For use on HVAC (Heating, Ventilation, Air Conditioning) courses offered in mechanical and some civil engineering departments, this text emphasizes the building envelope aspect of heating and cooling systems as opposed to the mechanical equipment involved, and focuses on design optimization. In view of the importance of energy use for lighting, approaches to energy efficiency are dealt with. It also presents the methods of ASHRAE, explaining the physical principles on which they are based. The emphasis on critical thinking is designed to encourage students to think in context and to ask whether claims and/or results make sense. Numerous examples are presented and solved in a uniform format which students are encouraged to use for homework problems and for calculations encountered in their professional careers.