If you coordinate upfront bid documents and are planning to have a dry sprinkler system on your project, you probably get the same question from electrical engineers as I do - how large will your compressor be?
It can be a difficult question to answer, considering there's multiple manufacturers and a handful of different options in choosing the right compressor for your project.
NFPA 13 requires that a dry system have an air supply capable of restoring normal air pressure for the system within 30 minutes (NFPA 13 2002-2010 Section 220.127.116.11.2, 2013-2016 18.104.22.168.2).
Fortunately, we've got a Sprinkler System Volume Calculator that indicates compressor sizes associated with your system volume.
One fundamental aspect of fluid movement is thrust force, which is created when a flow path bends, tees, wyes, dead ends, or reduces. In order to counter the unbalanced forces that are created at these locations, the pipe and fittings must be mechanically restrained from separating, welded together, or otherwise fixed from movement.
Push-On Underground Joints
One popular method of preventing pipe separation for underground pipe is gasketed push-on joints for underground pipe that do not have special locking devices, but permit pipe to be installed in any direction and at any point along the path.
Role of Thrust Blocks
In order to prevent the internal pressure from forcing the pipe and fittings to separate, blocking (or "thrust blocks") provide stability and allow the surrounding soil to accept the thrust force from the pipe assembly.
Soil conditions vary in its ability to handle forces. Thrust blocks allow a narrow point force to be spread and distributed across larger areas of soil down to a pressure that the soil can bear.
A QUICK CALC
With only a few "knowns" (pipe diameter and schedule, and distances to nearest structure), you can now quickly calculate the section modulus that's required, visit options for the trapeze bar, and see these options schematically in a to-scale detail.
Have multiple pipes on a trapeze? Calculate the section modulus required for each, add the two moduli together, and simply override the Section Modulus Required value below to see your options.
GET CAD DETAILS
Want a CAD version of the detail? The downloadable version of the Toolkit allows you to save and print these calculations as PDFs, which can then be imported directly into AutoCAD and use the ALIGN function to scale it to your drawing.
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 22.214.171.124 shows this well.
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 126.96.36.199). 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!
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:
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.
One of the most common and basic issues many of us encounter in fire sprinkler design or during on-site review is whether a sprinkler is considered to be obstructed. While the premise of the obstruction tables within NFPA 13 is fairly straightforward, there are a handful of variations in the tables that are dependent upon the edition of 13 being used, the sprinkler type, and in some cases the orientation of the sprinkler.
We built a cheatsheet to show all the options for providing code-compliant sprinkler spacing near obstructions. We call is our Obstruction Cheatsheet. Click the button here to download a copy:
We also took this a step further, and developed what we call our Ceiling Obstruction Calculator. This reference tool below was built to quickly determine whether a ceiling-mounted element is considered an obstruction. It can be especially helpful during sprinkler layout or during site review where lugging the entire code volume might not be practical.
Common examples of where obstructions are considered are with sprinklers adjacent to surface-mounted lights, soffits (not against a wall), mechanical equipment in walk-in coolers and freezers, signage, banners, lowered ceilings, thresholds above large openings, raised ceiling pockets, or exit lighting.
To use this tool, you can use your downloadable version of the Toolkit, or you can see it online here: Ceiling Obstruction Calculator. If you don't know your activation code, or have trouble installing the downloadable version, go here: www.meyerfire.com/support.
Occasionally I've been asked to look into storage quantities of flammable or combustible liquids.
This typically comes up in research and development facilities and laboratories, where the quantity of different liquid classifications becomes important.
Liquid fires present a different challenge than pyrolysis of solids as the shape of the fire can change quickly and the speed of ignition can be significantly faster than fire growth of solids.
Cabinets and sprinkler protection can contribute to increasing allowable storage quantities, but in order to do so, an evaluation must first be made to the different classifications for the liquids.
Many code and standard requirements depend on the classification of a Flammable or Combustible Liquid, such as storage locations, limits in quantity, limits in storage height, grouping, arrangement, whether control areas are necessary, and auxiliary requirements such as secondary containment and sprinkler densities.
Where projects are subject to the International Fire Code, Chapter 34 (2003-2009 Editions) or Chapter 57 (2012-2018 Editions) begin to address these limitations and impacts. Where NFPA 30 (Flammable and Combustible Liquids Code) is applied, the entire standard sets precedents for these limitations and impact.
This basic tool below is what I use to begin to assess and compile the classes and quantities for flammable and combustible liquids. Entering in only the Flash Point, Boiling Point, and quantity will identify and sum the totals that I can then use to assess against code and standard requirements.
Have you navigated the 2019 Edition of NFPA 13 yet? Many jurisdictions have not yet adopted the 2019 Edition, but it includes a complete reorganization of the entire standard.
For those that are still struggling with the changes like myself, we created a quick tool to bounce back and forth between the 2016 and 2019 editions of NFPA 13... but we didn't stop there. The NFPA 13 Translator tool will take any code section out of NFPA 13 and return the original or altered code section for every other edition between the 1999 Edition through the 2019 Edition.
If you have a tabbed copy, a handbook, or work through different jurisdictions, the NFPA 13 Translator can be a huge time saver when flipping between editions.
To give it a try, open the MeyerFire Toolkit and click on "NFPA 13 Translator" on the left-hand side. Just enter any code section below, and it'll then kick back the matching section from the other edition.
Ever get a code comment from a different version of NFPA 13 than you have next to you?
Do you see a code reference from a detail in a different edition? A forum discussion post that references a different version than you have?
Are you looking to check the very latest published edition to see what changes might have occurred since the edition that is adopted for your project?
This can be a quick and helpful tool for jumping right to the right spot in that new edition.
Welcome to the on-demand series, Introduction to Sprinkler & Standpipe Systems!
In our last segment we introduced the obstruction cheatsheet and the calculator for ceiling obstructions, today we're diving in on obstructions that are up against a wall - such as a soffit or a cabinet.
This calculator helps us determine whether a sprinkler needs to be located beneath a soffit or obstruction along a wall, or whether its thin enough or the throw is available to reach underneath or ignore the obstruction:
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