Friday, August 29, 2008

Passive Solar Heat Gain

One key element of passive solar design is to provide lots of roof overhang on south facing windows. Because the sun is higher in the sky in the summer, the overhang (if designed properly) prevents direct sunlight from impinging on the windows in the hottest months of the year. In the winter the sun is lower in the sky, so the overhang will not impede the sun from striking the windows and providing welcomed solar heat gain.

All summer, no direct sunlight has entered our great room through the large south facing windows. Recently, it has been cloudy and rainy in Kentucky, so the sun's rays haven't even reached the house. Today was sunny though and I was pleasantly surprised when I looked into the great room and saw a sliver of light beaming in on the floor. By December, this sliver of light will grow and move across the room, such that the entire north wall of the great room will be illuminated by direct sunlight passing through the south facing windows. I love it when the math works out!

It's still warm here in Kentucky, so ideally the sun wouldn't start peaking through for another month, but the warmest month (July) does not coincide with the sun's highest point in the sky, which occurs in June. Nor does the coldest month of January coincide with the sun's lowest point in the sky, which occurs in December. Therefore it was necessary to allow a little sun in the house in early September so that the benefits of passive solar heat gain could still be realized in late March. Life's a compromise.

I dug around and found this picture of the south side of the house that was taken at around Halloween 2007. As you can see, the sun (due to its annual journey to a lower position in the sky) is already fully illuminating the upper windows in spite of the overhang. Yep, that's how it's supposed to work!

The west side of the house has very few windows, because the sun always sets in the west, no matter what time of the year it is. It is hard to control unwanted solar heat gain through west facing windows on summer afternoons so we simply kept the size and number of those windows to a minimum.


Blogger Gene said...

Yay for passive solar! It's the cheapest, cleanest, easiest, greenest design feature you can put in a house, and it requires no maintenance. What's not to like about free energy?

August 29, 2008 at 8:20 PM  
Blogger oldmilwaukee said...

And free Vitamin D in the winter too!

Nice blog Gene - I got a chuckle reading Mr. Bildrong's advice.

August 30, 2008 at 8:04 AM  
Anonymous Carl said...

I have been reading your blog the past couple of days. Very inspiring stuff. I am in the navy right now, but I would love to take on a project like this when I get out.
It is uncanny how similar your house is to the type of house I have dreamed about. I have plenty of questions, most of which I will save until I catch up to the current post in case you cover it. One I would like to ask now; did you read a specific book on passive solar home design or was it somewhat covered in the timberframe books you have already reviewed? I have also heard of planting a deciduous tree on the south or west side of the house so that its leaves shade in the summer and lets light in in the winter. You just did not want the risk of a tree falling on your house after the ice storm?
Great blog, I am whizzing through it.

April 1, 2011 at 2:20 PM  

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