In mitigating the present day problem of energy and environment, enhancement of energy efficiency is a vital step that has been overlooked by many parties. Increasing the source of energy supply and control of emission are important, but without looking at how energy is utilized, those efforts can be regarded as meaningless. Enhancement of energy efficiency is not a new issue. Nevertheless, awareness on energy efficiency is still lacking in many parts of the world. This book intends to look at only some of the possible aspects of the numerous efforts on energy efficiency. Divided into two sections, the book first delves into pertaining efficient usage of air-conditioning and mechanical ventilation systems in buildings. The later section looks into the use of biomass energy as a potential source of renewable energy, and also issues that may arise when it is used widely one day.