Dear Friends, Thanks to all for mentioning the demand problem and special thanks to Richard for detailed answer about pumps, let me first explain why I assumed 2500 Gpm demand, I assumed a big factory with 4 sprinkler systems (4 x 700 Gpm demand) and a deluge system (1500 Gpm demand) and hose streams, so in the worst scenario I activated 1 sprinkler system plus deluge system and hose stream demand 700+1500+300 = 2500 Gpm. Actually I am not good at analyzing risk, perhaps above calculation is wrong, but this is just an assumption to talk about selecting pumps, this is not a real project. I will study more about risk analyzing in fire protection systems and I will ask my questions, thanks again for noting the demand problem. I am now more clear about splitting pumps(both pumps are required to meet demand). So I conclude that for normal situations (Not talking about special hazards like airport hangar, ... ) as the first choice I should choose a single diesel pump to supply my total demand, or I can choose a single electric pump to supply my total demand when my power source is 100% reliable ( When I have an alternate independent source of power dedicated to my fire pumps in addition of my normal source of power, Ex. diesel generator). In any case that I have to split my pumps (Which is very rare, may be for very big pumps after underwriters confirmation) I will buy two pumps from one manufacture with the same flow rate, pressure and curve to be able to easily figure out where the pumps settle out on their curves. and regarding time delay, as you explained very nice Richard, as an option, adding sequential start to one of the controllers will minimize time delay which is not that much significant, so paralleling pumps is ok and will not make any problems. Thanks to all for kind answers and sharing valuable experiences, Reza Richard Malek <[EMAIL PROTECTED]> wrote: Reza, Others have commented on your hose stream demand selection, combining deluge and sprinkler demands, etc. I'll just assume your trying to meet x demand with parallel pumps. I'm thinking out loud, so I might not have everything covered, but here's goes.
If you are going to parallel pump (e.g. both pumps are required to meet demand, not simply parallel redundant pumps), I think you have two main issues - pump starting and the combined water supply vs. demand. With regard to pump starting, I see a few options. One, you could start both pumps using the deluge start feature of the controllers. When the deluge valve(s) trip, both pumps start regardless of how they are sized. You could add sequential start to one of the controllers if you want to provide some minimal time delay to avoid simultaneous starting of both pumps. Another option would be to target simultaneous starting by attempting to duplicate low pressure starting configurations - sensing line taps at same location, the same starting pressure, etc. And finally, if the desire is to stagger pump starting pressures (more typical in redundant pump scenarios) and you want to ensure the 2nd pump will start, I would do a supply calculation on the system with the only the lead pump running. See where the pump settles out on its curve (likely pretty far out, but a big lead pump with a very flat curve could hold a more significant system pressure) and what pressure you have at the sensing line tap for the 2nd pump. The starting pressure for the 2nd pump has to be higher than the pressure with the 1st pump running. I don't think this delay or a short delay you add via a deluge start/sequential start combo in the controller is that significant. Theoretically, I think all of these are viable options, but as I said, I'm thinking out loud, so I might not have it all covered. If you would consider utilizing the deluge start, sequential start features, etc. I would always speak with the controller manufacturer or rep to ensure you understand the feature and interaction of such options. On the issue of the two pumps meeting the demand, I see two scenarios. If the pumps are identical, supply to the discharge flanges and piping to a common point of the system are the same, each pump will supply essentially 50% of the demand. You could do some hand calcs to ballpark your pump sizing, etc. However, if you are going to use different pumps (different gpm, pressure, or the same size from different manufacturers - different curves) or the supply/discharge arrangement is different for identical pumps, you would need to develop a combined water supply curve. It would difficult to determine exactly where each pump will settle out on its curve and how much each will contribute to the supply without creating the combined curve (supply) and running a supply calc on the deluge system. Once you know where on the combined supply curve you are operating, you can back out how much each pump is contributing. Any combination where each pump is operating within the 150% of rated max is OK. Well, I hope that helps and if I missed something or I'm off in some way, someone will probably jump in. Rich Richard Malek [EMAIL PROTECTED] -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Reza Esmaeili Sent: Wednesday, September 05, 2007 12:43 PM To: [email protected] Subject: RE: Fire Pump Selection - Another Question According to NFPA answer, you were right Richard, howeever NFPA answer was short for item 3. What I want to ask is simulating a real project like below: Imagine in a factory I want to select fire pump for my below demand: 1- Total demand of deluge system: 1500 GPM 2- Total demand of wet pipe sprinkler system: 700 GPM 3- Total demand of hose streams: 300 GPM. Total water demand: 2500 Gpm, Total pressure: 100 psi For this project as my source of power is reliable, I want select TWO parallel electric pumps with below specifications: Scenario 1: Two pumps( First: 1250Gpm ,100 Psi - Second: 1250 Gpm ,100Psi ) Scenario 2: Two pumps( First: 1500Gpm ,100 Psi - Second: 1000Gpm ,100Psi ) Scenario 3: Two pumps( First: 1500Gpm ,100 Psi - Second: 1500Gpm ,100Psi ) As my deluge demand is 1500 GPM, so which scenario is the best for my project? Note that I want to select one of the above scenarios and don't have any other options. Would you also please analyze each item. Thanks, Reza --------------------------------- Be a better Heartthrob. 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