Sunday, April 11, 2010

First sign of Summer Warming

10 April: When the external air temperature in the shade is above 15ºC, the Heat-pump is set to hibernate totally - it's using about 10 watts, and just checking the temperatures. Yesterday was the first day of the year this happened, and today was the first for any length of time.
    During this time, of course, the Sunboxes continue to work. We came back to the house at about 2pm on a nice sunny day, and I checked the system. We have a chance to see how they work on their own.
    The outside air temp was about 16º. Temperature in the Sunboxes was 38.4ºC (not very hot, only as hot as your blood temperature, but remember, the airspace is being cooled all the time by the circulating glycol). The temperature going down into the ground was 17.4º, and returning from it back up to the boxes was 13.9º - higher than the base temperature of the soil. So the heat must be moving outwards from the pipes into the surrounding soil.
   At about 8pm, when checking the meters, the soil had reached a stable temperature of 13.1º, which is higher than it would ever get normally, even at the end of a long summer. Of course, this heat will move out.... but it's free anyway - and the pump is powered by the PV roof most of the time.

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