This article is about general HVAC Control System Fault Definitions used in Integrated Automation System or Building Automation System.
HVAC Control System Fault Definitions
Fault Rule Name |
Fault Rule Short Description |
| AHU Cooling & Heating Cycling | Finds periods when the heating and cooling are cycling between each other within a threshold. This indicates that the unit is fighting back and forth between its mechanical components. |
| AHU Cooling & Heating Simultaneously | Finds periods when discharge fan is on, heating is on and cooling is on for over a duration. |
| AHU Cooling Failure | Finds periods when discharge fan is on, cooling is on, and discharge temperature sensor is not under mixed air sensor minus a threshold for over a duration. |
| AHU Cooling Valve Leaking | Generates a fault when discharge fan is on, cooling valve is closed, and discharge temperature sensor is under mixed air sensor by a threshold. |
| AHU Discharge Fan Failure | Generates a fault when discharge fan is on and duct static pressure is below a threshold. |
| AHU Discharge Pressure Setpoint Unreachable | Finds periods over a duration when discharge fan is on and discharge pressure is below or above the discharge pressure set point by a threshold. |
| AHU Discharge Pressure Unstable | Generates a fault when the discharge fan is on and the discharge pressure bounces above and below the discharge pressure set point by a dead band |
| AHU Economizing & Cooling Simultaneously | Finds periods when discharge fan is on, outdoor damper is open more than a threshold and cooling is on for over a duration. |
| AHU Economizing & Heating Simultaneously | Finds periods when discharge fan is on, outdoor damper is open more than a threshold and heating is on for over a duration. |
| AHU Heating Failure | Finds periods when discharge fan is on and discharge temperature sensor is not greater than mixed air sensor plus a threshold for over a duration. |
| AHU Heating Valve Leaking | Generates a fault when discharge fan is on, heating valve is closed, and discharge temperature sensor is greater than the mixed air sensor by a threshold. |
| AHU Outside Damper Stuck Closed | Generates a fault when discharge fan is on, outdoor damper is greater than a threshold and the calculated outdoor air percentage is lower by more than a percentage. |
| AHU Outside Damper Stuck Open | Generates a fault when discharge fan is on, outdoor damper is less than a threshold and the calculated outdoor air percentage is higher by more than a percentage. |
| AHU Low Outside Airflow | Generates a fault when the discharge fan is on and the outside airflow is below the outside airflow set point during occupancy. |
| AHU Unstable Outside Airflow | Generates a fault when the discharge fan is on and the outside airflow bounces above and below the outside airflow set point by a dead band. |
| AHU Unit On Discharge Fan Off | Generates a fault when discharge fan is off and anything is on; hot water valve is more than a threshold, any heating stage is on, chilled water valve is more than a threshold, or any cooling stage is on. |
| AHU Discharge Temperature Set point Unreachable | Finds periods when discharge fan is on and any discharge temperature cannot get within a threshold of discharge temperature set point for over a duration. |
| AHU Discharge Temperature Unstable | Finds periods when discharge fan is on and any discharge temperature bounces above and below the discharge temperature set point by a dead band. |
| AHU Low/High Pressure | Finds periods when the AHU supply pressure is outside of the set point (+/- 0.25”) over a duration (~15 minutes). |
| AHU Low/High Temperature | Finds periods when the AHU supply temperature is outside of the set point (+/- 2o F) over a duration (~15 minutes). |
| AHU Unit On Discharge Fan Off | Finds periods when discharge fan is off and anything is on; hot water valve is more than a threshold, any heating stage is on, chilled water valve is more than a threshold, or any cooling stage is on for over a duration. |
| Bad Energy Data | Finds periods when data contains values outside of low and high limits or the data is NaN for at least a duration |
| Heat Running During Warm Weather | Finds periods when heat is are running and the outside air temperature is above a threshold. |
| Building Running Too Late | Finds periods when the demand of the building does not drop off by at least a percentage or threshold for a duration after occupancy is over. |
| Building Starting Too Early | Finds periods when the demand increases by a percentage or threshold for a duration before building occupancy. |
| Boiler Cycling | Generates a fault when the boiler stays on or off for less than a duration. |
| Boilers Running During Warm Weather | Generates a fault when boilers are running and the outside air temperature is above a threshold. |
| Cabinet/Door Heater Zone Temperature Out of Range | Finds periods for longer than a duration when the space temperature is less than or greater than, the heating temperature setpoint by a threshold. |
| Chiller Cycling | Generates a fault when the chiller stays on or off for less than a pre-specified duration. |
| Chilled Water Plant Demand Peak | Finds chilled water demand peaks throughout the day, as measured against a facility benchmark. |
| Chilled Water Pressure set point Unreachable | Finds periods when any pump is on and the differential pressure cannot get within a threshold of differential pressure set point for over a duration(~15 minutes). |
| Chilled Water Pressure Unstable | Finds periods when any pump is on and the differential pressure cannot stay within a threshold of differential pressure set point for over a duration (~15 minutes). |
| Chilled Water Plant Temperature Setpoint Unreachable | Finds periods when any chiller is on and the leaving CHW temperature is unable to reach a pre-specified threshold of the CHW supply setpoint for over a duration. |
| Chilled Water Plant Leaving Temperature Unstable | Generates a fault when the leaving CHW temperature bounces above and below the supply temperature set point by a dead band. |
| Chilled Water Low/High Temperature | Finds periods when the chiller provides water outside of the set point (+/- 2o F) over a duration (~15 minutes). |
| Chilled Water Mixing | Finds periods when the chilled water return temperature is not more than 4o F above the chilled water supply temperature over a duration (~15 minutes). |
| Chilled Water System Failure | Finds periods when any chiller is on within the chiller plant and the chilled water leaving temperature is not within a specified range for over a duration (~15 minutes). |
| Chiller Running During Unoccupied Periods | Generates a Fault if the chiller plant is operating outside the normal occupancy schedule. |
| Cooling Set point Out of Range | Finds periods when the cooling set point is below a threshold for over a duration. |
| Cooling Tower Temperature Set point Unreachable | Finds periods when cooling tower leaving water temperature cannot get within a threshold of the leaving water temperature set point for over a duration. |
| Cooling Tower Temperature Unstable | Finds periods when cooling tower leaving water temperature bounces above and below the water temperature set point by a dead band. |
| Double Dipping Data | This searches the database and finds data which is duplicated (point readings being stored in separate areas) and notifies administrator to reduce duplicated points, trends or data. Finds periods when a point’s history contains two or more data points within a leeway of an interval for at least a duration. |
| EF Not Running When Emergency Generator is Engaged | Generates a fault when any exhaust fan serving an emergency generator is not operating when the generator has been engaged |
| EF Not Running Under Thermostatic Control | Finds periods when any exhaust fan controlled via thermostat is not operating when space temperature. |
| EF Running During Unoccupied Periods | Finds periods when any exhaust fan is operating outside the normal schedule. |
| Floor VAV Unstable Airflow | Generates a fault when the floor VAV is active and the supply airflow bounces above and below the supply airflow set point by a dead band. |
| Heat Exchanger Temp Set Point Unreachable | Finds periods when the secondary leaving water temperature cannot get within a threshold of secondary leaving water temperature set point, while either a heat exchanger pump is on or a hot water system pump is on, for over a duration. |
| Heat Exchanger Temp Unstable | Finds periods when the secondary leaving water temperature bounces above and below the secondary leaving water temperature set point by a dead band. |
| Heating Set Point Out of Range | Finds periods when the heating set point is above a threshold for over a duration. |
| Hot Water Circ Pump Running | Generates a fault when hot water heating coil pumps are running and no secondary hot water pumps are running in the system. |
| Hot Water Plant Demand Peak | Finds hot water demand peaks throughout the day, as measured against a facility benchmark. |
| Hot Water Pressure Setpoint Unreachable | Finds periods when any pump is on and the differential pressure cannot get within a threshold of differential pressure set point for over a duration. |
| Hot Water Pressure Unstable | Finds periods when any pump is on and the differential pressure cannot stay within a threshold of differential pressure set point for over a duration. |
| Hot Water Plant Temperature Setpoint Unreachable | Finds periods when any boiler is on and the leaving HW temperature is unable to reach a pre-specified threshold of the HW supply setpoint for over a duration. |
| Hot Water Plant Leaving Temperature Unstable | Generates a fault when the leaving HW temperature bounces above and below the supply temperature set point by a dead band. |
| Missing Data | Finds periods when a record’s history contains zero data points within a leeway of an interval for at least a duration. |
| Occupied Cooling Setpoint Out of Range | Finds periods over a duration when the occupied cooling set point is below a threshold. |
| Occupied Heating Setpoint Out of Range | Finds periods over a duration when the occupied heating set point is above a threshold. |
| Power Peak | Finds when power is 5% higher or 5% lower than the previous period or year (similar for day, week, month, year). |
| Pump Cycling | Generates a fault when the pump stays on or off for less than a specified duration. |
| Sensor Failure | Finds periods when a sensor does not change by a threshold for a 24-hour period. |
| Short Demand Peak | Finds short demand peaks throughout the day. |
| Split System A/C Unit Cooling Setpoint Out of Range | Finds periods over a duration when the room or zone temperature is unable to maintain a threshold above or below the cooling setpoint. |
| Terminal Unit Airflow Setpoint Unreachable | Finds periods over a duration when the discharge airflow cannot get within a threshold of discharge airflow set point (while the FCU fan is on). |
| Terminal Unit Airflow Unstable | Generates a fault when the discharge airflow bounces above and below the discharge airflow set point by a dead band. |
| Terminal Unit Heating Failure | Generates a fault when the FCU fan is on (if applicable), heating is on, and discharge temperature sensor is not greater than the discharge air sensor plus a threshold. |
| Terminal Unit Heating Valve Leaking | Generates a fault when FCU fan is on (if applicable), heating valve is closed, airflow is above a threshold, and the discharge temperature sensor is above discharge temperature by a threshold. |
| Terminal Unit Zone Temperature Out of Range | Finds periods when the zone air temperature is less than or greater than the zone set point(s) by a threshold for longer than a duration. |
| Underfloor Heating Space Temperature Out of Range | Finds periods when the underfloor heating space temperature is less than or greater than the setpoint(s) by a threshold for longer than a duration. |
| Unoccupied Cooling Setpoint Out of Range | Finds periods over a duration when the unoccupied cooling set point is below a threshold. |
| Unoccupied Heating Setpoint Out of Range | Finds periods over a duration when the unoccupied heating set point is above a threshold. |
| Zone Cooling Damper Malfunction | Finds periods when the cooling damper is open above a threshold and the zone damper discharge air temperature is not within a threshold of the cold deck discharge air temperature for over a duration. |
| Zone Heating Damper Malfunction | Finds periods when the heating damper is open above a threshold and the zone damper discharge air temperature is not within a threshold of the hot deck discharge air temperature for over a duration. |
| Zone Temperature Out of Range (Cooling) | Finds periods when the zone air temperature is less than the zone set point(s) by a threshold for longer than a duration. |
| Zone Temperature Out of Range (Heating) | Finds periods when the zone air temperature is greater than the zone set point(s) by a threshold for longer than a duration. |
| Underfloor Heating Space Temperature Out of Range | Finds periods when the underfloor heating space temperature is less than or greater than the setpoint(s) by a threshold for longer than a duration. |