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 for inclusion in a baseline model for predicting energy usage in the building by performing statistical hypothesis testing on potential variables; wherein the processing circuit is further configured to apply a regression analysis to the selected set of variables to generate the baseline model for predicting energy usage in the building wherein the processing circuit determines which of energy days and degree days to use in the regression analysis by calculating an enthalpy balance point estimated to minimize energy usage in the building, calculating a temperature balance point estimated to minimize energy usage in the building, calculating a historical energy day value based on the calculated enthalpy balance point, calculating a historical degree day value based on the calculated temperature balance point, and comparing a variance associated with the historical energy day value to a variance associated with the historical degree day value.