Efficient use of energy is one of the main strategic measures not only for the conservation of fossil energy resources but also for abatement of air pollution and the slowing down of anthropogenic climate change. The requirement of primary energy to cool and to heat buildings is an important part of the overall energy consumption in Western countries, summing up to about 30% of the U.S. and European global energy consumption, due to the increasing use of air conditioning units for cooling residential and office buildings during summer.