoor air damper is less than a projected position limit, which is 5% when supply fan speed is at 100% design speed proportionally up to 80% when the fan is at minimum speed.
• Return air damper minimum outdoor air control is disabled when the minimum outdoor air damper is not fully open or the economizer outdoor air damper is 10% above the projected position limit as determined above.
• When enabled, the maximum return air damper set point is reduced from 100% (retDamPhy_max) to 0% (retDamPhy_min) as the minimum outdoor air loop output rises from 50% to 100%.

Revisions

• August 1, 2020, by Jianjun Hu:
  First implementation.