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]" <[email protected]>, "[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]] 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]] 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
