An energy audit is an inspection, survey, and analysis of energy flows in a building, process, or system with the objective of understanding the energy dynamics of the system under study. Typically an energy audit is conducted to seek opportunities to reduce the amount of energy input into the system without negatively affecting the output(s). When the object of study is an occupied building, a primary concern is to reduce energy consumption while maintaining or improving human comfort, health, and safety. Beyond simply identifying the sources of energy use, an energy audit seeks to prioritize the energy uses according to the greatest to least cost effective opportunities for energy savings.
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As of the middle of 2007, there was no nationally recognized uniform definition of the term home energy audit. The organization called ResNET is currently investigating this topic and has formed a task force to come up with a working framework. The initial results of the task force have defined a home energy audit as a process (rather than a single event) that includes inspections by qualified personnel and remedies performed by general contractors. The task force is focusing on a health model of the home energy audit process involving periodic checkups, possibly followed by an evaluation, diagnosis, treatment recommendations, and a quality assurance evaluation.
An energy audit of a home may involve recording various characteristics of the building envelope, including the walls, ceilings, floors, doors, windows, and skylights. For each of these components the area and resistance to heat flow (R-value) is measured or estimated. The leakage rate, or infiltration of air through the building envelope, is of concern. This rate is strongly affected by window construction and by the quality of door seals, such as weatherstripping. The goal of this exercise is to quantify the building's overall thermal performance. A simplified approach called the UA delta-T method can be used for good approximate results. The audit may also assess the efficiency, physical condition, and programming of mechanical systems such as the heating, ventilation, air conditioning equipment, and thermostat.
A home energy audit may include a written report estimating energy use given local climate criteria, thermostat settings, roof overhang, and solar orientation. The report might show energy use for a given time period—say a year—and the impact per year of any suggested improvements. The accuracy of energy estimates is greatly improved when the homeowner's billing history is available to show the quantities of electricity, natural gas, fuel oil, or other energy sources consumed over a one- or two-year period.
Some of the greatest effects on energy use are user behavior, climate, and age of the home. An energy audit may therefore include an interview of the homeowners to understand their patterns of use over time. The energy billing history from the local utility company can be calibrated using heating-degree- day and cooling-degree-day data obtained from recent, local weather data in combination with the thermal energy model of the building. Advances in computer-based thermal modeling can take into account many variables affecting energy use.
A home energy audit is a good way to identify the most cost effective ways to improve the comfort of your home and, if upgrades are performed, may qualify your home for a substantial tax credit as provided under the Energy Policy Act of 2005.
Increasingly in the last several decades, industrial and agricultural energy audits have exploded as the demand to lower increasingly expensive energy costs and move toward a sustainable future has made energy audits popular.
The term energy audit is commonly used to describe a broad spectrum of energy studies ranging from a quick walk-through of a facility to identify major problem areas to a comprehensive analysis of the implications of alternative energy efficiency measures sufficient to satisfy the financial criteria of sophisticated investors. Three common audit programs are described in more detail below, although the actual tasks performed and level of effort may vary with the consultant providing services under these broad headings. The only way to ensure that a proposed audit will meet your specific needs is to spell out those requirements in a detailed scope of work. Taking the time to prepare a formal solicitation will also assure the building owner of receiving competitive and comparable proposals.
The preliminary audit (alternatively called a simple audit, screening audit, or walk-through audit) is the simplest and quickest type of audit. It involves minimal interviews with site-operating personnel, a brief review of facility utility bills and other operating data, and a walk-through of the facility to become familiar with the building operation and to identify any glaring areas of energy waste or inefficiency.
Typically, only major problem areas will be uncovered during this type of audit. Corrective measures are briefly described, and quick estimates of implementation cost, potential operating cost savings, and simple payback periods are provided. This level of detail, while not sufficient for reaching a final decision on implementing proposed measures, is adequate to prioritize energy-efficiency projects and to determine the need for a more detailed audit.
The general audit (alternatively called a mini-audit, site energy audit, or complete site energy audit) expands on the preliminary audit described above by collecting more detailed information about facility operation and by performing a more detailed evaluation of energy conservation measures. Utility bills are collected for a 12 to 36 month period to allow the auditor to evaluate the facility's energy/demand rate structures and energy usage profiles. If interval meter data is available, the detailed energy profiles that such data makes possible will typically be analyzed for signs of energy waste. Additional metering of specific energy-consuming systems is often performed to supplement utility data. In-depth interviews with facility operating personnel are conducted to provide a better understanding of major energy-consuming systems and to gain insight into short- and longer-term energy consumption patterns.
This type of audit will be able 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 detailed implementation cost estimates, site-specific operating cost savings, and the customer's investment criteria. Sufficient detail is provided to justify project implementation.
In most corporate settings, upgrades to a facility's energy infrastructure must compete for capital funding with non-energy-related investments. Both energy and non-energy investments are rated on a single set of financial criteria that generally stresses the expected return on investment (ROI). The projected operating savings from the implementation of energy projects must be developed such that they provide a high level of confidence. In fact, investors often demand guaranteed savings.
The investment-grade audit (alternatively called a comprehensive audit, detailed audit, maxi audit, or technical analysis audit) expands on the general audit described above by providing a dynamic model of energy-use characteristics of both the existing facility and all energy-conservation measures identified. The building model is calibrated against actual utility 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 situations that cause load profile variations on short- and longer-term bases (e.g., daily, weekly, monthly, annual). Existing utility data is supplemented with submetering of major energy-consuming systems and monitoring of system operating characteristics.
Energy audits initially became popular in response to the energy crisis of 1973 and later years. Interest in energy audits has recently increased as a result of growing understanding of human impact upon global warming and climate change.