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Passive solar heating for the rest of us: Smart window treatments

Vertical window blinds from SolarChoice Heat, Chaska, Minn., are said to offer homeowners and business several advantages when it comes to heating and cooling, including cutting heating bills by as much as 35%.

The aluminum blinds, which are 100% recyclable, have a flat black outer surface. Each aluminum blind is encased in a transparent PETG polymer sheath, which is also totally recyclable. When installed on south-facing windows and closed, the sun's radiation is absorbed by the flat black surfaces. Air trapped between the sheath and blind is warmed and rises, escaping at the top. As the air rises, it pulls cool air from near the floor up into the sheath which gets warmed as it travels up and out the blind at about 1.2 m/sec.

In the winter when the sun is low in the sky, the blinds are at their best, providing clean heat. Tests show that air exits the top of the blinds at about 120°F with no fans, heaters, or other power inputs. Thus, each day, the blinds cleanly generate about 5.5 BTUs per square inch. This means a 6×8-ft sliding glass door covered with SmartChoice blinds will put out approximately 40,000 BTUs daily.

In the summer, when the sun is higher in the sky, the blinds do not create nearly as much heat and can be turned 90° to the sun. But closing the blinds provides an insulating R value of 1.7, similar to that of double-pane, gas-filled windows.

There is no maintenance. Cleaning can be done with a damp cloth. The blinds come with several colors on the outside surface, And the SolarChoice blinds mount on existing vertical blind-head rails.

Resources

SolarChoice Heat, www.solarchoiceheat.com

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