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Solar roof collector questions - Page 2

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Posted by Gary on March 5, 2004, 3:58 pm
 
Hi David,


The water heater is basically a set of enhancments to the old batch style
(sometimes called "breadbox heaters")  It uses an 80 gallonish tank, and
also requires a common wall with the house.  Its really not compatible with
a roof installation.  I could use a conventional water heater with a flat
panel collector, and put it on the roof, but I think that the enhanced batch
concept that I have in mind has some real potential of providing good cold
climate water heating with a simple and low cost system, and I would really
like to give it a try.

If I did use the full wall space, I could probably get in a 16 ft wide by 6
or 7 ft high collector (or sun space) -- this provides about 100 ft^2 of
collection area.  When I looked at the roof mounted one at 250 ft^2 it looks
like it might provide about $00 a year in fuel saving, or about 1/3 of my
heating bill.  A 100 ft^2 collector would probably only provide about half
that.  The roof location would actually allow a collector of up to about 500
ft^2, and I am wondering why I shouldn't go larger than 250 ft^2?


We have made some efforts to reduce the 550 BTU/hr F heat loss in the form
of more insulation here and there.  The house is about 6 years old, and is
basically pretty well insulated (R38 ceiling,  2X6 walls with R19 glass).
We big problem is that a bit more than 50% of the heat loss is out windows,
and most of this is out the large ENE facing windows (no gain, lots of
loss).  All the windows are already double pane, low e.   On the lower set
of ENE windows we have special shades that actually have a kind of track
along the side that the shade engages to reduce air circulation -- I think
this works pretty well.  The top set of windows are of irregular shape
(triangles and trapozoids), so its tough to find anything to reduce heat
loss.  I am looking into cutting clear Acrylic panels to go inside these
windows and act like a kind of inside storm window, but the panels would be
big and difficult to handle.
I'm all ears to other suggestions for either the windows or other areas.


Thanks -- Gary




Posted by Jerry Ellinghuysen on March 5, 2004, 4:32 pm
 
Be sure to consider what the collector is going to be doing in the summer.

Is the collector going to be accessible such that you can cover it? I guess
the alternative is to figure a way to dump the heat, but it seems like
isolating the collector from the input is the easiest.

I'm planning on building using (probably) evacuated tubes for hot water and
partial radiant heating, but the real dilemma is what to do with the excess
heat in the summer time. If your collector  (of about any type) goes
stagnant in July, you are going to spike some pretty large temps. Right now,
my thought process seems to center on finding ways to keep it out of the
sun......

Collectors are like my old VW bus; the heater works best in the summer ;)


shingles.

needing


Posted by Ecnerwal on March 5, 2004, 4:48 pm
 
Absorbtion cooling/refrigeration, but you may not want to deal with
ammonia (the common one I know of). There are other options (lithium
chloride, perhaps?) which have been written up.

If you are in an area with humid summers, set up to dry dessicant with
the heat, then suck water from the house with dessicant. Not much point
in dry-heat areas.

Hot tub, swimming pool, and finally, a cupola/thermal chimney on the
house roof with several radiators in it, which would dump excess heat
from the collector and also suck more air from the attic space.

--
Cats, Coffee, Chocolate...vices to live by

Posted by Gary on March 5, 2004, 5:50 pm
 

The 250 ft^2 roof collector for space heating that I looked at delivers 250k
BTU/day in the summer -- I had thought that when the collector temperature
exceeds a set level, that the fan would turn on and vent the hot air to the
outside.  This seems wasteful in electicity, wear and tear on the fan, and
not making use of the heat.   But, if I could use the excess heat to heat a
hot water preheat tank, I would be getting some useful return from the
excess summer heat?    (similar to your hot tub thought)
In my house I could probably acually locate the preheat tank in the crawl
space and run the air duct down to it -- this would have less disaster
potential than in the attic.

Thanks -- Gary


Posted by Gary on March 5, 2004, 6:55 pm
 

I'm not to keen on trying to cover it -- we get some pretty good winds at
times.
I would like to work out a way to vent it that does not require running the
fan.


possible,

entry/exit

provide

up/down

absorber

weather


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