Abby Normal wrote:

Sensible heat gain of 10,000 Btu/hr -excludes make up air/infiltration

105F db 65F wb ambient

.... 100(Pw-Pa)/(105-65) = -1 (Bowen, 1926) makes the water vapor pressures
Pw-Pa = 0.4 "Hg, and Pw = e^(17.863-9621/(460+65)) = 0.6296, approximately,
using a Clausius-Clapeyron approximation, so Pa = 0.2296, and the absolute
outdoor humidity ratio wo = 0.62198/(29.921/Pa-1) = 0.00481 pounds of water
per pound of dry air.

maintain it at 80F inside.

.... (105-80)C+10K = 1000P makes P = 0.025C + 10 pounds per hour of water,
since C cfm of airflow moves about C Btu/h-F and evaporating each pound
of water takes about 1000 Btu. With wi = 0.0120 (an efficient corner of
the ASHRAE 55-2004 comfort zone), P = 0.075x60C(wi-wo) = 0.03236C, since
each cubic foot of air weighs about 0.075 pounds and there are 60 minutes
each an hour (want to argue about that? :-) so C = 1360 cfm and P = 44,
ie we evaporate 5.28 gallons per hour of water.

At 80 F, Pw = e^(17.863-9621/(460+80)) = 1.047 "Hg, approximately,
and Pa = 29.921/(1+0.62198/0.0120) = 0.5663, so 44 = 0.1A(Pw-Pa) makes
A = 915 ft^2, ie we might evaporate 44 lb/h of water from a 915 ft^2 damp
80 F floorslab (using an ASHRAE pool formula) with a soaker hose and
a solenoid valve from a dead washing machine and a thermostat that opens
the valve when the room temp rises to 80 F and a 1360 cfm window exhaust
fan with a humidistat that turns it on when the RH rises to 56%, or use
a swamp cooler with perfect controls.

It's more efficient to do this with cool night air, with 1) a damp slab or
2) a perfect swamp cooler and a hollow slab and a separate slab blower...

If we need 10K Btu/h with 105 and 80 F temps and the house conductance
G = 10K/(105-80) = 400 Btu/h-F and the 24-hour average outdoor temp is 95,
we might need 24h(95-80)G = 144K Btu/day of coolth. If it's 90 F for 6
hours per night and we need 144K/6h = 24K Btu/h (2 tons) of cooling with
lots of slab thermal mass, (90-80)C+24K = 1000P makes P = 0.01C+24, and
P = 0.03236C makes C = 1073 cfm and P = 34.7, ie 4.2 gallons per hour.

Nick