Water velocity in open systems

[rewatson]

Six cooling towers with a total of 6900 gpm are manifolded to a 18" pipe header and the velocity is 9.9 ft/sec. If we change to a 16" header de velocity will raise to 12.5 ft/sec. It is only occurring less than 1500 hrs per year. The most of the time (at nights) the system will have 1150 gpm and the velocity less than 2 fps.

 

[Yeldud]

From the old Carrier Handbook of AC Design, Part 3, Chapter 2 Table 14, they list a maximum water velocity to minimize erosion of 12 fps at 1500 hr/yr. So you are probably ok, as long as your water is not too nasty. Maybe you could compare heavier wall thickness 16" pipe to cost of standard 18" pipe, to justify heavier pipe or at least heavier elbows and fittings.

 

[lilliput1]

Check available NPSH to the pump suction. Use Carrier pipe friction loss for Open System (much more than that for closed system.