mult zone fire protection 3

[sparky9]

I have a stucture divided into 4 zones. 3 at approx. 49,000sf and one at 10,000sf. What is the requirements for hydraulic calcs to determine if I need a pump. Does each zone need to be calculated for demand at EACH farthest 1500sf demand? What type of service pressure is required for a large multizone building? thanks for you advice

 

[stookeyfpe]

The sprinkler design needs to be reviewed based on the greatest fuel load given the configuration of the hazard. You can have a light hazard design on the 4th floor but a high challenge commodity (i.e., group A plastics) in a storage configuration in the basement.

Elevation only influences your pressure loss for the final flow demand. You need to evaluate the hazards to determine what is required to apply enough GPM to control or suppress the hazard.

You have not told us enough to help you in your quest.

 

[SprinklerDesigner2]

So what you have here is one building covering 157,000 sq. ft.? Height of building is especially important if designing for plastic storage... we are looking for "clearance" between the top of storage and underside of ceiling or roof deck at the highest point.

You are going to need at least four systems each having at least one calculated remote area. It would be helpful to know the following:

1. What is the height of the building?

2. If storage what is the commodity stored? How is it stored (racks, pallets) and the height of storage? If it is plastic you need to get very specific.

The hydraulically most remote area is not necessarily the most remote. You can have a tree type system where branch lines get smaller as you get closer to the riser and, dpending on what you have. If you want to get cute it is possibe to configure the system so your hydraulically most remote area is adjacent to the riser and, as Stookey pointed out, if you have a system divided between storage and manufacturing with the storage adjacent to the riser, it is likely the hydraulically most remote area might end up adjacent to the riser even if the pipes are larger diameter.

 

[sparky9]

Thanks stookeyfpe and sprinklerdesigner2. The building is 1 story. No storage of any flammables or storage. This is basically a testing facility for industrial equipment like earth movers. Metal shed with dirt floor. Square footage requires separate zones based on the 52000sf rule. I need to know what zone drives the demand for a pump on psi/gpm requirements or do all zones count and the sum total of all demands determines the pump if necessary. thanks again

 

[TravisMack]

The system supply requirements are based on the single greatest demand. IF this is deemed OH Grp II, then you have .2/1500 design criteria with 250 gpm hose. Therefore, you have approx a 350 gpm demand (allowing 15% overage). You could get by with a 300 gpm pump. The pressure is just based on what pipe sizes you need to deliver the required density.

I always figure that once a pump is required, I take it up to the point where the churn is just below 175 psi. I figure if I have to buy a pump, I should get the most bang for the buck. That way, I can reduce the pipe sizes to help balance the cost of the pump.

For example, if I have a base of riser demand of 300 gpm @ 60 psi with a 4" x 3 x 2 grid, you may as well bump the pump to get the pipe sizing down to something like 2x2x1.25", provided you can live with the velocities.

I hope that makes sense.

T

 

[SprinklerDesigner2]

Sounds to me like you have an Ordinary Hazard Group II Occupancy which, assuming standard response heads are used and/or the ceiling or roof deck height exceeds 20', is going to require a density of .20 gpm over the most remote 1,500 sq. ft. with an additional 250 gpm for hose stream demand.

For rough figures, and this can certainly vary, you can rough guesstimate sprinkler demand by multiplying the density over area then adding say 20%.

Water for sprinklers is going to be around 360 gpm and it's important to understand the size of the building is not going to make an impact.

If you have a 1,500 sq. ft. building your design density and area is going to be .20 over 1,500 sq. ft. or the entire building. This 1,500 sq. ft. building will require somewhere around 360 gpm for sprinkler water.

If you have a 20 million sq. ft. building (being ridiculous here) your design density is still going to be .20 over the most remote 1,500 sq. ft. which will require somewhere around 360 gpm for sprinkler water.

The point I am making is the size of the building doesn't matter. The purpose of fire sprinklers is to stop the spread of fire in its incipient stages not wet an entire building.

I have seldom seen an Ordinary Hazard Occupancy need a fire pump unless public water wasn't available.

Remember that you have to add 250 gpm for hose stream so your total fire protection water will end up being around 600 gpm.

A 500 gpm pump would do very nicely but, if you have public water, I doubt a fire pump would be needed. Not saying it wouldn't be but it would be rare.

Also remember if the system is a dry system, subject to freezing, you will have to increase the ara of application by 30% and/or if the roof is steeply pitched you will have to increase the area by yet another 30%.

What do you have for city water?

 

[SprinklerDesigner2]

Hey Travis,

I noticed we were both posting a reply at about the same time because when I started my reply yours wasn't there yet.

I also noticed you mentioned velocities "For example, if I have a base of riser demand of 300 gpm @ 60 psi with a 4" x 3 x 2 grid, you may as well bump the pump to get the pipe sizing down to something like 2x2x1.25", provided you can live with the velocities."

I never designed a system where velocity exceeded 32 fps not because it was published anywhere (it isn't) but was just sort of accepted as an industry standard. Of course on FM, IRI or other HPR insurers the velocity was limited to anywhere between 20 and 25 fps.

But I did find this article written by Russell P. Fleming you might find useful.

http://findarticles.com/p/articles/mi_qa3737/is_200005/ai_n8899216

As for myself I am going to stick with the 32 fps because I feel better about it and I don't believe there would ever be a case where you could save a lot of money by exceeding the 32 fps limit.

 

[TravisMack]

SD2:

The velocity issue is always an interesting discussion. As sprinkler guys, we always do demand calcs. You can limit your velocity to 32 fps in a demand calc, but when you do a supply calc to determine what will actually be happening when the heads open, you are going to get velocities well above 32 fps in many cases. The city water mains don't "know" that you need to leave a 15 psi cushion to maintain velocities less than 32 fps

As such, I don't worry about it too much. When you get to velocities that high, you are burning up a lot of friction loss due to the volume of water. So, it is somewhat of a self limiting entity.

If I recall correctly, even FM has removed the velocity limits on their tree systems. They still ask for 20 fps in gridded branch lines, but that is about it from what I recall.

 

[LCREP]

"basically a testing facility for industrial equipment like earth movers"

Will they have any hydraulic oil reservoirs using combustible oil on any of the test equipment?? If so, depending on the size of the tank, number and psi the equipment is operating at it may be an extra hazard grp 1 occupancy .30/2500 + 500 for hose.

Sometimes a few pieces of equipment can make a big difference on what is required.

 

[SprinklerDesigner2]

"Will they have any hydraulic oil reservoirs using combustible oil on any of the test equipment??"

Good point I forgot to check that out.

Generally speaking isn't 50 gallons in a resevoir the typical call point?

 

[sparky9]

Thanks again to all who responded. I finally received some other parts to the puzzle. First there is no storage in or around the facility for oil or fuel. The concern is the 5000gal fuel truck to fill the equipment and the fueled equipment. I have a flow of 68st-955gpm-54res, 8" main on a dead end,500,000gal reserve gravity tank for FP and it is 88' above the sprinkler system. The density requirements will be .25gpm/3000sf with 286 deg sprinkler type. They prefer a diesel w/jockey pump package. I am losing 21.65psi just from the elevation from finished floor to 50' ceiling plus add in 16 for bfp then the distance from the tap in which hasn't been calculated yet because I don't know where they are going to tap at. Please send any pump recommendations and math. I am looking at a 8"suction-6"discharge 1000gpm. Also the requirements are 750gpm with 250gpm hose. let me know thanks again

 

[SprinklerDesigner2]

There's no need to be concerned so much with the height of the building what I would be most concerned about is the suction supply from the city main to the fire pump.

You're losing 16 psi though the backflow preventor? Must be an RPZ to be losing that much. Is it an RPZ and where did you come up with the 16 psi?

Also remember the sizes given in NFPA #20 for suction and discharge sizes are only the minimums and, depending on the legth and configuration, you could easily be required to run 10".

Pump size depends on whether or not hose stream will be taken off downstream the fire pump or not. Are there any hydrants to be installed downstream?

Without hydrants a 750 gpm pump would be OK but with hose stream taken off downstream you will want a 1,000 gpm pump.

Most critical would be the length of pipe from the tap to the pump suction. If you can give me a rough estimate with fittings (you are going to have at least 2 elbows, a tapping tee and gate).

 

[LCREP]

AsDesign2,

Yes from an insurance point of view we get concerned if over 50 gallons.

Sparky9,

.25/3000 sounds like Factory Mutual is involved or someone is using an FM standard. You may want to reach out to the insurance carrier, we are always willing to work with the designer, makes the plan review process easier.

 

[SprinklerDesigner2]

Sparky9,

The 50 gallons, am I safe in saying that is normally for a single resevoir? What if a piece of equipment has two separate resevoirs each with a capacity of 40 gallons?

In regards to an FM spec I was thinking the same thing except the 250 gpm hose kind of threw me off. My experience has been a HPR insurer would want 500 gpm for hose.

Also sound advice reaching out to the insurance carrier. I've never had a problem on a project where I reached out first so it's a hard policy with me I always do it first.

 

[LCREP]

"The 50 gallons, am I safe in saying that is normally for a single resevoir? What if a piece of equipment has two separate resevoirs each with a capacity of 40 gallons? "

Well it depends on how many of those 40 gallon units we are talking about and how far apart is each unit?? A few together I am starting to get concerned. If we have an entire area, say injection molding then perhaps go with the higher density. If I have 4 units all in different areas, then I can live with it.

Since I am on the insurance side, I always encourage our insureds to reach out to us. No use putting in a system we will not give the building owner credit for. Very true with ESFR and obstructions.

 

[SprinklerDesigner2]

Suction available to fire pumps always get my attention.

You're definitely going to want to confer with your insurance people.

"Also the requirements are 750gpm with 250gpm hose"

With careful design, and assuming the roof isn't steeply pitched, I would estimate the interior sprinker demand wil end up being between 780 gpm and 850 gpm which would give us between 1,030 and 1,100 gpm if we include hose stream.

I can see a potential problem using a 1,000 gpm pump and a definite problem if an RPZ is installed upstream the fire pump.

http://img237.imageshack.us/img237/3027/engtips1uh4.jpg

You are going to have 300 feet of equivalent loss even if you build the pump house adjacent to the city water main. An elbow, 20 feet of pipe and a tapping valve and sleeve will get you to 300 feet.

At 150% we need 1,500 gpm and at 1,500 gpm we are going to have 31 psi available at the pump suction flange. If we have the backflow preventor upstream the pump, with a loss of 16 psi, we're going to draw our suction down to 17 psi.

I would look at using a 750 gpm pump. You are not going to save any money with a 750, actually with larger overhead pipe you will probably be spending more, but the water supply should be able to easily provide 1,125 gpm while maintaining the suction above 20 psi.

Even with hose with careful design total demand for sprinkler and hose might be able to be limited not to exceed 140% of pump capacity.

I guess I am more sensitive then most on the issue of pump suction conditions. I come from Ohio and in most areas, including any test where the state fire marshal is involved, the state EPA requires a minimum 20 psi suction pressure be maintained at the pump suction or you fail the test. Couple this with the state fire marhsal having held intense classes on testing fire pumps, the inspector's know exactly what is needed and where to look, you can see how problems will develope.

I heard of one test where the pump suction drew down to 18 psi, the fire marshal called the test a failure and walked off. Could be very messy.

Will there be hydrants downstream the fire pump? If not the fire pump need only supply sprinklers in which case a 750 gpm pump would work very nicely.