An
energy audit is an inspection, survey and analysis of
energyIn physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
flows for
energy conservationEnergy conservation refers to efforts made to reduce energy consumption. Energy conservation can be achieved through increased efficient energy use, in conjunction with decreased energy consumption and/or reduced consumption from conventional energy sources...
in a building, process or system to reduce the amount of energy input into the system without negatively affecting the output(s).
Principle
When the object of study is an occupied building then reducing energy consumption while maintaining or improving human comfort, health and safety are of primary concern. 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.
Home energy audit
A
home energy audit is a service where the energy efficiency of a house is evaluated by a person using professional equipment (such as
blower doorA blower door is a piece of equipment primarily used to measure the airtightness of small to medium size buildings. It can also be used to measure airflow between building zones, to test ductwork airtightness and to help physically locate air leakage sites in the building envelope.There are three...
s and infrared cameras), with the aim to suggest the best ways to improve energy efficiency in heating and cooling the house.
An energy audit of a home may involve recording various characteristics of the
building envelopeThe building envelope is the physical separator between the interior and the exterior environments of a building. Another emerging term is "Building Enclosure". It serves as the outer shell to help maintain the indoor environment and facilitate its climate control...
including the walls, ceilings, floors, doors, windows, and skylights. For each of these components the area and resistance to heat flow (
R-valueThe R-value is a measure of thermal resistance used in the building and construction industry. Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux through it or R = \Delta T/\dot Q_A.The R-value being discussed is the unit thermal resistance...
) is measured or estimated. The leakage rate or infiltration of air through the building envelope is of concern, both of which are strongly affected by window construction and quality of door seals such as weatherstripping. The goal of this exercise is to quantify the building's overall thermal performance. The audit may also assess the
efficiencyEfficient energy use, sometimes simply called energy efficiency, is the goal of efforts to reduce the amount of energy required to provide products and services. For example, insulating a home allows a building to use less heating and cooling energy to achieve and maintain a comfortable temperature...
, physical condition, and programming of
mechanical systemsHVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...
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 orientationSun path refers to the apparent significant seasonal-and-hourly positional changes of the sun as the Earth rotates, and orbits around the sun. The relative position of the sun is a major factor in the heat gain of buildings and in the performance of solar energy systems...
. This could show energy use for a given time period, say a year, and the impact of any suggested improvements per year. The accuracy of energy estimates are greatly improved when the homeowner's billing history is available showing 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 dayHeating degree day is a measurement designed to reflect the demand for energy needed to heat a home or business. It is derived from measurements of outside air temperature. The heating requirements for a given structure at a specific location are considered to be directly proportional to the...
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 often used to identify cost effective ways to improve the comfort and efficiency of buildings. In addition, homes may qualify for energy efficiency grants from central government.
In the United States
In the United States, this kind of service can often be facilitated by:
- Public utility companies, or their energy conservation department.
- Independent, private-sector companies such as energy services company, insulation contractor, or air sealing specialist.
- (US) State energy office.
Utility companies may provide this service, as well as loans and other incentives to insulate. They also often provide incentives to switch, for example, if you are an oil customer considering switching to natural gas.
Where to look for insulation recommendations:
- Local building inspector’s office.
- Local or state building codes.
- US Department of Energy.
- Your local Builders Association (e.g. http://www.ba-ec.com/baec-green-homes.htm How Homes Become Green)
Residential energy auditors are accredited by the Building Performance Institute (BPI) or the Residential Energy Services Network (
RESNETA ResNet , which stands for residential network , is a relatively large local area network or a metropolitan area network provided by a university that serves the personal computers of students in their residence halls or dormitory buildings...
).
[http://www.energy.ca.gov/HERS/index.html]
Nevada will become the first state to mandate residential energy audits at time of re-sale. This new law will go into effect on January 1, 2011.
There are also some simplified tools available, with which a homeowner can quickly assess energy improvement potential (without the use of auditing equipment). Often these are supplied for free by state agencies or local utilities, who produce a report with estimates of usage by device/area (since they have usage information already). Examples include the
Energy Trust of Oregon program and the
Seattle Home Resource Profile. Such programs may also include free compact fluorescent lights.
In Lebanon
Since 2002,
The Lebanese Center for Energy Conservation (LCEC)The Lebanese Center for Energy Conservation a joint project of The United Nations Development Programme and the Lebanese Ministry of Energy and Water...
initiated a nationwide program on energy audits for medium and large consuming facilities. By the end of 2008, LCEC has financed and supervised more than 100 audits.
LCEC launched an energy audit program to assist Lebanese energy consuming tertiary and public buildings and industrial plants in the management of their energy through this program.
The long term objective of LCEC is to create a market for ESCOs, whereby any beneficiary can contact directly a specialized ESCO to conduct an energy audit, implement energy conservation measures and monitor energy saving program according to a standardized energy performance contract.
Currently, LCEC is helping in the funding of the energy audit study and thus is linking both the beneficiary and the energy audit firm. LCEC also targets the creation of a special fund used for the implementation of the energy conservation measures resulting from the study.
LCEC set a minimum standard for the ESCOs qualifications in Lebanon and published a
list of qualified ESCOs on its website.
In Australia
The Australian Government's new Home Insulation Safety Plan was announced on 1 April 2010.
Industrial & agricultural energy audits
Increasingly in the last several decades,
industrialIndustry refers to the production of an economic good or service within an economy.-Industrial sectors:There are four key industrial economic sectors: the primary sector, largely raw material extraction industries such as mining and farming; the secondary sector, involving refining, construction,...
and agricultural energy audits have exploded as the demand to lower increasingly expensive
energyIn physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
costs and move towards a sustainable future have made energy audit greatly important.
Types of energy audit
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.
Numerous audit procedures have been developed for non-residential (tertiary) buildings (ASHRAE; IEA-ECBCS Annex 11; Krarti, 2000). Audit is required to identify the most efficient and cost-effective Energy Conservation Opportunities (ECOs) or Measures (ECMs). Energy conservation opportunities (or measures) can consist in more efficient use or of partial or global replacement of the existing installation.
When looking to the existing audit methodologies developed in IEA-ECBCS Annex 11 , by ASHRAE and by Krarti (2000), it appears that the main issues of an audit process are:
- The analysis of building and utility data, including study of the installed equipment and analysis of energy bills;
- The survey of the real operating conditions;
- The understanding of the building behaviour and of the interactions with weather, occupancy and operating schedules;
- The selection and the evaluation of energy conservation measures;
- The estimation of energy saving potential;
- The identification of customer concerns and needs.
Common types/levels of energy audits are distinguished 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.
Generally, four levels of analysis can be outlined (ASHRAE):
- Level 0 – Benchmarking: This first analysis consists in a preliminary Whole Building Energy Use (WBEU) analysis based on the analysis of the historic utility use and costs and the comparison of the performances of the buildings to those of similar buildings. This benchmarking of the studied installation allows determining if further analysis is required;
- Level I – Walk-through audit: Preliminary analysis made to assess building energy efficiency to identify not only simple and low-cost improvements but also a list of energy conservation measures (ECMs, or energy conservation opportunities, ECOs) to orient the future detailed audit. This inspection is based on visual verifications, study of installed equipment and operating data and detailed analysis of recorded energy consumption collected during the benchmarking phase;
- Level II – Detailed/General energy audit: Based on the results of the pre-audit, this type of energy audit consists in energy use survey in order to provide a comprehensive analysis of the studied installation, a more detailed analysis of the facility, a breakdown of the energy use and a first quantitative evaluation of the ECOs/ECMs selected to correct the defects or improve the existing installation. This level of analysis can involve advanced on-site measurements and sophisticated computer based simulation tools to evaluate precisely the selected energy retrofits;
- Level III – Investment-Grade audit: Detailed Analysis of Capital-Intensive Modifications focusing on potential costly ECOs requiring rigorous engineering study.
Benchmarking
The impossibility of describing all possible situations that might be encountered during an audit means that it is necessary to find a way of describing what constitutes good, average and bad energy performance across a range of situations. The aim of benchmarking is to answer this question. Benchmarking mainly consists in comparing the measured consumption with reference consumption of other similar buildings or generated by simulation tools to identify excessive or unacceptable running costs. As mentioned before, benchmarking is also necessary to identify buildings presenting interesting energy saving potential.
An important issue in benchmarking is the use of performance indexes to characterize the building.
These indexes can be:
- Comfort indexes, comparing the actual comfort conditions to the comfort requirements;
- Energy indexes, consisting in energy demands divided by heated/conditioned area, allowing comparison with reference values of the indexes coming from regulation or similar buildings;
- Energy demands, directly compared to “reference” energy demands generated by means of simulation tools.
Walk-through or preliminary audit
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 covered 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. A list of energy conservation measures(ECMs, or energy conservation opportunities, ECOs) requiring further consideration is also provided.
This level of detail, while not sufficient for reaching a final decision on implementing proposed measure, is adequate to prioritize energy-efficiency projects and to determine the need for a more detailed audit.
General Audit
The general audit (alternatively called a mini-audit, site energy audit or detailed 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
http://www.energylens.com/articles/identify-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.
Investment-grade audit
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 stress 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 expands on the detailed audit described above and relies on a complete engineering study in order to detail technical and economical issues necessary to justify the investment related to the transformations.
Simulation-based energy audit procedure for non-residential buildings
A complete audit procedure, very similar to the ones proposed by ASHRAE and Krarti (2000), has been proposed in the frame of the AUDITAC
http://www.cardiff.ac.uk/archi/research/auditac/ and HARMONAC
http://www.harmonac.info/ projects to help in the implementation of the EPB (“Energy Performance of Buildings”) directive in Europe and to fit to the current European market.
The following procedure proposes to make an intensive use of modern BES tools at each step of the audit process, from benchmarking to detailed audit and financial study:
- Benchmarking stage : While normalization is required to allow comparison between data recorded on the studied installation and reference values deduced from case studies or statistics. The use of simulation models, to perform a code-compliant simulation of the installation under study, allows to assess directly the studied installation, without any normalization needed. Indeed, applying a simulation-based benchmarking tool allows an individual normalization and allows avoiding size and climate normalization.
- Preliminary audit stage: Global monthly consumptions are generally insufficient to allow an accurate understanding of the building’s behaviour. Even if the analysis of the energy bills does not allow identifying with accuracy the different energy consumers present in the facility, the consumption records can be used to calibrate building and system simulation models. To assess the existing system and to simulate correctly the building’s thermal behaviour, the simulation model has to be calibrated on the studied installation. The iterations needed to perform the calibration of the model can also be fully integrated in the audit process and help in identifying required measurements and critical issues.
- Detailed audit stage: At this stage, on-site measurements, sub-metering and monitoring data are used to refine the calibration of the BES tool. 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). When the calibration criteria is satisfied, the savings related to the selected ECOs/ECMs can be quantified.
- Investment-grade audit stage: At this stage, the results provided by the calibrated BES tool can be used to assess the selected ECOs/ECMs and orient the detailed engineering study.
Infrared Thermography Audit
The advent of high resolution thermography has enabled inspectors to identify potential issues within the building envelope by taking a thermal image of the various surfaces of a building. For purposes of an energy audit, the thermographer will analyze the patterns within the surface temperatures to identify heat transfer through convection, radiation, or conduction. It is important to note that the thermography ONLY identifies SURFACE temperatures, and analysis must be applied to determine the reasons for the patterns within the surface temperatures. Thermal analysis of a home generally costs between 300 and 600 dollars.
For those who cannot afford a thermal inspection, it is possible to get a general feel for the heat loss with a non contact infrared thermometer and several sheets of reflective insulation. The method involves measuring the temperatures on the inside surfaces of several exterior walls to establish baseline temperatures. After this, reflective barrier insulation is taped securely to the walls in 8 feet (2.4 m) by 1.5 foot (0.4572 m) strips and the temperatures are measured in the center of the insulated areas at 1 hour intervals for 12 hours (The reflective barrier is pulled away from the wall to measure the temperature in the center of the area which it has covered.). The best manner in which to do this is when the temperature differential (Delta T) between the inside and outside of the structure is at least 40 degrees. A well insulated wall will commonly change approximately 1 degree per hour if the difference between external and internal temperatures is an average of 40 degrees. A poorly insulated wall can drop as much as 10 degrees in an hour.
Pollution Audits
With increases in carbon dioxide emissions or other greenhouse gases, pollution audits are now a prominent factor in most energy audits. Implementing energy efficient technologies help
prevent utility generated pollution.
Online
pollution and emission calculators help approximate the emissions of other prominent air pollutants in addition to carbon dioxide.
Pollution audits generally take electricity and heating fuel consumption numbers over a two year period and provide approximations for carbon dioxide, VOCs, nitrous oxides, carbon monoxide, sulfur dioxide, mercury, cadmium, lead, mercury compounds, cadmium compounds and lead compounds.
History
Energy audits initially became popular in response to the
energy crisisAn energy crisis is any great bottleneck in the supply of energy resources to an economy. In popular literature though, it often refers to one of the energy sources used at a certain time and place, particularly those that supply national electricity grids or serve as fuel for vehicles...
of 1973 and later years. Interest in energy audits has recently increased as a result of growing understanding of human impact upon
global warmingGlobal warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
and
climate changeClimate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
.
Building energy rating systems
- Australia - House Energy Rating
A House Energy Rating is an index of a building's thermal performance for residential homes in Australia....
- Canada - EnerGuide
EnerGuide is the official Government of Canada mark associated with the labelling and rating of the energy consumption or energy efficiency of specific products...
- UK - National Home Energy Rating
The National Home Energy Rating Scheme is both a UK accreditation scheme for energy assessors and a rating scale for the energy efficiency of housing.The NHER is owned and operated by National Energy Services...
- US - Home energy rating
A Home Energy Rating is a measurement of a home’s energy efficiency, used primarily in the United States. Home energy ratings can be used for either existing homes or new homes. A home energy rating of an existing home allows a homeowner to receive a report listing options for upgrading a home’s...
See also
- Home performance
- Efficient energy use
Efficient energy use, sometimes simply called energy efficiency, is the goal of efforts to reduce the amount of energy required to provide products and services. For example, insulating a home allows a building to use less heating and cooling energy to achieve and maintain a comfortable temperature...
- Energy Efficiency Implementation
Energy Efficiency Implementation is an industry comprising firms which retrofit or replace inefficient equipment with more efficient parts or equipment, with the goal of reducing energy consumption....
- Energy recovery
Energy recovery includes any technique or method of minimizing the input of energy to an overall system by the exchange of energy from one sub-system of the overall system with another...
- Pinch analysis
Pinch analysis is a methodology for minimising energy consumption of chemical processes by calculating thermodynamically feasible energy targets and achieving them by optimising heat recovery systems, energy supply methods and process operating conditions...
Further reading
- Wulfinghoff, Donald. (2000). Energy Efficiency Manual. Energy Institute Press. ISBN 0-9657926-7-6
- Clark, William. (1998) Retrofitting for energy conservation. Mc Graw Hill. ISBN 0-07-011920-1
- Thumann, Albert. (1998). Handbook of Energy Audits. Edit. The Fairmont Press. ISBN 0-88173-294-X
- Krarti, M. (2000). Energy audit of building systems: an engineering approach. CRC Press. ISBN 0-84939-587-9
External links