AZGuy wrote:

People who use evap coolers know how much CFM is needed to be
comfortable on a 110 degree day with humidity of 20%.

How much, for a house with a 128 Btu/h-F conductance?

Pa = 0.2e^(17.863-9621/(110+460)) = 0.535 "Hg, so w = 0.62198/(29.921/Pa-1)
= 0.0113. At 80 F and w=0.012, 1000P=(110-80)(128+C) and 60C(0.075)(0.012-w)
= P make C = -142 cfm, so it can't be done. Do people who use evap coolers
know that? :-)

It's easy to see why it can't be done. Air has a specific heat of 0.24
Btu/lb-F. Each pound of air needs sensible cooling from 110 to 80 F,
which takes 0.24(110-80) = 7.2 Btu, but we can only add 0.012-0.0113
= 0.0007 pounds of water per pound of air to raise its humidity ratio
from 0.0113 to 0.012, which only provides 1000x0.0007 = 0.7 Btu of
latent cooling.

But there's still hope for evap cooling with cooler outdoor air at night or
outdoor air that's passed through earthtubes, as well as indirect schemes.

Nick