Attic fan

An attic fan circulates the air. It's especially good at pulling the hottest air (that's risen to the attic) out of the building. This also draws the cooler air up.

A fan uses less power than air conditioning. So for weather that is only a bit too warm, the attic fan can provide enough cooling. When the weather is hotter, or more cooling is desired, the attic fan can make the air conditioning more efficient.