Here’s how Low-E windows and porches work together to utilize passive solar energy in log homes…
In my opinion, an article by John Ricketson entitled “Energy Efficiency in Log Homes” provides the best explanation of passive solar energy and how it can be used to your advantage to lower heating and air conditioning bills in your log home.
Summarized, Ricketson says this…
To take advantage of passive solar energy in your new log home, you simply want to do 4 things:
It turns out that properly placed porches, combined with Low E (low emissivity) glass windows, will yield some pretty impressive results in terms of passive solar energy.
The best part: Passive solar energy is not expensive to incorporate into your log home because it is simply the result of good design and common sense.
Here’s how it works:
In the summer, when the sun is high on the horizon, a South-facing porch will block most of the heat from the windows and the front side of the home. Whatever infrared heat energy does get to the glass is reflected back off while still allowing visible light to enter the home. An added benefit is the filtering of approximately 84% of the harmful ultraviolet rays that damage and fade furniture, wall coverings, carpet, and window treatments.
In the winter, the sun is about 30 degrees lower on the horizon. Therefore, it can get ‘under’ the porch and reach the South wall of the home. Plus, the windows on the South side also have a bias coating on the Low E glass which allows the radiant heat into the home, while still blocking most of the damaging ultraviolet rays.
The biggest boost from passive solar energy comes when the sun goes down and the outside temperature drops. Heat will migrate from hot toward cold, meaning toward the windows. The Low E glass reflects the stored energy back into the home instead of allowing it to escape through the glass.
With single-pane windows… while your walls may be well-insulated, a single pane window has an R-value of less than R=.5 (that’s 1/2 of an R-value), therefore it offers no radiant or UV protection.
Whereas, insulated glass windows with a Low E coating offer an average R-value of about R=3, while also having the ability to block radiant heat and filter out harmful UV rays.
As an example, a $2,500 square foot home in Macon, Georgia can save approximately $400 per year in heating and cooling costs over a comparable home using only single pane clear glass. Combine this benefit with proper sitting, porch placement, and a natural western screen, extended roof overhangs, and you can increase those savings even more. Source
BONUS: When you face your home toward the South, you will also be maximizing your lighting possibilities all throughout the day!