1. A computer system for use with a building management system in a building, comprising: a processing circuit configured to use historical data received from the building management system to automatically select a set of variables estimated to be significant to energy usage in the building; wherein the processing circuit is further configured to apply a regression analysis to the selected set of variables to generate a baseline model for predicting energy usage in the building; wherein the processing circuit is configured to calculate enthalpy and to use the calculated enthalpy to calculate heating and cooling energy days; and wherein the processing circuit uses the calculated heating and cooling energy days in the regression analysis rather than degree days.