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Posted by Brian Graham on June 23, 2004, 2:16 pm
 
Hi All,

I've been doing a bit of reading and am starting to think about solar heating.
(Trouble brewing.. ;-)  What I have in mind is the following:

3/4" black plastic hose (hard plastic that we use at the cottage attached to the
jet pump) coiled on my roof. Boxed in on the sides, plexiglass above, but open
below. I have a tin roof and want radiant heating from the tin. (I'll use metal
studs and proper tin screws/washers to ensure a leak-free frame installation.) A
food-grade plastic barrel in the basement to store the heated water, and a small
pump to circulate the water slowly. A 30-60' coil of copper in the barrel is the
"cold water input" for the hot water tank. The roof coil will be drained for the
winter.

For the winter,

Part B. I want to have a copper coil behind/below my wood stove, with water
circulating from the same barrel as above.

Part C. I'm thinking radiant heaters, sourced from the same barrel for other
parts of the house.

Part D. Still thinking, but wondering about putting a coil in the forced air
ducts as a heat-exchanger as well.

The question I have centers around overheating. I'm not sure that's a problem in
the summer with the roof coils or not. But with the wood stove, it may be
possible at times to get the water to a boil. But perhaps I worry too much. If
the water's moving fast enough, it won't boil in the lines, and waste heat from
the wood stove won't bring a 60 gallon barrel to a boil, without burning the
house down first.

Anyway, does anyone see any problems? Recommended pumps? (I don't want to spend
all the money saved in heating the water on the pump to move it.. lol)

Suggested readings?

Thanks.

Brian

Posted by Brian Graham on June 25, 2004, 4:43 pm
 
Good news, I guess. Nobody sees any problems with my approach..  :-/

I've been doing a bit of reading and am starting to think about solar heating.
What I have in mind is the following:

Posted by Gary on June 25, 2004, 7:45 pm
 Brian Graham wrote:

(Trouble brewing.. ;-)  What I have in mind is the following:

the jet pump) coiled on my roof. Boxed in on the sides, plexiglass above, but
open below. I have a tin roof and want radiant heating from the tin. (I'll use
metal studs and proper tin screws/washers to ensure a leak-free frame
installation.) A food-grade plastic barrel in the basement to store the heated
water, and a small pump to circulate the water slowly. A 30-60' coil of copper
in the barrel is the "cold water input" for the hot water tank. The roof coil
will be drained for the winter.


circulating from the same barrel as above.

parts of the house.

ducts as a heat-exchanger as well.

in the summer with the roof coils or not. But with the wood stove, it may be
possible at times to get the water to a boil. But perhaps I worry too much. If
the water's moving fast enough, it won't boil in the lines, and waste heat from
the wood stove won't bring a 60 gallon barrel to a boil, without burning the
house down first.


spend all the money saved in heating the water on the pump to move it.. lol)

Hi Brian,

I guess one concern would be that on a sunny day with no water being
pumped through the collector, it may reach temperatures that are higher
than the plastic pipe and plexiglass can withstand.  But, if the back of
the collector is metal, and there is no insulation on the inside of the
metal, there will be quite a bit of heat loss, and this should help
limit the maximum temperature.  The other factor that helps is that the
water in the plastic pipe will be under low pressure(?)
Some experimentation might be in order (e.g. a small test panel), or the
use of higher temperature materials.

Running some rough numbers to match the collector size to the size of
your storage container might also be a good idea.  This would require
knowing your approximate location, the size of collector, and the size
of the storage barrel, and how you plan to use the stored heat.

If you heat the water in a 50 gal barrel from (say) 80F up to (say)
130F, you have stored:

    (50 gal) (8.3lb/gal)(130F - 80F) (1 BTU/lb-F) = 21000 BTU

This is equivalent to about a quarter gallon of propane -- i.e. not an
awful lot.

I am curious about your statement "I want radiant heat from the tin
roof".  What kind of experience have you had with this?  Does the inside
of the metal roof face a living area, or an attic area (i.e. does the
radiant heat warm up people or attic air)?  In your experience, has this
been a good way to heat?

Gary



Posted by Brian Graham on June 25, 2004, 9:01 pm
 Hi Gary,

  Thanks for your response..


pumped through the collector, it may reach temperatures that are higher
than the plastic pipe and plexiglass can withstand.<<<

Which begs the question, what is the melting point of Plexiglass, and the
plastic hose? Does anyone know this?


the inside of the  metal, there will be quite a bit of heat loss, and this
should help limit the maximum temperature. <<<


I was looking for radiant heat from the tin roof to heat the coil from the
backside, in addition to the heating from the sun. You are suggesting that I
would capture more heat in a sealed and insulated unit, as opposed to collecting
the heat from the tin roof. I'll have to think about that one some more..


130F, you have stored:

    (50 gal) (8.3lb/gal)(130F - 80F) (1 BTU/lb-F) = 21000 BTU

This is equivalent to about a quarter gallon of propane -- i.e. not an
awful lot. <<<

Well, if I heat the water to the point where the electric element in my hot
water heater no longer comes on, its enough.  ;-)


roof".  What kind of experience have you had with this?<<<

Its like sitting on the hood of your car mid-summer with only shorts on. You're
going to burn something!  Likewise, a tin roof is HOT in the summer. So I wanted
to collect heat from the roof, in addition to directly from the sun. A
plexiglass top to cut the wind. I guess the solution might be to use the roof as
the backing. Hmmm. :-)


(i.e. does the radiant heat warm up people or attic air)?  In your experience,
has this been a good way to heat? <<<


Attic. And you don't want to be in it in the heat of the day. And I live in
Canada, so it would be worse where the sun REALLY shines!

Posted by Gary on June 26, 2004, 1:22 am
 Brian Graham wrote:

plastic hose? Does anyone know this?

Acrylic (e.g. Plexiglass)  is listed as 125 to 200F
Polycarbonate (e.g. Lexan) is listed as 250 to 270F


the

inside of the  metal, there will be quite a bit of heat loss, and this
should help limit the maximum temperature. <<<

backside,

in addition to the heating from the sun. You are suggesting that I would
capture

more heat in a sealed and insulated unit, as opposed to collecting the
heat from the

tin roof. I'll have to think about that one some more..

I actually thought that you were trying to heat the space on the OTHER
side of the tin roof via radiant heat.
If the tin is a dark color, it would absorb heat well, and some of this
would transfer to the pipe via radiation and by heating the air in the
collector.   If you insulated the BACK side of the tin, it would reach a
higher temperature, and transfer more heat to the pipe.
But, in this case I think you will be over the temperature capability of
plexiglass or typical plastic pipe.  An glazed and insulated collector
will probably get to 200F or more on occasion -- especially if you are
not removing heat by pumping water through (and its hard to guarantee
that the circulation pump will always be working).


water heater no longer comes on, its enough.  ;-)

You're going to burn

something!  Likewise, a tin roof is HOT in the summer. So I wanted to
collect heat from the

roof, in addition to directly from the sun. A plexiglass top to cut the
wind. I guess the solution

might be to use the roof as the backing. Hmmm. :-)

(i.e. does the radiant

heat warm up people or attic air)?  In your experience, has this been a
good way to heat? <<<

Canada, so it would be worse where the sun REALLY shines!

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