Whole house fans can keep you and your household cool, at the fraction at the price of an air conditioning. They also are much more energy-efficient than air conditioning units, and running it during the more temperate seasons can save you a lot on your energy bill. Whole house fans will pull all the hot, stagnant air in your house so that the cool air can enter the house. This means that the temperature inside the house can't get lower than the temperature outside, which is why it's recommended in the more moderate seasons.
While you can save a lot on your energy bill, whole-house fans also need regular maintenance and proper installation. Call the whole house fan pros as Thermodynamics LLC to make sure you're recommended the correct size unit, and that your needs are met.