Monday, November 1, 2010

More datalogger wires added

1 Nov '10: For some time now Blaise has wanted me to fit thermocouples directly to some of the innards of the heat pump, as a means of estimating its COP. We had the GSHP side and front panels off on Sunday evening, and I have now got a thermocouple head on the pipe IN and the pipe OUT from the Condenser, both of these leading back to ports 5 and 6 on the Datalogger.
  So, we will now have temperature readings on the in port and export pipes of the Condenser.
  Other things? well I am pretty sure that some time I will take the mirrors off the West side sunbox for enough days to get reading - with three channels datalogged, input temp, and the two return temperatures.
  Ground temperature: Every Sunday, I take a reading of the deep ground. The good news.... Better ground temperature. In 2010, we had the heating season starting more than a week earlier than usual (at the Sept equinox), we had a mini winter in mid October (with below freezing night temperatures) and yet...... the ground temperature on the 1st November was last night 11.9 degrees, whereas at the same date last year in a much milder October it was 9.90 degrees.... 2 degrees is a big deal in the context of the mass of earth that the boreholes sit in, and considering the benefits that even one degree has on the COP of the GHSP. Let's continue with the experiment, and see how it works out in the colder months. There were times in January of this year when the GSHP consumption soared beyond 30kWh per day, and I am hoping this will not happen in 2011!
  Again, to remind you, the way I do this is to leave the GSHP off for a few hours, and at about 0100, I run the ground loop pump for 15-20 mins until the turbulent flow has evened out the temperature and revealed the answer. It gives time for the ring of soil around the borehole pipes to have evened out a bit.

5th November follow up: the Datalogger has had all its summer memory flushed out (stored on B's laptop) and is now catching data for the coming winter, including condenser temperatures. For the Summer, we were collecting every 15 mins so that the memory wouldnt fill up too quickly - and the main thing being recorded was the sunbox slowly charging. This wasn't good for Autumn, because sometimes the GSHP comes on, does its business and goes off in a shorter time. So for Winter, the collecting interval is every 3 mins, so we catch almost all the heating cycles of the GSHP.

See the Comments below, discussion between Chris Wood and myself as to whether the black collectors would work better with or without boxes around them.


  1. Hi David,

    I attended a GSHPA technical seminar the other day and heard a talk from Goran Hellstrom of Lund University (& NEOENERGY). I have read much of his work previously and is one of the early pioneers in ground thermal modelling etc. His current work is looking at the use of recharge and in Sweden they have a number of both domestic and non domestic real installations. Take a look at his presentation:

    Now look at the slides showing glazed and non glazed collectors. His tests have shown that when connected to the heat pump the annual energy yield is no different. He is stated in his talk that in fact the non solar collector on a north face will provide 90% of the energy yield of a southern face i.e the direct solar irradiance is not the key driver. He also has a number of sophisticated programs which he has developed and these tests correlate with his simulations.

  2. Hi Chris,
    It is probably true that on a week like we have been having - every day cloudy with rain later (apart from an hour of sun on Wednesday), my sunboxes would have worked just as well on the north, and probably better without the boxes - just the unclothed black collectors to get air heat.
    But over a whole year, we have to go for the best of the averages, and in the summer when the heat pump is almost totally dormant, the south is best located for interseasonal charging.
    Hope we can talk more about this next time we meet.

  3. Hi David,

    It is true that your sunboxes would work best in the summer for recharging only - but then again a flat plate solar collector would be better still. Goran is saying that on average across a year that the unglazed pipes provide as much heat as the solar collectors... its just that glazed ones provide more recharge in the summer, but the unglazed pipes fair better in the winter when the heat extraction from the air is the important parameter.

  4. Chris,
    we wouldn't be able to drive the ground loop through one of those.. but using a bypass and inject (trickle while we work) plumbing route, we could use one, and I will next time if I get the chance. Its worth trying out. To use one of those without a tank.
    However, for your point about the winter use. I know that theoretically, the air inside boxes can be colder than ambient air - this doesnt happen practically too often, even tonight the box air was 2degs warmer than the ambient (7º or 5º)
    I dont want to fit actuators that open and shut the vent for shade or sunny times, as this raises the cost too much, and is chasing after small gains in watts. What I have is quite a high delta T requirement (currently 4.5 degC) which avoids the pump operating needlessly when there isnt enough delta T.

  5. Chris, was the lecture more based on Swedish experience with very minimal winter sun hours? My sunbox capture is what you would expect on cloudy winter days, i.e. not very much 3-6KWH,
    ... but if there is sunshine, it is always in double figures - 16 and 14kWh on the last two days of the weekend.


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