System

Surya Sunbox System Layout
These diagrams shows the circuit layouts schematically, as built at stages through the research project, copyright David Nicholson-Cole with the help of David Atkins, Jason Philips, David Oliver. If anybody wants to build something similar, they are welcome to ask, and advice will be given. email dnicholsoncole@gmail.com Do you have a ground source heat pump? If so please contact me!
The original 'Trickle and Whoosh' layout, May 2010-Mar 2012, now discontinued.
This one is for the Sunbox only. The entire ground loop is/was routed through the Sunbox.
Addition of Evacuated Tubes and Heat Exchanger May 2012
with a 'trickle while we work' parallel layout
The System has been enlarged in May 2012. See Above, with the Evacuated tubes and Heat Exchanger added, plus an additional expansion vessel.


December 2012: This is how the system has finished up, with 2 sqm of metal radiator in a roof mounted polycarbonate box, called Surya Sunbox 4. Each sub-circuit has its own pump, energy meter, check valves, expansion vessel.

How does the system work in the different seasons? There are four modes:
  • Interseasonal: During the Summer, The Surya Sunbox pumps solar heat into the boreholes, 48m deep. There's a lot of clay down there! (assumed about 6,800 tons within 3.6 m of the pipes). Over the summer, there is little demand from the GSHP, so the ground may rise to 14ºC, and briefly higher than that around the pipes. The temperature does not get significantly higher than that, but the energy level rises as the 'bulb' of warmed soil gets larger.
  • Diurnial: During the Equinox, it buries energy on sunny days. This provides good diurnial support to the heat pump, because the thermal energy captured in the warmer daytime is available in the evening cool when the GSHP may be heating the building. 
  • Realtime: During the Winter, the sunbox does not function much except on good sunny days or if the GSHP is driving glycol at a low enough temperature so that the delta-T triggers them. The amount of heat buried in the ground in the previous months enable the GSHP to work more efficiently. On the Peveril Solar house, the deep ground temperature did not go below 10.0º at the coldest time of the last two winters. 
  • Restorative: This is the same as the Realtime described above, but it happens at any time of the year immediately after the GSHP has been running. If the ground loop is temporarily cooled after a heating cycle even in Summer or Equinox, there is energy delivered from the Sunbox for immediate restoration of the temperature close around the borehole pipe.
Schematic diagram of three possible systems
(the present system is none of these, see the diagram at the top of this page)
Left: As built in 2010 - directly tee'd in, extension of the ground loop. There is a choice of parallel trickle in , or of sending the whole loop to the panels in series. The annual capture totalled more than 3,000 kWh by mid-April 2011. It may be higher next year, if the Surya 3 sun box works better than the first version.
Centre: This would be required if using high temperature solar collectors such as evacuated tubes, because you cannot dump liquid at very high temperature into the plastic piping of a ground loop, or to a GSHP directly. I haven't built this, so do not know what it would produce thermally. But I want to try it out in another house. It needs an expensive water tank as a thermal buffer - the advantage being a reserve of warm water, the disadvantage being the risk of legionnaires flourishing in tepid water, and the cost+volume of a large copper insulated tank. Another method is to use a Heat Exchanger with metal plates, to provide some thermal inertia. This has been built in May 2012, with a 1.6 litre capacity heat exchanger.
Right: The more conventional separation of space heating and HW functions. According the SAP tables, 4 sqm of solar thermal panels would only contribute only 1100 kWh to the annual thermal equation because of stasis in the tank, and because it only serves hot water. My Suryas, are contributing 3,100 kWh annually to the combined heating and DHW.

For images of the internal plumbing, please see the Blog page:

Why use Sunboxes?
Our chillers in the Sunbox are SolarFocus swimming pool panels. The difference here is that they are enclosed. We could use black chillers nakedly on the wall or roof - so why enclose? Well, we could use unglazed 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 and 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. Using the Sunbox, we are still reliant on the ground, but we are now making the ground less reliant on itself - it gets actively recharged all the year round, every day, instead of just in the summer in a very slow natural way. The Sunbox is a warm and dry, not icy and dripping, 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!

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