Using a rocket mass heater to heat an aquaponic fish tank

I'm in the process of designing an aquaponic greenhouse. I am building it to be an off grid system and use minimal electricity. I want to be able to keep the fish tank warm in winter but an electric heater is not practical for an off grid solar system, not from what I have found so far. I would like to use a rocket mass heater but I am not certain how to best set it up. The tank will be an in ground design measuring 4x6x5. I was thinking of running the ducts under the bottom of the tank or along the sides buried about a foot down. Does anyone here have any advise for how best to arrange such a system and be sure not to cook my fish in the process? Thanks

I've been thinking of doing something similar, raising tilapia using a heated tank system. The solution I came up with was to build the tank from cob, with a pond liner to make it watertight and ducts running through the cob. That way any residual heat will escape into the greenhouse, allowing you to grow out-of-season crops. The cob and fishtank will act as thermal mass, keeping the temperature stable.

In terms of not cooking your fish, put a thermometer in the tank and, for the first winter, check it regularly several times a day so you can work out when is the best time to run the rocket stove and how long for.

I am thinking of building the same thing. I have two ideas so far:

#1 plan is for the RMH "bench" to be the base of one of the grow beds. The pump or drain line (depending on which way I run the setup) will be in the bench closer to the pipe.

#2 plan is to do a double tank setup. The first tank is purely storage/thermal mass pulling as much heat as possible from the RMH barrel. Then I will buy a stainless steel wort chiller to make a heat exchanger and a small fountain pump on a Tstat to pump fish water only when heat is needed.

In the end, I may end up doing both.

Interesting ideas. Its a tricky problem to solve and there doesn't seem to be a lot of information available. I live in a relatively warm climate so my heating needs are minor, I'm in I think a zone 9 so it gets cold enough to freeze but its not a lasting freeze. In the long run what I'd really like to achieve is an aquaponic greenhouse that is mechanical instead of electrical in design. I was thinking maybe wind pumps for moving the water and rocket mass heater for heating but I am far from there. To start with I am going with solar and trying to keep the design to a single pump and an indexing valve. The RMH bench has some interesting possibilities but where I keep getting stuck is on how to implament it. I first considered running the ducts under the grow beds and heating them thus heating the water for the tank and the greenhouse as well but I wonder if it would be sufficient to heat the water. I also worry about the ducts getting to hot and possibly catching the frames of the beds on fire or melting the liner, there is also the chance that the heat might damage the plants in the beds if it gets too hot or the extra heat might dry the beds out too quickly.

Brian Bales wrote:Interesting ideas. Its a tricky problem to solve and there doesn't seem to be a lot of information available. I live in a relatively warm climate so my heating needs are minor, I'm in I think a zone 9 so it gets cold enough to freeze but its not a lasting freeze. In the long run what I'd really like to achieve is an aquaponic greenhouse that is mechanical instead of electrical in design. I was thinking maybe wind pumps for moving the water and rocket mass heater for heating but I am far from there. To start with I am going with solar and trying to keep the design to a single pump and an indexing valve. The RMH bench has some interesting possibilities but where I keep getting stuck is on how to implament it. I first considered running the ducts under the grow beds and heating them thus heating the water for the tank and the greenhouse as well but I wonder if it would be sufficient to heat the water. I also worry about the ducts getting to hot and possibly catching the frames of the beds on fire or melting the liner, there is also the chance that the heat might damage the plants in the beds if it gets too hot or the extra heat might dry the beds out too quickly.

If you focus on keeping the tank warm, you won't have to worry about the beds drying out. The warm water will increase the rate of evaporation, but once the air inside the greenhouse reaches the maximum humidity for that temperature the beds won't be able to lose any more, and the system will reach equilibrium.

A warm, humid greenhouse should be ideal for growing vanilla orchids, if you provide them with something to grow up.

I think as long as the fish tank is inside the greenhouse and the greenhouse is the right temperature then the water inside it should also be the correct temperature. You can insulate a greenhouse to grow year round.
You may want to look into in ground heating and avoid digging the fish into the ground.

This may seem a bit radical but I do tend to think outside the box

If you built a water shed near the hot house specifically designed simply to heat water such as flexible copper tubing wrapped around the combustion chamber of the rocket stove mass heater and used a 12v Chain Drive Window/Skylight Opener ( http://rollertrol.com/store/en/72-12v-chain-drive-window-opener ) to vent into the hothouse from the water shed this would allow the ambient room temperature to be controlled thermostatically from within the growing area and keep the undesirable higher temperatures contained in the water shed (This is mainly to deal with large temp fluctuation as the rocket stove burns down or is re-stoked).

Then the water heated by the rocket stove can stored in open lid barrels (To produce a humid heat to be shared when called for with the hot house) circulated with a standard hot water circulating pump (http://www.backwoodssolar.com/catalog/pumps.htm#MARCH%20HOT%20WATER%20CIRCULATING%20PUMPS) and when activated they pump through the fish containers via tubing to avoid water contamination (Note a tempering valve could also be added to insure the tubing would be overheated should the water get hotter than expected in testing).

http://www.youtube.com/watch?v=v965YFy4vZs
This video is from http://solarproject.co.uk/ a supplier of a solar 12V controller system and how it works.

So after watching the video you can see that as the fish tank drops in temperature the controller would active the pump, pumping warm / hot water through tubing in the tank acting as a submersed radiator but not allowing the heated water to mix with the tank water and risking contamination. The same controller and pump could be used to circulate the water trough the copper tubing heated from around the combustion chambers and into the storage barrels or tank.

The parts are readily available from many sources I just chose the ones I thought best suited the project based on a google search

Hope this gives you a fresh perspective or ignites some ideas regarding your challenge

Seems someone has done what I was speaking of already

http://www.permaculture.co.uk/videos/2209111117/how-make-rocket-stove-water-heater

Very interesting indeed! Anyone know where I could find more technical data and possibly instructions on making that thing?

If you scroll down on the video frame there is a sketch on the build. Technical Data or Instructions I didn't see, but the build is pretty strait forward for the rocket stove water heater.

Connecting the copper tubing to a tempering valve for safe temperature and running plastic tubing to transfer the heat should be fairly easy.

If you want to use the idea I mentioned to run automatically and stabilize the temperature with the parts I mentioned... If you have a friend who has ever wired a low voltage controller and zone valves they could help you easily enough.
(I used to wire similar system when doing high pressure oil burners *Zone valves work similarly*) Also anyone who installs sprinkler systems would understand the basics as well.

The rocket stove water heater is concept in action and adapting it to a radiant heat system for either Aquaponics or floor heating would be simple enough, you just need to get someone who thinks outside the box rather than some old paper trained fart who says it cannot be done. Your treading fairly new water here so although what you ask for may be out there somewhere I think you may need to wing it a bit LOL

This thread has been closed for a while, but if any of you are still around and checking in, I'd love to hear what you finally came up with.

I have an aquaponics greenhouse as well and I built a rocket mass heater to heat the water in a floating raft table. The water from the sump tank gets pumped to the raft table, flows across it and back to the fish tank. The raft liner sits on a layer of permaboard that covers a series of brick channels that direct the exhaust from my heater, transferring the heat to the bricks and permaboard and then into the water in the raft system. The barrel for the heater heats the greenhouse directly, helping keep temps around 60 degrees at night. If you want to check out the thread that covers the project, it's: https://permies.com/t/42229/rocket-stoves/Replacing-cob-bench