physics solar

physics solar

« Previous12345Next »

This is part 2 of a continuation from Your Solar Screens aren't working properly:

Previously we discussed that your solar screen may not be functioning properly and if you want to have the most energy efficient product installed on your windows it is necessary to understand 3 basic principles of physics. Here they are.

1, Heat always seeks a colder atmosphere. This is evidenced by placing a room temperature spoon in a hot cup of coffee. We all know what happens next. The spoon gets warm and where did that heat come from? The heat from the hot cup of coffee sought and found the cooler atmosphere of the metal spoon.

Solarhade screens block, reflect, and absorb heat from the sun and ambient air. This includes the shade cloth and the frames holding the shade cloth. Now the heat is looking for a cooler place to move to. Typically it will be the surrounding ambient air which is cooler than the solar screen and frame. In the case of the shade cloth, assuming the cloth is ¾" - 1" off the glass, the heat dissipates and is assisted through air flow in and out of the open portions of the mesh. The frames are typically installed directly against the window frame and the heat from the frames transfers into the window frame.

Therefore, the most effective place to position the solar screen is on the exterior and ¾" to 1" off the glass. Ideally, the solar screen frames should be separated from the window frame to eliminate this heat also. If you position the solar screen on the interior, it absorbs heat and transfers it into the interior environment to create an uncomfortable space.

2, Dark colored objects absorb more heat than light colored objects. Do you remember back in the first grade when our science studies taught us this principle. What we did was to take two metal trash can lids and paint one white, the other black. We placed them out in the sun for a couple of hours and then went outside to physically check the temperatures. A simple touch of the hand to the lids evidenced that the black trash can lid was much hotter than the white lid. Another good example of this is the comparison between a white painted car vs. a black painted car. You also have the greenhouse effect but that is another discussion.

On the exterior, a darker color is better for solar shade screen products. A dark solar screen will absorb more heat. On the interior, a light colored solar screen is a better choice. A light colored solar screen will reflect some heat and absorb less heat on the interior. So, if you must install interior, light color is the way to go but it is still not as efficient as going on the exterior.

3. Heat always seeks the path of least resistance. When your solar screen absorbs heat like it is designed to do, that heat should be dissipated into the atmosphere. If your screen is too close to the window glass, or touching the glass, that heat will transfer directly into the glass and into the living space. It's just easier for heat to do that particularly since you are typically trying to keep the interior cooler than the exterior. This is a really overlooked principle and I sometimes wonder if it is not intentionally overlooked by manufacturers so they don't have to consider this in their solar heat gain figures. I have even seen tests designed to take advantage of this fact and completely mislead the customer, but that is another solar screen training for another day. Suffice it to say a solar screen will do the job. By properly installing a solar screen you eliminate this problem.

In conclusion, installing a solarshading screen you will keep the heat off the glass to begin with. With a little spacing of the screen from the glass the heat will be dissipated into the atmosphere rather than transferred through the glass. And, by shading the entire window, frame included, the transfer of heat through the window frame is minimized.

Mark is an online entrepreneur. With over 30 years experience in the solar shading business he is well suited to advise you on the best solution for stopping solar heat gain from entering your windows. Mark has advised companies globally on some of the best and most innovative solutions to solving heat gain problems through windows. You can learn about awning and solar screens at http://solarshadescreen.com

Ocean Physics 10 - Solar Radiation