Tuesday, August 18, 2009

Sobering Thoughts....

I had a chat with two of my colleagues at the University. The first (DE) seems wholly sceptical about the idea... unless I am prepared to accept a lot of inefficiency - insofar as that can be defined and measured - difficult when the active area is 50m deep, and has no real limit horizontally.
If the cylinders of clay were in a vast barrel of polystyrene it would be a splendid idea!
If 90% of the heat put down is lost, is the 10% retrieved worth it? Or is that figure 50% or 95%?
He feels that the summer heat will move too far away to be willing to return in winter.
Objects with high thermal mass work very well diurnally, eg daytime heat recovered in the same evening, as in thick adobe brick walls in middle east. So solar heat gains on sunny winter days might come back the very same evening.
The question is.... would heat stay around long enough to get the summer heat back 3-4 months later?

My other colleague (AH) is prepared to do some calculations for me (although is due to depart on holiday for next few weeks). He pointed out that conventional solar thermal heating was not as efficient as the sales people claim - because if hot water is not being used a lot, the tank and the panel reach stasis, that is, no more heat is sent to the tank because the 'delta-T' (temperature difference) is inadequate and the panel sits there doing nothing even on sunny days. Then you draw off hot water on a cold rainy day, and there is no more until the next sun.
He agreed that with one aspect of my idea, that the glycol going down to the ground (even if as hot as 40degrees) would come back cooled to something like 12 degrees, so that there would always be a workable Delta-T, and the panel would work at full efficiency even if sunshine was intermittent. And the hot water would always be hot because the Heat pump efficiency would be improved., and 50m down, the ground doesn't know if its summer or winter above.

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