Energy efficiency is defined as the ratio of energy required to perform a specific service to the amount of primary energy used for the process. Improving energy efficiency increases the productivity of basic energy sources by providing given services with less energy resources. For example, space conditioning, lighting or mechanical power can be provided with less input of coal, solar, wind, or uranium in a more energy efficient system. Efficient use of energy is in all countries the most important, economical, prompt, underused, overlooked, and misunderstood way to provide future energy services. If well done, such energy efficiency can displace costly and disagreeable energy supplies, enhance security and prosperity, speed global development, and protect Earth’s climate, not at cost but at a profit.
A large number of surveys carried out revealed that significant amount of energy had been wasted in buildings due to poor design, commissioning, maintenance and operation. It has been well understood that up to 22% of energy savings could be achieved in the building sector in Europe if the economic condition permits. The main actions include the improvement of windows, insulation, heat exchangers, reduction of air and moisture leaks in the building envelope, and appropriate siting in an integrated building design.