1. Preliminary Audit: Also known as a simple audit or walk-through audit, it involves a basic review of energy consumption and visual inspection of the facility to identify obvious areas of energy wastage. 2. General Audit: This is a more detailed audit that includes data collection, analysis of energy bills, and identification of energy-saving opportunities. It might involve some on-site measurements and data logging. 3. Investment-Grade Audit: The most comprehensive type, this audit includes detailed analysis, long-term data collection, and financial analysis to support investment decisions in energy-saving projects.