I am currently evaluating a 7-story building that is being partially renovated and has an existing standpipe system (2 standpipes), but no sprinklers. My scope was to add sprinklers to the renovated areas, creating a partially sprinklered building.
The lack of pressure is leading the AHJ to require a fire pump due the 100 psi required for the standpipe system. While the standpipe requires the fire pump, hydrant flow tests indicate that there may be sufficient pressure to supply a sprinkler system. My question is two-fold. Is there really such a thing as a non-combined sprinkler/standpipe system where they are both required? They both get their water supply from the same source. Also, can I evaluate supplying the sprinkler system through a separate riser that tees off before the fire pump, while the fire pump supplies only the standpipe, significantly reducing the size of the pump? The pump would be sized for 750 gpm total, 500 gpm @ 100 psi to the remote hose connections, and 250 gpm to the second standpipe. What would that sprinkler calculation look like? Would the sprinkler calculation remove the hose stream allowance and replace it with the 750 gpm to consider the flow to the pump/standpipes? The flow potential is there based on the hydrant flow test just not the pressure for the standpipes (and it's close for sprinklers). I'm just wondering if I can give the client and rest of the design team options. Thanks in advance. Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
26 Comments
Anthony
8/3/2023 07:19:17 am
Is there really such a thing as a non-combined sprinkler/standpipe system where they are both required? Yes it happens, more common in horizontal standpipe systems where you're over the minimum 200' or 130' hose travel requirements. Generally at large production facilities.
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Andy (OP)
8/3/2023 10:46:59 am
To clarify, work is being done on all floors, with 3 floors being completely renovated (approx 10,000sqft) per floor.
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Colin Lusher
8/3/2023 02:23:45 pm
Ahhh, interesting situation. To answer your question, in order to be considered a combined system, the sprinkler system must be supplied by the same piping that supplies the standpipe hose connections. So if you run a separate riser for the fire sprinkler system, that is NOT a combined system per NFPA 14 definition. You could pull from the suction side of the fire pump and as long is it's not interconnected downstream, this would NOT be a combined system.
Anthony
8/4/2023 06:54:32 am
I see the mix up here. With your floor area of 10K sqft and 2 standpipes you'll only have to calculate 750 gpm regardless of sprinkled/sprinkled. 500 from the most remote standpipe and 250 from the other. NFPA14-16 7.10.1.1.5 details the MAXIMUM flow required. not minimum flow.
COLIN LUSHER
8/4/2023 07:06:42 am
Anthony, you're missing the fact that this building is only partially sprinklered. OP is correct that NFPA 14 does indeed require an additional 500 gpm sprinkler flow to be added to the standpipe flow for combined systems in partially sprinklered buildings. So if he separates the systems, he can use a 750 gpm pump, but if he combines them, he'll need a 1250 gpm pump.
Anthony
8/4/2023 08:13:22 am
7.10.1.3.2 To partially quote a favorite movie, "I'm not a smart man", but couldn't you calc the entire building using the existing standpipes to feed each floor? That would allow each floor to be sprinkled in the future when and if there is any renovations to the other floors?
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Jesse
8/3/2023 08:21:57 am
Yeah, non combined systems aren't all that uncommon. We see them a lot in manufacturing.
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Casey Milhorn
8/3/2023 08:29:02 am
Anthony pretty much covered it. If you are dealing with a residential or office type building, there is no way your sprinkler demand will be more demanding than 100 psi @ 500 gpm at the top level (unless you just go super small on your pipe sizing and/or do a really bad layout of the system).
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Glenn Berger
8/3/2023 08:33:06 am
Having sprinkler riser separate from your standpipes does happen.
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James Evans
8/3/2023 08:47:20 am
Why use a fire pump at all? NFPA 14 allows for wet manual standpipes. this way you connect to the standpipes to feed your systems. The city pressure is sufficient to feed your sprinkler systems. When the pump truck arrives, he connects to the FDC and supplies the needed additional pressure to the standpipe through the pumper truck. In this scenario there would be no need for a fire pump at all. Standpipes are only used by the fire department, and they have the means to supply all the pressure they would want. You just have to make them aware by the posting of a sign above the FDC of how much additional pressure is needed to meet the 100psi at the top.
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COLIN LUSHER
8/4/2023 07:08:54 am
NFPA 14 does NOT allow for automatic standpipes in HIGH-RISE buildings anymore. They MUST be automatic if the building is over 75ft tall. Manual standpipes may be used on anything under 75-ft tall.
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COLIN LUSHER
8/8/2023 10:55:16 am
CORRECTION:
Dan Wilder
8/3/2023 08:58:20 am
There's a lot to digest here...
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Greg
8/3/2023 09:52:01 am
The one thing that crossed my mind in your question is the hydrant flow test.... If the "hydrant flow tests indicate that there may be sufficient pressure to supply a sprinkler system." , is that test representative of the demand of the fire pump (hose streams) operating simultaneous with the sprinkler system ?
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Pete H
8/3/2023 09:57:27 am
You can have them as separate systems and the sprinklers not fed from the standpipe and fire pump.... but in the case of a high rise, why would you?
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Colin Lusher
8/3/2023 10:23:35 am
Everything Anthony said is correct. At 750 gpm, your standpipe system is going to be more demanding than your sprinkler system, so the standpipe system is what is going to drive the fire pump size. Your fire sprinkler calculation should require no more than 400 gpm assuming light or ordinary hazard occupancy, and much less if it's residential.
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SCHULMAN
8/3/2023 11:04:57 am
Thank you James Evans ... Why put a pump on a standpipe ? Isn't that the "pump"er truck's job ? and if indeed you have enough pressure for your sprinklers ... am i missing something? Are you and the AHJ mixing up words or communicating on different levels? Is there a facility fire brigade in the building ? does this poor fire department need money for a new pumper truck ?
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Colin Lusher
8/3/2023 02:31:39 pm
Standpipe systems for high-rise buildings (anything taller than 75-ft) are required to be automatic, so a fire pump is normally required to achieve the 100psi required at the roof hose valves.
Reply
James Art
8/3/2023 11:56:24 am
1. Uses the extra pipe for testing
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Colin Lusher
8/3/2023 02:27:52 pm
"If the sprinklers can be supplied without the fire pump, then they are more reliable."
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AJ
8/19/2023 02:06:29 pm
James,
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sean
8/20/2023 09:43:45 pm
I dont know of any public numbers either from design/testing or real life.
sean
8/3/2023 01:07:24 pm
sure you can separate them but not for any good reason
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Steve
8/8/2023 08:33:56 am
Couple comments from the other (fire department) side of the fence.
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Mark Harris
8/10/2023 04:58:20 pm
Is the plan to eventually totally sprinkler the building as floors are leased or renovated? If yes a conversation with the AHJ asking if they will allow an exception to sizing the pump for the standpipe system only but using as a combined sprinkler supply can be made. May require owner to provide a letter stating that total sprinkler protection is intended and with a completion date for total sprinkler protection. That would make the sprinkler piping smaller and less expensive and have to assume the AHJ would like to see the building eventually totally sprinklered..
Reply
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