Developing a simulation model is an added expense and you may need it to provide a demonstrable payback if you’re going to use it as part of your compliance path. It can be well worth the cost, however, especially on larger projects with greater scope. If the scope of the project is larger (>100,000 ft2) and includes a central plant in addition to HVAC distribution and lighting, it can make sense to develop an energy model to assist in system selection and lighting design.