I am evaluating an existing pipe schedule system that was installed in 1961 in an old house. It is now used as a business-type occupancy and the AHJ has asked that the system be evaluated to the current (1999) edition of NFPA 13. In addition to evaluating the available flow and pressure against the requirements of Table 7-2.2.1 for pipe schedule systems, I set up a hydraulic calc for the upper floor and found that while Table 7-2.2.1 was met, the system fell 132 psi above the water supply curve. Ouch! And I didn't even have enough floor area to get to 1950 square feet for this dry-pipe system, even assuming the combustible concealed spaces meet the limits that would make me go to a 3000 sq. ft. area. Section 7-2.2 says to take the residual pressure at the flow in Table 7-2.2.1 and subtract the elevation head of the highest sprinkler. Is my interpretation correct? Is this unusual for a pipe schedule system? I see that in light hazard up to 30 heads may be fed from a 2.5" pipe, but at 7 psi each that's over 450 gpm. In my building there are a lot of extra elbows and fairly long runs of 2.5", but I'm still taken aback by the results of my calc. Thanks in advance, Eric J. Shelton, PE Senior Fire Protection Engineer
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