Fire Pump Sizing
Fire Pump Sizing
(OP)
Let me start off by saying that this website is a HUGE help for a young designer like myself. I'm working on a high school design that will have 5 systems. The water flow for this area is very poor and the School district, Architect, and GC are now exploring the option of adding a fire pump. This will be my first fire pump design so I'm a little hesitant. Can anyone suggest a good reference material that outlines the steps on how to properly size a fire pump.
Or even better if any senior designers have a method that they use that seems to work nicely. Thank you once again for any help on this matter.
Or even better if any senior designers have a method that they use that seems to work nicely. Thank you once again for any help on this matter.





RE: Fire Pump Sizing
Sprinkler flow will be sized based on the occupancy and area, with hose stream added. Sprinkler pressure will be determined by the highest elevation of sprinklers and the minimum pressure allowed (I use 10 psig).
Standpipes, if Class I or III, start at 500 gpm and go up from there to 1,000 gpm in sprinklered buildings. You will have to check with the building code, but the pressure at the top of the standpipe is typically 100 psig, but you can sometimes be allowed to use the fire pumper truck so you just have to size the piping but not size the pump for 100 psig.
Since you have a school, you might have a stage which sometimes requires a standpipe connection on each side depending on the size of the stage.
Get your hydrant flow test to determine available pressure - do not forget the backflow preventer. In some jurisdictions, you have to have a minimum suction pressure so check that out. It is typically 20 psig. So make sure the flow test indicates what the flow is at 20 psig. If not, you will have to calculate it.
If the water supply is too poor to provide adequate pressure and flow, you might need to have onsite storage, which is another issue altogether.
Reach out to the pump manufacturer's rep. They can be a great help.
RE: Fire Pump Sizing
Ensure all penetrations into the controller maintain the NEMA damp-proof rating. This means listed water-tight hubs. Certain controller manufacturers provide a removable gland so the electrician can drill out gland panel for conduit and reinstall it so as to maintain the integrity of the pump controller. Make sure an opening is provided for fire alarm conductors and that the fire alarm contractor programs the correct signals.
If you cannot locate the pump room on an exterior wall, the pathway to the pump room will need to be constructed with the same fire-resistance rating as the the room enclosing it, which will be 1-hour in your scenario.
For acceptance testing I've attached the questionnaire we ask the contractor every time I am asked to approve a fire pump installation. I also included my canned plan review comments for electric and diesel drivers. If they don't answer the questions correctly the test isn't scheduled. If we arrive on the job site and the pump is not ready I walk off it.
RE: Fire Pump Sizing
I figure if we are going to be paying for a pump, I want to get the biggest bang for my buck. You should be able to determine capacity pretty easy. If you have all light hazard, you may only need a 250 gpm pump at most. If you have some OH2 areas in there, and you can use the QR reductions, you may need a 300 or 400 gpm pump. You will have to calculate your areas without the pump to determine the best flow rate. I like to choose the smallest pump I can because of the fittings and valves that go in a pump room. Sure, you could just go with a 500 gpm pump and be fine. But, that is all 6". If you go with a 400 gpm pump and can do just as well, all of your pump room devices will be 4". That is a significant savings.
Once flow is set, you are pretty much paying for pressure or horsepower. Find out from the electrical contractor how much horsepower you have available. At that point, choose the greatest pressure you can for that horsepower and calculate the system. If you are fine with your pipe sizing, then just finish it up. If the pipe sizing is very small, see what the difference is in costs if you drop the horsepower rating a bit. It may be that you save $5000 in pump costs, but only see a material increase of $3000 for a net savings of $2000.
Lastly, be sure that your pump churn pressures + static pressures do not exceed the rating of your components. If churn + static is 185 psi and your components are rated to 175 psi, then you need to drop your pump pressures.
One more thing. Are there fire hydrants down stream of the fire pump? If so, you have to take into account the outside hose allowance flowing through your pump.
I hope that helps.
Travis Mack
MFP Design, LLC
www.mfpdesign.com
"Follow" us at https://www.facebook.com/pages/MFP-Design-LLC/9221...
RE: Fire Pump Sizing
RE: Fire Pump Sizing
Travis Mack
MFP Design, LLC
www.mfpdesign.com
"Follow" us at https://www.facebook.com/pages/MFP-Design-LLC/9221...
RE: Fire Pump Sizing
HP = (Flow x Pressure) / (3960 x Pump Efficiency)
Flow: gallons per minute
Pressure: ft. hd
Pump Efficiency: 50%-70%
That will give you an idea of what flow and pressure you can use.
RE: Fire Pump Sizing
RE: Fire Pump Sizing
RE: Fire Pump Sizing
RE: Fire Pump Sizing
RE: Fire Pump Sizing
RE: Fire Pump Sizing
Travis Mack
MFP Design, LLC
www.mfpdesign.com
"Follow" us at https://www.facebook.com/pages/MFP-Design-LLC/9221...
RE: Fire Pump Sizing
(since there is more pressure). Also, if you have an area that due to compartments/ceiling fixtures/whatever has 'a lot' of sprinklers in the area of operation, but one or more sprinkler is spaced to cover a 'large' area, then you could have a lot more water coming out of the sprinklers with a smaller area of coverage than the .2*actual floor space would compute. You are probably fine with your 2*21,000 tanks, but you won't have 9,000 gallon safety (using a 1500 ft2 area of operation and needing the 250 hose).
RE: Fire Pump Sizing
RE: Fire Pump Sizing
Travis Mack
MFP Design, LLC
www.mfpdesign.com
"Follow" us at https://www.facebook.com/pages/MFP-Design-LLC/9221...
RE: Fire Pump Sizing
Pr = Residual pressure of water supply (Since my tanks are at ground level this would be 0
Pe = Elevation changes in my pipe in relation to suction flange elevation
Pfl = Pipe friction loss this also includes a backflow if present
My question is since my tank is at ground level when I figure my friction loss for the water in the pipe from the tank to the pump would my (Q) be 0 because there is little to no pressure on my supply since its at ground level. or would (Q) be the demand of my system?
RE: Fire Pump Sizing
Travis Mack
MFP Design, LLC
www.mfpdesign.com
"Follow" us at https://www.facebook.com/pages/MFP-Design-LLC/9221...