Hot Water Idea
Nick Pine
> way...@dpla.net > wrote
> >What If:
> >
> >You purchased a large stainless steel tank and painted it flat black,
> >and it sat out in the sun right before entering your hot water heater?
>
> That's a nice idea in principle, but wouldn't be very effective the way >
you have presented it-
It might work reasonably well in a warm sunny climate, altho the wind could
blow away lots of heat, with no glazing, and it would lose lots of heat at
night and on cloudy days, with no night insulation. Even with no sun, a
tempering/preheating tank in the house could help.
> there wouldn't be enough steel to water contact to
> quickly transfer the heat.
I disagree. You might check this out with a double boiler on your kitchen
stove, and a couple of thermometers and a clock...
I measured a still water film thermal conductance of about
60 Btu/h-F-ft^2 this way.
A gallon of water in contact with a square foot of steel has an RC
time constant of about 8 Btu/F/60Btu/h-F hours, ie 8 minutes, so starting at
say, 50 F, in contact with 130 F steel, it would warm to
100 F when 100 = 130-(130-50)exp(-t/8), ie when t = -8 ln(30/80)
= 7.84 minutes.
>You'd be much better off with a network of copper tubing (say
>3/8" o.d.), painted flat black and placed in a glassed-over box
>oriented to catch most of the day's light.
Rubbish. This might work better with fins and a pump and an insulated tank,
or larger plastic tubing, altho that's unlikely to survive normal water
pressure. That copper tubing's too small to hold much water or work well by
thermosyphoning, and it needs more sun-gathering surface.
>...Personally, I'm much more in favor of building a heat storage
> building, and keeping a hot water tank in it-
Sounds nice. Big polyethylene tanks are cheap, eg $899.99 for Tractor
Supply's 2100 gallon 87" diameter x 87" tall version. Put it inside an 8'
x2" foamboard cube surrounded by bags of leaves?
That makes RC about 2100x8Btu/FxR28/(6x64ft^2) = 1225 hours,
or 51 days. Yum :-)
> then you just burn your trash, and whatever wood you need
> to keep things hot, and no worries about burning down
> your house.
Wood pollutes, and it's lots of work. How can we solar heat that sucker? For
potable water storage, one might efficiently bubble a
little air through the higher temperature water it to keep it pure
and free of bacterial nutrients, as in a sewage treatment plant.
Nick
Anthony Matonak
>
> <br...@camalott.com> wrote
>
> > way...@dpla.net > wrote
>
> > >What If:
> > >
> > >You purchased a large stainless steel tank and painted it flat black,
> > >and it sat out in the sun right before entering your hot water heater?
> >
> > That's a nice idea in principle, but wouldn't be very effective the way >
> you have presented it-
>
> It might work reasonably well in a warm sunny climate, altho the wind could
> blow away lots of heat, with no glazing, and it would lose lots of heat at
> night and on cloudy days, with no night insulation. Even with no sun, a
> tempering/preheating tank in the house could help.
How about this for an idea.
You take a large stainless steel tank, painted flat black and plumb
it into your hot water heater as a pre-heater tank.
Then enclose that tank in a triangular shaped box with a few inches
of that foil-faced foam insulation panels (and maybe plywood on the
outside) with the foil on the inside to reflect the light, on two
sides and the third side being a sheet of glass.
This describes a batch water heater as people have been fond of
building for years and it works fairly well, usually from old
(thrown out) electric water heater tanks whose heater elements
have burned out. Have to remember to strip off the outside
insulation on the tank though.
As I recall they are more popular in sunny climates where it's
unlikely to have a month without sun and freezing isn't such an
issue.
Anthony
You take
JimMcCarty
this. Fill a tub with water. Add 2 to 12 women in bikinis or less,
depending on size of tub. Water gets HOT! Enjoy tub! :)
--
Jim McCarty
Sent via Deja.com http://www.deja.com/
Share what you know. Learn what you don't.
Nick Pine
> How about this for an idea.
> You take a large stainless steel tank, painted flat black and plumb
> it into your hot water heater as a pre-heater tank.
Some objectives: a) gather enough sun (about 100ft^2 for a house,)
b) get the sun into the tank, c) save the heat at night, d) keep the
tank from freezing, and d) do all that simply and inexpensively...
> Then enclose that tank in a triangular shaped box with a few inches
> of that foil-faced foam insulation panels (and maybe plywood on the
> outside) with the foil on the inside to reflect the light, on two
> sides and the third side being a sheet of glass.
Say 4'x8' of glazing, and 2 4'x8'x2" foil-faced foam (R-10)sides. In Phila,
this collects about 0.9x4'x8'x1000 =28.8K Btu/day of sun in January, when
the average outdoor temperature is 30 F. The box
has a thermal conductance of about 32ft^2/R1 = 32 Btu/h-F for the glazing
and 78ft^2/R10 = 7.8 for the other sides, ie a total of about
40 Btu/h-F.
With no water flowing, the tank absorbs about 28.8K Btu and
loses 24h(T-30)40 = 960(T-30) Btu over an average day, so
T = 30+28.8K/960 = 60 F. Not very promising. It would work better indoors,
in a 70 F house.
Say we preheat enough 50 F water for 6 110 F 3gpm 10 minute showers per day,
ie 180 gallons per day, so 28.8K = 960(T-30)+180x8(T-50), and T = 54 F, so
the tank provides 180x8(54-50)
= 5760 Btu/day of useful heat, 7% of the water heating energy,
with a solar collection efficiency of 5760/(1000x4'x8') = 18%.
> This describes a batch water heater as people have been fond of
> building for years and it works fairly well, usually from old
> (thrown out) electric water heater tanks whose heater elements
> have burned out...
It's my impression that few water heaters have stainless steel tanks, and
they are usually discarded because the tanks are leaky, and their electric
heating elements are replaceable.
This arrangement might work better in an attic, with a long "tank" (a
30' long x 4" diameter black-painted PVC pipe, with a 3/4" copper
pressurized pipe inside?) along the ridge line, and a transparent sloping
south roof, and a concentrating parabolic reflector below the tank, and
foil-faced foam above the tank, which extends down below
the tank bottom to make a secondary concentrating reflector...
The tank might be suspended from ropes, and swung north and south to track
the sun, with a high concentration ratio. Nielson's
(253) 941-7281 aluminized Mylar film costs about 15 cents/ft^2 in 4'x100'
rolls. It lasts for years indoors, and can be "glued" to curved masonite or
scored foil-faced foamboard with a roller and axle grease, says Duane
Johnson, who reports it's sufficiently mirrorlike
for 100:1 concentration.
Be careful about fires.
Nick
Fred McGalliard
Nick Pine wrote:
>
> Anthony Matonak <ant...@matonak.org> wrote
>
> > How about this for an idea.
> > You take a large stainless steel tank, painted flat black and plumb
> > it into your hot water heater as a pre-heater tank.
>
> Some objectives: a) gather enough sun (about 100ft^2 for a house,)
> b) get the sun into the tank, c) save the heat at night, d) keep the
> tank from freezing, and d) do all that simply and inexpensively...
I think this is easier to resolve if the tank is well insulated and
above the level of the solar collector. Then you can use simple
convection to trap the heat away from the night sky and cold air
circulation. There is no easy way I know to keep the freezing under
control. The simplest, in terms of active controls, is just to put scads
of antifreeze in the fluid, and use a heat exchanger to get it back out
in clean water. A bit nastier, never seen a design for this, would be a
set of pneumatic valves that would drain the heat exchanger when the
insolation is low and refill it when things warm up a bit. This would be
an automatic regulation powered by the solar heat. Technically simpler,
but more likely to be trouble prone, a set of electronic valves and a
thermal sensor, doing the same job. And last, and in my opinion
nastiest, you operate the drain valves manually. Forget one night when
an early frost comes in, and you have a repair job.
Edward Haas
and it has a rate of heat transfer (or whatever the proper engineering term
is...) that is only about 1/30 that of copper, i.e. it takes a long time for
heat to soak through it and get to the contents. Plastic might be a better
choice in terms of price, too.
--
"Steamboat Ed" Haas : Deep in my guts
Watch link rot in action! : I know I'm nuts...
http://www.nmpproducts.com
---Decks a-wash in a sea of words---
Nick Pine
>...There is no easy way I know to keep the freezing under
>control. The simplest, in terms of active controls, is just to put scads
>of antifreeze in the fluid, and use a heat exchanger to get it back out
>in clean water.
Heilotrope General, inter alia, make solar controllers that will circulate
water through the collector when temperatures approach freezing.
Nick
Nick Pine
> --The trouble with stainless steel is twofold: it's very expensive
> and it has a rate of heat transfer (or whatever the proper >engineering
term is...) that is only about 1/30 that of copper...
Ain't the Internet wonderful :-) How curious that you opine in this
direction without even knowing the proper terminology. Nonetheless,
this difference is unimportant, given the wall thinness.
Nick
Sarlock T.
Why not construct an empty box out of a thin sheet metal, or copper
plates. Say 8-10" wide, by 2-3' long and let's say, 1" thick. Have a water
inlet on one side, and outlet on the other side. Paint the box flat black.
On top of this build a simple motor driven solar tracker which controls
a set of fresnel lenses focused against the small black box. Run water, via
a circulation pump between this and a well insulated storage tank. When the
sun set's, or the water temp reaches below a certain point, the circulation
pump stops for the night. When the temperature picks back up the next day,
the circulation pump starts again. For better performance, maybe use a
couple of clean heater cores or a radiator painted flat black(high temp
paint obviously). The sun by itself may not be enough to warm the water
very much in some cases, but by using some simple and available technology
you can focus more of the sun on a smaller area.
Jonathon Caywood
Nick Pine wrote in message ...
Robert Free
elements for optimum solar energy capture. Black and flat black are the
color choices. Wouldn't green be a better color? It seems that the color
of foliage in thousands of species of plants evolved the green color and not
black. I think that if black gave plants more solar energy absorption for
the plants' photosynthesis the plants would all have black leaves. Perhaps
black works as well as it does because it contains green along with the
other colors that make it up. I could be wrong.
Randy Elliott
Green probably absorbs only the rays that are helpful to the plant. Black
is a broadband approach that I figure is better suited for water heating.
Sarlock T.
plants are also designed/evolved to protect themselves from the sun, while
at the same time taking in energy from it. In an instance like solar
heating where you want to suck in as much heat as possible, black seems most
efficient and absorbs the many wavelengths of energy provided.
Robert Free wrote in message ...
Duane C. Johnson
Robert Free wrote:
>
> There seems to be a consensus as to the best color to paint
> water system elements for optimum solar energy capture.
> Black and flat black are the color choices. Wouldn't green
> be a better color? It seems that the color of foliage in
> thousands of species of plants evolved the green color and
> not black. I think that if black gave plants more solar
> energy absorption for the plants' photosynthesis the plants
> would all have black leaves. Perhaps black works as well as
> it does because it contains green along with the other
> colors that make it up. I could be wrong.
Actually, green is the color that, generally, plants don't
use. Think about it. If the chlorophyl were absorbing the
green color it would not escape.
--
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These are my opinions, and not that of Unisys Corp. ===
Nick Pine
Sarlock T. <sarlock@no!spam.twcny.rr.com> wrote
> Just a thought here, dissect it as you may.
OK :-)
> Why not construct an empty box out of a thin sheet metal, or copper
> plates. Say 8-10" wide, by 2-3' long and let's say, 1" thick. Have a
water
> inlet on one side, and outlet on the other side. Paint the box flat
black.
>
> On top of this build a simple motor driven solar tracker which
controls
> a set of fresnel lenses focused against the small black box. Run water,
via
> a circulation pump...
Sounds expensive and complicated to me.
Nick
Nick Pine
Robert Free <rmf...@nospam.cnw.com>
> There seems to be a consensus as to the best color to paint water system
> elements for optimum solar energy capture. Black and flat black are the
> color choices. Wouldn't green be a better color? It seems that the color
> of foliage in thousands of species of plants evolved the green color and
not
> black.
I can't speak for plants, but dark green can be a nice aesthetic choice for
solar collectors because it can be very dark (absorbing) for solar radiation
and brighter-looking for people whose eyes are most sensitive in that part
of the visible spectrum.
Nick
Joe
was then and I'm 29 now... it was at least 12 years ago) that showed flat
dark green absorbed more sunlight and converted it to heat than any other
color.
--
Best regards,
Joe
(973) 571-1456 - 24-hour recorded hotline for the Tri-State Open Mat
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Come spar with us September 19 and the third Sunday of every month.
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Nick Pine wrote in message ...
>
Sarlock T.
Nick Pine wrote in message ...
>
John Galt
plants' development to take advantage of it. Photosynthesis produces
chlorophyl, which is green.
Robert Free wrote:
> color choices. Wouldn't green be a better color? It seems that the color
> of foliage in thousands of species of plants evolved the green color and not
> black. I think that if black gave plants more solar energy absorption for
> the plants' photosynthesis the plants would all have black leaves. Perhaps
> black works as well as it does because it contains green along with the
> other colors that make it up. I could be wrong.
--
John Galt
"If we have the potential to create a Utopia,
why do we often resemble a primitive society?"
jg...@starwarp.com http://www.starwarp.com/The_Observatory
All rights reserved Copyright (c) 1998 by John Galt
(Remove NOSPAM from address when sending email)
Anthony Matonak
Nick Pine wrote:
>
> Anthony Matonak <ant...@matonak.org> wrote
>
> > How about this for an idea.
> > You take a large stainless steel tank, painted flat black and plumb
> > it into your hot water heater as a pre-heater tank.
>
> Some objectives: a) gather enough sun (about 100ft^2 for a house,)
> b) get the sun into the tank, c) save the heat at night, d) keep the
> tank from freezing, and d) do all that simply and inexpensively...
>
> > Then enclose that tank in a triangular shaped box with a few inches
> > of that foil-faced foam insulation panels (and maybe plywood on the
> > outside) with the foil on the inside to reflect the light, on two
> > sides and the third side being a sheet of glass.
>
> Say 4'x8' of glazing, and 2 4'x8'x2" foil-faced foam (R-10)sides. In Phila,
> this collects about 0.9x4'x8'x1000 =28.8K Btu/day of sun in January, when
> the average outdoor temperature is 30 F. The box
> has a thermal conductance of about 32ft^2/R1 = 32 Btu/h-F for the glazing
> and 78ft^2/R10 = 7.8 for the other sides, ie a total of about
> 40 Btu/h-F.
>
Um, lets see if I understand the math (I might not)...
Area of collection (front glass) 4'x8', aprox 2.9728 sq meters.
(Lets call it 3 sq meters for simplicity sake)
Assuming 1000 watts/sq meter of sunlight, that's about 3kw.
1 watt hour is about 3.4144 btu so 3000 watt-hours = 10243 Btu.
So for 28800 btu/day that assumes 2.8 hours of sun. I don't live
in Phily but assuming a yearly average of 4 hours/day of full
sun and an hour difference between summer and winter I could see
that working out as 3 hours of sun in winter and 5 in the summer.
> With no water flowing, the tank absorbs about 28.8K Btu and
> loses 24h(T-30)40 = 960(T-30) Btu over an average day, so
> T = 30+28.8K/960 = 60 F. Not very promising. It would work better indoors,
> in a 70 F house.
Next, heat loss. To find T (final temp) the formula seems
to be T = AvgtempF + BTUin / (BTUout_hrs_F * 24hrs).
For R10 insulation and R1 glass with 40 btu/hr/F this then works
out to a final temp of 60 F. This is obviously much above freezing
so that at least is one concern taken care of as long as the tank
size is large enough that it doesn't swing under 32 F at night.
Lets see if beefing up the insulation helps matters...
Make it 4 inches of insulation instead of 2 for an R20 walls and
double glass for an R3 front. 32ft^2/R3 = 10.6, 78ft^2/R20 = 3.9
Total about 15 Btu/h-F. For T = 30+28.8K/(15*24) = 110 F.
This is hot enough for most folks.
Lets try those formulas out with 6 inches of insulation (R30) and
three layer glass giving about R5 (Not impossible, but probably not
cheap either).
32ft^2/R5=6.4, 78ft^2/R30=2.6, total=9 Btu/h-F.
T=30+28.8K/(9*24) = 163 F.
Now that should be hot enough for anyone but all that glass
could get pretty expensive.
Lets try another idea. Put a mechanical shutter over the glass at
night (aprox 12 hours) made out of 2 inches of that insulation stuff.
The same thing as the walls are made out of. Heat loss at night would
be 110ft^2/R10 = 11 Btu/h-F in place of 40 Btu/h-F during the day.
I don't know the formula for calculating this but I'd think you're
going to get more than 60 F out of it.
I know the math is off, but say an average of 26 btu/h-F with this
shutter arrangement day and night. T = 30+28.8K/(26*24)= 76 F.
Hmm. Maybe I've got the wrong formula, doesn't seem to have helped
much here.
How about instead putting up two 'wings' of reflectors like foil or
mylar outside the glass, each the same size at x degrees so that
they effectively double the energy collection during the day.
Then T = 30+57.6K/(40*24)= 90 F. Certainly that's pretty good and
as the temps will get higher in the afternoon it might be enough.
If we go with R30 walls and keep the R1 glass front and use the
reflectors to (about) double the collecting then heat loss would
be 78ft^2/R30=2.6, 32ft^2/R1 = 32, total 35, T = 98 F.
Not enough of a difference to really matter is it?
Ok, double paned glass with R3, and R10 sidewalls, with the above
reflector.... 78ft^2/R10 = 7.8, 32ft^2/R3 = 10.6 = 19 Btu/h-F.
T = 30 + 57.6K/(19*24) = 156 F. This sounds like it could
work pretty well and still be inexpensive. Might even get too
hot in the summer but I guess you could always shade the reflectors.
>
> Say we preheat enough 50 F water for 6 110 F 3gpm 10 minute showers per day,
> ie 180 gallons per day, so 28.8K = 960(T-30)+180x8(T-50), and T = 54 F, so
> the tank provides 180x8(54-50)
> = 5760 Btu/day of useful heat, 7% of the water heating energy,
> with a solar collection efficiency of 5760/(1000x4'x8') = 18%.
>
> > This describes a batch water heater as people have been fond of
> > building for years and it works fairly well, usually from old
> > (thrown out) electric water heater tanks whose heater elements
> > have burned out...
>
> It's my impression that few water heaters have stainless steel tanks, and
> they are usually discarded because the tanks are leaky, and their electric
> heating elements are replaceable.
>
I'm not in the water heating business so I don't know for sure.
I suspect you may be right and used water heater tanks that don't
leak might not be all that easy to find.
> This arrangement might work better in an attic, with a long "tank" (a
> 30' long x 4" diameter black-painted PVC pipe, with a 3/4" copper
> pressurized pipe inside?) along the ridge line, and a transparent sloping
> south roof, and a concentrating parabolic reflector below the tank, and
> foil-faced foam above the tank, which extends down below
> the tank bottom to make a secondary concentrating reflector...
>
> The tank might be suspended from ropes, and swung north and south to track
> the sun, with a high concentration ratio. Nielson's
> (253) 941-7281 aluminized Mylar film costs about 15 cents/ft^2 in 4'x100'
> rolls. It lasts for years indoors, and can be "glued" to curved masonite or
> scored foil-faced foamboard with a roller and axle grease, says Duane
> Johnson, who reports it's sufficiently mirrorlike
> for 100:1 concentration.
>
I don't think we need to get that complicated (and dangerous) for
just some hot water. According to the numbers I wrote above mirrors
giving just 2:1 concentration and double-glass should be enough
most of the time even for Phily.
Anthony
Ray Manning
I've always found the psychology of color interesting in that we say
something has a color when really it not the color of the item we are
seeing, rather the color of the light it reflects (really the light is
green, the chlorophyl may or may not be).
I would tend to believe that flat black is the most efficient for two
reasons: it doesn't reflect since it's flat and it absorbs at least the
visible spectrum of light.
- Ray
John Galt <jg...@starwarp.com> wrote in message
news:37CDEDE7...@starwarp.com...
Fred McGalliard
Joe wrote:
>
> There was supposedly a study done years ago (Seeing as I remember how old I
> was then and I'm 29 now... it was at least 12 years ago) that showed flat
> dark green absorbed more sunlight and converted it to heat than any other
> color.
I have no idea what you are remembering but the best absorption is a
very very flat black. If you can see it, against a night black
background, then too much light is getting away. But we only see in
visible. If it reflects strongly in UV or IR, it could trash a lot of
energy without us noticing. All this means is that black paint may not
be as black as we really want. I would consider the flat black barbecue
paint a good choice, but without any research this could be wrong for
the above reasons.
Fred McGalliard
David Hatunen
Blackness can be very misleading. It is quite possible for
something to be very "black" in the IR and be fairly non-black in
the visible range. Consider, for instance, water, which is
transparent in the visible range but quite black in the IR.
Many modern dyes and coatings have unexpected absorption
characteristics in the IR, although they *appear* to be black.
--
********** DAVE HATUNEN (hat...@sonic.net) ***********
* Daly City California *
******* My typos are intentional copyright traps ******
Nick Pine
Nick Pine's spellchecker wrote
>...y^2 = 4 vex makes f = 1.33' if y = 8' when x = 12'...
Whoops. That's y^2 = 4fx.
Nick, getting used to his non-vi editor.
Nick Pine
> I'll go through this once and then I'm off to other things...
> Um, lets see if I understand the math (I might not)...
Choost a little high-school algebra...
> Area of collection (front glass) 4'x8', aprox 2.9728 sq meters.
> (Lets call it 3 sq meters for simplicity sake)
> Assuming 1000 watts/sq meter of sunlight, that's about 3kw.
> 1 watt hour is about 3.4144 btu so 3000 watt-hours = 10243 Btu.
> So for 28800 btu/day that assumes 2.8 hours of sun.
Sounds like the right ball park, altho I also figure that each layer of
glazing
absorbs and reflects about 10% of the incoming sun power.
> > With no water flowing, the tank absorbs about 28.8K Btu and
> > loses 24h(T-30)40 = 960(T-30) Btu over an average day, so
> > T = 30+28.8K/960 = 60 F.
That stagnant water just keeps itself warm, at about the same temperature
for 24 hours a day,
with no night insulation, and it provides no useful hot water for showers,
etc. Ohm's law for heatflow
says the heatflow in Btu/h is the (F) temperature difference times the
thermal conductance (1/resistance.)
And we assumed that the solar energy that flowed into the box over an
average day was equal to
the heat energy that flowed out, ie Ein = Eout, ie 28.8K =
24h(T-30)40Btu/h-F, ergo T = 30+...
> Next, heat loss. To find T (final temp) the formula seems
> to be T = AvgtempF + BTUin / (BTUout_hrs_F * 24hrs).
And BTUout increases with increasing box temperature and decreases with more
insulation.
> For R10 insulation and R1 glass with 40 btu/hr/F this then works
> out to a final temp of 60 F. This is obviously much above freezing
> so that at least is one concern taken care of as long as the tank
> size is large enough that it doesn't swing under 32 F at night.
But some of the pipes might freeze at night, unless they have insulation,
and a cold cloudy week might partially freeze the tank.
> Lets see if beefing up the insulation helps matters...
> Make it 4 inches of insulation instead of 2 for an R20 walls and
> double glass for an R3 front. 32ft^2/R3 = 10.6, 78ft^2/R20 = 3.9
> Total about 15 Btu/h-F. For T = 30+28.8K/(15*24) = 110 F.
> This is hot enough for most folks.
Sure, if they climb in the tank to take a bath :-) The temperature will be
cooler
if we heat some incoming 50 F water... (Btw, I figure R2 for two layers
of glass, and 80% solar transmission.)
> Lets try those formulas out with 6 inches of insulation (R30) and
> three layer glass giving about R5
Or maybe R3, with 0.9^3 = 73% solar transmission?
> 32ft^2/R5=6.4, 78ft^2/R30=2.6, total=9 Btu/h-F.
> T=30+28.8K/(9*24) = 163 F.
> Now that should be hot enough for anyone...
Parboiled people, If they climb into the tank.
> but all that glass could get pretty expensive.
Replex polycarbonate only costs $1.25/ft^2 in 49" wide rolls. It's 200X
stronger than glass against hail and children with baseball bats, and
it can be cut with scissors and has a 10 year light transmission
guarantee...
> Lets try another idea. Put a mechanical shutter over the glass at
> night (aprox 12 hours) made out of 2 inches of that insulation stuff.
> The same thing as the walls are made out of.
Styrofoam. Lasts for years with latex paint on the outside. But the shutter
might not,
in wind and snow, and it is likely to have lots of air leaking around the
cracks at the edges,
and who wants to operate it twice a day? A bubblewall might help here... I
figure "night"
lasts 18 hours in Phila in January, BTW.
> Heat loss at night would
> be 110ft^2/R10 = 11 Btu/h-F in place of 40 Btu/h-F during the day.
> I don't know the formula for calculating this but I'd think you're
> going to get more than 60 F out of it.
Ein = 32ft^2x1000Btu/ft^2/dayx0.73transmission = 23.4K Btu.
Eout = 6h(T-30)32ft^2/R3 (for the glass, during the day)
+ 18h(T-30)32ft^2/(R3+R10) (for the glass, at night)
+ 24h(T-30)78ft^2/R10 (for the rest of the box, all day.)
Ein = Eout ==> 23.4K = (64+44.3+187.2)(T-30), so T = 109.2 F.
I'd add more back and side insulation. And make the water move...
> How about instead putting up two 'wings' of reflectors like foil or
> mylar outside the glass, each the same size at x degrees so that
> they effectively double the energy collection during the day.
Sounds better, but foil degrades in the weather. Maybe white painted
plywood...
More heat gain, less loss: 46.8K = 295.5(T-30), so T = 30+46.8K/295.5 =
188.4F,
theoretically-speaking, but reradiation begins to rear its ugly head, at
these higher
temperatures, vs the lower temps where glazing R-values are usually
measured.
>...as the temps will get higher in the afternoon it might be enough.
That's another little improvement. The 24 hour average temp in Phila in
January is about 30 F,
but the average daily max is about 38, so we might figure the box is exposed
to an average of 34 F
during the day (when it is less well-insulated), and a bit less than 30 F at
night, when it is better insulated.
To be honest, we could pick the 18-hour night temp to make the 24-hour
average 30 F again.
> If we go with R30 walls and keep the R1 glass front and use the
> reflectors to (about) double the collecting then heat loss would
> be 78ft^2/R30=2.6, 32ft^2/R1 = 32, total 35, T = 98 F.
> Not enough of a difference to really matter is it?
>
> Ok, double paned glass with R3, and R10 sidewalls, with the above
> reflector.... 78ft^2/R10 = 7.8, 32ft^2/R3 = 10.6 = 19 Btu/h-F.
> T = 30 + 57.6K/(19*24) = 156 F. This sounds like it could
> work pretty well and still be inexpensive. Might even get too
> hot in the summer but I guess you could always shade the reflectors.
Some numerical fooling around helps get the proportions right...
> > Say we preheat enough 50 F water for 6 110 F 3gpm 10 minute showers per
day,
> > ie 180 gallons per day, so 28.8K = 960(T-30)+180x8(T-50), and T = 54
F...
Aha, moving waters! Let's try this with 2:1 side mirrors (say SE and SW so
they
don't block much of the winter sun), double-glazing, no night shutter, and
4" of foam
on the back. Say we collect 48.6 Btu/day of sun. The thermal conductance of
the box
is 32ft^2/R2 = 16 Btu/h-F+ 78ft^2/R20 = 3.9, about R20 total. If Ein = Eout
(including
heating 180 gallons of water from 50 to T degrees F),
46.8K = 24h(T-30)20Btu/h-F + 180x8(T-50), so 1920T = 133200, and T = 69.4 F.
Hooboy. Cold showers, without a post-heater...
But better than before. The tank provides 180x8(69.4-50) = 27.9K Btu/day of
useful heat,
32% of the water heating energy... At 70 F, It still might work better
indoors.
> > This arrangement might work better in an attic, with a long "tank" (a
> > 30' long x 4" diameter black-painted PVC pipe, with a 3/4" copper
> > pressurized pipe inside?) along the ridge line, and a transparent
sloping
> > south roof, and a concentrating parabolic reflector below the tank, and
> > foil-faced foam above the tank, which extends down below
> > the tank bottom to make a secondary concentrating reflector...
> >
> > The tank might be suspended from ropes, and swung north and south to
track
> > the sun, with a high concentration ratio. Nielson's
> > (253) 941-7281 aluminized Mylar film costs about 15 cents/ft^2 in
4'x100'
> > rolls. It lasts for years indoors, and can be "glued" to curved masonite
or
> > scored foil-faced foamboard with a roller and axle grease, says Duane
> > Johnson, who reports it's sufficiently mirrorlike
> > for 100:1 concentration.
>
> I don't think we need to get that complicated (and dangerous) for
> just some hot water.
But we could heat a whole house that way, with a few large insulated poly
tanks...
Or make electricity (wow!) It only takes 6:1 to make steam... OKOKOK. For
house heating,
3:1 seems fine, and maybe a 4' wide galvanized water trough lined with EPDM
rubber as the target,
vs a moving target, with a layer of foamboard above it. Let's see: a 24'
wide house with a 1:1 pitched roof
and y^2 = 4 vex makes f = 1.33' if y = 8' when x = 12'. That would still
collect lots of summer sun for hot water
if the parabola were aimed at the horizon for good winter collection... And
houses need roofs anyhow, and
we could use the space under the parabola for storage... And skateboard on
the parabola.
Nick
David Hatunen
Ken H. <kha...@NoSpam.hiwaay.net> wrote:
>On Thu, 2 Sep 1999 15:57:44 GMT, Fred McGalliard
><frederick.b...@boeing.com> wrote:
>
>>
>>
>>Joe wrote:
>>>
>>> There was supposedly a study done years ago (Seeing as I
>>> remember how old I was then and I'm 29 now... it was at least
>>> 12 years ago) that showed flat dark green absorbed more
>>> sunlight and converted it to heat than any other color.
>>
>>I have no idea what you are remembering but the best absorption
>
>
>I, too, agree that flat black is color for total radiation
>absorption. By definition a black body is one that reflects no
>wavelengths which strikes it.
You're confusing a body that is black in the visible range with the
"black body" of physics, a hypothetical ideal of a body that
absorbs all radiation (and emits all radiation, a fact that must
not be forgotten) by definition.
>A green body does not absorb all energy received since it is
>reflecting the green wavelength (the light reflected is what our
>eyes perceive as a visible object).
An object looks green because it reflects green; this frequnetly
means it heavily absorbs red and infrared.
>Place a heat source near a reflectometer (flat black plates) and
>it will rotate in proportion to energy absorbed. I have never
>heard of a reflectometer being painted green and if it were, it
>would not rotate as fast because the green wavelength is
>reflected. In other words, Planck's radiation laws have not been
>repealed.
Nice try at a gedankenexperiment, but you're wrong. An object that
LOOKS green may actually absorb in the IR, while a body that LOOKS
black may actrually reflect in the IR.
Randy Elliott
Fred McGalliard wrote
>I have no idea what you are remembering but the best absorption is a
>background, then too much light is getting away. But we only see in
>visible. If it reflects strongly in UV or IR, it could trash a lot of
>energy without us noticing. All this means is that black paint may not
>be as black as we really want. I would consider the flat black barbecue
>paint a good choice, but without any research this could be wrong for
>the above reasons.
Interesting thought. A good example is standard "white-out" is black to IR,
while the latex-based "white-out for copies" is actually white to IR. I
found this out when painting an index stripe on a motor hub to count
rotations with an IR-based reflective sensor.
Larry Caldwell
writes:
Thermomax sells a nice solar collector that will operate below freezing
ambient. The design uses an anodized aluminum fin tube inside a
transparent vacuum bottle. I have a friend with a solar house north of
Moscow, Idaho who says that on a sunny minus 20 degree day he gets 170
degree water out of the collectors.
The collector itself uses an alcohol vapor cycle to transfer heat to an
ethelyne glycol heat exchanger system.
-- Larry
David Hatunen
Ken H. <kha...@NoSpam.hiwaay.net> wrote:
>On 3 Sep 1999 14:42:32 GMT, hat...@bolt.sonic.net (David Hatunen)
>wrote:
>
>>In article <37cf1f5c...@newstoo.hiwaay.net>,
>>.........
>>>Place a heat source near a reflectometer (flat black plates) and
>>>it will rotate in proportion to energy absorbed. I have never
>>>heard of a reflectometer being painted green and if it were, it
>>>would not rotate as fast because the green wavelength is
>>>reflected. In other words, Planck's radiation laws have not been
>>>repealed.
>>
>>Nice try at a gedankenexperiment, but you're wrong. An object
>>that LOOKS green may actually absorb in the IR, while a body that
>>LOOKS black may actrually reflect in the IR.
>
>green plates will rotate as fast or faster than one with black
>plates? I am confused by your use of the word <may> and you made
>no definitive statement of fact. Could you expound?
The subject isn't reflectometers; it's heating water. Water is
black to IR, and simply exposing the water to sunlight would be
efffective; transparent tubing and all, or better, perhaps, matte
surface tubing.
Anyway, if heat via IR is the concern one would be well served to
look up the absorption/reflection spectra of he paint or coating or
whatnot in a reference.
I once worked for a company that made flexible printed circuits.
They wanted to use a continuous web process for curing the
tranparent coating wet-applied to the copper. AS the machine
designer I suggested that they pass the sheet between two IR heat
panels, but I was told it wouldn't work. Seems one of their
engineers had placed a sheet of the copper material between heat
lamps and the copper didn't even get warm. As a person with a
physics degree I tried to explain whay that experiment was a bad
one: copper is so reflective to IR that it scarcely absorbs any of
it. They argued that a transparent coating wouldn't make any
difference, but it did: the coating was not transparent in the IR
and the material heated up nicely in the machine I designed.
Fred McGalliard
Larry Caldwell wrote:
>...
> Thermomax sells a nice solar collector that will operate below freezing
> ambient. The design uses an anodized aluminum fin tube inside a
> transparent vacuum bottle. I have a friend with a solar house north of
> Moscow, Idaho who says that on a sunny minus 20 degree day he gets 170
> degree water out of the collectors.
>
> The collector itself uses an alcohol vapor cycle to transfer heat to an
> ethelyne glycol heat exchanger system.
Neat. Isn't this a bit expensive? Is such a large vacuum system actually
practical for a low maintenance system? I don't actually maintain our
vacuum systems here, but my impression was large ones with a lot of
connections are a bit hard to maintain. Does this have to be constantly
repumped?
Fred McGalliard
Steve Spence
Due to the atmospheric pressure and the technical problems related to the
sealing of the collector casing, the construction of an evacuated flat-plate
collector is extremely difficult. To overcome the enormous atmospheric
pressure, many internal supports for the transparent cover pane must be
introduced. However, the problems of an effective high vacuum system with
reasonable production costs remain so far unsolved.
It is more feasible to apply and adapt the mature technology related to the
lamp industries with proven mass production. Building a tubular evacuated
solar collector and the maintenance of its high vacuum, similar to light
bulbs and TV tubes, is practical. The ideal vacuum insulation of the tubular
evacuated solar collector, obtained by means of a suitable exhausting
process, has to be maintained during the life of the device to reduce the
thermal losses through the internal gaseous atmosphere (convection losses).
The whole article as found at http://www.thermomax.com/tech.html:
Thermomax Evacuated Heat Pipe Solar Collectors (tubes) operate differently
than the other collectors available on the market. These solar collectors
consist of a heat pipe inside a vacuum sealed tube, as shown.
Each tube contains a sealed cooper pipe (heat pipe). The pipe is then
attached to a black copper fin that fills the tube (absorber plate).
Protruding from the top of each tube is a metal tip attached to the sealed
pipe (condenser). These tubes are mounted, the metal tips up, into a heat
exchanger (manifold). As the sun shines on the black surface of the fin, the
alcohol is heated and hot vapor rises to the top of the pipe. Water, or
glycol, flows through the manifold and picks up the heat from the tubes. The
heated liquid circulates through another heat exchanger and gives off its
heat to water that is stored in a solar storage tank. A Thermomax system is
simple to install and easy to expand.
In the newly developed Memotron tube the maximum working temperature is
controlled by means of a memory metal spring which is positioned inside the
heat-pipe's condenser.
The memory metal is programmed to change its shape at a pre-set temperature.
This allows for the condenser fluid to be retained inside the condenser.
When the programmed temperature has been achieved, the memory metal spring
expands and pushes a plug against the neck of the heat pipe blocking the
return of the condensed fluid and stopping heat transfer.
At temperatures below the maximum programmed limit, the spring contracts
allowing the condensed fluid to return to the lower section of the heat
pipe. It is than evaporated due to the heat from the absorber plate,
transferring thermal energy to the condenser. Thermomax's patented Memotron
tube is the state of the art technology and provides complete safety through
effective temperature control.
Thermomax system is designed for all weather conditions. While the ambient
temperature is in sub-zero range, the condenser can experience super high
temperatures (300 F).
A patented flexible neck system absorbs both thermal and mechanical shocks.
Thermomax's advanced evacuated "heat-pipe" solar collector is a breakthrough
in solar technology. It is an efficient and durable solar energy system. It
is effective throughout the year and saves its user a considerable amount in
expensive fuels.
Thermomax's collector performs not only at noon or on clear sunny days, but
also when the sun is low or the weather is cloudy. Wind or low temperatures
have less effect on its performance.
The high quality of Thermomax products is the result of ongoing refinement
and optimization of the product process guided by Dr. Framarz Mahdjuri. The
quality and durability of Thermomax solar products have contributed to an
unequaled history of achievements in the development and implementation of
solar technology. This continues a tradition of innovation begun over four
decades ago when NASA invented the Heat Pipe. Thermomax brings this superb
space technology to the market place as an economically competitive option
for Solar Energy. Our ISO 9001 & 9002 Quality Management Certifications
ensure that Thermomax quality systems meet the highest standard.
Transfer of heat from the absorber plate (collector) is via an efficient and
very fast heat conductor, the "heat-pipe." This has a very low heat capacity
but an exceptionally rapid conductivity. The "heat-pipe" also provides the
system with a diode function. Due to the physical properties of the
"heat-pipe,. the maximum working temperature of the system is controlled.
The vacuum in the glass tube, being the best possible insulation for a solar
collector, suppresses heat losses and also protects the absorber plate and
the "heat-pipe" from external adverse conditions. This results in
exceptional performance far superior to any other type of solar collector.
A solar collector absorbs solar radiation and converts it into heat
(photo-thermal conversion). The high efficiency solar collector implies
maximum absorption of incident solar radiation with a minimum thermal and
optical loss. Selective coating characteristics of the absorber and the
vacuum insulation are the most important parts of an advanced collector. A
selective surface has high absorption (low reflection) for the solar
spectrum and low emissivity for the infrared heat radiation. The selective
coating used in the collector consists of a very precise thin layer of an
amorphous semiconductor plated on to a metal substratum having a low
emission for long-wave radiation.
Due to the atmospheric pressure and the technical problems related to the
sealing of the collector casing, the construction of an evacuated flat-plate
collector is extremely difficult. To overcome the enormous atmospheric
pressure, many internal supports for the transparent cover pane must be
introduced. However, the problems of an effective high vacuum system with
reasonable production costs remain so far unsolved.
It is more feasible to apply and adapt the mature technology related to the
lamp industries with proven mass production. Building a tubular evacuated
solar collector and the maintenance of its high vacuum, similar to light
bulbs and TV tubes, is practical. The ideal vacuum insulation of the tubular
evacuated solar collector, obtained by means of a suitable exhausting
process, has to be maintained during the life of the device to reduce the
thermal losses through the internal gaseous atmosphere (convection losses).
A heat pipe acts like a high conductance thermal conductor. Due to its
thermal-physical properties, its heat transfer rate is thousand's times
greater than that of the best solid heat conductor of the same dimensions.
The basic heat pipe is a closed container consisting of a capillary wick
structure and a small amount of vaporizable fluid. The heat pipe employs an
evaporating-condensing cycle, which accepts heat from an external source,
uses this heat to evaporate the liquid (latent heat) and then releases
latent heat by reverse transformation (condensation) at a heat sink region.
This process is repeated continuously by a return feed mechanism of the
condensed fluid back to the heat zone.
In the solar collector, the condensation zone is at a higher level than the
evaporation zone. The transport medium condensed (in the condensation zone)
returns to the evaporation zone under the influence of the gravity. Then,
there is no need of capillary wick structure.
The maximum operating temperature of a heat pipe is the critical temperature
of the used heat transfer medium. Since no evaporation/condensation above
the critical temperature is possible, the thermodynamic cycle interrupts
when the temperature of the evaporator exceeds the critical temperature.
--
--
Steve Spence
Survive2k's Survival Pages
http://www.webconx.com/survive2k
http://www.webconx.com/biodiesel
--
Fred McGalliard <frederick.b...@boeing.com> wrote in message
news:37D54D96...@boeing.com...
Steve Spence
Thank you for visiting our web sites.
You will be served directly from our offices in Maryland. Thermomax
Collectors will be packed in a wooden crate and will be shipped to you by a
common carrier. Our technology is the most developed of all solar thermal
energy systems. A Thermomax solar water heating system provides your hot
water demand depending on local climate conditions and the system size. Our
two popular systems are:
MAZ 2-20S ($1,864.00), rated 1,400 W (50 gallon hot water delivery per day)
MAZ 2-30S ($2,759.00), rated 2,100 W (75 gallon hot water delivery per day)
A Thermomax collector tube is a closed chamber (Heat Pipe) consisting of a
small amount of heat transfer liquid. The heat pipe employs an
evaporating-condensing cycle, absorbing heat from the Sun, using this heat
to evaporate the liquid (latent heat) and then releasing latent heat by
reverse transformation (condensation) at a heat sink. A Thermomax collector
tube has inherent protection from freezing or overheating. In the Thermomax
Memotron tube, the maximum collector temperature is controlled by means of a
memory metal spring inside the collector tube. It prohibits/permits the
transfer of heat from the heat pipe by the expansion/contraction process of
the spring. The collector efficiency remains high even at low light.
If you need design/engineering specifications or installation suggestions,
please do not hesitate to contact any of our offices. You can order the
Thermomax Solar Energy video tape by sending a check of $15.00 to our
Maryland office. It shows the manufacturing process of the Thermomax
products and installation examples. We value your business and welcome every
opportunity to prove it.
Sincerely,
Dr. F. Mahjouri, PE
President
Thermomax USA
_________________________________
Thermomax USA
5560 Sterrett Place, Suite 115
Columbia, MD 21044
Website http://www.thermomax.com
Voice (410) 997-0778
Fax (410) 997-0779
_________________________________
--
--
Steve Spence
Survive2k's Survival Pages
http://www.webconx.com/survive2k
http://www.webconx.com/biodiesel
--
Steve Spence <ssp...@bellatlantic.net> wrote in message
news:_MsB3.621$oF4.1...@typhoon2.gnilink.net...
Davy
some information maybe state how to installation and different system...
Tony wrote
Nick Pine +ZLBb62W8ZYd64A- ...
+AHwAPA-brian+AEA-camalott.com+AD4- wrote
+AHw-
+AHwAPg- wayward+AEA-dpla.net +AD4- wrote
+AHw-
+AHwAPg- +AD4-What If:
+AHwAPg- +AD4-
+AHwAPg- +AD4-You purchased a large stainless steel tank and painted it flat black,
+AHwAPg- +AD4-and it sat out in the sun right before entering your hot water heater?
+AHwAPg-
+AHwAPg- That's a nice idea in principle, but wouldn't be very effective the way +AD4-
+AHw-you have presented it-
+AHw-
+AHw-It might work reasonably well in a warm sunny climate, altho the wind could
+AHw-blow away lots of heat, with no glazing, and it would lose lots of heat at
+AHw-night and on cloudy days, with no night insulation. Even with no sun, a
+AHw-tempering/preheating tank in the house could help.
+AHw-
+AHwAPg- there wouldn't be enough steel to water contact to
+AHwAPg- quickly transfer the heat.
+AHw-
+AHw-I disagree. You might check this out with a double boiler on your kitchen
+AHw-stove, and a couple of thermometers and a clock...
+AHw-I measured a still water film thermal conductance of about
+AHw-60 Btu/h-F-ft+AF4-2 this way.
+AHw-
+AHw-A gallon of water in contact with a square foot of steel has an RC
+AHw-time constant of about 8 Btu/F/60Btu/h-F hours, ie 8 minutes, so starting
at
+AHw-say, 50 F, in contact with 130 F steel, it would warm to
+AHw-100 F when 100 +AD0- 130-(130-50)exp(-t/8), ie when t +AD0- -8 ln(30/80)
+AHw- +AD0- 7.84 minutes.
+AHw-
+AHwAPg-You'd be much better off with a network of copper tubing (say
+AHwAPg-3/8+ACI- o.d.), painted flat black and placed in a glassed-over box
+AHwAPg-oriented to catch most of the day's light.
+AHw-
+AHw-Rubbish. This might work better with fins and a pump and an insulated tank,
+AHw-or larger plastic tubing, altho that's unlikely to survive normal water
+AHw-pressure. That copper tubing's too small to hold much water or work well by
+AHw-thermosyphoning, and it needs more sun-gathering surface.
+AHw-
+AHwAPg-...Personally, I'm much more in favor of building a heat storage
+AHwAPg- building, and keeping a hot water tank in it-
+AHw-
+AHw-Sounds nice. Big polyethylene tanks are cheap, eg +ACQ-899.99 for Tractor
+AHw-Supply's 2100 gallon 87+ACI- diameter x 87+ACI- tall version. Put it inside an 8'
+AHw-x2+ACI- foamboard cube surrounded by bags of leaves?
+AHw-That makes RC about 2100x8Btu/FxR28/(6x64ft+AF4-2) +AD0- 1225 hours,
+AHw-or 51 days. Yum :-)
+AHw-
+AHwAPg- then you just burn your trash, and whatever wood you need
+AHwAPg- to keep things hot, and no worries about burning down
+AHwAPg- your house.
+AHw-
+AHw-Wood pollutes, and it's lots of work. How can we solar heat that sucker?
For
+AHw-potable water storage, one might efficiently bubble a
+AHw-little air through the higher temperature water it to keep it pure
+AHw-and free of bacterial nutrients, as in a sewage treatment plant.
+AHw-
+AHw-Nick
+AHw-
+AHw-
RWK
find. We would mount elevated above a shower hut about 10'. If we filled
in early morning the temperature would be about right by late morning and
too hot by late afternoon. Of course we didn't have any cold water to mix.
Paul
Davy <ske...@giga.net.tw> wrote in article <CWEUuqg$#GA.175@news1>...
> Visit website http://members.xoom.com/skenley/solarwater.htm
> some information maybe state how to installation and different system...
> Tony wrote
>
> Nick Pine +ZLBb62W8ZYd64A- ...
> +AHwAPA-brian+AEA-camalott.com+AD4- wrote
> +AHw-
> +AHwAPg- wayward+AEA-dpla.net +AD4- wrote
> +AHw-
> +AHwAPg- +AD4-What If:
> +AHwAPg- +AD4-
> +AHwAPg- +AD4-You purchased a large stainless steel tank and painted it
flat black,
> +AHwAPg- +AD4-and it sat out in the sun right before entering your hot
water heater?
> +AHwAPg-
> +AHwAPg- That's a nice idea in principle, but wouldn't be very effective
the way +AD4-
> +AHw-you have presented it-
In MN it get's below zero a lot, is always below freezing in winter.
Sitting black tank of water outside will result in a frozen tank of water.
Putting the tank inside the house in front of a window will warm the water,
but the sun will no longer heat the house so the furnace has to run more.
Creating a new window just for the tank sitting inside the house will warm
the water, but since glass is not as good at insulating as a wall is, you
will lose more heat at night causing the furnace to run more.
In short, there is not a simple answer here. You need to understand what
you are doing. I couldn't design a good system, but it can be done. But
certainly not just with one big tank of water...
--->Paul
Fred McGalliard
Paul wrote:
...
> In short, there is not a simple answer here. You need to understand what
> you are doing. I couldn't design a good system, but it can be done. But
> certainly not just with one big tank of water...
Depends on how big the tank is and how simple the system has to be. For
a place with long very cold dark winters, one needs a very large tank,
small swimming pool sized, a lot of insulation over the tank, and a
separate set of windows just to warm the tank when you can get some
warmth. Done right, this would give you very hot water all summer, and
warm water for a month or so while all those about you freeze their
keesters. I believe, without proof, that you can take advantage of the
cold as well. A tank of antifreeze at -20C, and another tank with water
at +80C, would let you run a low temperature heat engine to drive a heat
pump and an electrical power system. A large dry soil mass under the
house could provide an excellent heat dump to cool things in summer, and
heat in winter. A bit less technologically demanding than a month of
very hot water storage, or a heat engine system, but these have been
done with a lot of success.
Paul Vines
solar batch heater in his book "EARTHSHIP". It is available trough amazon,
barnes and noble,.......Many ideas for cheap well functioning systems for
independent living.....
Nick Pine <ni...@early.com> wrote in message
news:H%Ty3.1167$kf5....@iad-read.news.verio.net...
> <br...@camalott.com> wrote
>
> > way...@dpla.net > wrote
>
> > >What If:
> > >
> > >You purchased a large stainless steel tank and painted it flat black,
> > >and it sat out in the sun right before entering your hot water heater?
> >
> > That's a nice idea in principle, but wouldn't be very effective the way
>
> you have presented it-
>
> It might work reasonably well in a warm sunny climate, altho the wind
could
> blow away lots of heat, with no glazing, and it would lose lots of heat at
> night and on cloudy days, with no night insulation. Even with no sun, a
> tempering/preheating tank in the house could help.
>
> > there wouldn't be enough steel to water contact to
> > quickly transfer the heat.
>
> I disagree. You might check this out with a double boiler on your kitchen
> stove, and a couple of thermometers and a clock...
> I measured a still water film thermal conductance of about
> 60 Btu/h-F-ft^2 this way.
>
> A gallon of water in contact with a square foot of steel has an RC
> time constant of about 8 Btu/F/60Btu/h-F hours, ie 8 minutes, so starting
at
> say, 50 F, in contact with 130 F steel, it would warm to
> 100 F when 100 = 130-(130-50)exp(-t/8), ie when t = -8 ln(30/80)
> = 7.84 minutes.
>
> >You'd be much better off with a network of copper tubing (say
> >3/8" o.d.), painted flat black and placed in a glassed-over box
> >oriented to catch most of the day's light.
>
> Rubbish. This might work better with fins and a pump and an insulated
tank,
> or larger plastic tubing, altho that's unlikely to survive normal water
> pressure. That copper tubing's too small to hold much water or work well
by
> thermosyphoning, and it needs more sun-gathering surface.
>
> >...Personally, I'm much more in favor of building a heat storage
> > building, and keeping a hot water tank in it-
>
> Sounds nice. Big polyethylene tanks are cheap, eg $899.99 for Tractor
> Supply's 2100 gallon 87" diameter x 87" tall version. Put it inside an 8'
> x2" foamboard cube surrounded by bags of leaves?
> That makes RC about 2100x8Btu/FxR28/(6x64ft^2) = 1225 hours,
> or 51 days. Yum :-)
>
> > then you just burn your trash, and whatever wood you need
> > to keep things hot, and no worries about burning down
> > your house.
>
> Wood pollutes, and it's lots of work. How can we solar heat that sucker?
For
> potable water storage, one might efficiently bubble a
> little air through the higher temperature water it to keep it pure
> and free of bacterial nutrients, as in a sewage treatment plant.
>
> Nick
>
>
>