No, you don’t have to provide two calcs when you have a tank, there’s no value in that.
All you are required to prove is that the system can operate at the minimum required density over the minimum required area within the most hydraulically remote area. All our calculations are made to be simple. The physical performance of hydraulic balancing and flows in sprinkler systems is quite complex. But for all intents and purposes trying to perform any kind of intricate analysis is really of little value. I got to review a sprinkler layout drawing by an engineer who was actually putting balancing valves on each branch line because he thought that was the only way to guarantee equal and balanced discharge from each line. That was really special. A 1000 gpm pump isn’t going to run at 1800 gpm, and it doesn’t have to. If your criteria only requires 1400 gpm over the specified hydraulically remote area and if the area happens to flow nearest the riser, the system is still only required to provide a minimum discharge rate, the required minimum rate doesn’t increase. It doesn’t need to. There’s no Code saying it has to. It comes down this, find the remote area, select a pump, run the calc and see if it works. Adjust as necessary and move on to the next task. Don’t waste time over-analyzing things for which there is no return value. Time is money. Craig L. Prahl Fire Protection Group Lead/SME CH2M 200 Verdae Blvd. Greenville, SC 29607 Direct - 864.920.7540 Fax - 864.920.7129 CH2MHILL Extension 77540 [email protected] From: Sprinklerforum [mailto:[email protected]] On Behalf Of Brad Casterline Sent: Monday, January 30, 2017 4:34 PM To: [email protected] Subject: RE: Selecting a Fire Pump/ Europeans vs. Americans [EXTERNAL] Isn't the requirement for calculating the area closest to the pump only when the water supply is water storage tank, to verify the tank capacity against flow rate and duration? You are right though - American codes do not require the two sets-- we calc 'most remote' and use that size all the way back because the closer you get to the riser the more you will be flowing, hence the concern about tank capacity. It is a can of worms that has not yet been opened here in 'the states'. Brad A 1000 GPM rated pump will not likely produce a flow rate of 1800 GPM. It will limit out most likely around 1650 to maybe 1700 GPM. It should then, nonetheless provide the minimum design density at the lest demanding design area. There is no code requirement to produce the maximum flow capacity of a design area, only the minimum. Mark at Aero 602 820-7894<tel:602%20820-7894> -----Original Message----- From: Sprinklerforum [mailto:[email protected]<mailto:[email protected]>] On Behalf Of Reza Esmaeili Sent: Monday, January 30, 2017 1:56 PM To: [email protected]<mailto:[email protected]> Subject: Selecting a Fire Pump/ Europeans vs. Americans I am glad to write in this nice forum again! I don’t understand NFPA 20 for selecting fire pump: “Maximum system demand flow should be between 90% and 140% of pump’s rated capacity, but, in no case, greater than 150% of the pump’s rated capacity”. That is to say if my total sprinkler and hose demand is 1400GPM, I can simply choose a 1000GPM rated pump. 1400GPM is calculated based on the most remote sprinklers, so what if the sprinklers nearer to pumps are activated and my demand jump to 1800GPM? Then at high flow, there is a possibility for cavitation and overloading the motor. Am I wrong? Europeans calculate differently. They calculate the demand both at the most unfavourable area (most remote area) and most favourable area (near the pump). For example if they calculate 1400GPM at most unfavourable and 1800GPM at most favourable area, then based on these figures they choose a pump. They also check 1800GPM on the pump curve to be sure it’s less than 140% of rated capacity and also less than 16m NPSHr. VdS CEA 4001 Standard in Europe: The pump set shall be capable of providing at least the flow and pressure of both the most favourable and the most unfavourable areas. The maximum flow demand (Qmax) for supplying the most favourable area may exceed the permitted rate by up to 40 %. The pressure shall not fall by more than 30 % (of the pressure prevailing with the permitted rate). The flow demand for the most unfavourable area shall fall below the permitted rate at all times. NFPA 20 and VdS are somehow the same. They limit the maximum flow demand up to 140% of rated capacity, but Europeans really calculate the minimum and maximum demand and check this is less than 140% but American don’t check anything. So if like the above example an American designer make a tight selection (Choosing a 1000GPM pump for 1400GPM demand), is there any possible problem if the sprinklers near the pumps are activated and the pump runs at 1800GPM? Best, Reza Esmaeili Email:[email protected]<mailto:email%[email protected]> Cell: +98 912 2444875<tel:%2B98%20912%202444875> Web: www.sarian.ir<http://www.sarian.ir> _______________________________________________ Sprinklerforum mailing list [email protected]<mailto:[email protected]> http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org _______________________________________________ Sprinklerforum mailing list [email protected]<mailto:[email protected]> http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
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