How much energy is there in one vertical ton of earth loop?

Posted by on Apr 8, 2015 in Blog | 0 comments

Imagine a column of rock that is 200′ tall and has a 15′ radius. The volume of this column is 141,428 cubic feet. Converted to cubic yards / 27 = 5,238 cubic yards. Lets say that this particular rock weighs 3,500 lbs per yard. This means the column weights 18,333,000 lbs.
Lets say that it has a specific heat of 0.25. This would mean that this column of rock would have a thermal capacity of 4,583,250 BTU per degree.

As we know, we cannot “pull” on this entire column at the same time with a single bore hole in the middle of it. We will create layers of differential temperatures as we suck the heat from the center of it. We are “done” when the first radius of earth outside the borehole has been lowered to a temperature that is too low to support a high enough differential into the loop pipe.

Lets use 25F as our minimum fluid temp and lets say that the first radius outside the borehole allows the fluid temp to drop to 25F when it reaches 38F. If that were the reality of the situation then I would say that this could represent the bottom of the capacity of the borehole.

But what if we slow down the flow of the fluid? If we do that then we can keep “mining” the borehole even after the first radius reached the “bottom” of the operational capacity.

How can we slow down the fluid and not shut down the system? By using a thermal battery we separate time direct requirements from cumulative totals.

So if we put a constant slow pull on the bore hole and such heat out of that rock column… how many BTU do you think we could get?

Lets say that over the three coldest months of the winter the deficit energy (not provided by solar input) is 24 million BTU over 90 days.

The rock column would have to give up about 5.24 degrees across its entire mass to do this. Could it do it? If it did it would have delivered an average of 11,111 BTU per hour into the system for the entire 90 days. This seems too high to me and I would tend to doubt that we could expect this arraignment to keep up.

The problem is that we keep doings that we expect to cause system depletion and we keep getting surprised by the results.

Thoughs or questions? Comment below.

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