In order to keep the energy footprint of a newly planned cleanroom (grade C and D) as low as possible, we want to recirculate a certain amount of air over HEPA filters. The question specifically concerns the amount of air that can be recirculated in a cleanroom. What percentage is usually used here for fresh air/recirculated air? What is the advised minimum fresh air exchange rate in a cleanroom.

Yes, it is true that it is possible to clean a CG net, but we would advise against it. The liquid causes the fibers to swell, the mesh size and thus the air flow rate to change, which in turn changes the outflow properties (low-turbulence displacement flow).