Problem for Passive Heating - the IECC codes

Lee Dodge

I think that the new International Energy Conservation Code 2012 makes it even more difficult to achieve passive solar heating than it was under previous IECC codes. The IECC keeps reducing the maximum U-value (thermal conductivity) of windows, but reducing the U-value also tends to reduce the solar heat gain coefficient (SHGC), reducing passive solar heating. This is especially a problem in high altitude locations (mostly in the West) where gas-filled windows can generally not be used (with some expensive exceptions like Serious Windows), and it is difficult to get a low U-value to meet the IECC spec and still have a high enough SHGC for effective passive solar.

My calculations for cities throughout the U.S. show that if you live in a predominately heating environment, and have sun available, i.e., climate plus no winter shading, that using high SHGC windows is much more important than having a slightly lower U-value:
http://www.residentialenergylaboratory.com/window_codes.html

Anybody else share this concern?

Cariboocoot

Re: Problem for Passive Heating - the IECC codes

Put in simple terms: windows that block more heat from getting out also block more heat from getting in.

If you look at window applications over-all it is a minor concern. The majority of installs will gain more from the increased energy retention than they will lose from the reduction in passive solar.

It does present problems for specific passive solar applications and will probably result in more active solar applications. Even so, it will still be a net improvement.

Perhaps they could allow an except for windows specifically intended for passive solar? Knowing that those would not be installed on the wrong side of the building or in locations that would not benefit from the gain. Or maybe windows will have to be handmade for those applications.

Nothing is ever perfect. There is always a compromise.

Lee Dodge

Re: Problem for Passive Heating - the IECC codes

Cariboocoot-

Thank you for your reply. You say "The majority of installs will gain more from the increased energy retention than they will lose from the reduction in passive solar."

I have shown you calculations in the link provided that for EVERY city in the northern tier of the U.S. that I simulated, and for EVERY city in the central U.S., and even for some cities in the southern U.S. that the use of high SHGC windows (also higher U-values) on at least some sides of a house that was designed to include overhangs on the south side, and that did not have excess shading in the winter would reduce energy consumption for combined heating and air conditioning over the year. These calculations include both energy gains and losses throughout the year using historical meteorological data, and using typical low and high SHGC windows.

I have shown you calculations to support my thesis. What information or references can you provide to support your statement?

Cariboocoot

Re: Problem for Passive Heating - the IECC codes

I'm not interested in debating the issue; merely pointing out the reasoning behind it.