Fault detection and diagnostic lab

The purpose of establishing this facility is to develop, identify, and analyse faults in HVAC systems. This will help in development of effective HVAC FDD techniques for common faults such as variable air volume boxes, its dampers, actuators, controllers, airside economiser, AHU fan controllers, belts and bearings, valve leakage etc. Laboratory is consists of two identical side by side test chambers having 5.0 TR cooling capacity. Test chambers can be operated between 18°C and 30°C Indoor temperature range.

Cooling and Heating load calculation has been done using EnergyPlus simulation for all three outdoor conditions: summer, monsoon, and winter. For peak summer, air conditioning requirement for each test chamber is 3.5 TR and air supply flow required is 1145 CFM.

The implementation methodology of the faults identified is provided in Table 3. Faults related to Chiller is not considered for the analysis as sizing of the chiller is quite small and FDD techniques for the chiller are already well established.

Table 3 Faults, type and implementation method

Fault Type Proposed implementation
VAV Faults
VAV damper stuck Abrupt Physical intervention: disconnect actuator input, position manually
VAV actuator fail Abrupt Physical intervention.
VAV leakage Installation Physical intervention: remove damper-blade seals
Controller hardware failure Degradation Install faulty controller
Air Handling Unit
Fan Faults
Unstable supply fan


Abrupt Software override: change controller gain until oscillation

observed at low airflow rate

Slipping supply-fan belt Degradation Physical intervention: move fan motor to reduce tension in fan belt
Fan belts too tight Degradation Physical intervention: move fan motor to increase tension in fan belt
Dry bearings Degradation Physical intervention: Removal of lubrication
Case Faults
Improper AHU Drain connections Installation Physical intervention
Improper installation of fan motor Installation Physical intervention
Cooling Coil Faults
Leaking cooling coil valve Degradation Physical intervention: connect by-pass around control value
Reduced cooling-coil capacity (water side flow restriction) Degradation Physical intervention: restrict water flow to coil
Filter Faults
Blocked filter Degradation Physical intervention: Use of blocked filter
Pump Faults
Foreign material deposits Degradation Physical intervention: Use of old pumps
Corrosion Degradation Physical intervention: Use of old pumps
Oscillations Abrupt Physical intervention: Provide unstable foundation
Leakage Abrupt Physical intervention: Use of old pumps
Sensor Faults
Sensor offsets Degradation Use of faulty sensor
Positioning of Thermostats Installation By changing position of sensor
Duct Faults
Rusting in Duct Degradation Use of ducts with rust
Poor sensor placement in ducts Installation By altering position of sensor
Pipe Faults
Cleaning of chilled water strainers Degradation By installing used and un-cleaned strainer
Poor pipe insulation/ Condensation on pipe Installation By removing insulation
Air Side Economiser
Economiser Damper Failure Abrupt Physical intervention
Non-optimal economiser set-point Degradation By change of set point
Air temperature sensor failure Abrupt Use of faulty sensor