Ventilation collection:
https://3dsky.org/collection/shared/5333943 

CORONA + VRAY (2013)
FBX CORONA + VRAY (2009)

Ventilation system for ceilings.
The kit includes a pre-assembled ceiling consisting of several ready-made modules and a set of individual elements for assembling various options.
Elements used in the kit: straight air ducts, bends, transitions, tees, plugs, ventilation grilles, air conditioners, fasteners.
Dimensions of square air ducts: 600 x 600, 400 x 400 mm.
The set contains 6 types of materials that can be used for any element.
The parts are edited using Edit Poly and adjusted to the required dimensions.

Other sets:
https://3dsky.org/users/solomon5555/models