Energy consumption to provide thermal comfort conditions, especially in hot and humid areas is tremendous. Ways to reduce and save energy are indeed possible and needed. Simulation of HVAC energy consumption in buildings is of considerable interest and benefit for engineers and architects. Energy simulation programs can be used to analyze cost effective energy conservation measures before the building is built or modified. There are both open type simulation programs and proprietary programs. The main components of an open type simulation program ar e presented, and its development is reviewed. Some of the difficulties encountered by first users of these programs are pinpointed with some suggested remedies. An annual weather data file for Jeddah, Saudi Arabia, was prepared. A three story, three zone typical school in Jeddah is considered. Building loads analysis and system thermodynamics input and output files are generated to show the capabilities of the program. Three case studies were considered.