Exhaust Fans are used to exhaust air.
The fan system chosen will depend on the air being exhausted, if it is air for ventilation, such as from washrooms, or general exhaust, it may be a simple dome fan.
For process exhaust the factors to be considered, will be the quality of the air, will it contain chemicals, what will the temperature be.
Will there be a need for redundancy, or can the systems be turned off for maintenance and services?
Many process related fan systems have replaced the “high stack” with the “high plume” design, which shoots the air into the atmosphere to allow dilution.