Two-stage cooling AC units operate at two separate power levels or speeds -- 67 percent or 100 percent. Which speed it operates on depends on the current temperature as compared to the temperature you would like it at. When the ambient temperature is only a few degrees from the temperature desired, the unit will kick on at 67 percent and stay on to maintain the temperature. It runs at 100 percent when the ambient temperature is far from the desired temperature. Because two-stage units do not go through the typical on-off cycle that one-stage units go through, energy efficiency is increased since energy is wasted in starting up.
Two-stage cooling AC units are on or running more often than conventional air conditioners. Because two-stage units keep a steady continuous stream of cooled air pumping, they are on longer but since most often this is at a lower capacity, less power is used.
Two-stage cooling units produce less humidity than one stage. This is because in the second stage, as the cooled air passes through a water-soaked pad, it picks up less water as cool air cannot hold as much moisture as warm air. The resulting air has between 50 and 70 percent humidity which is less than the 80 percent of a conventional one stage system.
Because two stage cooling units operate at a lower capacity the majority of the time, the operating cost is lower than conventional systems. Energy costs for operating a two-stage system are 60 to 75 percent lower than conventional cooling systems, although energy use varies by climate.