Energy Audit
Bibi Mohanan
July 03, 2013
An
energy audit is an inspection, survey and analysis of energy flows for energy
conservation in a building, processor 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 doors 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 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, both of which are strongly affected
by window construction and quality of door seals such as weather stripping. The
goal of this exercise is to quantify the building's overall thermal
performance. 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. 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 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 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.
Recently,
the improvement of smart phone technology has enabled homeowners to perform
relatively sophisticated energy audits of their own homes. This technique has
been identified as a method to accelerate energy efficiency improvements.
Industrial
energy audits
Increasingly
in the last several decades, industrial energy audits have exploded as the
demand to lower increasingly expensive energy costs and move towards a
sustainable future have made energy audits greatly important. Their importance
is magnified since energy spending is a major expense to industrial companies
(energy spending accounts for ~ 10% of the average manufacturer's expenses).
This growing trend should only continue as energy costs continue to rise.
While
the overall concept is similar to a home or residential energy audit,
industrial energy audits require a different skill set. Weatherproofing and
insulating a house are the main focus of residential energy audits. For industrial
applications, weatherproofing and insulating often are minor concerns. In
industrial energy audits, it is the HVAC, lighting, and production equipment
that use the most energy.
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 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.
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 behavior 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
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 andto 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.[12] 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 and HARMONAC 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.[16]
• 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.
Energy Audit
![Energy Audit]()
Reviewed by Bibi Mohanan
on
July 03, 2013
Rating:
