Our most powerful in-house analysis tool, Energy Valuation System (EVS) was developed twenty years ago and is continually refined to keep abreast of technology. The EVS program was developed to provide accurate and reliable comparisons of energy use for buildings or systems operating under various control strategies, mechanical system types, or building envelope options. The EVS has been employed to better understand the dynamics of building operation at other than "design" (extreme) conditions. The greatest efficiency improvement potentials usually occur at "normal" (intermediate) load conditions.