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Home Energy
Audits
 A home energy
audit is the first step to assess how much energy your home
consumes and to evaluate what measures you can take to make your
home more energy efficient.
An audit will show you problems that
may, when corrected, save you significant amounts of money over
time. During the audit, you can pinpoint where your house is
losing energy. Audits also determine the efficiency of your
home's heating and cooling systems. An audit may also show you
ways to conserve hot water and electricity.
A professional auditor uses a variety of techniques and
equipment to determine the energy efficiency of a structure.
Thorough audits often use equipment such as blower doors, which
measure the extent of leaks in the building envelope, and
infrared cameras, which reveal hard-to-detect areas of air
infiltration and missing insulation.
Preparing for
an Energy Audit
 Before the energy audit of your home, make a list of any
existing problems such as condensation and uncomfortable or
drafty rooms. Have copies or a summary of the home's yearly
energy bills. (Your utility can get these for you.) Auditors use
this information to establish what to look for during the audit.
The auditor first examines the outside of the home to determine
the size of the house and its features (i.e., wall area, number
and size of windows). The auditor then will analyze the
residents' behavior:
- Is anyone
home during working hours?
- What is
the average thermostat setting for summer and winter?
- How many
people live here?
- Is every
room in use?
Your answers may
help uncover some simple ways to reduce your household's energy
consumption. Walk through your home with the auditors as they
work, and ask questions. They may use equipment to detect
sources of energy loss, such as blower doors, infrared cameras,
furnace efficiency meters, and surface thermometers.
Blower Door Tests
Professional
energy auditors use blower door tests to help determine a home's
air tightness.
These are some
reasons for establishing the proper building tightness:
-
Reducing energy consumption due to air leakage
-
Avoiding moisture
condensation problems
-
Avoiding uncomfortable drafts caused by cold air leaking in from the
outdoors
-
Making sure that the home's air quality is not too
contaminated by indoor air pollution.
How They Work
A blower door
is a powerful fan that mounts into the frame of an exterior
door. The fan pulls air out of the house, lowering the air
pressure inside. The higher outside air pressure then flows in
through all unsealed cracks and openings. The auditors may use a
smoke pencil to detect air leaks. These tests determine the air
infiltration rate of a building.
Blower doors
consist of a frame and flexible panel that you can place in a
doorway, a variable-speed fan, a pressure gauge to measure the
pressure differences inside and outside the home, and an airflow
manometer and hoses for measuring airflow.
There are two
types of blower doors: calibrated and uncalibrated. It is
important that auditors use a calibrated door. This type of
blower door has several gauges that measure the amount of air
pulled out of the house by the fan. Uncalibrated blower doors
can only locate leaks in homes. They provide no method for
determining the overall tightness of a building. The calibrated
blower door's data allows the auditor to quantify the amount of
air leakage and the effectiveness of any air-sealing job.
Preparing for
a Blower Door Test
Take the
following steps to prepare your home for a blower door test:
- Close
windows and open interior doors
- Turn down
the thermostats on heaters and water heaters
- Cover
ashes in wood stoves and fireplaces with damp newspapers
- Shut
fireplace dampers, fireplace doors, and wood stove air
intakes.
Energy auditors
may use thermography—or infrared scanning—to detect thermal
defects and air leakage in building envelopes.
How They Work
Thermography
measures surface temperatures by using infrared video and still
cameras. These tools see light that is in the heat spectrum.
Images on the video or film record the temperature variations of
the building's skin, ranging from white for warm regions to
black for cooler areas. The resulting images help the auditor
determine whether insulation is needed. They also serve as a
quality control tool, to ensure that insulation has been
installed correctly.
A thermographic
inspection is either an interior or exterior survey. The energy
auditor decides which method would give the best results under
certain weather conditions. Interior scans are more common,
because warm air escaping from a building does not always move
through the walls in a straight line. Heat loss detected in one
area of the outside wall might originate at some other location
on the inside of the wall. Also, it is harder to detect
temperature differences on the outside surface of the building
during windy weather. Because of this difficulty, interior
surveys are generally more accurate because they benefit from
reduced air movement.
Thermographic
scans are also commonly used with a blower door test running.
The blower door helps exaggerate air leaking through defects in
the building shell. Such air leaks appear as black streaks in
the infrared camera's viewfinder.
Thermography
uses specially designed infrared video or still cameras to make
images (called thermograms) that show surface heat variations.
This technology has a number of applications. Thermograms of
electrical systems can detect abnormally hot electrical
connections or components. Thermograms of mechanical systems can
detect the heat created by excessive friction. Energy auditors
use thermography as a tool to help detect heat losses and air
leakage in building envelopes.
Infrared
scanning allows energy auditors to check the effectiveness of
insulation in a building's construction. The resulting
thermograms help auditors determine whether a building needs
insulation and where in the building it should go. Because wet
insulation conducts heat faster than dry insulation,
thermographic scans of roofs can often detect roof leaks.
In addition to
using thermography during an energy audit, you should have a
scan done before purchasing a house; even new houses can have
defects in their thermal envelopes. You may wish to include a
clause in the contract requiring a thermographic scan of the
house. A thermographic scan performed by a certified technician
is usually accurate enough to use as documentation in court
proceedings.
The energy
auditor may use one of several types of infrared sensing devices
in an on-site inspection. A spot radiometer (also called a point
radiometer) is the simplest. It measures radiation one spot at a
time, with a simple meter reading showing the temperature of a
given spot. The auditor pans the area with the device and notes
the differences in temperature. A thermal line scanner shows
radiant temperature viewed along a line. The thermogram shows
the line scan superimposed over a picture of the panned area.
This process shows temperature variations along the line. The
most accurate thermographic inspection device is a thermal
imaging camera, which produces a 2-dimensional thermal picture
of an area showing heat leakage. Spot radiometers and thermal
line scanners do not provide the necessary detail for a complete
home energy audit. Infrared film used in a conventional camera
is not sensitive enough to detect heat loss.
Preparing for
a Thermographic Inspection
To prepare for
an interior thermal scan, the homeowner should take steps to
ensure an accurate result. This may include moving furniture
away from exterior walls and removing drapes. The most accurate
thermographic images usually occur when there is a large
temperature difference (at least 20°F [14°C]) between inside and
outside air temperatures. In northern states, thermographic
scans are generally done in the winter. In southern states,
however, scans are usually conducted during warm weather with
the air conditioner on. |
