I have seen (older) racks which are fully-closed. For example similar with plexiglass doors:
Or with metal doors without any grid/holes. Are such racks designed for data-centers with raised floors and take cold air from the bottom and push hot air out from the top? Or are they simply for equipment which do not create (much) heat?
Such rack with limited airflow are usually done for industry where the environnement are hostile, such as production server in a not closed room. (SCADA system in example)
As usually the industry got a clean server room, but often production machine can end up in not controlled space. As often you could install EPA air filter on the air entry for the cabinet.
Usually those gears are done to resist more to heat, but we fall on industrial grade gear.