Empire state building saves 20% more energy after retrofits

Improving the 6500 windows of the empire state building is expected to save 4.4 million USD in operating costs in the next 3 years. It is such a wonderful example of how retrofitting old buildings can reduce the energy usage of the building. In a similar context even at small homes a big deal of difference can be observed with minor changes like turning to CFL's, using shades, insulating the windows, installing sensors etc. Retrofits can save a lot of energy and the returns are usually fast. In my opinion it is usually more efficient to retrofit a building than to break it down and build a new one.

http://www.huffingtonpost.com/2012/05/08/empire-state-building-makeover-upgrade_n_1497918.html