This is basically a batch water heater, made out of an old pressure tank, pig water nipple, and spare lumber, insulation and single pane windows that I had lying around. The cost of this project was practically nil.
Its purpose is to keep the pig water from freezing on the cold nights during the last few months before slaughter. It’s turned out to be effective, especially with a low power tape heater as a supplement.
I framed a simple box with 1×4’s and put thin plywood on the two sides and back. I wanted it lightweight as it will be lifted over the tank to install/remove. I added furring strips in order to accommodate double glazing.
The Differduino PCB is an arduino clone circuit designed with thermal control, or differential control in mind. The resistor needed for Dallas DS18B20 1-wire thermometers is on-board, and there is a “1-wire” screw terminal position. These solid state sensors are accurate, and easy to use and work well in thermal control systems.
There is also an on board relay circuit with high voltage rated screw terminals and a mechanical relay. This can be used for switching on/off pumps etc.
This PCB is ready made to use the Wiznet 812MJ ethernet module. This is like the ‘ethernet shield’ that stacks directly on a commercial Arduino, but in a more compact form factor. It uses the same wiz5100 chipset, and the standard Arduino ethernet libraries. It also includes an lcd header to simplify the connection of an lcd display.
I always prototype my circuits on a non-solder breadboard before assembling anything. Start with the 1-wire (DS18B20) portion of the circuit using only one thermometer at a time. Load the 1-wire example sketch (file /examples/DallasTemperature/Single) to the arduino. The serial monitor should now display the address of the 1-wire sensor. I take note of each address and also decide where in the system it will be placed.
My latest differential controller sketch is available on my code page. With any sketch look through the code and get familiar with what it is doing. The comments should help explain what’s going on. The thermometer addresses are pasted in the proper place in the sketch before uploaded to arduino.
I used pex tubing for all the plumbing. Pex is great. If your thinking about using it, do. The fittings and crimp rings are available at most hardware stores, and it uses less fittings because it’s flexible. Pex does not build up scale from hard water, is more durable than copper, and can even handle freezing several times without splitting. Pex will degrade and weaken in the sun, so it must be covered when outside. It is usually recommended that the final headers to the panel be made of stainless steel due to high temperatures, but I’ve yet to run into any issues.
The solar thermal storage tank is built out of 3/4″ exterior grade plywood, and 2×4 lumber. It was custom sized to fit in an under stairs cubby that used to house the washer and dryer. It is right next to the conventional water heater. It has a 3′ x 5′ footprint, and is a bit over 3′ high. This puts the final capacity at around 150 gallons. It is glued and screwed together using coated decking screws and waterproof wood glue. It is important that this thing be strong, as it will hold about 1200lb of water. The top frame has lap joints for high strength. I reinforced the corners with uprights, and also put an upright in the middle of the long sides.
The inside is lined with 2″ poly-iso rigid foam. I cut these carefully so they would fit nice and tight against each other. I did not glue them in. This is then lined with an EPDM rubber pond liner. The EPDM was laid flat out on the lawn and cut to size. It’s then placed in the tank and worked into large folds in the corners. There is no easy way to do this. You just have to jump in and start going at it. It is not that critical that it turns out pretty. The main thing is to get enough material in there so there is no bridging of the rubber. The box should hold the weight, not the liner. I ended up with a couple spots that looked sloppy and loose inside, probably with some extra material.
Once I was satisfied with the liner placement, I attempted to smooth out the top with scrap pieces, so there was the same amount of layers all the way around. I stapled this down with stainless steel staples, caulked it liberally, and then screwed down composite decking boards. These waterproof boards function as the gasket. This gasket is then notched for the exchanger and solar loop entry points.
This is a 4’x8′ panel, which makes getting standard materials easy. It is made heavy duty so it can be self supporting. Using a table saw, I notched the 2×6’s so the backing board could be inset. They are then glued and screwed together using quality coated decking screws and waterproof wood glue. The back is exterior grade 3/4″ plywood that is glued and pin-nailed into place. All joints and seams are sealed with quality caulk. 1″ polyiso is glued inside the frame using canned foam, and then weighted down while the foam cured.