.Buildings.Controls.OBC.ASHRAE.G36.TerminalUnits.Reheat.Subsequences.DamperValves

Information

This sequence sets the damper and valve position for VAV reheat terminal unit. The implementation is according to Section 5.6.5 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 be mapped to the airflow setpoint from the cooling minimum VActCooMin_flow to the cooling maximum VActCooMax_flow airflow setpoints. The heating coil is disabled (yVal=0) unless the discharge air temperature TDis is below the minimum setpoint (10 °C).
   • If supply air temperature TSup from the AHU 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), then the active airflow setpoint shall be the minimum airflow setpoint VActMin_flow. The heating coil is disabled unless the discharge air temperature is below the minimum setpoint (10 °C).
3. When the zone state is Heating (uHea > 0), then the heating loop shall maintain space temperature at the heating setpoint as follows:
   • From 0% to 50%, the heating loop output uHea shall reset the discharge temperature setpoint from current AHU SAT setpoint TSupSet to a maximum of dTDisZonSetMax above space temperature setpoint. The airflow setpoint shall be the heating minimum VActHeaMin_flow.
   • From 50% to 100%, if the discharge air temperature TDis is greater than room temperature plus 3 Kelvin, the heating loop output uHea shall reset the airflow setpoint from the heating minimum airflow setpoint VActHeaMin_flow to the heating maximum airflow setpoint VActHeaMax_flow.
   • The heating coil shall be modulated to maintain the discharge temperature at setpoint.
4. The VAV damper shall be modulated by a control loop to maintain the measured airflow at the active setpoint.
5. In occupied mode, the heating coil shall be modulated a discharge temperature no lower than 10 °C (50 °F).

The sequences of controlling damper and valve position for VAV reheat terminal unit are described in the following figure below.

As specified in Section 5.6.7 of ASHRAE Guideline 36, the airflow setpoint could be override by providing software switches that interlock to a system-level point to:

1. when oveFloSet equals to 1, force the zone airflow setpoint VSet_flow to zero,
2. when oveFloSet equals to 2, force the zone airflow setpoint VSet_flow to zone cooling maximum airflow rate VCooMax_flow,
3. when oveFloSet equals to 3, force the zone airflow setpoint VSet_flow to zone minimum airflow setpoint VMin_flow.
4. when oveFloSet equals to 4, force the zone airflow setpoint VSet_flow to zone heating maximum airflow setpoint VHeaMax_flow.

Revisions

• August 24, 2023, by Jianjun Hu:
  Added AHU supply fan status for damper position reset.
  This is for issue 3257.
• 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.