Reza, I like your questions, it's sort of like a quiz and after we've answered, you post the NFPA response as the solution! On the issue of reliability, I think Stewart and others said that there are no absolutes. On the issue of reliability and risk, there often is no clear prescriptive guidance. I have seen a trend toward diesels, but diesels are maintenance intensive and for those owners not committed to the required IT&M and without significant AHJ and/insurer oversight, I don't think it is a slam dunk that the diesel beats the electric even when you consider power reliability. A diesel drive pump and tank arrangement is often considered the gold standard, but what if the water tank or diesel fuel tank is empty?
Many of the sites I've worked with have 2 water supplies. That typically would be an electric drive paired with a diesel on the 2nd supply. The power supply is considered sufficiently reliable for the water supply with the electric drive to be credited as one of two supplies. You wouldn't typically provide 2 electric drives since the goal of the redundant supplies is to provide an improved level of reliability. That improved reliability is enhanced with a diesel drive to address what might be a low probability of loss of power to the electric drive. Also, there are cases where every so many years, electrical equipment maintenance is required which forces a planned shutdown of the electric drive pump. Having a diesel drive leaves that pump unaffected by such maintenance. Where is the electric power considered sufficiently reliable - on site power generation backed up with ties to the local grid is one example from my experience. Depending on plant size, that's 30 - 200 MW in my experience on site with very well developed load shedding plans. Most large industrial sites don't connect to the grid and cross their fingers. Unplanned power outages are very costly (direct costs and the indirect and uninsurable costs of loss of market share, brand damage, etc. when you can't supply customers in a just-in-time business world) and there is a lot of work that goes into the equipment, procedures, etc. to avoid unplanned outages. If there are unavoidable planned or unplanned outages, fire pumps would be a critical load and one of the very last to go. If you have this level of infrastructure, equipment, load shedding plans, etc. you probably have what might be a sufficiently reliable power supply for the electric drive. I have gone the 2 diesel route, but I do often prefer at least one electric drive in the lead position. In a real world large plant environment, fire water supply isn't always 100% static for emergency fire protection supply. You have other demands that might include emergency boiler feed water, emergency chemical process cooling, fire brigade training, filling high pressure wash trucks, etc. You plan for this with appropriately sized jockey/booster pump(s), permitting processes, and system monitoring. However, sometimes, while plant personnel are trying their best to control these other demands, it is not an exact science and you can start the first fire pump. These pumps can be at remote locations within the plant and if you're looking at diesel drive with manual stop, you increase the risk of that pump starting and operating unattended for not an insignficant period of time, which with a diesel, can be a real risk. Electric drive takes most of that away. Add remote start and stop and you have good control and plant personnel aren't spending their time driving all over the site, chasing an inadvertent fire pump start. Hope that helps. Let us know what you end up with for a design. Richard Malek [EMAIL PROTECTED] -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Reza Esmaeili Sent: Tuesday, September 04, 2007 8:14 AM To: [email protected] Subject: RE: Fire Pump Selection - REVISED Thanks Rechard, you are great! As a NFPA member I have asked this question from NFPA-20, I think they will answer in couple of days, I will attach their answer here. I agree with you over item 3-3 which is not reasonable, so you mean if I am even less than 1% unsure about reliability of power source, I am not allowed to use electric pumps (as main without reserved diesel) and should use diesel pumps, right? From your experience, would you please let me know in what kind of industries (May be powerplants,...) or situations we can be sure of 100% reliability of power source to use only electric driven pumps as main? Thanks in advance, Reza Richard Malek <[EMAIL PROTECTED]> wrote: -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Reza Esmaeili Sent: Tuesday, September 04, 2007 3:28 AM To: [email protected] Subject: RE: Fire Pump Selection - REVISED Richard, Many thanks for your great explanation. I think my previous question about selecting of fire pumps was a bit confusing, so I revised it as below. - Actually this is for a big deluge system, not sprinkler system, I mistyped sprinkler system in my previous email. Let me ask my question in another way. I want to asume 3 scenarios for selecting fire pumps for a water demand of 3900 GPM at 90 Psi. 1- Want to be economical and and I don't afford to buy reserve pumps: (is it allowed as per NFPA not to have reserve pumps)? If you are referring to basic NFPA 13, 15, 20, etc. requirements, a reserve pump isn't required although if you have an electric drive without a reliable power source, maybe in that case you could say you need a reserve (i.e. diesel drive) although I wouldn't look at that way. One supply (water supply + pump in this case) is required and satisfy with diesel or electric. I'm not sure if there is an occupancy type NFPA standard that requires a reserve pump (I would doubt it, but I'm not familiar with every NFPA occupancy type standard) 1-1: I have a very reliable power source: I will buy only an electric driven main fire pump 3500GPM at 102 psi working at about 112% of rated capasity ( I won't buy diesel, because I have a reliable power source and also I want to be economical) 1-2:I doN't have a reliable power source: I will buy only a diesel fire pump 3500GPM at 102 psi to work as my main fire pump. 1-1/1-2 sound OK 2- have too much money, I will buy reserve pumps: 2-1: I will buy a main electric pump 3500GPM at 102 psi and a diesel pump 3500GPM at 102 psi and my eletric fire pump would be main pump and diesel pump would be reserve pump which will work at power failure conditions. 2-2: is above arrangement as per NFPA? or I should arrange diesel pump as main? Either is OK per NFPA from my perspective. If you're only concerned about power failure, the diesel drive addresses that and the electric would be unnecessary (diesel is your main AND reserve). If you are looking at reliability more broadly, an electric paired with a diesel probably provides some increase in reliability (diesel addesses power availability and electric addresses the some of the inherent complexity in the diesel drive) 3- Want to be very very economical: I don't want to buy expensive pumps like Pattreson, Peerless, ... who are producing big pumps, I want to be very economical and buy the cheap pumps from my supplier who can't make a 3500 GPM pump, so I have to split the pumps and buy two sets of 1500 GPM at 129 psi working at about 130% or rated capacity. 3-1: I have a very reliable power source: I will buy 2 electric pumps each 1500 GPM at 129 psi working as main pumps. Sounds OK, nothing stops you from using 2 50% pumps in my opinion. 3-2: I doN't have a reliable power source: I will buy 2 diesel pumps each 1500 GPM at 129 psi working as main pumps. Sound OK, 3-3: I am not 100% sure about reliability of power source: I will buy one electric pumps and one diesel pump at the same capacity of 1500 GPM at 129 psi, electric pump will start first and when water demand exceeds than 1500 GPM, then diesel pump will start, this arrangement is because in case of power failure, I can supply at least 50% of water demand to control half of fire. I know this is not logical, but imagine that power failure possibility is less than 1%. Wouldn't agree with your logic here. 50% supply for a deluge system isn't of much use. Particularly with the deluge systems, have to meet or exceed the demand or the protection isn't there. Regarding the 2 pumps, if you're demand is down to 3900 gpm, you could likely make that work with a single 3000 gpm. That's nothing that extraordinary. I would be looking at my estimates for installed cost and life cycle costs as well for a single vs. 2 pumps. I thnk typically the owner would be better off with a single 100% pump vs. 2-50%. Good luck. Would you kindly please analyze these three scenarios and let me know if any of them is aganist NFPA? If you have to choose one economical choice (among item 1) and one non economical choice (among item 2), and one very economical choice (among item 3), which ones you will choose? Many thanks for your kind help in advance. Thank, Reza --------------------------------- Sick sense of humor? Visit Yahoo! 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