Uncertainty of 'measured' energy savings from statistical baseline models

Baseline models are a crucial element in determining savings from energy conserving measures. The baseline model is obtained by regressing the energy consumption data for the period prior to the implementation of the energy conservation measures. The widely used criteria for determining adequacy of a particular baseline model is based on statistical cutoff criteria that do not give the user a knowledge of the error inherent in the savings determination. The absolute cutoff criteria may not be appropriate since baseline model development is not the desired end. It is proposed that models be evaluated in terms of the ratio of the expected uncertainty in the savings to the total savings (ΔE _save/E _save). This physically and financially intuitive measure permits the user to vary the criteria according to factors most relevant for a particular energy conservation project. Simplified expressions for (ΔE _save/E _save) appropriate for use by practitioners as applicable for cases with uncorrelated data and for use with correlated time series data are developed and discussed in the context of case-study data. The use of this concept to logically select the most appropriate measurement and verification protocol to verify savings is also described.