1. A building characterization apparatus, comprising: baseline data stores, configured to store a plurality of baseline energy use data sets for buildings; a building lag optimizer, configured to receive identifiers for said buildings, and configured to retrieve said plurality of baseline energy use data sets from said baseline data stores for said buildings, and configured to generate energy use data sets for each of said buildings, each of said energy use data sets comprising energy consumption values along with corresponding time and outside temperature values, wherein said energy consumption values within said each of said energy use data sets are shifted by one of a plurality of lag values relative to said corresponding time and outside temperature values, and wherein each of said plurality of lag values is different from other ones of said plurality of lag values, and configured to perform a regression analysis on said each of said energy use data sets to yield corresponding regression model parameters and a corresponding residual, and configured to determine a least valued residual from all residuals yielded, said least valued residual indicating a corresponding energy lag for said each of said buildings, and regression model parameters that correspond to said least valued residual; and a facility processor, coupled to said building lag optimizer, configured, for said each of said buildings, to receive said corresponding energy lag, and configured to categorize said plurality of buildings in types according to similar energy lags.