Warehouse Sprinkler Main Sizing

[Maximusprime]

Hi All,

I am designing a truck freight terminal, and though the sprinkler design will be handled by a different contractor, I need to size the sprinkler main and RPZ, and the sprinkler contractor will take it from there. I want to be conservative in my design, but also don't want to oversize if I can avoid it.

This will be about 30,000 sf of what I assume to be Ordinary hazard type 2 storage (client has been very light on details). I do not anticipate storage to be piled high or on plastic pallets, no racking, etc.

As I am not designing the sprinkler system, and don't have a lot to go on, I am assuming 0.6gpm/ft^2 which is resulting in a 12" main and RPZ assembly.

Can anyone here recommend some resources for where to start on this? How would you typically approach designing for unknowns in a space like this?

Thanks!

 

[TravisMack]

If you are thinking it is to be OH2, then why such a high density as 0.6 gpm/ sq ft? What design area are you anticipating? Even 0.6/2000 is only 1200 gpm. That could be 6" or 8" at most.

OH2 is .2/1500 or 300 gpm. Give some overage and maybe 400 gpm inside. 250 gpm hose allowance. 6" fire line into building. Depending on pressures, 4x4x2 grid should be good. Again, this all depends on what your water supply is and truly what density you are designing to.

It is impossible to answer your questions without further details.

Travis Mack, SET, RME-G,
MEPCad, Inc
AutoSPRINK | AutoSPRINK FAB | AutoSPRINK RVT

 

[Danefre]

Is this in the US? What state? FM Global requirements?

Sorry to be a downer and not providing much help but have you consulted with a FPE licensed in your state? An FPE can gather all the info, make an educated determination of the hazard and provide design criteria so you can size the underground. Not the other way around.

All I can say is 0.6 density sounds like an overkill especially since you don't anticipate high piled storage. Ordinary Hazard Group 2 would be 0.2 so not sure where the 0.6 comes from.

If you can provide more information regarding storage we might be able to help a bit more. Specifically storage of plastics would be a big factor. That being said.. 12" is a red flag

 

[UFT12]

Outside infrastructure to upgrade is expensive, time consuming and can introduce considerable downtimes. So consider criteria for the future that may come into play, not only what you get today. Do not assume. Get the client to give you full information s much as possible or at least understand the various occupancies in the building.

 

[trashcanman]

If I were the Sprinkler Contractor, I would be leery of accepting your sizing of the main. The Contractor is usually responsible for the entire piping system, from the tap on the water main to the last fire inspector connection.

You see if your main size is too small, the Sprinkler Contractor will demand a huge change order if his system design requires a larger line size. City tapping fees depend on the tap size. That fee is (usually) paid by the Contractor.

Re think who is responsible for what.

 

[SprinklerDesigner2]

It the occupancy is OH-2 we are looking at 607 gpm assuming worst case which would be a dry pipe system under a steeply pitched roof (.20*2535)+100=607 gpm. The 100 gpm is simply added to the minimum theoretical discharge. If it is a wet system under a not steeply pitched room then we would be looking at (1500*.20)+100 gpm or 400 gpm at worst case.

At 607 gpm our friction loss will be .0092 psi/linear foot through 6" C900 DR18. Figure 200 linear feet plus 56 equivalent feet for the tee, gate valve and elbow at flange and spigot our total loss through the underground would be 256*.0092=2.35 psi.

Add an additional 3.0 psi under the assumption your backflow will be an Ames 3000ss double detector check valve [URL unfurl="true"]http://media3.wattswater.com/ES-A-3000SS.pdf[/url] our total friction loss would be 5.35 psi and that is for the worst case of an OH-2 occupancy.

In my opinion a 6" main would easily handle 95% of the OH-2 systems out there but I recently had a job where I had a OH-2 occupancy (a garden center) where where the system was dry pipe with a steeply pitched roof and a city water supply of only 46 psi static, 40 psi residual @ 1,113 gpm when we consider the existing 6" underground was 700' long with a tee, gate valve, 3 elbows and a double detector check valve thrown in for good measure. Yeah, it was possible but in Georgia the state fire marshal requires we maintain a minimum 7.0 psi "safety factor" in our calculations which made the job impossible unless we heated the garden center which would reduce the area of application or replaced the 6" underground with 8". The owner ended up heating the garden center but I would say a situation like this is rather rare.

And to the total water supply required remember we have to add 250 gpm at the nearest hydrant so if you have a fire hydrant downstream the backflow then you got to factor that in as well.

In my opinion, unless you have a real rotten city water supply, 6" would most likely handle the situation for an OH-2. Like I said if the underground from the street to the base of the riser is 100 linear feet the 6" wouldn't be a problem but if you have 1,500 feet plus a fire hydrant then 8" might be called for. Unless the situation was really strange I can't envision where we would need more than 8" to supply an OH-2 system.