Fault Detected - Inefficient Heat Recovery

Heat Recovery Wheels in Air Handling Units are an efficient way to provide continuous fresh air while avoiding the need to heat the air from outside levels. At the point in a building’s ventilation system where fresh air and exhaust air run counter currently, but adjacent to each other, heat recovery can take place. This process is passive, and can significantly reduce the energetic and monetary cost of using new energy and moisture to treat incurrent air. In some conditions, energy recovery wheels can reduce the energetic demand of conditioning incurrent air by up to 95%. However, like all mechanical components they can fail and/or become less effective over time.


During the continuous monitoring of a supply and return air handling unit with a heat recovery wheel, the OPNHVAC automated rules engine detected low levels of effective heat recovery while the unit was active.

The OPNHVAC software picked up the fault by analysing the behaviour of the intake, post heat recovery and return air temperatures of the unit. Once detected, the issue was sent to the facility manager and maintenance provider for actioning.


The validation of this fault was easy, once the temperature sensors were checked for accuracy and the position of each sensor was verified then the detection of the fault was valid and the system could self verify by looking for further occurrences of the issue during normal operation.

The difference between the intake air temperature and the post heat recovery temperature (supply air temperature) was negligible at 0.1°C. Similarly the temperature recovered from the return airflow was very low. The average delta temp between the return air and exhaust air was 2°C. These temperatures were all occuring while there was a large amount of heat available from the return air to be captured.


The issue was resolved promptly as the maintenance provider was armed with all the relevant information and knew exactly what component to look at, the heat recovery component. The maintenance personal found that the linkage between the return air duct and the heat recovery wheel was damaged causing the return air heat to leak out prior to be being recovered by the unit.

The impact of this fault was hard to measure as the heat that wasn't being recovered was hard to quantify. However what was obvious was the fact that the heater battery in the unit was running unnecessarily at 100% during the operation of the unit in order to meet the heat demands of the unit. Therefore we were able to quantify a wastage amount of the fault based on a full years operation of the heater battery.

6,957 kg CO2e

Avoided Emissions


Avoided Cost


Reduced Heating Use

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