It's an old wives tale the 220 cost less to run then 110 volts. It does draw about half as much amperage but uses the same amount of eletricity.
A 220 volt motor also runs cooler and most often last longer.
Have you concidered try to find out why that room is hotter?
Not enough insulation under the floor and in the ceiling, unbalanced HVAC system, old windows, furniture sitting on top of the registers. All simple things to check and cheaper then an A/C and the power to run it.