firepump size with standpipes

[coarts]

If a low rise building can be allowed to have a manual standpipe, i.e. calc it with supply by fdc only, but sprinkler system needs a firepump, could you size the pump just for sprinkler demand? This would be a difference between a 200 gpm pump for sprinkler or 1000 gpm pump for 3 standpipes. In other words, if there was no firepump it would be ok with fdc, but if we add a firepump does the standpipe requirements somehow kick in so that it has to be supplied with same min psi and gpm through the automatic supply. It would be combination class 1 standpipes. Thanks for any help.

 

[TravisMack]

I have done several as you mention. We calculate the standpipe system and size the piping based on using the FDC. You need to realize that a manual wet standpipe has a fire pump, it is just located on the responding fire truck.

We then size the fire sprinkler system and pump based on the fire sprinkler demand. It is not uncommon to see a 300-500 gpm pump used in a building like this.

Most of these I have done, we have a 6" FDC and 6" bulk to the split in the standpipe bulk to go up each stair. We also bring in a 6" underground and use a 6" bypass. The fire pump and all valves are sized per NFPA 20. It greatly reduces the costs of installation.

Travis Mack
MFP Design, LLC

 

[SprinklerDesigner2]

So much depends on where you are located. IMO of all the standards NFPA #14 is the one most fiddled with by AHJ's.

Howard County, Maryland for example.

Standpipe Policy: May 24, 2001
Memo to: Sprinkler System Designers / Installers
Fromonald L. Mock, Fire Protection Engineer
Subject: Standpipe Design Criteria

The International Building Code requires standpipe systems to be installed in accordance with NFPA 14. Howard County has adopted by reference the 2000 edition of NFPA 14. Section 5-7 requires a minimum residual pressure of 100 psi at the most remote hose connection. The authority having jurisdiction can allow the residual pressure to be reduced to 65 psi at the most remote hose connection. We will allow standpipe systems to be designed to a minimum residual pressure of 65 psi at the most remote hose connection.

Howard County will also allow the following exception to the minimum residual pressure of 65 psi at the top most hose connection in fully sprinkled buildings when the building does not otherwise require a fire pump to meet the minimum sprinkler system design pressure.

The residual pressure of 65 psi is not required in fully sprinkled buildings where the highest floor level is not more than 75 feet above the lowest level of Fire Department vehicle access. The riser shall be sized so that the Fire Department can supply the minimum 65 psi at the most remote hose connection, based upon an FDC input pressure of 150 psi.

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IMO I like what Howard County did. I could live with that.

Here in Georgia for all buildings you must meet the 100 psi, 65 psi if local AHJ agrees, except in buildings, other than a high rise, where all standpipe piping is 8" in diameter then you don't have to design to anything. When they made everything 8" Georgia did away with allowing manual standpipes but, before this passed, I did a number as you and Travis suggested.

In my view you need to ask the local AHJ some specific questions.... doubt you will find your answer here.

Best of luck.