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MADE IN THE SHADE
By Helmut Blum - European Rolling Shutters, San Jose, Calif.
Exterior shading devices work far better than do the interior
kind.
That's important to know if you're attempting to design or build a
house, office or other
structure and you want to keep the occupant's heating and cooling
bills low.
The reason exterior shade devices result in greater energy
efficiency has much to do with
the physics of light.
Sunshine consisting of visible light and, for the most part,
ultraviolet and infrared
light beats down on a dwelling or other structure, which causes
the interior to heat up.
The wavelength of infrared light is relatively long. It's long
enough that it cannot pass
through glass windows. Instead, it stops when it reaches the
glass. The energy contained in that
light then converts to heat, which then dissipates into the
atmosphere.
On the other hand, the wavelength of ultraviolet light is much
shorter and so is able to pass
right on through glass windows. When the ultraviolet light is
stopped by an interior wall or floor,
its energy likewise converts to heat.
But heat is also energy and in longwave form. Because of that, it
cannot easily pass back
out through the glass. It remains mostly trapped in the building's
interior.
COMFORT ZONE
Interestingly, the temperature inside a house seldom ever rises
above 90 degrees
Fahrenheit, even on days when the temperature outside has soared
to 120 degrees.
However, the vast majority of people were they to spend time
inside so warm a house
during the summer would quickly be made very uncomfortable by the
heat. It's been
demonstrated that the average adult feels most comfortable when
the indoor temperature is
somewhere between 60 and 80 degrees.
The most energy-efficient and cost-effective way to achieve that
comfortable interior
temperature range during the summer is by preventing sunlight from
striking the windows at all.
For that purpose, there are three main exterior shading devices.
They are awnings,
sunscreens and rolling shutters.
Each performs differently with regard to sun-blocking.
Awnings. Able to produce an interior temperature drop of 10 to 30
degrees.
Sunscreens. Can pare temperatures by 20 to 30 degrees.
Rolling shutters. Best performers of all. Temperature reductions
of 20 to 40 degrees are
common.
COLD BLOCKER
During winter, the problem is loss of heat energy as a result of
cold wind at night hitting
the windows. Approximately 40% of a building's heat energy is lost
in this manner.
Using double-panel glass in all windows will reduce the energy
loss to just 10%. But,
considering how expensive double-panel glass windows are, that
reduction needs to be lower still
in order to justify the cost.
The to accomplish that is to add rolling shutters to the exterior
side of the glass. The
shutters, when fully deployed, prevent the cold night wind from
ever striking the glass. Thus
blocked, the cold wind cannot contribute to interior heat loss. |
