AN energy audit is the key to a systematic approach to decision-making in energy management. The primary function of an energy audit is to identify all the energy streams in a facility to balance total energy input with energy use. While the first article in this series presented the three energy audit levels briefly, Part II will dive into the details and illustrate with examples.
ASHRAE Level 1 —
Walk-through
analysis/preliminary audit
The Level 1 audit is also called a simple audit, screening audit or walk-through audit and is the most basic. It involves minimal interviews with site operating personnel, a brief review of the utility bills of the facility (which can for example be a heating/refrigeration unit, a whole building, factory or hotel) and other operating data, and a walk-through of the facility, all geared toward the identification of glaring areas of energy waste or inefficiency.
The data compiled is then used for the preliminary energy use analysis and a report detailing low-cost/no-cost measures and potential capital improvements for further study.
Typically, a Level 1 audit will only uncover major problem areas. Corrective measures are briefly described, and quick estimates of implementation costs, potential operating cost savings, and simple payback periods are provided. The savings and costs estimates are generally calculated from rule of thumb and prior experiences in similar facilities.
This level of detail, while not sufficient for reaching a final decision on implementing proposed measures, is adequate to prioritise energy efficiency projects and to assess the need for a more detailed audit.
ASHRAE Level 2 —
Energy survey
and analysis
A Level 2 audit begins with the preliminary ASHRAE Level 1 analysis, and goes to more detailed energy calculations and financial analysis of proposed energy efficiency measures.
The financial analysis or life cycle cost analysis provides the facility owner with comprehensive understanding of the financial benefits of implementing specific energy efficiency measures. Utility bills are collected for a 24 to 36 months’ period to allow the auditor to evaluate the facility’s energy/demand rate structures and energy usage profiles.
Figure 1 is a typical outcome from billing analysis.
Equipment details are also collected and sometimes spot measurements of important parameters are taken. Using estimated operation time provided by maintenance and operation staff, the energy consumption by each piece of equipment is calculated and an energy end-use breakdown is developed.
Figure 2 depicts the results of a typical end-use analysis for a hotel.
The next step is to identify all energy conservation measures appropriate for the facility given its operating parameters. A detailed financial analysis is performed for each measure based on implementation cost estimates, site-specific operating cost savings, and the customer’s investment criteria. Sufficient detail is provided to justify project implementation for low cost measures.
ASHRAE Level 3 — Detailed
analysis of capital
intensive modifications
This level of engineering analysis focuses on the potential capital-intensive projects identified in the Level 2 audit and involves more detailed field data gathering as well as a more rigorous engineering analysis. For example, field data such as outdoor temperature are used to establish a statistical model of the system and is used to determine the baseline accurately.
Figure 3 shows a typical statistical model for a refrigerated facility where consumption is plotted against weather data. It reveals that the energy usage of the facility depends on the outdoor temperature.
The above model which is built from data collected for 4-6 weeks is applied to calculate energy consumption baseline extrapolated to a whole year based on weather data for the region.
Level 3 audit also provides detailed project cost and savings calculations with the high level of confidence required for major capital investment decisions. This audit is alternatively called a comprehensive audit, detailed audit, or investment grade audit. It expands on the Level 2 audit by providing a dynamic model of energy use characteristics of the systems under investigation and all energy conservation measures identified.
The simulation model is calibrated using actual measured data to provide a realistic baseline against which to compute operating savings for proposed measures. Extensive attention is given to understanding not only the operating characteristics of all energy consuming systems, but also the situations that cause load profile variations on both an annual and a daily basis.
Completing an energy audit of a facility provides an organisation with customised energy conservation measures designed to ensure significant energy savings as well as CO2 emissions reductions.
The final part of this series on energy audit and energy efficiency will consider a specific case study for the Pacific, and illustrate how the ideas developed above can actually be used to reduce the energy bills of a facility.
* This is the second of a three-part series of articles on Energy Auditing and Energy Efficiency produced by the South Pacific Physics Society (SPPS).
* Soorianam Narsiah is the CEO of the Toronto, Canada-based GoldSun Energy Inc a company specializing in the energy auditing of domestic, commercial and industrial facilities. The views expressed are those of the author and do not reflect the views of the institutions the author is associated with.
