GSHP to dry grain

Discussion in 'Renewable Energy' started by Hutcho, Dec 4, 2017.

  1. Hutcho

    Hutcho New Member

    Hi. Wondered if any one had used a GSHP to dry grain? We do it with a biomas boiler and chp plant at the home farm through a heat exchanger on air floor but wondered if I could use GSHP plus heat exchanger on air flooron my other farm where we have a 80 kw wind turbine. I understand temperature will be a bit low at 50 Degc.
     
  2. akaPABLO01

    akaPABLO01 Member

    Wouldn’t qualify for RHI and heat grade is too low
     
  3. sjt01

    sjt01 Member

    Location:
    North Norfolk
    You would need a really big GSHP to get any air volume at 50°C. Heating to a lower temperature would help, even 35°C dries grain but not fast. An alternative that was pushed 30 or so years ago was a refrigeration unit that basically chilled the air down so the moisture condensed out, then heated it back up again. I think they were called DAG - Dry Air Generators. Could be worth looking for an old one to recondition, although the refrigerant would have to be updated.
     
    Hutcho likes this.
  4. Hutcho

    Hutcho New Member

    Thanks for the reply, has the Rhi scheme changed recently to make grain drying no longer a eligible use?
     
  5. akaPABLO01

    akaPABLO01 Member

    I wouldn’t even like to try as it would fail to meet demand I suspect. But, let us know how you go?
     
  6. I very much doubt that will ever happen.

    You will need a lot of output to do any good drying, 200kw at least I would say. Dry air dries grain as well as hot air, if you can dry it below say 60% RH you will still help it along . There may come a point where the slower drying time costs more in fan power and thus less viable.
     
  7. Hutcho

    Hutcho New Member

    Thanks for advice guys. I have been drying grain on air floors for some years now. Initially using a gas burner (expensive) to lower rh, ambient air only (difficult when near coast), using a 185kw straw burner (much less than 185 kw continuous with 2 bales a day) and lately with 100 kw (continuous) chp plant. To dry grain from 20 percent to 14 percent could take well over a month using ambient, 3 weeks say with the straw burner but can get done it easily under a week with chp plant, it does run 24/7 though. I was considering a 75 kw gshp and picking my drying time to optimise rh hopefully extending a 8 hour day to 14 hour. Probably 200 tonne batch with 4 batches.
     
  8. akaPABLO01

    akaPABLO01 Member

    Coastal area, are you thinking ground loop, pond mats or bore hole? The last would cost an absolute fortune, tens of thousands so would get ruled out. Pond mats would offer a better return flow temp but for that size the body of water needed would be huge. The cheapest is ground loop.

    How have you come to the size of system needed at 75kW, £177k tier 1, 98,550kWth? If you can’t demonstrate a 2.2 cop then ofgem may send in Ricardo.
     
  9. Hutcho

    Hutcho New Member

    Hi. Yes was thinking ground loops can drive a digger and plenty of easy digging soil there. Would need 1.25 acre for a 75 kw system apparently. Heat use is 75 kw minimum as per post considered double that but if I can optimise gshp/drier use with windy dry days should work well. The figure you quote is the 20 year total rhi income I assume. Sounds like I might be of guinea pig here, if anyone has a gshp I appreciate any advice as to how reliable, what maintenance is required and if they achieve the advertised efficiency.
     
  10. akaPABLO01

    akaPABLO01 Member

    For this usage I expect so. Most have Biomass installed.

    What soil type is it for thermal conductivity and what annual heat output with flow temperature do you expect?
     
  11. Hutcho

    Hutcho New Member

    Soil type is deep loam but parts of field could have a gravel base. Annual heat heat output is a difficult one probably in the region of 100,000 kwhth hopefully running at 45 to 50 Degc. Are you asking to see if ground loops can achieve cop? Does the fact it will be used mostly in July to Oct effect this? Thanks again
     
  12. akaPABLO01

    akaPABLO01 Member

    Look, your heat extraction is in the region of 0.4/0.5 W/mk. A poor but average extract is about 1.7, this is acceptable with excellent being 2.4. This is how heat travels through material.

    It won’t work even if you load the buffer with thermal. Although, if you dig out some land and put a lake in then maybe pond mats, this would need to be some 50x50m at a guess
     
  13. scotston

    scotston New Member

    7degC lift in ambient temperature gives you 65% RH and 14.5% grain, so right now you only need air at 7degC to give you dry grain, albeit, slowly. In summer, at 25degC this would be 32degC air whereby you will dry much faster. Both of these are in the sweet spot of gshp with a coefficient of 3-4. No need to worry about 50degC, not important unless you want to stir. My drying floor needs around 75kwth to dry 200T wheat, with two 15kwe fans. So a terrific idea to use the rhi to 'multiply' the value of your turbine electric from 5p to around 40p (for tier1). I'm using the available grid export from my chp to run phase 1 of 3 gshp installs which will total around 76kwth of heating using the remaining 25kwe of export from my 50kwe chp.
     
    Fowler VF likes this.
  14. akaPABLO01

    akaPABLO01 Member

    Rural lift is 10% and poor thermal conductivity means more pipe. Then this is coastal so ground conductivity will be poor with wind.
     
  15. scotston

    scotston New Member

    apologies, I have no idea what you mean - rural lift is 10%? I have a 20kw unit running with 1.2km of pipe for the last 5 years around 4 cop. No idea what the thermal conductivity is, just that it works. This new 26kw setup has around 3 times the pipe in slinkies only because mcs or whoever have uprated the original specs. In my opinion cop is more defined by the flow temp, so keep it low and you'll be right.
     
  16. akaPABLO01

    akaPABLO01 Member

    Hmm, I’ve just completed an analysis for 16kW gshp with 1500m (1.5km) at 1.7W/km so you must have really good thermal conductivity, 2.2 or your original install hasn’t been sized correctly.
     
  17. Wouldn't it be better to use air source heat pump in July-Sept?
     
  18. akaPABLO01

    akaPABLO01 Member

    Commercial application is poor tariff 2.61 versus 9.09
     
  19. Ah right, I see.
     
  20. Hutcho

    Hutcho New Member

    Thanks everyone for the advice, it sounds like either a GSHP or air source could be a good option, good point about keeping the flow temp low to improve cop. I guess it is more important to have a higher kw rating and lower flow temp to aim for a constant 7.5 Degc uplift on ambient temp. Air source has the appeal of lower install cost and no chance of leak in years to come, and removes problems of ground conductivity issues. But it will have a lower cop and tariff. Lots to consider!
     

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