One of the best investments I made on our house was to replace the standard Essex coolers with high efficiency Breezair units (EXV155). http://www.breezair.com/us/ They are superior in every way with vastly better cooling, quietness, energy efficiency and much less maintenance.

The 4" thick pads are fixed and will last 6-10 years depending on water quality/minerals. A water sensor automatically flushes the unit, keeping the water and pads fresh. In the Grand Junction area when temps hit 100, our house stays a cool 66-70 degrees. The best the old coolers could do was about a 12-16 degree differential, still sweltering at 84-88F.

Our Breezair coolers were about $4400 ea. installed and we got two $500 Xcel rebates. Worth every penny.