Is it energy efficient to run both units simultaneously? Is there a way where one themostat controls both units? How do you duct it?

Never ever run your AC and Swamp (evaporative) cooler at the same time. Your AC recirculates and cools the air in your home while removing moisture. The Swamp cooler continually brings in outside air through water soaked pads. The influx of air needs a way to escape; ether through a slightly open window or Up-Ducts that puts the cooler air into your atic space. When I added a Swamp cooler to my home, they just cut a hole in the main branch of my duct, and joined the cooler to the duct with a large flex duct. A barometric dampener or a piece of sheet metal that slides in at the base of the cooler will prevent air loss through the cooler when you run the AC. Your AC unit and the Cooler each need their own thermostat. When I installed both AC and a Swamp cooler on my new garage addition, I had a sheet metal shop build a plenum that provides an inlet from the AC and the Cooler, allowing me to use the same duct work for both. They work fine without the need for a separate air handler. The Cooler is designed to work well when the humidity is low. When the dew point gets about 50-55 degrees it is time to switch to AC. I hope this helps. The above info is for a down draft cooler. If you don't want to bother with duct work, a side draft unit mounted outside a window might do the job. Check out Adobe Air -makers of Mastercool.