I know this may seem stupid, but I need to know how thermal energy is transferred in a double glazed window - how does the window keep the heat in the house, and also stop the cold air from getting in etc? I know the air trapped between the 2 panes is for insulation, I also know that the metal is good for radiation and conduction - (am i right?) but can someone explain this in physics. Thanks in advance.
2006-12-12 11:07:31 · 7 answers · asked by Anonymous in Science & Mathematics ➔ Physics
You seem to have answered most of the question already. The three main transfer modes of heat are conduction, convection and radiation.
Conduction losses are due to heat going straight through frames and glass of old windows. The air gap in double glazing is a very good insulator and UPVC frames are also good insulators. This is the main difference and heat saving for double glazing.
Double glazing does not really stop loss due to convection, but it generally fits better than old warped frames, so it cuts out draughts -imagine the cold wind howling through the nooks and crannies of you old window frames!
The 'greenhouse effect' is all about radiation. High frequency, short wavelength rays readily pass through glass (eg UV radiation). When this hits surfaces, they heat up and the UV is converted to infra red. Infra red emissions do not easily pass through glass so in a 'greenhouse' the heat is trapped. Two layers of glass give a better 'greenhouse effect' than one so they help to keep your house warm.
We replaced our double glazing a couple of years ago and we definitely notice the difference - the theory works in practise.
2006-12-13 11:26:39 · answer #1 · answered by Billy 2 · 0⤊ 2⤋
Ok, so... firstly heat transferred by particles: First, galss isn't a great conductor. Heat has to be conducted thought the first pane of glass to get out. Then it gets to the air between the two panes. Air won't reall conduct heat, so the heat has to get across by convection. There isn't a huge space between the two panes so only small convection currents can be set up, once again making heat's journey from the inside to the outside pretty tricky. Then we have another pane of glass so more difficult conduction. That's what makes double-glazed windows better at keeping heat in the house than normal windows where there is only one pane so just conduction.
now, infrared radiation- this doesn't require any particles to be transferred. Infrared radiation can get through (it can even travel through a vaccum which is how it reaches us from the sun). Infrared can penetrate glass and go straight through, there isn't much you can do about that. The glass will basorb some of it (as photons) but not all. Which explains why you can feel heat from the sun through a window.
2006-12-13 11:35:38 · answer #2 · answered by roberta 3 · 0⤊ 0⤋
First of all, Double glazed windows are not much better than normal windows in keeping the heat in a house. You are right that the air pocket between the two panes of glass is for insulation. The metal frame is actually bad, it is a good conductor of heat so it will transfer heat out of a house through the metal frame. The two panes of glass will stop any air leaks trying to get in and out so convection is out of the question (that's heat transfer by air motion) as a side note, glass is one of the worst insulators, and there is nothing that can really be done to make it a good insulator.
2006-12-12 11:18:55 · answer #3 · answered by almost done 2 · 0⤊ 0⤋
Glass is a bad conductor but air is even worse, so essentially you are making a window out of air by double glazing. Also, glass obviously lets energy in the form of light and UV through but reflects quite a lot of infra-red (heat) energy back - that is why greenhouses are so warm. It will only stop the cold air getting in if it is shut... The biggest heat losses in a house are due to the warm air in the house convecting up and out, so the roof is the main problem, double glazing, although 50 % better than normal windows for stopping heat passing through, is generally only worth the money for the noise reduction.
2006-12-14 06:07:13 · answer #4 · answered by may_contain_nuts 2 · 0⤊ 0⤋
How Does Double Glazing Work
2016-09-28 01:22:34 · answer #5 · answered by ? 4 · 0⤊ 0⤋
Hermetically sealed double glass windows are generally used to minimize conduction of heat.
2016-05-23 16:03:38 · answer #6 · answered by ? 4 · 0⤊ 0⤋
as above
2006-12-15 05:01:11 · answer #7 · answered by dream theatre 7 · 0⤊ 1⤋