Solar Thermal Heating liquid based

[Brian McGowan]

I have made solar air heaters and they work great. It is very easy and efficient to make heat from the sun. The problem with solar air heaters is storage. Unless you want to blow the hot air you make through a large box of rocks basically there is no real method of storage.
I intend to store heat in water when I collect more than I need. This is kind of my plan which at this point is a few brain farts, a spreadsheet and a pile of parts I need to assemble. Start with a large trashcan full of water in the basement, pump from the bottom of the trashcan through pex tubing to the collector and back into the house to the 29 ft of tube and fin I already own mounted under the joists in the basement so the heat goes up to the bottom of the floor and then dump into the top of the trashcan in the most "gentle" way possible so it will stratify in the trashcan from coldest in the bottom to warmest in the top. Drain back can happen through the small submersible 12V pump I got pretty quickly.
https://www.walmart.com/ip/DC-12V-Submersible-Pump-Immersible-Pump-Under-Water-Pump-Bath-Pump/835326283
My first collector will be a little over 8FT2 and guessing at 85% efficiency I should be able to collect around 1958BTU.
The tube and fin I have should be able to dissipate around 14500BTU. That is about what 2 collectors measuring 4x8ft should be able to collect.
As I grow the system I was thinking about dividing it up into the collection part, the storage part and the dissipation part.
The collector part would have multiple barrels connected to each other for storage with a hot barrel at one end and a cold barrel at the other.
The collection end would have a 4x8ft collector with a dedicated pump which would pump from the cold barrel through the collector into the hot barrel. More collectors could be built and added with their individual pumps.
The dissipation part would have it's own pump and would pump from the top of the hot barrel, perhaps by floating the submersible pump on a piece of foam so it stays on the top of the water, through the tube and fin and back into the cold barrel.
That is my thought at the moment. I am sure it will go through many renditions.
First thing to do is make the collector and get water pumping through it then get water pumping through the tube and fin. Growth can occur after that.

[Ralph Day]

Hi Brian
Do you have to worry about the sustem freezing? You either need to drain in the cold/dark or use a glycol fluid. My daughter's outdoor boiler has glycol medium and it wasn't cheap. 45 gallon drum was over $900., and then it's diluted to 50%.

I think I'd go for a drainback system myself. Have fun.

Ralph

[Brian McGowan]

Oh yes system freezing is an issue. It is -3.5 today here.
Yes it will be a drain back system. One of the considerations in my collector design is to make sure there are no "low spots" where water can collect and freeze.
The other thing I was trying to do was to get some kind of backpressure relief valve that would let air in to the system so only the outside stuff would drain out and not the whole system. Not sure how worried about that I am considering when I expand to more than one box I will have a separate pump for each box and the dissipation portion of the system so they won't be physically connected and the dissipation part won't drain out. Only the collectors will.

[Joe Blake]

If you are concerned about freezing, have you considered using brine, as salt concentration can lower the freezing temperature of water. Perhaps have a concentrated salt water solution in the lower half of the storage bin with fresh water on top, separated by a non permeable barrier, eg a plastic garbage bag. Theoretically, the fresh water would freeze leaving the brine as liquid which could be pumped round. Further, the ice itself would act as an insulator.

Might be an idea to investigate whether the salt would increase or decrease the thermal holding capacity of the solution.:idea:

To take the "cheap" road putting the storage bin completely in a garbage bag filled with polystyrene "packing peanuts" would help insulate the tank. Or even straw if you want a biodegradable insulator.

[Brian McGowan]

I have considered brine. I actually have several trash cans full of brine that was output of my water softener system. It is pretty salty. I could always toss some softener salt in the tank also.

My only concern with the salt is how it will interact with the copper pipe I will make the collector out of and the copper pipe in the tube and fin and the pump. I don't think it will affect the PEX tubing.

I intend to keep the storage trash cans in my basement so I am not worried about them freezing and I am not worried about them being insulated. The only place they can lose heat to is still the inside of my house.

[Joe Blake]

Re copper piping reacting with brine, would there be any value in making some sort of sacrificial anode such as used on ship's hulls?

https://en.wikipedia.org/wiki/Galvanic_anode

The more reactive anode will sacrifice itself to reduce the copper's reaction.

[Brian McGowan]

I was in the Coast Guard. I am familiar with sacrificial anodes and salt water. Also all water heaters have them and you can buy replacement ones for your water heater.
These are things to be considered.
My concern is that there will be plastic non-conductive pipe between the tanks and both of the copper parts. Not sure how that will work.

[Brian McGowan]

1st picture is all the pipe parts for the collector.
2nd picture is the pipes ready for soldering.
3rd picture is soldering all finished.
4th picture is the completed pipe assembly and also the tube and fin I salvaged from the bathroom renovation after I took the right angle out of the middle and made it straight and cleaned and straightened the fins. Initially this will go under the living room but eventually when I get the other 24 feet from the side of the garage to install under the living room this part will go under the kitchen.
The pipe assembly I am going to try to solder to a piece of galvanized steel from an old heating duct I have to help collect heat and conduct it to the pipe and then paint the whole assembly flat black and put it in a box with a salvaged window in front and that will be the collector.

[Brian McGowan]

So I got that piece of duct out and separated the two halves then beat the larger half flat and cut it to size.
As a test after that I soldered a small piece of pipe to a small scrap of the galvanized steel from the duct. It soldered fine. Not as pretty as I would like but good physical connection so there will be good heat transfer.
Next step is solder my piping to that piece of galvanized steel.

[Brian McGowan]

So scratch tall that building a solar water heater stuff.
I managed to acquire from the company that installed my grid tied solar PV system on the roof 3 fairly large solar water heating panels and am in the process of working them up. These panels are Vitosol 200-F Type SV2.
I have acquired a small 12v pump that will do 800lph and pump a 5 meter head and have been pumping water through one of the panels and have seen 119 degree water coming out of it.
I am in the process of straightening out the fins on the tube and fin I have so I can hang it under the living space floor in the basement ceiling.
I am thinking about an arduino controller to run the whole operation.