There is a difference because we select pumps based on our codes and our codes are different.
All pumps have a Required Net Positive Suction Head that is independent of site specific Available NPSH and so-called 'demand'. NFPA 20 requires a minimum Available NPSH that is conservative (~27 ft). For most pumps I have seen the Required NPSH is 10-15 ft, so that should take care of that unruly area closest to the pump. Brad On Feb 3, 2017 1:53 PM, "Reza Esmaeili" <[email protected]> wrote: > Thanks for all the comments. > > Foreword: If your total flow demand is 1000GPM, you MUST select a 1000GPM > rated pump! > > Some years ago, when I was reading about fire pumps, I came across two > points as follows: > Point 1- Pumps shall furnish not less than 150 percent of rated capacity > at not less than 65 percent of total rated head. > Point 2- Motors should operate on any point of the fire pump curve without > exceeding the motor service factor. > > To me the philosophy behind mentioned points are: If the calculated flow > demand at the most remote area is for example1000GPM, there is a > possibility that more sprinklers are activated in fire condition (or the > sprinklers closer to pumps are activated) and the flow may increase up to > 1500GPM, in this case both the pump and the motor should be able to endure > such increase. The above point 1 guarantees that the pump can provide > 1500GPM at a reasonable pressure drop not making serious problem for the > sprinkler system. The point 2 also guarantees that the motor can endure > working at 1500GPM. In other words, in my opinion, if flow demand at the > most remote area is 1000GPM, I should select a 1000GPM rated capacity pump > which can run up to 1500GPM. This is like having 50% safety factor. This is > my understanding of the above two mentioned points. > > My problem is the below point 3 which destroys the above theory. > Point 3- 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. > Based on point 3, if my flow demand at the most remote area is 1000GPM, I > am allowed to simply choose a pump rated at 750GPM, this is not a tight > selection and every fire protection engineer accept such selection. But > imagine a designer select a 750GPM rated pump for 1125GPM flow demand and > NFPA allows this selection. However I don't accept a 750GPM for my 1000GPM > flow demand because it's against my theory in point 1 & 2. I believe that > the pump rated capacity should fall below the flow demand. That's what > European standards require as follows: > > VdS CEA 4001 Standard in Europe: The flow demand for the most remote area > shall fall below the permitted rate at all times.(In other words: If your > flow demand is 1000GPM, the pump should be rated at least for 1000GPM). The > maximum flow demand may exceed the permitted rate by up to 40%. The > pressure shall not fall by more than 30%. (In other words: Pumps shall > furnish not less than 140 percent of rated capacity at not less than 70 > percent of total rated head.). > > Would you please let mw know where I am making mistake and why there is > such a big difference between Americans and Europeans in selecting fire > pumps. Thank you! > > All Best, > > Reza Esmaeili > > Email:[email protected] > Cell: +98 912 2444875 > Web: www.sarian.ir > > > > > -------------------------------------------- > On Tue, 1/31/17, Steve Leyton <[email protected]> wrote: > > Subject: RE: Selecting a Fire Pump/ Europeans vs. Americans > To: "[email protected]" <sprinklerforum@lists. > firesprinkler.org>, "[email protected]" <[email protected] > > > Date: Tuesday, January 31, 2017, 12:58 AM > > And if an area closer to > the water supply - i.e. LESS hydraulically remote - than the > design should flow, it will not overflow more than the water > supply can produce. If a design area requires 1,400 GPM, > more hydraulically efficient groups of sprinklers might > theoretically flow more at the same residual pressure, but > that doesn't create an 1,800 GPM demand in one or more > of those areas. It's all on paper ... > > So the pump will produce to > its rated residual pressure at overload (150%) and that will > adequately supply any area in the building up to the demand > that was calculated at the MRA. We only need > 1,400 and the less remote areas will flow that at a higher > residual at the pump than will the MRA (higher net K), so > everything's okay. > > Right? > > SL > > -----Original Message----- > From: Sprinklerforum [mailto:[email protected]. > org] > On Behalf Of [email protected] > Sent: Monday, January 30, 2017 1:14 PM > To: [email protected]; > [email protected] > Subject: RE: Selecting a Fire Pump/ Europeans > vs. Americans > > 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]. > org] > 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 > > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler. > org >
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