Thermal bench without veranda

[kae]

I read thermal diffusivity on wikipedia. Indeed this coefficient brings a lot of interesting information.

I would therefore retain the candidates marble, granite, clay, mortar.

How to isolate such a mass? Air knife then glass box on the top but rock wool or polystyrene on the sides and the bottom?

[dedeleco]

It takes the thermal convection of the hot air which rises, which passes around blocks of about 10 cm thick (if diffusivity of 1mm2 / s, it takes 100x100mm2x1 = 10000s to diffuse over 10cm or 4 times less = 2500seconds for 5cm of a brick or 10cm thick block heated on both sides), because otherwise, if too thick, the heat will never reach the deep interior.

Therefore, the thermal air sensor must be lower than the mass of blocks to be heated, traversed by this hot air on the surface, which descends from the top, after having given up its heat, in a closed circuit, to be recycled in the thermal sensor. , under the glass.

Otherwise, you need a fan to circulate unnatural !!

The sides must be insulated with a good usual insulation, thick enough, approximately 10cm, even cotton wool or paper full of still air.

[kae]

Um, my idea is a black concrete block in a safe. Point. Talk about convection of the air from the sensor to the store, but that's not what I imagined.

[dedeleco]

The concrete block (not cinder block, more insulating) under the glass must not exceed 8 to 10 cm in thickness given the heat diffusion time over 10cm, nearly 3 hours, the same for clay, limestone, granite, !!!

So it should not be thicker, if not more, will be useless on a few hours of sun especially in winter rather short in sun.

It is already quite heavy, around 200Kilos for an m2 on which the sun falls 2 to 3 hours for a yield of 50% to 30%.

This to store approximately 0,8KWh by heating all these 200Kgp from 20 ° C to 56 ° C, which is obtained by burning 0,2 to 0,25 kilos of wood in an insert !!! A saving of around € 0,08 !!!

Or the mechanical energy released by pedaling for 4 hours while pedaling the body to its maximum !!!

We can better see how much energy is not expensive, in hours of tired cyclists!


Energy is not expensive !!

[kae]

Hey, thank you for the clarification.

[antoinet111]

the idea is good, but the result not sufficient.
I wouldn't do either then (I had planned one in my veranda with glass bottles)

Goods.

[Obamot]

If I understand correctly, Kae wants to make a mobile thermal balloon! The idea is good, except that ... It is not only the thermal diffusivity that comes into play! I point out that in the table you already have an equation with four unknowns articulated around the "thermal skin depth"relating to the chosen material ... etc.

But! The most important and I am surprised that no one has yet asked the question: is the state of the construction in which this “mobile thermal balloon” will be inserted? Is she:
- well thermally insulated, passive house type?
Because otherwise, honestly, the gain will hardly be noticeable ...

And if we ignored that, we would quickly realize that the calculation would give a sinusoidal response ... (Whereas in this thread we tend to reason "Gaussian curve") Since to that would be added the variations in local and seasonal atmospheric temperatures ... It is therefore very random, even if not zero. We have to see if the game is worth the candle. But without extremely well-made insulation, there is no salvation!

Because if the idea is good - even if the right conditions are met - it is not easy to implement: it would be necessary to reckon with the fact that this mass - before using the stored heat - should first warm up itself, and that it would take time, and that this duration would vary from day to day, from season to season!

You don't need to be Einstein to understand that the heavier the mass, the more heat it could store, but that on the other hand, the longer it would take to heat up before reaching the maximum available T °! So in this case, indeed, concrete would prevail, but to say point blank that it would be necessary "200 Kg", that's a joke, amha! ... Because the ideal would be to vary the mass according to the delta T ° possible day-to-day, and for that it would be necessary to base everything on forecasts of temperature and sunshine! And have several dimensions of boxes! Problem that we do not have with a thermal balloon (internal to the construction) and supplied by a fluid, since we close / open the valve only when it is useful ...!

Without paying attention to that, the part of the mass not heated at the climax, would cool the rest, and this very quickly, with a scarcely favorable balance. So there are precautions to take! A few avenues for reflection, just to reflect a little, and see the practical difficulties:
- The body should be carefully thermally insulated (I mean totally airtight, so that the mass heats up through double glazing, and that the accumulated heat does not diffuse outside, as the temperature of the sun would decline ...! but keep increasing for as long as possible!)
- This insulation should be removable, so that once inside the house, the stored heat can be released!
- For optimal performance, it would be necessary to be able to follow the course of the sun, so in winter, the ideal would be for the mass to be inclined in the body (obviously, on the practical side this is hardly possible), thus, it it would be better if at least the part facing the sun is double glazed, ditto for the top;
- There would therefore necessarily be several compromises: thus, in the absence of good insulation, this "mobile balloon" should not be taken out until the outside temperature under the box would approach the temperature available inside the house. Because if we take it out too early, we cool it even more before trying to reheat it, and if we take it out too late, we are heading for a shortfall ...
- It would therefore be necessary to add a thermostat with an audible alert indicating: when to bring in the balloon, and when to take it out ... Insulation or not (with greater room for maneuver). And of course do the ad hoc calculations.
- It will be understood that according to the same principle, this heat should not be released all at once ... Otherwise, it would amount to overheating, then after nothing or almost nothing ...
- and in the equation, we must add the most important point: "Will Madame be okay with going out and / or bringing in this damn .... ∫Åß ¢ øœπø∑Ç® † ± ≠ Ç {¿} fi“ {# | Ç fi ... when Môssieur is not not here!". Not to mention that if the two couples are working outside, it is hardly possible to take it out and / or bring it in at the right time (or then it is really necessary that the box is extremely well insulated when the mass is in the 'outside)

This is why thermal technicians much prefer a thermal balloon present inside the house permanently, or buried in the depths at -300m minimum after drilling a well (some would say the opposite of all of the above , but it is that they have never really tried ....).

This is also why some people have created a thermal balloon inside in a boiler, with the external thermal solar box / panel (equipped with reflectors + copper tubing). They circulate a fluid, then a thermostat opens AND / OR closes the valve when it is favorable / unfavorable!

Obviously, pipes and caissons are thermally insulated with small onions ... They save 60% of heating on average, per year! But they are at medium altitude, above the stratus layer! In the plains, I'm not sure it would be profitable ... It depends on the level of sunshine in the region where you live ... And necessarily on the altitude: otherwise we have peanut.

Theoretically and practically:
- if you do not already have a passive house (or very, very well insulated), I advise against it.
- if this is the case, as long as you make a box, you might as well leave it outside permanently and use a fluid, right?

Conclusion: if you don't have your house very well insulated, you have to start there ... The fact of not losing internal energy will be much more interesting than what you would hypothetically obtain with such a mobile thermal balloon variable dimension amha.

[dedeleco]

Clearly kae wants something simple, cheap !!!

Clearly, he does not want to rebuild his house with € 30000 to € 40000, or even more, from ITE, roof spaces, triple-glazed windows, double-flow ventilation, boiler, etc .;

Once he has returned his 200kilos, he lifts the window to let out the heat, to save about 0,1 € each time !!!

Obamot is always angry with the numbers, never giving orders of magnitude in € and KWh saved !!!

Some think :

Down the talkers and ceiling fans!

[antoinet111]

and I wouldn't change my mind.
I had for free (leboncoin) a double glass door to make almost 4m² of solar panels, a heating wall which only cost me the cost of a PER multilayer.
it is possible to manufacture yourself for cheap (APPER Solar)

[Obamot]

We cannot even recommend the veranda, even if it is not a bad idea, as long as there is no inventory of fixtures with if possible photos ... But since a veranda does not replace a facade insulation, we can only offer it in appropriate cases ... And what matters is the insulation. If we put a veranda on a wall, it will insulate the wall but will inevitably create a cold bridge elsewhere! As soon as we take it second-hand, we have little choice but to adapt to the available format: it's not great, as long as we don't know exactly in which direction to go!

As for calculations, it is still necessary to have data! But Dedeleco is so strong that he can do "without", he who is the specialist in the plow in front of the horse. Thanks to its "infused science" in all fields and its magic tool: wikipédia

All kidding aside, under the conditions described above, a surface area of ​​5 to 6 m2 of solar thermal collectors connected to a storage tank of 400 to 500 liters is sufficient for a family of 4 people. And since you are never careful enough (the sky can be overcast for several days ...), I would rather say 1000 liters. Which corresponds to the ton that I wanted to recommend above. But I gave up, because it doesn't seem realistic to me, to move a concrete block or a roller boiler of this weight!

So we come back to the first step: the evaluation of the building!

NB: The simple and inexpensive thing to do yourself: it is to review all the thermal insulation of the construction by removing ALL the airways, using polyurethane foam, silicone gaskets, double hollow body joints in "d" profile at each door and windows (which if they are not double, can be lined with cellophane film, such as those used by florists and glued with bodybuilder's tape) etc ...

PS: Now if we want to know who is talking in the air in this forum just follow this link:
https://www.econologie.com/forums/que-faut-i ... 2-280.html