In other words, how would you lower heating and cooling output of your existing AC/Heating?
Doors, windows, and vents are already weatherized, and lighting, electrical Appliances, and plumbing fixtures are at maximum efficiency, and standard r-value insulation is installed around the building exterior walls..
The only issue is how much heat and cool air in the building is escaping through the building walls,floors, and roof.
In most homes, air infiltration is a common problem both in the winter and summer. In addition to the common places such as outside doors and windows, other culprits are chimneys and opening to attic spaces. Pull down stairs for attic spaces is a really big one. All you have to do is take a plastic trash bag and place it horizontally under a pull down stairs and see the result. Conventional doors that lead to stairs and attic spaces are typically no weather stripped and that is also a problem. Chimneys, even those with the dampers closed, are an avenue for a very large amount of heat to escape in the winter.
Large overhangs on exterior walls to keep direct sunlight from the side of buildings is also overlooked in most cases. If you look at many very old houses in the southern US, they have large overhangs or porches on the east and west sides to minimize direct sunlight hitting the walls.
Where buildings have an outside makeup air stream, heat exchangers can be installed to recover some of the interior heat (or cool) from the outside going air.