Icepak FAQ: When to use openings vents and fans
What are the differences between openings fans and planar resistances
Fans: If you want to fix flow (volumetric or mass rate) use external fans. External fans can only be used on domain boundaries (namely, cabinet and hollow block surfaces). Fans may also be used to specify flow nased on a fan curve. If the fan lies interior to domain bounadry, use internal. YOu cannot fix flow on internal fans.
Vents: If you want to exhaust or intake flow through a porous planar structure. The porosity is accounted for by the loss coefficient.
If you use loss coefficient = 0, its equivalent to using an opening in its place (which is also allowed). Vents should only lie on domain boundary.
Resistance: If you want to model a porous planar structure interior to the domain. When the loss coefficient is 0, the resistance is equivalent to an opening.
Opening: Openings allow flow to pass through them. In addition you can also impose velocity, pressure and temperature distriburion of flow. However, in order to impose a distribution, the opening must lie on domain boundary.