How can I choose the K-factor for sprinkler
How can I choose the K-factor for sprinkler
(OP)
hello every body, I am new in the field of automatic sprinkler system and I wont to know if there are rules to follow in choosing the K factor depending on type of hazard
Thak's
Thak's





RE: How can I choose the K-factor for sprinkler
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)^0.5
Q=gpm through the sprinkler
P=pressure across the sprinkler
Note: 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. 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
If you decide to use extended coverage sprinklers to save some labour, the k factor will be different also.
RE: How can I choose the K-factor for sprinkler
RE: How can I choose the K-factor for sprinkler
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 Mack
MFP Design, LLC
www.mfpdesign.com