20 TA=93.6'max average temp, Phoenix in May (F)
30 WO=.0045'outdoor humidity ratio
40 TI=80'indoor temp setpoint (F)
50 PWI=EXP(17.863-9621/(460+TI))'wet surface vapor pressure ("Hg)
60 WI=.012'indoor humidity ratio setpoint
70 PAI=29.921/(1+.62198/WI)'indoor air vapor pressure ("Hg)
80 EVAPRATE=.1*(PWI-PAI)'evaporation rate (lb/h-ft^2)
90 EVAPAREA=2*2*4*40'evaporation area (ft^2)
100 P=EVAPRATE*EVAPAREA'indoor water evaporation rate (lb/h)
110 RV=P/(4.5*(WI-WO))'average outdoor ventilation rate (cfm)
120 FANCAP=2*RV'reversible fan capacity (cfm)
130 EFF=.9'air-air heat exchanger effectiveness
140 TV=TA-EFF*(TA-TI)'incoming fresh air temp (F)
150 CCAP=1000*P-1.08*(TV-TI)*RV'sensible cooling capacity (Btu/h)
160 PRINT P,FANCAP,TV,CCAP

water flow fan cap fresh air cooling
(lb/h) (cfm) temp (F) (Btu/h)

30.78896 1824.531 81.36 29449.03

When indoor air rises to 80 F, we might evaporate 30.78 lb/h of water into
slow-moving air from a 1'x2'x4' vertical water sculpture made from 40 2'x4'
4 mm Coroplast sheets with spacers (about $80, including some 3M 4693H glue)
in a folded Coroplast tank with a float valve. Sandwich the sheets together
with vertical corrugations and horizontal spacers and a plastic film manifold
at the bottom, with water flowing out corrugations at the top and running
down both sides. Initial film coverage might improve as mineral films build,
until we clean it by pumping vinegar. Harbor Freight's $5 10 watt fountain
pump can do 1 gpm with a 5' head.

When the indoor RH rises to 56%, we might run Lasko's $53 2155A 2470 cfm 90W
reversible fan with a cycle timer in a wall that divides the house into 2
partitions to make a bidirectional "Shurcliff lung" air-air heat exchanger.
A 40'x60'x8' tall house with 1600' of 6" walls has 800 ft^3 of stud cavities.
If they contain 800 pounds of unfaced fiberglass insulation with a 144 Btu/F
heat capacity and lots of surface and we move 1824 ft^3 of air with 29 Btu/F
through it, the heat capacity ratio is 20%, so we might get 90% effectiveness.

And walls with inflowing air might gain less heat from the outdoors...
http://www.cibse.org/pdfs/8cimbabi.pdf has an equation for the dynamic
metric U-value of a breathing wall, as corrected:

Ud = VRhoaCa/(e^(VRhoaCaRs)-1) W/m^2K, where

V is the air velocity in meters per second,
Rhoa is air density, 1.2 kg/m^3,
Ca is the air's specific heat, 1000 J/(kg-K), and
Rs is the wall's static thermal resistance in m^2-K/W.

Using V = 1/3600 (1 meter per HOUR :-), and Rs = 5.7 m^2K/W (a US R32 wall),
Ud = 0.058 W/m^2, like a US R98 wall. A more typical V = 10 meters per hour
makes Ud = 1.7x10^-8 W/m^2K, like a US wall with an R-value of 334 million :-)

Nick