Scot: It is believed where and by whom? 14 is very clear: 7.10.1.3.1.1 states that in combined systems the water supply for sprinklers and an AUTOMATIC standpipe system, “… shall be based on the sprinkler system demand (including any hose stream demand) or the standpipe demand, whichever is greater.” And such a calculation is only required of an automatic standpipe system because a manual is calculated from the FDC and represents a completely separate water supply from the sprinklers.
And not that anyone asked, but let’s also clarify that standpipes are a separate system from sprinklers hydraulically even when they’re combined. We’ve witnessed a robust debate for years about whether standpipe flows should be included in sprinkler calculations as inside hose streams and 7.10.1.3.1.1 adds to the confusion by referencing hose streams in the sprinkler demand. But in order to assess the intent of 13 regarding what to include as a hose stream or not, we turn to 13, particularly 11.1.6.4 and A.11.1.6.4. Taken together, they very clearly inform that in combined systems, the practice is to evaluate the standpipe demand and then the sprinkler demand including hose stream allowances (per 13) in order to determine which is greater, as set forth in 14. And the annex material clearly states that the sprinkler calculations are not required to include an allowance for the standpipe system. Inside hose streams are reserved for hose connections – both 2½” and 1½” - that are directed connected to the sprinkler system per building code or 13, but does NOT include standpipes per 14. In summary, you do your standpipe calc’s (regardless of whether it’s manual or automatic) and then your sprinkler calc’s and that’s that. To Reza’s question: as others have already stated, you have to size your pump for your standpipe demand or sprinkler demand, whichever is greater. I’m sure there’s relatively little cost difference between a pump that is sized for 65 PSI min. at 50 GPM vs. one that might be sized for less pressure (say 50 PSI) at your sprinkler demand if it’s Light or Ordinary Hazard. Both of these scenarios are small pumps. The foregoing is my opinion only and is not intended to represent the NFPA 14 Technical Committee, nor serve as an interpretation of the standard. Steve Leyton Protection Design & Consulting San Diego, CA From: Sprinklerforum [mailto:[email protected]] On Behalf Of å... .... Sent: Thursday, February 09, 2017 6:39 AM To: [email protected] Subject: Reducing Sprinklers' Pressure in a Combined Standpipe/Sprinkler System In a partially sprinklered building, it is believed NFPA 14 would have us calculate both sprinkler and standpipe demands simultaneously. Scot Deal Excelsior Fire & Risk Engineering
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