Wednesday, March 10, 2010

Morning and Evening ground temperatures

10 March: We turn our heat pump off at about 10.30pm at night and it comes on in the morning, on at 0900 or 0930, so it has 11 hours to recover every night. I notice that the ground seems to recover amazingly quickly (by absorbing heat from the surrounding cylinder of soil).

My 15 minute deep-bore evening tests are always done at about 8pm, after the ground has been giving up its heat all day - currently, these reveal a temperature of 5.8-6.2 ºC.

In the morning, if you run it, and wait about 2-3 mins, the first incoming temperature is presumably, a fair indication of the deep temperature, after which the HP starts putting out refrigerated fluid, and then the temperature goes down. In the morning, at start up, this incoming temperature after 2-3 mins is 9.8-10.2ºC.

I am resolved to start recording this on the spreadsheet, if I can remember to be there when it starts. This will help especially in the summer if we leave the solar charging panels on through the night. I shall also modify the Sunbox plumbing to make it possible to test the ground loop temperature independently of the GSHP.


  1. David,

    To see the recovery over the night period, you could start the ground circulation pump at 9.30pm and with a small data logger, record the return temperature every so many minutes until the morning. - you will then see the borehole recovery!


  2. Chris, I wish I could, but I have found that if I run it for more than 15 mins, the heatpump gets fed up and reverts to normal operation. The exact figure might be 20 mins, I dont know. I come back to it, and find that it reverted... and then started heating the house, thus altering the result.
    there is some sort of delay built in to it.
    It would be worth doing it for ONE special occasion, repeatedly trying it, and timing it with great care.


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