Heat storage

[Obamot]

Yes Dedelco, I had seen a TV show about it (I would have to find it). This house entirely passive, it seems to me that it was the Germans who were interested in it (like many people of the northern regions), and it seems to me that there was a "rotating house" following the race the sun ...!
But obviously, let's be realistic: it is the immense size of the tank (placed inside the construction itself and which makes almost its full height !!!) which does all the work of a good buffer and the recovery of heat is obviously ALL year round. They just sized the panels very well with circulation of the fluid heated by the sun.
It is very clear that under our lattitudes, as elsewhere, it would not be desirable in view of current techniques, to store for long periods. @ +

[chatelot16]

Heat diffusion formulas which include thermal resistance as a limit case (read the references given in past posts), allow to calculate everything.
We can also simulate everything in a reduced storage model, on a reduced scale, as I explained and clearly visible in the equations. it's easier and more concrete in my opinion.

of course we can calculate everything: whoever can do it, because when I read your references I see hours and hours to pass to make valid calculations: if you are faster than me do not hesitate

but why do a complete calculation of diffusion since what interests me is the average loss of energy after several years of operation (what you call borderline case, in mathematical language)

as usual the complete calculations are too complicated, and it is the good limit case which is practically significant

study in reduced model, it is good if the result of the reduced model can be compared to an exact theoretical calculation to validate something, otherwise I do not see the interest: without validation compared to a theoretical model I will not even be on formulas allowing to transpose the results of the reduced model to the real case

[Obamot]

How could we properly size an installation without doing a calculation, I don't see?
And how would a calculation be an obstacle? Are not those who know how to do them ready to contribute, something must escape me!

[dedeleco]

The orders of magnitude with clear and simple calculations make it possible to define the limits of what detailed calculations will give, and to avoid errors that precise and heavy calculations can sometimes hide, because the main thing is the calculation hypotheses which must correspond to the concrete reality of the phenomena, well before the precision of the calculations.
So simple analyzes but corresponding to the reality of the phenomenon are much more essential than very precise calculations that we often do not understand and that we have to believe with our eyes closed (unless we work hard on their demonstration).
Personally, I am wary of sophisticated simulations, if I cannot know the fundamental assumptions which were used to carry them out and I prefer simple and rudimentary calculations of order of magnitude, to check, that there is no divergence fundamental with reality.
Many professional software have this defect, complex with unknown assumptions. Thus, we provide precise diagnostics to sell, to believe with eyes closed, missing crucial elements, overlooked. we nitpick from 1 to 10%, but we hide or forget elements that can change 100%.

It is important to understand the basics of thermal diffusion phenomena because otherwise the usual intuitive reactions do not correspond to reality.
The heat does not propagate at constant speed like a mobile, but diffuses by arriving at a distance (or length of diffusion) which believes like the square root of time and therefore with a speed of the heat front which slows down like time in square root !!
After a time 10 times longer, the heat front only reaches 3 times further, and beyond, given the Gaussian curve, nothing, strictly nothing, heat has not yet reached, not even a trace at 2 or 3 times the length of diffusion !!
The most precise calculations will always give this basic result of the simple calculation of the diffusion length over time !!
The geometry will change 10 to 30%, but this general fact remains true and is enough to avoid huge errors.
Everything is based on this fact that the heat remains stored on the starting volume plus that of the length of diffusion of the heat in the past time, basic result, that all simulation will verify for the main part.
This calculation is simple, understandable, 30% accurate, visible in the exact solution equations used for the precise calculations !!
Everything is in length x on the square root of (time diffusion constant) and this allows an immediate simulation in reduced model at reduced time.

On the contrary, a flow of underground water, like a river, propagates at a constant speed and therefore we must be sure that it does not occur under the earth used, by looking at the geological structure, (drainage, groundwater, nearby wells), by diverting rainwater, by stopping it by injecting product or cement making the earth waterproof, this is much more essential than a very precise calculation.
The earth should be a tank with few leaks for at least a year.
Given the uncertainties on this subject, my point is to have low prices for each element (summer sensor at 30 € per m2, pipes at 17 € per 50m, simple drilling) to easily oversize and absorb the uncertainties that even very precise calculations cannot avoid.

This method is the opposite of many professionals, who seek to pump the maximum amount of money and avoid inexpensive solutions and who only offer Panurge sheep standard solutions that bring them money, such as Heat Pump dear, famous, to be changed every 8 years thanks to pseudo-ecological standards that change like weather vanes (my personal case with architect and precise calculations hide it) !!

In geothermal energy (misleading term), they never offer to heat the earth and remove the heat pump, with EDF which pushes nuclear with that !!

Innovating is difficult, yet some have been using this method for over 30 years and it works outside of France !!
http://en.wikipedia.org/wiki/Earth_sheltering
http://en.wikipedia.org/wiki/Annualized ... rmal_Solar
Read the summary with all the possibilities which in my opinion are not all the best and simplest:
http://en.wikipedia.org/wiki/Passive_solar_design

The risk is that with standards the choices are not the best as in the past !!

obamot writes:

It is very clear that under our lattitudes, as elsewhere, it would not be desirable in view of current techniques, to store for long periods

This sentence shows the unconscious influence of our conditioning by energy lobbies to avoid the best common sense solutions:
You do not think about it, no more heating, no more nuclear EDF, by heating with the heat of summer for winter in a simple way with the natural reservoir of the earth under our feet, which works for 5 billion d 'years without us !!!

chatelot1- writes:

study in reduced model, it is good if the result of the reduced model can be compared to an exact theoretical calculation to validate something, otherwise I do not see the interest: without validation compared to a theoretical model I will not even be on formulas allowing to transpose the results of the reduced model to the real case

shows the difficulty of assimilating heat diffusion and the scale law methods verified by theoretical diffusion models, clearly visible in all equations in x / rac (D * t).
This difficulty stems from the French teaching method which often favors the theoretical formula, instead of its deep meaning, hypotheses, orders of magnitude, much more important to avoid errors.
However, this catches the eye:
on x / rac (D * t) if we take 10 times smaller the time becomes 100 times shorter!
If 100 times smaller, it becomes 10000 times smaller, 6 months and more, even years, become a few hours.
The mathematical formula is unchanged !!
Read and understand the basics used for precise calculations in heat diffusion:
http://en.wikipedia.org/wiki/Heat_equation
and the version typically French to decode :
http://fr.wikipedia.org/wiki/Noyau_de_la_chaleur

[chatelot16]

time is one thing, but the system must work continuously forever!

so the distribution distance corresponding to half a year corresponds to the distance where the temperature will be variable around the storage mass: so I understood this way of determining a minimum dimension so that seasonal storage is possible

but it doesn't give me lost power

the calculation that made me is wrong, you only count the heat lost in heating the layer of earth during the cooling time of the tank, but alas it continues to get the hell away all the year even when the winter is over and we no longer need heating ...

the power lost is simply linked to the average temperature of the storage mass, the thermal resistance, and the average outside temperature

for example if the top of the storage mass is under 3m of earth, it will be the same as covered by 8 cm of glass wool: it seems a little light and makes me fear big loss: and again the top of the storage area will be drilled by a multitude of drilling: as many thermal bridges

this is what makes me prefer a water tank: just 2 small pipes to use it perfectly

and I only count on the earth to isolate the bottom of the tank, or we are on a long way in the earth to go: but for the top and part of the sides I only count on real insulation

I do not yet plan to build a heat storage tank now: it is too expensive for me: but I have exactly the same questions to solve, to isolate as efficiently as possible a methanization tank which must stay at 37 ° all year round

[bernardd]

the calculation that made me is wrong, you only count the heat lost in heating the layer of earth during the cooling time of the tank, but alas it continues to get the hell away all the year even when the winter is over and we no longer need heating ...

It reminds me of the first computer memories: a cable :-)

We send the impulse, and we get it a little later at the other end ...

Here, it's a bit the same idea, we inject in the center:
- a part leaves towards the surface, thus warmed: it is in your interest to put the house on it, with the downside of the stability of the foundations;
- the other part goes down, and we put tubes to recover, ie cool, on the good enveloping surface.

In addition, the heat which leaves without being intercepted is not really lost, since if it had not been injected, it would anyway be part of the earth and the atmosphere, since it is solar heat .

However, this does not regulate the storage of hot water at high temperature. But we can store in hot water only the necessary, using the earth for the low temperature complement, when the high temperature storage is anyway saturated in summer, the unused sensors and the heat lost anyway.

[bernardd]

The realizations exist in inter-seasonal water storage at Jenni : 100% of the annual hot water needs (heating and sanitary) of a building comprising 2 T3 (82m²) + 3 T5 (115m²) + 3 T6 (130m²) with 205 l storage tank (000m high and 17m diameter (insulation included!) with 4m² of solar thermal panels on the roof! pdf.
It represents size constraints and is only possible for a small new collective, but it is a proof of the viability of these words.

I just received the book in French edited by jenni. It is really very interesting, at first rapid reading, with lots of very concrete information.

We can also see in real time the monitoring temperatures of their control building: http://www.jenni.ch/index.html?html/Hei ... rinzip.htm

and the annual curves: http://www.jenni.ch/pdf/MFH_Speichertemperatur.pdf

[dedeleco]

The Canadian solution www.dlsc.ca is much better to store underground rather than in huge tanks that are always too small !!
It is staggering to note that their tank of x m3 (x unknown, because I could not quickly find the pdf on their site) is at most 80 ° C to 90 ° C from mid April to mid October !! Totally aberrant !!
So it is an insufficient volume and not insulated enough (2m of optimized insulation necessary) not optimized to store from summer to winter !! !!

They sell large tanks and large equipment, but it is not at all the most economical possible, far from the optimal solution, by storing underground.
.
Compare to dlsc.ca !!

[denis]

thank you, I was going to see that, I'm in the middle of it, with my construction! 40 m of Canadian well with glass heating provided, from 4.5 m to 2.5 m deep ... over-insulated house all straw

[dedeleco]

It is a beautiful Canadian well:

40 m of Canadian well with glass roof heating planned, from 4.5 m to 2.5 m deep ... over-insulated house all straw

depth and volumes a little limited to keep the heat from summer to winter (because heat spread over 3 m approximately). it is ordinary earth, I suppose, because the diffusivity of the heat is variable according to the nature of the ground, the fastest is in granite or limestone which diffuses over 6m !!
So you can store the summer heat on the volume of earth at 2 to 3 m around your Canadian well which is how wide?
if a single cylinder, the summer heat will diffuse over a radius of about 3m, i.e. a surface of pix3 ^ 2 = 28m2 over 40m gives a volume of hot earth of 1131m3 in principle very good for storing from summer to winter, but not deep enough, which means that a part, the one less than 3m deep, is lost at the end of winter towards the surface and the cold of winter.
So a little more than half of this heat will be found to heat during the winter.
The thermal capacity of the soil changes according to its nature, but if arable land at 1KJ / ° C. liter (can be double) at more than 20 ° C + 36 ° C = 56 ° C we can recover 10KWh / m3 roughly, and so with half the volume of earth keeping its heat at 56 ° C, for the winter we can hope to have 1131m3 / 2x10 = 5655KWh in heat coming from the summer, after having well overheated the Canadian well in summer at 60 to 80 ° C with solar collectors during especially the months of late summer and early fall with solar collectors of good surface to give in total at least 2x5655 = 11310KWh in summer in the Canadian well, {forgetting the refreshing function of the Canadian well (that it is possible to have again with a small Canadian summer well of small size with small depth between night and day, for the few days of heat wave)}.
If the house with efficient winter solar collectors and very very good straw insulation (33KWh / m2 over winter?), Consumes less than 5000 to 6000KWh over the whole winter (1 / 6th of 30000KWh (200KWh / m2 ), that consumes a usual house of the French 70s not well insulated), then it must allow to spend the winter only with this summer solar heating on winter in the Canadian well in addition to what the sun gives in winter !!
The biggest and difficult is the realization of the Canadian well and therefore it is worth trying on this existing Canadian well.
The solar collectors can be purely hot air circulating in the Canadian well or hot water circulating also in the Canadian well, provided that the heat with 60 ° C with 80 ° C, arrives in the ground of the Canadian well.

This house with 40 m of Canadian well is ideal for storing part of the excess heat in summer from summer to winter on solar collectors, which can be very rudimentary like black pipe under glass or plastic, for their more big party..

It is just a very very rough estimate which can be specified, depending on the structure of the Canadian well, the earth and rock around it and other precise characteristics.
If soil can be brought over the Canadian well to make it deeper, its thermal capacity can be doubled.

For more details see the values ​​of:
http://www.terre-crue.fr/etudes-techniq ... mique.html
http://www.worldlingo.com/ma/dewiki/en/ ... %A4higkeit
http://de.wikipedia.org/wiki/Temperatur ... %A4higkeit