If heat from the sun travels millions of miles through the vacuum of space, why does the vac between 2 panes..

Question

of glass stop 95% of the heat? And how does it work even with no coloring or mirroring embedded in the glass?

Thanks!

Answer 1

First, heat is an "energy transferred from one body or system to another due to a difference in temperature".

Heat is transmitted either by:

- radiation.

- convection (extremely limited).

- conduction (very limited as space is a near-vaccuum).

The heat radiated from the sun we receive is mostly in the form of infrared which has a wavelength which can typically transmit energy to molecules. Infrared accounts typically for 50% of the heat we receive on earth.

First some of this (all wavelength) we receive is reflected to space (30%). A further part (mostly IR) is absorbed an/ord scattered by greenhouse gases and clouds which make for a higher and more even average temperature (day/night difference).

The result is a limited direct solar radiation.

Whether it is a cloudy or sunny day has an importance as the direct radiation is not the same.

When passing the window, some radiation will be refracted, some other reflected

http://en.wikipedia.org/wiki/Refraction

The heat that you do not lose between the 2 panes is mostly in convection and conduction since there is almost vacuum.

Also to limit the radiation of the inner pane and trigger this refraction/reflection (so that the heat is radiated back into the room) a film of polycarbonate is used as a coating on the inside pane facing the vacuum. And this does the trick.

(On the contrary in space, no reflection/refraction is encountered)

Answer 2

Dear Someone, this has a relatively easy answer. Sunlight or more properly, short wave solar radiation, peaks in the visible portion of the E-M spectrum. In this vacuum of space there is nothing which converts the energy to long-wave  heat energy, or more properly, infrared energy. The vacuum between two panes of glass will not prohibit the transmission of short wave radiation. However, the long wave IR from inside the home will be reflected back into the room just as it is in a greenhouse as it is unable to be transmitted through the glass. When the inside pane of glass is warmed by conduction from the inside, it will transmit IR through the vaccum towards the opposite pane of glass. Since the space between the two is a vacuum, the space does not warm and the wavelength of the radiation remains the same and simply is reflected back and forth within the vacuum.

Answer 3

Actually, the "heat" from the Sun does not really travel through space.  Heat needs some sort of medium to travel through, and space has little density for heat transfer.  What happens is that the electromagnetic energy from the Sun does travel through space and some of it impacts the Earth.  Upon impact, various amounts of this energy are absorbed by whatever surface the energy impacts.  This energy absorption is then balanced by an increase in emitted heat from that surface.

In the case of double paned glass, the outside pane absorbs the incoming energy and heats.  Air is a relatively poor transmitter of heat, thus the air between the two panes is warmed only slowly, even though the outside pane warms quicker.  The same effect works for cold air, where the air space in between the two panes helps to keep inside heat from being lost as fast as it would if there was only a single pane.