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Old 10-01-14, 04:33 PM   #1
buffalobillpatrick
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Default IBC tote tanks in series as low cost HP source

I can buy HDPE 275g IBC tote tanks for $75

Idea is to bury 10x of them in 4' wide by 8' deep trench at 10' spacing in between each.

Each tank has about the same surface area as 300' of 3/4" pex.

I would add heat to them from my 300ft2 solar panel array.


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Old 10-02-14, 12:52 AM   #2
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Quote:
Originally Posted by buffalobillpatrick View Post
Each tank has about the same surface area as 300' of 3/4" pex.
I think there is good and bad news.

The good news is that your calculation looks way off, and a tote has the same surface area as much longer pex. Can you check your figures?

The bad news is that the surface area to volume ratio of a tote is less than half as good as for the pex, so a tote would not be as good at replenishing the energy you extract - but should hold a lot more embedded energy at the start of your heating season.

The overall result should be good though, because the number of tanks (10) should more than make up for their lower efficiency.

Would you insulate the pipe runs between the tanks?

How would you plumb everything together? I think I would run a pipe from the top of tank 1 to the bottom of tank 2 and so on, so the water would get hotter as you go through the series of tanks. A sort of horizontal stratification. I would also try to promote vertical stratification within each tank.

The ideal feed to the solar panels would then be from the bottom of tank 1, which should be to coldest water in the tanks, but where would you feed back the heated water? It is not obvious to me what the best strategy would be, nor how to make the connections for keeping the levels constant.

Would you circulate the fluid in the tanks, or circulate fluid through coils in the tanks? Coils would probably be better.

Would you insulate tank 10 (if that is where you put the heat from the solar panels)? If not, you are going to have a lot of losses with heat flowing out of tank 10 to the ground.

If you use the solar panels to heat the final tank, feed water from that to your heat pump, then feed the cooled water back into tank 1, will tank 1 then be hotter than the surrounding ground? If so, you will have more losses. It depends what heat drop you expect through your heat pump, but I can envisage that being a problem.

It could be worth insulating the top of all your tanks, leaving the sides and bottom open, so that you don't lose so much of your solar heat, but still can gather heat from the ground when that is warmer than the tanks. This will of course make the surface area to volume ratio even worse, so it is swings and roundabouts.

Will you add some mechanism to top up the tanks? I would not rely on there being no fluid loss for decades and you don't want to have to dig to replenish any losses. In theory there should be no losses but I know someone who used a large number of plastic pop bottles as a heat store and he found there were losses over the years so I wouldn't rule it out.

How much energy do you need to extract during a heating season? You could calculate the energy in the tanks and so work out what replenishment rate you would need. My gut reaction is that this should be a good system but it is worth doing some detailed planning at this stage before committing to a design.
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Old 10-02-14, 06:43 AM   #3
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Quote:
Originally Posted by buffalobillpatrick View Post
I can buy HDPE 275g IBC tote tanks for $75

Idea is to bury 10x of them in 4' wide by 8' deep trench at 10' spacing in between each.

Each tank has about the same surface area as 300' of 3/4" pex.

I would add heat to them from my 300ft2 solar panel array.
Unless they're always full the backfill will likely crush them.
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Old 10-02-14, 10:17 AM   #4
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Good points, thx.

Property has great solar potential at 8,800' altitude in Colorado.

Tanks will be uninsulated on sides & bottom so as to add solar heat into earth, or during extended periods of low solar gain, pull heat out of ground.

Solar panels will be drain down setup, heating tank 1. No HX's
Then pump pressure with a check valve through HP evaporator, then into bottom port of tank 2.
Out of top port of tank 2, through 10' of uninsulated pipe into bottom port of tank 3.
Etc. etc. finally out of top port of tank 10 & back to tank 1.
So tanks 2 - 10 should remain full.

The pump will run with HP, or to move solar heat throughout uninsulated tanks.

Tank 1 will have a float switch to auto fill. I will add drip system emitters around top of tanks 2 - 10 to assist in heat transfer with soil.
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Old 10-02-14, 10:56 AM   #5
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I'm not so sure that a series connect would be more efficient than a parallel with the way you are planning to run the system. With tank 1 on its own, it probably will be valved. It could be used in many different ways. With it fuller (or higher in head level) than the other 9, it could naturally burp the other tanks. In a parallel setup, the tanks would naturally stratify and equalize the stored or harvested heat and transfer more evenly.

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Old 10-02-14, 02:29 PM   #6
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I want the pump to burp tanks 2-10 this should get almost all of the air out.

I think low flow drip emitters & bedding tanks in sand with EPDM below will increase heat transfer through tank walls.

As top of tank will only be about 3' below grade, I think that 3" of EPS above tanks will reduce winter loss.

Parallel would be hard to balance with tanks back filled.

I think that my 2 ton HP evaporator will need about 6gpm. I could use one of my 10W 3gpm 30VDC El-Sid pumps to continuously move heat between tanks.

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Old 10-02-14, 03:14 PM   #7
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IBC 275gal totes are 40" x 40" x 50" high

((40 x 50 x 4) + (40 x 40)) / 144 = 66.66 ft2 surface area not insulated.

In post #1 I made mistake of including top of tank.

3/4" pex has 1" outside diameter, circumference = 3.1416"

(3.1416 x 12 x 255) / 144 = 66.76 ft2

So exposed area of tank is about the same area as 255' of 3/4" pex.
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Old 10-02-14, 03:30 PM   #8
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I was thinking of doing latent ice storage with glycol inside pex loops inside some of these tanks, but am unsure if I could fish the pex loop into tank?

The top port is 6" diameter, bottom is 2"

I could buy 1 tank & try it.

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Old 10-02-14, 04:49 PM   #9
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Quote:
Originally Posted by buffalobillpatrick View Post
I want the pump to burp tanks 2-10 this should get almost all of the air out.

Unless you have a tap in the high point of each series connecting pipe, it will be impractical to purge the air out. It doesn't really matter much unless you want your tanks to thermosiphon through the segments.

I think low flow drip emitters & bedding tanks in sand with EPDM below will increase heat transfer through tank walls.

As top of tank will only be about 3' below grade, I think that 3" of EPS above tanks will reduce winter loss.

Parallel would be hard to balance with tanks back filled.

Naturally, you would want to plumb, fill, and leak check the tanks before back-filling. If you had a header for pipes leading to the tops of the tanks and a header down low (or up top running to dip tubes), so that natural convection could occur, the parallel flows would balance due to the large horizontal cross-section and stratification due to density. With under a gallon per minute flow per tank, density and gravity would overcome your pressure difference.

I think that my 2 ton HP evaporator will need about 6gpm. I could use one of my 10W 3gpm 30VDC El-Sid pumps to continuously move heat between tanks.
If you go with a series connect, you would need the pump to overcome all the air in the tops of the interconnecting tubes. This would work against the "thermal battery" scheme the series connect offers, in effect somewhat swirling the source water a little bit between each tank while the pump is running. The tanks would sequentially charge or discharge heat, with corresponding sequential heat loss or gain with the ground. Looping discharge to intake would deplete your remaining neutralized source water.

The real difference here is not so much in efficiency or total heat transfer, because both configurations will net close to the same heat gain or loss. The big difference is how your supply would act.

With the series connect, any temp change introduced would take a long time to work its way through the tanks. Like a common water heater, you would have a predictable amount of constant-temp source water to draw from, then the source would quickly change behavior for the worse. It would then take a long time to recharge.

With the parallel connect, the source water would react more quickly to any changes. The source temperature would begin to stray sooner than the series connect, but it would exhibit a more gradual drop-off. When the flow was cut, the store would immediately begin to recover.


Here's a research paper that deals with this topic directly:

EDIT: http://ecorenovator.org/forum/attach...1&d=1412291207
Attached Files
File Type: pdf 00b7d528cb2bee6100000000.pdf (352.8 KB, 527 views)

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Old 10-02-14, 05:20 PM   #10
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Unable to create account as I'm not with a college.

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