Talk:Low-emissivity
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it sounded like the only sensible thing to do BUT here in southern Spain, our low e- glass does not seem to perform to well if fact - it does so badly, that I started doubting the glass IS LOW E...
?anybody knows how one can tell weather the glass IS what the sticker that came on it syas?
thanx YOU SHOULD BE ABLE TO HOLD A LIGHTER UP TO THE GLASS AND ON THE CLEAR SIDE YOU SHOULD SEE 2 REFLECTIONS AND ON THE LOW-E SIDE OF THE GLASS YOU SHOULD SEE 4 REFLECTIONS.
"Coating a glass surface with a low-emittance material reflects a significant amount of this radiant heat, thus lowering the total heat flow through the window."
- Shouldn't it be the other way around? The pure definition of Low-emissivity as its name suggests, is that its ability to emit energy is low. Because of this inability to lose energy, it inevitably reflects radiant heat.
"Low-E coatings are transparent to visible light, and opaque to infrared radiation. Different types of Low-E coatings have been designed to allow for high solar gain, moderate solar gain, or low solar gain."
Low-E coatings are opaque to long-infrared rather than near-infrared. The latter is the IR from the sun while the former is converted from other wavelengths like UV, Visible Light, Near-Infrared, etc.
The reason why Low-E coatings are now able to allow for moderate- or low-solar heat gain is because of solar control coatings that have been added to the glass or coated onto IGUs.
Soft-coat or Sputtered Low-E Coatings must be placed within IGUs. Pyrolytic or Hard-coat Low-E can be on single-pane (monolithic) but its effectiveness cannot match up to the sputtered ones. Also, for pyrolytic Low-E glass to achieve low-solar heat gain, the glass can be tinted. Again, it is not the Low-E coating which reduces heat. This is a gross misunderstanding in the glazing industry.
So in essence, Low-E coatings are primarily for heat retention (for winter in temperate countries or heating environments), and NOT for keeping out the heat from the sun. That probably explains why your Low-E window in Southern Spain is not working. --NVX 02:23, 19 July 2007 (UTC)
NVX, while what you say is essentially true, it is also true that most window coating products on the market now are both low emissivity and solar control coatings (not two seperate coatings but one product that achieves both). --Chapuisat 21:19, 13 August 2007 (UTC)
Chapuisat, thanks for your point. There are a handful of products which are like that. A typical one has a soft-coat (or sputtered), probably fabry-perot stack coating, which enables it to cut out huge amounts of infra-red radiation without compromising on its visible clarity. This coating is primarily a solar control coating but its exposed surface (within an IGU's air gap) enables it to be Low-E as well. This is extremely costly and not common at all. Make no mistake, this is a classic product!
That said, what bugs me to no end is the fact that many glass suppliers jump on to the bandwagon and claim that their Low-E glass can do that when in actual fact they can't.
Take pyrolytic ones for example. They are cheaper and need not be in IGUs. The fact that their surfaces are not exposed, means that the emissivity of the window takes the value of the glass (since emissivity is a surface characteristic). This means the Low-E function is sort of muted.
Sputtered ones: there are those which are a single-layer of metal sputtered onto the glass (within the IGU). This does indeed give it a Low-E capability, but its solar control ability is very limited. These are more expensive than the pyrolytic ones but cheaper than the first one I mentioned. (ie. the "classic" product)NVX 04:59, 14 August 2007 (UTC)
Sorry, message was truncated.
The bone I'm picking is that glass suppliers are using the capability of the "classic" products, and spreading the word that ALL Low-E windows are the same! The thing is that Low-E windows are not meant for tropical climates because they keep the heat in, unless they definitely have that solar control capability (like the "classic" product).
A colleague of mine shared this true account: A building in a tropical country had Low-E windows installed. According to the glass supplier, it would reduce the heat gain. So when a visitor remarked that the place was still very warm, the building facilities manager responded saying that thankfully they had Low-E windows installed, else it would have been EVEN hotter! The fact was that Low-E windows had been the reason the interior was hotter. In fact, in a case like this, leaving the original plain windows would have been a better option.
NVX 06:44, 20 August 2007 (UTC)06:40, 14 August 2007 (UTC)
Misunderstandings still persist about the qualities of both low, mid and high solar gain glass. Unfortunately the window industry has many overzealous sales and marketing people who misrepresent the characteristics of their competitors coatings in order to increase market share for themselves.
The anecdotes referred to earlier in this discussion show that glazing choices must be made after considering information from knowledgable, unbiased sources. Many glass suppliers offer all types of coatings to help lower energy load on buildings. Many window companies can provide windows with different levels of solar control AND heat gain qualities within the same building depending on the exposure, size of glazed area and other conditions in order to achieve comfortable temperatures while reducing Greenhouse Gas emmissions. —Preceding unsigned comment added by 70.49.12.136 (talk) 14:18, 19 November 2007 (UTC)
