How Does Home Heating & Cooling Affect Your Energy Cost ?
Posted June 14, 2009
As we enter the warmer part of the year in Florida, it is useful to remember that as much as 50% of the energy used
in your home goes to heating and cooling. If you are trying to save money or you're trying to embrace a "greener", or more eco-friendly lifestyle,
do you know enough about the nature of heat transfer to make the right decisions? Let's review the basics of how "heat" works.
Heating and cooling your home are both instances of "heat transfer." First, let's dispense with the notion that heat always rises. That is true
in only one form of heat transfer. In general, heat energy flows in all directions equally. There are three different ways in which heat is transferred;
conduction, convection and radiation.
Conduction is the form of heat transfer through a material, for example, the walls of your home in summer and winter. For any given amount of
in-wall insulation, measured in its R-value, conduction is what accounts for the heat loss (or for cooling, heat-build-up) through the walls and roof.
Convection heat transfer occurs when heat travels in a moving fluid or gas, for example the heat energy that moves
along with the passage of air. The "wind chill factor" you hear about in northern state weather reports
is a measure of how much heat energy is transferred by convection when you're outside due to the effect of wind.
The third form of heat transfer is radiation. Radiation is the transfer of heat energy through empty space, or the way the sun warms the Earth. Radiant heating
is not affected by being in contact with a solid material the way conduction loss does, or by moving along in a fluid or gas the way convection does.
Radiant heat transfer is what warms your home when the sun is out.
You can use your knowledge of these 3 forms of heat transfer to make your home building or remodeling project more energy efficient.
You can reduce the amount of heat build-up or conversely, cooling loss due to conduction through your walls by increasing the R-value of the
insulation in the walls by adding more. Installing double pane windows and sliding glass doors, if your home wasn't built with them originally, will reduce conductive loss of those items. The gases
between the two panes of glass (like argon and krypton) along with films and coatings (like "low-E") can increase the insulating value of your doors and windows from R-2 to R-6 or more.
Caulking or using foam insulation material to seal crevices or openings around doors, windows and electrical outlets will reduce convection heating or cooling loss caused by air infiltration.
Fireplaces are a big source of convective heat transfer as air continuously flows up the chimney if the
flue damper isn't air-tight. If you have, or are planning, on a fireplace put air-tight glass doors in front of it and
keep the flue damper closed when the fireplace is not in use. But, beware, don't forget to open that damper before
your start the fireplace. Just remember to close it again when the fireplace has cooled back down.
Many sources of heat build-up (or cooling loss) are affected by more than one form of heat transfer. Since windows and sliding glass doors suffer from both
conductive and convective heat transfer, consider using high energy-efficiency Energy Star doors and windows for any building or remodeling project.
As another example, while radiant heat transfer is why a home with a roof exposed to the sun gets warmer due to radiation, you can
use convection to your advantage to alleviate part of the problem. Installing a heat-activated fan system in your attic will use convection to blow the heated air
in your attic out through vents preventing it from transferring its heat energy, through conduction and convection, into your living space below.
If your home is in a particularly sunny locale, you may want plant large deciduous trees, such as river birch, on the south side of the home for shade from the sun in the summer. Equally,
you can avoid radiant heat build-up from the sun by closing drapes and blinds on the southern side of your home in the summer, yet take advantage of the sun's radiant heat transfer by
keeping the drapes and blinds open during the day to allow sunlight to enter and warm your home during cooler months.
If it's time to replace your heat pump or any appliance, look for Energy Star-rated appliances.
Energy Star-rated appliances like clothes washers, dryers, refrigerators, dishwashers and dehumidifiers not only use less
electricity; they also transfer less heat into your home through all three forms of heat transfer,
conduction, convection and radiation.
Pay attention to smaller changes that offer big savings, many of which are more efficient because of their lower heat transfers. Use energy-saving
compact fluorescent lamp bulbs. Turn off all lights when not in use; lights generate radiant heat. Keep shrubs and other obstructions from blocking free air flow around
your external heat pump unit which relies upon convection to dissipate its heat build-up. And, change your furnace filter every 3 months. A dirty filter slows down air movement
reducing the effectiveness of the convection heat transfer your air conditioning system relies upon.
Understanding the different kinds of heat transfer and how to use that knowledge to reduce your home's energy consumption can save you a serious amount of money as well as make your home more comfortable to live in.
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