2 1/2" Standpipes valves for theatre stages IBC [F]905.3.4

[SprinklerDesigner2]

[F] 905.3.4 Stages. Stages greater than 1,000 squre feet in area shall be equipped with a Class III wet standpipe system with 1 1/2" and 2 1/2 inch hose connections on each side of the stage."

The building is fully sprinkled but the project engineer specified 2 1/2 inch hose connections wanted to be safe.

My question has to do with calculating the water supply.

The entire complex has but two 2 1/2 inch hose connections both at the stage. The theare itself does not have standpipes.

I am thinking the total demand would be 500 gpm and not 750 gpm.

Where do I start calculations or, more to the point, where is my "end head"? I don't calculate through the 2 1/2 inch pipe, do I? If I don't calculate the 250 gpm through the 2 1/2 inch pipe dropping down to the hose valves then do I start at the 4 inch x 2 1/2 inch overhead tee?

For for both comes from a dedicated 4" overhead line supplied by a fire pump.

Thanks.

 

[TravisMack]

I calculate to where the water comes out. I figure the pressure loss through the 2½" valve (2-6 psi depending on manufacturer), the 2½" nipple, 2½" pipe, etc. This is what I do for all standpipe systems. Just like calculating sprinklers on a pipe. I go to where the water comes out

I always try to err on the side of caution.

Travis Mack
MFP Design, LLC

 

[SprinklerDesigner2]

NFPA 14 is going through a revision cycle right now and I just received a heads up through NFSA's Tech Notes edited by Ken Isman.

Here's a snapshot of what got my attention.

http://img178.imageshack.us/img178/5494/standpipenote1hq7.jpg

It's always been unclear to me so what I've always done is take the 500 gpm through the most remote 2 1/2" pipe and now it dawns on me that was never the intent.

So yeah, looks like everything I've done is overdone/cautious as well.

So here's the question. It's a single floor with two outlets... looks to me like all I need is 500 gpm total because there isn't a lower outlet to take water from.

Heads up. They're going to take the requirement of a second hose outlet at the top of the most remote riser out of the standard.

They clarified the requirement to take water to the FDC on a manual standpipe. And here I always included a length of hose which, I guess, works if you like overdesigned systems.

 

[Cidona]

Was there meant to be an image on that snapshot?
IMO, NFPA 14 2007 section 7.3.2.2 requires an additional hose connection at the most remote part of the standpipe to facilitate testing. Therefore in a 'usual'(vertial) standpipe, when calcing your 500 gpm the intention would be for 250gpm to be flowing out of both of those connections giving you the required 500gpm at the remote part of the system. I think this is just to prevent hose having to be run up 2 flights of stairs to get to the roof to discharge. Your situation does not have the same restriction and i think the AHJ would not require it in your case.
I think the information you uploaded is just to clarify that you are not meant to flow 500gpm through the top 2½' valve. The friction loss of 500gpm through a 2½" valve would be more that what that valve is intended to deal with.
It seems 7.10.1.1.1 (2007 and referenced in your upload) states that the minimum flow shall be 500gpm and it seems that your calc falls into this catogary.
I think you would have to account for the friction loss through the 2½" and therefore you would need to flow throough the valve, drop, etc as Travis mentioned. See 8.3.1.2. Not sure what is making you think otherwise. Please let me know in case I'm missing something.
Given the stage arrangement, it might not be that much more difficult to test your 500gpm by attaching hoses to each of the 2½ outlets (flowing 250gpm through each to get your 500gpm) and not have the extra outlet mentioned 7.3.2.2. Of course you would want to get approval from the AHJ on this prior to installation, but i think they would see it from a practical point of view.
I think I'd be flowing 250gpm @ the most remote hose valve, back through the 2½' drop to your 4" (if that's what the calc required), back through your feed main to the connection point where you drop to the other 2½" valve, adding the extra 250gpm and calcing the 500gpm from there back to your supply.
Feel free to set me straight

 

[SprinklerDesigner2]

Cidona,

Among changes in the works are elimination of that second 2 1/2 inch valve referenced by section 7.3.2.2.

http://img11.imageshack.us/img11/3927/standpipenote2zc1.jpg

Good deal because I believe I was the only contractor down here providing the second valve for testing.

Also gone, or will be gone, is the standpipe schedule system.

"I think you would have to account for the friction loss through the 2½" and therefore you would need to flow throough the valve, drop, etc as Travis mentioned. See 8.3.1.2. Not sure what is making you think otherwise. Please let me know in case I'm missing something."

I agree the 250 needs to flow through the pipe, valve, drop etc but but I guess it only needs to be 250 gpm and not 500.

I've had a seniors moment when it comes to "standpipes" like this for years. It really isn't a standpipe except I suppose you could call it a two valve standpipe system on a horizontal plane.

I am embarrassed. Over the years I've installed maybe half dozen of these "stage standpipe systems" and I always calculated them 500 gpm at the most remote outlet with 250 gpm at the second outlet for a total of 750 gpm. Most of the time instead of having the drop 2 1/2 inch pipe I would put it in as 3 inch just to keep the friction loss to a somewhat manageable level.

I had this "500 gpm at the top of the most remote standpipe" going on in my head so I made it work. I was never really sure and I figured this would keep everyone happy.

Nothing wrong with this, certainly didn't hurt anything it's just a few over-designed systems as I understand it now.

All I need to feed both outlets is a total of 500 gpm and not 750 gpm. Right?

Thanks

 

[Cidona]

I think so. Section 7.10.1.1.1 states that the minimum flow rate for the hydraulically demanding standpipe shall be 500gpm. Then 7.10.1.1.2 states on a horizontal standpipe with more than 3 hose connections the minimum flow would be 750gpm. Since you don't have the 3 connections, I think you fall into the 7.10.1.1.1.
Not sure how I feel about the elimination of the 2nd valve at the top. Was nice when you had a roof manifold to have both valves and not deal with any hose inside the building. Like it says, it can be provided so I guess that'll just be a contractors call.
Thanks for the info on the upcoming changes. Not sure why I didn't get the Tech Notes on this regards. Better find out as those always have good stuff in there