Hydro Heat

So, I bought another house, and it happens to be on a river. Not a stream, creek or rivulet, but a real river, with a hydroelectric dam 2 miles above me, and one a few miles below me. I have not lived there a year yet, so I am not sure about river level fluctuations, but being between two dams, I think the fluctuation is minimal. That also means the headpond to tailwater ratio would be low, but the flow is pretty good, somewhere between 7000 cubic feet per second to 17,000 cubic feet per second.

I was thinking of building a small floating hydrokinetic turbine to pull a little energy from that high flow. Specifically, a double helix hydrokinetic turbine that meshes both turbines into an epicyclic speed increaser, and have it tethered to my shoreline, so I do not violate any laws.

But here is my question: how to put that flow to work?

Electricity is not a huge motivator for me because I am on the grid, my electrical needs are low, and morally and ethically speaking, my power is coming from the dam just above or below me, not to mention many others that are in the area. So, I really do not need to make electricity, but heating water... now that I could use.

It would be interesting to couple the hydrokinetic turbine mechanically for a means in which to heat water. I think the potential is there based on two factors:

1. There is enough flow in the river to do meaningful work
2. The river flows 24/7/365

But what design would mechanically heat water?
Baffle and paddle agitation?
Cavitation heating?

Just providing domestic hot water would be nice, but it is a big house with baseboard heating, so supplemental heat would be nice off-shoot?

Any thoughts?

Regular Energy needs for House = 24kWHr/day or 1kW per hour
Energy needs for Space + Water Heating = 48kWHr/day or 164,000BTU/day = 2kW per hour
Flow = Net Power / (0.1 * Head) = 3,000W / 0.1 = 30,000gpm or 67cf/s or 2m/s

https://www.smart-hydro.de/renewable-energy-systems/hydrokinetic-turbines-river-canal/

I wonder about using your mechanical energy to compress air. When air is compressed, it heats up a lot. That heat can be recovered for other purposes.

Edit: Here are some related links I found interesting.

https://www.refrigeration-engineer.com/forums/showthread.php?37901-compressed-air-to-heat-question

https://www.nexflow.com/blog/vortex-tubes-use-compressed-air-generate-cold-hot-air-simultaneously/

https://engineering.stackexchange.com/questions/19092/what-is-the-best-method-to-generate-heat-from-a-compressed-air-canister

I have a Low Head Stream Engine (LH1000).  I get anywhere from 700 to 1,000 watts at 800 to 1000 gallons a minute with 26" of drop at 60 volts.  It did take some work to set up, but all hydro has a high start up cost IMO if done right.  We also have solar.

Our larger loads are set wired up to the grid with a lot of the convent items in life.  The important things are set as an "off grid power system" in our house, pottery, and shop.  At the time grid tie would of not been worth it to us.  When the power goes out part of the time we do not notice right away.

I never thought of compressed air, although I do know the Amish near me use windmills to make compressed air for their heating and energy needs. A lot of their motors are actually pneumatically powered. It would be an easy system to convert to because it is a proven and readily manufactured energy source, not to mention needing a bubbler system in the winter anyway to prevent ice from forming around the hydrokinetic turbine.

I did find out the dam just above me only produces 1.5 megawatts for power, but even then it is not really accurate because my place is located just downstream from where a major stream dumps into the river, so I would have much higher flows. The dam below me is not really accurate either because it has several big streams dump into below my house. That increases its output, but still is only a 4.5 megawatt dam. I guess if I divide the two it puts my place at having the potential for around 2 megawatts if my place had a conventional dam. Doing quick math, it seems 3000-17,000 cubic feet per second would be just about right.

I always loved the idea of cavitation heating, but I am not sure how efficient that heating system is. It might take a lot of rpms to get any sort of heat out of that system, and that is not conducive o slow turning hydro.

I was kind of thinking of a heater something like this, although this is driven by wind. For hydro, it is a little more productive only because the river always flows by...

Low Tech Magazine

So my idea was, to make my hydro heater legal, I would pour a decent footing underground on my riverbank, and to it imbed a pipe into that footing. Inside this pipe I would weld a smaller one that would spin around inside it. To that pipe I would weld a simple engine hoist, but modified so its arm was a lot longer. It would also be jointed so that the hydrokinetic turbine would float, and float level, but when struck by floating debris like a log or something, it would swing out of the way to let the log pass without inflicting damage. Then by spring pressure, it would snap back to being directly in the current again. With this cantilevered design, I would not be building in the river, which would be even less intrusive than a camp owner putting a dock out into a lake. My turbine would just arch out from the riverbank, and float the turbine in the river.

The turbine itself would be just as I said earlier, an S-type rotor, coupled to a speed increaser. That would power a flexible shaft going into an underground, and well insulated box with a rotor and baffles fitted inside it. As the rotor/baffle combination stirred and heated the veggy based hydraulic oil, a circulator pump would then circulate water from the water heater in the house, through a coil in the underground well insulated tank, and then go back to the water heater.

Before I added the latter part, I would do a temperature check to see just how hot the rotor/baffles would get the veggy based hydraulic oil in the tank.

For starters I would just like to make the hydro-heater take care of my domestic hot water needs. I would think it would all depend on how big my hydrokinetic turbine was. The beauty of the whole thing is, it runs by the house 24/7/365 so heat would accumulate, but also be used in time to domestic hot water use.

Note: my hydro-heater would have the tank, rotor and baffles mounted horizontally, and not vertically because that is how the rotation would happen on a river.

I was kind of thinking of a turbine design something like this...but of course 4 to 6 feet long and not this big of course.