From what I have read so far, the Germans make the best windows, followed up with the Canadians.

Passivhaus

But I did find some American companies catching on and going the route of the German & Canadian companies.

Serious Windows


Being that windows are the 2nd highest loss of energy within a home, why are American window companies so slow to develop high energy efficient windows?

The one German company created a R-10 window?!?!? Wow!

There is a misconception that is often reinforced by some of the active participants on this forum that windows always represent an energy loss for houses.  This can lead to the idea that window areas should be minimized, leaving folks living in a cave.  Windows can be a problem in areas that are cooling-dominated, as they let in solar energy. In those cases, shading from trees, overhangs, internal or external shades. and proper window placement are probably more important than simply paying a lot of money for low U-values (thermal conductivity), although U-values should certainly be considered in the decision process. 

Windows can also be a problem in heating-dominated climates where the sun rarely shines, like some marine climates or areas that are perennially cloudy in the winter.  In those climates, chosing a low U-value window makes good sense (along with energy saving shades unless inhabitants are too lazy to use them - insulating shades).  The use of free models developed by the U.S. government (DOE) like RESFEN or BEOpt can help with financial tradeoffs for how much extra should be paid for windows that can pay back the investment in a reasonable time. RESFEN does not include window prices but it does include fuel prices, so the user must get his/her own quotes for window prices, while BEOpt does include window prices.

HOWEVER, windows are not always a bad thing from an energy standpoint.  Look at solar heated homes in heating dominated climates where the sun does shine. How does the solar energy get inside -- through windows.  RESFEN will quantify the fact that windows can result in a net energy gain in places where the sun shines, and that the solar heat gain coefficient (SHGC) is more important than U-value in those cases.  Generally, these areas where windows can be helpful in meeting heating needs are heating dominated areas in the west. There is a report that contains window tradeoffs for many northern and central heating dominated areas of the U.S. showing that high SHGC windows with higher U-values perform better than low SHGC windows with lower U-values.  The report only compares low and high SHGC windows, and does not include tradeoffs with different window areas.   

It is inherent that very low U-value windows will have lower SHGC than what could be achieved by changing the coatings for higher SHGC.  Also, more window panes will tend to reflect more light.  Too confusing to consider both U-value and SHGC?  That is where RESFEN can be used to account for local climate, local energy prices, and a wide variety of window types, and ANY window can be added to the database.

Posted By Lee Dodge on 12 Feb 2012 01:06 PM
There is a misconception that is often reinforced by some of the active participants on this forum that windows always represent an energy loss for houses.  This can lead to the idea that window areas should be minimized, leaving folks living in a cave.  Windows can be a problem in areas that are cooling-dominated, as they let in solar energy. In those cases, shading from trees, overhangs, internal or external shades. and proper window placement are probably more important than simply paying a lot of money for low U-values (thermal conductivity), although U-values should certainly be considered in the decision process. 

Windows can also be a problem in heating-dominated climates where the sun rarely shines, like some marine climates or areas that are perennially cloudy in the winter.  In those climates, chosing a low U-value window makes good sense (along with energy saving shades unless inhabitants are too lazy to use them - insulating shades).  The use of free models developed by the U.S. government (DOE) like RESFEN or BEOpt can help with financial tradeoffs for how much extra should be paid for windows that can pay back the investment in a reasonable time. RESFEN does not include window prices but it does include fuel prices, so the user must get his/her own quotes for window prices, while BEOpt does include window prices.

It is inherent that very low U-value windows will have lower SHGC than what could be achieved by changing the coatings for higher SHGC.  Also, more window panes will tend to reflect more light.  Too confusing to consider both U-value and SHGC?  That is where RESFEN can be used to account for local climate, local energy prices, and a wide variety of window types, and ANY window can be added to the database.

In the area where I will build, it would be considered more of a heating-dominated climate (Prescott, AZ), and the area gets A LOT of sun even during winter. The home would have the majority of windows on the south elevation and the home would be positioned to face due south to take advantage of the southern exposure during winter. During summer it does get hot but the sun would be directly overhead of the home and I will have overhangs of 18".

I guess it would it make sense to install the lower SHGC windows on the west, east & north sides and the higher SHGC windows on the south side.

So would triple pane windows on the east, west and north sides be overkill or unnecessary?

These are some results from RESFEN for Prescott Arizona. House is 2000 sq. ft. 1-story, with basement, new masonary, insulated ceiling R-49, walls R-28, basement R-30. Windows are 66.7 ft^2 on all four sides. First case is Serious Windows, U=0.19, SHGC=0.22 all the way around. Second case is Serious Windows north only, Pella triple pane, U=0.31, SHGC=0.49 on S, E, and W sides. Total utility costs for case 1 are $357.66, excluding connection fees and with older utility rates, and case 2 are $320.59. Cases with only the S side with high SHGC are slightly higher utility bills. Using interior shades at night in the winter and to block sun during the day would make second case look significantly better. Connection fees would significantly increase costs, but are independent of window choice. Serious Windows are about twice the cost of the Pella triple-pane windows. Do you really want those super low U value windows?

Notice in the tables below that the energy costs for case 2 for the S, E, and W windows are NEGATIVE, meaning that those windows are not a net loss, but a net GAIN in energy. Using prefernetially more windows on the S and less on N would improve results.

RESFEN5 ResFen 5.0 (5.0.00) House Report 02/13/12 14:19:21

House Data
==========
ID: 1
Name: Sample - New Construction
Location: AZ Prescott
House Type : 1-Story New Masonry
Foundation Type : Basement
HVAC System Type: Gas Furnace / AC
Total Floor Area: 2000 ft2
Total Window Area: 267 ft2

Whole House Results
===================
Heating Cooling Total
============== =============== ==============
Annual Energy Totals 28.5 MBtu 448 kWh 33.1 MBtu (Source)
Annual Energy Intensity 14.2 kBtu/ft2 0.22 kWh/ft2 16.5 kBtu/ft2 (Source)
Peak 35.0 kBtu/hr 1.13 kW
Cost $ 324.44 $ 33.12 $ 357.56

Window Annual Energy Results
============================
North East South West Skylight
======== ======== ======== ======== ========
Cooling intensity* (kWh/ft2) 0.51 1.35 0.70 1.18 0.00
Heating intensity* (kBtu/ft2) 21.47 1.46 -20.89 4.31 0.00
Cooling (kWh) 34.19 90.00 47.00 79.00 0.00
Heating (MBtu) 1.43 0.10 -1.39 0.29 0.00

*per unit area of window

Window Energy Cost Results
==========================
North East South West Skylight
======== ======== ======== ======== ========
Cooling* ($/ft2) 0.04 0.10 0.05 0.09 0.00
Heating* ($/ft2) 0.24 0.02 -0.24 0.05 0.00
Cooling ($) 2.53 6.69 3.47 5.83 0.00
Heating ($) 16.31 1.11 -15.87 3.27 0.00
Total ($) 18.84 7.80 -12.40 9.10 0.00

*per unit area of window

Window Peak Energy Results
==========================
North East South West Skylight
======== ======== ======== ======== ========
Cooling intensity* (W/ft2) 1.01 1.24 0.99 3.18 0.00
Heating intensity* (Btu/h/ft2) 16.15 15.90 15.11 15.72 0.00
Cooling (kW) 0.07 0.08 0.07 0.21 0.00
Heating (kBtu/hr) 1.08 1.06 1.01 1.05 0.00

*per unit area of window

Utility Costs
=============
Electricity: 0.074 $/kWh
Natural Gas: 1.139 $/Therm

Window Data
===========
Orien- Window Type Area U-factor SHGC Air Leakage Solar Gain Source
tation (ft2) (Btu/h-ft2-F) (cfm/ft2) Reduction
------ ---------------- ----- ------------ ---- ----------- ---------------- ------------------
North 454 Serious Glas 66.7 0.190 0.22 0.30 Typical C:\Program Files\L
s 9 Low-SHGC 40x BNL\RESFEN5\RESFEN
60 5Windows.mdb
East 454 Serious Glas 66.7 0.190 0.22 0.30 Typical C:\Program Files\L
s 9 Low-SHGC 40x BNL\RESFEN5\RESFEN
60 5Windows.mdb
South 454 Serious Glas 66.7 0.190 0.22 0.30 Typical C:\Program Files\L
s 9 Low-SHGC 40x BNL\RESFEN5\RESFEN
60 5Windows.mdb
West 454 Serious Glas 66.7 0.190 0.22 0.30 Typical C:\Program Files\L
s 9 Low-SHGC 40x BNL\RESFEN5\RESFEN
60 5Windows.mdb
Skylight 311 W/V 2 Clear 0.0 0.490 0.56 0.30 Typical C:\Program Files\L
BNL\RESFEN5\RESFEN
5Windows.mdb

Location Data
=============
Location Name: AZ Prescott
Weather File Name: .\Weather-US\AZPRTMY2.BIN


RESFEN5 ResFen 5.0 (5.0.00) House Report 02/13/12 14:14:52

House Data
==========
ID: 1
Name: Sample - New Construction
Location: AZ Prescott
House Type : 1-Story New Masonry
Foundation Type : Basement
HVAC System Type: Gas Furnace / AC
Total Floor Area: 2000 ft2
Total Window Area: 267 ft2

Whole House Results
===================
Heating Cooling Total
============== =============== ==============
Annual Energy Totals 23.3 MBtu 750 kWh 31.0 MBtu (Source)
Annual Energy Intensity 11.6 kBtu/ft2 0.38 kWh/ft2 15.5 kBtu/ft2 (Source)
Peak 36.5 kBtu/hr 1.54 kW
Cost $ 265.09 $ 55.50 $ 320.59

Window Annual Energy Results
============================
North East South West Skylight
======== ======== ======== ======== ========
Cooling intensity* (kWh/ft2) 0.51 3.27 1.84 2.93 0.00
Heating intensity* (kBtu/ft2) 21.00 -10.42 -57.38 -3.77 0.00
Cooling (kWh) 33.73 218.00 123.00 195.00 0.00
Heating (MBtu) 1.40 -0.69 -3.83 -0.25 0.00

*per unit area of window

Window Energy Cost Results
==========================
North East South West Skylight
======== ======== ======== ======== ========
Cooling* ($/ft2) 0.04 0.24 0.14 0.22 0.00
Heating* ($/ft2) 0.24 -0.12 -0.65 -0.04 0.00
Cooling ($) 2.50 16.14 9.07 14.44 0.00
Heating ($) 15.95 -7.91 -43.59 -2.86 0.00
Total ($) 18.45 8.23 -34.52 11.58 0.00

*per unit area of window

Window Peak Energy Results
==========================
North East South West Skylight
======== ======== ======== ======== ========
Cooling intensity* (W/ft2) 0.99 2.44 1.93 6.81 0.00
Heating intensity* (Btu/h/ft2) 16.02 23.43 21.70 23.06 0.00
Cooling (kW) 0.07 0.16 0.13 0.45 0.00
Heating (kBtu/hr) 1.07 1.56 1.45 1.54 0.00

*per unit area of window

Utility Costs
=============
Electricity: 0.074 $/kWh
Natural Gas: 1.139 $/Therm

Window Data
===========
Orien- Window Type Area U-factor SHGC Air Leakage Solar Gain Source
tation (ft2) (Btu/h-ft2-F) (cfm/ft2) Reduction
------ ---------------- ----- ------------ ---- ----------- ---------------- ------------------
North 454 Serious Glas 66.7 0.190 0.22 0.30 Typical C:\Program Files\L
s 9 Low-SHGC 40x BNL\RESFEN5\RESFEN
60 5Windows.mdb
East 455 Pella Triple 66.7 0.310 0.49 0.30 Typical C:\Program Files\L
Hi-SHGC 41x59 BNL\RESFEN5\RESFEN
5Windows.mdb
South 455 Pella Triple 66.7 0.310 0.49 0.30 Typical C:\Program Files\L
Hi-SHGC 41x59 BNL\RESFEN5\RESFEN
5Windows.mdb
West 455 Pella Triple 66.7 0.310 0.49 0.30 Typical C:\Program Files\L
Hi-SHGC 41x59 BNL\RESFEN5\RESFEN
5Windows.mdb
Skylight 311 W/V 2 Clear 0.0 0.490 0.56 0.30 Typical C:\Program Files\L
BNL\RESFEN5\RESFEN
5Windows.mdb

Location Data
=============
Location Name: AZ Prescott
Weather File Name: .\Weather-US\AZPRTMY2.BIN

Posted By Lee Dodge on 13 Feb 2012 04:34 PM
  Do you really want those super low U value windows?

Notice in the tables below that the energy costs for case 2 for the S, E, and W windows are NEGATIVE, meaning that those windows are not a net loss, but a net GAIN in energy. Using prefernetially more windows on the S and less on N would improve results.

Thank you for that detailed report! I must admit that some of the data is beyond my field of knowledge.

I can see how a window with a high SHGC would benefit the south side of the home during winter from the solar heat gain. Would there not be a drawback to that window during winter AT NIGHT? Wouldn't a window with a high U-value start to cause convection during a cold winter night?

Lbear said:
"I can see how a window with a high SHGC would benefit the south side of the home during winter from the solar heat gain. Would there not be a drawback to that window during winter AT NIGHT? Wouldn't a window with a high U-value start to cause convection during a cold winter night?"
Yes, the high SHGC window does lose more heat at night than the low SHGC window with a lower U-value. However, that is what the computer models are for, since they compute both the higher heat gain in the day and the higher heat loss at night, and compute that overall, the high SHGC windows are superior in your sunny climate in Prescott, Arizona. In Nova Scotia, the low SHGC with lower U-value would be the better choice. Note that the model results that I provided also showed that the high SHGC windows increase the cooling energy during the summer, but not as much as is saved during the winter. Computer models are great at quantifying all these different effects at different times of the year and doing the tradeoff for you.

To tilt the odds even more in your favor, consider taking the high SHGC window with a U-value of 0.31, corresponding to an R-value = 1/U-value = 1/0.31 = 3.2, and add a insulating light-blocking, double-cell, cellular shade with side seals with an R-value of 2.0 or greater, and now you have an R = 5.2 window at night that also has high solar gain during the day. I have simulated this in RESFEN and it improves the energy performance even more than the other cases, and it certainly improves the comfort factor when sitting near the windows. Plus, at no additional cost, you can use the same shades to block much of the solar gain in the summer when the sun is on that part of the house.

Posted By Lee Dodge on 13 Feb 2012 08:37 PM

Yes, the high SHGC window does lose more heat at night than the low SHGC window with a lower U-value. However, that is what the computer models are for, since they compute both the higher heat gain in the day and the higher heat loss at night, and compute that overall, the high SHGC windows are superior in your sunny climate in Prescott, Arizona. In Nova Scotia, the low SHGC with lower U-value would be the better choice. Note that the model results that I provided also showed that the high SHGC windows increase the cooling energy during the summer, but not as much as is saved during the winter. Computer models are great at quantifying all these different effects at different times of the year and doing the tradeoff for you.

To tilt the odds even more in your favor, consider taking the high SHGC window with a U-value of 0.31, corresponding to an R-value = 1/U-value = 1/0.31 = 3.2, and add a insulating light-blocking, double-cell, cellular shade with side seals with an R-value of 2.0 or greater, and now you have an R = 5.2 window at night that also has high solar gain during the day. I have simulated this in RESFEN and it improves the energy performance even more than the other cases, and it certainly improves the comfort factor when sitting near the windows. Plus, at no additional cost, you can use the same shades to block much of the solar gain in the summer when the sun is on that part of the house.

Too bad they don't make windows that have a high SHGC but have a low U-Value. That way I can have my cake and eat it too.

The one issue with the shades is that some of the windows will be towards the vaulted ceiling and some windows will be a trapezoid, so installing a proper shade will prove to be difficult if not impossible.

"Too bad they don't make windows that have a high SHGC but have a low U-Value. That way I can have my cake and eat it too."

It depends on whether you want to have bragging rights about what low U-value windows that you have, or whether you want to minimize overall energy consumption. You can choose a coating that will let in more solar energy, but at the same time it will have higher emissivity and, therefore, a higher U-value. Just physics. The best approach to having both is to go to triple pane, and in your area, high solar heat gain coefficient (SHGC) coatings.

"The one issue with the shades is that some of the windows will be towards the vaulted ceiling and some windows will be a trapezoid, so installing a proper shade will prove to be difficult if not impossible."

Vaulted ceilings can be hard to insulate to high levels, and waste some volume of hot air trapped near the ceiling. You could do your trapezoidal windows as two separate windows, with a regular lower rectangular window that would accept shades, and a small upper trianglular and/or trapezoidal wndow that would not have a shade with a small wall space between. That would probably be much more practical and less expensive for cutting glass, window design, etc.

Posted By Lee Dodge on 14 Feb 2012 08:16 AM

It depends on whether you want to have bragging rights about what low U-value windows that you have, or whether you want to minimize overall energy consumption. You can choose a coating that will let in more solar energy, but at the same time it will have higher emissivity and, therefore, a higher U-value. Just physics. The best approach to having both is to go to triple pane, and in your area, high solar heat gain coefficient (SHGC) coatings.

Serious Windows makes one window which has a 0.45 SHGC and a 0.18 U-Value. That beats out the Pella triple pane U-Value,  SHGC=0.49 & U=0.31

 Would that work for letting IN the wintertime solar heat gain but keep it inside the homes envelope during cold nighttime temps?

Can you run the above window through that software program to see what is says?

THANKS!

Do not forget to compare the VT of the windows as well. Not much point to have a window you cannot look through, even if it does have a low U-value.

Posted By Bigrig on 15 Feb 2012 01:07 PM
Do not forget to compare the VT of the windows as well. Not much point to have a window you cannot look through, even if it does have a low U-value.

The VT of those windows are: 0.54

Would that be dark?

A visible transmission of 0.54 is relatively high for a low U-value window. Your eyes are approximately logarithmic detectors, so you would not perceive those windows as cutting out almost half of the visible light.

Lbear, you said, "Serious Windows makes one window which has a 0.45 SHGC and a 0.18 U-Value. That beats out the Pella triple pane U-Value, SHGC=0.49 & U=0.31."
The SHGC for the Serious Window is lower, so solar heating is LESS efficient than for the Pella window, and the U-value is also lower, so heat losses are lower. You would need to run RESFEN to see which window performs better. In my climate, the high SHGC Pella windows outperformed the high SHGC Serious Wndows according to RESFEN, and were maybe half the cost. I am almost certain that even if the Serious Windows have slightly better performance (and I am not sure that they would), by maybe a few dollars a year, you would have to live a long life, maybe 500 years, so pay off the savings. There is also concern about the long-term durability of the plastic film used in the Serious Windows. We know glass will last a long, long time.

But, it is your money, and either of those two choices would perform well. My point was that in your climate, solar gain is more important than simply looking for very low U-value windows that will always be low SHGC. BigRig also makes a good point that extremely low U-value windows (your mentioned an R-10 window) will usually be low in visual transmission (VT).

Posted By Lee Dodge on 15 Feb 2012 09:27 PM
A visible transmission of 0.54 is relatively high for a low U-value window. Your eyes are approximately logarithmic detectors, so you would not perceive those windows as cutting out almost half of the visible light.

Lbear, you said, "Serious Windows makes one window which has a 0.45 SHGC and a 0.18 U-Value. That beats out the Pella triple pane U-Value, SHGC=0.49 & U=0.31."
The SHGC for the Serious Window is lower, so solar heating is LESS efficient than for the Pella window, and the U-value is also lower, so heat losses are lower. You would need to run RESFEN to see which window performs better. In my climate, the high SHGC Pella windows outperformed the high SHGC Serious Wndows according to RESFEN, and were maybe half the cost. I am almost certain that even if the Serious Windows have slightly better performance (and I am not sure that they would), by maybe a few dollars a year, you would have to live a long life, maybe 500 years, so pay off the savings. There is also concern about the long-term durability of the plastic film used in the Serious Windows. We know glass will last a long, long time.

But, it is your money, and either of those two choices would perform well. My point was that in your climate, solar gain is more important than simply looking for very low U-value windows that will always be low SHGC. BigRig also makes a good point that extremely low U-value windows (your mentioned an R-10 window) will usually be low in visual transmission (VT).

The Pella U=0.31 series barely even pass the Energy Star rating.  While I am not completely sold on Serious Windows and I am exploring my options, I must say I have read A LOT of complaints about Pella and quality control. From my research I really don't think Pella is all that great. Compared to Canadian windows, Pella is a Chevy, while the Canadian & Serious Windows are the Bentley.

They also have a 525 Serious Window: U = 0.19    SHGC =  0.51     VT =  0.60   (dual pane - Argon Fill  R-Value = 5.3)

Serious Windows also make a 1125 series:  U= 0.09 SHGC =  0.24     R-Value = 11.1     VT = 0.39  (Dual Pane, 3 Low SHG Films Xenon) - While overkill for my climate, it just shows you that SW is light years ahead of anything that Pella or Anderson can offer.

SERIOUS WINDOWS SPEC SHEET

Serious Windows also make a 1125 series: U= 0.09 SHGC = 0.24 R-Value = 11.1 VT = 0.39 (Dual Pane, 3 Low SHG Films Xenon) - While overkill for my climate, it just shows you that SW is light years ahead of anything that Pella or Anderson can offer.

RESFEN results:

U-value  SHGC   Heat (MBtu)   Cool (kWh)   Total (source MBtu)  Cost (USD)
0.09       0.24      23.7                490                  28.8                  306.66
0.24       0.41      23.8                688                  30.9                  322.31
0.31       0.49      23.8                801                  31.9                  328.74
Add insulating shades to last windows and use at night in winter only
0.24       0.49      21.3                813                  29.6                  302.53

If the insulating shades are also used in the summer, then the cooling energy for the last case can be greatly reduced.

What was the cost for the U=0.09, SHGC = 0.24 window?  We can use that to estimate payback times.

Posted By Lee Dodge on 16 Feb 2012 06:16 PM


What was the cost for the U=0.09, SHGC = 0.24 window?  We can use that to estimate payback times.

I don't have those costs yet but for a dual pane U - 0.14 window with an R-Value of 7.1, these are the costs:
For a 5060 fixed glass window you are looking at $400.00
A 4' x 5' window would be around $300.00

"I don't have those costs yet but for a dual pane U - 0.14 window with an R-Value of 7.1, these are the costs:
For a 5060 fixed glass window you are looking at $400.00
A 4' x 5' window would be around $300.00"

I can see that you are not yet convinced that having a high solar heat gain coefficient (SHGC) window in the sunny, predominately heating environment of Prescott, AZ is important. Nor a window with a high visible transmission, since you provide neither of those values. Assuming that those values are acceptable, that looks like a very attractive price.

I must add something after seeing this post. I sold and manage the Schuco Window here in the US for some 7 years. The Germans do make (did make) a good window however with 27 years of experience talking there is no better window than Bristol Windows. Pound for pound, hands down the finest American made replacement window product including their patio doors. The Bristol Window is manufactured by Winchester Industies since 1983 and has always been a triple pane window product. No other window compares.

window-wizard-

And may we assume that you have no economic interest in Bristol Windows, since I am sure you would have acknowledged that fact if you were? This forum should not be used for advertising products that you have a financial interest in.

My apologies, yes I have a $$$ interest in the product I wrote about, sorry about that. I do not sell in Az and I was not looking for business. I have researched the replacement window industry for many years, including going to the BAU, in Munich Germany. Yes in my little corner of NJ we do business, but the still does not mean the product I mentioned isn't the best there is, because it is. The Bristol Window has stood the test of time, no other window product on the earth bets their quality, that is why I sell them and nothing else. But your point is well taken, ....however I doubt if I'll be back.

Bristol Windows are junk. Visit the website, look at the cutaways and see for yourself. Great window if you like seal failures.

I love how the entire website only mentions triple pane, not a hint of double pane option, but in their big sweepstakes there are prizes for the triple pane upgrade.