How Double Glazing Materials Reduce Heat LossHow do double glazing materials prevent heat loss or gain? For particles that are free to move like gases and liquids, heat is speed. Hot particles move faster than slower ones. There's a good experiment to demonstrate this on the
solar energy education 8+
page. That means hot air particles are moving faster than cold ones. I will represent these like this:
The length of the arrow indicates the speed of the particle. The hot particles have longer arrows and so they are going faster. Think of two billiard balls, one still and one moving fast. When the fast moving ball hits the stationary one, the energy is shared between them. This is what is happening on the hot side of the glass. Hot air particles are hitting the glass and the glass is gaining some energy from them. This means the air particles are cooling down. Glass is a solid so the particles in it can't move. Instead they vibrate more the hotter they get. (Aside: If they eventually vibrate enough they break free of the solid and can move, which is what is happening when ice melts.) Let's say it's a cold day and we have the heating on in the house. Hot air particles collide with the glass. When this happens they transfer some of their energy to the glass. So this is what's happening INSIDE THE HOUSE:
So now we have a warm window. The window's heat is pretty much evenly distributed through it. That means that the heated glass is also exposed to the outside. Looking at the particles again, here is the view OUTSIDE THE HOUSE:
The heat from the window is taken by the cold air particles. Since those air particles can move freely, they are swept away and replaced with more cold ones. In effect heat is leaking through the windows and being swept away. This is one reason why the heating needs to be turned on regularly to keep the home at the desired temperature.
Of course, the reverse is true if the house is cool and the outside air is hot; the windows will be letting the heat in. How do Double Glazing Materials Stop This? The two layers of glass between the heat in the house and the cool air outside provide a pocket of air that cannot be swept away by the wind. This air will still heat up as in the single window pane, but since it is not being continuously replaced with cold air it will soon warm up and then take less heat from the first, inner pane of glass. Yes, there will still be heat lost to the outside from the second outer pane of glass. However the warm air between the glass sheets that this outer pane is exposed to is very still and small in quantity, reducing heat loss potential. This is how it looks in picture form:
Vacuum.Clearly a vacuum would be even better insulation than an air layer. However, double glazing materials and workmanship required to produce this vacuum are REALLY expensive. I'll go for the ordinary version when I can afford it, or the do-it-yourself variety. |
