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How do you heat your house?
This graph below shows what kind of energy people use in their homes in Michigan.*
*Primary
Energy Consumed in Michigan by Source, 1997
Coal, oil and wood all pollute the air when they are burned.
Only
a limited amount of coal, oil and gas exist, so we call them non-renewable
resources. There will never be more of them than there are today. If
we keep using them at the rate we do today, they will eventually run
out.
Oil spills pollute the oceans and kill wildlife.
Wood is a renewable resource. We can always plant more trees. But cutting trees can hurt wildlife.
Plus, can you imagine getting up before school and chopping wood?
Solar energy is clean. There is no smoke or water pollution.
Solar energy is unlimited. It keeps coming every day. Solar energy is FREE!
We all use at least some solar energy to heat our homes. But, some people actively collect, store and move the sun's energy to where they need it.
What does it cost?
The equipment to capture solar energy, store it and move it to where you need it is not free.
Hot air at Impression 5
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Solar
& Transpired Air Collector at Impression 5
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The transpired air collector (image at right) is made up of sheets of corrugated metal, coated with a special paint that absorbs solar radiation and then releases it into the air behind the panel. Why do these panel use special dark paints?
In the summer, which will make you feel cooler, a black t-shirt or a white one?
Light or shiny colors reflect the sun's energy, but dark colors absorb it. That's why the Transpired Air Collector is painted black.
We call the sun's energy radiation. Unfortunately, we also call the heat coming from a fireplace "radiant", but they are two different things. Heat radiating from a fireplace cannot be reflected. A white sock drying in front of a fireplace will get just as hot as a black sock. But, if you put the two socks in the sun, the black sock will get hotter.
When sunlight strikes the black sheet of metal in the Transpired Air Collector, the energy is absorbed. The metal gets hotter and hotter.
Heat moves in four ways:
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Conduction. Did you ever sit on a hot car seat with shorts on? If you did, you will remember that it felt really hot. The heat of the car seat was conducted into the skin of your legs. On the other hand, if you touch a metal playground swing in the winter, the heat from your hands is conducted into the metal. (Don't try this with wet hands!)
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Convection. Did you ever watch a pot of macaroni boiling on the stove? The pieces of macaroni rise to the top then move to the side and fall back to the bottom in a continuous motion. That's convection. The hot water rises, becomes cooler than the water close to the burner and then falls back down.
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Radiation. Think back to that hot car seat in the summer. You don't have to touch it to know that it is hot. The heat is radiating up from the seat and you can feel it from a distance. There is no wind current carrying the heat to your hand—it's radiating.
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Transport. In your house, are there heat registers that hot air blows out of? That hot air is transported to you by a metal duct.
The Transpired Air Collector is perforated—it has little holes in it. The blower inside sucks air through the little holes. That helps draw the heat away from the metal surface and into the building.
Big buildings pull in cold air to add to the warm air already in the building. If they didn't pull in cold air, pretty soon we would be breathing stale air filled with dangerous levels of carbon dioxide, plus bacteria and viruses we have breathed out.
The
Transpired Air Collector preheats fresh air and pushes it into the building.
Because the air is preheated, less fuel is needed to heat it up to room
temperature. That way, Transpired Air Collectors lower heating bills.
The Transpired Air Collector is a fairly low-cost way to collect and
use the sun's energy. This Transpired Air Collector cost $970, plus
$935 to install. How much money will this system save?
We can figure that out after time passes and we compare heating bills from one year to the next. You can see that we also collect information about the temperature of the air outside, the air as it leaves the Transpired Air Collector, and the air in the room. That will help us see how efficient this Transpired Air Collector is.
The common parts of a solar heating system are:
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Collector: Usually a flat metal plate painted a dark color to absorb heat and built into a glass covered-box. Glass lets sunlight enter, but it doesn't let heat out very fast. The amount of sun received is called "insolation". (Get it? It's inSOLation, with the same s-o-l found in the word solar.)
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Transport system: Pipes run through the box. Air in the pipes gets hot and carries the heat into the building.
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Storage: The air passes through a closed container of crushed rocks. Heat is transferred to the rocks. They cool more slowly than air, so in this way the heat is stored. Sometimes on a summer evening you can feel heat radiating from brick walls when the air has already turned cool. Brick and stone let heat travel only slowly. A house made of brick or stone will stay relatively cool during the day. The bricks and stone will give off heat at night, when the air outside is cooler and the heat may be wanted in the house.
Insulation, not insolation, can reduce the loss of heat from the storage tanks. Insulation is any material that slows down the transfer of heat. A good insulator is a non-conductor. Metal is usually a good conductor. That means heat moves rapidly through it. That's why cooking pans are made of metal. Wood and paper are good examples of non-conductors. Materials that are neither good conductor nor good insulators are called semi-conductors. Solar cells are made of semiconductors.
The
Transpired Air Collector gathers the sun's energy and transports it,
but it doesn't store the heat. If it is very warm during the day but
cool at night, the Transpired Air Collector doesn't help at all. It
only brings heat when the sun is shinning. To rely on solar heating,
there must be a way to store the heat. Heating water often does that.
The Transpired Air Collector also helps to reduce heat loss from the side of the building because it creates a "dead air" space between the Transpired Air Collector and the wall. Without the Transpired Air Collector, heat radiates from the wall to the surrounding atmosphere and the heat is swept away by air blowing past the wall. With the Transpired Air Collector, the wall itself is more insulated.
Plus, the Transpired Air Collector has a special coating. Not only does this coating readily absorb heat, but it also does not readily emit heat. That means it does not radiate heat to the surrounding air as well as the plain brick wall.
Click here to see what a typical solar hot air system looks like.
Saving energy—not using it to begin with—is the fastest and least expensive way to reduce the need for oil, coal, or gas. Saving, or conserving, energy is an even better idea than solar energy!
Some scientists think that if we were very careful in our energy use, we could save 40 to 50 percent of the energy we use now! Learn more about the conservation of energy.