Do you know of any resources which will help me do flow calculations for a fire sprinkler system?
I’m building a house (my own) in California–F.D. requires me to have a sprinkler system. I am confident that I can actually do the work, and I have the basic concept of how to do the flow calcs, but need a resource listing what the losses are for each foot of pipe, elbow, transition, etc
Thanks for the help,
Syd
Replies
Syd: There are a number of ways to do it. I usually look on a chart of GPM versus pipe size and pick out the corresponding pressure drop (for 100 feet of pipe) and then multiple by the equivelant pipe length. The downside is that if your flow is between table entries (e.g. you have 12 gpm, but the table only gives 10 and 15 gpm) then you have to interpolate. But for quick estimates, you can just eyeball it.
Or you can whip out any lower-division university text on fluid flow and plug in density, viscosity, diameter and velocity to get the Reynold's number. Then look at the chart to get the friction factor and plug that into the pressure drop equation. I don't recommend that technique.
Or let a computer do the previous technique for you. Here's a free on-line pressure drop calculator:
http://www.processassociates.com/process/fluid/dp_1.htm
For water, use 62.4 lb/cubic foot and 1.0 cP (centipoise). For metal pipe, I'd use "fouled, typical". For plastic, I'd use "fouled, new". They nicely offer nominal pipe sizes which saves you looking up the actual inside diameter of schedule 40 steel pipe.
So you need to figure out how much flow goes to each sprinkler head and add those contributions in each leg of the distribution piping. Then add up the linear feet of, for instance, 1" pipe and account for the fittings. That takes a little more work.
A 90 degree ell is the equivalent of 30 pipe diameters (e.g. a 12" 90 is the same pressure drop as 30 feet of 12" pipe; a 1" 90 is the same as 2.5 feet of 1" pipe.
Here's a list of fittings and their equivalent length:
going out (or coming in) through the side of a tee: 65
90 ell or straight through a 1/2 reducing tee: 30
45 ell: 15
straight through a standard tee: 20
sudden contraction (reducing bushing, reducing tee) where d/D = 1/4: 15
sudden contraction where d/D = 3/4 or fully open gate valve: 7
fully open globe valve: 320 (don't use a globe valve!)
Group all your 1" fittings with your 1" pipe and add up the lengths. Group all your 3/4" fittings with the 3/4" pipe, etc.
Check what criteria they want you to use. What incoming pressure can you assume (worst case?) from the city? What do the sprinkler heads each need?
Professionally done systems have total mishmash of pipe sizes, running from 2.5" down to 3/4" (or 1/2"?) risers. And all the pipe sizes in between. I suggest you definitely skip 1.25" because it is a bastard size and is hard to find and often more expensive than 1.5". Play with your layout and try to minimize the number of fittings and size transitions. Reducing fittings are more expensive than standard ones. Check if any fittings are disallowed (for instance reducing bushing aren't allowed in some fuel gas piping - one must use bell reducers).
Good Luck. This may be the highest $/hour sweat equity possible for an owner/builder. Talk to the inspector early and often!
Oh, and avoid those Chinese fittings at home depot. With all the tees you'll have, it would be a real pain to replace a fitting with a pinhole leak or one that just won't tighten up. A plumbing supply house has to provide their customer with either US fittings or at least the better Chinese ones. Also check if telfon tape is allowed by your inspector. I like tape AND dope to minimize leaks, but sometimes tape isn't allowed because it might get washed downstream and clog an orifice.
And if you don't have aluminium-handled Ridgid-brand pipe wrenchs (14, 18, 24"), treat yourself to them now. No reason to be swinging around a bunch of cast iron while you're on top of a ladder and absolutely no reason to use pipe wrenches without decent jaws on them.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
David--
I don't care that everyone complains about the new site. As far as I can tell, Breaktime still has the best poster knowledge base around. Thank you so much for the information--it was way above and beyond what I had expected. I think I can proceed with the project on my own. As you say, I think that I can save in the neighborhood of $4-5K by doing it myself. Thanks for sending me on my way.
Anyone else have input on designing or installing a system like this?
Thanks a ton,Syd
You might take a look at the following:
http://www.usfa.fema.gov/pdf/usfapubs/fa-155.pdf
As you are undoubtedly aware, building a fire sprinkler system is more than just calculating flow rates and installing the pipes. Inspectors can be sticklers about placement of the heads and I believe that the bracing is supposed to allow you to use them as a trapeze (they require that the braces support the weight of the filled pipe plus a 250lb person swinging on them). California eathquake bracing is particularly stringent.
http://www.nfpa.org/NFPAJournal/Columns/HeadsUp/Heads_Up_Nov_Dec_2001/heads_up_nov_dec_2001.asp
A brief discussion of computer programs to do hydrualic calculations for fire sprinklers:
http://www.sprinklernet.org/sprinklerage/pastfeatures/2002/0202safeature.html
http://www.echoscaninc.com/products/m2-18.html
I found some of the information in the second half of this article to be interesting. It discusses home sprinkler systems which are inter-tied to the plumbing system.
http://www.fmam.org/rethinki.htm
Edited 5/1/2002 11:05:03 PM ET by CaseyR
Wow David. that is the quickest course on piping design I ever read. Good tho.
And Casey comes through with URLs yet again.
Janation: Thanks. If it was brief but understandable, it's because I spend my real life explaining engineering to geologists.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Look for the following Publications by NFPA
NFPA Automatic Sprinkler Systems Handbook, 1999 NFPA 13: Installation of Sprinkler Systems, 1999 NFPA 13R: Standard for Installation of Sprinkler Systems in Residential Occupancies up to and Including Four Stories in Height, 1999 Edition NFPA 13D: Standard for the Installation of Sprinkler Systems in One- And Two- Family Dwellings and Manufactured Homes, 1999 Edition The last two are probably most pertinent although there is some information in the Handbook that is not in the residential manuals.