I suggest you reduce pipe size on the main run to increase pressure and reduce the flow hydraulically.
You should be able to balance flow and pressure with the proper pipe sizes. Art Tiroly ATCO Fire Protection. From: Sprinklerforum [mailto:[email protected]] On Behalf Of Reza Esmaeili Sent: Thursday, February 09, 2017 10:50 AM To: [email protected] Subject: RE: Reducing Sprinklers' Pressure in a Combined Standpipe/Sprinkler System Thanks for your reply Steve. * The local code requires 100gpm@65psi <https://mg.mail.yahoo.com/neo/b/compose?to=100gpm@65psi> for the hydraulically most remote hose connection which are class II 1 1⁄2 in hose stations. Both hose stations and sprinklers are connected to a single wet pipe riser. The pumps should be selected based on sprinklers demand + standpipe demand. The local code ask to simply add 100 gpm to sprinkler demand. For example, if sprinkler demand is 400gpm, just add 100 gpm for standpipe. These 1 1⁄2 in hose stations are not for occupant use and not small hose connections as stated in NFPA 13. Fire fighters in my country use 1 1⁄2 connections, not 2 1⁄2. * The city water main is not able to supply the demand, so a private water tank, located in the basement is supplying both the sprinklers and standpipe. * Travis also suggested using 4.2k sprinklers which is a good idea, but there are some problems. First the water is not clean for such a small orifice. Second 4.2k is not available in our market! * As each sprinkler is covering 130 sq.ft, and the required density is 0.15, so the minimum required flow for each 5.6K sprinkler is 19.5GPM. That is to say 13psi is the minimum pressure at the most remote sprinkler. After installing the restrictor, the minimum pressure is 21psi which is ok. Coming back to the original question: Am I allowed to install a restrictor? For example, if the main sprinkler pipe at each floor is 3", can I install a short 1" pipe just at the beginning to reduce sprinklers pressure? This 0.5m length, 1" pipe can suddenly drop the pressure from 65psi to 30psi. Then the most remote sprinkler pressure at the top floor would be around 20psi which I like. If required, the more I get nearer to the pump located at the basement, I have higher pressure, and I can cut more pressure using this small pipe. For example if the pressure behind the hose station at the ground floor is 110psi, I can use a 2m length, 1" pipe just at the beginning of the pipe supplying the sprinklers to drop the pressure from 110psi to 20psi. Do you see any problems? Best, Reza www.sarian.ir <http://www.sarian.ir> From: Reza Esmaeili [mailto:[email protected]] Sent: Thursday, February 9, 2017 6:29 PM To: '[email protected]' Subject: RE: Reducing Sprinklers' Pressure in a Combined Standpipe/Sprinkler System Hi Craig, Travis, Scot and Tim, Thanks for your replies. I am using Pipenet Spray/Sprinkler software which is mainly a hydraulic colocation software not used in the US. You are right Craig, when less sprinklers are activated, the restrictor can't lessen the pressure, but in this case I have low flow because of less opened sprinklers. Look at the below scenarios. The first scenario is without restrictor and the second and third are with restrictor. If I don't install a restrictor, my sprinkler system demand is 451gpm. But if I install a restrictor, my maximum sprinkler system demand is 314gpm. 1- First scenario: No restrictors, 12 sprinklers activated at the most remote area at the top floor: - The pressure at the beginning of sprinkler piping: 65psi - The pressure just behind the most remote sprinkler: 45psi - Total flow for all 12 open sprinklers: 451gpm 2- Second scenario: 0.5m length, 1” pipe, 12 sprinklers activated at the most remote area at the top floor: - The pressure at the beginning of sprinkler piping: 65psi - The pressure after restrictor: 31psi - The pressure just behind the most remote sprinkler: 21psi - Total flow for all 12 open sprinklers: 314gpm 3- Second scenario: 0.5m length, 1” pipe, 3 sprinklers activated at the most remote area at the top floor: - The pressure at the beginning of sprinkler piping: 67psi - The pressure after restrictor: 61psi - The pressure just behind the most remote sprinkler: 56psi - Total flow for all 3 open sprinklers: 127gpm Best, Reza Cel: +98 9122444875 www.sarian.ir <http://www.sarian.ir/> Here’s a question, are you going to try to reduce the sprinkler system pressure to lessen the flow based on one sprinkler or two or ten flowing? If you base it on ten but only have three flowing, your pressure reduction does not work the same. The sprinkler demand we calc to prove is a product of required pressure and K-factor not provided pressure and K-factor. Your calcs are to prove the system works based on the supply pressure and flow. Every sprinkler system design will typically flow more than what is calculated since we are only proving the supply can meet the minimum design requirements. We calculate a 1500 sq. ft. area and find a required flow and pressure to accomplish that. But when only one or two sprinklers flow and the supply flow and pressure to that system are the same as when we calculated 10 or 12 sprinklers, the discharge from a few will always be more than what is needed. Also, actual flow, even for the entire remote area will be more than the minimum calculated if there was any cushion in your calcs. What calculation software are you using? Basically, calculate what is required for the sprinklers, then calculate the standpipe and do not worry about the overage on the sprinkelrs. Craig L. Prahl Fire Protection Group Lead/SME CH2M 200 Verdae Blvd. Greenville, SC 29607 Direct - 864.920.7540 Fax - 864.920.7129 CH2MHILL Extension 77540 [email protected] <mailto:[email protected]> From: Sprinklerforum [mailto:[email protected]] On Behalf Of Reza Esmaeili Sent: Thursday, February 09, 2017 7:05 AM To: [email protected] <mailto:[email protected]> Subject: Reducing Sprinklers' Pressure in a Combined Standpipe/Sprinkler System [EXTERNAL] Hi forumites, As per NFPA 14, in a combined standpipe/sprinkler system, the minimum pressure at the outlet of most remote 1 1⁄2 in. hose station should be 65psi. As standpipe and sprinkler riser in shared, I want to reduce the pressure to the sprinklers to around 15psi in order to reduce the total sprinklers flow demand and finally to select a smaller fire pump. What is the most cost-effective way to do that? Can I use a restrictor? For example, if the main sprinkler pipe at each floor is 3", can I install a short 1" pipe just at the beginning to reduce sprinklers pressure. Can I do that? I checked this in a hydraulic calculation software and in works fine, but I am not sure if this is a right way. Best, Reza www.sarian.ir <http://www.sarian.ir/>
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