Standpipe retrofit

[fireprotect]

I have been assigned a class II standpipe design for an existing 3 story residential building which will have an additional 4th story. The existing 3 story building has a 2" riser and a 1 ½" Fire hose on each floor. The boiler room and garbage room in the basement are sprinklered (6 sprinkler heads in total). The system is served from a 2" incoming city water without any pump or FDC (A 3 story building does not require a standpipe system according to code). We are looking for the most cost effective design.

The city water test result is: 58 psi static and 54 psi @1200 gpm.
A fire pump is required since required pressure at 1 ½" fire hose is min.65 psi and max 100 psi.

Currently the sprinklers are connected to the main 2" in the basement.

If I don't change this piping and add a new 3” riser for FHC’s on the 4th floor and connect them in the basement, then my pump will serve fire hoses (6x FHC) and 6 sprinkler heads in the basement. Should I size my pump for 100 gpm or should I add sprinklers flow too?

I have done my hydraulic calculation with Hydracalc for standpipe only and have selected my pump for 100 gpm,50 psi (without considering the sprinklers flow.)

Perhaps I can just connect the sprinklers with an alarm check valve to the header before the fire pump, since the city pressure is enough for the sprinklers in the basement.

Please advise me on the best solution.

Thank you.

 

[sfallows]

Another consideration is if the building will be fully sprinkled.

But the volume of the fire pump should be increased even if there is no additional flow.

 

[fireprotect]

The building is not fully sprinklered and it is not required to be, by code.

Perhaps, if I connect the 6 sprinkler heads to the main incoming water with an alarm flow switch, then my pump will just serve the standpipe (fire hose cabinets) and I can keep my pump for 100 gpm (for the standpipe system.