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WEEKLY TAKEAWAYS AS A FIRE PROTECTION ENGINEER

Compare Flow of K-Factors with New Calculator

8/8/2018

 
When conducting or reviewing hydraulic calculations, I very often face scenarios where the initial (very first) hydraulic demand exceeds the potential for the water supply.

At that point I lose all hope and add a fire pump to the job.

Just kidding, of course - there's at least a half dozen hydraulic elements I analyze and refine to better match the capabilities of the water supply to the design of the sprinkler system.

Refining Hydraulic Calculations with K-Factors
One of the more fine-tooth aspects I look at is the k-factor used on the sprinklers.

The k-factor for a fire sprinkler is the discharge coefficient, or in normal human terms just relates to the amount of water that is permitted through the sprinkler.

The k-factor is dependent upon the orifice diameter of the sprinkler - a low k-factor (such as K2.8) restricts the flow of water, while a larger k-factor (such as K22.4, K25.2, or K28.0) permit much more water to flow through. K-factors were originally created to be multiples of the discharge of a K5.6 sprinkler. A K2.8 sprinkler, for example, is 50% discharge of a K5.6 sprinkler, while a K11.2 sprinkler is 200% of the discharge of a K5.6. NFPA 13-2016 Table 6.2.3.1 shows this well.

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Use In Design
We find K5.6 sprinklers in light hazard all the time. Residential sprinklers often have k-factors less than 5.6. ESFR and CMSA require minimum K11.2 (NFPA 13-2016 6.2.3.5). ESFR are tied directly to the hazard it protects.

Back to refining the hydraulics in a system - increasing the k-factor of a sprinkler allows more water to flow through a sprinkler with less pressure loss. This becomes very important when trying to reduce pressure loss in a system.
​
Light Hazard Example
A light hazard system (0.10 gpm/sqft) with widely spaced sprinklers (at 225 sqft each) would require a minimum flow through each sprinkler of 22.5 gpm (0.10 gpm/sqft x 225 sqft = 22.5 gpm).

In order to flow 22.5 gpm, a sprinkler with a k-factor of 5.6 now requires 16.1 psi to do so (Q=k√p, or rearranged, p=(Q/k)^2). This is 9.1 psi higher than 7 psi, or the minimum that NFPA 13 requires.

In order to flow 22.5 gpm, a sprinkler with k-factor of 8.0 only requires 7.9 psi to do so, or less than 1 psi more than the minimum NFPA 13 requires.

In this scenario, flowing the same amount of water (22.5 gpm) results in a 8.2 psi difference in the pressure required at the most remote sprinkler. Can 8.2 psi be important? Absolutely! 

Other Scenarios
Similarly, consider Ordinary Hazard Group 1 (0.15 gpm/sqft) and Ordinary Hazard Group 2 (0.20 gpm/sqft) systems.

For Ordinary Hazard Group 1 and sprinklers spaced at 130 sqft, a K8.0 sprinkler requires 5.1 psi less than a K5.6 sprinkler (7.0 psi vs 12.1 psi). 

This same methodology applies to extended coverage sprinkler requirements, specific densities for traditional storage design, and more.

The K-Factor Selector
Want to quickly compare fire sprinkler k-factors across different design densities and sprinkler spacing? Easy. Here's the calculator I've created that quickly compares pressure requirements and flow rates across different sprinkler k-factors.
​

Toolkit Update
Want all these tools in a downloadable, printable & PDF-saving capability? Great! The MeyerFire Toolkit will include this tool as well. You can download and try it out now through September for free.

Sprinkler Database
Other than the Toolkit, users of the comprehensive Fire Sprinkler Database can sort & search among k-factors as one of the parameters when comparing sprinklers.

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Gerard Crimmins
4/5/2019 10:08:51 pm

I was reviewing a sprinkler plan using flexible house from an arm over. The head had a k factor of 5.6 and the flexible hose had a k factor of 4.86 with the pressure and flow at the head. This seems like a mistake. Wouldn't you want a flexible hose with a k factor of 5.6 or larger?

MODERATOR
7/24/2019 07:01:54 am

Gerard - this was just posted as a daily question here: https://www.meyerfire.com/daily/flexible-drop-with-smaller-k-factor

Do you recall what model flexible hose was used and where you saw a k-factor of 4.86?

Silvano Tongco
3/27/2020 02:20:47 am

just for studying

Nestor Antonio Gomez Rivera
4/26/2020 10:52:29 pm

So, it will be ok to install K=5.6 sprinklers 4 meters away from each other in a 2.50 mts tall ceiling?

Joe Meyer
4/27/2020 07:53:48 am

The k-factor is relatively unrelated to your question. Sprinkler spacing is more complex than just the distance between sprinklers and the ceiling height. It depends on the type of sprinkler, listing limitations for the sprinkler, and the hazard category of the space it's protecting (among other things). Best place to go is NFPA 13 if you're protecting your building in accordance with that standard.

Giri
7/3/2020 05:30:48 am

Hi,
i want to design for standby diesel engine generator plant. inside 13 gensets are there. My company side said, design normal Automatic sprinkler system only. Dont go Gas suppression, deluge valve system and preaction systems (Due to High Cost).

Now please tell me which model upright sprinkler i can choose? it is 12 meter height.

javed Iqbal link
7/21/2020 03:00:07 pm

Very Nicely designed calculator for Sprinkler Design Calculations


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The views, opinions, and information found on this site represent solely the author shown and do not represent the opinions of any other party, nor does the presented material assume responsibility for its use. Fire protection and life safety systems constitute a critical component for public health and safety and you should consult with a licensed professional for proper design and code adherence. Some (not all) outbound links on this website, such as Amazon links, are affiliate-based where we receive a commission for orders placed elsewhere.
  • Blog
  • Daily
  • Exam Prep
    • CFPS Tools
    • NICET Tools
    • PE Forum & Errata
    • PE Problems
    • PE Store
    • PE Tools
    • PE Prep Series
  • TOOLS
    • TOOLKIT (FREE TRIAL)
    • *TOOLKIT (PURCHASE)
    • SUBMIT AN IDEA
    • BACKFLOW DATABASE*
    • CLEAN AGENT ESTIMATOR
    • CLOUD CEILING CALCULATOR
    • DOMESTIC DEMAND
    • FIRE PUMP ANALYZER
    • FIRE PUMP DATABASE*
    • FIRE FLOW CALCULATOR*
    • FRICTION LOSS CALCULATOR
    • HANGER SPACER
    • IBC TRANSLATOR*
    • K-FACTOR SELECTOR
    • NFPA 13 EDITION TRANSLATOR ('19 ONLY)
    • NFPA 13 EDITION TRANSLATOR ('99-'19)*
    • LIQUIDS ANALYZER*
    • OBSTRUCTION CALCULATOR
    • OBSTRUCTIONS AGAINST WALL*
    • PLUMBING FIXTURE COUNTS
    • REMOTE AREA ANALYZER
    • QUICK RESPONSE AREA REDUCTION
    • SPRINKLER DATABASE*
    • SPRINKLER FLOW*
    • TEST & DRAIN CALCULATOR
    • THRUST BLOCK CALCULATOR
    • TRAPEZE CALCULATOR
    • UNIT CONVERTER
    • VOLUME & COMPRESSOR CALCULATOR
    • WATER SUPPLY (US)
    • WATER SUPPLY (METRIC)
  • TOOLKIT
  • LOGIN
  • STORE
  • About