water pipes in your bench?

[canyon]

Has anyone built in copper pipes into their mass bench to either heat up water for something else (I'm thinking mass floor) or allow the bench to be heated by other means (active solar perhaps) What do ya'll think?

Lasse

[Donkey]

I dont know of anyone doing this..
Seems well worth a try.
Though the thought of pipes full of water all through a cob structure gives me pause..
I would try to keep junctions, tees, etc out of the cob. Its at those places that such things tend to fail first.

[canyon]

I appreciate the wisdom! I guess I'll plan on a 60' roll of annealed tubing and forego the soldered grid I had in mind. I won't be building my bench until next summer (we are in full white winter mode!) so it will be awhile before I can report anything about how this works.
Thanks,
Lasse

[Donkey]

You can get good bent coils and whatnot in copper if you temporarily cap the ends and fill it with water. The water will prevent kinking and you can bend it all over the place without hassle..

[Dan Roesinger]

Hi there!

I'm new to this forum, and hoping to play with both cob and rocket stoves in the coming year.

Try PEX tubing. A lot of folks are using it instead of copper for plumbing, and especially for hydronics. PEX is an abbreviation for cross-linked (X) polyethylene (PE). I know, I hate the idea of using plastics, too. But it has the advantage of being seamless, and even if the water in the tubing were to somehow freeze, the tubing doesn't burst.

I guess I'd stick with hot air. I'm full of that, anyway.

Dan

[Donkey]

As a general rule, the fewer conversions, the better..
Rocket Stoves produce heated gasses. Why transfer to water, then to the bench?

[canyon]

With water pipes in the bench you could transfer from the hot gases to the bench and then from the bench to water for remote charging where a flue isn't practical. Or if there's another heat source such as solar you could charge the bench with hot water when available and avoid burning some wood. Or if you overheat you could even cool the bench. Lots of possibilities. I'd be concerned about using PEX for the high temperature potential (melted PEX followed by leakage) although I admit I try to avoid plastic whenever posible anyway.

[johng]

Canyon--

I agree that you probably want to go with copper tubing in the bench, since you don't really know how hot it will get in the bench. The flexible copper would probably be the best, to avoid any junctions. The PEX just seems a bit dangerous that close to your heat source. It might be ok, but I'd go with copper just in case.

IMO, this could be an excellent added heat source to to tie into a solar hot water system. It allows you to go with solar when it's sunny, and you can use the rocket stove when it's cloudy, or when it's really cold.

I'm pretty excited about the possibility.... Keep us posted, if you decide to try it out (once things thaw out up in AK!)

-john

[creeky]

Hi Canyon & Donkey

Did you manage to build water pipes into your bench Canyon - what were the learnings.

The following is from a thread I have just started on Permies - permaculture/alternative energy - title is "Rocket Mass Heater to heat a fish tank in aquaponics" - the following was my first post on the thread

The Fish Tank Challenge
How to hold water in a fish tank (1000 litres or 225 gallons) to a temperature range of 20-23 deg C (73 deg F) in a well insulated but unheated greenhouse, when outside temperatures fall to 0 deg C (32 deg F) at night and 6 deg C (43 deg F) during the day. This fish tank is part of an aquaponics system under development.

Proposal - Rocket Mass Heater for heating fish tank water :-

Install a RMH in the Greenhouse with a Cob bench in which water reticulation pipes are embedded in loops between the top surface of the Cob Bench and the RMH’s 150mm (6 inch) exhaust ducting embedded low in the Cob Bench.
The fish tank water to be pumped through the water pipes (with pressure relief valves) to pick up the residual heat held by the Cob – then back to the fish tank.
Fish tank to sit on top of the Cob Bench to absorb heat
Cob Bench sits on a concrete floor in the insulated building and will warm the floor around the fish tank.
Ambient temperature in the Greenhouse will be held up by heat radiated from the Cob and the concrete floor.

Unknowns – where I need advice

What are the temperature gradients in the Cob at different points along its length & at different heights above the ducts from the RHM when the RMH is operating.
How long is the heat retained in the bench and how do the temperatures & gradients change as the cob cools after a period of RHM burning ends
Can the water reticulation be through cob that is not hot enough to cause localized boiling & the risk of explosions – can safety pressure valves be incorporated.
Will heat transfer up into the fish tank from the cob bench it sits on
What temperature controllability would there be for the Fish Tank water
Will the cob hold together with the piping heating & cooling

There could be common interest here & so I wanted to catch up with your progress.

Regards Creeky (in both body & mind)

[canyon]

Creeky,
Sounds like an interesting project. I did end up putting approximately 60' of 3/4" type K copper tubing in my mass bench. I did it in four runs with the joints outside the bench (jumpers and supply/ return) and can recommend the effort and use of materials. However, the rest of my system (solar/ hydronic loops) are not online yet so I have only partial experience to share so far.

The thought of coupling your fish tank to a mass is a little sketchy when you have such an important temperature range needed for the fish etc. I would think you might want to have the tank insulated from the mass and add heat when you need it from your mass via h20 'cuz the mass surrounding your flue will vary in temp too much and might mess up the swimmers. There is a time delay of 4-6 hours from what heat you put into a basic mass bench to when you feel the effect on the surface. It is not easy to hit an accurate "target surface temp" whereas you can control heat extracted from a mass via hydronics to keep your fish tank right at the sweet spot range. So again, I think you might want to reconsider placing your tank on the rocket heated mass and instead let it buffer ambient temps and extract heat via hydronics to your tank with controls. Not sure if I answered enough of your questions but it is a start. I look forward to more conversation and sharing of experiences.

[jeremiah2913]

I don't see the practicality of using the bench to heat something else but I do like the idea of using solar as another means of heating it. Not much different than solar radiant floors but I have seen very little information pertaining to it's performance on an earth mass.

[creeky]

Hi Canyon

You wrote - "...I did end up putting approximately 60' of 3/4" type K copper tubing in my mass bench. I did it in four runs with the joints outside the bench..."

What risks are there of localised boiling in the piping and how would you place the piping to best minimise this risk. Also, does the installation you describe incorporate pressure release valves for safety.

Thanks for the advice re not placing the Fish Tank directly on top of the cob bench - point taken on board.

I need to better understand temperatures generated in a Cob Bench - Does anyone have guidelines on what temperature gradients are developed in cob benches - along the bench surface and in the duct itself as the bench during both heating then cooling (after the RMH is left unattended). How long does a bench hold its heat. I realise this must depend on the design of the RMH, ducting & bench. My system will be 6 inch throughout with about 30 feet of duct (15 feet out from the RMH, a U bend then another 15 feet back towards an exhaust point close to the RMH)

Thanks

Creeky ( both in the bones and the brain)

[canyon]

Creeky,
I don't think there is much risk of localized boiling in the bench pipes as long as the water is moving. I do have prv's (pressure relief valves) for safety anywhere where the piping can be isolated. I think it is good to have 3 to four inches of mass between the flue and the pipes and I think it is wise to surround the pipes in clay/sand mortar without rocks that could perhaps damage the pipe. If possible, it is wise to have the pipes continuously sloping from one end to another to limit the chance of airlock.
The temperature gradients are hard to describe as there are many variables. If you build with a lot of large stones, (depending on the type of stone also) the bench tends to get hotter faster and cool faster than urbanite or claycrete. Urbanite or claycrete has shown to be more comfortable and even for what I have to work with (actually approaches soapstone comfort). For 6 inches of clay/crete or urbanite on top of the flue it takes roughly 4 hours to feel the added heat from a fire. The further away from the flue you get the less the heat is felt as it spreads out and is carried away by radiation/convection. The use of insulation is another variable that I employ. I can bank up my bench (6"with roughly 27' of flue) and leave for three or four days and not have my place freeze in single digit farenheit temps with insulation on the bench. Without insulation I speculate that the place overheats for a time and then cools more rapidly. You kind of end up in a relationship with your bench and it takes getting to know it and the amount and kind of wood you burn and the outside temps and what to do to take care of your needs. Sudden weather shifts can be a short term problem because of the lag times.

When you do that u bend you might consider an H so you can have cleanout access to both runs if possible.

[creeky]

Hi Canyon

Thanks for the detail on pipes in the bench & temperature gradients. It gives me enough to proceed further with the design.
I am getting close to starting a first build effort.
After many iterations my design is as follows
1. SHWP solar HW panels (home made) that cycle water by thermosiphon from a storage tank (ST) sitting above the panels on the roof of a greenhouse.
2. WWST "warm water storage tank"in the greenhouse that stores hot water drawn as required from the ST with corresponding volume pumped back to ST from the WWST.
3. RMH 6 inch 39 inch riser fed from outside the greenhouse
4. CB Cob bench 39 inches wide (provisional) & height still to be determined and 15 feet long, with 30 feet of 6 inch ducting & the exit flue to outside the greenhouse right next to the RMH
5. WWST sits on & in the CB & has cob surround to about half its height
6. CHWP Cob hot water pipes in steel in 4 runs in the cob (using Canyons guidelines) that can either thermosiphon to the HWST sitting above it - pumping if thermosiphon is not sensible
7. CB,HWST,CB,RHM all provide air heating (controllability??) for the greenhouse and linked chicken shed -
8. Concrete floors will absorb & radiate heat
9. Aquaponics system (I will describe the design later) has 250 gallon (1000 litre) fish tank that can draw warm water from HWST in order to maintain water temperatures in a range of 20-23 deg Centigrade year round.
10. Pumps - Pump 1 to circulate water in the Aquaponics, Pump 2 to transfer water from HWST to ST & possibly through CHWP (if not this will be Pump 3)
11. Gravity feed - ST to HWST, Fish Tank to Grow Beds, Grow Beds to Sump (Pump 3 to return water from Sump back to Fish Tank)
12 Temperature controls - mechanisms not yet designed for activating & shutting off water flows to keep the Fish Tank water within range
13 FT Fish Tank kept separated from the CB with HW exchange from HWST done through the Sump - to get better controls (as per Canyon advice)

A diagram would explain it better
Lots of maths done to balance volumes, flow rates, fish density, fish feed & fish waste, grow bed size fish density in the fish tank etc

I will keep you posted as I progress through planning and build

Thanks for the interest and input

Regards
Creeky

[creeky]

Oops WWST is the same item as HWST