ASHRAE (American Society of Heating, Refrigeration and Air-conditioning Engineers) defines best practices for energy audits and assessments. As per ASHRAE standards, there are three types of energy audit as given below.

ASHRAE Level 1: Walkthrough/ Preliminary Audit

Level 1 audit involves an analysis of historical energy use, a review of energy bills, operating data, discussion with plant personnel and a walkthrough of the facility. This helps to identify a few areas where there is a potential for energy savings. The energy consumption pattern is typically benchmarked against a similar type of facility to determine potential capital improvements for further assessment. The preliminary audit helps to plan a detailed study of the facility and gives an idea of the possible energy conservation measures which can be implemented.

ASHRAE Level 2: Energy Survey and Analysis

Level 2 audit includes Level 1 practices and procedures but also includes a more detailed evaluation of system/process and cost-benefit analysis of the proposed energy conservation measures. The cost-benefit analysis of the proposed energy conservation measures helps the client to have an idea about the return of investment. Sufficient details are provided to justify the proposed energy efficiency projects.

ASHRAE Level 3: Detailed Analysis of Capital Intensive Modifications

Level 3 audit focuses an on analysis of potential capital intensive projects identified in the ASHRAE Level 2 Audit. There is a more detailed field study which will be a long term study of the facility to gather more data.  Long term trend data of systems installed in the facility is collected or recorded for detailed analysis and identification of energy conservation opportunities. Detailed analysis of the installed systems in the facility helps to understand the operating efficiency/performance of various installations. The cost-benefit analysis will be more detailed and more accurate since the analysis is based on large data recorded or collected from the plant.