Originally Posted by JohnnyWilkinson
Awesome. Thanks for this - really useful info.
I was thinking something similar, but had no idea on volumes needed. Was also debating whether it needs air conditioned air or not. It sounds like in your setup at least it's not needed. I may run into problems though when outside air temps reach 40+ in summer :/
Here is the proposal I put to my architect, which would allow air conditioned air if needed, but also just normal extraction in cooler months. Do you think it'd work?
If you can get air-conditioned air into the hush box, even better, and probably a must is you're hitting those kind of ambient temps. I'm in the UK and fortunately (or unfortunately depending on how you look at it!) ambient temps rarely get above 30 degrees C, even in the height of Summer, so that's fine for me as intake air temp.
Its difficult to see from your drawing, but as long as you have a way for cool replacement air (when not using the air conditioning) to get into the cabinet, you should be fine. This cooler make-up air can be from in room if you don't want to run separate ducting from it, just make sure the intake is a folded path with sound absorption along the route, to prevent noise escaping from it.
With regards to the extract fan, just place it as far from the room as you can, and use lined acoustic ducting if you can, to minimise noise from it. These fans are particularly good, and run very quite (I have one extracting air from my equipment rack):
Just pick a size that suits your requirements, and bear in mind that the further away the fan is placed, the the more turns in your ducting, the more power (or more correctly the greater static pressure) your fan needs to achieve.
As Craig says his 170cfm fan provides enough extraction, and my 360cfm fan runs no more than 50% (probably on average less than that - I just like to over-specify). So as long as you're running 150-200cfm at the exit point in the hush box, you should be fine.