Describes the results of an analysis of energy use in buildings in the commercial sector and discusses the potential for energy conservation. Calculations were made for the effects of various building design variables on annual heating and cooling requirements and the effects of various building energy systems on purchased energy requirements. Heating and cooling requirements are driven primarily by internal loads such as lighting and the heat generated by occupants; heating requirements increase as the area of glass in the building shell is increased whereas cooling requirements in air conditioned buildings are more dependent on the level and schedule of lighting. A comparison of a number of generic building energy systems on a energy use, first cost, and life-cycle cost basis indicates that total energy systems (on-site electricity generation with waste heat utilization) offer significant potential for energy conservation. 205 pp. Ref.