.Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.SetPoints.ReliefFan

Information

Sequence for controling relief fan that is part of AHU. It is developed based on Section 5.16.9 of ASHRAE Guideline 36, May 2020, with the modification to accommodate the single relief fan control.

1. The relief fan shall be enabled when the AHU supply fan is proven ON (u1SupFan=true), and shall be disabled otherwise.
2. Building static pressure (dpBui) shall be time averaged with a sliding 5-minute window and 15 second sampling rate (to dampen fluctuations). The average value shall be that displayed and used for control.
3. A P-only control loop maintains the building pressure at a set point (dpBuiSet) of 12 Pa (0.05 in. of water) with an output ranging from 0% to 100%. The loop is disabled and output set to zero when the relief fan is disabled.
4. Fan speed shall be equal to the PID signal but no less than the minimum speed.
   1. When relief system is enabled, and the control loop output is above 5%, open the motorized dampers to the relief fans; close the dampers when the loop output drops to 0% for 5 minutes.
   2. When the control loop output is above minimum speed (relFanSpe_min) plus 15% by 7 minutes, start the relief fan.
   3. When the control loop output is below minimum speed (relFanSpe_min) by 5 minutes, shut off the relief fan.

Revisions

• March 5, 2024, by Michael Wetter:
  Corrected wrong use of displayUnit.
• September 20, 2022, by Jianjun Hu:
  First implementation.