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 -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of Reza Esmaeili Sent: Monday, January 30, 2017 1:56 PM To: [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] Cell: +98 912 2444875 Web: www.sarian.ir _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
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