Multi level space 3

[tyfullerton]

Hi All,

I'm an Architect working on a project that has a multi-story space, small mezzanine above a large living room, which is above a large cellar. All are open to each other. Our HVAC engineer is showing supply cooling along the perimeter ceiling at the mezzanine level. My worry is that the cold air will settle at the first floor and/or cellar and the hot air will rise, filling up the mezzanine and leave it feeling uncomfortable.

I am being assured that the system will be balanced and that the falling cold air from the ceiling will cause a convective loop that will thoroughly mix the air in the entire space. This makes some sense but does not seem, to me, a thorough enough strategy to rely on. It seems like the convective loop would almost be negligible in terms of mixing the air.

Anyone out there have two cents to throw into this?

Thanks,

Tyler

 

[MintJulep]

ceiling at the mezzanine level

Is that the level of the underside of the mezzanine - the "ceiling" of the first floor, or the ceiling above the mezzanine?

 

[tyfullerton]

Its the ceiling of both the mezzanine and living room. See attached section.

http://files.engineering.com/getfil...3d0-4912-8aed-6bc525f406ca&file=photo_(3).JPG

 

[MintJulep]

If the air is thoroughly mixed there won't be convection because it's all the same density. Convection relies on a lack of mixing, so yes, you need something more than unsubstantiated assurances.

 

[tyfullerton]

He is saying that the introduced cold air passing through the warm air of the space will fall from the ceiling, warm and then rise again. This action will create a convective loop and thus mix the air and leave the entire space at the desired temperature.

Not that the loop will exist in the thouroughly mixed air condition but that it will create the mixed condition.

 

[MintJulep]

Unless there is no load in the cellar. In that case cold air will pool there.

 

[Drazen]

it does not sound bad to me. in case that cold air settles on lower level more than it is initially desired, than for the sole fact that air will be more dense down there, air from ceiling will fall at slower rate, which makes some sort of natural self-balancing.

you did not mention which type of air supplying terminal is to be used, but in general the most important thing is that engineer makes provisions for in-field balancing within some range, so that system can be somewhat adjusted to what will be observed during start-up at load.

 

[berkshire]

Air of different temperatures will not mix unless you force it to by mechanical movement, which means velocity and noise .
If the return air is in the cellar, you are just going to get a cascade of cold air from those slots dropping to the cellar, with a pool of hot air at your Mezzanine level.
You may have better results if your return air is in the ceiling to strip off the hot air.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[tyfullerton]

Thanks for all the responses everyone.