MeyerFire
  • Blog
  • Forum
  • THE TOOLKIT
    • SUBMIT AN IDEA
    • BACKFLOW DATABASE*
    • CLEAN AGENT ESTIMATOR*
    • CLOUD CEILING CALCULATOR
    • DOMESTIC DEMAND*
    • FIRE FLOW CALCULATOR*
    • FIRE PUMP ANALYZER*
    • FIRE PUMP DATABASE*
    • FRICTION LOSS CALCULATOR
    • HANGER SPACER*
    • IBC TRANSLATOR*
    • K-FACTOR SELECTOR*
    • NFPA 13 EDITION TRANSLATOR ('19 ONLY)
    • NFPA 13 EDITION TRANSLATOR ('99-'22)*
    • LIQUIDS ANALYZER*
    • OBSTRUCTION CALCULATOR
    • OBSTRUCTIONS AGAINST WALL*
    • PLUMBING FIXTURE COUNTS
    • QUICK RESPONSE AREA REDUCTION
    • REMOTE AREA ANALYZER*
    • SPRINKLER DATABASE*
    • SPRINKLER FLOW*
    • SYSTEM ESTIMATOR*
    • TEST & DRAIN CALCULATOR
    • THRUST BLOCK CALCULATOR
    • TRAPEZE CALCULATOR
    • UNIT CONVERTER
    • VOLUME & COMPRESSOR CALCULATOR
    • WATER STORAGE*
    • WATER SUPPLY (US)
    • WATER SUPPLY (METRIC)
  • UNIVERSITY
    • ABOUT
    • CATALOG
    • CONTENT LIBRARY
  • PE Exam
    • PE Forum & Errata
    • PE Store
    • PE Tools
    • PE Prep Series
    • PE 100-Day Marathon
  • LOGIN
  • PRICING
    • SOFTWARE & TRAINING
    • STORE
  • THE CAUSE
    • ABOUT US
    • BECOME AN INSTRUCTOR
    • HELP/SUPPORT
Picture

K-Factor Versus Density/Area for Sprinklers

9/1/2021

0 Comments

 
REFINE THE HYDRAULIC CALC WITH THE IDEAL K-FACTOR
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.
Picture
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.
​
A 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.

A K-FACTOR SELECTOR
Last week we talked about the two drivers that set the minimum pressure.

Does our k-factor and minimum pressure drive what our flow and pressure are at the sprinkler?

Or, does the density and coverage area drive our flow and pressure at the sprinkler?

We've created a tool that helps answer that in the
Toolkit, which is the K-Factor selector. It's one of the more popular tools in the kit, and it quickly shows what the optimal K-Factor is to minimize flow, and what the optimal K-Factor is to minimize pressure:
Picture
MINIMIZING FLOW OR MINIMIZING PRESSURE?
Both flow and pressure can each be important in different applications. 

Most of the time, I want to minimize the starting pressure at the remote area. Reducing the starting pressure means I have more room to work with and can allow for more pressure loss in the pipe network. In essence, I can allow smaller pipe sizes and have a more efficient system if my starting pressures are as low as possible.

However, I have had projects where flow was the primary concern. One was a wedding venue in a remote area without a water supply. We had a fire pump and a tank, and the owner's biggest concern was the tank size. There were limitations on how much space the tanks could take and the location in which they were located. Those tanks were our limiting constraint.

Our fire pump in the building (a little downhill from the tank) could add just about as much pressure as we needed it to provide. However, the tank size couldn't. Our biggest concern in the hydraulic calculation was making sure we limited the flow overall to as low as possible. We dialed-in the k-factor to match the hazard and the density as best as possible to limit the overall flow, and make up for the pressure loss when we sized the fire pump. In the end, we were able to use the anticipated water storage tanks the owner provided only because we limited the amount of water we needed on the system.

This was a rare case. Much of the time, minimizing flow and pressure at the remote area go hand-in-hand. If we reduce the starting pressure, then the next sprinkler down the line has a lower pressure and spits out less water than it otherwise would.

That said - using a k-factor optimized for flow is often a different selection than a k-factor optimized for pressure. Close, but not exactly the same. You can see in the above image as the coverage area and density changes, so too does the optimal k-factor.

The K-Factor can be an overlooked design decision for many buildings. When water supplies are difficult or situations are tight - understanding and honing in the best K-Factor can make a difference for a project.
USE THE K-FACTOR SELECTOR

< PREVIOUS
NEXT >
TL501 SERIES:
  1. What is the Sprinkler Database?
  2. How to Use the Obstruction Calculator for Beams?
  3. How to Use the Obstruction Calculator for Soffits?
  4. How to Use the NFPA 13 Translator?
  5. What is Driving Design; the K-Factor or Density?
  6. How to Estimate Clean Agent Quantities?
  7. How to Calculate a Domestic Demand?
  8. How to Select an Optimal K-Factor?
  9. How to Quickly Calculate Friction Loss?
  10. How to Analyze Fire Pump and Water Supplies from a "Big Picture" perspective?
  11. How to Determine Fire Flow with the IFC Method?
  12. How to Quickly Estimate Hydraulics for a Sprinkler System?
  13. How to Estimate a Water Storage Tank Size?
  14. How to Calculate Hanger Spacing by Weight?
  15. How to Calculate the Size of a Trapeze Member?
  16. How to Summarize Notes for Fire Alarm and Suppression?
  17. How to Calculate Thrust Block Size?
  18. How to Quickly Classify Combustible & Flammable Liquids?
  19. Calculate the Volume & Air Compressor Size for a Dry System?
0 Comments



Leave a Reply.

    Sentry Page Protection
    Please Wait...

    FULL CATALOG

    SEARCH

    FILTER BY:

    All
    By: Aaron Johnson
    By: Al Yakel
    By: Ben Brooks
    By: Chris Campbell
    By: Chris Logan
    By: David Stacy
    By: Edward Henderson
    By: Franck Orset
    By: Joe Meyer
    By: Kelsey Longmoore
    By: Steve Frederick
    By: Steven Barrett
    By: Tyler Mobley
    Category: Business
    Category: Documents
    Category: Fire Alarm
    Category: Fundamentals
    Category: Life Safety
    Category: Smoke Control
    Category: Suppression
    Category: Tools
    Course
    Crossword
    Exercise
    Level: Advanced
    Level: Intermediate
    Level: Introductory
    On-Demand Course
    Simulation
    Workshop

    ARCHIVES:

    March 2023
    February 2023
    January 2023
    December 2022
    November 2022
    October 2022
    September 2022
    August 2022
    July 2022
    June 2022
    May 2022
    April 2022
    March 2022
    February 2022
    January 2022
    December 2021
    November 2021
    October 2021
    September 2021
    August 2021
    July 2021
    June 2021
    May 2021

    INSTRUCTORS:

    Aaron Johnson, CFEI
    Al Yakel, SET
    ​Chris Campbell, PE
    ​Chris Logan, CFPS, RSE
    ​
    David Stacy, PE
    Ed Henderson, PE
    ​Franck Orset
    Joe Meyer, PE
    Steve Frederick

    RSS Feed

Picture
​Home
Our Cause
The Blog
The Forum
PE Exam Prep
The Toolkit

MeyerFire University
​Pricing
Login
​Support
Contact Us
Picture

MeyerFire.com is a startup community built to help fire protection professionals shine.
Our goal is to improve fire protection practices worldwide. We promote the industry by creating helpful tools and resources, and by bringing together industry professionals to share their expertise.

​MeyerFire, LLC is an International Code Council Preferred Education Provider.

All text, images, and media ​Copyright © 2023 MeyerFire, LLC

We respect your privacy and personal data. See our Privacy Policy and Terms of Service. 
The views, opinions, and information found on this site represent solely the author 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.

Discussions are solely for the purpose of peer review and the exchange of ideas. All comments are reviewed. Comments which do not contribute, are not relevant, are spam, or are disrespectful in nature may be removed. Information presented and opinions expressed should not be relied upon as a replacement for consulting services. Some (not all) outbound links on this website, such as Amazon links, are affiliate-based where we receive a small commission for orders placed elsewhere.

  • Blog
  • Forum
  • THE TOOLKIT
    • SUBMIT AN IDEA
    • BACKFLOW DATABASE*
    • CLEAN AGENT ESTIMATOR*
    • CLOUD CEILING CALCULATOR
    • DOMESTIC DEMAND*
    • FIRE FLOW CALCULATOR*
    • FIRE PUMP ANALYZER*
    • FIRE PUMP DATABASE*
    • FRICTION LOSS CALCULATOR
    • HANGER SPACER*
    • IBC TRANSLATOR*
    • K-FACTOR SELECTOR*
    • NFPA 13 EDITION TRANSLATOR ('19 ONLY)
    • NFPA 13 EDITION TRANSLATOR ('99-'22)*
    • LIQUIDS ANALYZER*
    • OBSTRUCTION CALCULATOR
    • OBSTRUCTIONS AGAINST WALL*
    • PLUMBING FIXTURE COUNTS
    • QUICK RESPONSE AREA REDUCTION
    • REMOTE AREA ANALYZER*
    • SPRINKLER DATABASE*
    • SPRINKLER FLOW*
    • SYSTEM ESTIMATOR*
    • TEST & DRAIN CALCULATOR
    • THRUST BLOCK CALCULATOR
    • TRAPEZE CALCULATOR
    • UNIT CONVERTER
    • VOLUME & COMPRESSOR CALCULATOR
    • WATER STORAGE*
    • WATER SUPPLY (US)
    • WATER SUPPLY (METRIC)
  • UNIVERSITY
    • ABOUT
    • CATALOG
    • CONTENT LIBRARY
  • PE Exam
    • PE Forum & Errata
    • PE Store
    • PE Tools
    • PE Prep Series
    • PE 100-Day Marathon
  • LOGIN
  • PRICING
    • SOFTWARE & TRAINING
    • STORE
  • THE CAUSE
    • ABOUT US
    • BECOME AN INSTRUCTOR
    • HELP/SUPPORT