As per the Density/Area Curve and Table 220.127.116.11.2 my total flow requirement is as follows:
Biggest Hazard: Car Park - Ordinary Hazard Group 1 - Area 392m2
As per Figure 18.104.22.168.1 Density/Area Curves - 4.1(mm/min) x 372(m2) =1525.2L/Min =402.92GPM ..(i)
Further, as per table 22.214.171.124.2 Total Combined Inside and Outside Hose - 250GPM ....(ii)
Adding .(i) & (ii)
Total Flow required is = 250 + 402.92 =652.915GPM
Now as per NFPA 20, A.4.9 The performance of the (centrifugal) pump when applied at capacities over 140 percent of rated capacity can be adversely affected by the suction conditions. Application of the pump at capacities less than 90 percent is not recommended.
If I go purely based on the above statement a 500USGPM should be a perfect fit.
But the consultant is forcing to go with a 750GPM pump, if I use a 750GPM pump then how will the pump cater to a flow rate below 90 percent?
Please clear this confusion.