Which surface is most effective for low-e coating in 2-ply laminated glass?
hTuPAgboAR
| Posted in Green Building Techniques on
Which surface is most effective for low-e coating in 2-ply laminated glass. I am using it in Thailand (sunny and hot). Some says that I should use on surface 4 because low-e can not work if it does not contact to the air. But there are some cases that use on surface 2. Which surface is better?. I also would like to know how the kinds of coating (soft coat and hard coat) affect in this case?
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Replies
Puri,
Low-e coatings are most commonly used when constructing IGUs (insulated glazing units) with at least two panes of glass separated by a space filled with air or an inert gas. It doesn't sound like the laminated glass you are discussing has an air space.
If the low-e coating is subject to abuse -- if it is on the outside of the glass where people can touch it -- you must use a pyrolitic (hard-coat) low-e coating, not a sputtered (soft-coat) low-e coating.
You should apply the low-e coating to the surface of the glass which is least likely to suffer from physical abuse.
If I really have to use laminated glass (8mm Heat-strengthened + 1.52PVB +8mm Heat-strengthened) with low-E. Which one will work better between soft-coat on surface 2 and hard-coat on surface 4
Puri,
Is this an IGU (with two panes of glass separated by an air space)?
no, it's a 17.52mm laminated glass. not IGU
Puri,
A low-e coating must face an air space to function, so you can't laminate anything to the side with the low-e coating. It must either face the exterior of the building or the interior of the building.
My common-sense guess is that it would make more sense for the low-e coating to face the interior of the building, because you don't want the hot glass surface to emit heat toward the interior -- that is the surface where low emissivity is most beneficial. However, I would talk to you glass supplier to be sure my advice is correct. Whatever you do, order a hard-coat pyrolytic coating, not a soft-coat sputtered coating.
Puri,
If your primary concern is solar heat gain control then you can use a softcoat LowE coating on surface 2 (interior surface of the exterior lite) of the laminated glass.
As Martin Holladay noted, placing the coating between the lites of the laminated glass will nullify any U-value advantage of the coating, but it will have no effect on the solar heat gain blocking properties of the coating.
Enclosing a softcoat LowE coating inside a monolithic laminated construction is actually a fairly common configuration in parts of the US that require laminated glass for storm impact protection but also want solar heat gain control as well in a non-IGU configuration.
If you want both solar heat gain and u-value performance while using a monolithic laminated unit then you would need to use a low solar heat gain pyrolytic such as Pilkington's Solar-E glass on surface 4; but if you choose to use a pyrolytic coating make sure that it is a low solar heat gain version since most pyrolytics are intended for high solar heat gain applications - again assuming that your intent is to keep heat out of your building.
As an aside, the laminated glass make-up that you proposed (assuming impact protection) would be considered to be a bit unusual in North America where thinner glass and thicker interlayers would be more the norm. None of my business of course, but I am curious if you are looking primarily for impact protection or for sound attenuation performance based on heat strengthened 8mm over 1.52mm interlayer? Or for something else entirely?
Greg,
The use of low-E in architectural glass in Thailand is mainly for keeping heat out of the building. Even in our winter (which is very short), it is around 17-25 degree celcius, we don't want any heat from the sun. According to our building code, we have to use laminated glass for safety reason. Normal case of curtain wall, we use "6 mm + 0.76 mm PVB + 6 mm". For my case, I use with point fixed spider fitting, so I use 8mm heat strengthened + 1.52 mm + heat strengthened for drilling and more strength purpose. In Thailand we don't use IGU much (and I am not sure if it's suitable or not for Thai weather) . Which one I should use for keeping heat out of my building, for the use of monolithic laminated, soft coat low-E on surface2 or hard coat low-E on surface4.
Puri,
In your situation I would use a triple silver low solar heat gain coating on surface 2.
In my opinion, that would be the better choice for your application.