Efficiency is legislated for different reasons in different states and provinces. As a result, each administrator is running programs for various purposes and measuring different aspects of efficiency. For example, one state may want to reduce summer peak load, while others want to create jobs or reduce carbon emissions. Evaluation, as a result, uses varying definitions and methodologies. For that reason, it's difficult to point to one comprehensive source of information about evaluation the way you might for accounting. You may find the following documents a helpful overview of energy efficiency program evaluation.
The CEE Principles of Evaluation reflect consensus among CEE members on important principles that, if followed, increase the likelihood that evaluation of energy efficiency programs will be undertaken in a responsible and effective manner. These principles were adopted by the North American Energy Standards Board (NAESB) for further distribution to the regulatory community. They are offered as the perspective of the energy efficiency program industry on evaluation, and are not meant to be a comprehensive, prioritized list.