There are several energy modeling programs available to our industry.  We regularly use two different programs eQUEST and Trane Trace™, depending on the application, both of which are approved by the USGBC for LEED certification.  These programs require detailed input related to building orientation, building location, building materials, systems, hours of operation and location.  The programs use weather data and calculate the heating and cooling requirements and the annual energy usage.  This is an excellent tool to use for comparing multiple building or system alternatives.