Can Fire Pump Feed Standpipe But Not Sprinkler?

8/3/2023

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.

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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.

Yes you can evaluate the systems separately prior to the fire pump. You're supposed to evaluate them separately and not carry the 750gpm in your sprinkler calculations. you should carry (LH) 100gpm at the city supply or if you're using a simplified calc at the pump suction.

What will the sprinkler calculation look like? - A regular one?

The hose allowance should be take at the test hydrant outside the building. See yesterdays post and NFPA 13-2016: 11.1.6.3.1

Unless you have an ESFR system on your 7th floor your standpipe calc should be your most demanding calculation.

Furthermore in a high rise where the work area is limited to 2 floors I'm surprised you're required to upgrade the standpipe system. I believe there is language in IBC limiting when standpipes need to be upgraded in existing buildings. Anyone else have that code handy?

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.

Before this post I was doing a lot of digging and definitely understand you would normally evaluate them separately. The problem is the requirement in NFPA 14 that a partially sprinklered building requires you to add the sprinkler flow to the standpipe calculation or 500gpm (because we do have an OH in the building), whichever is less. It doesn't clarify whether this includes the 250gpm hose stream from the sprinkler calculation.

So it comes down to what constitutes a combined system and can you technically have separate systems from the same water supply. Another post on meyerfire seemed to conclude in the comments that a fire pump supplying independent standpipe and sprinkler risers/verticals up through the building was still a combined system. Which is what led me to ask the question. A nearly 1250 gpm fire pump vs a 750 gpm fire pump is a large difference, especially when the electrical engineer has expressed concerns about capacity.

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.

So in this case, you're going to want to evaluate the cost of running a completely separate fire sprinkler riser and supply main vs the cost different between a 1250 gpm and 750 gpm pump. I would guess the cost difference will be in favor of providing the larger pump, as the labor to install a separate riser and supply main likely won't be cheap.

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.

in short you have 500 gpm for your first standpipe then add 250 gpm for each standpipe in the building up to a MAX of 1250 gpm

Example: if you have a partially sprinkled building with 7 stairs each having a standpipe you wouldn't calculate all 7 standpipes for 2000 gpm. You would only calculate the 4 hydraulicly most demanding standpipes (500+250-+250+250).

Buy a 750 GPM pump, run a combined system. Look into a PRV for those lower floors or have all your components rated for 300 psi as others have mentioned.

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.

8/4/2023 08:13:22 am

7.10.1.3.2

Got it, thanksColin!

Ray J link

8/3/2023 08:20:46 am

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?

Jesse

8/3/2023 08:21:57 am

Yeah, non combined systems aren't all that uncommon. We see them a lot in manufacturing.

Your pump sizing leads me to conclude this is an automatic standpipe system, not manual. Would love to know more.

Your AS calcs swill be just like all of the other AS calcs. Assuming control mode - density / area calc.

Two different standards. Your standpipe system is using NFPA 14. Your AS calc is NFPA 13, so you'll need to include the appropropriate hose allowance in your sprinkler calc..

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).

I've done a few projects like this, and you do want to have a combination standpipe setup. The things I would worry about:

-Right around 5 stories you have to start considering PRV valves on some of the lower floors. Depending on the elevation, length/size of standpipe, fittings, etc... you might be pushing over 175 psi at the pump discharge to get 100 psi to a 7 story building. If I had to take a stab at it, probably looking at 180 to 190 psi at pump discharge (depending on the distance between floors).

-What condition is your existing standpipe in and is it time to consider replacing it? A lot of these older standpipe only buildings have sch. 40 6" standpipes and they should last 100 years or more depending on the city water and/or environmental conditions. I would also make sure an obstruction investigation is done. This pipe is probably used to seeing a lot less than 100 psi, and may now be subject to 200 psi+/-. Make sure existing fittings/valves are listed for over 175 psi. As an alternative to PRVs, you ask for everything to be rated for over 175 psi, and it is getting easier to find the properly listed valve/fittings/sprinklers.

-Finding a place for a drain stack, and if you end up needing a few levels of PRV valves, a drain stack in each stairwell that will be sized at a minimum of 3".

-Make sure your tie in the existing FDC (assuming there is one) to the discharge side of the fire pump.

Sorry, not the questions you were asking, but it is the ones I would think of when doing a project like this.

Glenn Berger

8/3/2023 08:33:06 am

Having sprinkler riser separate from your standpipes does happen.

You do need to perform two sets of hydraulic calculations. One calc is for the NFPA 13 sprinkler system and the second calculation would be for the NFPA 14 standpipe system. You do not and should not try to integrate both systems into one calculation.

You should consider, making one (or more) of the existing standpipes into a combination riser.

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.

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.

8/8/2023 10:55:16 am

CORRECTION:
***does not allow MANUAL standpipes in high-rises***

Dan Wilder

8/3/2023 08:58:20 am

There's a lot to digest here...

I'm going to assume this is a Class 1 standpipe system that already complies with NFPA 14. Also, the AHJ is requiring an "Automatic Wet" standpipe system in lieu of a Manual Wet system allowed for buildings below 75' (High Rise Consideration). Also, the floor areas do not exceed 80,000 ft².

Yes, you could have 2 separate systems, 1 sprinkler-1 standpipe

IBC 2018

Sprinklers
903.2.11.3 - Automatic sprinkler system shall be required for buildings with occupant loads over 30 or more than 55' tall from fire department access.

Standpipes
905.3 "Allowed to be combined..." not required to be combined.
905.4.1 - Protection of Riser & Class 1 standpipes
-This means the standpipe system will need to be enclosed in a rated assembly (stairs won't likely be an issue, but any horizontal piping will be in play)
NFPA14-19'-Table 6.1.2.2 (in my eyes) is in conflict with this section but says that horizontal & branch lines of standpipe systems do not have to be protected for a Non-High-Rise Building that is partially sprinklered?

There really shouldn't be a reduction in pump rating, the standpipe should be the driving factor for both pressure and flow in a combined system and unless the sprinkler system needs more than 750GPM, it wouldn't be the deciding factor.

Sprinkler calculation would be standard, but there will need to be inside hose allowance added at the point of interconnection between the sprinkler and standpipe systems. I don't see anything about having to combine the sprinkler & standpipe flows...There is Section 14-19' 7.10.1.3.2 but this is under "Combined Systems" which you do not comply with. I can see an argument to provide the total expected flow from the point of interconnection (sprinkler & standpipe) to the source but don't see the requirement.

Issues I see:
-A separate feed (horizontal & vertical) for sprinklers for the floors, including doubling up on the vertical supply piping within the stairwell in addition to the drain. Thats a lot of extra work for an infrastructure that is already existing.

-Two FDC's for each of the system types

-In partially sprinklered buildings, or the case of a retrofit in stages from a previous project, the AHJ required us to provide protection (sprinklers or fire ratings) for all feed piping that was not located within a sprinklered area. Typically, we placed uprights or pendents along the length of any bulk piping within unsprinklered areas. Make sure to discuss with the AHJ so there are no surprises.

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 ?

We would assume the sprinklers will operate first and have the most opportunity for pressure / gpm but does the hydrant flow test provide a curve that both systems will fit under the line during full design operation ?

I'm gleaning from all of the other posts that it should but I wasn't entire clear that the curve , well, has enough curve

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?

If you have to put in a pump to make the existing standpipe calculate out, why not tap your sprinkler system off the standpipe system?

You calc it the same as you calc any other sprinkler system. Your standpipe is a separate calculation, even in a combined system.

Hose stream allowance for your sprinkler calc is as per your hazard like any other NFPA 13 calculation.

And then you could probably drop pipe size pretty low because you're tapping off a pumped standpipe system.

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.

So the question is, if the standpipe system is driving your fire pump size, why NOT supply the sprinkler system from the same pump? There should be NO disadvantage to doing so, except maybe with the exception that you'll likely need PRV control valves on the sprinkler supply for the lower floors. But the pump will reduce pipe sizes for the fire sprinkler system, so it should be good trade off.

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 ?
I would get clarification before I bought a pump - maybe he assumes you are combining the systems ?

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.

James Art

8/3/2023 11:56:24 am

1. Uses the extra pipe for testing
2. Collin,
If the sprinklers can be supplied without the fire pump, then they are more reliable. Fire Pumps are notorious for poor maintenance and testing. Some data suggests electric fire pumps have a 9 % failure rate, Diesels are more like 20 %.

And yes, more complicated if pressures require PRV's
Pressure Regulating (or Reducing?) Valves.
-------------------------------------------------------------------
War Story:
How do you get a large test flow off a high roof?

I designed fire systems for a DOE Facility, a high rise office building outside of Chicago.
Due to Unions there, it needed separate standpipes, installed by C-36 Plumbers; and fire sprinkler riser, installed by the C-16.
Years later they converted the Riser to a combination system,
and now use the former standpipe for required periodic discharge flow tests of the Standpipe.

8/3/2023 02:27:52 pm

"If the sprinklers can be supplied without the fire pump, then they are more reliable."

Not true at all James. A properly designed fire pump system should have a pump bypass supply main which will serve the fire sprinklers regardless of whether or not the pump is functioning. So there is redundancy if the pump fails. I don't doubt your pump failure numbers, but if properly designed, there is some redundancy if the pump doesn't start.

8/19/2023 02:06:29 pm

James,

Where can I find more information and data on fire pump failure rates?

AJ

sean

8/20/2023 09:43:45 pm

I dont know of any public numbers either from design/testing or real life.

8/3/2023 01:07:24 pm

sure you can separate them but not for any good reason

Steve

8/8/2023 08:33:56 am

Couple comments from the other (fire department) side of the fence.

I like the idea of simplifying systems to reduce the chance for failure; however, not using a fire pump because of a chance of failure sounds shortsighted. Reliability is t he cornerstone of the maintenance and testing requirements of virtually all NFPA standards. If the system is not being maintained properly, there is no standard that can fix that problem.

As a fire officer showing up at the scene of a high-rise building fire, I would want the fire protection system as simple as possible. By that, I mean one FDC to supply the entire buildings fire protection systems. At 3AM, trying to shake the cobwebs out of your head to make and execute a tactical plan, I appreciate simplicity. I have bigger things to think about than if the sprinkler and standpipe systems are connected or not!!!

With those thoughts in mind, as the Fire Marshal, I would argue against a split system. I'd look for a way to force the system to be entirely separate all the way to the water authority's water line...i.e, not just separate risers, but separate fire lines as well.

I get it that money does play a factor, but let's not forget the intent is to provide a SAFE building.

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..

Can Fire Pump Feed Standpipe But Not Sprinkler?

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