Stair Pressurisation Fans - High Rise 1

[MechEng001]

Has anyone designed a stair press system for a high rise building (about 30 floors). Have you had trouble the maintaining required pressure throughout the entire stair?

I have designed stair press systems for smaller buildings but have been told there can be issues with achieving the required airflow and pressure in high rise buildings. I would have thought that if you calculate the static pressure required and select fan(s) to suit there shouldn't be an issue. Any thoughts on this?

Have you used one, two or three fans to accomplish the required stair pressure? Our client specifically does not want mid-level plant. Any previous experiences would be helpful.

Thanks!

 

[317069]

You have designed one for smaller building, then you should be able to design it for a larger building, you have been told??????

 

[tys90]

Do you have a copy of the Handbook of Smoke Control Engineering? There is a chapter that extensively covers stairwell pressurization. For that building height, it recommends a thorough analysis using CONTAM. You may end up wanting multiple injection points, if they don't want a mid-level plant, you could do a top and bottom. There are a lot of factors at play here and it would be hard to just answer the question of 1, 2 or 3 fans.

 

[MechEng001]

Thanks tys90, I will have a look at the ASHRAE handbook.

317069 I was hoping for lessons learnt on previous experiences - I am sure people have found some things work better than others and you can always learn from this and improve on design.

 

[MarineHVAC]

NFPA90 A will cover for the calculation. But not very sure to achieve the static at pratical

 

[SAK9]

Inject 50% of the air flow at ground floor level and the remaining at level 15 or wherever your intermediate mechanical floor is.Avoid putting them on roof as they are meant to operate when the building is on fire!

 

[ChasBean1]

I like to advocate feeding pressurized stairs from the ground level. Buoyant smoke tends to rise to the top of a building, not fall. Roof level intakes for these systems can therefore tend to re-inject smoke.

For a high rise pressurized stair, you have very little pressure loss floor-to-floor because there is a low velocity through the stairwell relative to the open area between each floor. Injection locations are not very relative.

For a 30 story building you are looking on the order of 40,000 cfm to pressurize the stair. It would not hurt to inject this air at levels 0, 10, and 20 (fed from 0), out of principle.

Of much more significance is the temperature of the air. It should be heated or cooled to match the average building temperature; about 70-72°F. An air column in a 30 story building at 70-72°F compared with an equal column of stairwell air at 20°F (by pressurizing in the winter without heat) would have a difference of about 0.4” between the ground floor and the top of the structure. Tolerance is 0.10-0.35 so you’d exceed this level at the ground while being below tolerance on the 30th floor.

So if the system is just right at the 15th floor and you don’t have any conditioning from the pressurizing unit, make sure you demonstrate performance to the fire department when it is about 70°F outdoors…