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Passive solar techniques...?

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Posted by JNJ on July 27, 2003, 7:46 pm
I'm looking to retrofit our house to take advantage of renewable energy
techniques.  I've pretty well got the cooling in hand -- with ample trees on
the lot and awnings over the windows we've gotten by with just fans for all
but a week this year.  (It was kinda nasty out today so we ended up turning
on the AC for a while.)

Now I'm looking at the other side of the equation -- namely, heating the
house this winter.

The first floor of the house has forced air ventilation to two rooms
(kitchen and living room) and if I ever get around to it, the bedroom will
have it as well (we ripped the bedroom and master bath out but never got
around to putting the vent back in).  The second floor has one vent in one
room and puts out little to no air.  It's the upstairs that I *REALLY* want
to get under grips and anything I can do downstairs is just a bonus and a

$$$$ are a major issue in this economy ('specially since we ain't got 'em)
so I'm looking for any inexpensive retrofitting ideas I can get.


Posted by Jetgraphics on August 5, 2003, 9:00 pm

(1) Find the heating degree day data for your area, so you can make
reasonable projections.
(2) Determine your current energy consumption (use old fuel bills,
etc.), and get a rough figure on the BTUs you pay to replace. Also
factor in the waste heat from your electrical appliances! They become
a liability when cooling time arrives.

Once you have that data, you can then do a cost benefit analysis for
various techniques.

Based on data from the "Saskatchewan House" experiment back in the
1970s, superinsulation will reduce one's cost for replacement BTUs,
since waste heat from appliances will be sufficient. The reports of
the first year were somewhat alarming - the occupants couldn't use
their oven because it made the house too hot. Since they were
instrumenting the house, they couldn't open a window and vent. Their
total bill for space heating (electrical) was $.15 - from testing the
unit. It never turned on during the winter.
[Superinsulation also means you need to make house tight - reducing
infiltration losses. In the case of Saskatchewan, they designed the
wall insulation for R48, and the ceiling = R60. In my own area, I
found that R33 or better was sufficient to balance the loss rate with
gain from appliances and people.]

After sizing insulation, then adding "thermal mass" to reduce
temperature swings is next important. Cheapest efficient thermal mass
is encapsulated water - like 55 gallon drums (carbonated soda syrup
drums are nice) or recycled milk jugs. You can add and subtract the
amount of water until the system is tuned to your liking. Externally
insulated masonry and concrete are fine, but few homes are built like
that. If the house is wood frame, probably water drums will be the
most effective.

Finally, you had better put in an air-to-air heat exchanger to allow
for sufficient air changes without losing all your heat. Mitsubishi
has a nice system.

Depending on your wall system, and budget, insulation will probably be
your biggest expense. After all your effort, you have to consider
those gaping holes in your insulated shell known as windows. Windows
can be an asset and a liability. Solar collection is great, but not
all windows will be collecting. Multipane glazing systems rarely rise
above R3. You might consider insulated window shutters (or pop in
panels) for those _cold_ days and nights. Of course, there's a host of
issues to deal with - from condensation to decorating.

Good luck!

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