.Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.Controller

Information

Block that is applied for multizone VAV AHU control. It outputs the supply fan status and the operation speed, outdoor and return air damper position, supply air temperature setpoint and the valve position of the cooling and heating coils. It is implemented according to the Section 5.16 of ASHRAE Guideline 36, May 2020.

The sequence consists of eight types of subsequences.

Supply fan speed control

The fan speed control is implemented according to Section 5.16.1. It outputs the boolean signal y1SupFan to turn on or off the supply fan. In addition, based on the pressure reset request uZonPreResReq from the VAV zones controller, the sequence resets the duct pressure setpoint, and uses this setpoint to modulate the fan speed ySupFanSpe using a PI controller. See Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.SupplyFan for more detailed description.

Minimum outdoor airflow setting

According to current occupany, supply operation status ySupFan, zone temperatures and the discharge air temperature, the sequence computes the minimum outdoor airflow rate setpoint, which is used as input for the economizer control. More detailed information can be found in Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.

Economizer control

The block outputs outdoor and return air damper position, yOutDamPos and yRetDamPos. First, it computes the position limits to satisfy the minimum outdoor airflow requirement. Second, it determines the availability of the economizer based on the outdoor condition. The dampers are modulated to track the supply air temperature loop signal, which is calculated from the sequence below, subject to the minimum outdoor airflow requirement and economizer availability. See Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.Economizers.Controller for more detailed description.

Supply air temperature setpoint

Based on the Section 5.16.2, the sequence first sets the maximum supply air temperature based on reset requests collected from each zone uZonTemResReq. The outdoor temperature TOut and operation mode uOpeMod are used along with the maximum supply air temperature, for computing the supply air temperature setpoint. See Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.SupplyTemperature for more detailed description.

Coil valve control

The subsequence retrieves supply air temperature setpoint from previous sequence. Along with the measured supply air temperature and the supply fan status, it generates coil valve positions. See Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.SupplySignals for more detailed description.

Freeze protection

Based on the Section 5.16.12, the sequence enables freeze protection if the measured supply air temperature belows certain thresholds. There are three protection stages. See Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.FreezeProtection for more detailed description.

Building pressure control

By selecting different building pressure control designs, which includes using actuated relief damper without fan, using actuated relief dampers with relief fan, using return fan with direct building pressure control, or using return fan with airflow tracking control, the sequences controls relief fans, relief dampers and return fans. See belows sequences for more detailed description:

• Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.ReliefDamper
• Relief fan control Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.ReliefFan is not included in the AHU controller. This sequence controls all the relief fans that are serving one common space, which may include multiple air handling units.
• Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.ReturnFanAirflowTracking
• Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.ReturnFanDirectPressure

Plant request

According to the Section 5.16.16, the sequence send out heating or cooling plant requests if the supply air temperature is below or above threshold value, or the heating or cooling valves have been widely open for certain times. See Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.PlantRequests for more detailed description.

Revisions

• September 18, 2023, by Jianjun Hu:
  Removed the connectors uCooCoi_actual and uHeaCoi_actual, added 2-position relief damper position output y1RelDam, added coil type enumeration so to avoid using flag parameters.
  This is for issue 3526.
• March 1, 2023, by Michael Wetter:
  Changed constants from 0 to 0.0 and 1 to 1.0.
  This is for #3267.
• December 15, 2022, by Jianjun Hu:
  Removed input connectors uRelFan and uSupFanSpe_actual.
  This is for issue 3139.
• December 20, 2021, by Jianjun Hu:
  First implementation.