Various air distribution systems are available for industrial production plants. Important criteria are personal safety against air pollutants, thermal conditions in the working environment and energetic expenditure.
At the design stage determine the thermal and pollutant loads. Thermal loads in industrial halls are often removed by free cooling with outdoor air.
Pollutant loads do not appear in all industrial halls. Only very low emissions are found in final assembly, shipment or stock.
Variants of air distribution systems
Ventilation systems for industrial applications use turbulent mixing ventilation, displacement ventilation (height of 3 m above the ground) and displacement ventilation at the floor (called stratified ventilation).
The turbulent mixing ventilation with radial and twist outlets or jet nozzles. Features the assembly of the air outlets in the ceiling area or at the top part of the wall and air discharge velocities of 4 to 6 m/s with twist outlets or 8 to 12 m/s with nozzles. Heat and pollutant loads are evenly distributed over the entire room.
Displacement ventilation, the air outlets are arranged at a height between 3 and 4 m. The discharge velocity of 0.6 – 0.9 m/s of the supply air is lower than the velocity by turbulent mixing ventilation. Less indoor air is inducted into the supply air. There are lower temperatures and pollutant loads in the occupied zone than in higher zones of the building.
Displacement ventilation (stratified ventilation), high heat and pollutant load the air outlets should be positioned on the floor. This stratified ventilation is achieved by displacing supply air with low air velocities of 0.3 to 0.4 m/s in the proximity of the workplaces. The air will be transported to higher regions of the hall, where it will be removed with the exhaust air.
Air balance between supply and return air volume flow rate
An essential target of the design is the collection and extraction of air pollutants directly at their source. The airflow that replaces the extracted air usually comes from the occupied zone in the factory building.
If the proportion of the decentralized machine exhaust air to the total exhaust air in the lower zone of the building is too high, not enough exhaust air is extracted below the ceiling of the industrial hall. There are backflows of polluted air from the upper parts to the occupied zone. It is important to make sure that 50% of the supply air can be removed as exhaust air in the higher parts of the industrial hall.
It is recommended to equip the HVAC system with a reserve regarding the supply airflow rate.
Adjustment to thermal load
Different mechanisms are installed in the air outlets by the manufacturers for heating and cooling needs. To adjustment of the air outlet either manually or automatically.
The automatic adjustment can be carried out by electric servomotor or by the self-acting thermostatic control unit. The advantage of the adjustment with thermal control is that there is no need for electric wiring and controllers. It receives the operating energy directly from the supply air and a special wax mixture (expandable material) delivers the adjustment mechanism for the piston stroke.
For the selection of a ventilation system for industrial halls, the heat load and the pollutant load have to be considered first. There needs to be a balance between supply air and exhaust air. The adjustment of the supply airflow to the different thermal loads can be made by economic thermostatic control units. Work areas can be provided with outside air, thanks to a project design that considers the best-suited ventilation system for the respective application.
