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] From: Sprinklerforum [mailto:[email protected]] On Behalf Of Reza Esmaeili Sent: Thursday, February 09, 2017 7:05 AM To: [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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