Developments in information technology are providing methods to improve current design practices, where uncertainties about various design elements can be simulated and studied from the design inception. Energy and thermal simulations, improved design representations and enhanced collaboration using digital media are increasingly being used. With the expanding interest in energy-efficient building design, whole building energy simulation programs are increasingly employed in the design process to help architects and engineers determine which design strategies save energy and improve building performance. The purpose of this research was to investigate the potential of these programs to perform whole building energy analysis during the early stages of architectural design, and compare the results with the actual building energy performance. The research was conducted by simulating energy usage of a fully functional research laboratory building using two different simulation tools that are aimed for early schematic design. The results were compared with utility data of the building to identify the degree of closeness with which simulation results match the actual energy usage of the building. Results indicate that modeled energy data from one of the software programs was significantly higher than the measured, actual energy usage data, while the results from the second application were comparable, but did not correctly predict monthly energy loads for the building. This suggests that significant deviations may exist between modeled and actual energy consumption for buildings, and more importantly between different simulation software programs. Understanding the limitations and suitability of specific simulation programs is crucial for successful integration of performance simulations with the design process.