INVISCO now offers the Thorwaldson Tornado Hybrid Rooftop Ventilator with a 48 inch diameter fan blade that is rotated by a 1-1/2 HP infinitely variable speed motor running at just 990 watts and that uses a VFD with 0-5 VDC speed control input from building control systems. Hybrid means you get excellent free gravity ventilation built in.
Below is an email send to over 2,000 building engineers on March 14, 2018.
An example is this 48 inch diameter fan installed on a plastics manufacturer in Escondido. It was protected from rain by a carport-like roof so that it has the best air flow possible. It puts out over 20,000 CFM at full speed!