Paul Jones

There are two issues here.

Cold air brought from outside is denser - more oxygen for volume. Once it falls below zero it is dry. On the face of it a win win situation. This is why grain dryers work best in freezing conditions, and why race engines have larger jets fitted in cold weather.

So bringing cold air in from outside can only be good?

There is always a but……..

Cold air directed into the burner will significantly cool the flame temperature. If you have a gas oven duct some cold air directly under the burner - go and get a takeaway - see how long it takes to cook something. You might even be lucky if it does.

In my opinion a couple of air changes per hour is good in a living space. As a rough guide you should have enough ventilation for you and your rocket to breath if allow 36 sq inches for a 6 inch burner, but do your own research and find out. Yes that’s a big cold hole!

AL.

Thank you for taking the time and trouble to post this detailed explanation. The penny, as we say, has dropped. Well almost.

When you say 'the final burning of hydrocarbons freshly mixed with Oxygen in the Toroid' where does this oxygen come from? Is there sufficient oxygen still left in the riser after the initial burn or is it created in the burn? I can see that when the fire is first started this oxygen will exist.

Refuelled the experiment continues!

Al.
Firstly, may I apologize to you and all for a basic assumption that further research has shown to be wrong.
In my innocence I took it that wet central heating systems are the norm. In the UK warmed air systems are in the minority as a means of heating homes. I am not suggesting that wet is right, or the only way, to heat your dwelling, but it is pretty standard here. These systems are powered by wood and coal/coke, oil, but mostly gas. As a result of this we grow up, and live, with very hot water. A controlled gas system would not unusually deliver 80c (176f) to every room. Because the coal/coke/wood options are almost uncontrollable heat sources, avoiding boiling problems by system design is second nature. On the rare occasions there is a problem people just run a bath.

The J tube differs in that it is totally uncontrollable. It requires more care to avoid overheating the water. This is why I don't think a combined mass and water system is a good idea. That isn't to say I think it is impossible, but you raise very valid issues that can result from this combination. So for me it is one or the other. I have chosen to explore the water route purely because it suits me. Attempting to build any type of instantaneous water system into a mass, in my opinion, takes stupidity to a new level. The potential dangers of this cannot be overstated.

You have raised a couple of questions:

'Any water jacket that tries to extract heat too soon from a rocket mass heater will find that it has extracted so much heat energy that the Rocket Mass Heater is running sub par
due to there being not enough Heat Energy left to keep combustion temperatures in the zone where near-complete combustion can occur'

I have pondered at length on this statement. Could you expand on it? The reason I ask is because surely the barrel in a standard rocket, with mass, is extracting heat at a high rate with a gap of only a couple of inches from the riser? Mr Evans suggests, if I have not misunderstood, that the riser provides the push, and the cooling of the barrel, a pull. Does this relate solely to extracting heat for water whilst still trying to heat a mass?

'If the needed heat energy is taken off
at some point further down within the Thermal Mass We would like that temperature to ether be a near match or higher for TheTemperatures we are trying to extract !'

Does this not require an exchange rate of 100%?

Your input is always very thought provoking - caused a few sleepless nights as I've chewed it over, and this might be another one!

This is an ongoing experiment in Rocket no mass water heating. It is built out of stuff I had about except for the firebricks. I do not recommend anyone tries it.



This is sited outside, it's all in the name!

4.25" J tube with a Baxi Bermuda gas boiler cast iron heat exchanger. It runs about 60c after about 1 hour. After a couple of hours it will run central heating but it is too warm at the moment to be sure how effective it will be. A 7 hour burn did give me 30 gallons of stored hot water and raise the house temperature about 3.5 degrees. At 60c you can put your hand on the top (an old meat tray) above the heat exchanger, and it is not uncomfortably hot. You won't leave your hand on the flow pipe! This suggests a fairly efficient conversion of heat to water.

It has already undergone some changes so if there is any interest I can do a thread on the build and what I got wrong/right.

For the record I have no qualifications in solid fuel. I do have a fair bit of experience from the days before such qualifications were required, but I am qualified in another fuel.

Sorry Calvin I missed the mass storage.

No, it won't gravity feed downhill. So a diagram which may give you something to think about.



The RMS would ideally have 28mm minimum pipework running vertically all the way to the tank. There are limits to horizontal runs and each joint adds resistance to the flow. The lower 50 gallon drum could be reduced in size for quicker heat up of the mass water and lagged. The header tank might be better in galvanized steel than plastic, which won't melt if boiling water does get that high. You really can't avoid the sprung return motorized valve on the top tank for automatic action if the power drops out. This should give you some time to run the RMS down before disaster strikes.

This is just an idea - it needs work. The principles are sound, but I strongly recommend a lot of controlled testing before relying on anything. Please remember that if anything can go wrong, it will!

http://www.dunsleyheat.co.uk/neutralizer%20layouts.html

My system is a variation on this. The installation instructions provided with the Dunsley offer, or did when I bought mine, far more options. It has been working for the last 10 years untouched!

Footprint of 100 square feet? Mine sits in a cupboard with a floor area of less than 2 x 4 feet and that includes the header tank, HWC, Dunsley, pumps, controls, and gas boiler! My solar heating is connected to a coil in the HWC which, had I ordered a Dunsley with enough tappings, would have fed directly into that. Sometimes the water is too hot.

Gravity circulation is God. It is the only safe way to disperse heat. Even my solar is gravity fed so that if I have a pump failure it really wouldn't affect it.

If you must continue down the route you are considering, and who am I to say you shouldn't, think about adding a 50 gallon drum of water above your rocket - open vented - that can gravity feed heat away just in case. If you use a normally open motorised valve your power supply will keep it shut off until the power goes off. You could add a pipe stat to the flow side of the heat exchanger to release the valve if the primary water starts to overheat in normal operating conditions. This tank of cold water will give you ample time to allow your Rocket to burn down. My other thought is if you want to use pipe as a heat exchanger keep it short to lower the water content, but increase the surface area with multiple metal fins. It is far easier to control half a gallon of water that wants to boil than 10 gallons.

It is far better to build in more safety features than you need at the start. If they prove to be unnecessary the option exists to remove them. If they are not there you may not have the option to put them in!

A question for those who might know: Would a CO2 fire extinguisher coupled to a sealing plate for the feed tube be successful in shutting down the fire rapidly?

If our exhaust Temps are in this range and the pump that we are using to move the water thru the system fails, we can have the
water in the Tubing Flash to Steam !

My point exactly. Any pumps used are incidental to the system and the system is not reliant on them. They should not be used inline, but parallel to the return as an assist to flow, (and efficiency of the heat transfer) and not the cause of it. Large bore gravity systems into a separate hot water storage unit/s is the only safe way. Using a pump as the primary source of circulation with an uncontrolled heating unit is insanity. There is no point in heating water you do not have a use for. I have seen a solid fuel system fitted and only capable of working with a pump. In a power cut the householder was shoveling burning coal out of the boiler because the solder on the copper joints was melting!
The potential dangers should not be underestimated, I agree. But there are many ways of doing this safely. Sealed and/or pumped systems are definitely not included. I have serious doubts about high volumes of water at the heat source.

In my opinion, for what it is worth, combining mass storage with water heating is about the worst of all worlds. Build one, or the other, or both. That way they can then be sized to suit requirements. I can't get into the house with a spec of mud on my boots, so sneaking 3 tons of cob in just isn't going to happen. Hence my interest in heating water. If the project proves to be a success, or a failure, I shall post the results as pointers to others attempting to heat water.

I strongly recommend that the Dunsley neutralizer system is looked at if heating water is your thing. I have ad ons of my own to this to further increase the safety for use with a rocket if anyone is interested. I believe this can be done, more importantly, I believe it can be done safely. But I might be wrong............

Am I missing something here because I don't see what makes these things Big Al's "flaming units of death".

For what it is worth I think what you are missing is quite simple. If you heat stored water in a sealed system with a heat source over which you have no control you have a sporting chance of raising the overall standard of the gene pool.
However, if you use an open vented system and move the water, you don't. In the UK the use of a sealed system for any solid fuel appliance is an absolute no no. Uncontrolled heat sources have to have the means to leak the hot water away (by cooling it in some part of the system) in order to maintain safe working temperatures. People were being killed by open fire back boilers which were disconnected when heating systems were introduced, but capped off. They retained a small amount of water which when the fire was lit it had no where to expand to. The result was generally an explosion.

If you Google Dunsley you should find the answer to all your problems. It may take a bit of studying but the inbuilt safety devices prevent problems without a blow off valve in sight. I use one to connect a Propane boiler, a wood burner with back boiler, and have now added a small rocket water heater which I am experimenting with as well. In a properly designed system the loss of the electricity supply will still give you adequate time to get the heat source under control, and even if you don't it will be safe. The rocket alone will raise the temperature of the circulating water to 60c in a couple of hours. This translates to enough hot water in the hot water cylinder for a days use (3 showers and washing). BTu's are great for theory, but they are so dependent on the quality of the fuel that in reality they are at best, only a guide.

Hope this helps.

The statement by Al about the effect of cooling the heat from the riser too soon had me wondering too. As an experiment I added a fan to increase the draw of the flue. He is absolutely right. The temperature of the water in my system rose 30c in minutes with it, but much slower - best part of an hour - without! So the work is not all done in the J tube as I, and I would guess others, had assumed. Thanks for that, it has proved to be one of the most useful bits of info on here.

Open vented addition to water mass.

As the water remains in the system the only corrosion is initial use and a small amount for evaporation replacement. This can be overcome by central heating corrosion inhibitor.
It would be a good idea to add a pressure release valve to the vent pipe especially if the expansion tank could be subject to freezing conditions.

If a tapping was taken from the top and bottom of the barrel and run through the coil of a hot water cylinder it could supply household hot water. Well that's the theory.

The only problem would be getting the exhaust heat through the barrels with enough surface area to heat the mass.

Hello all.

For the last year I have been studying the book by Mr Evans, and just about every thread and you tube video available. The proportions of the feed, burn tunnel, and riser are not a problem - I have got my head around those.

However, at risk of appearing incredibly stupid and despite the research, I am unable to find, or have missed, an answer to this:

What ratio is the riser height (and therefore all other dimensions) to the cross sectional area of the burner tunnel?

Or:

Does the burning flame/gas/smoke length remain the same whatever volume (CSA of burn tunnel) of wood is burned?

For example:
Ianto says the riser should be twice the height of the burn tunnel length, but anything between 25 and 50 inches will work. But, a 4 inch burner tunnel will have a cross section of 16 sq in, a 6 inch = 36 sq in, an 8 inch = 64 sq in, a 10 inch =100 sq in. This would suggest to me that for complete combustion a 10 inch J tube would need to be considerably bigger in all dimensions than a 6 inch. Approximately 3 times as big? Probably not, but surely bigger.

If you take the Erica and Ernie plan for a 6 inch as being tried and tested dimension, the burn tunnel is 21 inch the riser 47 inch. Would it follow that a 4 inch (roughly half the CSA) work best with a burn tunnel of 10 inch and a riser of 25 inch, an 8 inch at say 36 inch and 84 inch?

Clearly this cannot be the case because I cannot find any RMH with those extremes of dimension.

Would it be safe to assume a state of complete combustion has not occurred if flame, rather than just hot exhaust products, are coming out of the top of the riser? Therefore the optimal dimension of the riser would be when the flame tip is level with the exit from the riser? This, to my simple mind, would mean the air to fuel ratio, and burn tunnel/riser dimensions, are correct because no secondary oxygen is being supplied (without the barrel fitted) to the flame exiting the riser and a state of complete combustion has occurred within the J tube. Am I right in believing this is the aim?
If so, this poses more questions. Does the resistance in the exhaust and barrel of the completed RMH hold back the burning gas and smoke inside the riser long enough to achieve a complete burn? Does this resistance increase when an incomplete burn (if it is) tries to draw oxygen back through the exhaust system to achieve a complete burn? Is this why some RMH systems fail with smoke back?

Or is none of the above relevant?

Thanks, in advance, for any comments. Please be kind I'm in Wales, UK, and this is my first post!