Tuesday, November 3, 2009

Meeting Chris Wood: Diurnial, Interseasonal and 5 yr cycles

Nov 3: in my meeting with Chris Wood, we also discussed the way that heat stays or moves in the ground, relative to the boreholes. He has done tests with sensors at different distances from GSHP borehole pipes.
Diurnial: We drew a diagram, a bit like ripples on a pond of the heat moving out from the borehole centre to the surrounding layer, showing that on a day-night basis, the daytime harvest of heat has nowhere to go than back up in the evenings, and any surplus moves out through the rings. The thermal curve is modified and will be added to this blog soon.
Interseasonal: This is very interesting, as we both know that the ground immediately around the pipe gets cooler month by month, and in Feb-April when the ground is at its coolest, the heatpump is having the most difficult task with cold ground - this is when the immersion heater element of the heatpump comes on, and ruins our Coefficient of Performance (CoP). During the long summer (with heatpump only drawing a small amount of heat for domestic Hot water) the ground recovers. However, in this spring period the sun is shining on the surface and if we can send solar heat down directly, the curve is changed. (See diagram - the area around pipes gets colder).
During the remainder of the summer when our solar heat is put down enough to exceed the heat taken out for hot water, some of this surplus heat may fortify the ground for the long winter.
5-10 year cycle: Chris explained how the ground gets colder year by year. It can be represented by a declining SIN wave. After each year, the highest temp that the ground recovers to in summer is never as high as in the previous year. Eventually it reaches a new stasis - this could be 5-20 yrs after installation, depending on the conductivity of the soil and the size of the house pulling heat out.

If the Solar Geocharging raises ground temperature, this will be remarkably successful, but is unlikely. What is very desirable is that the SIN wave has the same nadir (bottom) year after year (instead of dropping), and perhaps we might achieve a higher zenith - if this occurs, and we discover that it will maintain or improve the heatpump's CoP at that of a new machine in new ground, that will have been worth achieving.

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