Smoke control system for atrium

[cme]

I've just been handed a task of calculating and designing the smoke control system for an atrium.

The project is a 9 story (occupied) hospital in Atlantic City, NJ with a mech/elect penthouse and heliport directly above that.

The atrium in question is 3-stories in height with the opening larger in size as you go vertical. The opening is skewed also, shewed rectangular in shape actually.

The code enforced is IBC 2000 New Jersey Edition.

Just about 3 hours reading thru multiple times, this appears very complicated (i.e "bag of worms") for an introduction. Analysis has to take into account stack effect and wind effect and given formulae for certain criteria.

Even the design fire has engineering analysis factors to be considered such as fuel, fuel load, steady and unsteady fire. They give you a design fire rate of 5000 btu/sec but this does not include those factors. In fact, I do not see the factors in a formula so that's a question I have.

Any professionals here have experience in this area?

 

[lilliput1]

See NFPA & ASHRAE Smoke Exhaust Guide. The Code changes made it hard to follow. The new requirement to not exceed a very low velocity for makeup & the requirement to locate it low was so ridiculouse that the Architect gave up & just made the atrium (2) story high to avoid providing smoke exhaust.

 

[HVAC68]

I did design something similar (though not so big), sometime back. Will check and revert to you, if I can lay my hands on the old working sheets.

Another easier way to handle this would be talk to companies like "Colt" or any other company who specialise in smoke ventilators. They have inhosue softwares to do these calculations.

HVAC68

 

[cme]

I am using 2003 IBC since we don't know what code will be applicable by the time the project bids.

Anyway, P184 of IBC 909.9.2 has an equation with a factor q'' "Incident radiant heat flux for non-piloted ignition in btu/ftsec"

Anybody know that factor?

 

[lilliput1]

See NFPA 92B. The q'' value is not given because it is not realistic to design for a fixed fire size per 3.2.2.3. Instead other equations are used based on a t-squared profile of fire growth. See text of NFPA 92B for the other equations plus examples.

 

[lilliput1]

Also see NFPA 92A - Recommended Practice for Smoke Control Systems in addition to NFPA 92B - Guide for Smoke Management Systems in Malls, Atria, and Large Areas

 

[xitrum]

I am in California. We are using UBC. Refer to UBC-section 905 for different methods: Pressurization or exhaust. I did lots of Atria using exhaust method 'cause it's cheaper in construction cost and it's easier to achieve. Good luck.

 

[cme]

Thanks lilput and xitrum

Its back to 2000 IBC per the Architect

The atrium is triangular in shape with balconies. The only open space clear to the top is in the one corner because there is a stair going from the 1st to 2nd floor smack dab in the middle of the opening. The opening is a skewed rectangular shape and increases in size as you go vertically.

I calculated an axisymmetric plume in the vertical clear area vertically and the design plume does not contact the walls as you go vertically. Plume expands vertically. The cfm is around 170,000.

I also ran some balcony spill plume calculations for each floor and the worst case is on the order of 600,000 cfm based upon a fire occuring at the one of the exit openings (worst case horizontally from the vertical opening). Or should the balcony spill plume calculations be based upon a design fire located at a fixed piece of fuel such as a chair or operator's desk within the space?

 

[lilliput1]

How do you plan to exhaust this amount of air & provide makup per requirements?

 

[cme]

Aren't those figures bizarre?

That is with the design fire of 5000 btu/sec. That's 18,000 mbh! I'd have to see if the code official will let us use a rational analysis of a fire.