Industrial extraction removes contaminated air from a building, while the HVAC or make-up-air system introduces and conditions replacement air. If these systems are designed independently, building pressure, capture performance, comfort and energy use can all become unstable.
Why air balance matters
The air mass leaving the building must be replaced. Excessive negative pressure can make doors difficult to open, draw unfiltered air through gaps and reduce exhaust airflow. Uncontrolled positive pressure can push odours or contamination toward adjacent areas. The desired pressure relationship depends on the process and room function.
Problems caused by poor coordination
- excessive negative pressure: uncontrolled infiltration, draughts and loss of designed extraction capacity;
- uncontrolled positive pressure: migration of process air into cleaner zones;
- high energy demand: conditioned air is exhausted without a coordinated replacement strategy;
- unstable source capture: strong supply jets deflect fumes or dust away from the hood;
- temperature complaints: cold or hot replacement air enters occupied areas at the wrong location or velocity.
The role of local extraction
Extraction airflow is determined by the capture requirement at each process, not by the HVAC capacity left over. Gates and variable controls can adapt demand to active machines, but minimum transport velocities and safety constraints must remain satisfied.
The role of HVAC and make-up air
The supply system replaces the extracted volume, filters and conditions outdoor air where necessary, and distributes it without interfering with capture. Air should generally move from cleaner areas toward controlled process zones, following the pressure concept defined for the facility.
Balancing strategies
Direct compensation
Make-up airflow follows the main extraction demand. This is suitable where operating states are predictable and the air can be distributed without creating local draughts.
Zonal compensation
Large buildings are divided into zones so that air is introduced close to the volume from which it is removed. This limits crossflows between unrelated processes.
Automated control
Fan speed, damper position and supply airflow can respond to machine status, duct pressure or building-pressure sensors. Control sequences should be commissioned under representative simultaneous loads.
Heat recovery
Heat recovery may reduce energy use where the contaminated and clean air streams can remain safely separated. Its suitability depends on pollutant type, fouling, condensation, leakage risk and maintenance. It is not applied automatically to every exhaust stream.
Influence on source capture
A cross-draught at the hood can overpower the velocity of a rising fume plume or carry dust past the extraction point. Supply terminals should therefore be located and selected as part of the capture design. Measurements or CFD may be useful where the interaction is complex.
Monitoring and commissioning
Useful operating data include building pressure, extract and supply airflow, representative hood measurements, filter pressure drop and temperature. Alarm limits can identify a failed fan, blocked filter or damper fault before the process environment deteriorates.
ALWO supplies extraction and industrial ventilation equipment that can be coordinated as one airflow system. Contact us to assess an existing imbalance or a new facility design.
