For about $45 I built a misting system that uses an electronic sprinkler valve controlled by the existing HVAC thermostat.
The water feeds through from an unused hose bib near by into the sprinkler valve.
How cool and and refreshing is this?
The misting system reduces the outside air temperature, in turn reducing the pressure of the whole system, in turn reducing the air conditioner's power consumption 850 watts (or 21%) while it is running its cooling cycle. This results in a 4.8 kWh/day air conditioner energy savings.
I still need to run a soft water line out to the misting system, before the A/C coil is sentenced to a corroded, rusty fate.
Between the A/C trellis shade (1.9 kWh savings), the A/C misting system (4.8 kWh savings) and the attic fan (4.7 kWh savings), our whole house net energy savings is 11.4 kWh/day or a 22% reduction. COOL!
With the energy saved by not using an extra 11.4 kWh/day all summer long, I could drive an electric vehicle 3420 miles, or commute in it to work for 5 months, FOR FREE!
Update 7/27/2011:
I have since plumbed our hose bib to the soft water line. Now the misting system will not corrode the coil nearly as fast; maybe not at all.