water heating

[kbhale]

This is about the six time, I rebuilt this rocket. I still have the copper coil wrapped around the riser. I think it causes turbulence because the coils are not tight. Even going more chimney I still got to keep an eye out for smoke back.

In this build I placed a 50 gallon open top drum on top and cut a hole so the flame could strike the bottom of the drum. I put a bulkhead fitting in at about the 35 gallon level. To avoid to much weight. So far I have a 20 degree rise in little over an hour. Also a 1.5-2 degree rise in the 500 gallon tank.

So far the bad thing about the rocket stove is the fire goes out within an hour or so. The good thing is the fire goes out in about an hour or so.



Couple old hot water tanks that I JD welded. I'm experimenting with them as radiators. To heat the out building. I have a 12 VDC bilge pump to circulate the water. Going to set it up on a demand switch. I'll move the tanks where needed later.

I have a building, that me and my father built some twenty years ago. From wood recovered from a tornado. It has 110V to it but no plumbing or heat. Very well insulated. Anyway I'm going to making it ready to live in. Plan to use hot water from a rocket built to supply the hot water needs for heat and water.




While cobbing I decided to use it as insulating mass for my smoker. Very happy with the results. Better balanced temperature and needed less wood and charcoal.

[twohorsepower]

hi from ireland. this is a great forum.

have you seen ernie wisener's rocket water heater?
www.rocketstoves.com/wisner.htm

i've been thinking about ways to reduce unnecessary cooling by the 'stack coil' in the barrel as the flue gas exits the riser. what if we keep the riser extremely well insulated, and use a thermic mixing valve designed for boilers (such as the esbe or laddomat) to ensure that the return water temperature to the stack coil is maintained high enough to prevent overcooling in the barrel? And/or, bury the coil in the cob/refractory surrounding the barrel?
Is this sensible?

also, can anyone suggest the smallest working dimensions of a small rocket mass heater? E.g. could I get away with a 4" or 5" diameter feed and riser pipe or does it always have to be 8"?

Thanks
2HP

[canyon]

Definitely sensible to reduce the cooling effect of a coil on the riser. I prefer the lower tech of insulating the riser extra well and or putting the coil in an outer cob or whatever layer surrounding the barrel over the expensive mixing valves and controls (I install and maintain those buggers on hydronic systems and they are very costly and eventually need attention or replacement and it can be a drag when they don't work).

One very important thing to note- use at least 3/4 inch tubing for your coil and put in a safety blow off valve on a tee without any way to isolate!

Smaller rockets work and you can search the forum here for some examples. You really have to burn only kindling size wood and it takes alot of messing with. I am going to build a 4 or 5 inch for my daughters room (small bench/space). But 6 inch is really a practical minimum. Why do you want to do a smaller system?

[twohorsepower]

thanks canyon for the advice. i want to build a smaller rocket because i want it to be half portable. the war office wouldn't let me construct something in the house but i figure if i make it half mobile, bit like the lynx rocket steam boiler but with thermal mass too, i could negotiate a permit using the usual 'temporary measure' excuse. i've a bunch of SS 5" double walled flue pipe i could use for the riser and the final vertical stack, so would 5" work as an acceptable system size?

also, i've built a 12vdc powered pellet auger affair and i'm keen to try a mini rocket mass cum water heater on pellet. i know rockets are really meant to be non-mechanized, but pellet here is cheap and very easy to handle (and recycled too).

any ideas gratefully received.

2HP

[hpmer]

I was thinking about eliminating the radiant barrel and just continuing the heat riser into a down loop. The two would form an upside down 'U' with the up part insulated and the down part surrounded by 3/4" copper tubing and the entire setup enclosed in an insulating cob structure. That way the heat riser keeps its heat to do its thing, and the water coil is close enough to get maximum heat. The pipe would then continue into bench storage.

[twohorsepower]

I like the idea of the upturned U.

Here's a pic of what some aussies did to heat shower water using a heat exchanger just above the riser (full build history pics)

www.flickr.com/photos/cicada/sets/72157613058564419/detail/?page=2

[Donkey]

Umm.. Yeah, I remember this one..
Couple comments..

Usually, for thermosyphon systems, the heat exchanger should be below the tank, between one and two feet (of separation between the top of the heat exchanger and the bottom of the tank) is good. It prevents reverse circulation which can happen once the fire goes out, cooling the tank. That kind of separation can be a pain in the butt though.. It means putting the tank way up in the air, dangerously overhead, on something sturdy.

I'd like to see a safety relief valve on the heat exchanger itself. That's where the rubber meets the road, where the highest temperatures will be and where the greatest pressure buildup will happen. Also, if somehow something (unnoticed) happens to the pipes between the tank and the exchanger, some shift in the ground or even hard water deposits, the pipes can get pinched or clogged and THAT can result in catastrophic removalence of the shower house! Not a situation you want to be involved in.

[twohorsepower]

Yeah, the more blow-off devices the better, but at least they have one on the hot flow from the heat exchanger.

You're also right that the rule of thumb is to keep your heat exchanger below your tank for thermosyphon to work. However, worth noting that, assuming suitable water temperatures are available, external side-arm heat exchangers can be made to work provided the top of the HE is lower than the top of the tank they are heating. Or, the case of a vented tank, the top of the HE is below the top of the 'tee in' point in the vent pipe.

The other thing i believe is not ideal with the HE used on the aussie rocket is, whilst i can see the rationale for the width of the device due to the baffles, it would have been better being a taller HE. If a taller HE of the same width cooled the flue too much, a taller and thinner HE would still be better than their short and fat HE. (Width is not critical to make thermosyphon work in a sidearm HE, and the height of the HE is more critical).


Here's an interesting example of a sidearm HE, albeit using solar thermal rather than rocket thermal. We have a fellow irish co-oper who's had quite good results from a sidearm plate HE salvaged from a gas boiler. See his pics on..

s626.photobucket.com/albums/tt341/leonardermo/Solar/

[Donkey]

Umm.. sidearm heat exchange works as you say.. Good solution where vertical space is at a premium, though I'm a big proponent of using the TANK ITSELF as the HE, bell stove style, and eliminating the extra, unnecessary (IMHO) bits.

Again, it's REVERSE THERMOSYPHON that we're trying to avoid in placing the HE under the tank.
If you don't care that your HE is working to (actively) cool the water in your storage tank back down again (once the fire goes out).. Then go for it!

[Dan (Upstate NY, USA)]

I wonder what would hold the temp of the hot water longer, an insulated hot water heater or a hot water tank in a bell stove?

In the Aussie example you could just put a shut off valve in the cold return so after you fire the rocket you just shut the reverse thermosyphon off.

[Donkey]

Jan 5, 2011 8:11:01 GMT -8 Dan (Upstate NY, USA) said:

I wonder what would hold the temp of the hot water longer, an insulated hot water heater or a hot water tank in a bell stove?

Dunno that. Probably depends..

In the Aussie example you could just put a shut off valve in the cold return so after you fire the rocket you just shut the reverse thermosyphon off.

Yikes! That's the kinda thing that can lead to a disaster..
All you gotta do is forget to turn the thing back on ONCE!
Unless there's a safety valve on the heat exchanger itself, you'd stand a pretty fair chance of it blowing up.

[twohorsepower]

yes, you would need a blow off valve on the HE itself (or teed onto the pipework before any other valve) to be belt and braces.

some people over here use a low resistance 'flap type' (rather than a 'spring type') check valve (non return valve) on a thermosyphon loop to prevent reverse thermosyphing. This type doesn't impede the positive thermosyphoning.

One advantage of having your tank external to the heat source, in addition to being able to insulate it properly, is that you can use a multiple of heat sources, e.g. solar, rocket mass heater, woodburner, GSHP, etc. but I guess it depends on how simple you want to keep things. there's a lot to be said about keeping it simple!

Rgds

2HP

[Donkey]

Jan 7, 2011 12:51:22 GMT -8 twohorsepower said:

there's a lot to be said about keeping it simple!

Absolutely agree there!

[twohorsepower]

I agree entirely KDM, keeping it simple should be an objective. I feel however there are some circumstances where you may be forgiven for compromising and making things more complex to try and woo/entice/educate people about great DIY technologies like the rocket mass heater. Here I'm suggesting there may be a case for compromising simplicity & making it more complex by using an external insulated hot water tank, but only where you can't get away with the simple solution.

I live in a 'business as usual' urban environment, where not only would I not have a chance of persuading my neighbour to build a rocket heater and cob bench in their house, my wife wouldn't allow me to build one in ours either! Well, not at least until they'd/she'd got some exposure to the technology on a small scale, figured it out and got to like it. So methinks, if I come up with something that can be wheeled in (& out if required), something along the size/shape of the lynx rocket steam boiler (but better designed re insulation, only taking the heat off after the main burn, etc..), hook the HE up to the existing house's hot water tank as the 'battery' instead of a solid mass, it would be easier to bring one of these things inside the house to start off with, & then once inside, the idea might grow on the people using it. good for wheeling around to workshops too!

could something on the same scale as the lynx be do-able? or am i barking up the wrong tree?

2HP

[kramer]

If it hasn't been mentioned yet, you could heat water in an open system with straight pipe bringing cold water down to the bottom of the water heater, then coming back up in a rising coil and out the top. (a big counterflow heat exchanger) This way the water water in the tank can boil, but never pressurize. The water in the coil (your pressurized water supply) will be entirely encapsulated by the water in the tank, and thus will not get above 212. No need for pressure relief valves unless you run the tank low.