A Las Vegas homeowner might do better with Sam's portable 797895 Arctic
Breeze cooler...
Or a soaker hose on a slab and a solenoid valve from an old washing machine
and a ceiling fan with a room temp thermostat and an occupancy sensor? :-)
Turn on the cooler when the house temp reaches 80 F and turn on the
exhaust fan when the RH reaches 60% to keep the house air at the upper
right corner (80 F and w = 0.012) of the ASHRAE 55-2004 comfort zone.
Herbach and Rademan (800) 848-8001
http://www.herbach.com sell a nice
brass $4.95 Navy surplus humidistat, item number TM89HVC5203, with a
20-80% range, a 3-6% differential, and a 7.5A 125V switch that can be
wired to open or close on humidity rise.
Keeping that house 80 F while evaporating P lb/h of water into C cfm of
outdoor air means 1000P = (91.1-80)(128+C). P = 60C(0.075)(0.012-0.0066)
= 0.0243C makes C = 108 cfm and P = 2.62 lb/h, ie 7.6 gallons per day.
If the house has significant thermal mass (eg a floorslab), we can save
more water and energy by only running the cooler at night.
A 30'x40' 4" slab has at least 4/12x30x40x25 = 10K Btu/F of capacitance,
making RC = C/G = 10K/128 = 78 hours. Outdoor air is about 84 F at night
and 99 F for 12 hours per day in Las Vegas in July. If the slab cools to
to Tmin by dawn and warms to 80 by dusk, 80 = 99+(Tmin-99)e^-12/78, so
Tmin = 77. If 12hx1000P = 12h(84-78.5)(128+C)+(80-77)10K and P = 0.0243C,
C = 170 cfm and P = 4.14 lb/h, ie 6 gpd.
Nick
...a research study initiated by the Office of Arid Lands Studies at
the University of Arizona and the Water Services Department at the City
of Phoenix with funding from the Arizona Department of Water Resources
monitored evaporative coolers at 46 homes in Phoenix. Preliminary data
from this study indicates that water usage... was about 7.6 gallons for
each hour that the cooler was operated (4.4 gallons per hour for systems
without bleed-off and 10.4 gallons per hour for systems with bleedoff.)
from "Evaporative cooler water use" by Martin Karpiscak and
Mary H. Marion at
http://ag.arizona.eduj/pubs/consumer/az9145.pdf