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re: an a-frame solar water heater concept
22 jul 2005
harry chickpea becomes unpleasant:
>>we might build a 12'x16' equilateral a-frame with a 4'x12' shallow pond
>>at the top (view above, in a fixed font) and 2 poly film water ducts
>>along the north and south edges to avoid wind sliding and overturning...
>gotta laugh. note the concept of putting water near the peak of a
>triangular prism to absorb and store heat. this wonderous idea is
>presented by the same nickie that pooh-poohed the idea of
>inexpensively preheating water for a domestic water heater via the
>simple expedient of placing a 4" pipe underneath and along the
>ridgeline of a roof. iirc, his comments were along the lines of what
>if it leaks, what if it freezes? yet, he has no comment or solution
>for the same questions about his own nickie special design.
since you ask, i'll comment. the pond above is much more efficient than
a pipe in the attic, and it's a draindown system with no exposed water
to freeze at night.
>nick would have people construct a special a-frame greenhouse instead,
>to attempt to capture enough heat to warm an entire house...
just hot water for showers. the "special greenhouse" might cost $200.
>making the cost/benefit ratio of heating water to the same temperature
>totally impractical...
what does that mean?
>especially on those cold winter days when 90% cloud cover can be common
>for weeks at a time.
that might happen north of the arctic circle :-)
>...a more simple alternative to a frame plan "a" might be the less
>pretentious plan "b,"
unpretentious is nice :-)
>where a b shape holds a tank or pool at the base (on the ground),
>contained within strawbales, and a more or less vertical wall of
>inexpensive construction grade 2" x4" lumber forms the staff of the b,
the staff of the b?
>partly braced by the tank and strawbales. this structure would be on the
>south side of a house, with a vegetable garden just south of the structure.
vegetable gardens don't reflect much sun...
>1 clear plastic
>2 clear plastic
>3 black shadecloth
>4 black plastic
>5 insulation and frame
>6 winterime tempered herbs cloche
>sun > >
> 12345
> ///// i
> ///// i
> ///// i
> ///// ihouse
> ///// i
> ///// i
> ///// plastic pla i
> ///// straw straw stic p i
> // 6/ pool or tank straw l i
> // /straw straw straw astic i
>garden south // /ground ground ground north house
...6 is the garden? looks like your ascii art got corrupted.
>the southern side of that b wall would be double glazed with plastic,
>while the north side of the wall would have black plastic and black
>shadecloth over insulation and a simple frame. the wall might even
>tilt, like an italic letter b for a better solar angle. cold water
>from the bottom of the tank would be pumped by a low volume pump
>(bilge pump?)...
attwood's $30 pumps have a 3 year guarantee and a 600 hour lifetime.
>to the top manifold and allowed to trickle down through the shadecloth
>(which would spread and even the flow) and over the black plastic,
>underneath the first closely-spaced layer of plastic glazing.
nice, altho this requires more pump power than a horizontal pond above
a tank with a spiral pipe heat exchanger in the bottom which leaves
the water level of the supply and return pipes just below the pond when
the pump isn't running. what would you use for a pump and a tank, vs
a $98 ez-set setup?
>since the pump would be controlled by a thermostat or solar sensor
>at the top of the b, it would only run when it could accumulate
>heat energy, and no water would be exposed to the cooling effects of
>night air or have to be drained or pumped without benefit. the heated
>water drips into and is allowed to accumulate on the top of the tank,
>thus preserving a greater delta t between the pumped water and the
>solar collector, increasing efficiency.
nice. you might turn the pump on with grainger's $8 2e247 snap-disc
thermostat in a 1 liter soda bottle (closed above 130 f and open below
115) and turn it off with grainger's $10 2e365 thermostat (closed below
120 and open above 140) sensing the water temp, if you plan to use a
pressurized flat pe pipe spiral as the cold water heat exchanger.
>hot water for the house is taken from the top of the tank, and the
>return pipe enters below mid-level in multiple low-flow horizontal
>outlets to help preserve the stratification.
you might pressurize the hot water, unless you live in the basement.
>the staw bale insulation for the pool or tank could be seeded with
>fertilizer or dried manure during the fall in preparation for the
>coldest part of the winter. during that period a small amount of
>water would be allowed to saturate the inner layer of straw, setting
>up an exothermic composting process underneath the pool that would be
>buffered by, and add to the heat of, the pool of water during those
>cloudy and short days that nick's design fails to address.
sounds like work. you mightr say more about this compost process.
i did address the cloudy and short days, using actual numbers :-)
>with this design, the weight of the large amount of water safely rests
>on straw which is on the ground, without requiring an expensive and
>possibly dangerous permanent structure.
same for the a-frame, with most of the water on the ground.
>...the issue of freezing is avoided with the simple expedient of a small
>drainback hole in the pipe or hose from the pump to the top of the frame.
sounds familiar.
>when spring arrives, the plastic, shadecloth, and insulaton are
>removed from the frame, the hay from the south side of the tank is
>spread as compost and mulch, and a layer of clear plastic replaced to
>form a low tent along the south side of the tank, for use as a
>cloche/greenhouse in starting seedlings for the garden.
"work!" -- maynard g. krebs
>this design is superior to nicks in that it has
>1. far lower cost
>2. far greater safety
>3. far simpler and easier construction
>4. year around use compared to seasonal use
>5. no problems with freezing
>6. secondary heat source for cold cloudy days
>7. lower pumping costs per unit of useful heat
>8. no structural permits and inspection required
>9. less impact from vandalism
>10. less environmental impact
>11. portability
>12. lack of acompanying psuedomath justification
i disagree.
nick
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