DOE EnergyPlus Modeling Software

EnergyPlus is used by architects and engineers to design more efficient buildings, by researchers to investigate new building and system designs, and by policymakers to develop energy codes and standards. The advanced physics calculations within EnergyPlus allows it to model a wide range of residential and commercial buildings and HVAC system types, including passive building designs and low-energy systems.

The link address is: http://apps1.eere.energy.gov/buildings/energyplus/