Wednesday, March 10, 2010

More about ground temperatures

10 Mar: Following my observation of the difference between morning and evening ground temperature (below), my technical guru, David Atkins says that I might be a bit optimistic to think it can recover this fast. But during this 11 hour period, no heat is put down from the solar panels, and no heat is drawn up by the heatpump. So yes.... it may take a full summer (without heating) to recover to its best. But the change in over just 11 hours is worth recording regularly in future spreadsheets. It is highly significant to the research concept around which this whole project and blog is built.

     My other technical guru, Dr Chris Wood tells me that this phenomenon is quite possible, and that if I had the patience, it would be interesting to stay up all night during the 11 hour period, monitoring the rate of change.... I don't think my family would allow that! and the heatpump doesn't allow it either, as it always tries to get back to heating after the 15 mins is up.
   What I could do is have the heatpump turned off and use the Wilo-pump in the loft running all night, with a closed circuit (not going through the solar panels), then measure the temperature of that circuit every 15 mins. I can feel another plumbing complexity coming on, of which Heath Robinson would be proud.

    Chris has also mentioned to me the concept of 'Superposition of Thermal Waves' - wow! Superposition is when a phenomenon occurs because of more than one cause or one time event, and is commonly used in Geology and Biology. A simple example that links to what I am doing with my deep ground is that of throwing a pebble into a puddle, and throwing a second but differently sized one in a second later. So the ripples from one are still affected by the second. If the ripples bounce off the edges of the tank and reflect back, it gets more interesting and the ripple shape gets very complicated. If sometimes stones are dropped into the pond, and sometimes others are ejected from the pond, imagine the complexity! I can feel a photoshop diagram coming on, even as I write. We have TWO boreholes, and are alternately putting heat down and getting it out.
     In our case, we are alternating: 1. Pulling heat out during the day, 2. Putting heat down there when the sun shines, 3. Nightly incoming of surrounding warmth when the heat pump is not pulling heat out, and finally 4. Long term recovery of the earth over the summer months - when both recovery and solar thermal input is occuring - the recovery heat comes from the perimeter, and the solar thermal from the centre.

   Left to itself in summer, the ground will even out completely (like a pond after the pebbles have sunk), because the original provider of the heat, Solar heat onto the ground takes decades to get down to 48m, and rising mantle heat is too small to measure.
   If we call Warmth movement 'positive' and Coolth movement 'negative', we must have 'Rings' around our borehole pipes that are moving in or outwards, drawn by the attraction either of the borehole pipes or of the surrounding mass. And there are two boreholes 5m apart, so the rings are crossing each other in both directions. Left long enough all these rings smooth and merge.
  My mind is so boggled after all that, I need to go to B and Q or Screwfix for a quick dose of reality! :)

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