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What is Automatic Pressure Balancing, and how does it eliminate contamination?

Automatic Pressure Balancing ensures any air leakage inside an AHU, when a Rotary Heat Exchanger is used for energy recovery, is always in the direction of clean supply air to dirty extract air.


This feature, which FläktGroup has had for over 5 years, fulfils the requirements for pressure balancing recently stated by REHVA.


  • Secure correct pressure balance between extract and supply air over the rotor
  • Ensures an Exhaust Air Transfer Ratio (EATR) of 0% in accordance of EN 16798-3:2018
  • Prevents contaminated extract air being re-circulated into the supply airstream


The leakage at the rotor from extract to supply air is minimized, by measuring and controlling the differential pressure from the extract to the supply air to a low but negative set point.


As default the set point is -10 Pa.


To achieve this, the extract air damper is equipped with a modulating actuator (0-10VDC), which is controlled to close to reduce the pressure and controlled to open to increase the pressure.


Note: the software function in the Climatix controller can also control a modulating damper in the outdoor air. This part of the function is used for Active mixing to create the mixing flow.



This feature is especially important for healthcare applications, such as ventilation in hospitals, where a mix of vulnrable and healthy people will spend extended periods of time in the same indoor space. But it can also help to protect people in offices, shops and schools among other indoor areas that require HVAC systems to maintain air comfort and safety.


Diagram of Automatic Pressure Balancing in AHU

On Friday 3rd July REHVA published updates to their guidance documents referring to Automatic Pressure Balancing to control air leakage inside an AHU when a Rotary Heat Exchanger is used for energy recovery. This update comes as studies by health experts continue in order to understand how viruses can be transmitted through particles suspended in the air.


Link to REHVA publication:



FläktGroup have successfully sold products with a solution to the problem for a number of years as part of our eQ product offering and soon this function will be available with our CAIRplus ISYteq controls.


For more information about this we invite you to get in touch with our experts:


eQ Master:


ISYteq Controls: