Passive solar DIY #2

[txlibdem]

You cannot underestimate the importance of siting on how much benefit you will get from passive solar heat gain in winter and avoiding overheating in the summer.

Your house should ideally be oriented so that the long axis is oriented east to west. As close as you can come to this the better.

Sometimes it's not possible due to terrain or setback requirements but you can still benefit from passive solar:

The longest wall of the home should face within 15 degrees, plus or minus, of true south to receive the most winter solar heat gain and reduce summer cooling costs (Figures 1 and 4). At 30 degrees east or west of south, winter heat gain is reduced by 15 percent from the optimum. Minimizing east and west facing walls and windows reduces excessive summer heat gain.

From: Passive Solar Home Design Checklist
http://www.p2pays.org/ref/49/48004.pdf

...snip...

Good passive solar homes are not difficult to design or expensive to build. However, they do require the use of basic, common-sense methods of working with the climate rather than against it. When you build a solar home that responds well to the climate in which it is built, you can count on it being:

• Comfortable – warm in the winter and cool in the summer;
  
• Economical – homeowners receive a positive cash flow or excellent return on their investment;
  
• Durable – often built from locally available, long-lasting, low-maintenance materials;
  
• Attractive – full of light and well connected to the outdoors; and
  
• Environmentally Responsible – passive solar homes make efficient use of our energy resources and provide a healthy space for owners.

New England climate energy costs are heat related and southern climates deal with air conditioning costs. Each area has its' site issues to deal with proper house orientation to help lower respective costs. New England calls for a southern exposure with windows to capture the sun's rays during the winter months and help warm your home. Passive solar heating doesn't cost extra, so let the sun shine in! Having sunlight enter your home during the short winter days adds psychological benefits to your life as well. If you have the possibility of the sun reaching your home than this should be considered. Your house design needs to take into account the land you're building on. This simple concept is often overlooked.

http://www.theinfomine.com/2010/10/01/siting-your-home/

Another design rule for passive solar is having few windows on the East and West sides of your passive solar house. These windows lose heat when you want to stay warm and warm your living space too much when you want it to stay cool. But so many homes are built with windows on the east or west walls so you will have to work with what you've got sometimes. My house has this problem, several medium size windows on the east wall and one huge window on the west wall. My solution? I went to the Home Depot and bought the material to build solar screens for those windows. I chose a screen fabric that blocks 90% of the sun's heat to limit the unwanted summer heating as much as possible. To make things worse, the overhangs on my house are 12" all around so we get a very welcome warming effect in the winter but a very unwelcome blazing heat along the east and south walls all summer and fall (which sends the air conditioning bill through the roof!).

I wonder if building a porch on the east and west sides of your house would help. My other thought was to use the Solartex 90 fabric to make some roll up sun block screens that I could put away in the winter but roll down in summer and fall to reduce the overheating.

Any thoughts, DUers?

[txlibdem]

1. Ideal orientation for solar glazing (windows)

In order for passive solar systems to work effectively, care must be take to ensure that the building is oriented to take advantage of year-round energy savings. The ideal orientation for solar glazing is within 5 degrees of true south. This orientation will provide maximum performance. Glazing oriented to within 15 degrees of true south will perform almost as well, and orientations up to 30 degrees off—although less effective—will still provide a substantial level of solar contribution. In Albuquerque, magnetic north as indicated on the compass is actually 13 degrees east of true north, and this declination should be corrected for when planning for orientation of south glazing. When glazing is oriented more than 15 degrees off true south, not only is winter solar performance reduced, but summer air conditioning loads also significantly increase, especially as the orientation goes west. The warmer the climate, the more east and west-facing glass will tend to cause overheating problems. In general, southeast orientations present less of a problem than southwest. In the ideal situation, the house should be oriented east-west and so have its longest wall facing south.

http://www.nmsea.org/Passive_Solar/Passive_Solar_Design.htm

[WolverineDG]

2. look at the homes built before a/c

they had porches all the way around the house. not just for looks, but for air circulation & to shade the walls to keep them cooler in the summer.

dg

[txlibdem]

3. Exactly

They didn't understand the science behind passive solar design yet they still did a lot of things right. Deciduous trees blocking the sun's heat in summer but losing their leaves in winter so as to allow the winter sun's light and heat. Lots of examples.

Green building codes should be expanded.

[WolverineDG]

4. I frequently visit a restored home built over 100 years ago

it's essentially a square, and the interior (if you view it from above) looks like a tic-tac-toe board, with the middle section serving as the main hallway (for air circulation), with the left & right sections divided into 3 rooms each. All the rooms have connecting doors as well as opening onto the main hallway (again, air circulation). As an added bonus, above each doorway is a transom window. Very thick walls, too, based on the depth of the windows & the sills.

Only the front porch remains (the rest was such bad shape, it was too expensive to renovate) & an addition has been added to the back (an extra bathroom). Might be something to consider for your house.

dg

[Kolesar]

5. The only double-pane windows I could find block half the sun coming in

Because that is how they make low-e windows these days. Low SHGC

Later, I learned that Marvin Windows offers high solar heat gain coefficient windows. Canadian companies offer high SHGC windows.

There is a down side to the windows I want, IIRC. One needs to close the blinds when the sun is no longer hitting the window (late in the day or when it is cloudy).

[txlibdem]

6. You are right on both counts

That's the problem with the double pane low-E argon filled windows that are so great on the NORTH side of a house. When you are trying for solar heat gain in winter (and have properly designed overhangs that will prevent solar heat gain in summer) you want the high solar gain windows you found, on the south-facing wall. That way you will get the heat of the sun coming in to warm your thermal mass and keep you nice and toasty well into the night.

But you're so right about needing to cover them with something insulating when the sun starts to go down or you'll lose it as fast as you gained it (the heat that is).

There are curtains with an insulated side that you can draw (I read about one guy who motorized his and set it on a timer so he didn't have to remember to do it (and could go out to dinner or the game without massive heat loss)).

You could also make insulated panels that either slide or fold out of the way during the day. Just need some styrofoam insulation, plywood and piano hinges. But you'll have a lot harder time automating that...

Good tip!