You cannot do passive solar heating with the windows they are selling

[Kolesar]

The vast majority of "replacement windows" have a treatment to lower the Solar Heat Gain Coefficient to 0.32 or less (on a scale of 0 to 1). An ordinary double pane glass window is rated 0.68.

Solar blocking windows are probably an appropriate choice for most window installations. To get "the tax credit", a homeowner MUST buy a solar blocking window. (Even if it is a north window).

However, if you want to do passive solar heating, or start seedlings on your window sill, you are losing half your solar gain. Cats should be unhappy with this, too.

[Statistical]

1. That is something a lot of people don't consider.

Even when trying to do the right thing they end up buying the "best". Well the "best" isn't best in all situations.

Generally speaking if your annual AC bill is higher than your annual heating bill then cutting solar exposure if better.
If you heating bill is higher than your AC bill then passive solar works out a lot better.

Bad news is in US most homes are poorly designed for passive solar. The sun rides much lower on horizon in winter compared to summer so for good passive solar design you want properly sized overhangs above the windows. The overhang should be short enough to allow winter sun to hit windows but long enough to block summer sun.





This is a good magazine for people interested in that kind of stuff:
http://homepower.com/home/

It is mostly PV solar but they have info on solar heat, passive solar, small scale hydro (I would love some property and build a small scall run on the river hydro turbine), and efficiency.

[Kolesar]

2. Thanks

I'm a subscriber. I had the windows article open when you posted!
http://homepower.com/view/?file=HP117_pg56_Boulac

[Statistical]

3. Sweet. I use to have paper subscription but recently I just opted for 2 year digital version.

So much easier to lookup old articles. The digital version is a really a can't miss deal for anyone interested in the subject.

Despite being the resident "nuclear shill" (according to some) I do believe solar, wind, hydro, good designs (this is really lacking in US), and efficiency are all necessary.

I have a solar hotwater (pre) heater. Me and my wife are looking into PV solar but currently math just doesn't work out. The solar tax credit expires in 2016. I am hoping price of solar drops enough prior to 2016 to lock in low price & credit.

[elocs]

4. The picture of the house mirrors the situation at my home.

Lots of sun comes through the south windows in the winter, but when the sun get higher in the sky it does not. My cat does love to stretch out in front of those windows because where she is it can get to be over 85 degrees.

[Statistical]

5. Your home has a good passive efficiency design then.

We are considering lengthening the overhangs on the south facing side of our house to gain "passive solar / passive shading" effect. However it may not be worth it from an energy ROI standpoint. Physical structure renovation isn't cheap in terms of $$$ or energy.

If we ever purchase another home that will be something I will look for. It is easy to change appliances, furnaces, air conditions. You can even add solar heating, or PV but changing the structure of the house is not as easy.

Sadly most homes in the US are built to "look good" not be efficient. If you start with an inefficient design there is only so much you can do to improve it.

[elocs]

6. Where I live we have a number of prairie homes inspired by Frank Lloyd Wright,

which look beautiful but don't do much for passive solar heating.

[Dogmudgeon]

7. This is probably an easy rule to get changed

If you contact one of the solar trade associations (activist groups tend not to have the same clout or legal connections), you may be able to get the rule changed, and pretty quickly.

Good luck!

--d!

[skids]

8. Thank you.

This has been a pet peeve of mine for a while now, being I live in the Northeast.

It's always good to see more people complain about it. Feels less like I'm screaming
into the forest.

[madokie]

9. You know what I love my low gain .32 windows

and will be installing more this summer. They not only block the heat coming in in the summer they also block the heat going out in the winter so a low E glass window makes as much sense on a north facing wall as they do on a south one. I guess if you are wanting to use solar gain in the day maybe other windows would be better on the south facing windows but if not covered well in the evening they leak some of the heat you gained during the day during the nighttime. Covered well is not simply some window shades or curtains if they are not sealed up at the top and the bottom as the temperature will cause the air to flow across them either upwards or downwards depending on the inside temperature and the outside temperature and with that air flow and contact with the glass heat transfers. I'll put them in all my windows by the time I finish the job as I only have one south facing window and lots of trees to block the sun even in the coldest days and no leaves on them they still cast a shadow.

[Kolesar]

10. Low-e Glass … A Nation Divided

http://sunhomedesign.wordpress.com/2007/05/03/low-e-glass-a-nation-divided/
May 3, 2007 · 20 Comments
Low-e glass, first introduced in 1979, has transformed window energy performance. Low-e glass is manufactured with a microscopically thin and transparent layer of metal or metal oxide that reflects infrared “heat” energy back into the home, greatly enhancing the thermal performance of the window.

In the simplest of terms, there are basically two kinds of Low-e glass:

:redbox: Low-e glass with a low Solar Heat Gain Coefficient (SHGC) that also reflects and keeps much of the Sun’s heat energy out of the home. This is the best choice in climates dominated by cooling.
:bluebox: Low-e glass with a high Solar Heat Gain Coefficient (SHGC) that allows the Sun’s heat energy into the home. This is the best choice in climates dominated by heating or for south facing windows in climates with a mix of cooling and heating requirements.


...snip...
The Northern zone is the perfect candidate for a Low-e glass with a high SHGC and the North/Central and even the South/Central can greatly benefit from high SHGC Low-e glass on southern exposures. Unfortunately, even though the average American family spends far more on heating than air conditioning, both Energy Star, LEED, and the International Energy Conservation Code (IECC) seem to be color blind when it comes to space heating and the benefits of Low-e glass with a high SHGC.

Energy Star requirements for SHGC seem to be all about cooling as the following requirements for SHGC for each climate zone indicates. The IECC is no better, only requiring a SHGC of ≤ 0.40 for any residence with less than 3,500 Heating Degree Days (HDD). LEED only takes the cooling bias further by requiring even lower SHGC’s in the South/Central and Southern climate zones.

As an unintended consequence of the regulatory bias in favor of cooling, window manufacturers have all but abandoned Low-e glass with high SHGC’s. The result is a nation divided, with more than half of the country left out in the cold without ready access to high performance windows that take advantage of the free solar energy that strikes our windows everyday. With very few exceptions you just cannot find a window manufacturer willing to give you the glass options we need and require in heating dominated climates.

So what’s the consequence of the current regulatory bias? First of all it makes no sense, according to the U.S. Energy Information Administration’s (EIA) 2001 Residential Energy Consumption Survey, Americans consume more than 7 times more energy for space heating than for air conditioning. ...more...

Great comments section, here is one:

Paul S // July 28, 2009

The situation has been worsened with the American Recovery and Reinvestment Act of 2009 (ARRA), which offers a tax credit for home improvements that include window and door upgrades. The tax credit requires the window to have a maximum U-Factor (inverse of insulation R-Factor) of 0.30, and a maximum Solar Heat Gain Coefficient (SHGC) of 0.30.

This may have two effects: (1) homeowners may forego their desired passive solar heating in favor of a short-term savings, (2) manufacturers may gear up to make only those windows that will qualify for the tax credit.

I wrote to Energy Secretary Steven Chu and to both Colorado senators to ask for a review of the ARRA. If we as a country are going to encourage energy efficiency, we should do it more intelligently. I encourage you to write to your representatives in support of a review of ARRA terms, especially the SHGC maximum.

[Kolesar]

11. Ask Kevin: Window coatings and passive solar heating

05 Jun '07 from John Van Doren

Hi Kevin,

We're building new, and will be putting in vinyl windows, and were wondering if the "Suncoat" on Milgard windows will actually interfere significantly with the passive solar heating that we're seeking here in Alaska? Our home will face south and, in the winter, could collect quite a lot of warmth through the windows. What would you recommend?
Jane

Thanks Jane,

The short answer is YES, Suncoat will NOT give you the passive solar gain that you're looking for in your new home. However, the solution is a bit more complex. There are basically two types of low-e glass—low solar heat gain glass, which keeps the energy from the sun out but also keeps longer wave energy within the home from escaping, and high solar heat gain glass, which keeps the longer wave energy in but also lets in the sun's energy for natural, free solar heating. The problem is that, due to the bias in favor of cooling found in our codes and with Energy Star, the U.S. window industry has all but abandoned offering high solar heat gain, low-e glass as an option. (To better understand this issue you might want to read this.)

Milgard is not really any different than the rest of the U.S. manufacturers in that regard. Here is what you'd be giving up: A dual-pane Suncoat window has a center of glass solar heat gain coefficient (SHGC) of 0.36 and a winter U-value with an argon fill of 0.29. That means that it is rejecting 64 percent of the solar energy. By comparison, a high solar heat gain low-e dual pane Energy Advantage system from Pilkington Glass has a center of glass SHGC of 0.70 and a winter U-value with argon fill of 0.29. So basically you can get the same insulation value but with the ability to let in TWICE the amount of free solar energy for your passive design.

So here's my recommendation: First, because of wallet issues, if you're going to use any vinyl in a home, windows are probably the best and only place to make that compromise. However, I recommend you find a manufacturer that provides foam filled vinyl frames. This will greatly improve the overall window performance. Second, you can ask the manufacturer to substitute a high solar heat gain glass for their standard offering; however, in talking with several manufacturers I have found that only Marvin has been willing to do that, and they only make wooden windows. If you can't find anyone to substitute the glass you need, have a window fabricator near you fabricate insulated glass units (IGU without frames) to your specification and then frame them directly into your south facing wall. Depending on the window size and wind loads in your area, a reasonable specification for the IGUs would be 1/8" float glass outer pane, 1/8" Pilkington Energy Advantage glass on the inner pane with the low-e coating on the third surface, 1/2" argon filled space between panes and a non-metallic warm edge spacer.

All the best with your project!

John Van Doren

LETTERS:

On May 28th, 2009 Dave T says:
I face the same problem passive solar home built 1985 (received a federal grant for my home design) need to replace glass found the perfect glass Cardinal LOe 179 made for passive solar homes. Found a window manufacturer (Mercer industries in Oregon) to get them , but found out that they will not qualify for the federal tax rebate. They have high SHGC .70 which I want and need.
So now is the time to wake the federals up that their U<0.30, SHGC <0.30 is not good for those of us who live in the Northern climates.

Thanks Dave t
Palouse WA