In my opinion, that is not dual water supplies. If the tank is down your water supply is down. You need one connected to the city and one connected to the tank. Yes. It can be quite tough to balance that calc. I’ve had to put a PRV on the incoming line so as to basically kill most of the supply pressure.
Travis Mack, SET M.E.P.CAD | 181 N. Arroyo Grande Blvd. #105 I Henderson, NV 89074 www.mepcad.com<http://www.mepcad.com/> | m: 480.547.9348 AutoSPRINK | AutoSPRINK FAB | AutoSPRINK RVT | AlarmCAD Book appointment time in my calendar https://calendly.com/t_mack_mepcad ________________________________ From: Micah Davis <[email protected]> Sent: Monday, September 25, 2023 9:17:40 AM To: Discussion list on issues relating to automatic fire sprinklers <[email protected]> Subject: [Sprinklerforum] Re: Standpipe PRV Question Thank you for the response, Steve! Does the redundant fill valves for the tank satisfy the secondary supply requirement of the IBC without an additional tank? I was interpreting the city main connected to the pump as the primary supply and the tank as the secondary supply (or vice versa). If my interpretation is wrong and the tank with redundant fill valves meets BOTH the primary and secondary water supply requirements, I can NOT connect the city water main to the fire pump, and the problem is solved using your method above. Am I tracking correctly? My thought is that if the city main stays connected to the pump and my demand calcs and PRV settings are based on the supply from the tank (which I think is correct), how do we avoid overpressurization with the added pressure from the city? I'm probably overthinking this somewhere! That tends to be my M.O.! Micah Davis Ferguson Fire Design [email protected]<mailto:[email protected]> On Mon, Sep 25, 2023 at 12:02 PM Steve Leyton <[email protected]<mailto:[email protected]>> wrote: Micah: The best way to stabilize the pump discharge pressure and give yourself a (nearly) straight line suction pressure curve is to arrange the required secondary water supply as a break tank. Fill the tank with city water (recommend to manifold at least one automatic plus one manual fill; in my neck of the woods we use two automatic and one manual) and base your calculations on the lowest potential water level in the tank. We simply use the pump’s performance curve as a water supply assuming 0 psi suction head. Depending on water column height, your actual discharge pressure variation will be ≤ 5 psi, unless the tank is uniquely configured and multi-story. The foregoing is my opinion only and does not represent NFPA or the NFPA 14 Technical Committee, nor intended to serve as an interpretation of the standard. Protection Design and Consulting Steve Leyton, President T | 619.255.8964 x 102 | www.protectiondesign.com<http://www.protectiondesign.com/> 2851 Camino Del Rio South | Suite 210 | San Diego, CA 92108 Fire Protection System Design | Consulting | Planning | Training From: Micah Davis <[email protected]<mailto:[email protected]>> Sent: Monday, September 25, 2023 8:55 AM To: SprinklerForum <[email protected]<mailto:[email protected]>> Subject: [Sprinklerforum] Standpipe PRV Question Good morning, Forum! I've got a head-scratcher and am interested in the Forum's collective opinion! Important project parameters are as follows. - 42-story high rise with an automatic standpipe - Seismic Design Category - C - IBC 2018 - Fire pump supplied by city water supply - Secondary supply, as required by IBC 403.3.3, is a tank of adequate size - 305 psi @ 1000 gpm pump sized based on the feed from tank - Direct-acting pressure reducing valves on each floor Here is my issue. If I base my PRV settings on city supply, I cannot get 100 psi at the remote valves when calculating tank as supply. If I base my PRV settings on tank supply, I am over 175 psi discharge on the valve when calculating city as supply. If I try to get my settings using the city as static and the tank as residual pressures, there is no PRV setting that works. I have my opinions about what I think should happen here, but I want to see what the Forum thinks. I will not bother the group with what the design team is suggesting I do. Micah Davis Ferguson Fire Design [email protected]<mailto:[email protected]> _________________________________________________________ SprinklerForum mailing list: https://lists.firesprinkler.org/list/sprinklerforum.lists.firesprinkler.org To unsubscribe send an email to [email protected]<mailto:[email protected]>
_________________________________________________________ SprinklerForum mailing list: https://lists.firesprinkler.org/list/sprinklerforum.lists.firesprinkler.org To unsubscribe send an email to [email protected]
