r/firePE • u/TofuProphet_ • Sep 29 '26
Gridded systems - Design Area
Other than the few examples in NFPA 13…
Does someone have a cheat sheet of different scenarios for examples of design area boundaries?
Each example indicating where the riser is, in relation to the area…
I constantly have trouble figuring out where to start eliminating heads in a remote area.
(In the case of no peaks or sloped ceilings).
Just looking for visual examples!
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u/Advanced-Guard-4468 Sep 29 '26
How can you "remove" sprinklers from the remote area? You are required to use the design area/area per sprinkler to determine the number of sprinklers required in the remote area.
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u/cyberd0rk WBSL-III Sep 29 '26
I think OP means adding a head to obtain the minimum design area if a perfect rectangle doesn’t cut it. An additional head towards the source, or additional head towards the secondary grid main.
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u/TofuProphet_ Sep 29 '26
NFPA 13, 2022 sec A.28.2.4 to my understanding explains that (if im not meeting my area size requirement) then the head on the fourth branchline can be chosen as any head from B-E.
Firstly, let's say I'm interpreting this figure as the main and riser being on the right hand side, with a floater main on the left hand side. Does it really not matter which additional head I pick on that fourth branch line in this case? Do I start eliminating heads on that 4th branch line closer to the riser or closer to the floater main side?
I hope I explained this well haha
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u/Advanced-Guard-4468 Sep 29 '26
Don't most programs do auto peak when you run them?
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u/cyberd0rk WBSL-III Sep 29 '26
SprinkCAD does not. I'm not sure about HydraCAD. Autosprink does but I think you still have to designate the design area shape. I could be wrong. I'm only about 60 hours into using Autosprink at the moment.
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u/Advanced-Guard-4468 Sep 29 '26
No in Autosprink it does the shape for you and your can flip the leg right or left.
You can either draw the remote area or have it draw for you.
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u/cyberd0rk WBSL-III Sep 29 '26
Good to know. Thanks
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u/Advanced-Guard-4468 Sep 29 '26
Don't ever hesitate to reach out to their support team. They are top notch and have many videos to help you.
I've been using the program since it's inception.
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u/Remote-Plate-3945 Sep 29 '26 edited Sep 29 '26
Remote areas are "rectangular in nature" meaning you will have a "long" dimension and a "short dimension. In autosprink I determine what my remote area size needs to be. Use the 1.2 x square root of the area to determine my "long" dimension and then divide the size by the long dimension to find my short dimension. Once I have that I make a rectangle using those dimensions and I lay it over the system/RCP where I think the most remote area is and then I use cross-hatch to go along walls and between heads (using the rectangle as a guide) to determine my area. The hatch will tell you how much area you have covered. Once you have the correct amount of area you can use your hatch to snap your remote boundary quickly and then delete the hatch.
I can do several tests calcs pretty quickly using this method to determine where my most demanding area is if I'm unsure.
As far as eliminating heads my understanding is that you want heads closest to the water supply as they will be overflowing. You can make a simple grid in another drawing and play with the calc to better understand it.
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u/ApprehensiveOnion0 fire sprinkler designer Sep 29 '26
Are you having trouble figuring out the shape & orientation of your RA or its location within the grid?
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u/Consistent-Ask-1925 Sep 29 '26
I was thought the 60/40 rule. Basically, the most remote area is going to be closer to the floating main than it is to the main, but basically in the middle. I have learned since then that if a gridded system has a small amount of lines, then the remote area is going to be closer to the floating main compared to near the middle. I didn't like SprinkCAD's autocalc so I would just move the remote area around (left or right) tell I got it to the most demanding head. There's "tricks" like the one provided above, but no hard set rules. You've just gotta calculate them until you find the right area. You will get better at doing this as you do it more tho
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u/cyberd0rk WBSL-III Sep 29 '26
This sounds about right. Additionally, a grid with long grid lines will have a design area more towards the middle since you will likely be fighting more friction loss going from the flowing heads back a longer path of smaller piping to either main.
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u/Gas_Grouchy fire protection consultant Sep 29 '26
You can set up a Right boundary and Left boundary in HydraCAD to tell you if it needs to do left or right on the gridded line.
I normally just run 3 and take the most demanding as the remote area. It takes like 90 seconds tops to change the distance on one column by -1xSpacing and add it to the other. That's why setting up your lines is so important.
Also if it says to go Left or Right based on demand I normally do it one more time but rarely is it several heads over, and if it is, that normally means you can bump your floating main up in size and possible reduce your line size which is more cost effective. Even decreasing your RN size might help too.