Depending on the severity of your summers, a whole house fan can work as an efficient pre-cooler before you turn on your AC, or even as your sole source of cooling. Whole house fans us a fraction of the power as your AC. A whole house fan brings in cooler night and/or morning air lowering the inside temperatures. Homeowners living in dry climates with wide day/night temperature swings may be able to do without their AC system by simply switching the fan on during cool hours and then turning off the fan and shutting the house during the hottest times of the day.
Whole house fans are not a complete replacement for air conditioning, they cannot cool inside temps lower than outside temps, nor can they dehumidify. If you live in a humid region, you’ll still need to use your AC in the dog days of summer.