Fault Detected - Severe Heat Stratification

Stratification is the tendency for hot air to rise towards the ceiling in large buildings with tall ceilings, and grocery stores often face this problem due to the variety of temperatures present in the store. From the cold cases to the deli, with the front doors opening and closing for every new customer, maintaining a consistent temperature can be difficult. Furthermore, if not considered in the design stage stratification can cause extreme cases of excess energy consumption as can be seen in the following findings.


The OPNHVAC software identified a severe case of heat stratification in a Grocery zone of a Large Retail store. This heat stratification fault is one that had a multifaceted impact on comfort, energy and component lifespan.

The OPNHVAC software picked up the fault by analysing the zone air temperature sensors in the space as well as the return air temperature sensors in the AHU ducts during operation of the units. Once detected, the issue was sent to the facility manager of the store for further investigation.


Portable temperature loggers were used to validate the existence of this problem. Measurements were taken at different heights and at different locations throughout the grocery. The additional sensor data confirmed that warm air was layering in temperature gradients at ceiling height and in a large void above the false ceiling. Whereas temperatures below the desired zone setpoint of 22°C were measured in the occupied space.

In essence, the control strategy on the air handling units providing heat into the space was failing. As the temperature at ground level, where the control sensors were placed, was never achieving setpoint the air handling units were continuously supply high volumes of heat into the space, yet this heat was stratifying and not effecting the space appropriately.


In order to remedy this issue, invasive remediation works would be needed to be carried out. As a result the client in this case is carefully considering their options. As a starting point, the air handling units were shut down as their operation was having no impact on the space temperatures in order to avoid wastage. Furthermore, the installation of de-stratification fans is being considered.

Monitoring of the gas consumption on the units while the fault was detected allowed us to assess the potential waste energy/cost that could be avoided over the course of a full year if the issue was resolved.

86,489 kg CO2e

Avoided Emissions


Avoided Cost


Reduced Running Hrs

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