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Forums > Green Building Technologies > Solar and Wind Power > Subject: Passive Solar?

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richntiffUser is Offline
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Posts:24
04/25/2008 2:21 PM  
Thanks again to all who frequent this site - such a great info source.  I'm in 'design/dreaming' mode on our 2200sf home that we hope to construct this year (if we can sell the current home....) 

Reading a LOT on passive solar, how it's just the greatest thing ever.  Here's my question - it's quite intuitive that the number of solar heating days available (i.e.- the sun being out) is a big factor in the effectiveness of passive solar.  So, suppose I build my house south facing with a huge bank of windows - in northern Wisconsin, climate zone 7. First of all - I have reservations that even with a ton of sunny days, the heat loss due to that volume of window area is going to outweight the benefit - no matter the thermal mass added inside the structure. Bear in mind my design temp is -25F.   Secondly - we can go for days, sometimes 2 weeks, with no sun at all.  So in a nutshell - is it safe to assume that in certain areas of the country, passive solar is a poor option?  Or am I totally missing something?
Stephen TUser is Offline
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Posts:9
05/04/2008 12:43 PM  

You are right, windows lose a lot of energy at night - especially in northern WI.

But, on the other hand, they also gain a lot of energy during the day.  Facing south, even a clear double glazed unit will, on average, gain more than it loses over your heating season. In general the better insulating the window the greater the net benefit ---  with one warning.

The best low E for passive solar is not the best insulating low E. This goes against all intuition. But in the north, the lowest heating bills come from south facing low E windows with the highest SHGC (not the lowest U).

Stephen Thwaites P.Eng.
Thermotech Fiberglass Fenestration
Stephen Thwaites P.Eng.
Thermotech Fiberglass Fenestraion
Ottawa, Ontario
DteltechUser is Offline
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Posts:9
05/10/2008 3:46 PM  
It is very important to look at the over all building heat loss as you design your passive solar home. As Stephen has mentioned, material selection is critical and the location of windows will effect the type of glass that you will want to use.
When you minimize the amount of heat energy that your home requires, it becomes much easier to obtain respectable solar fraction ( the percentage of heat that you procure from the sun). Having designed, built and lived in solar homes for nearly 30 years, I am partial to an indirect system (ie:sunspace) that will be allowed greater temperature fluctuations than the rest of the home. We also use our sunspace to extend our growing season.

Get familiar with your local climate data and think super insulated. You can see some examples of sunspaces that work very well at a similar latitude to yours (Montana). www.mysunspace.net
They lacked the knowledge of houses - Aeschylus
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