Rallapalli, H. (2010) 16, described that building energy simulation has a significant role not only in making new building design but for the existing buildings evaluations such as the operation , diagnostics, and commissioning that will lead them to energy efficient designs. Building energy simulation can also help facility managers and engineers identify energy saving potentials and evaluate the energy performance and cost- effectiveness of energy saving measures to be implemented. There are many building energy simulation software available nowadays. Some are simplified energy analysis tools that only provide a quick analysis of annual energy use of buildings, but some use more detailed models and run on hourly basis that provide detailed hour-by-hour energy analysis of buildings. No matter which software is used, calibration of simulation models is necessary and crucial for the accuracy and usability of energy simulation. The calibration process compares the results of the simulation with the measured data then tunes the simulation until its results closely match the measured data. Whole building simulation tools are widely used and are applied to the entire building as an integrated system; these take into account all parameters and components together.