Laboratory Pressurization

[nuuvox000]

I've just read through the ASHRAE laboratory design guide but I'm still a little confused about pressurization techniques for laboratories. I have two fume hoods which will exhaust air so I believe I need to supply makeup air while they are running. But I also need to keep the laboratory space at a negative pressure with respect to surrounding spaces. The dilemma as I see it is that I will have to introduce makeup air for the exhaust hoods but this means I still need to have general exhaust to keep the space negative. But if I keep the space negative, don't I risk pulling fumes out of the exhaust hoods?

My other question is on air leakage area (sq in/100 sqft). Have any of you had experience using certain values? ASHRAE says it can vary from about 2 to 30 sq in per 100 sqft of surface area. Based on the study they referenced, I'm using about 20 (non-gasketed ceiling tiles, one door, two windows, 155 sq ft room).

I'm just starting out so thanks for your patience. Thanks in advance!

 

[IRstuff]

The exhaust hoods are at an even more negative pressure than the room; there's no conflict with ASHRAE.

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[itsmoked]

Trivial.
Given the correct equipment.
The vent hoods create negative pressure. A lot at their entrances. This makes the room negative too.

You want to control how negative so people can actually get in and out of the door. There are many companies that provide the equipment to do this. You should start talking to them. Provide them with room dimensions, hood count, room construction info(suspended ceiling), and hood exhaust flow information.

You should include a clear active display showing the room pressure differential to anyone entering the room. This is required in case something goes wrong with the controls or equipment. Many rooms here in Silicon Valley have Magnahelics mounted in the wall directly above the the doors.

Room Pressure Controls



Keith Cress
kcress -

http://www.flaminsystems.com

 

[nuuvox000]

Thanks for your input, all.