Tuesday, September 18, 2007

Free Heat

It’s an ambitious goal but it’s do-able. I’m going to get close to 100% of my heat from direct solar radiation.

I’m building a 12 by 40 attached room on the south side of my house -- a greenhouse or solar room. I’ll have almost 240 square feet of double-paned glass to capture the energy of the sun. The room will provide additional living space, an area to start and raise plants and will include a solar closet.

Last year I took a class in passive solar greenhouse design at the community college. I learned that buildings in Flagstaff with a south-facing wall reduce their heating costs by 50% by constructing a version of the type room I’m building. A neighbor who lives a few miles away estimates he gets 60-70% of his heat from the sun. We’re about 1,400 feet lower than Flagstaff and northeast of the city so we get more sunshine which may help explain the better performance.

To get closer to the 100% mark, I plan on including a solar closet which is a well insulated room with mass to accept heat from the sun and store it until it’s needed after dark. It is simple math and physics. I’ve done the calculations on my house to determine how many BTUs are needed based on heating degree days, size, construction and insulation. To check this figure, I divided by 93,000 which is the number of BTUs in a gallon of propane. The net figure matched the number of gallons of propane that I’ve bought each of the last two years. The next step was to calculate the amount of glass and quantity of mass needed to capture and store the heat. Water is the best mass – better than stone, concrete or steel. At present I have enough barrels to store about 2,000 gallons of water and plan on adding another 1,000 gallons.

We've signed an agreement to fix the price for half the propane this winter that we've used the last two years. Based one my experience this winter, I'll add more glazing next summer to get to the optimum amount to collect enough heat. I think I'm a little short at this time but have plans for the future.

For more information about solar closets and passive solar design, see these sites: http://www.ece.villanova.edu/~nick/solar/solar.html and http://en.wikipedia.org/wiki/Solar_design

In future articles, I'll post photos and some details about costs, materials and construction. The sun provides free heat but collecting and storing it isn't free. However, it's much less expensive than you might think.

This is a major hurdle to significantly reduce our contribution to greenhouse gases. The last two -- which are the toughest -- are transportation and food.


Blogger Anvilcloud said...

Way to go!

9/18/2007 12:51:00 PM  
Blogger natala said...

that's amazing! good job!

9/18/2007 02:57:00 PM  
Blogger Alex Pendragon said...

Wouldn't it be neat if we could store all that excess heat we get in the summer for use in the winter?

9/18/2007 06:50:00 PM  
Blogger arcolaura said...

I've never heard of a solar closet - sounds intriguing. (Wish I'd heard of it back when I was designing, instead of now that the building is well underway!)

I have heard of somebody doing passive annual heat storage - i.e. all their annual heat from the sun - somewhere between your area and ours, so it should be doable. In this case, though, they had an earth-sheltered home with insulation and water-shedding membrane extending over the house and outward to enclose a huge mass of earth. That earth mass smoothed out both daily and annual temperature fluctuations into a comfortable zone.

9/19/2007 07:14:00 AM  
Blogger Malcolm said...

Looking forward to reading of progress on this project; I don't think it could be quite so succesful in the north of England!

9/19/2007 01:21:00 PM  
Blogger Whitesnake said...

I shall be watching with interest.

9/19/2007 04:53:00 PM  
Blogger MojoMan said...

Best of luck to you Paul! I, too, will be following with great interest.

How will you keep all that heat out in the summer?

How well is your existing home insulated? The tighter it is, the less solar heat you'll need.

Just 'wondering': Is the solar closet really worth the space and cost? Could a well-insulated massive concrete slab with a dark finish do almost as much for less?

9/20/2007 04:19:00 AM  
Blogger Mysti said...

Very interesting project indeed! I can't wait to see the out come. Best of luck, and i'm sure it will go smoothly.

9/20/2007 06:22:00 AM  
Blogger Tossing Pebbles in the Stream said...

"the Michael" is asking the right question. In fact this happens in Nature. Ground source water furnaces supply heat in the Winter and cooling in the Summer at low cost to run.

9/25/2007 04:28:00 PM  

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