These units are pretty standard equipment for agricultural barns housing confined animals - hogs, chickens etc. Most of the control circuitry can be bought off the shelf with inputs for various activation triggers like CO2 levels, Temperature, ammonia, humidity etc. In operation the worse the condition the more ventilation needed etc (or reverse). They also have the ability to incorporate outside sensors so you dont open up the throttle for full blast ventilation in the middle of winter.
Here's an example:
http://www.qcsupply.com/Products/10555.aspx?ref=fp
