Manual Wet Standpipes fed from an undersized fire pump

[robfipro]

Hello

I have a project in which the client wants to use a 750 gpm fire pump to feed a building that is less than 75 feet in height with three standpipes. The standpipe demand would be 1000 gpm for this building. His consultant wants to designate the standpipe system as a “manual wet” type as described in NFPA 14 (2007) 5.2.5

I am somewhat unsure about approaching the design this way. Wouldn’t the fire pump have to be upgraded? Do any of you have experience with a situation like this? Please lend a helping hand.

Thanks in advance for your time and efforts.

 

[skdesigner]

Per NFPA 20, fire pumps must be able to flow at least 150% of rated capacity. For a 750 usgpm pump, this would be 1,125 usgpm.

1000 usgpm standpipe demand would be 133% of rated pump capacity.

 

[cdafd]

calculate as if the pump was not there???

A.5.4.1.1 A fire pump can be installed to supply the sprinkler demand and inside hose requirements only. The fire pump is not required to supply the manual wet standpipe system demand at the most remote hose outlets.

 

[stookeyfpe]

Calculate the pump demand for the sprinkler and let the fire truck make up the hose stream if you are in the US and you have a competent fire department.

 

[DavidCR]

It looks that the building is not little, so don´t go on a risky condition.
"Manual wet" is against the NFPA spirit, ask the AHJ/insurance/? for a special consideration that will stand by itself in the future.
I´d go on the line of skdesigner if the pump has an acceptable design curve. Remember that designing for a point up to 150% of the pump nominal flow is OK with the code (note that the most efficient point of most NFPA20 pumps is around the 140% flow aprox.).