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Local Exhaust + Ambient Exhaust

Local Exhaust + Ambient Exhaust

Local Exhaust + Ambient Exhaust

I have a very large industrial building with a few concentrated sources of chemical air contamination. I am using local exhaust hoods to exhaust these areas at the source.

My question is what to use for the remainder of the building. When I take the air volume being exhausted from the point sources and apply an ACH calc to the total building volume it works out to be only about 1.5 ACH. Should I add additional ventilation to bump the total building ventilaion up to 3 ACH? I am in a Northern climate so energy usage is very high for high ventilation rates due to makeup heat.

RE: Local Exhaust + Ambient Exhaust

Where are you getting the 3 ACH number from? Air changes are not a good way to determine ventilation unless you're in a lab.

For ventilation per people or area, ASHRAE 62.1 2004 is a good start.

Local exhaust for processes aren't additive to the above.

RE: Local Exhaust + Ambient Exhaust

Your situation cannot be fully answered without additional details
Large industrial building??--Warehouse? fab shop? light industrial? heavy industrial? Truck loading docks in space?
Obviously, you do not have heat loads to address.
Depending on your situation, can you recirculate the air??
During the winter months you can recirc the air and mix with outside make-up air as required.  Temper the make-up air ( Most large ventilation manufacturers furnish Air Tunover Units)  

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