Sunday, August 29, 2010

Summer not always good for Sunboxes!

28 August: It seems paradoxical that the Sunboxes do not do so well in late Summer. They are designed to do better in Winter, being driven by the heat pump and being vertically oriented. At this time of year, there are some 'flat' days that we would not get in the Spring.
  There are only two things that stimulate them into action - one is air temperature in the Sunbox above 19ºC. The other is a 5 degsC difference between the air and the groundloop.
  At this time, there have been some cool days when the sun didn't shine, and for Thursday recently, with rain much of the day, the Sunboxes only ran for 6 mins in the entire day. This was because the Heatpump needed heat and got some in the morning. For the rest of the day, it was too cold outside for the boxes to work, but the house was comfortable due to its good insulation, so too warm to need heating. For water, the heat pump didn't need heat again during the day except for brief bursts, and there was so much warmth already in the borehole that it reached temperature before the delta-T was large enough to turn on the Sunboxes. This is likely to occur sometimes in the autumn equinox.
  In the Spring equinox, it was different, the air temperatures outside are still cold, so the heating is on, and the heat pump frequently needs heat from the soil and hence, from the Sunboxes. Having glycol rushing through the panels, the boxes perform well in the spring, even if the air temp inside the box isn't 19º.

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