This is a fishing expedition, but I was running the hose in our green
house trying to cool the flow enough to water the plants, when the
thought occurred, why are we paying to heat water. It ran for roughly 5
minutes water too hot to touch. The supply runs through a 200 ft
commercial hose lying on top of the ground from the wellhouse then
through ~ 200' of hose which runs through the greenhouse and then the
watering hose is coiled in a
plastic drum-half stored out doors in partial shade. The other half of
this equation is that we get freezing temperatures in December January
and February. It seldom lasts more than a day, but I've seen winters
with 2 weeks of sub 32 degree weather with deep wind chills. I can see
that we could easily heat enough water with say 500' of
black pipe or hose on the roof top, but the change over could be a
bear, and not one of those things you'd want to put off till the last
minute. How do others deal with this?
Ok, this is basically how solar collectors work, but to increase the
efficiency, and use a lot less pipe, we usually have a collector structure
that consists of a box, with a flat metal collector plate in it, that is
painted flat black (usually using something like flat black enamel paint,
which bakes onto the aluminum plate nicely in the heat of the sun, by the
way), and we make grooves in the plate before mounting it in the box. this
can be accomplished by making a pounding jig to make the grooves in the
aluminum flashing metal, which is generally what is used to make the plates.
The spacing, to simplify matters, will be about 5 inches between grooves,
and the width of the groove slots will be about 1/2 inch. I recommend
putting sideboards on the jig , to hold the flashing straight as you make
each groove. You can use aluminum roof flashing material, which comes in
20 - inch wide rolls. Two of these side by side slightly overlapped will
give you almost 40 inches of plate width. The length is up to you, but
remember, these have to fit into the box when you assemble this ! What to
use to make the grooves ? two pieces of 7/16 solid steel rod do nicely. put
the flashing into the jig, and pound the first rod, which will be cut to 20
inch length, into the first groove. ;leaving maybe two inches or so hanging
off the end of the pounding jig. Cut two pieces of 3/4 inch plywood to about
a 4-inch width, and a 20 - inch length. Lay the plywood strip over the first
rod that you pounded into the groove, and pound her flush with the face of
the jig. Now, put your knee on the board, and pound the second rod into the
second groove, and repeat the "pound it flush" operation. You work your way
down the jig this way, leap - frogging the rods into each new groove, while
holding the one before it down with the knee. use a good heavy hammer for
this, about a 5- pounder works well, and take your time ... Hitting your
fingers with the hammer will smart if you do it ! Be sure your hand isnt
where you are about to hit ! Once you have made a couple plates, its time to
bend the pipe to fit into it.
make a bending jig for the 3/8 inch serpentine copper tubing, that is
basically of the same spacing as the the grooves in the plate. We dont worry
about the rounded ends of the serpentine tubing, as they wont be in the
plate grooves anyway, they will stick out the ends of the plate. You make a
series of short boards that are 1/2 the width of the collector plates, and
round off the ends. (i use a router with a circle cutter to do this) . You
then mount these on a sheet of 3/4 inch plywood , alternating from side to
side, and leaving a space of about 1/2 inch between each set of bender
boards rounded ends toward the outside ! It helps to draw a line down the
center of the sheet of plywood before you start this. And remember, the
total width from the bend on one side to the bend of the other side must
still fit into the box !
Now you bend your 3/8 copper tubing around the rounded ends , forming a
serpentine tube that fits into the grooves you made in the collector plate.
This is why when making the bending jig, you should make sure that the
centerlines of the grooves in the bender will be the same as the centerlines
of the grooves you pounded into the collector plates. This produces a
serpentine tube that can be directly laid into the collector grooves when it
its time to mount the collector plates in the box. Cut a sheet of 1 inch
thick foam insulation that fits into the box. just put it in there and dont
worry about it. get a sheet of 1/2 inch isocyruranite foam insualtion, and
cut squares that correspond to a little less than the flat space between
grooves. glue these to the back of the collector plates, two rows about 4
inches in from the edges, and one row down the middle. This will support the
collector plate without too much of a path for heat loss. run a few screws
down thru the collector plates once you have em lined up ( 2 inches works
good). A good rule to follow is to go along the outside row of squares
underneath the collector plates as a reference, and hit a screw trhough
every other one. this will support the plates nicely
get some roofing tar, and its time to glue the tubes into the plates. The
black rubberized kind is about the best for this. put a little into the
bottom of each groove in the collector plates. now, carefully lay in your
serpentine tube, and press them firrmly into the grooves in the plates. Out
at the edges of the serpentine tubes, where the curves are, mount a couple
strips that press down on them, to keep them flat in the box. This is easily
done, by simply cutting a strip that is slightly shallower than the sides of
the box, and the proper length, then press it down on the ends of the
serpentine tubes while you put a screw thru it and into the side of the box.
Usually three or four screws will do this nicely. Now, cover the tubes with
a another layer of the roofing tar. Stand the collector up in the sun, at
about a 45 degree angle, and let the roofing tar "cook" in the sun for a
couple days until it starts to get a skin on it.
Now get some flat black enamel paint and paint the collector plates with it.
three coats will be just about right, let each coat cook in the sun for a
day, and each coat will "bake" onto the plates.nicely.
What you got there is one highly efficient solar heat collector. Put some
solar glazing on the box, like KalWal. the idea is to run water thru the
pipes and collect the heat in a storage tank filled with water. this is
usually accomplished by winding a coil of copper tubing around the lower
half of the water storage tank, and circulating the hot water from the
collector thru the coil with a small pump. this will cause the coil to give
off the heat into the water in the tank. the cool water than returns to the
collector to be heated again.
This , of course, is an oversimplification, but it does demonstrate the
general construction and use of these thermal solar collectors. The details
i leave to you , gentle reader. look up solar pumps, and differential
switches , and i should mention in passing here that having the in/out pipes
from the serpentine tube on the collector both on the same side of the
collector is considered "standard procedure", and also facilitates plumbing
multiple collectors together for increased heat output/ multiple tanks..
I should also mention that in cold climates, people often run antifreeze in
the collector circuit, but not automotive antifreeze. I forget the name ,
but it is easily found. this prevents the collectors from freezing up.
look up thermosiphoning while you are at it, in case your situation allows
for it (storage tanks higher than the collectors) this would mean no pump or
differential switches would be needed. Hot water, like hot air, tends to
rise, which is how thermosiphoning works.
For your consideration.
I have a friend who made his own solar collector using a patio door and 100' of
black plastic hose. He gets warm (80-100F) water from it for 30-45 seconds every
I know of someone else who has a pair of true flat plate collectors, essentially
commercially made. His pump was maladjusted due to a power failure, and when the
pump started, 223F water came down to his Pex lines and burst them.
2 quick points. 1, don't use Pex. 2, don't skimp and you can get all the hot
water you need. No more electric element required.
Thanks for that excellent response, I saved a copy. For now I'm going
tank-less, but when I get tired of paying to feed that, solar will no
doubt be the way to go. I have a friend who passively heats his house,
and his theory is that the minute you try to store it, efficiency and
cost effectiveness go out the window. So when the sun shines he heats,
when it doesn't he builds a fire. That was how I was approaching the
solar hw thing, heating the water in the pipe in the day time,
tank-less back-up at night and during the winter. I have a foggy plan
for change over, it involves pipes to the roof with valves and drains,
then quick release fittings on the line or panel which would then be
blown out with compressed air and stored in the case of the line or
covered in the case of the panel. Thinking about it, though I'm not
sure I've uncomplicated things.