Wednesday, April 14, 2010

The system working faithfully!

14 April: It was very rewarding this morning to watch the system performing efficiently, by monitoring the temperatures. It was a cold morning, 8.5º and the air temp in the Sunboxes was 12.3º despite it being cold and cloudy outside. The start up deep temperature of the ground loop was 11.9º which is only so high thanks to the amounts we have pumped into it during the days before.
  When the GSHP was turned on, the outgoing glycol temperature gradually crept downwards, and when it was more than 5 degs colder, 6.8º, the sunbox pump came on faithfully. The glycol leaving the pump was still cold, but having gone through the sunboxes, it rose in temperature, going down to the ground at 7.3º, reducing the workload of the ground - thus, directly contributing to house heating.
    I notice that as the glycol cools the air in the boxes, the air temp falls a bit, and the pump goes off, as it should. Then, as the sun gets higher, and the sunbox air temp recovers, and the GSHP lowers the output temp, the sunbox pump came on again, and the process continued - with the glycol warming again, and the air-temp dropping slightly. There is a gentle alternation, but with the 5 deg C difference and a 1 deg C hysteresis, it is not 'hunting frantically' - I would call the process 'responding faithfully'.
  Later in the morning, the day brightened up, and with less heating to do, the GSHP goes quiet, and the sunbox air temp zoomed up to the high 20s (26-30 range), and all that heat is now just charging the earth, going round the loop at about 12.8ºC.
(Unfortunately, the GSHP is still not performing faithfully, it frequently gets the idea that it's a kettle and starts pushing the water temperature way up to 60 before shutting itself down, so we really must get this seen to.)
See my later article on 7 June which discusses and explains the overheating problem - now explained! In short, it is doing a Pasteurisation cycle every morning, instead of every 2 weeks!

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