Tony: You (or the submitter) are over-simplifying what the annex says. It's not the intent that you take the city flow test and add it to the pumper curve. NFPA 1901 sets the basic performance curve for a pumper at 150 PSI/1,000 GPM. NFPA 13E is the standard for FD Operations for buildings equipped with sprinklers and standpipes - that standard goes into the company engineer's procedure for calculating the discharge pressure of the pump based on suction pressure, friction loss in hose and other variables. But the bottom line is that it's all targeted at discharging 150 PSI residual at 1,000 GPM. This has NOTHING to do with pressure at the FDC; it has to do with calculating the performance of the apparatus. What gets to the FDC is up to the engineer.
Which is why 7.7.4 states, "When the system demand to be supplied by the fire department at the fire department connection is being determined, the local fire department shall be consulted regarding the water supply available from a fire department pumper." FROM A FIRE DEPARTMENT PUMPER. It's up to the incident commander and his or her engineer to determine the suction pressure and set their discharge to whatever is required to make their programmed starting pressure. And based on the nationwide standard and best practices, that is almost certain to be 150 PSI at the prescribed flow rate. The engineer will calculate the friction loss in the discharge hose that's connected to the building. If you are reviewing plans that show 150 PSI residual plus a positive suction head at that flow rate as the inlet pressure, then that is almost certainly not correct. To answer your question, if I have a building with two (750 GPM) or three or more (1,000 GPM) standpipes, we plug in a "flow test" static pressure of 151 PSI and a residual of 150 PSI at the target flow rate and we run the calc' using the FDC as the "city connection". We plug in a 500 PSI hose stream allowance at the most remote standpipe outlets and at 250 GPM hose streams at those points in the bulk main system where the other risers take off. We allow 5 PSI for loss in a standard hose valve so the minimum pressure at any node is 105 PSI. The foregoing is my opinion only and does not represent the opinion of or any manner of interpretation by NFPA or the Technical Committee on Standpipes. Steve Leyton -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of Tony Eggster Sent: Monday, March 14, 2016 3:24 PM To: [email protected] Subject: Standpipe Calc: Adding City Demand to Pumper Truck? Quick question: I'm reviewing some plans for a manual class I standpipe and the designer added the city flow test to the usual 1000gpm fire pumper curve in order to keep all the pipe down to 4". I see in the NFPA 14 appendix that you can do this but personally I've always just calculated solely to the pumper curve. How do you guys do it? Also, I'm assuming that if you do factor in city supply wouldn't that frequently require high pressure pipe and fittings depending on city supply psi? _TONY _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
