My questions is regarding avoiding contaminadtion from one room to another. For example,some product in the air my contaminate another product at a different rooms. I am refering to avoiding the air from one room to contaminate the air in another adjacent room. The question is?: Can that be achieve using the same AHU for both room or they need different AHU for each room ?
It is possible to use one supply fan and one exhaust fan. The supply fan needs to be in the the least contaminated area and the exhaust fan in the most contaminated so that air flow is always from least to most contaminated. You will obviously need a damper that will prevent backflow if the exhaust fan quits working.
Patricia Lougheed
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As long as you have volume dampers, you can control flow. The idea is "differential volume". Depending on how much relative differential pressure you need, you might use anywhere from 10% to 30% differential. For the "dirty" side, have a set percentage less supply than exhuast. For the "clean" side, reverse that proportion. Hard wall and transfer grille greatly improves the differential volume.
You cannot prevent cross contamination if the 2 rooms need to be totally segregated from one another. "Clean side" and "dirty side" assumes that one room will always be contaminating the other. Differential pressure controls and all that just require more complex systems, airlocks, etc, which just add further cost and the probability of incidental system failure. If these are critical application clean rooms, don't take the chance. Short answer=no.
Funny, it's worked quite well (for decades) for BSL-3 applications, lab applications, as well as medical. Endorsed by IMC and ASHRAE. Differential volume is much more simple than differential pressure. Either is more simple than cascading. Going from "relative" levels of "clean" is also included in ASHRAE 62.1. Method is also endorsed for recirculation in ISO class clean rooms, unless 100% OA or HEPA/ULHEPA is required. Simple answer is obviously "yes". Unless you know of some virus or micobe that can swim against the tide, it will work. If you do know of such agent, you should probably contact the CDC.
In cooler areas of the world, the air handling units recirculate a percentage of the air. Cross contamination cannot be avoided with recirculating systems.
Bill
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"Why not the best?"
Jimmy Carter
That's one of the problems with posting on a free Internet forum -- you don't really know. In the end, you need to make a decision based on sound engineering principles.
Part of your problem is that both answers might be correct, depending on the application and arrangement of the fans.
For example, my earlier reply was based on a "constant loss" scenario to use Waross' term. The intake is in the cleaner room and an exhaust fan is in the more contaminated room. Air flows into one room, through a damper, and then out the other room's exhaust. Flow is always from the clean to dirty room. There is no recirculation of air between the rooms. While this doesn't strictly "segregate" the flow between the rooms, it does ensure that the clean room doesn't get contaminated.
In a later post you asked about using the same air handling unit for both rooms. That is a slightly different question then "is it ok to use one supply fan and one exhaust fan and still keep the rooms segregated". An air handling unit cools/warms the air within a room and could be entirely separate from the intake and exhaust fans. Again, this would depend on your setup and what the limitations are for each room.
Having one intake fan, one air handling unit and one exhaust fan to handle the airflow for multiple rooms is not uncommon in the nuclear world (which is my experience base). The design engineer just needs to ensure that the design is adequate to keep each room within the desired temperature range and that the airflow is always in the desired direction.
Patricia Lougheed
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
This is generally how it's done, but be warned, if the belt brakes on your exhaust unit while person A is cooking dried stinky fish and "stinky tofu", the those odors could be introduced into person B's room through the exhaust vent if person B happens to have the window open (because of the pressure difference). Now, suppose person B has similar culinary desires as person A, then person A & B could conceivably end up moving in together whereby the building owner will loose a tenant and not be happy about it.
