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

Information

This block outputs alarms of snap-acting controlled dual-duct terminal unit. The implementation is according to the Section 5.11.6 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 unit has dual inlet sensor (have_duaSen=true):
  • If the cooling fan serving the zone has been OFF (u1CooFan=false) for 10 minutes (fanOffTim), and the cold-duct airflow sensor reading VColDucDis_flow is above 10% of the cooling maximum airflow setpoint VCooMax_flow, generate a Level 3 alarm.
  • If the heating fan serving the zone has been OFF (u1HeaFan=false) for 10 minutes (fanOffTim), and the hot-duct airflow sensor reading VHotDucDis_flow is above 10% of the heating maximum airflow setpoint VHeaMax_flow, generate a Level 3 alarm.
• If the unit has single discharge flow sensor (have_duaSen=false):
  • 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 unit has dual inlet sensor (have_duaSen=true):
  • If the cooling damper position (uCooDam) is 0% and airflow sensor reading VColDucDis_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), generate a Level 4 alarm.
  • If the heating damper position (uHeaDam) is 0% and airflow sensor reading VHotDucDis_flow is above 10% of the heating maximum airflow setpoint VHeaMax_flow for 10 minutes (leaFloTim) while the fan serving the zone is proven on (u1HeaFan=true), generate a Level 4 alarm.
• If the unit has single discharge flow sensor (have_duaSen=false):
  • 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.