Sprinkler & Standpipe Hydraulic Calculation 1

[jpuy]

Hi,

Hope you can help me on this.

As per NFPA 13, the most distant is not necessarily the HYDRAULICALLY most remote.

How do we identify the most hydraulically remote if not the most distant?

Appreciate any feedbacks.

Regards,

Jeff

 

[TravisMack]

You may have to do multiple calculations to prove what is your most hydraulically demanding.

If you have an Ordinary hazard area in an otherwise light hazard building, and the OH area is not the most physically remote, you may have to calculate both to prove your pipe sizing.

With current calculation programs and drawing packages, calculations can be completed relatively quickly, so it is crazy not to run additional "proof" calculations if there is any concern as to what is the most demanding area.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[Oremus]

You can usually just grab your calculator and determine what's going to be the most demanding area and it only takes a minute or two. In Travis's scenario you could calculate the design area for the two areas in question and start multiplying the number of sprinklers by their densities and look for the GPM for the overall system while also paying particular attention to the gpm flowing through each branchline since that is where you're going to encounter the most friction loss. Of course this will give you a bare bones calculation not showing any delta pressures and the actual demand will be substantially larger but it's good for a quick snapshot.

Consider the following: I've seen NFPA 13 residential plans where designers calculate the manufacturer's 1,000 sq. ft. for concealed space sprinklers yet they did not do a four head calc which was actually more demanding since they were utilizing 400 sq. ft. spacing. One area consisted of the 12 upright sprinklers, the other four pendants. But a simple hand calc with a calculator would have shown that the four sprinklers were more demanding when you consider four sprinklers flowing 40 gpm each (.10 X 400 sq. ft) equals 160 gpm on ONE line. That's a lot of friction loss for one line in a residential design. By comparison the concealed space uprights were flowing roughly 130 gpm but it was distributed over 3 lines, each line getting roughly 43.2 gpm (.10 X 144 sq. ft. = 14.4 gpm x 3 sprinklers = 43.2).

The calculator is your friend.

 

[jpuy]

thanks for the help.

Appreciate it...

one more thing... looks like there is a problem on this:
1. ordinary hazard
2. area of sprinkler - 139m2
3. density - 6.1 LPM (0.15gpm/ft2)
4.no. of sprinkler calculated - 13nos
5. max coverage per sprinkler - 12.1m2
6. total discharge through sprinkler - 1,034.1 LPM

Question:
Item 4 : should be 12nos and not 13nos (=139/12.1)
Item 6 : should be 885.72 LPM and not 1,034.1 LPM (=6.1x12.1x12)

Am I correct?

Thanks.