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

Information

This block outputs alarms of series fan-powered terminal unit with constant volume fan. The implementation is according to the Section 5.9.6 of ASHRAE Guideline 36, May 2020.

Low airflow

1. After the AHU supply fan has been enabled for staTim, if the measured airflow VPri_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. After the AHU supply fan has been enabled for staTim, if the measured airflow VPri_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.

Low-discharging air temperature

1. If heating hot-water plant is proven on (u1HotPla=true), and the discharge temperature (TDis) is 8.3 °C (15 °F) less than the setpoint (TDisSet) for 10 minuts (lowTemTim), generate a Level 3 alarm.
2. If heating hot-water plant is proven on (u1HotPla=true), and the discharge temperature (TDis) is 17 °C (30 °F) less than the setpoint (TDisSet) for 10 minuts (lowTemTim), generate a Level 2 alarm.
3. If a zone has an importance multiplier (hotWatRes) of 0 for its hot-water reset Trim-Respond control loop, low discharing air temperature alarms shall be suppressed for that zone.

Fan status alarm

Fan alarm is indicated by the status input being different from the output command after a period of 15 seconds after a change in output status.

1. Command on (u1FanCom=true), status off (u1TerFan=false), generate Level 2 alarm.
2. Command off (u1FanCom=false), status on (u1TerFan=true), generate Level 4 alarm.

Airflow sensor calibration

If the fan serving the zone has been OFF (u1Fan=false) for 10 minutes (fanOffTim), and airflow sensor reading VPri_flow is above 10% of the cooling maximum airflow setpoint VCooMax_flow, generate a Level 3 alarm.

Leaking damper

If the damper position (uDam) is 0% and airflow sensor reading VPri_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 (u1Fan=true), generate a Level 4 alarm.

Leaking valve

If the valve position (uVal) is 0% for 15 minutes (valCloTim), discharing air temperature TDis is above AHU supply temperature TSup by 3 °C (5 °F), and the fan serving the zone is proven on (u1Fan=true), gemerate 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.