What are the types of Energy Audit?

The type of industrial energy audit conducted depends on the function, size, and type of the industry, the depth to which the energy audit is needed, and the potential and magnitude of energy savings and cost reduction desired. Based on these criteria, an industrial energy audit and its types can be classified into two types: Preliminary Energy Audit (Walk-through Energy Audit) and a Detailed Energy Audit (Diagnostic Energy Audit).

1. Preliminary Energy Audit (Walk-through audit). In a preliminary energy audit, readily-available data are mostly used for a simple analysis of energy use and performance of the plant. This type of audit does not require a lot of measurement and data collection. These audits take a relatively short time and the results are more general, providing common opportunities for energy efficiency. The economic analysis is typically limited to calculation of the simple payback period, or the time required paying back the initial capital investment through realized energy savings. 
2. Detailed Energy Audit (Diagnostic Energy Audit). For detailed (or diagnostic) energy audits, more detailed data and information are required. Measurements and a data inventory are usually conducted and different energy systems (pump, fan, compressed air, steam, process heating, etc.) are assessed in detail. Hence, the time required for this type of audit is longer than that of preliminary audits. The results of these audits are more comprehensive and useful since they give a more accurate picture of the energy performance of the plant and more specific recommendation for improvements. The economic analysis conducted for the efficiency measures recommended typically go beyond the simple payback period and usually include the calculation of an Internal Rate of Return (IRR), Net Present Value (NPV), and often also Life Cycle Cost (LCC).