Recycle buried oil tank thermal buffer

Solar thermal energy in all its forms: solar heating, hot water, choosing a solar collector, solar concentration, ovens and solar cookers, solar energy storage by heat buffer, solar pool, air conditioning and solar cold ..
Aid, counseling, fixtures and examples of achievements ...
Aumicron
Éconologue good!
Éconologue good!
posts: 387
Registration: 16/09/09, 16:43
Location: Bordeaux




by Aumicron » 18/10/13, 09:02

Hello dede2002,

Your project is interesting but before looking for technical solutions you should perhaps carry out a mini thermal study to fix orders of magnitude and answer this question:

how much energy will be available for storage?
0 x
To argue.
User avatar
chatelot16
Econologue expert
Econologue expert
posts: 6960
Registration: 11/11/07, 17:33
Location: Angouleme
x 264




by chatelot16 » 18/10/13, 16:58

what good is it to insulate above if the heat is lost and never ends up on the ground?

I am not able to calculate exactly how heat is lost in the ground

calculate the energy it can store with the specific heat of water it is easy to do

predict how long heat will be lost, it's harder

wait until next summer: plug in a few solar collectors to raise the temperature of the tank, then stop the heating and measure the temperature every day to see how quickly the temperature goes down

another way of doing it: this winter when it's cold, balance the ice inside to cool it: then record the temperature to see how quickly it warms up to the usual temperature of the ground
0 x
dede2002
Grand Econologue
Grand Econologue
posts: 1111
Registration: 10/10/13, 16:30
Location: Geneva countryside
x 189




by dede2002 » 18/10/13, 19:00

This winter when it will be cold, there will still be fuel oil in it ...

I can already measure the temperature of the fuel oil :D .

Indeed 6000 liters makes 7 kWh per degree.

The soil will absorb part of it, it will also heat up.


The amount of energy to be stored will be the solar panels for an installation of around 1500 l. DHW.

The installers all say that if you put too many panels it could overheat in the summer, others install overheating radiators which struggle to dissipate the excess heat in the air, in the height of summer!

I think that by oversizing I will have more useful kWh over the year, even by wasting the surplus ...?

Hence my idea to use the water from the tank to dissipate this heat, and think about how to recover it.

Before the tank starts to boil, I will have time to react :P
0 x
User avatar
Did67
Moderator
Moderator
posts: 20362
Registration: 20/01/08, 16:34
Location: Alsace
x 8685




by Did67 » 19/10/13, 18:22

I had asked for help to find out if someone could calculate the "heat wave" in the case of underground storage (for the porjte you know, chatelot: the waste heat from the cogenerator).

I did not find.

It is quite complex, because the front will extend, the gradient will decrease, so I have the intuitive impression that the losses decrease, because there comes a time when the gradient between say the 12 ° of the ground and say 52 ° of the tank will for example extend over a thickness of 4 m; these 4 m will behave, it seems to me, like an insulator ... There will be a delta t of 40 ° for 4 m, or 1 ° only for 10 cm! So the flow should be badly slowed down.

Am I wrong ???
0 x
User avatar
chatelot16
Econologue expert
Econologue expert
posts: 6960
Registration: 11/11/07, 17:33
Location: Angouleme
x 264




by chatelot16 » 19/10/13, 19:03

do not let error permeate by dedeleco with its history of heat wave ... that the temperature variation of a buried tank does not propagate quickly does not prevent that the heat fout camps with a simple calculation of thermal resistance

the problem is that when you put 20cm of glass wool on a house that has 100m2 of wall surface you can easily calculate

for a buried tank the thickness of earth is large but the surface (section) by or passes the heat is variable ... the more you move away from the tank the larger the section ... so beyond a certain distance the ground does not make any more additional insulation because the passage section is very large

it reminds a little of the electronic component cooling calculations: we define the thermal resistance to infinity of a component in the air

a tank buried at great depth in a soil at 12 ° would have a thermal resistance to infinity at 12 ° measurable simply by heating this tank long enough and by measuring the power it takes

for the tank just below the ground there is in addition the problem of the heat which leaves towards the surface

there is in addition the problem of the circulation of the water each time it rains ... and the enormous specific heat of the water is terrible to take away the heat

for the one who would have the money to spend, heat the tank to 50 ° with electric resistance and thermostat and record the consumption: I am sure that with each rain we see the KWh fuck the camp at high speed

not only would additional insulation be required above, but also a complete waterproofing of the ground above to avoid the circulation of water

is earth a usable insulator?

did67 you almost have the answer! Have the manufacturers of your methanizer counted on the insulation of the ground to insulate the underside of the tank? no he put a good layer of a known insulator
0 x
User avatar
Did67
Moderator
Moderator
posts: 20362
Registration: 20/01/08, 16:34
Location: Alsace
x 8685




by Did67 » 20/10/13, 10:32

1) No, I did not let myself be "smoked" by dedéco!

2) I also agree that there will always be leaks; trying to calculate this only makes sense for "free" energy (fatal heat); it is then a question of whether the cost of the installation can be amortized with the share of heat that we don't lose.

I wish someone could model this for me. There must be some integrals in there! But should not be unbearable for someone who still has good memories of math and physics!

Of course, it will depend on the conductivity of the soil, therefore on its characteristics (composition - or grain size), its humidity, its compactness (density) ...

3) Yes, okay with the flow of water that will "cool this". We know that water is efficient in this area. It is not for nothing that it is used for that everywhere: engines, heating ...

4) For the methaniser, I think that this has played a role in relation to the recovery coefficient. The objective was to obtain the maximum valuation. To pass the 60% milestone, it's a bit difficult given the fact that hygiene is no longer counted in the valuation! So we fought against "any unnecessary loss". It was a clause in the specifications.

I don't know if at Naskéo, they had someone capable of calculating this. I had mentioned underground storage, with no response from them! [but it was not in their mission; I just think that if someone had done this in their home, in a friendly way, they would have given me the result!]

5) In short I am intuitively without calculation of agreement with the fact that:

a) the gradient decreases as the front propagates; so effusiveness

b) but the surface enhances

c) so we tend towards a limit! For sure. There will be a drop below which we cannot go, even after an infinite time with unlimited free energy!

This is what I would like to know, for a given soil [with us, a loess = aeolian wind, probably quite effusive! It is not sand!]. Without idolizing dedeleco.

[if a student from one of our major engineering schools passes by; here is a TP which he could tackle! I unfortunately only have an "organic" beer to thank him!]
0 x
User avatar
chatelot16
Econologue expert
Econologue expert
posts: 6960
Registration: 11/11/07, 17:33
Location: Angouleme
x 264




by chatelot16 » 20/10/13, 13:49

to make a calculation easy to integrate, it will be necessary to simplify the problem: imagine a spherical tank entered very deep so as not to have to take account of the soil, and in a homogeneous soil, with a single figure of thermal resistance to take into account

so the heat will leave equally in all directions

you have to calculate an integral on the radius of the surface of the tank to infinity ...

the heat passage surface is a sphere whose surface increases with the diameter ... beyond a certain distance from the tank the passage surface is so large that it is no longer useful ... 10 times the diameter of the tank it may already be infinite because it's 100 times the surface of the tank

it would take a math player to do the math for us ... if I do it, it requires stuff that I haven't used in a long time, and it's going to be long enough to put everything in order in my head

if nobody can do the math here i will try to ask the question on the forum physics futura science

once the integration done in the simplified case of the sphere, if the result is encouraging it will be worth it to calculate the real case

if the simplified case of the sphere shows that the heat leaves too quickly to be useful, useless to calculate in more detail

the calculation of the spher will give an interesting result: storage time depending on the dimension: it and easy to predict that a very small sphere will lose half of its heat in a few hours ... and that a huge sphere of more km in diameter will lose half of its heat in several years
0 x
User avatar
Did67
Moderator
Moderator
posts: 20362
Registration: 20/01/08, 16:34
Location: Alsace
x 8685




by Did67 » 20/10/13, 19:13

1) I never had the mathematical skills to "integrate" this ...

2) But "intuitively", I agree with you: the more massive the tank, the longer it can last.

So in addition to the effusiveness of the heat in the ground (depending on its nature), the length of the charge / discharge cycle will play a role.

Because once the tank starts to cool, the heat flow will slow down, or stop? or maybe reverse ???

If we take 4 months of storage (summer) and 6 months of destocking, we should be able to simulate, on the x kWh injected into the tank, how much we recover ... In theory.
0 x
dede2002
Grand Econologue
Grand Econologue
posts: 1111
Registration: 10/10/13, 16:30
Location: Geneva countryside
x 189




by dede2002 » 20/10/13, 21:58

Will the heat be stratified in the sphere?

To insulate the top I have modular construction partitions that I can lay flat, it will divert the runoff water.
0 x
User avatar
chatelot16
Econologue expert
Econologue expert
posts: 6960
Registration: 11/11/07, 17:33
Location: Angouleme
x 264




by chatelot16 » 20/10/13, 22:04

don't complicate for nothing! already consider the sphere full of water at uniform temperature!

and only if the heat is kept long enough to be useful it will be time to go into detail
0 x

Back to "Solar thermal: solar collectors CESI, heating, hot water, stoves and solar cookers"

Who is online ?

Users browsing this forum : No registered users and 132 guests