Monday, July 4, 2011

Sunbox modification needed?

3 July 2011: As stated in the July report, the Sunbox annual capture is falling slightly and I notice that the temperatures in the boxes are not at high as the same time last year.
   I suspect that this is because of the high sun angle on the face of the boxes, and the air tightness of them. They were more leaky and more productive, this time last year. In a month when the average temperature is above 18º, it makes sense to leave the lower louvre open all the time. I am sure that David Atkins and Chris Wood would agree with this.
  This will probably get higher temperatures in the middle of the day, and yes, it will cause a shut off earlier in the evening when it cools quicker. The black slabs in the boxes contain about 48 litres of glycol, and the cold liquid takes about 10 mins to move through, so they are cooling the airspace quicker than it can be re-warmed by the Sun - at the very best, the temp gets up to about 37º whereas in February and March (with more direct sun angles), I was seeing box temperatures of 40-45º. In July and August, they would probably work better in fresh air, as I originally intended when building them with openable bottom louvres.
  In the short term, I can cut the tape that makes the lower louvres airtight. In the longer term, I can work on the design of a new box shape, and decide if it's to be done this summer or next summer.

4 July 2011: As a special celebration of US independence, I climbed up the ladder and took the tape off the bottom louvre of the right hand sunbox. (lied about the first half of that sentence....)
I will keep an eye on the internal temperatures, and really, should have enough self-belief to take it off the left hand box too.
5 July 2011: Oh here goes, I'll take the tape off the left hand box too... and give the aluminium reflectors a good cleaning while I am up the ladder.

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