When sizing a water storage tank for exclusive re protection use, and fed by a re pump, should the tank be sized on 150 of pumps rated capacity !at the re"#d duration$or %ust the re sprinkler demand & inside hose' (ire (ire sprinkler demand & inside hose x duration) tank capacity* capacity* +f u have any dry pipe or preaction system then as per (-. 1/ u have to add the gpm re"uired to ll the systems for your total gpm for the tank* +f you have standpipes per (-. 1, you have to consider the ow2duration for those 3 if it exceeds what the sprinklers re"uire* +t is my opinion that the water tank is to be sized for the greatest demand* +f you have hydrants, that is often your greatest demand* 4econd is usual ly standpipes, followed by sprinklers* +f you have a pump taking suction from the tank, you want to be sure you have enough water in the tank to be able to complete the pump test* ravis, ravis, so what do you think in this case 3 make the tank able to supply /0 minutes at 150 capacity & /0 minutes at 100 capacity and compare that with the sprinkler & hose demand at 60 minutes and see which whi ch is greater' 1500 gpm pump 7 150 ) 8850 gallons 9 /0 minutes ) 6:,500 gallons & 1500 gpm pump 7 100 x /0 minutes ) 5,000 gallons 333333333333333333333333333333333 ) 118,500 gallons
compared to sprinkler demand !& hose stations inside$ ) 1,68 gpm 9 60 minutes ) ;<,580 gallons
=f course the pump test durations were %ust arbitrary 3 not that anyone is going to need the pump running at 150 for /0 minutes to test it*** but it would be embarassing to run out of water for the pump test and the above seems to dictate at least a 100,000 gallon tank*
+#m late to th e party but + have a "uestion> What is the re ow' ravis stated this, but sprinkler demand is not the same as reghting water demand, and that#s the "uestion in my arena* ravis ravis answered it, and the original poster neglected to even raise the "uestion* Without all the facts this is not a simple "uestion* We don#t know if this a community re pump, a building re pump, a campus re pump or what the heck you are trying to protect* ell ell me what is ?exclusive? as you originally asked* 4tookey, pump @ tank are for re sprinklers and inside hose stations3 exclusively* exclusively* o hydrants, no domestic, no nothing 3 but re sprinklers* + don#t see why you would need to run the re pump for /0 minutes at 150 and /0 minutes at 100* +t looks like your sprinkler demand is going to be the driving force* Aoes this tank have an automatic oat for rell* Bou can even use that to reduce the size of the tank if needed* =remus, + stand corrected* + should have read the "uestion more closely* closely* (-. <512<50 <512<50 !protection for power plants$ states that the design water capacity of the system should able to be relled in
When you run your pump test can#t you run your hoses back to the tank so you don#t have to rell the tank after your annual pump test' +#ve done this on a few pro%ects and doing this combined with using a ow meter makes the pump test easy* (-. 88, 0< 1**8 he means to ll the tank shall be sized to ll the tank in a maximum time of < hours* Chevy Why bother with hoses, use a ow meter into the tank and make it easy it is permitted by (-. 85,0< see below* <*/*/ .nnual ests* <*/*/*1*8*8 Dse of the -ump Aischarge via the Eypass (lowmeter to Arain or 4uction Feservoir* -ump suction and discharge pressures and the owmeter measurements shall determine the total pump output* <*/*/*1*/ Where the annual test is conducted periodically in accordance with <*/*/*1*8*/, a test shall be conducted every / years in accordance with <*/*/*1*8*1 or <*/*/*1*8*8 in lieu of th e method described in <*/*/*1*8*/* Gow about a solved example that everyone agrees with ' +f re ows are an issue + could calculate it for my own purposes but would want verication by a -H or (-H before proceeding* .fter reading everything about it + could nd + concluded +4= re ows are an area sprinkler layout technicians aren#t "ualied to navigate* What the heck, a set of plans with I/00 or so on a I10 million pro%ect could save me a lo t of headache down the road so why take the risk' Why the 1500 gpm pump on a pro%ect that re"uires but a /0 minute supply' 4ounds l ight hazard to me unless there are +4= re ows involved* (rom (-. J80 appendix .383/ . stationary pump for re protection should be selected i n the range of operation from ;0 percent to 150 percent of its rated capacity* he performance of the pump when applied at capacities over 10 percent of rated capacity can be adversely aKected by the suction conditions* .pplication of the pump at capacities less than ;0 percent of the rated capacity is not recommended* 4eems a 500 gpm pump would handle anything up to =G8* Ly understanding the correct way is to calculate t otal sprinkler demand plus hose stream allowance for whatever time re"uirement there was* 00 gpm sprinkler & 850 hose ) 650 gpm which would call for a /;,000 gallon water storage regardless of the pump size* -ersonally + like to size the tank for the pump at 150 for whatever time is re"uired* +n the case of a 500 gpm pump + prefer to size the tank at :50 gpm for 60 minut es and provide a 5,000 gallon tank* Come on, the cost diKerence between a /;,000 gallon and 5,000 is very minimal* What are we talking about, I6,000 more on a pro%ect that might be sellign for I10 million' +#ve always been able to oKer it to the owner as an alternate which they always accept when you explain the larger tank would take care of any additions or a density increase should something change down the road* Eut the answer to the "uestion !not addressing +4= re ows$ is sprinkler demand plus inside and outside hose stream allowance if any*
+#m working my way through an automatic ?wet? sprinkler design for an =rdinary Gazard Mroup 8 area* +#m having trouble denitively determining whether to use the pipe schedule method or the hydraulic method !:38*8 @ :38*/ in (-. 1/$ to determine water demand* +t seems to me that sometime in the past + read that the hydraulic m ethod was ?preferred? by most modern designs, but can#t recall the source of that comment* +#ve read and re3read (-. 1/ for clues as well as the (ire -rotection Gandbook from (-., but can#t seem to nd the reference* (or previous designs, +#ve used the Gydraulic Lethod and have spreadsheets already set up to assist me* Eut it seems that the pipe schedule design is a "uicker, ?cook book? design approach* =ne advantage of the Gydraulic method is that the water demand typically appears to be smaller !i*e* lower ow rate$* his can be a bit of a concern in most of my designs, as the areas + deal with don#t typically have access to ?public wat er? and therefore the water must be supplied and ?dedicated? to the re suppression system by the owner of the property* his dedicated water supply costs money so the lower the ow rate, and the lower the total volume, the lower the costs* +#m trying to develop a design guideline for myself !and my company$ so that + don#t have to wrestle through these comments every time + do a sprinkler design !every couple of years it seems$* .ny comments'
+ believe if you read the lat est editions of the Code, only existing -ipe 4chedule 4ystems may be replaced* .ll new must be hydraulically designed2calc#d* We always check over pipe schedule systems with a hydraulic calc to check* +t all depends on the situation which re"uires more water*
hank you for your response* + believe your statement is correct for the Hxtra Gazard =ccupancy* Eelow is text from (-. 1/ 3 1;;; Hdition* Ly interpretation of this is that the -ipe 4chedule method can still be used for new systems of the =rdinary !and Nigh t$ Gazard =ccupancies* + have based all of my designs on the hydraulic method, but was %ust wondering if + couldn#t do it more "uickly by using the pipe schedule method !if the available water supply was suOcient$* :38*8 Water Aemand Fe"uirements P -ipe 4chedule Lethod* :38*8*1 able :38*8*1 shall be used in determining the minimum water supply re"uirements for light and ordinary hazard occupancies protected by systems with pipe sized according to the pipe schedules of 4ection <35* -ressure and ow re"uirements for extra hazard occupancies shall be based on the hydraulic calculat ion methods of :38*/* he pipe schedule method shall be permitted only for new installat ions of 5000 ft8 !65 m8$ or less or for additions or modications to existing pipe schedule systems sized according to the pipe schedules of 4ection <35* able :38*8*1 shall be used in determining the minimum water supply re"uirements* Hxception o* 1> he pipe schedule method shall be permitted for use in systems exceeding 5000 ft8 !65 m8$ where the ows re"uired in able :38*8*1 are available at a minimum residual pressure of 50 psi !/* bar$ at the highest elevation of sprinkler* Hxception o* 8> he pipe schedule method shall be permitted for additions or modications to existing extra hazard pipe schedule systems*
Qust as a note the latest version of (-. 1/ is 8008 Hdition* + %ust read it over and recalled that the local .GQ is the reason we don#t use pipe schedule* he y do not permit it unless replacing existing and even then only i f you can show a redesign to hydraulic would be very diOcult due to pipe locations* Ruote from the (-. 1/ Gandbook> he use of pipe schedule design approaches is restricted to rather small systems, unless high residual pressures are available* While the pipe schedule approach had previously served as an acceptable design option for a wider range of buildings and spaces, it#s misuse has resulted in its restricted application*
(-. 1/, 8008, table 11*8*8*1 for a light hazard re"uires 15 psi at 5003:50 gpm* . light hazard hydraulic system re"uires *1021500 or about 150 gpm plus 100 gpm for (A hose for a total of 850 gpm about 50 less gpm then a pipe schedule system* 4ection 11*8*8*5 re"uires the residual pressure of 50 psi at the highest elevation if the system is larger then 5,000 s"* ft* + think the (-. 1/ committee is saying you can do it but why' 50 psi owing 500 gpm on t op of a /0 foot buildingSS and if the sprinkler system is a local alarm only, the ow is increased to :50 gpm as per section 11*8*8*:* + would think a hydraulic designed system would be much cheaper to install particularly if you have a marginal water supply* With the advent of hydraulic calcul ation programs for re sprinkler systems, pipe schedules are mostly a thing of the past* .ddtionally, + have run into many pipe schedule systems that don#t always calculate out* +f you are concerned about water supply re"uirements, you can calculate the system using "uick response sprinklers !light and ordinary hazard wet pipe systems$and reduce the design area as long as the ceiling or roof deck !if exposed$ is less than 80#* Bou can get between a 0 and 60 reduction in the design area* + have not done a pipe schedule system in probably the last 10 years, and + do re sprinkler systems every day* + hope this is helpful* +f you have any further "uestions, please feel free to email me*
Gydraulic calculations and systems designed with hydraulic calculations re"uire an understanding of the eKects the layout can have on the demand* . poorly designed system can have a higher demand than a pipe schedule system* +#ve noticed with some of our newer designers that they don#t necessarily understand the eKect balance can have on their demand as the software is doing the work for them* Bou are correct on that one* + remember being re"uired to calculate tree systems by hand when + rst started* We had the computer programs to do it, but the lead engineer wanted to make sure + understood what the computer was doing with the calculations* hat was one of the best lessons + was given in the re sprinkler industry* =nce you understand how it works you start to lay your systems out so that they balance* +t#s really fun with some of the programs available now* Bou can try diKerent sprinklers, diKerent pipe, diKerent areas* Linutes to do what once took days* Bou can play with a pipe sizes, hit the button, and get instant feedback* Aon#t like the results %ust undo it* echnology, my favorite tool*
