Many buildings feature return air columns, but the size selection varies depending on the environment and design requirements. For a cleanroom's return air column, what size of column should be used?

The return air columns in cleanrooms typically feature 300x500mm louvered windows and filters for air supply. Additionally, the outer layer is supported by color steel panels, which should be 500x500mm uprights. These are standard practices in construction projects. If you wish to design based on wind conditions, that's fine. I believe 2-2m/s is acceptable, as long as the frictional resistance isn't excessive. The key is to pay attention to construction techniques and avoid using the fresh air system to fill in.

The return air column can be divided into two types: one as an application for return air ducts, and the other as an application for return air outlets, which is calculated based on the exhaust air volume. As a passageway, it requires consideration of indoor space maintenance for mechanical equipment and also depends on your processing technology specifications. This is fundamental; it's not as simple as using it as you wish.

Designs for the return air column in a clean room typically involve adding an extra column head in areas with column caps, installing an air supply louver at the bottom, and connecting the return air duct at the top. That should suffice. Naturally, the distribution should be based on the size of the building to ensure natural ventilation.

For cleanrooms with a cleanliness level of 1000, a double-sided downflow approach is employed. For cleanrooms with a cleanliness level below 1000, when the total width of the cleanroom does not exceed 3 meters, a single-sided downflow can be chosen; when it exceeds 3 meters, a double-sided downflow should be selected. For larger cleanrooms, if double-sided downflow does not meet natural ventilation requirements, an additional air outlet should be placed at 1/2% of the total width of the cleanroom (such as using a return column), to reduce the swirl area. In the actual design, flexibility should be maintained based on cleanliness levels, process technology locations, and other standards. The overall standard for layout of air inlets is: integrate positive pressure inlets, coordinate with positive pressure inlets, to ensure full dispersion of clean air swirls, sufficient dilution of liquid heat transfer by convection, and even exhaust of the room.