Monday, August 22, 2011

Clock and Pump Speed

22 August 2011: The annual total for the Clock on the sunboxes was a record this week - this has touched 2,230 hours. This is a variable amount, because I could make it do more hours by working with a smaller delta-T and trigger temperature, and fewer the other way. But then the kilowatt-hours per hour would be poorer. I have a balancing act between them. The overall annual efficiency (measured as the power capture) of the Sunboxes over the year is 1.3 kW -  it seems to be about 1.8 kW during the winter (when the GSHP is driving the glycol round fast) and 1.1 kW during the summer (when the glycol is trickling round at the slower rate).
Should I run the pump at the faster speed? perhaps.... There is a choice of 30W, 46W and something higher, perhaps 60W. ....thinking about it....

Perhaps, Yes!  I should have a policy of running it faster in the five summer months and slow in the seven months of the heating season Oct 1-May 1. I will try this for the final part of August, and for the first half of September. My daily and weekly measurements will reveal if this works. The majority of the pumping time is when there is power from the PV roof, and if the 'chillers' cool the sunbox space more quickly, then good! the valve will close until the air temperature builds up again.
September 2011 Postcript: Later, NO! I changed it back to 30W, the slow speed. I have an instinct about this. If the pump runs too fast, the volume flow is greater but the temperature difference between the pipes at the point in the illustration is too close, making it too difficult for the SuperCal energy meter to pick up the difference. Slow speed gives us more accurate readings.

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