Thursday, July 28, 2011

Summertime better to be naked!

28 July 2011: Well it's been 4 days since the covers were taken off, and I have kept an eye on performance. At this time of year, they are doing pretty well.
   The daytime temperature has been above 19ºC so the unenclosed 'boxes' have ticked over nicely even when it has been overcast. When the sun shines, the panels do better. I noticed, after an hour of work by the GSHP (boosting the hot water) that the panels were black and glistening with droplets of condensation. When you take material through a phase change, you extract a lot of useful heat. Later, those droplets will evaporate off during the night. They've averaged about 1.25 kW, with an average of about 0.95 kW in the previous week. That seems pretty clear.
   Does this mean I would be better leaving them exposed all year? Big question for me, as I have staked a lot on the idea of the greenhouse effect enclosure. I've written articles etc.
   However... I know that in the good time with the sun shining at equinox angles, the old boxes frequently exceeded 40ºC interior temperatures. In February, the boxes reach over 30º when the air temperature outside is 10º. I am hoping that in the newly designed boxes, with better insulation and sloping fronts and larger volume, the raised performance will make it worth doing all this, averaged over the whole year. I hope there will be more occasions with above 40º temperatures.
  I am trying to get higher temperatures. If naked panels were better over 12 months, then commercial flat plate solar panels would have bare metal fronts, and no glass or insulation. I'd like to push my deep ground up to 16º or 18º, but at the moment, they seem to be comfortably stable but stalled at 13.4ºC.
  If they were naked, they would run at a much lower temperature in Winter, benefitting from the latent heat of freezing. I didn't want to have very frozen pipes passing through the house (covered with condensation), and the external panels coated with ice.
  One thing I can do is more manual control. I cannot open and shut the large front panels, but I can operate the lower louvre. I will keep the upper roof as an openable component. During the Summer on sunny days, the panels can be tight shut and contain the heat that builds up. During long overcast days, the air temperature is high enough and the louvres should be wide open, so that warm air flushes through. On overcast days below 19ºC, the greenhouse effect will warm up the boxes if they are tight shut.
   What about the Winter?.... well, I have to think that through. I will fix the fronts on and complete the boxes and monitor the whole set up for another autumn and winter, through to the same time next Summer, and will mark the anniversary of these boxes by having another big think - end of July 2012.

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