howdytom - Any idea of the amount of heat you'd like to store summer to winter?
As Paul says, what you outlined above wouldn't amount to much. For an example, Tony thought a quite modest 8000kWh/yr would suit him, which if stored in water between 70C and 30C would need a tank about 6mx6mx6m.

<blockquote><cite>Posted By: tony</cite>My store is now going to be the soil. There was no water and I bored down to 9m through hogging, ballast and a layer of sand at 8m.

Will heat up the ground by pushing excess solar from the summer down there.</blockquote>

Are you thinking of putting any temp measuring devices down there to keep a check on how its working? Im sure many people here would be interested to know how your system works out.

The idea of a tank was:

1, a way to heat the ground over a large area without hot spots.

2, a lot cheaper to install (for me) than lots of bore holes or trenches for ducts/heat exchangers (and their associated costs).

3, as a secondary issue, by being insulated on the sides and top(open underneath) a supply of DHW or at least preheated DHW supply, as the heat is removed from the tank/store it would "suck" back the heat in the ground (maybe)

eventually the house would gain most of the heat directly back from the ground, as per the initial thread.

Mike7
the proposed location of house is on/near the top of a high spot. 200m to one side and down hill a bit is a swallow(sink) hole where all the existing house/buildings/yard drains run (roof and surface water only) We are on boulder clay over open limestone with a small limestone quarry 600m away, maybe 60m lower than us, at its top edge with a 15-20m face.

I hope that helps, keep the comments coming

tom

Have read this thread with great interest,

"AGS by Don Stevens" where can I get more detailed information about Don's adaptation of the PAHS concept??

Have reviewed all of the links given by fostertom.

Planning a similar setup to Howdytom's

A very interesting project, but does anyone know the damage done to the environment. Admittedly a small, uninteresting (?) environment, but if we were all to start doing this?

Howdytom
I agree, but it still needs thought. Energy manipulated in any manner is going to have an affect (effect?) - butterflies flapping and all. I dont want to change thread with new discussion, but it seems to me the only solution is to shrink our demands on the planet rather than maintain our houses (and surrounding soil) at umpteen degrees permanently.

Further to my earlier musings on heat storage and heat loss, I found this site showing heat flow into earth from a periodic heat source, derived from an excel spreadsheet finite element effort:-

http://www.faculty.virginia.edu/ribando/modules/xls/

The various curves on the second graph show how the heat spreads through the ground in the course of a year. (The value of diffusivity used is 1.38E-7m2/s). The ripples have just about petered out after 4 metres, which is what I was expecting in my wee graph posted earlier.

There are 20 colours, each showing the temperature distribution at a particular time - the year is divided into 20 intervals, stated in seconds (!). The run starts with the temperature at +1 ie. top left, goes down to -1 at six months in, then back up to 1 again.
The 4 metres figure depends on the particular diffusivity of the soil involved, so if the soil were more conductive or had lower specific heat the ripples would reach further.

Edit. Just trying to add the pretty picture:

Posted By: mike7There are 20 colours, each showing the temperature distribution at a particular time - the year is divided into 20 intervals, stated in seconds (!). The run starts with the temperature at +1 ie. top left, goes down to -1 at six months in, then back up to 1 again.
The 4 metres figure depends on the particular diffusivity of the soil involved, so if the soil were more conductive or had lower specific heat the ripples would reach further.

OK, thanks for the explaination. I get it now.
I can think of a lot more intuitive ways of representing the data, but since I'm not willing to do that myself, I can't complain.

-Ralph

<blockquote><cite>Posted By: bot de paille</cite>I dont understand the graph, partly because im not sure what is being measured/ modeled exactly
?</blockquote>

It is being modeled, not measured. The vertical axis on the left could be ground surface temperature (plotted as a ratio, so no units needed) and the horizontal axis would show depth below ground.


<blockquote><cite>Posted By: bot de paille</cite>
However, is the conclusion that the temp of the ground is only augmented down to 4m, after which any heat input is dissipated into the ambiant ground temperature???</blockquote>

Not quite. You might say that the graph shows how the annual surface temperature fluctuation is felt at various depths, becoming less and less evident until after 4m or so it is negligible. The temperature below 4m is constant at the average of the surface temperature, so there is no heat flow in or out of the sub-4m region.

All the heat absorbed from the surface in summer is thus stored in the levels above 4m, and released back to the surface in winter.

<blockquote><cite>Posted By: ralphd</cite> The waveform at 3M is not sinusoidal; it seems altered towards sawtooth.
-Ralph</blockquote>

Interesting data, thanks. The input isn't very sinusoidal either - look how little the 5cm temp changes over 5 winter months, no doubt due to snow cover.

<blockquote><cite>Posted By: ralphd</cite>
I think the best way to do PAHS is circulating water instead of air (given the much higher heat capacity of water). Instead of digging the pipes deep into the ground, I think insulating between the pipes and slab is better (easier to construct). I'm uncertain as to the best lateral distance of insulation from the heating pipes. I know it will be different for different soil types. I have damp clay soil under my foundation and I used 2' of insulation from the sides of the heating pipes. I'm now convinced that was less than optimal. I think somewhere between 6 and 10' would be optimal.

-Ralph</blockquote>

I suspect you're right re. the water vs. air, only then strictly speaking it won't be passive. Is that right? I wouldn't like to comment on your store design - I'm really only just creeping toward understanding how things might work in broad terms.

Posted By: djhThe motivation for digging is power transmission and hence energy storage capacity. From a square metre of surface, you can only push heat into it at a particular rate (power), given a limit on the temperature of the heat source. So that limits the total heat energy you can store over the summer.

Quite. Likewise ground conductivity limits the rate at which you get heat back during the winter. As I understand it, the argument for using air is that the ground can't absorb or release heat at a rate faster than tubes of air (polypropylene, clay, etc). Also, could be that air can reasonably be heated to a higher temperature than water using simple solar collectors and possibly have greater flow through the tube. Only way to find out is to do the sums though...

And I like the idea that air can be managed passively or using minimal mechanical effort.

Posted By: pmcc

And I like the idea that air can be managed passively or using minimal mechanical effort.

Going from memory, the specific heat of air is 0.018 BTU/ft^3/F vs 1BTU/lb/F for water.

-Ralph

Great if you can pass on to this forum, whatever you learn.

That is only showing the first few months of data isnt it?-- I would expect an interseasonal store to take several years to reach equilibrium, I seems to me that the heat is trying to be stored to shallow too.

icax have done some work on building heating which may be of interest.

http://www.icax.co.uk/iht_suits_new_buildings.html