Attention Everybody (and Sean): It is time for us as an industry to move outside the box. Prescriptive codes and standards are convenient, and most AHJ's will defer to them without amendment or interpretation because it's usually not required to do so. But sometimes we have to address situations that ARE subjective and this is one of those - you have to meet with the serving fire department to verify their operational practices and pumping capabilities. Your statement that the pumper is "... sized for 150psi at 1000gpm" isn't accurate; generally, modern pumpers and engines can make up to 300 PSI at either 1,000 or 1,500 GPM so available pressure isn't the issue. Design of the system and identification of the demand are the issues. 150 PSI is an industry practice, not an absolute threshold that can't be crossed and NFPA 14 has a requirement that you must hang a sign on the FDC informing the FD of the required pressure to meet the calculated demand.
As with sprinkler systems, Pressure = $$, so the more you have the smaller the piping can generally be and you save $$. 150 is a safe starting pressure so most FD's will require that you use that as a source pressure; if a manual standpipe system is a little longer or taller and requires more pressure we can make that up by subbing 6" for 4" and it still works at 150. But in taller buildings, you will need more pressure so, if you want to do a 70' tall building with 4" risers all the way up the shafts, then you have to obtain FD approval to pump at 195 or 215 or whatever it turns out to be. And, you have to build the system out of components rated for that pressure, which is actually no big deal these days. And when it's over, you badge the FDC with a sign that states, "PUMP 1000 GPM AT 215 PSI TO MEET DEMAND AT STAIR #2 ROOF" or something like that (your FD will tell you how to word the sign). Partner up people ... The preceding is my opinion only and does not represent the opinion of or an interpretation of the standard by NFPA or the Technical Committee on Standpipes. Steve L. -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of [email protected] Sent: Tuesday, March 22, 2016 8:31 AM To: [email protected] Subject: RE: Standpipe Calc: Adding City Demand to Pumper Truck? Sorry for coming into this a week late. We have recently been dealing with specs and AHJ requirements that state we need to supply 130psi and/or 140psi at the top outlet regardless of whether it is manual or automatic. Same flows as outlined in NFPA 14 (500gpm +250gpm per standpipe up to 1000gpm). The fire pumper truck is still sized for 150psi @ 1000gpm. What do you suggest we do if we can only set the FDC to be the source of 151@0 and 150@1000? Some building are still 70ft tall and the standpipe is still a manual wet. Only accounting for elevation we are looking at 160psi/170psi demand at the FDC. Even if your answer is make it an automatic standpipe, the 140psi requirement limits the "manual" standpipe building height to 23ft when we don't account for friction loss using your calculation procedure. So we can't even meet these manual FDC 150psi calcs on a building that doesn't even need a standpipe. Thanks, Sean VG -----Original Message----- From: Sprinklerforum [mailto:[email protected]] On Behalf Of Steve Leyton Sent: Monday, March 14, 2016 3:57 PM To: [email protected] Subject: RE: Standpipe Calc: Adding City Demand to Pumper Truck? 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 _______________________________________________ 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
