The minimum design density is to be 0.15gpm/SF for the hydraulically most remote 1500 SF. If there are open areas greater than 5,000 SF, or if combustible construction is used, the minimum design density shall be 0.12 gpm/SF for the hydraulically most remote 3,000 SF. For dry systems, increase the area of application by 30%.
Hello Yassin, and welcome to the forum.Generally the NFPA 13 'K factor' for sprinklers is K=5.6. Generally sprinklers are 1/2' (DN15) connection size.The K factor is determined experimentally, but NFPA 13 currently mandates the use of a nominal K factor (e.g. 5.6) rather than the actual K factor. Makes things less confusing I think.It is used in the following formula:Q = K.
(P)^0.5Q=gpm through the sprinklerP=pressure across the sprinklerNote: If you are already familiar with K factors, the NFPA 13 'K factor' is not to be confused with K factors used as loss coefficients in Darcy Weisbach based hydraulic calculations (fL/D). This one is wholly unique to sprinkler design.You can use sprinklers with K factors smaller than 5.6 but only in certain restricted instances (see NFPA 13). You can use K factors larger than 5.6 also, for example K=8.0 sprinklers are often used when a water supply is poor.I act as both the owner's agent and the AHJ, and often have sprinklers contractors say 'please issue a change order for a pump' when I already accepted the engineering design with a documented flow test, and they must think I am an idiot or a pushover one to let them get a fat change order.
![Density Density](https://www.sfpe.org/resource/resmgr/FPE_Magazine_Archives/2012/2012_Q2_3_Fig4.jpg)
I simply tell them to increase their pipe size and/or use K=8.0 heads. Problem solved.As for larger K factors, use them as necessary for the hazard involved, and install them within the limitations of their listing. K factors larger than 8.0 are only for specialized use like extended coverage (EC), CMSA, storage, and similar uses.Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.
RE: How can I choose the K-factor for sprinkler (Mechanical) 31 May 11 02:31. You can't use less than 5.6k for Ordinary hazard. In light hazard, you can go down to 2.8k before you need to put a strainer on the line.In storage, you are typically going to start with a 8k sprinkler.
If the density is 0.34, then you need a 11.2k sprinkler as a minimum.I use a lot of 4.2k sprinklers in wet attics. A max spacing of 130 sq ft in most attics.
More realistic to be around 100 sq ft. A 5.6k sprinkler will discharge about 15 gpm at 7 psi. A 4.2 is about 11.1 gpm at 7 psi. I can often save a pipe size or 2 with 4.2k sprinklers in the attics.It all comes from experience with calculations.Travis MackMFP Design, LLC.