Fault Detected - Hunting In Air Handling Unit

Hunting is a common problem in Air Handling Units that is very difficult to detect. The AHU control function becomes ineffective as it oscillates about a setpoint trying to find equilibrium. This fault causes significant wear and tear to the components as they cycle on and off, and results in wasteful energy consumption.


The OPNHVAC software identified a Hunting Fault on two air handing units, which condition a Drapery zone in Large Retail store. The AHUs are supply and return air packaged Rooftop Unit with mixing dampers. Heating is provided by two-stage gas burners and cooling by two-stage DX Coils.

The OPNHVAC software picked up the fault by analysing the heating and cooling components as well as the movement of the supply air temperature during operation of the units. As soon as the issue is detected the diagnosis information was issued to the contractors maintaining the site for immediate action.


Validation on this fault was easy to achieve, the OPNHVAC Engine was able to self validate the fault as the behaviour repeated itself over multiple days.

However as an additional manual validation, a portable energy meter was installed on the electrical supply to AHU 01 in order to validate that rapid cycling was occurring. The energy consumption on the DX Cooling Compressor was cycling on and off approximately every three minutes in line with the rise and fall of the supply air temperature.


Control tuning took place on the AHUs in order to dampen the response from the heating and cooling components which has successfully stopped the hunting fault from occuring. Validation of the fix was made via the OPNHVAC platform as the fault was no longer detected as present during the automatic daily analysis from the software after the tuning took place.

Monitoring of the gas and electric consumption on the units before and after the fault was resolved allowed us to assess the waste energy/cost avoided over the course of a full year. Further more the fix results in increased longevity of the components by reduced mechanical wear and tear on the rapidly moving components.

10,846 kg CO2e

Avoided Emissions


Avoided Cost


Reduced Wear & Tear

Client Feedback

" Within days of starting a trial with OPNHVAC we identified a number of operational and energy saving improvement opportunities within our buildings. After successfully using the software within two of our pilot buildings, we are now investigating the potential for further integration with other Ervia offices. Continuous Monitoring and Reporting enables the FM Department to measure and demonstrate the performance of our office led assets. "

- Dermot Walsh Facilities Energy Manager at Ervia