Home Energy Audit to Evaluate Building Heat Loss or Heat Gain & Choose Heating or Cooling Improvements
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Home Energy Audits help a building owner to Evaluate Building Heat Loss or Heat Gain & Choose Heating or Cooling Improvements
How to measure or calculate heat loss (or gain) in a building
How to measure heat transmission in materials: definition of R-values, U-values, K-values, BTU, calorie, and rates of heat loss or gain
Building design temperatures & how to use a home energy audit or heat loss analysis
What insulation "R" values should be used in a building insulation?
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This article explains how to make best use of a home energy audit to reduce home heating or cooling costs. We provide related insulation and heat loss or heat gain analysis procedures including how to measure or calculate heat loss in a building, defines thermal terms like BTU and calorie, provides measures of heat transmission in materials, gives desired building insulation design data, and shows how
to calculate the heat loss in a building with R values or U values.
Because no amount of insulation can keep a drafty building warm, also review ENERGY SAVINGS PRIORITIES. Also see HEAT LOSS INDICATORS (where is the building losing heat during the heating season, or gaining un-wanted heat during the cooling season), and see HEAT LOSS R U & K VALUE CALCULATION for a guide to calculating heat loss (or gain) rates for buildings and building insulation.
Formula-R™ and Owens Corning™ which may be visible in this photograph of pink Styrofoam™ insulation boards are registered trademarks of Owens Corning® and were photographed at a Home Depot® building supply center.
How to Get the Most Benefit from a Free Home Energy Audit
Many people have heard of using "R" values to describe "how good" a building's insulation is. Here we discuss three
measures of the flow of heat out of or into a building: R-values, K-values, and U-values. Each of these is defined below.
But before moving on to these basic concepts of building heat loss (or gain) theory, it is essential that this still
more basic point be considered:
It doesn't matter much how wonderful the building insulation is, how thick it is, or what the insulating material's
"R" value is (see R defined below) if the building is leaky. If, for example, we're considering an older home with
leaky windows or doors, or if we're considering a tall building with poorly controlled heat in winter, such that
occupants of the upper floors are leaving windows open in winter then the heat flow out of these openings
will be so terrific that the amount of insulation won't matter much.
How to make use of a home energy audit or free home energy use survey
A less precise and less computerized method for calculating building heat loss (or gain) is used
by people who perform an "energy survey" or energy audit for a building. Home energy audit services may be free from your local utility company. The
energy survey technician uses a pre-printed form whereon s/he records the areas of the building's walls, top floor ceilings,
foundation walls, floors, and the number and type of windows and doors.
An "R" value is assigned to these and the sheet
is used to manually calculate the building's rate of heat loss. We had one of these "free" surveys performed on a home built
in 1900 when we were renovating it years ago. Regrettably the surveyor was either poorly trained or simply not very observant.
The free energy audit surveyor rated our building walls at a very high
rate of heat loss by assuming that they were not insulated whatsoever (and then proceeded to try to sell us
an insulation service).
What that particular home energy audit surveyor failed to notice was that the building walls had
been insulated (with blown-in foam) - a condition that was quite easy to see since we had removed the building's exterior
siding and wall sheathing. He just didn't look.
So while home energy audits are a great idea, make sure your auditor is awake
before you believe the results of the home energy survey.
And remember that some "home energy auditors" are really trying to
sell you replacement windows (very long payback time) or building insulation. (Remember the urban legend about the home energy
auditor who was using a camera light meter as an "energy loss" indicator to convince home owners that they needed new windows?)
Using infra-red or thermography to screen buildings for un-wanted heat loss, leaks, or heat gain points
Home energy loss surveys using thermography or simple infra-red thermometers are a great way to pinpoint individual points of
heat loss (or unwanted heat gain) in a building.
In the hands of a properly-trained expert (not a window salesman) this equipment
can help find unexpected building air leaks or heat loss points even when you think that the building has already been insulated.
Having a "high-R" insulated wall or ceiling is not going to be enough to make a building energy efficient if there are many
unidentified air leaks or insulation voids in the building's walls, ceilings, or floors.
What is the Typical Design Temperature for Buildings and Building Insulation?
The "indoor design temperature" for a building refers to the assumed target indoor temperature that the building owner or occupants
want. Typically 70 deg.F. is used unless the owner specifies something different.
The "outdoor design temperature" for a building is (for heating purposes) assumed to be the average lowest recorded temperature
for each month between October and March (the heating season in most climates).
If we are specifying a "design temperature" for
cooling climates we'd use the average outdoor highest recorded temperature during the heating season, perhaps April through September.
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