Combined Standpipes/Manual Wet & Multiple FDC' Etc. 2

[Jeremiah187]

Folks,
I have just went through the 2006 thread with regards to Standpipes and Multiple FDC's etc. However I still have a couple of long winded questions. I apologize in advance.

When designing a combined system (standpipe/sprinkler system)the hydraulic calcs. includes calculating 500 gpm @ 100 psi for the most remote standpipe, and 250 gpm for each additional standpipe up to a max. 1,000 gpm. If the bldg. is partially sprinklered then up to max 1,250 gpm. If the building is completely sprinklered then you do not add the flow of the sprinkler system to the standpipe calculation.

NFPA 14-(5.2.5) Talks about a Manual Wet Standpipe System connected to a water supply that can maintain the water in the system but cannot deliver the system demand to the standpipe. The system demand is left for when the pumper truck arrives on-site.

So to my question. Do you then just base your hydraulic piping sizing on the most demanding sprinkler area: 1500 ft2 @ 0.1 gpm/ft2 + the combined hose allowance = approx. 250 gpm.

If so what size is the riser pipes for when the pumper truck arrives on site? Does the pumper truck have pretty much unlimited flow and pressure? Can they provide 1,000 gpm @ 100 psi at the top of a 4 story building? Typically what are the size of these pumper trucks pump?

Basically when sizing the riser for the Combined System do you just ignore the 500 gpm @ 100 psi at most remote standpipe if your considering it a manual standpipe? Why wouldn’t you always call it a manual standpipe, seems it would save a lot of dollars? Does this need to be accepted from the AHJ?

Getting on to the multiple FDC’s? I see from the 2006 thread, that most AHJ want a max. of 1 FDC and if there are multiples they want them interconnected inside of the building. My boss is questioning me (since I’m the most familiar with sprinkler in our HVAC firm, scary I know) on him seeing buildings with 4 FDC’s on the side of the building. Each with their own sign: “EAST STANDPIPE” “WEST STANDPIPE” “NORTH STANDPIPE” and one final FDC for “SRPINKLERS”. Does anyone know if this was an old requirement for each stairwell to having it’s own FDC. Or if we went inside of these buildings would they all be interconnected. Which would be stupid then why would you ever install more then just one. Even if you had a building over 52,000ft2 foot print with 2 alarm valves would you even need more then 1 FDC? Where would you ever need more then 1 FDC? Never ever Ever?

And one final rant before signing off. I’m working out of Canada and our National Building Code feels the need to throw in their 2 cents worth. NBC 2005-3.2.5.9 States the following “ If more then one standpipe is provided, the total water supply need not be more then 30 L/s (475 gpm).” And pretty much refer to the NFPA 14 right after, why wouldn’t they just say for buildings 4 stories or higher, standpipes are required see NFPA 14.

As well NBC 2005 3.2.5.9. 6) “A fire department connection shall be provided for every standpipe?” LIKE WTF?


Anyway if anyone actually makes it through the whole rant and feels like replying to one or all questions, it is very much appreciated!!

Love the posts on here very informative!

Cheers and Happy FRIDAY, Enjoy those beers,
Jeremiah

 

[TravisMack]

Jeremiah:

Virtually all standpipe systems will need some type of pump. The exception is if you have very high city water pressures as seen in some areas of the country.

You can have manual or automatic standpipe systems. A manula standpipe is to be used when the building is between 30' - 75'. Once you break 75', you must have an automatic standpipe. A manual standpipe system will have a fire pump. It is the one that comes on the pumper truck from the fire dept. You still need to calculate your standpipe system just like any other. Check with your local FD, but it is likely that the Fire Dept will be able to provide a minimum of 150 psi @ 1000 gpm at the inlet of the FDC. Therefore, you calculate the standpipe as you stated, but the supply is the fire dept connection.

For combined systems, you will have separate calculations. You will calculate the standpipe system to size the bulk mains and standpipes. You will then need to calculate the fire sprinkler system utilizing the city supply. I have seen several small 4-6 story office buildings where a 4" fire line is brought into the building, with a 4" backflow preventer, but is upsized to 6" at the FDC because the standpipes req'd 6" bulk pipe based on the calculations. We have also had jobs where a 300 gpm pump was installed to supply the sprinkler system. The standpipe demand was 1000 gpm, but that is satisfied through the fire dept connection.

As far as multiple FDC connections, I have frequently seen that with manual dry standpipes. Just run the standpipe up the stairwell and put an FDC at that stairwell. I have also seen more AHJs ask for a second FDC on larger projects. It is just to have a second line of supply to the standpipe system if the primary FDC is not usable for some reason.

I hope this makes sense. Have a good weekend.



Travis Mack
MFP Design, LLC