# An A-frame solar water heater concept

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• posted on July 21, 2005, 9:31 am
. ---- . . . . 30 F . . . . . pond . .-----------. ---- 12' . s 4' . 12' 10.4' . s . <--S . s T . . s . 6.92' . s . . s . . s . .duct duct. ---------------------------------------------------------------------- 12'
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... 20 psf makes 208 lb and 1082 ft-lb on each 1' EW slice of the greenhouse, so we need 12W = 1082 ie W = 90 pounds of water in each foot of duct, eg 1.44 ft^3 of water in a 16" duct.
We could make each of the 10 slightly curved "half-bows" on 4' centers with 2 12' 1x3s with 1x3 spacer blocks every 2' and a hinge at the top, and use 3 horizontal 1x3 purlins.
The south side could have 80% shadecloth to make hot air rise under the pond (which could be poly film over EPDM over foil over welded-wire fence.)
If we can somehow arrange that most of the greenhouse stays cooler while the airpath between the shadecloth and glazing and under the pond is temp T during the day, and the space above the pond is also temp T, we might figure 0.9xsqrt(1000^2+620^2)12' = 12,712 Btu enters a 4' slice of south glazing on an average 30 F Jan day in Phila, and 0.81^2x4x1177 = 3813 of that enters the pond. At 130 F, it might also gain 6h(T-130)4ft^2x1.5 = 36T-4680 Btu/day from the bottom, and more, if the ground to the south is reflective.
If the glazing loses 6h(T-30)12ft^2/R0.8 = 90T-2700 Btu/day and the daily energy that flows into the slice equals the energy that flows out, 12712 = 3813+(36T-4680) + 90T-2700, so T = 129 F, and the pond slice gains about 3813 Btu, and 50K/3813 = 13.1', so a 16' greenhouse might provide most of the heat in January. With about 3813x16'/6h = 10.2K Btu/h during solar collection, 5 gpm (2400 Btu/h-F) would rise 4 F, and 400'x1/2" PE pipe with 75 ft^2 of U30 surface would rise 10.2K/(75x30) = 5 F.
A row house with a flat roof might have a \$98 12' diameter x 3' tall EZ-Set pool in the basement with a \$60 300'x1" fresh water pressurized PE pipe heat exchanger near the top of the pool under floating Styrofoam and a low-head pump with a \$40 400'x1/2" PE pipe heat exchanger in the pool bottom. With lots of insulation and 0.8xPi(11/2)^2x3x62.33 = 14216 pounds of water at 110 F after 5 cloudy days, after supplying 5x50K Btu, it needs to be 110+250K/14216 = 128 F on an average day. Then again, it might melt :-) It might need reinforcing, eg a tarp tied up around it. Or maybe we need a different kind of pool.
This might also be a standalone structure in a yard, with the filter pump that comes with the pool.
Nick
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• posted on July 22, 2005, 2:45 am
Nick Pine wrote:

You used the word "Might" 8 times, "Could" 3 times, "If" 3 times, with a "Maybe" and "Somehow" once each.
"Could" it be that you "Might" be proposing that "If" "Somehow" you "Maybe" actually built one you could prove your point without using those words that only confirm that you are in fact just guessing.
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<%-name%>
• posted on July 21, 2005, 2:17 pm

Thank you for counting.

The only big risk is the plastic pool losing strength at 130 F, and there are solutions for that. I go overboard on the "mights" to avoid ignorant people like you raising angry challenges to 300-year-old settled physics.
Nick
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• posted on July 21, 2005, 8:06 pm
snipped-for-privacy@ece.villanova.edu wrote:

Perhaps a scale model would help settle the mights, coulds and maybes.
--
Humbly--Ed

"If the man doesn\'t believe as we do,
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• posted on July 21, 2005, 5:36 pm
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wrote:

Possibly.
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-john
wide-open at throttle dot info
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• posted on July 21, 2005, 9:10 pm
EEs abandoned models 20 years ago in favor of simulations, and they don't do simulations for simple systems. Any sufficiently advanced technology appears to be magic, and the less you know, the more it seems to be magic. George Ghio measures risistors in amps, so a large part of the world is magic to him.
Nick
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• posted on July 22, 2005, 2:25 am
snipped-for-privacy@ece.villanova.edu wrote:

If thermal simulation software is available, by all means, use it.
--
Humbly--Ed

"If the man doesn\'t believe as we do,
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• posted on July 22, 2005, 1:43 pm
snipped-for-privacy@ece.villanova.edu wrote:

There is no magic involved when a Rheostat is clearly rated by the manufacturer in amps. I did not make the said Rheostat. I did not rate the Rheostat. I commented on the fact that it was rated in amps as a point of interest.
Now, can you prove your theory with a working unit or not.
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• posted on July 22, 2005, 1:15 pm
snipped-for-privacy@ece.villanova.edu wrote:

Nick,
You want someone else to do the work. I suggest that you do the work.
The words you use indicate that you are just guessing.
I have the greatest faith in your maths and the physics. The questions are; "Can you prove your theory? Can you in fact build this? Test it? Prove it? Present the results in plain English?
Ignorance generates words like "Might" "Could" "If" "Maybe" "Somehow".
You have presented a theory riddled with doubts.
It is now time to remove the doubts.
Go for it.
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<%-name%>
• posted on July 21, 2005, 6:41 pm

greenhouse,
fence.)
temp
daily
of
pump
LOL, that was good. Nothing personal Nick. :-)
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• posted on July 22, 2005, 3:32 am

fence.)
Nick
I read the first paragraph and there was nothing to tell me what all this was about, so I stopped reading. What is the function of the A frame? Then I may read the rest of it.
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• posted on July 21, 2005, 9:46 pm

greenhouse,
temp
daily
of
pump
Then
SAT: 780 math / 410 verbal
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<%-name%>
• posted on July 22, 2005, 8:57 pm

<snip>
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.
Nick would have people construct a special A-frame greenhouse instead, to attempt to capture enough heat to warm an entire house, making the cost/benefit ratio of heating water to the same temperature totally impractical, especially on those cold winter days when 90% cloud cover can be common for weeks at a time. Maybe if Nick hurries, he can still get a job for NASA designing a solar powered outhouse to be towed behind the shuttle.
Now - half tongue-in-cheek, and half-serious, I present an alternative. Cost-wise, a more simple alternative to A frame plan "A" might be the less pretentious plan "b," 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, 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.
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
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?) 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. 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.
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.
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.
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. The covered pool or tank is simply enshrouded in hay and leaves for the winter, and an outer covering of plastic prevents that material from being blown away or saturated with water from late fall rains or melting snow. 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.
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. (A smaller cloche is shown in the diagram, where a shelf allows midwinter growth of herbs in the area beneath where the water has to drain back into the tank.) Once the spring seedings are safely started, the plastic is again removed. The plastic might be used during the summer for water catchment or to solar sterilize parts of the garden. In early summer, the frame is used to support pole beans, the bulk of the straw is spread, and the tank or pool allowed to cool and supply water to the garden during parched periods. The outflow of the gutters of the house are redirected to keep this pool as filled as possible and reduce watering costs. After the August/September dry spell, the pool will be empty, and the final remaining straw and manure can be removed and set out as winter mulch for the garden. The pool is then remounted on fresh straw, and any rainwater from the roof again channeled into it to help fill it.
Come fall, the vines are removed, the plastic is remounted and the process is repeated.
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
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• posted on July 22, 2005, 7:00 pm
Harry Chickpea wrote:

And your problem is??? In a stand-alone greenhouse, you don't have a serious problem if it springs a leak. If it's in your house, you sure do.
--
derek

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<%-name%>
• posted on July 22, 2005, 10:38 pm

It isn't my problem. As I pointed out to Nick at the time, a 4" pipe contains enough thermal mass, and the location is inherently warmer than the rest of the attic, to preclude freezing in all but the most extreme climates, and allowing a small cushion of air at the top for expansion would resolve the issue even if it did freeze. The pipe would be no more or less likely to spring a leak than any other pipe. I suggest that you and Nick might want to remember that people have plumbing and even <gasp!> bathtubs on the second floors of their homes, and condos and apartments and office buildings have plumbing that reaches to the sky. Somehow, they survive.
Compare the likelihood of standard pipe leaking in a properly designed and protected tempering tank system to the potential for catastrophic leaks in "a 4'x12' shallow pond at the top and 2 poly film water ducts along the north and south edges to avoid wind sliding and overturning.." contained in a minimally protected A frame covered in plastic. Can you say "BB gun?" Can you say "mouse nibble?" Mice would find such a structure a nice winter home. Poly film - pipe. Poly film - pipe. Hmmm.
Nope. I don't have a problem.
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• posted on July 23, 2005, 12:49 am
Harry Chickpea wrote:
....

What do you consider "the most extreme climates"? Most of the US, and practically all of Canada, are subject to regular conditions _well_ under freezing, and we do NOT have plumbing along the ridgelines of our roofs. To prevent ice-damming, attics are kept as cold as possible, and all plumbing is kept below the insulation. If your attic is warm enough in winter to prevent a pipe freezing, you're wasting too much energy.
I haven't a clue (and don't really care) if Nick's idea is sound, but his objection to a 4" pipe under the ridgeline of a roof certainly is.
--
derek

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• posted on July 26, 2005, 3:28 am

do.
A vented attic, in which the only function of the rood is to keep off the house, nothing else.

Only in Canada type of climates.
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• posted on July 26, 2005, 5:53 am

Well... since I live in south Florida, where we haven't had a freeze in years, and a really low air temp during the winter is 50 degrees F, I have to respectfully disagree. :-)
You'd have to refer to the original thread for the complete proposal. I lived in Vermont for many many years, and I'm aware of the issues there. I would consider that an extreme climate, since as a kid I delivered papers in -30 degree F windy weather, and moved out of state after one winter where the sun never broke through clouds for two months. Nick's stomping grounds of PA don't qualify as an extreme climate in my book.
The full idea included a reflective barrier above the 4" pipe to reduce heat loss, and the capability of drain down for those times when the system wouldn't act as a preheater. IIRC, Nick was proposing a solar pond or other involved project to preheat water with limited results, and I tossed back a simple preheater idea that used minimal materials, took minimal time to build, and had a faster payback.

Nick objects to a lot of things. You would have to ask him why.
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• posted on July 26, 2005, 3:43 pm
Harry Chickpea wrote:

What's to disagree with???? You live in the warmest part of the US! Even most of your compatriots suffer real cold. My statement was still correct.

I don't know which part of PA Nick's in, but the northern part can easily hit -10F for lengthy periods (more than two weeks). That's _not_ what I would call extreme, either, but it's too cold for piping above the insulation in the attic.
--
derek

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• posted on July 26, 2005, 3:37 pm
News wrote:

You're wrong there. The majority of people reading usenet are in North America. The majority of North America is subject to extreme freezing - ie, all of Canada except the lower BC area, all of the American northeast & midwest, the plains states down to north Texas and all the mountain states.
I know, a 4" pipe under _your_ roof ridge should be fine, but you're practically in the tropics :-)
--
derek