IMO, if you are going to super insulate, you should look at shuttered windows and be very concerned about air infiltration (maybe seal with a little spray in foam).

www.seriouswindows.com offers insulated fiberglass framed windows with a ratings of R-11, R-9 and R-7 with center of glass ratings of R-20. www.consERV.com is my recommendation for an ERV system. These are state-of-the-art systems that use an engineered nanotechnology polymer instead of paper to separate the air flows.

THE BEST SHGC DEPENDS ON THE CLIMATE YOU LIVE INT NORTHERN CLIMATES SHOULD HAVE HIGHER SHGC - SOUTHERN CLIMATES REQUIRE LOWER SHGC.

Solar Heat Gain Coefficient (SHGC)
The SHGC is the fraction of incident solar radiation admitted through a window, both admitted through a window, both directly transmitted, and absorbed and subsequently released inward. SHGC is expressed as a number between 0 and 1. The lower a window's solar heat gain coefficient, the less solar heat it transmits.

Northern Climate: To reduce heating, select the highest SHGC you can find (usually 0.30-0.60 for the U-factor ranges required in colder climates) so that winter solar gains can offset a portion of the heating energy need. If cooling is a significant concern, select windows with a SHGC less than 0.55. Use RESFEN to understand trade-offs.

North/Central Climate: If you have significant air conditioning costs or summer overheating problems, look for SHGC values of 0.40 or less. If you have moderate air conditioning requirements, select windows with a SHGC of 0.55 or less. While windows with lower SHGC values reduce summer cooling and overheating, they also reduce free winter solar heat gain. Use a computer program such as RESFEN to understand heating and cooling trade-offs.

South/Central Climate: If you have moderate air conditioning requirements, select windows with a SHGC of 0.55 or less. While windows with lower SHGC values reduce summer cooling and overheating, they also reduce free winter solar heat gain. Use a computer program such as RESFEN to understand heating and cooling trade-offs.

Southern Climate: A low SHGC is the most important window property in warm climates. Select windows with a SHGC less than 0.40.

I met a bigwig of H window, he wanted an ICF house in Ashland WI. We talked a lot about his windows and I checked them out. Impressive.

ICFs here in MN add less than 5% to the build cost.

I don't rep ConsERV and I agree their website isn't the best, but their polymer membrane is engineered not to let water molecules through and they don't need a defrost cycle. They are about $1K.

John,

I beg to differ. I have received a list of over 50 glazing possibilities from Serious windows with many of them being U<0.2 and SHGC>0.50. I will probably use them on a Passive solare project soon. Perhaps you can call them in Boulder and get the complete info.

Dave

John,

If you want to send me your email address I will send you a scanned copy of the window options I have received. My contact there is Dennis Bartolo: 303 530 1150 x241. When I told him about the need to tune windows to orientation, he was quite enthusiastic and provided me the aforementioned data.

I have seen the standard 2 page flyer for their 725, 925 and 1125 series windows like the one in your PDF. They do a lot more by using lowE and suspended films in a variety of configurations. One example is with heat mirror HM88(2 sheets) argon gas for their 925 window. U=0.141(R7.4), SHGC=0.504. I count 7 other configurations on this list with U<0.2 and SHGC>0.5. Let me know if you want this data from me.

Dave

Other real issue is that Serious Windows gets their values through Heat Mirror film, not glass. There are advantages to Heat Mirror (light weight, lighter hardware, etc), but there are real disadvantages as well (durability of film, optical quality over time).

Odd, I checked NFRCs website and the numbers best listed for Unilux is U-Value .22 and SHGC .25.

Best is a relative term.  First, you need to understand the features of a window that define it energy efficiency.  For a better explanation see SHGC, U-Value and Visble Light Transmission.  You need to understand how these factors intermingle to govern the interior atmosphere.  For instance If you focus solely on SHGC, ou may select a makeup that leaves the interior too dark and causing you to keep the lights on durrig the day.  Come to understand the light to solar gain ration.

Second, visti the Efficient Window Collarborative.  They will have more great information and a directory to guide you to the various manufactureres in the country.

Lastly,  research thouroughly recoommended installation methods.  They vary depending on the area of the country and the exterior finsihes and structure of the home.  Understand which is best for your situation.  DO NOT SKIMP on installation.  If you allow drafts to penetrate the house you may also allow water in and that can destroy windows and the energy efficiency of them.