Wednesday, January 11, 2012

Why consider the tubes?

10 Jan 2012: I ask myself that too, but it comes back to the idea of =Research=. This house is performing splendidly, and if that is all it must do, then some would say: "don't change anything!" I don't have another house to play with, and I am desperate to know if a high temperature supply like evacuated tubes (ETs) will work better than my low temp Sunbox (SB). If it is a lot better, then I am better off changing direction slightly in future installations, and future lectures or conference papers.
This symbolises the concept. And when I drew
this I didnt realise how much more beneficial
two holes would be than one.
    The fundamental constant is the idea of STORAGE. I am completely convinced about that now, providing the soil is good. The technological means of achieving it should be subject to improvement.
     The Sunbox works off delta-T for much of the equinox and winter, and I have upped the trigger delta-T to 7 degrees for it to work. This reduces the hours of working, but makes it work better when it does, i.e. more efficient - more Kilowatt capture. The accuracy of the energy meter is better with a larger delta-T.
     Having a panel of evacuated tubes will actually reduce the effectiveness of the Sunbox because it may deliver enough heat that the liquid going down to the ground is warmer, and then delta-T activates the SB system less often. The thermal sensor that triggers the Sunbox is downstream of the place where hot liquid from the ETs will be introduced. At the moment the SB produces over 3,000 kwh/yr because it is working to a cold store. I shall just have to take that risk.
   In the summer there is no problem as the SB works on actual temperature, e.g. if the SB temp is above 20degs C. This trigger temperature can be raise if the ETs consistently raise this figure too easily.
    One key difference is that the SB works at 5 litres/min (at slow rate) but the ETs have a slower pump, with a recommended flow rate of 1 litre/min. With this slow rate of dilution, I hope that the effect on the sensor for the Sunbox will not cause too much loss of activity by the SB.
    At a 'mere' 2.2 sqm, the panel of ETs would be smaller, but if it can produce 2,500 kwh and the SB reduces to 2,500 kwh / year, that would still be satisfactory.
   Also.... The whole point of the experiment.... Will the delivery of higher temperature liquid actually raise the final summer temperature of the deep soil beyond 14 degrees? Will that have a more significant effect on the GSHP than the present SB system has had?

Where to put them?
I did a quick calculation with PVGIS and found that an array on the roof at 40degs pitch facing east will get about 16% more than a vertical array of the same size facing south but vertical. That helps to decide which location is best. 

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