13D water supply rate requirements 1

[fsck]

I'm an EE working on a planned multistory 3800ft^2 residence in Northern CA.

The house must have sprinklers running off a single combined domestic/fire pump. I'm trying to SWAG the needed capacity for pump & power planning purposes. We are 6-8 months away from a sprinkler designer.

The house will have >10Kgals of potable storage, with 20 feet of positive head.

NFPA 13D <

http://rrdocs.nfpa.org/rrserver/browser?title=/NFPASTD/13D10>

talks about water supply in Chap. 6.

Specifically, 6.1.3 states the quantity is at least 7 minutes times "the two sprinkler demand rate" unless the house is bigger than one story or 2kft^2.

I do not find a direct statement as to the required flow rate from the water system. I do find in 8.1.1.1.1 that the system must be able to provide 13pgm simultaneously to all sprinklers. (That's a LOT of water! With say 40 sprinklers... I must not be understanding it correctly....)

a) What does 8.1.1.1.1 mean?

b) Is there a direct statement re: required flow? If it is "two sprinklers" then a 1200 ft^2 house and a 4500 one would need the same pump.....

c) 6.1.3. addresses houses smaller than this one; what applies here?

d) The usual approach to meeting the varying pump demand is a variable frequency drive feeding the pump motor. (One brand name I find is "Aquaboost") But this house will be fed with 208/3ph. Has anyone found a VFD controller that accepts 3ph? [Yes, we could run it off of the 208, but that's a topic not 100% germane to this forum...]

e) The owner asked about external connections; so an outdoor pump could be used when the power is down. (CalFire requires a Emergency Power Off on the outside wall. But using it kills the fire pump...) Commercial building sprinklers have those for FD connections; has anyone seen such on a house?

 

[TravisMack]

As long as you don't have any crazy ceilings with slopes >8:12 causing you to go outside of the sprinkler head listing, your worst case should be 2 heads flowing 20 gpm. You need that for 10 minutes. Allow for some over discharge and your stored water should be around 450 gallons.

With regard to pressures, I would shoot for about 18 psi for the head, 20 psi in friction losses, 8 psi for the riser (assuming a backflow preventer) and then whatever elevation you have.

Again, this is just a WAG based on a lot of assumptions.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[fsck]

Well, it is a log cabin with a big great room and cathedral ceilings.

OK, so that's 40GPM plus 5gpm (from 6.5.2).

The 450 gallons is not an issue; CalFire requires 10,000g and the owner is going well beyond that.

BTW, CalFire is not keen on using swimming pools for that reserve. [This house will have a large one.] Their reason is in rainy season, they may pop out of the ground when emptied. If you insist, there's a big seismic report required, and a deed covenant forbidding abandoning the pool.

 

[TravisMack]

3.3.4 Dwelling Unit. One or more rooms, arranged for the use of one or more individuals living together, as in a single housekeeping unit, that normally have cooking, living, sanitary, and sleeping facilities.

6.5.2 In common water supply connections serving more than
one dwelling unit, 5 gpm (19 L/min) shall be added to the sprinkler system demand to determine the size of common piping and the size of the total water supply requirements where no provision is made to prevent flow into the domestic water system upon operation of a sprinkler.

I am assuming you are only serving ONE dwelling unit. If so, the 5 gpm is not needed. It may be good practice, but is not req'd.

If your ceilings have slopes >8:12 as is not uncommon for log cabins, you will not find a residential sprinkler listed for that slope. I had one jurisdiction where the AHJ said that if residential heads aren't listed, you have to use a standard where you can use QR heads. We had to do the system in the house per NFPA 13 because that was the only way we could get to use QR heads. 13R would not work because we had more than 4 heads in the dwelling unit, and 13R limits you to no more than 4 QR heads in the dwelling unit. It was a pain, but that is what we had to do.


Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[fsck]

I suppose I should have mentioned it's a ~3800 ft^2 log cabin, not quite the one Daniel Boone built....there's a planned adjacent indoor pool of about the same footprint. It will have large PV arrays for electricity and heat. One of my tasks involves Internet access and getting HiDef TV over fiber.

I misread 6.5.2; I thought it was about any combo systems.

That's not encouraging re: the slope; I'll mention it to the owner.

Still looking for the best VFD.

 

[spkreng]

13D does not have any sq ft limitations, provided it is a single family dwelling, your case would require a 10 minute duration, a 1 sprinkler (lower gpm/higher psi) and a 2 sprinkler calculation (higher gpm/lower psi), multi times the higher gpm times 10 for your fire water need, the psi really depends on the specific sprinkler and piping arrangement used, TravisMack is righton in his estimates. one concern is that it seems you are using the pool as the supply (standby?) you'll have to check to see if it's capadable (sp) with cvpc pipe, but sounds like exposed piping which will have to be copper or steel.

 

[fsck]

The pool is NOT the required reserve. CalFire requires 10Kgal, which will be poly tanks ~20' above the house. We'll have 20Kgal. Since they demand a combo system, potable and sprinkler, that is also the potable supply. We don't plan any crossfeed from the pool.

So the "10 minute rule" is moot in face of the CalFire requirement. My question is about the pump size, and thus power needs. I could not find the cite for "two sprinklers" in 13D.

I do have other questions but I'll put them in other threads.

 

[TravisMack]

From NFPA 13d, 2010

8.1.2* Number of Design Sprinklers. The number of design sprinklers under flat, smooth, horizontal ceilings shall include all sprinklers within a compartment, up to a maximum of two sprinklers, that require the greatest hydraulic demand.

Pump size is going to be determined by the piping configurations and elevations. One can typically do a residential fire sprinkler system for 60 psi.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com