Standpipe Question

[devaneff]

Ok, I had someone ask me a question today and I have no idea how to answer him so I'm looking for some help. His question is,

What is the difference between the hydraulic method and the pipe schedule method of sizing for sprinklers and standpipes? The reference would be from NFPA 14 but I don't have the NFPA guidelines on hand.

Thanks,
Chris

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Chris DeVane
[email protected]
CS Major, Georgia Institute of Technology
Firefighter, Peachtree City Fire and Rescue
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God bless our fallen brothers and sisters
9-11-01 FDNY - Lest we forget
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"We will not tire, we will not falter, and
we will not fail."
-- President George W. Bush - 9/20/01
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[FFMcDonald]

The difference between pipe schedule- and hydralic method is this --

When using pipe schedule you are relying on already computed charts that will tell you how many sprinkler heads can be fed by a certain diameter pipe - for example--- 2 sprinklers require a 1 in. diameter pipe to deliver the required 7 psi to the head. According to the pipe schedule charts - you would need 1 1/4 in. pipe to deliver that same amount of water to 3 sprinkler heads -- and 1 1/2 in. pipe to deliver the required flow for 5 sprinklers. And so on....

The problem is that these are very general charts, and the larger a system, the larger the cost -- including the cost for all that pipe.... Hydraulic method means that you can use a smaller diameter pipe (less costly) if you can prove through calculating the hydralics, that it can in fact flow the required 7 psi at the head.

Most of your answers can be found in NFPA 13 Standard for the Installation of Sprinkler Systems.

If you have any more questions - drop me an e-mail....



[ 10-31-2001: Message edited by: FF McDonald ]

[Grit76]

The man asked about standpipes, not sprinklers. But the concept is the same. schedules sizes are given, hydraulic sizes are calculated to obtain a certain flow/pressure, given a flow/pressure at the supply point (FDC or city supply).

And to provide a friendly correction to mr mcdonald [this is a common misconception], the calculation sometimes results in larger instead of smaller sizes when the supply is poor. It is a custom design, not necessarily cheaper...........

[devaneff]

Thanks guys, this was very helpful and he said it answered his question exactly.

Stay safe

[FFMcDonald]

What is the difference between the hydraulic method and the pipe schedule method of sizing for sprinklers and standpipes?

Ughh -- correct me if I am wrong... but that does say SPRINKLERS and Standpipes....

I know that the concept is the same.....

[gah74]

It sure looks a lot like the word sprinkler in the original post. I may be wrong here, but I don't think there is such a thing as pipe-scheduling as far as standpipes are concerned...but I'm not 100% positive on that.

I'm also not sure what Grit is talking about in his "correction" of McDonald. Pipe schedules specify the pipe size that must be used to supply a given number of sprinklers, based on occupancy classification (light, ordinary, or extra hazard) according to NFPA 13. In theory, this provides for economy in sprinkler system design...and it actually is cheaper to design. The problem is...it is usually NOT cheaper to buy and install. These systems usually become more expensive than hydraulic calculated systems because they require larger pipe sizes...to make up for their generalized design.

It is possible to make use of hydraulics to calculate the pressure losses of water flowing through sprinkler pipe. These calculations ensure that the system will meet minimum design discharge requirements. The majority of sprinkler systems installed today make use of hydraulic design. In addition to resulting in better fire protection, hydraulic design USUALLY permits the use of smaller pipes...thus making them cheaper to install...

[Grit76]

First order of business: MY APOLOGIES..... I did misread Mr. Mcdonald..... no excuses I was outta line.... my tail's between my legs......

Usually is correct on the pipe sizing, When the water supply is good. When it's not, sizes far greater than schedule are common. Reduced friction loss is necessary to deliver the density when supply pressure is low, resulting in larger pipes, looped mains, dual feeds, grids, and so on.

Which is cheaper depends on alot of variables, which you all have basically covered.

Yes, NFPA 14 has a schedule design. If I remember right [not a geek with the codes at home], it is limited to low rises. Likewise, new pipe schedule sprinkler systems are severely limited in size.

[FFMcDonald]

Grit -- No problem. Just glad we could help a fellow brother out. That's all that matters these days.

FTM-PTB-EGH-RFB

Enough Said.... No reason for your tail to be between your legs. Takes a big man to admit he made a mistake. Stand tall.