5.2. Define the Energy Audit

There is no one agreed upon set of definitions for the various levels of facility and system energy audits. The terms preliminary audit and detailed audit refer to the level of detail with which the audit is concerned. 

Level of detail considered is the first significant measure of an audit.  The second significant measure of an audit is the physical extent or scope with which it is concerned.  By physical extent we mean the size of the system in terms of the number of sub-systems and components that comprise it.

• The Preliminary Audit starts at a relatively high level in the structure of energy consuming systems—perhaps the entire site or facility—and addresses a level of detail that permits at minimum the identification of areas of the building that potentially may yield energy management opportunities; preliminary audits have broad physical extent and lower level of detail.  

• The Detailed Audit begins where the preliminary audit ends and works through analysis to greater levels of detail; the focus of a detailed audit might be the entire building if that is warranted by the findings of the walk-through, a specific energy consuming system such as building lighting, or an individual piece of equipment such as a chiller.

Generally, as the level of detail of the audit increases, the physical extent would decrease.  The opposite is also true; if the extent were increase the level of detail of the analysis would tend to decrease. The potential energy efficiency savings will then be described or calculated and a report prepared explaining recommendations and next steps.

5.2.1.   Information required before the site visit

The auditor needs to obtain some data from the facility prior to the site visit.  As a minimum, it is suggested that this include:

• Historical energy and water consumption and billings data for at least 12 months, preferably multi-year;
• Facility layout, building configuration information, including at least conditioned floor area;  
• Building schedule, operating hours and occupancy data; 
• Breakdown of building uses by area (i.e. general office, computer facilities, library, cafeteria, etc.) ;
• Any other energy assessment data that may be available, including demand profiles, equipment inventories, etc.  
• Degree-day information applicable to the building location.

5.2.2.   The Client Meeting

It is important to have a clear understanding between the auditor and the client before the work is undertaken.  This understanding may include:

• the cost of the audit, both for the preliminary audit and the detailed assessment, and how that cost will be paid;
• commitment to proceed on the implementation of measures that are shown to have a favorable business case;
• the initial schedule for the preliminary audit and reporting milestones;   points of contact between the auditor and the organization.

5.2.3.   Historical data analysis before the site visit

Energy management practitioners may have typical average energy intensities (energy consumed per unit floor area) for buildings; however, a more thorough assessment of the impact of variables such as occupancy rates and, in particular, weather can be done fairly easily using linear regression analysis. 

The purpose of this analysis is to determine a functional relationship (i.e. a mathematical statement) between energy consumed and weather.  The impact of weather is expressed in terms of heating degree days (HDD) or cooling degree days (CDD).  These factors quantify the difference between the average ambient temperature per day and a specified base temperature (usually 18^oC for HDD and 22^oC for CDD).  For example, the number of cooling degree-days in one 24-hour period is the difference between the average daily temperature for that day and 22^oC.

As we shall see later in this course, energy can be related to weather by an expression similar to the following:

Energy consumed = non-space conditioning energy (e.g. for domestic hot water) + space conditioning incremental energy factor x HDD or CDD.