Room pressure control in dust extraction systems

If you have more air exhausted from a space than you supply make up air with a ventilation fan, the pressure inside the space will drop until it reaches a point where the differential pressure between outside air and inside air is such that the differential volume flows through cracks in doors, windows, and permeance of building envelope, that is if the blower can produce such differential pressure.

ASHRAE has method to calculate the flow through cracks in doors, windows and building envelope under given differential pressure. A sample of this calculation is attached. To be safe I would use a pressure relief damper that will open at a safe inside pressure even if the calculations predict enough air will flow through cracks to maintain a safe inside space pressure. Or you could just add an air intake louver or duct. Here is link to relief dampers:

Depends on your fan curve.

Essentially moving more air out than you can get in will lower the pressure. That creates a higher differential pressure accross the fan and hence flow will go down until things get to steady state. But doors will whistle, might fly open or become difficult to close and people.e might experience ears popping if our fan is powerful enough.

Get the fan curve and see what it's differential pressure is at whatever in flow you think you can get. How much lower is it than 2000 cmh?

A spring loaded or powered inlet flap sounds like a good idea to me.

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