This document discusses building simulation tools. It explains that simulation tools can calculate indoor temperatures, heating and cooling needs, HVAC system consumption, natural lighting needs, interior comfort, and ventilation levels. They can also determine appropriate HVAC sizes, predict energy consumption and bills, estimate CO2 emissions, compare efficiency options, and determine payback periods for different options. Common thermal, energy, lighting, and airflow simulation tools are identified. The document outlines the input requirements for simulations and discusses the advantages of being able to analyze performance variables over time and test different scenarios. Potential disadvantages include training requirements, time and cost demands, and difficulty interpreting results. A demonstration of the DesignBuilder tool is presented.