ESFR FIRE PUMP QUESTION 2

[bob smith]

So I am trying to figure out what size fire pump I need. I have a guy that is storing tires and insurance is calling for k25 at 75 psi. My flow test is 162 psi 110 psi @ 1653 gpm. Newbie here just need a little help.
Thanks

 

[LCREP]

Ask the insurance carrier…..some will not let you exceed 100% capacity…FM….some say you can go to 140%. I believe NFPA 20 says 150%.

 

[LCREP]

Bob,

I may have not understood your question. Do you need to know the gpm rating of the fire pump based on the sprinkler demand? To calculate the flow you need to know the demand of the system. How many sprinklers did the insurance carrier indicate needed to be flowing? K25 head @ 75psi is about 216.5 gpm per head. 216.5 gpm is based on the square root of pressure times the K factor of the sprinkler. Are they referencing NFPA 13 or an insurance requirement?

So if they indicate 12 heads flowing( I am making the number up in this example) the sprinkler demand is 2598 gpm. So a 2500 gpm pump would work if the insurance company indicated a maximum pump rating of 150%. But if they require a max pump rating of 100% then you need to go to the next size pump 3000 gpm. Do not forget you need to add hose stream demand to the sprinkler demand.

You may want to get a fire protection engineer involved.

 

[bob smith]

So its a straight NFPA system ESFR 12 heads at 75psi is what was recommended with 250 gom hose. So you are saying a 2500 gpm pump?

 

[UFT12]

12 x sqrt(75) x 25 x 1.1 (10% overflow) = 2600 gpm + 250 gpm allowance = 2850 gpm

NFPA 20 handbook recommends the demand be within 90% to 140% of rated flow. Although this is not mandatory to follow, highest efficiency is expected within this range. Assuming this, you can select a pump of 2500 or 3000 gpm. A 2000 gpm could also provide the flow but due to a high start pressure it may be difficult to keep the system under 175 psi at churn. Final determination of the pump would require to know the exact hydraulic demand of course.

 

[bob smith]

Thank you for your response. It looks like a fire pump with that rated capacity has a 10" suction and 10" discharge but the fire line looks to be 8". I am assuming that would be problem.

 

[UFT12]

Not necessarily. The 10" pertains within the scope of NFPA 20 which ends at the discharge shut-off valve. Downstream that you are either under the scope of NFPA 13 or NFPA 24 or other. However as already said, you need analytical hydraulic calculations of the entire run, including the suction pipe too to see if 8" could work for your case.

 

[LCREP]

Bob,

So it is now time for a call to the insurance carrier to see what they want. I was on the insurance side for 35 years and fielded questions like yours all the time. If I took the time to tell you want I wanted and you did something different well can you say plans rejected. The rejection letter to you, the GC and more importantly the building owner. Never fun to be in a meeting with a lot of yelling why did you not listen to what he wanted. Ah retirement a wonderful thing never have to be in those type of meetings….lol

 

[SprinklerDesigner2]

In my opinion something doesn't smell right. K25 @ 75 psi sound off and off by a lot. Where is this coming from?

218.3 gpm minimum head flow?

Also remember the 10" suction line is the minimum allowed and depending on the water supply it could be more.

LCREP,

My first NFPA #13 was the 1972 edition of the little red book.

Today I get EVERYTHING backed up in writing.

 

[UFT12]

There is just one set of criteria in NFPA 13 that requires that much water.

 

[LCREP]

Sprinkler 2

Man are you old…lol I started in 1978.

Even back in 78 everything got communicated via a letter. And then the calls started asking questions about what we wanted. Often it was just NFPA but sometimes it was an internal document taken from FM, IRI, IRM etc. particularly if not covered by NFPA say handing garments, flammable liquids, etc. But even a reference to NFPA we still had crazy questions. My office came up with a list of sprinkler contractors we worked with often and had a good working relationship with ie great design department when asked for recommendations.

So the process was meet with the client/insured get an idea what they were planning to do. Develop a letter outlining what sprinkler design we wanted, pump electric or diesel, PIV and WPV, hydrant location, etc etc. All driven by how much value or in insurance terms how much could we loose including building, contents (everything inside stocks, machines, racks etc)and business interruption(BI). Most times the BI would drive the numbers. Building and contents could be $25 million but BI could be $100 million depending on what they made. Remember when we actually made stuff in the USA???

We would review the plans with a letter of our approval or not. Visit the site when the system was going in to see what they said was going in was put in. Back to the site to review after everything was installed, witness fire pump acceptance tests. Again everything was documented during the process.

ESFR systems were so much fun when they 1st came out. I remember going to a new 1 million sq. ft warehouse with a ESFR system going in. All the heads were too far from the ceiling for ESFR. Contractor said been installing sprinklers for 30 years this how it is done you crazy insurance guy! I pull NFPA 13 out and show him… what it says. I do not think he made $$ on the job after raising all the pipe in the building.

So yea we got just a few calls from contractors…..lol

Thanks for the trip down memory lane…..

 

[TravisMack]

I'm assuming this is an FM requirement, as they get that high at times. I am assuming 12 ESFR sprinklers in the design area. You are going to be looking at a demand of ±2950 gpm including 250 hose allowance. Since the flow data you posted only leaves you with 9 psi, you are most likely going to need a pump and tank. Most water purveyors won't let you draw down below 20 psi. Being that it is tires, you may be looking at a 750 gpm hose allowance, so if the pump is feeding sprinklers and hydrants, you are looking at a demand of ±3450 gpm. The flow test you gave hits 0 psi at ±3000 gpm.

Many insurers want you to stay between 90-120% of rated capacity. A 2500 gpm pump would get you out to 3000 gpm under those parameters. If you don't have hydrants downstream of the pump, you could get by with a 2500 gpm pump. If you have hydrants downstream of the pump and also have that 750 gpm hose demand, you are looking at a 3000 gpm fire pump. The 2500 gpm pump is 10" suction, the 3000 gpm pump is 12". I'd start to look real hard at a pump/tank setup.

Travis Mack, SET, CWBSP, RME-G, CFPS
MFP Design, a Ferguson Enterprise

http://www.mfpdesign.com