.Buildings.Controls.OBC.ASHRAE.G36.TerminalUnits.DualDuctMixConDischargeSensor.Subsequences.Alarms

Information

This block outputs alarms of dual-duct terminal unit using mixing control with discharge flow sensor. The implementation is according to the Section 5.13.6 of ASHRAE Guideline 36, May 2020.

Low airflow

1. If the zone is in occupied mode and after the AHU supply fan has been enabled for staTim, if the measured airflow VDis_flow is less than 70% of setpoint VActSet_flow for 5 minutes (lowFloTim) while the setpoint is greater than zero, generate a Level 3 alarm.
2. If the zone is in occupied mode and after the AHU supply fan has been enabled for staTim, if the measured airflow VDis_flow is less than 50% of setpoint VActSet_flow for 5 minutes (lowFloTim) while the setpoint is greater than zero, generate a Level 2 alarm.
3. If a zone has an importance multiplier (staPreMul) of 0 for its static pressure reset Trim-Respond control loop, low airflow alarms shall be suppressed for that zone.

Airflow sensor calibration

• If the cooling and heating fans serving the zone have been OFF (u1CooFan=false and u1HeaFan=false) for 10 minutes (fanOffTim), and the discharge airflow sensor reading VDis_flow is above 10% of the cooling maximum airflow setpoint VCooMax_flow, generate a Level 3 alarm.

Leaking damper

• If the cooling and heating damper position (uCooDam and uHeaDam) are 0% and airflow sensor reading VDis_flow is above 10% of the cooling maximum airflow setpoint VCooMax_flow for 10 minutes (leaFloTim) while the fan serving the zone is proven on (u1CooFan=true or u1HeaFan=true), generate a Level 4 alarm.

Revisions

• August 29, 2023, by Hongxiang Fu:
  Because of the removal of Logical.And3 based on ASHRAE 231P, replaced it with a stack of two Logical.And blocks. This is for #2465.
• August 23, 2023, by Jianjun Hu:
  Added delay staTim to allow the system becoming stabilized. This is for issue 3257.
• August 1, 2020, by Jianjun Hu:
  First implementation.