How would you increase building interior energy efficiency using the same heating and cooling systems?
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.
The efficiency is related to the heat flux, Q, the higher the flux the more work you have to do heating or cooling. In general the flux is determined by the following equation: Q = (UA)*dT Where A is the area of heat transfer, U is the overall heat transfer coefficient, and dT is the temperature difference in the system and surroundings. Adding insulation adds a resistance to heat transfer in series with whatever already existed, and insulation has a much lower thermal conductivity, so the value of U is decreased, which decreases the heat flux and increases the efficiency.