HVAC location of exhaust grilles
HVAC location of exhaust grilles
(OP)
Hi everyone,
I need your help again.
I'm having trouble about locating my exhaust grilles in the room I'm designing the HVAC for.
I'm worry about the air stratification because of the temperature differential (ie hot air is lighter than cold air)
If the air I'm supplying to the room cools the air inside most of the time, then should I locate the exhaust grilles at the highest level possible?
Because if the HVAC supplies cold air, then it will have the tendency to "stay" near the floor so by putting an exhaust grille near the ceiling, it will force that air to "go up".
Am I right?
I need your help again.
I'm having trouble about locating my exhaust grilles in the room I'm designing the HVAC for.
I'm worry about the air stratification because of the temperature differential (ie hot air is lighter than cold air)
If the air I'm supplying to the room cools the air inside most of the time, then should I locate the exhaust grilles at the highest level possible?
Because if the HVAC supplies cold air, then it will have the tendency to "stay" near the floor so by putting an exhaust grille near the ceiling, it will force that air to "go up".
Am I right?





RE: HVAC location of exhaust grilles
Is the room going to be positively or negatively pressurized? That may help determine the answer as well.
RE: HVAC location of exhaust grilles
I should have said that the airflow is supplied by textile duct diffusers (but I don't know if it changes anything).
RE: HVAC location of exhaust grilles
RE: HVAC location of exhaust grilles
The air movement in the room will be turbulent and mixing of supply air and room air will be the dominant effect.
If it is laminar flow you want in the room (cleanroom, operating room) then you have higher air change rates and you want the exhaust to be located low.
The supply of the air is what counts if the air change rate is relatively low and the flow is turbulent.
The effect of an exhaust grille will not be noticeable at a short distance from the grille. Do the math yourself: calculate the air velocity through the surface of an imaginary half-sphere with a radius of 0,5 metres.
This velocity will be low and so of no consequence to the actual air flow patterns in the room.
Supply grilles located flush in the ceiling often make use of the coanda effect to make the air travel further away from the grille and mix better.
Or, burn a candle and try sucking it out instead of blowing it out...
RE: HVAC location of exhaust grilles
The air change rate is just 3 volumes per hour so I won't have to worry about the location of the exhaust grilles.
Thanks everybody
RE: HVAC location of exhaust grilles
That can create sort of laminary pattern with very strong influence of thermal rise power, so I would strongly suggest that you put exhaust high, and supply should be preferably low, so thermal rise and your equipment will "work together" to drive air quantities through the room.
RE: HVAC location of exhaust grilles
If you only have 3 air changes per hour then a textile duct does not seem the right choice to me.
I would choose supply grilles that can still generate some mixing of supply air and room air.
A textile duct will not be able to do this at this low exchange rate, as Drazen already mentioned. You need a textile duct when you have to supply lots of air at a relatively large temperature difference in which case draft might be an issue with regular grilles.
Unless you have other resasons for choosing a textile duct, I would consider choosing supply grilles.