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From: John De Armond
Subject: Re: Un-insulated water heater tank by woodstove!
Date: Sat, 29 Mar 2008 14:39:28 -0400
Message-ID: <>

On Sat, 29 Mar 2008 07:19:16 -0700, "Bill" <> wrote:

>"ransley"  wrote in message
>> If you have the time get another tank, put it outside with bypass
>> valves, when nightime temps are above incomming water temp
>> let the tank fill, the sun will heat it fast
>Actually for the summer, I am thinking about running a bunch of plastic
>pipes in my attic which gets to be very hot. Plastic because I will need to
>drain it each fall to prevent the pipes from freezing.

You'd probably be dollars ahead to simply get that heat out of your attic and reduce
the load on your AC.

>Also with this idea, I am thinking of installing another insulated water
>tank and using a solar powered pump to circulate water slowly from the
>insulated tank through the attic pipes and back to the insulated tank.

Why would you waste money on an under-powered and over-priced solar pump that quits
working when the sun goes behind a cloud when a conventional pump works so well and
draws so little power?

Solar water heat from the roof works well but generally, the tubing itself needs to
be exposed to the solar radiation.  Radiative energy transfer is much more effective
than convective in this situation.

I did a similar system on my restaurant's flat tar roof.  I simply laid several
hundred feet of direct burial black PVC pipe directly onto the tar.  I tried
industrial black garden hose before that but it wasn't sufficiently UV-resistant to
last very long.

On bright sunny days, the water would almost boil.  In all cases when the sun was
shining, this system made all the hot water the restaurant needed.  There was a
NG-fired tankless heater for other times, of course.  This system used no tank and no
fancy plumbing.  City water went in one end of the tubing and hot water came out the
other.  A three-way valve let me quickly switch the solar heater in and out as
needed.  All manual control which was good enough.


From: John De Armond
Subject: Re: Heating a greenhouse at night...
Date: Tue, 02 Sep 2008 14:32:33 -0400
Message-ID: <>

Radiant heating is wonderful but I immediately see two problems here. One,
what/where is your thermal mass?  Two, where is your insulation to prevent
heat from conducting down into the earth.

With slab radiant heating, the slab forms most of the thermal mass.  With a
solar collector, it would heat up during the day and then give it up at night.
With no thermal storage, the heat would stop when the sun goes down.

Second, slab type systems that sit on dirt have some form of insulation
between the slab and dirt, normally some closed pore poly sheeting.  Without
the insulation, you'll end up sending a portion of your heat into the earth.

Here's an alternative suggestion.  Your objective is to keep the plants warm
so why not heat them directly?  Run the water tubing down the rows of plants.
Circulate the warm water through these tubes to warm the plants.  This assumes
that the plants are in pots.

If the plants are in dirt beds then simply zig-zag the tubing through the
dirt.  Enough heat will be given off by the dirt to keep the plants warm.

My late uncle was a rather famous orchid and camellia breeder.  He used the
later technique for his camellia beds.  He used semi-rigid electrical heaters
instead of water pipe but the principle's the same.  He used almost no aux
heat in his greenhouses.

At 3kW, you'll have to store considerable heat.  Assume the night is 12 hours
long, that 36kWh.  1 pound of water stores 1 BTU per deg F.  36kWh is 122,837.
If you could heat the water to 180 deg and let it cool to 80 degrees by the
end of the night, that's a delta-T of 100 degrees. 122,837/100 = 1,228 lbs of
water.  At about 8 lbs per gallon, that's 153 gallons.

Heating that much water to 180 during a short winter day is probably
optimistic unless you build a large array of collectors.  You'd also have to
arrange a tempering system to maintain the water circulating around the plants
at a safe temperature.  A tank that large would be kinda expensive, large and
a chore to insulate.

As an alternative, you might consider phase change storage.  phase change
means melting or freezing.  The two major advantages of phase change storage
are a) the temperature remains the same until all the medium is melted or
frozen and b) phase change requires many more BTU than simply changing the
temperature of the material.

As an example, the heat of fusion of 1 pound of solid water (ice) is 143 BTU
per pound.  That is, it takes 143 BTU to turn 1 lb of ice at 32 deg into 1 lb
of water, also at 32 degrees.  To raise that water to 33 deg takes only 1
additional BTU.

Water is one of the best phase change heat storage mediums if you happen to
need your heat at 32 degrees :-)  There are other materials that freeze/melt
at more convenient temperatures.

Paraffin is an excellent phase change storage medium.  Alloys are available
that melt/freeze at anywhere from just above ambient to above the boiling
point of water. A number of companies sell paraffin and other phase change
materials conveniently micro-encapsulated in tiny spheres.  Fill a tank with
the spheres, circulate water through the interstices and you have your phase
change storage device.

If you're interested in this route, say so and I'll dig up some old info that
I have.  A few years ago I converted a client's RV water heater into a phase
change water heater.  That involved simply filling the water heater tank with
phase change spheres and employing an external diesel heater.  It tripled the
available hot water, which was his goal.


On Mon, 01 Sep 2008 22:57:53 -0500, john
<> wrote:

>I built the wife a small 8.5 x 12.5 greenhouse to winter her plants in.
>    I am building a small solar thermal collection and storage system to
>use for heat on cold nights; trying to ween away from electric and gas
>(seemed cheap at first, but project has developed a life of its own...)
>  Someone suggested using underfloor radiant heating which seems like a
>good idea as opposed to forced air, except I am familiar only with the
>concept radiant heating, not the application and most of the
>installation web sites I have visited show installation in either pier
>and beam or slab; my little greenhouse has a floor backfilled with about
>+12" of wood chips.  Putting the pipe in is not an issue, but where do I
>start on figuring the pipe diameter, composition, spacing, flow rate,
>distribution manifold (if needed?) water temp, etc.  Are balancing
>valves needed on the return manifold? etc.  I see a lot of opportunity
>for "I gotcha" and the repercussions of freezing the wife's plants are
>just too horrible to consider...!
>Any help or suggestions for this or alternative methods would be greatly
>BTW, the electric heat size calculated for 20F night is about 3kw.

From: John De Armond
Subject: Re: Cheap DIY solar collector
Date: Tue, 26 Aug 2008 10:35:27 -0400
Message-ID: <>

On Mon, 25 Aug 2008 16:18:48 -0700 (PDT), Jim Wilkins <>

>On Aug 25, 4:15 pm, Morris Dovey <> wrote:
>> amdx wrote:
>> > I ran across this site, the guy has a neat idea for an inexpensive solar
>> > collector.

>I was wondering how well that stuff would work in a solar collector.
>TekSupply sells it for greenhouse covering but it isn't cheap.

Works like crap.  This isn't the greenhouse glazing.  Coroplast is that cheap
signboard used to make political and other short-lived signs.  If you listen
closely you can hear it decompose when sunlight shines on it.  Painting it
black will help a little with the solar degradation but it won't stop it.  If
that thing lasts a summer, I'd be quite surprised.

The stuff you're talking about would probably make an excellent collector
since it's UV-resistant and strong.  Too bad it costs so much.

>My nearly free solar water heater, which isn't worth photos because
>it's all salvaged material and home-made parts and would be difficult
>to duplicate in detail, is a batch heater made from a 40 gallon
>electric water heater tank in a close-fitting greenhouse with
>aluminized bubblewrap insulation over styrofoam behind and whatever
>glazing I'm testing over the top and front. The insulated top and
>front covers fold out to reflect the sun onto the tank, sort of. Trees
>limit its sun exposure to 10AM to 2PM so it doesn't need to track over
>much of an azimuth anyway.

The cheapest one I ever made was on my restaurant's flat roof.  I started out
simply tossing out a couple hundred feet of black industrial-grade 1" water
hose onto the roof.  The combination of the black tar roof and the black hose
would have the contents near boiling in under an hour.

The hose wasn't very UV-resistant so when the first leak appeared, I replaced
it with that semi-rigid direct-burial PVC pipe that is used for underground
water and well service.  I can't recall whether it was 1.5" or 2" but it held
enough to fill a 50 gallon compartment of my dishwashing sink.  That one was
in place for several years until I closed the place.

For more conventional circumstances, the cheapest and longest lived collector
I ever made was based on some plans TVA published in the wake of the first
A-rab oil embargo.  It consisted of a sheet of (preferably) galvanized metal
or fiberglass corrugated roofing material, framed in wood (I used redwood
1X6s) and painted flat black.  A PVC pipe with holes in it at the top dribbled
water down the grooves in the roofing.  It was caught in a slit PVC pipe
gutter at the bottom.  The glazing initially was window glass but after the
first hail storm :-(, I had tempered glass made for it.  No fancy e-coatings
or anything like that existed back then but the unit still performed well. The
back of the panel was insulated with foil-backed fiberglass batting held in
place with screen wire.

Initially I had trouble with condensation on the inside of the glass causing a
significant loss in output, probably due to reflections.  I solved that
problem in, IMHO, a fairly clever way.  On every other trough, I made mounds
of semi-solid epoxy shaped to cause the water to splash up in the air, far
enough to strike the glass.  After experimenting, I found that 6 such mounds
along every other trough would cover the glass adequately with splashed water.

I then put a tiny bit of surfactant in the water.  This caused the water to
sheet off the glass rather than bead up.  Back then I used just a little
automatic dishwashing rinse additive (which doesn't foam).  Now I'd try one of
the spray shower treatments.  They don't foam either.

A small boiler circulating pump circulated water up to the collector and back
through a copper coil inserted between the element holes in an old electric
water heater tank.

I used two parallel runs of 1/2" dead-soft copper tubing.  I pushed it in
through the top hole at a tangent.  With a little help from a pusher stick, I
could get it to follow the inside curve of the tank and form several turns of
a spiral.  I brought the tubing out through holes drilled in the flange-type
elements.  The tubing was silver-soldered in place.

I built a simple little controller that ran the pump whenever the collector
temperature was a few degrees hotter than the tank water.  It consisted of two
thermocouples, one fastened to the corrugated roofing and one immersed in the
tank water.  They were connected voltage-bucking so that the output voltage
was the difference between the two junctions. (actually, you could view this
as a single thermo-COUPLE with one junction at the collector and the other in
the water heater).

A simple comparator operated a relay when about 0.1 millivolt of positive
output was detected.  This was a Type T (copper-Constantine) TC so 0.1 mv is
about 7 degrees differential.  That is, the roof collector was about 7 deg
hotter than the tank.   The comparator has enough hysteresis so that the
difference would have to be near zero before turning the pump off.

My mounting was also clever.  I made a V-shaped device out of two pieces of
2X6 about 2 ft long.  I placed this on the crown of the roof to protect it.
Over the top of that I ran a couple of stainless steel cables.  On one end
they attached to the collector.  On the other they attached to a cast iron
sewer vent pipe.  On the bottom of the collector were attached two more
cables.  They played out at about 45 deg angles and attached to gutter
mounting nails.  I didn't want to mar my roof in case this didn't work out -
thus the non-invasive mounting technique.

I was concerned a little about this mounting relative to wind but after a
near-tornado passed through that blew off shingles without bothering the
panel, I rested easy.  Of course, the plumbing also helped anchor it down.

This system supplied all my hot water needs whenever the sun shown and help
even under light overcast.  It was a total loss during the long heavy overcast
periods we experience here in winter.  The unit was naturally freeze-proof, as
the water drained back to an insulated surge tank (old well-pump tank) when
the pump turned off.  I lived in the house about 3 years after building the
thing and it worked fine.  The subsequent owners kept it operational for quite
some time.  I went on the road and lost touch after a few years.  I do know
that it is gone now, not surprising since it's been 30+ years.

Modern black-anodized aluminum corrugated roofing should work about as well,
if not a little better, though it'll probably need cross-bracing to remain
rigid.  Today I'd look at some tempered E-glass or maybe that greenhouse
glazing mentioned above.  I'd look at it but not necessarily use it, depending
on the cost.  Plain old glass worked well enough.  The cost of this is so low
that if one panel is marginal then simply build another.


From: John De Armond
Subject: Re: Cheap DIY solar collector
Date: Tue, 26 Aug 2008 21:46:33 -0400
Message-ID: <>

On Tue, 26 Aug 2008 18:06:21 -0700 (PDT), Jim Wilkins <>

>On Aug 26, 10:35 am, Neon John <> wrote:
>> ...
>That's elegantly simple and impressive. Thanks for describing it.

You're welcome.

>How was it integrated with the backup heater?

I didn't have a backup heater.  I installed the copper coils in the existing
electric heater.  I drilled the flange-type heater element flanges so that the
tubing could be brought out beside the element.  The electric element remained
in place and functional.  I silver-soldered the tubing to the flange to make
it water-tight.


From: John De Armond
Subject: Re: Heating a greenhouse at night...
Date: Tue, 02 Sep 2008 23:45:45 -0400
Message-ID: <>

On Tue, 02 Sep 2008 20:24:20 -0500, john
<> wrote:

>I like this idea, but the reason for putting the piping in the floor is
>to get it out of the way.  The same with the pots of water (I actually
>have two big barrels for this, but they take up too much space.)  Also,
>some of the plants are tropicals and need to stay above 50F.
>Wonder if a commercial quality hot water rated hose would be durable
>enough to use as a radiator, then we could move it around as needed and
>it would handle a little kicking around.  That wouldn't send as much
>heat into the ground.

I would think so.  I used that kind of hose in my restaurants for 180 deg
wash-down water and it lasted well.  Life was usually terminated by one of my
hired monkeys cutting it or rolling heavy equipment over it.

You'll want to get the fairly thin wall, uninsulated hose.  Some hot water/low
pressure steam hose has a foam layer that reduces heat loss and makes it more
pleasant to handle.  You don't want that.

>Any idea what temperature water I should plan on running through the
>loop?  nominal pipe size, etc?  I suppose a lot of this will become
>evident after I install everything, but would like to have a clue up
>front to keep from having to rework everything.

The embedded tubing in slab installations that I've worked on are typically
3/8 to 1/2 inch, depending on the length of the loop.

A major decision that you have to make is whether to run hot water from the
tank directly through the loops or to temper the water.  Hot water is simpler
but it requires distance between the tubing and the plants.  Plus it'll dry
out soil that it's placed upon or next to.  Tempered water is more complicated
and requires more tubing but eliminates the possibility of burning up plants
or overheating the greenhouse.

>> If the plants are in dirt beds then simply zig-zag the tubing through the
>> dirt.  Enough heat will be given off by the dirt to keep the plants warm.
>> My late uncle was a rather famous orchid and camellia breeder.  He used the
>> later technique for his camellia beds.  He used semi-rigid electrical heaters
>> instead of water pipe but the principle's the same.  He used almost no aux
>> heat in his greenhouses.
>Are you referencing heat trace tape used on exposed water lines to
>prevent freezing?

No, these were metal sheathed elements (Calrod-style) perhaps 10-15 ft long.
Very low energy density.  The ends were bent and extended up out of the dirt
where the power was connected. Undoubtedly these were made for greenhouse
applications.  Unc was VERY serious about his breeding and spared no expense
on his greenhouses.

I don't see why self-regulating type heat trace tape (NOT the cheap
unregulated stuff that they sell in the big box stores) wouldn't work as well.
It would be vulnerable to a spade hit, of course.

I know almost nothing about camellias or orchids but I do know that he kept
the greenhouse environment hot and saturated with humidity, even in winter.  A
true jungle environment.  I didn't enjoy being in there at all.

>I would be interested in the phase change setup if for no other reason
>than intellectual curiosity.  (Works great for transferring heat in my
>A/C.)  Please, tell me more.

Google around for "phase change energy storage".  That's what I did when I
started the water heater project.  If you get to the point where you want to
duplicate my work I can dig out a backup disc and retrieve the project
details.  What brand and specifics of balls I used and so on.

As far as architecture, my client wanted to eliminate all but diesel fuel from
his motor coach and he wanted more hot water than the 10 gallon heater could
supply.  We did two things.  One, we removed the propane burner hardware from
the heater and had a single U-tube welded to the aluminum tank.  Antifreeze
circulated through this loop.  Then we filled the interior of the heater with
storage balls designed for 160 degree operation.

He installed an Espar diesel-fueled micro hot water boiler and plumbed it and
the water heater loop in with the engine coolant loop.  We also installed a
radiator and a homemade controller to supply comfort heat.

The plumbing was arranged so that when the coach was underway, engine coolant
circulated through the water heater loop, melting the paraffin in the balls
and through the radiator to supply comfort heat to the coach.

When the engine was turned off, a pair of valves isolated the engine block
from the loop. (manual over-ride provided for warming the block in cold
weather).  The Espar supplied heat for both comfort heat and the water heater.
The Espar is factory-programmed to 180 deg F and is not changeable.  The 160
deg phase change media melting point provided 20 deg of headroom to ensure
that it melted completely while still providing very hot water.  The water
circulated around the balls, ensuring intimate contact and good thermal

We designed a custom PID temperature controller around a BASIC stamp for the
comfort heat controls and used a small programmable logic controller to
sequence the valves and fire the Espar and generator as needed.  The PLC only
cost about $125 and operated directly on 12vdc.  I think that it was a Siemens
but I'd have to look to be sure.

All that is way more complicated than what you want.


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