3 May '11: Lyndsey (writing a dissertation about the Peveril Solar house) brings me back to one of the fundamental questions : why have a Sunbox at all?
Dr Chris Wood believes that we could use black chillers nakedly on the wall or roof - he is building a test rig in Burton on Trent using the same black panels as on the Peveril Solar House, but is omitting the glazed boxes. His intention is also to charge the ground.
So why enclose? Well, we could use unglazed black chillers and with enough of them, they could partially or completely take the place of the ground, making the GHSP into an Air source. But for this to happen they would be coated with Ice for much of the winter because they could benefit from the latent heat of freezing and thawing. But I believe that they would be prey to all the faults that ASHPs have in winter. The pipes running through the house would be dripping with condensation every metre along the way, and the GSHP would have to work hard to get the loop temperature low enough for form that ice.
Using Sunboxes, we are still reliant on the ground as our primary source and battery, but we are now making the ground less reliant on itself - it gets actively recharged all the year round instead of just in the summer in a very slow natural way. During the winter of 2010-2011, the deep temperature never went below 10 degs.
The Sunbox system is a warm, not icy, form of augmentation. The thermostatically controlled pump ensures that it is never wasting energy pumping for futile or marginal benefits - when there is no warmth to collect, it turns off!