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lil
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Recycling loop furnace thermosiphon boiler

Unread Messageby lil » 25/02/18, 09:19

Hello,

I am about to install a boiler furnace connected to a ball of 200 liters and two radiators. All in THERMOSIPHON.

The furnace boiler is a second hand and I was very pleased to see that the user manual offers very simple connection diagrams in thermosiphon, which is really rare in the current times ... Cf
poele_deville_bouilleur_8544.pdf
Operating instructions boiler furnace.
(383.68 KB) Downloaded times 280
.

I made my diagram:
image.png
Thermosiphon Schema
image.png (40.55 KB) Viewed times 1000


A friend told me about a problem of drilling of the boiler due to accelerated corrosion caused by the condensation of the moisture of the wood on the wall of the boiler on the fire side because of a return too cold from the radiators or the balloon hot water. (sorry for this phrase with drawers :? )

I thought about it and looked for information and the solution is to create a "recycling loop" that consists of mixing the return water (cold) with the water coming out of the boiler (hot) to make sure that the water water entering the boiler is always more than 55 ° and thus avoid condensation.

This does not appear in the drawings recommended by the manufacturer. So maybe it's not that bad. But at the same time, all those who were kind enough to answer me tell me that this is a real problem that reduces the life of boilers in a very important way.

To do this we apparently use a thermostatic three-way valve (eg Thermovar) that manages the mixture of hot water with cold water to maintain the return to> 55 °.

My question is how to integrate this into my diagram so that it remains compatible with the thermosiphon. And is it possible? Here is a piece of diagram to validate, I hope that someone experienced will want to advise me.
IMG_20180222_135331.jpg
Recycling loop
IMG_20180222_135331.jpg (72.97 KB) Viewed times 1000


Thank you in advance
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Ahmed
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Re: Recirculation loop boiler boiler thermosiphon

Unread Messageby Ahmed » 25/02/18, 18:44

On your diagram, I suppose that 2 brown rectangles are solar collectors not mentioned in your description?
The question of dew point corrosion is indeed serious, not so much by the effect of simple condensation, but by the fact that it is an acidic liquid resulting from the burning of wood. In general the attack of the metal is maximum at the low point of the heater.
The difficulty of installing a mixing valve actually holds that it creates a significant loss of load (friction-slowdown) and that in a circuit operating thermosiphon, the water flow generated remains low. Besides and in addition to this general consideration (and to be confirmed by more competent that this message may incite to manifest), if you decrease the differences in boiler output temperature, it may violate the principle of thermosiphon.
The installation of a circulator would overcome these limitations, it would even have the advantage of better manage the interaction between the stove-boiler and solar panels ...

Edit: I had not paid enough attention to your second pattern and it seems clear to me that nothing helps to think hot water, boiler outlet, will go down to mix with incoming water, colder.
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lil
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Re: Recirculation loop boiler boiler thermosiphon

Unread Messageby lil » 26/02/18, 11:27

Thank you Ahmed. Yes I know that everything is simpler with a circulator. But I really want to do without it to the extent that it is possible. Already, I like the simplicity and elegance of simple installations. And in addition, there are often power outages at home and I'm trying to set up simple systems that do not depend on electricity.

Regarding the solar panels, yes, they will also be connected to a second heat exchanger in the 200 liter flask and will work as a thermosiphon. I have no reason to believe that the solar panel circuit will have a significant influence on the boiler circuit.

Regarding your last remark, I think that if we realized that the little bit of diagram that connects the hot outlet to the cold input, it would circulate thermosiphon. Of course, it would explode after a few minutes : Cheesy:

What makes me think that it could work is that if the thermovar closes the valve that controls the return cumulus-radiators, the water will have no choice but to make the small loop. Then, before it explodes 8) the valve will open gradually to mix the hot water and the return water until no more pass that the return water is actually more natural in a thermosiphon operation.

But I think that this system requires intelligence and experience to understand what will happen and that is why I hope that a connoisseur will give me his opinion.
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lil
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Re: Recirculation loop boiler boiler thermosiphon

Unread Messageby lil » 26/02/18, 14:33

Hello,

I just spoke to a plumber who is used to old installations that work in thermosyphon.

According to him, my diagram incorporating the thermovar will not work because it is incompatible with the thermosiphon.

He says it's better to do without it and stick to the scheme recommended by the manufacturer.

His parents had an installation like this. The boiler finally broke through. After decades of use ...

I think I do not have much choice, I will stick to my original scheme.

Unless another expert comes to tell me how can I integrate a thermosiphon recirculation loop in my diagram?

Maybe there are behaviors to avoid or little things to do to preserve the boiler?

Thank you in advance
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Cerisedaniel
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Re: Recirculation loop boiler boiler thermosiphon

Unread Messageby Cerisedaniel » 26/02/18, 14:49

lil wrote:Hello,

I am about to install a boiler furnace connected to a ball of 200 liters and two radiators. All in THERMOSIPHON.

The furnace boiler is a second hand and I was very pleased to see that the user manual offers very simple connection diagrams in thermosiphon, which is really rare in the current times ... Cf poele_deville_bouilleur_8544.pdf.

I made my diagram:
image.png

A friend told me about a problem of drilling of the boiler due to accelerated corrosion caused by the condensation of the moisture of the wood on the wall of the boiler on the fire side because of a return too cold from the radiators or the balloon hot water. (sorry for this phrase with drawers :? )

I thought about it and looked for information and the solution is to create a "recycling loop" that consists of mixing the return water (cold) with the water coming out of the boiler (hot) to make sure that the water water entering the boiler is always more than 55 ° and thus avoid condensation.

This does not appear in the drawings recommended by the manufacturer. So maybe it's not that bad. But at the same time, all those who were kind enough to answer me tell me that this is a real problem that reduces the life of boilers in a very important way.

To do this we apparently use a thermostatic three-way valve (eg Thermovar) that manages the mixture of hot water with cold water to maintain the return to> 55 °.

My question is how to integrate this into my diagram so that it remains compatible with the thermosiphon. And is it possible? Here is a piece of diagram to validate, I hope that someone experienced will want to advise me.
IMG_20180222_135331.jpg

Thank you in advance


Hello,

What metal do you use as a boiler? For my part, I used aluminum as a boiler and I treated with a corrosion inhibitor Sentinel X100, In principle, it already resists corrosion due to the presence of a protective film of oxide on its area.
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Ahmed
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Re: Recirculation loop boiler boiler thermosiphon

Unread Messageby Ahmed » 26/02/18, 19:15

Lil, you write:
What makes me think that it could work is that if the thermovar closes the valve that controls the return cumulus-radiators, the water will have no choice but to make the small loop. Then, before it explodes 8) the valve will open gradually to mix the hot water and the return water until no more pass that the return water is actually more natural in a thermosiphon operation.

I understand and approve your desire to be simple ... 8) but considering the small loop, ignoring the thermovar, the large loop, and the risk of boiling, there is no physical reason that can force warm (lighter) water to descend towards the cooler water (and therefore more dense) and the presence of the thermovar or whatever you want (apart from an accelerator), nor change anything. The opinion of your plumber is therefore relevant.


If it is assumed that it is difficult to avoid corrosion and knowing that this phenomenon will still take some time * before the breakthrough, it would be interesting to know if it is possible to intervene ** at the bottom of the boiler, because in the affirmative it would be possible, if necessary, to resold a steel plate on the defective part and thus give a new "youth" to this heater. I have seen it practiced many times successfully.

* By keeping the water temperature high enough, it is possible to slow down the corrosion considerably; the installation of thermostatic valves to your radiators (not all!) would accommodate this temperature.
** As needed by cutting the bottom of the stove for easy access.
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lil
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Re: Recirculation loop boiler boiler thermosiphon

Unread Messageby lil » 26/02/18, 21:53

Cerisedaniel wrote:Hello,

What metal do you use as a boiler? For my part, I used aluminum as a boiler and I treated with a corrosion inhibitor Sentinel X100, In principle, it already resists corrosion due to the presence of a protective film of oxide on its area.


Hello and thank you for the reply,

It's steel I think. I do not have too much experience in metallurgy so I do not know if my boiler is supposed to have been protected by an anti-corrosion film or if this possible film could be replaced ...
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Ahmed
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Re: Recirculation loop boiler boiler thermosiphon

Unread Messageby Ahmed » 26/02/18, 22:13

When Cerisedaniel "film" is, as it is partly stated, the surface of aluminum which spontaneously oxidizes in contact with air and which constitutes a barrier slowing down the deeper corrosion, as it does. is also the case of zinc. Unfortunately, ordinary carbon steel behaves differently (except for a particular shade) and superficial oxidation does not protect it at all.
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lil
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Re: Recirculation loop boiler boiler thermosiphon

Unread Messageby lil » 26/02/18, 22:25

Ahmed wrote:if we consider the small loop ignoring the thermovar, the large loop and the risk of boiling, there is no physical reason that can force the warm water (lighter) to descend towards the colder water (and therefore more dense) and the presence of the thermovar or whatever you want (apart from an accelerator), nor change anything. The opinion of your plumber is therefore relevant.


Yes, it's true. On the other hand, in a thermosiphon installation, the hot water rises then it goes down again to be cooled. This is what we see in the diagrams recommended in the instructions for use. So what is missing in my little bit of diagram integrating the thermovar, it is a vertical part at the exit of the boiler to launch the thermosiphon and create a depression in the boiler to suck back water.

If I had only the ball to warm, I could place the thermovar between the two vertical tubes, a little above the boiler.
If I had only the radiators to warm, I could place the thermovar on the right of the boiler, on the return tube, connected by two elbows which create a bypass with the tube that goes up the boiler outlet (cf http://www.freeheat.fr/wpimages/wp6595cca7_06.png).
So I guess traffic would start and it could work. But as I have two parallel circuits, I must place myself in the only place where their returns meet, ie just before entering the boiler ...

Or two thermovar?


Ahmed wrote:If it is assumed that it is difficult to avoid corrosion and knowing that this phenomenon will still take some time * before the breakthrough, it would be interesting to know if it is possible to intervene ** at the bottom of the boiler, because in the affirmative it would be possible, if necessary, to resold a steel plate on the defective part and thus give a new "youth" to this heater. I have seen it practiced many times successfully.


Ahmed wrote:* By keeping the water temperature high enough, it is possible to slow down the corrosion considerably; the installation of thermostatic valves to your radiators (not all!) would accommodate this temperature.

I do not understand. How now is the temperature high enough? In any case I plan to have at least one radiator without tap, so as not to risk seeing all the radiators closed and the circuit overheat.

Ahmed wrote:** As needed by cutting the bottom of the stove for easy access.

Yes that I think it can be feasible. The boiler is at the bottom of the hearth, we can even consider that it is outside.
Last edited by lil the 26 / 02 / 18, 22: 39, 1 edited once.
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lil
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Re: Recirculation loop boiler boiler thermosiphon

Unread Messageby lil » 26/02/18, 22:38

lil wrote:Or two thermovar?


I think that with two thermovar a circuit would take precedence over the other and that one of the two thermovar would never open ...
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