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

Information

This sequence sets the dampers for snap-acting controlled dual-duct terminal unit with dual inlet airflow sensors. The implementation is according to Section 5.11.5.1 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 cooling supply airflow setpoint VColDucDis_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 cooling aiflow VColDucDis_flow at setpoint. The heating damper shall be closed yHeaDam=0.
   • If the cold-deck supply air temperature TColSup from the cooling air handler is greater than room temperature TZon, cooling supply airflow setpoint shall be no higher than the minimum.
2. When the zone state is deadband (uCoo=0 and uHea=0), the cooling and heating airflow set points shall be their last set points just before entering deadband. In other words, when going from cooling to deadband, the cooling airflow set point is equal to the zone minimum VActMin_flow, and the heating set point is zero When going from heating to deadband, the heating airflow set point is equal to the zone minimum VActMin_flow, and the cooling set point is zero.
3. When the zone state is heating (uHea > 0), then the heating loop output uHea shall reset the heating supply airflow setpoint VHotDucDis_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 heating aiflow VHotDucDis_flow at setpoint. The cooling damper shall be closed yCooDam=0.
   • If the hot-deck supply air temperature THotSup from the heating air handler is less than room temperature TZon, heating supply airflow setpoint shall be no higher than the minimum.
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 dual inlet 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.