Soft coat vs hard coat for passive solar design (cold climate)
Last Post 04 Dec 2012 09:26 AM by KZQ. 26 Replies.
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benoUser is Offline
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06 Jan 2008 01:35 AM
Hi there,

I am looking for criterias to choose the energy star windows for our future passive solar (ICF) house, in Ontario, Canada. Should the windows on the different sides of the house be different? Is the soft or hard coat important or shall I look only for the U factor and SHGC and ER? Should I choose triple glaze instead of double glaze?
Any feedback about these companies: Arcor, Del, Marlboro? They all have energy star windows.

Many thanks,
Beno
rancovUser is Offline
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16 Jan 2008 03:41 PM
Energy Star ratings take into account difference in climate in a generic sense.  In your zone, the ratings guage the ability to absorb heat into the window in the coldest months which is by far the more imprtant factor.   From my experience that means that you can put windows with that generic rating and you would be alright.  

You migh look at putting clear glas (not Low-e) where you are exposing the heat sink in the house (floor, block wall etx to maximize the solar heat gain in that particular area.  You should try to have a low-e to reflect heat back into the house in the other locations, particulary on the north side of the house where U-value will be more important.

See the Efficient Window Collaborative for more info.  You will also find more information at custom windows.
Randy
benoUser is Offline
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16 Jan 2008 10:40 PM
Thanks Randy. So, in your opinion doesn't matter if I choose soft coat or hard coat?
Stephen TUser is Offline
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13 Feb 2008 07:41 PM

In case some of our American friends were wondering the ER is a one number rating system for windows - kind of like an EnerGuide rating for appliances. It  takes into account both the heat gain (SHGC) and heat loss (U) through a window over an average heating season. The higher the number, the lower the heating bill. It is based on an average orientation in an average Canadian location. So it could also be used in the northern US or any heating climate for that matter. It doesn't work well (or at all) if your cooling bill is bigger than your heating bill.

The original question was about passive solar and glazing by orientation.

There is no question that the south facing windows should have the highest possible ER. That is they should be selected to be net 'gainers' over the heating season to the strongest practical extent.  In reality this means a selecting a solar gain low e. The best of the lot from a passive solar/ ER point of view is Pilkington's Energy Advantage. It is a hard coat.

(It is true that during the day a clear double out gains a solar gain low e window, but it also true that at night a clear double out loses a solar gain low e by an even greater extent. )

Solar gain low e does experience a higher solar gain than solar shading low e in the summer as well as the winter. However, in northern latitudes, south facing glass experiences its biggest gains in the winter, not the summer.  In the summer months the sun is high in the sky and south facing glass experiences about half the solar gain of the winter months.  This means summertime solar gains are relatively modest and possible to further reduce with overhangs or other shading strategies

Summertime overheating is more likely to come from east or west facing glass. These windows typically benefit from a solar shading low e.  A solar shading low e is almost always a soft coat.

Hope that helps

Stephen Thwaites
Thermotech Fiberglass Fenestration

Stephen Thwaites P.Eng.
Thermotech Fiberglass Fenestraion
Ottawa, Ontario
benoUser is Offline
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13 Feb 2008 11:35 PM
OK, so for east and west I need solar shading low e with soft coat. For south I need solar gain low e with hard coat. Now, what about the north facing windows? And, can I find a company that produces windows with both soft and hard coat? I noticed that companies choose for their windows either soft or hard coat. If I can't have a choice, and all the windows must have the same type of coat, should I go with soft or hard coat?

Many thanks!
rancovUser is Offline
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15 Feb 2008 08:59 AM
In your Northern Clime, I would go with a soft coat on North facing windows. Soft coats are specifically designed to cut down on solar heat gain, but will reflect more heat back into the home in the winter. Given they are North facing, there is little to no value to solar heat gain through those windows. The feature to look at in these windows will be overall U-value. Stick with a hardcoat to maximize the heat gain on those orientations. Gas fill can improve the U-value on the North face, but at high altitude the life of the gas fill is not likely to be long and might not be worth the investment.  Hardcoats on South Facing would be preferable to soft coats, same on East and West. 

In the West, altitude is important as UV is more intense.  Depending on your altitude, you might  ask your neigbors how much heat they gain on South, East and West (and what kind of glass they have) faces to  guage what impact on comfort on the house their particular glass might have on heat gain from those exposures.  Follow this link to access the Cardinal Red Book which has loads of information on glazing systems.

Green Built Windows

Randy
OberonUser is Offline
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15 Feb 2008 10:00 PM

Not all softcoat LowE coatings are designed to block solar heat gain, there are high solar gain softcoats....and not all hardcoats are designed to pass direct solar gain - there are low solar gain hardcoats.

As a general rule, the high solar gain hardcoats will pass about 12-14% more solar heat than do the high solar gain softcoats - but the softcoats will have about 12-14% higher insulating value when compared with the hardcoats.  

For maximum benefit, high solar gain products should be applied to the number 3 surface (sometimes number 4) of the IG, whereas low solar gain products should be applied to surface 2 (or sometimes 1) of the IG. 

You may find that not all window sales folks will really understand the difference between high solar gain and low solar gain products, nor will they understand the importance of applying the coating to a specific surface in the IG. 

rancovUser is Offline
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07 Apr 2008 06:51 PM
Low Solar Gain is generally defined as a SHGC of .4 or less. You will find that glass fabricators are all using so-called soft coats for this specific performance level because pyrolytics do not achieve this level of performance. Pyrolytics (hard coat) typically wil reflect a SHGC of .60 or higher, hence higher solar heat gain.

In the far Northern Climates Energy Star guidelines allow any SHGC while in the Southern Zone .40 or less is a prescriptive (required threshhold) see chart

Climate Zone U-Factor1 SHGC2
Northern <= 0.35 Any
North/Central <= 0.40 <= 0.55
South/Central <= 0.40 <= 0.40 Prescriptive


So there is no quote low or high solar heat gain low-e. The general classifications for low-e coating relate to how they are applied (pyrolytically or sprayed after float process) High or low soalr heat gain is only determined by the SHGC as dictated by Enery Star,WDMA and NFRC definitions.
Randy
Barney LoweUser is Offline
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14 Apr 2008 06:57 PM
General Rule of thumb is hard coat in North and soft in South
bwheeler1User is Offline
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23 Apr 2008 04:32 PM

One of the window manufacturer's offered me this advice. We live in Northern Ontario.

Q. What type of glass would I specify for south-facing windows to enable solar gain in the winter and reduce solar gain in the summer. Any difference for the North, East and West windows?
A. There are two types of Low E Glass worth looking at. Solar Gain Glass, know as a hard coat maximizes solar gain (SHGC) with very good U value. Our brand is xxxxx and it is probably the best for passive solar heat gainSolar Shield Glass is a soft coat and lowers solar heat gain and gives slightly better radiant control so its U value is 10 to 15% higher. We sell PPG Solarban 60.

[snip]

If you are going with one or the other, it is generally considered that the hard coat overall is better on your energy dollar. Some engineers talk about tuning a house by putting solar gain on the south and solar shield on the north where perhaps the U value benefits out weigh potential heat gain. East and West would be based on a home's specific circumstances such as shading. Since the two glasses "refract" light differently, putting them in locations where they can be seen together is generally a no no since they look slightly different.

In our case, the West offers some of the best views in the house but in order to minimize solar gain, I thought I would use Solar Shield glass there.

Brian.
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24 Apr 2008 09:04 AM

Addressing a couple of possible misconceptions -

Hard coat and soft coat LowE coatings are fundamentally different beasties. 

Hard coats (as previously mentioned) are applied to the glass while it is still in the float process.  Hard coat LowE coatings are primarily tin oxide and since they are applied while the glass is still hot in the furnace they are referred to as pyrolytic . 

Pyrolytic coatings (Pilkington's Energy Advantage - again, as already mentioned) is an example of a coating that will pass near or shortwave infrared and block far or longwave infrared. 

The direct solar heat that passes thru your window glass and warms you does so as near infrared.  Hard coats are referred to as High Solar Heat Gain coatings because that is exactly what they are (with a few exceptions in the market - there are a few hardcoats with additional properties that make them low solar gain coatings) . 

Solarban 60 (again, as mentioned) is an example of a soft or sputter coat.  Soft coats are not "sprayed on" the glass after the float process.   The actual process to produce soft coats is called sputtering (hence the name - clever, eh? (Sorry Stephen - attempt at Canadian humour!)). 

Sputter coating takes place in a series of interconnected vacuum chambers where electrically charged ionized gas is used to deposit layers of metals and metal oxides directly on the negatively charged glass surface.  Soft coats are measured by (a) how many layers of various metals they contain and (b) by how thick the finished coating is - in atoms.  A typical sputter coat is less than 1000 atoms thick - and may contain as many as 11 (or a few more) separate layers of metal.   
 
The active ingredient in soft coats is typically silver,  although both titanium and stainless steel can (and have been) used as well.   SolarBan 60 is an example of a "dual-silver-layer" coating meaning that there are two layers of silver among the half dozen (give or take) total metallic layers in the coating.  There are currently single, dual, and triple silver layer coatings on the market.  Solarban 70XL would be an example of a triple-silver layer coating. 

Silver does a very good job of reflecting infrared light.  It is better at it than is tin oxide, particularly in the near infrared band.   Remember that direct solar heat gain occurs in the near infrared band.   And as an aside, technically LowE coatings do not reflect IR (or any other sort of radiation).  They are "low emissivity" which is not the same thing as being reflective.  I am using reflect or reflective in this posting because it is easy to understand (and picture) the coating as being reflective and it works for a basic understanding of different coating properties.

Soft coats are also a little better at blocking far infrared energy as well.  This is why soft coats generally have better insulative values than do hard coats, but at the cost (in heating dominated climates) of less solar gain.   Thus, they are Low Solar Heat gain coatings.  

A typical hardcoat will have SHGC numbers from about 60 to 70.  A typical single silver soft coat will have SHGC numbers of about 50 to 60.   And, as mentioned previously, a dual or triple silver soft coat will typically have SHGC numbers below 40.   These are "raw" numbers, and installation in a sash frame will change them.  They will go lower when installed.

Also, the numbers are affected by placement in the IG unit.  For example a typical dual-silver LowE coating will have a SHGC number below 40 when on the number two surface of an IGU - but move that coating to the number 3 surface and you may increase that SHGC number by as much as 10 points.  So that a SHGC of 40 on surface 2 could be as high as 50 is the coating were applied to surface 3.  

This is why coatings are applied to surface 3 in areas where a person might want maximum solar heat gain and why they are applies to surface 2 where one wishes to block the maximum of heat from entering the home. 

 

 

bwheeler1User is Offline
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24 Apr 2008 02:50 PM
With respect to our situation where we want solar gain in the south and solar reduction and/or energy loss reduction in the other directions, do you recommend a specific configuration?

Also, is the impact on finished window cost a consideration with any of these coatings?

Brian.
rancovUser is Offline
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24 Apr 2008 03:48 PM
In general, there is some cost diffeerence from hard coat to soft coat, but the gap has diminished over the last few years.  Some manufacturers have settled on the soft coats as a standard to reduce inventory handling costs.  Tuning your windows this finitely though in a far northern clime will payback in (my gues) within about 5-6 yeasrs.  If you get wildly divergent costs from hard coat low-e to soft coat, keep shopping(or if you want the wind - just tell them you won't pay the upcharge for the more expensive one, go ahead negotiate).

Download Cardinal Redbook
Randy
xexpatUser is Offline
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25 Apr 2008 07:42 AM
Posted By bwheeler1 on 04/24/2008 2:50 PM
With respect to our situation where we want solar gain in the south and solar reduction and/or energy loss reduction in the other directions, do you recommend a specific configuration?

If you are going to mix high performance glass types on different elevations, be aware that they will likely look different from both the interior and exterior due to the different coatings and will likley have different visible light transmission values as well.

This is usually not a problem if you cannot see both at the same time, but if used in the same room, you will likely notice a difference from the inside.

xexpat
benoUser is Offline
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25 Apr 2008 10:43 AM

I think that, one company, will produce either soft or hard coat windows, but not both. Correct me if I am wrong.

Second, I think the solution should be a trade off between window's performance (solar heat gain, U factor) and price.

rancovUser is Offline
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25 Apr 2008 04:04 PM
Typically, most manufacturers have settled on soft-coast as a standard because that is what you need for Energy Star qualification in most of the U.S. Also the price  differential is such that it does not make sense to actively market the 2.  That said, it should not be a problem for them to get you the hardcoat and for no premium. Ask your rep.  If they have a problem see custom windows and find a dealer.
Randy
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25 Apr 2008 09:48 PM
Keep in mind that the window companies don't "produce" LowE coatings.  They buy LowE coatings from the folks who actually do produce it. 

Some companies (PPG, Guardian, Pilkington) produce both hard coat and soft coat LowE coatings. 
Others (Cardinal, Viracon), produce only soft coats.  Off hand I can't think of any company that produces a hard coat exclusively. 

As Randy noted, most of the larger window companies in the US have opted for soft coats.  About 85% of the residential LowE coatings applied in the US are soft coats (2006).  The remaining 15% are the hard coats (obviously).  And by a significant majority, most of the soft coats used are of the LSHG variety.  

In Canada, there is a much greater use of hard coat LowE coatings.  I would guess (and I am guessing) that it might be about 50-50 between hard coat and soft coat.   Folks in the Great White North think of heating season - a lot.   (Oddly enough, I actually live north of a good bit of the Canadian population.  The town where I live is at 45 degrees 31 minutes north latitude.  Ottawa is 45 degrees 25 minutes and Montreal is 45 degrees 28 minutes.  Toronto - now that is practically a southern city at only 43 degrees north lattitude!)  

Again, as Randy noted, those companies that have opted for one coating or another often, for inventory or other reasons, simply don't offer other alternatives.  If you want maximum solar gain on your south facing windows and maximum U-factor on the other three sides of your home, you may have to do a bit of research with the window companies that interest you. 


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13 Aug 2008 11:59 PM
There is a local company which produces (I think) a very good window for the south side:
Casement, vynil, hard-coat, double pane, Argon, Spacer = non-metal, EnergyStar = Zone D (arctic), U = 1.66, SHGC = 0.47, ER = +31.

Is this a good window indeed? I'd rather go with one (local) company, is it OK if I put the same kind of window on the other sides of the house?

Thanks!
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06 Aug 2009 08:59 PM
So Beno, which window did you choose? I am in the same predicament as you. The worst part is getting this information (SHGC, U-factor, low E coatings) from the businesses--some people don't even know what I'm talking about.
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07 Aug 2009 07:35 AM
I chose the same window for all the sides of the house, just to keep it simple. I went with the best deal I could find.
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