Home Fire Sprinklers — Why I Did It

When I was fiddling around in my “research” phase of what it would take to make my home compliant with contemporary standards, I stumbled across the requirement (in California at least) to have new construction homes be equipped with a fire sprinkler system. Being a veteran of the Navy, where there is a fetish about fire protection and safety — think about it, you’re surrounded volatile fuels and explosives in the middle of nowhere — it, needless to say, piqued my interest. I found out that IF you are involved in a fire (unlikely because I have been careful about minimizing the root causes of fire), then the statistics show that protection with a residential sprinkler system increases your survival rate by 80% and decreases your property damage by 70%. How could I not continue? Did I mention a fetish?

It turns out that installation of a residential fire sprinkler system is within the DIY realm. If you’re trying to go with a “modern” plumbing system, which has all sorts of headers and networks and PEX pipes, then it’s probably not DIY. If you don’t know what PEX or a networked plumbing system means, then it’s DEFINITELY NOT DIY. However, if it’s just a retrofit or a new construction, you can install a simple “tree-branch” design.

A “tree-branch” design is simply a source of water that has runs and branches to distribute the water to the individual sprinklers. The basic design mimics the design of a standard plumbing system. The source of the water needs to come from the main water supply to the house, and then branches off before the supply to the rest of the domestic water system. The sprinklers can be thought of as a “complimentary” plumbing system. So, if you can install plumbing using CPVC (Chlorinated Poly Vinyl Chloride) pipe, you’re GTG with a DIY installation. Except…..

There is a pesky requirement called a “hydraulic calculation” which involves a litany of limitations and specifications which, if followed, will ensure that your sprinkler system will spray the correct amount water over the area that it is designed to cover. There are a lot of variables, and the interaction of these variables (e.g., pressure, flowrate, pipe diameter, K-factor) can be intimidating if not fully understood.

FORTUNATELY (for me), this is right up my alley. My studies in chemical engineering involved fluid flow, so I had a good background in what the calculations were all about. I dug back into the recesses of my tiny brain, and , with the help of Wikipedia, reconstructed the seldom used  neural synapses to come up with a spreadsheet which helped me figure out the required water pressure at the street main, and the required water pressure of my design. So I called the water authority to get the pressure at my residence (105 psi) and I went merrily to work. I submitted my design, and got told that it was F/U.

First, the assumed pressure was wrong. I had to submit a request for the available water pressure at worst case conditions. It turns out that the fire department and water authority have this dance figured out. I was just not invited to it. Bottom line is that I had to request a “residual” pressure base on worst case conditions. Once I received that, I was back to ground zero. Second, I was not properly accounting for the pressure at the “second” sprinkler. Code requires that whenever you have two or more sprinklers in the same room (compartment), then you must use the most limiting flowrate from two of those sprinklers. I had to lick my wounds and remember the lessons that I learned (and apparently forgot) in my sophomore fluids flow class, and revise my handy-dandy spreadsheet to make it reflect reality.

With the new available pressure, and the right methodology with my spreadsheet, I had to re-do the entire design. In the end though, I actually was able to make the design easier and less expensive to install. The key was to make the k-factors similar. If you don’t understand what I’m talking about, then maybe you shouldn’t be designing a residential fire sprinkler system.

The upshot is that my sprinkler design was approved today. I’m actually quite proud of it because the majority of designers plug their designs into a computer program which tells them whether they are right or not. I did the calculations by hand, so I know that the design will work because I understand the underlying principles. OK, I used a spreadsheet, but I had to put the Hazen-Williams formulas in. I’m sure that if you contract a designer to provide a sprinkler plan for you, that it will be correct and will work just fine. It’s just that the designer won’t know exactly why. Let’s just keep that as our personal secret.

Here is my advice (for what it’s worth):

  • Get a residential fire sprinkler system. The cost is more than worth the peace of mind and the protection it offers your family and your home.
  • If you’re DIY, but perhaps not so interested in the nuances of hydraulic calculations, then try to hire a designer who will give you plans. Having said that, you’d better understand some of the nuances of fire sprinkler installation. There are very specific requirements for the mounting of the supply lines and sprinklers so that they don’t jump around when they get activated.
  • If you’re interested in the design, here are some references:

Residential Fire Sprinklers

Fire_Sprinkler-Installation_Instructions-English

ResidentialSprinklerInstallationGuide

Here are my plans:1370 BFD Fire Supression R 2.5

And the spreadsheet for the hydraulic calcs: 1370 BFD Hydraulic Calculation Worksheet CPVC

OK, I know I’m a geek at heart. I really do love to design and to manifest my ideas, in terms of numbers and letters (in the correct sequence) so that they can be created in the physical world. This is what I’m all about, and this is what I hope you can see as I take my next steps on the DIY highway.

 

P.S.  Did you notice that “Why I Did It” contains DIY backwards?

🙂

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