looking to buy a submersible pump for a flood cooling system and need to calculate for pump gph and hp. Here are some calcs out of a book but I still have questions. #1 calc. H.P.=gpm x total head in feet / 3960. not sure what gpm i'll need. #2 gpm=.0408 x pipe diameter inches squared x feet per minute water velocity. whats my water velocity gonna need to be? Any comments?