Why talk about energy design?

A smart energy design aims at creating a comfortable indoor climate, in a way that very little energy is needed to keep a comfortable indoor air temperature. Once the energy demand is reduced, efficient systems for securing the supply of the remaining energy are added to the system – preferably using renewable sources like solar energy to increase the independency on fossil fuels and minimize CO₂ emissions.
This strategy is not only basis for legislation in various European countries and for many architects, it is also a very simple principle everyone will normally apply in every day’s life: In order to keep coffee at a warm temperature it is usually put into a thermos flask (which minimizes the heat loss) rather than put on a heating plate (which would demand continuous heat supply).