Practical Fluid Mechanics: inversions & mixing

  • #1

Main Question or Discussion Point

I'm trying to think through a situation, and develop some confidence I've got it right.
The situation is a apartment building, about 60'/20m high, with a courtyard in the middle about 60'/20m square. In the middle of the courtyard, is an low exhaust stack, about 8' high and around 8' square, that exhausts a 2-level underground parking garage.
My sense is that it is not certain that the emissions of that garage will make it out of the courtyard: They will be a mix of CO2, CO, volatile organics, particulate matter and other things. On a warm & windless day they may well emerge well below the ambient temperature, which could create a microclimate or small inversion layer...
I'd be interested in hearing opinions, being pointed to relevant research, or anything else people might think is helpful.
Thanks!
 

Answers and Replies

  • #2
berkeman
Mentor
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I'm trying to think through a situation, and develop some confidence I've got it right.
The situation is a apartment building, about 60'/20m high, with a courtyard in the middle about 60'/20m square. In the middle of the courtyard, is an low exhaust stack, about 8' high and around 8' square, that exhausts a 2-level underground parking garage.
My sense is that it is not certain that the emissions of that garage will make it out of the courtyard: They will be a mix of CO2, CO, volatile organics, particulate matter and other things. On a warm & windless day they may well emerge well below the ambient temperature, which could create a microclimate or small inversion layer...
I'd be interested in hearing opinions, being pointed to relevant research, or anything else people might think is helpful.
Thanks!
Welcome to the PF. :smile:

Yikes, it doesn't sound like that is built to code. What country and city is this building in? You should ask your local building code enforcement folks if an extension should be added to that exhaust stack, IMO.
 
  • #3
Nope, it's not in code explicitly: there are always special cases though. It would be extraordinarily hard to capture every possible scenario in the code, unless you just make really restrictive code. I can do the code analysis (the synopsis: it's not addressed) -- I'm curious about people's opinions/gut reactions/related research/whatever.
 
  • #5
The problem is, the limits wrt the roof are: at least 3' above any roof within 10'. Well, the courtyard is definitely big enough to not be within 10' of any roof, for a vent near the middle.
Interesting thing, there's also a limit in our code of 20' from an operable window, and they can't QUITE do that in this particular courtyard. However, I'm trying to think of this a little more generally: if their courtyard were 4' wider, they could get 20' from all windows, and (it seems likely, to me) it would still be a terrible idea: pushing garage exhaust into a courtyard that might be filled with children playing while an inversion situation concentrates garage emissions at ground level just seems like a bad idea, or at least a very-hard-to-prove-that-it's-ok idea..
 
  • #6
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It should not be you that does the code analysis. I second @berkeman 's advice.
You should ask your local building code enforcement folks if an extension should be added to that exhaust stack
Let those people to the analysis.
 
  • #7
Just to be clear: I'm not seeking code advice. I was looking for insight into a real-world physics problem involving gas mixing under various situations. For the purpose of my question, there's no one else who's going to do the analysis. There are two specific questions is love to see addressed: do you believe this courtyard situation could be troublesome or dangerous? ( No, your answer doesn't make you legally responsible!). And, what solutions can you think of...
 
  • #8
LURCH
Science Advisor
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I think I see what you’re saying, and I understand your concerns. Basically, you are thinking that this arrangement may, by mere technicality, be legal, but that wouldn’t make the fumes any less harmful, right? Completely reasonable.

However, I don’t think I would worry overmuch about the inversion layer scenario that you have mentioned. One question; is the vent powered by a fan? If it isn’t, then on any day that the air in the parking structure is heavier than the air outside, nothing is coming out of that pipe. I am assuming here that the entrance/exit for the garage is lower than the ground level in the courtyard, right? If so, then on any day like the one you describe, air is going in the vent, and out the the driveways.

Additionally, I am certain it had to pass some kind of inspection before being Occupied.
 

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