Light Hazard - Pre K School

[comphvac]

I have a sprinkler contractor designed a 2 inches main for entire building (approximately 120 sprinkler heads). It is no a loop system!

Is the sprinkler need to be sized per NFPA table 22.5.2.2.1?

It appears to me that at least 4" main need for entire building.

Thank you.

 

[MGXFP]

The size of the main is dictated by hydraulic calculations and the hydraulically remote 1500 square feet (or less if a remote area reduction for using QR sprinklers and ceiling height is used) of system operation based on the available water supply.

Read more in chapter 22 of NFPA 13 for more info.

 

[spkreng]

A 2" main is not unreasonable, it all depends on the water supply (psi and gpm), room configuration, type of sprinkler heads and most assuredly that the system is hydraulically calculated.

spkreng, CET

 

[comphvac]

Here is the remote area cal.

Remote area - Light Haz.
Density - 0.10gpm/ft@ for 1500 (actual 1530 sqft)
Total head - 5
K-Factor - 8
System Flow Demand - 300 GPM
System Pressure demain - 90 Psi
Base of Riser - 92
Safety Margin - 30 Psi

 

[TravisMack]

It seems like extended coverage heads were calculated. There could be 5 heads calculated at 40 gpm each for a flow of 200 gpm + 100 gpm for inside hose giving a total of 300 gpm.

Now, it is rare to have a system where you do not have any over discharge of the sprinklers. If you have 120 psi available, then it may make sense.

Has a competent reviewer been tasked with plan and calc review? If so, then it it possible. If not, you should really have the plans/calcs reviewed by a competent reviewer for accuracy and compliance with an applicable codes/standards/insurance/local requirements.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[spkreng]

comphvac is there an existing fire pump on site, the water supply seems to be on the high side.

spkreng, CET

 

[comphvac]

Travis - 5 flow at minimum at 38 gpm at 24 psi.

spkreng - Yes, there is a fire pump house draw water from the pond.

Thank you all for quick respond.

 

[TravisMack]

Something doesn't jive.

1 - K8 at 24 psi = 39.19 gpm
2 - Assuming heads are pendent and ex cov, 33 gpm is min flow for most 18x18 coverages. At 20x20, you would need 40 gpm.
3 - If you have a pump drawing from the pond, any pendents must be on return bends.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[spkreng]

comp, how old is this system, or is it in the installatiob phase?

spkreng, CET

 

[SprinklerDesigner2]

The 200 gpm seems suspect to me only because it is such a nice round number.

200 gpm flowing through 2" Dynaflow with an ID of 2.203 produces a friction loss of 0.164 psi/ft so with 150' of main and 50' equivalent fitting losses he'd be looking at 32.9 psi.

Using the Viking VK602 add 17 psi for end head pressure and it is probable a 2" main is all that is needed.

5 flowing heads @ 33 gpm = 165 gpm which means 35 gpm overage to get to the perfect 200 gpm. It's totally possible.

 

[comphvac]

Spkreng - It is a brand new system for 4 buildings.

How many sprinkler heads in 1 1/4" pipe? The designer got 18 heads for 1 1/4" pipe.

Thank you

 

[TravisMack]

If you can calc it, you can have 100 heads on a 1" branch line. It is not limited by a number of heads / line. Sizing is dictated by pressure losses and available water supply.

You seem to be thinking "pipe schedule" methodology. We typically size pipes by calculation methods. He is probably calculating 3 heads on 1 line and 2 heads on another for a total of 5 sprinklers in the design area. Or, it may be 5 heads on a single line calculated in a corridor.

There are many different options as how to properly size and calculate a fire sprinkler system per NFPA 13.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[spkreng]

so comp, what exactly is your concern? as shown above the system seems to be within normal design criteria, sometimes alot of sprinklers on one pipe look weird, but if that pipe is separated by numerous block walls for instance, where only three heads are in each room, then under certain design parameters the remote room is all that counts, look at it as if each room is a fire compartment, then only the remote one has to be proven, "flowed" to dictate the pipe sizing. On the other hand how many toilets are being flowed off one 1/2" line? jk

spkreng, CET