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Renewable Energy: Monitoring Ground Temp

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  1.  
    • CommentAuthorwoodgnome
    • CommentTimeAug 27th 2015 edited
     
    I'm soon going to be digging to install the collectors for my GSHP.
    I would like to monitor the ground temps at various areas in the field.
    What's the best equipment/ system for doing this?
    I might do something similar to this

    http://chargingtheearth.blogspot.co.uk/p/system.html

    But not sure yet as the ground is wet, so I might monitor it for a year to keep an eye on the temp.


    Thanks
    • CommentAuthortony
    • CommentTimeAug 27th 2015
     
    I use thermocouples. I put them in little vials full of air so they couldn't get wet. Ran back to data collection centre
    •  
      CommentAuthorSteamyTea
    • CommentTimeAug 27th 2015
     
    Tony
    How long are the cable runs, are they all the same length and did you adjust for their resistance.

    You could try some 1Wire devices attached to a logger. I have some running on 10m cables with no problems, same with the DH22s. Not sure how long the cable can be before reliability is an issue though.

    Alternatively, you could bury some iButtons, dig them up later and get the data off them.

    A simple way to check the ground temperature is to run your main cold water tap for a few minutes, then measure the temperature.
    • CommentAuthorwoodgnome
    • CommentTimeAug 28th 2015
     
    Thanks

    Steamy, running the tap won't give me the temp where the collectors are, and i want to see if the ground where the collectors are is recovering after a winters use.

    I need to be able to leave the probes in place, digging them up periodically would be a PITA.
    •  
      CommentAuthorSteamyTea
    • CommentTimeAug 28th 2015
     
    You could put a bit of plastic pipe into the ground and attach the iButton to a cord, then pull them out when you want to check them.
    • CommentAuthormarktime
    • CommentTimeAug 28th 2015
     
    What are you aiming to gain by monitoring ground temps? At the depth your concerned with the temp is essentially constant. Look here for some back-ground:

    http://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm
    • CommentAuthorskyewright
    • CommentTimeAug 28th 2015
     
    Posted By: marktimeWhat are you aiming to gain by monitoring ground temps? At the depth your concerned with the temp is essentially constant.

    Wet ground was mentioned. That can make a big difference, especially if the water is moving.
    • CommentAuthorskyewright
    • CommentTimeAug 28th 2015 edited
     
    Posted By: SteamyTeaTony
    You could try some 1Wire devices attached to a logger. I have some running on 10m cables with no problems, same with the DH22s. Not sure how long the cable can be before reliability is an issue though.

    I have some 1-wire soil sensors ~30m from the PC at 1000mm, 300mm & 100mm. The 1000mm one failed after 3-4 years. The 300mm is now intermittent (after 4-5 years). The 100mm is still logging in. I embedded the sensors in epoxy, placed them in a 1200mm piece of MDPE with "windows" cut out at the sensor depths, made a hole with a fencing bar, fed the pile down the hole, then trickled sand into the (small) gap. The wires from the pipe end up plugging into an RJ45 in a control box, from where it's ~30m of CAT5 back to the PC (actually a 1-wire hub, by the PC). I suspect the sensor failure is most likely down breakdown of to the insulation on the wiring in the waterlogged ground (I didn't use anything special), possibly not helped by using silicone to fix the sensors in position in the pipe (& not considering its acid setting aspects). At present I'm unlikely to bother replacing the sensors, but it wouldn't be a big job (make up a new unit, unplug & pull the old one, replace).
    •  
      CommentAuthorSteamyTea
    • CommentTimeAug 28th 2015
     
    Wish I had 300mm of soil to punch a hole in. I sit on nice solid granite.

    Never thought of using some CAT5e, that is a cheap way to wire things in, could easily wire in up to 7 DH22 sensors, or several hundred DS's. Thanks for the tip.
    •  
      CommentAuthordjh
    • CommentTimeAug 28th 2015
     
    Posted By: SteamyTeaYou could put a bit of plastic pipe into the ground

    I was going to suggest putting a plastic pipe in the ground for a different reason, which is to be able to use a dipstick to find out the level of the water table.
    • CommentAuthorskyewright
    • CommentTimeAug 28th 2015
     
    Posted By: SteamyTeaWish I had 300mm of soil to punch a hole in. I sit on nice solid granite.

    Very variable here, from visible rock on the high side to accumulated silt on low side. My geographer neighbour assures me that the wetland we are next to is technically a fen, so home from home for a Lincolnshire lad...

    Posted By: SteamyTea
    Never thought of using some CAT5e, that is a cheap way to wire things in, could easily wire in up to 7 DH22 sensors, or several hundred DS's. Thanks for the tip.

    Just to be clear, I use the CAT5 wired according to a standard mentioned below. At the PC end it goes to an RJ12 connection to a 1-wire USB host adapter that's plugged into the PC.

    http://www.sheepwalkelectronics.co.uk/wiring_info.php
    • CommentAuthorwoodgnome
    • CommentTimeAug 28th 2015
     
    Posted By: marktimeWhat are you aiming to gain by monitoring ground temps? At the depth your concerned with the temp is essentially constant. Look here for some back-ground:

    http://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm" rel="nofollow" >http://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm


    I want to make sure that the collector for the GSHP isn't extracting too much out of the ground.

    I might put some vertical pipe in today and see where the water level is in different places.

    JSH on the "other" forum suggested DS18B20 sensors.

    Trouble is, I haven't got a clue regarding arduinos, raspberry pi's, might as well be speaking Chinese.
    •  
      CommentAuthordjh
    • CommentTimeAug 28th 2015
     
    Posted By: woodgnomeDS18B20 sensors

    Those are the 1-wire sensors being discussed here.
    • CommentAuthorJonG
    • CommentTimeAug 28th 2015
     
    Not sure whether you will gain anything from this woodgnome, a more useful exercise would be trial pits to ascertain the composition of the ground once the pipework is in.

    The heat pump will have sensors that confirm inlet and outlet temps once in use and these will vary across the year depending on load.

    Annually you can monitor the really important factor which is how well the ground recovers year on year whilst the heat pump is in use.
    • CommentAuthorwoodgnome
    • CommentTimeAug 28th 2015
     
    Jon

    Almost 2 years since I started asking about GSHP's!

    The reasons for the monitoring is exactly as you say, I want to make sure the ground is recovering year on year. My ground is clay to about 1200 - 1500mm down, then its "stoney clay", still clay, but a bit stonier. I known this from digging the founds and treatment plant and enlarging the spring fed pond. The ground is wet, I dug a few holes around the field and they filled with water after few days, even with no rain.
    The next thing is, what would be the optimum depth of the collectors?

    I have got revised quotes for Nibe, Kensa and Thermia units, this time around it doesn't make sense to self install with the Kensa. I'm erring towards Nibe, as I can get the 7 yr warranty through their VIP installer, however I'm still considering opting out of the MCS stuff as I don't know what will happen after April next yr with the RHI and I'm unsure if I'll get it done before then. The quotes are roughly as much for the MCS install etc as the unit and bits and bobs.
    • CommentAuthorJonG
    • CommentTimeAug 28th 2015
     
    The brine passing through the unit will tell you to what extent the ground is recovering. Most of our installs are in mudstone or claystone if its wet its great, try and avoid using sand use the top soil instead and check what lambda your installer has used for tge ground you can tgen ask them to adjust down to be cautious if you are worried but tge MCS sizing is pretty cautious already. The lamba ranges are on MCS website.

    NIBE or Thermia would be our recommendation in that order but doing some IDM too cos it will take a direct output from pv.

    Still no news either way on the RHI although manufacturers who sre close to DECC are quetly confident but who knows.

    As for depth 1 to 1.2 is fine.
    • CommentAuthorwoodgnome
    • CommentTimeAug 29th 2015
     
    Posted By: JonGNIBE or Thermia would be our recommendation in that order but doing some IDM too cos it will take a direct output from pv.


    IDM?
    • CommentAuthorJonG
    • CommentTimeAug 29th 2015
     
    Austrian heat pump manufacturer, comes as standard with Internet capability, PV interface (needs a relay in the inverter), works with a Hygenik tank so no stored water uses a plate and modulating pump.

    Very malleable in terms of functionality if you have something a bit more esoteric in mind. If you let me know where you are I can probably put in you touch with a local installer.

    BTW forgot to say if you do decide to go non-MCS/RHI ignore the stupid 100% sizing rule.
  19.  
    Posted By: JonGBTW forgot to say if you do decide to go non-MCS/RHI ignore the stupid 100% sizing rule.


    Ain't that the truth! Over here in cold Canada (well, hot in summer), the usual rule of thumb for sizing is 80% - this covers more than 98% of actual operating conditions. For the other 2%, we just use a 10kW in-duct direct electric heater. The extra cost of the electricity to run this is way less over 20 years than the additional cost of drilling to size to 100% would have been. As we also do cooling in the summer (and the cooling load is quite a bit less than the heating load), it's even more important so that proper dehumidification takes place as well as avoiding short-cycling.

    Paul in Montreal.
    • CommentAuthorJonG
    • CommentTimeAug 29th 2015
     
    The same sizing approach is true of n europe and s ireland both of which are way ahead of the uk, but hey the british govt knows best.

    With the oversizing comes higher install costs with potentially bigger fittings/pipework, bigger buffering volume and therefore inc. losses and more energy to run a bigger compressor that is sized for a peak load that occurs 2-3% of the year, more glycol, more chemicals, more risk of cycling etc. etc.

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