Thursday, May 20, 2010

More thoughts on Borehole or thermal store

20 May : Earlier, I wrote: "In the work by companies like ICAX, they use an entire large playground or carpark for heat collecting, but we are using a humble 1.1 cu m of Sunbox, and 4.2 sq m of black collector, so can only expect 2kW at best."

So if one built a full 'double skin facade' on the south wall, filled with black thermal collectors, how much more could one use this to heat the house? Judging by the earlier calculation, would it be any better than just 4 sqm? The existing boxes are doing a grand job of contributing to realtime/diurnial heating and at reasonable pump and material cost compared with the GSHP itself. Could 12 sqm do a better job? Could one also harness some MVHR to bring some of the heat in directly as warm air?

My feeling about this is that in its present form, the cost would outweigh the advantage because polycarbonate, metal and the plumbing costs rise, and the huge volume of uncontained deep soil remains unknown and would still dissipate the heat more than we could use. The glycol going through the panels would reach its optimum temperature earlier, and just go through the remaining panels without picking up any more heat - because it's the Delta-T that decides how much it will pick up.
    It now seems clearer that if one can work out a finite capacity for a fully insulated container that can be permitted to get hotter, there is a good possibility of relating heating demand to thermal store capacity. It has to be big enough to ride the highs and lows, just like water reservoirs have to be balanced with predicted rainfall. So such a store doesn't have to be big enough to store the entire annual heating demand exclusively -  perhaps only 6 or 3 or 1 month's worth, because it is being trickle charged every day. And one can tolerate a body of clay getting high the Summer and descending to single figures in the winter.
   I am quite excited at the possibility of calculating this, based on what I have learnt recently. Could it be cheaper than drilling deep boreholes. Could it just be in the foundation under the house? Does it have to be under the garden (would not need concrete if a box is formed in close fitting polystyrene). This comes full circle to my original conversation with Mike Siebert.
Let's look at this later on.

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