.Buildings.Controls.OBC.ASHRAE.G36.TerminalUnits.DualDuctSnapActing.Subsequences.DampersSingleSensors

Information

This sequence sets the dampers for snap-acting controlled dual-duct terminal unit with single discharge airflow sensors. The implementation is according to Section 5.11.5.2 of ASHRAE Guideline 36, May 2020. The calculation is done following the steps below.

1. When the zone state is cooling (uCoo > 0), then the cooling loop output uCoo shall reset the discharge airflow setpoint VDis_flow_Set from the minimum VActMin_flow to cooling maximum setpoint VActCooMax_flow. The cooling damper shall be modulated by a control loop to maintain the measured discharge aiflow VDis_flow at setpoint. The heating damper shall be closed yHeaDam=0.
2. When the zone state is deadband (uCoo=0 and uHea=0), the discharge airflow set point VDis_flow_Set shall be the zone minimum VActMin_flow, maintained by the damper that was operative just before entering deadband. The other damper shall remain closed. In other words, when going from cooling to deadband, the cooling damper shall maintain the discharge airflow at the zone minimum set point, and the heating damper shall be closed. When going from heating to deadband, the heating damper shall maintain the discharge airflow at the zone minimum set point, and the cooling damper shall be closed.
3. When the zone state is heating (uHea > 0), then the heating loop output uHea shall reset the discharge airflow setpoint VDis_flow_Set from the minimum VActMin_flow to heating maximum setpoint VActHeaMax_flow. The heating damper shall be modulated by a control loop to maintain the measured discharge aiflow VDis_flow at setpoint. The cooling damper shall be closed yCooDam=0.
4. Overriding above controls:
   • If heating air handler is not proven ON (u1HeaAHU=false), the heating damper shall be closed (yHeaDam=0).
   • If cooling air handler is not proven ON (u1CooAHU=false), the cooling damper shall be closed (yCooDam=0).

The sequences of controlling dampers position for snap-acting controlled dual-duct terminal unit with single discharge airflow sensors are described in the following figure below.

Revisions

• January 12, 2023, by Jianjun Hu:
  Removed the parameter have_preIndDam to exclude the option of using pressure independant damper.
  This is for issue 3139.
• August 1, 2020, by Jianjun Hu:
  First implementation.