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Author Topic: Recharging the ground  (Read 19722 times)
Stuart Ian Naylor
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« Reply #15 on: January 26, 2016, 09:18:19 AM »

Its a bit of a Necro post but the idea hit with some idea's I have been having for some time.

Starts with solar thermal heating and trying to spec against an annual season rather than the excess we have in summer.
There are a few Micro ORCs starting to turn up on the market which could be fed with solar thermal excess.
So oversized collector arrays feeding an ORC which kicks in at system stagnation...

The cold loop from an ORC could be fed under the ground loop of a GSHP and rather than store seasonal heat this is purely a daily top up.
The trench GSHP take up a hell of a lot of area, but recharging the ground could reduce that and the two systems sort of compliment each other.

But out of interest does anyone know of any finite limits to the minimum area of a trench per system Kw if you where recharging daily.
Or could work out some guestimates on daily recharging?
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Fionn
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« Reply #16 on: January 26, 2016, 09:22:11 AM »

What's an ORC?
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« Reply #17 on: January 26, 2016, 12:39:12 PM »

What's an ORC?

I assume Stuart is referring to The Organic Rankine Cycle....

https://en.wikipedia.org/wiki/Organic_Rankine_cycle

Roger
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3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
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« Reply #18 on: January 26, 2016, 01:02:22 PM »

Hello Stuart,
           And welcome to the forum.This thread was started on a 1st of April. Some time ago we had a genius who went to great lengths to pump solar hot air down into the ground and convince us that it was a great storage idea. I recall that the same man was/is highly educated and clever to boot. However, there were differences of opinion,which he disliked. He made is differences known to the Navitron office after we gave him a holiday. We were not quite ready for such abuse on the laws of physics.
   I think Ivan met him at a renewable energy show afterwards and he was quite nice. He also got some German company interested in his idea but we have not seen it reach the general public as yet.
  So you will understand that there are a few among us, who are a tad suspicious of anyone resurrecting that old thread.
 There is no problem. The rules of the forum are very clear and you are well within them. Good luck.
                                                     Biff
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Stuart Ian Naylor
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« Reply #19 on: January 27, 2016, 05:00:48 AM »

No I remember all that and was extremely dubious about seasonal heat stores and this isn't where I am going.

I am a total noob with GSHP in that I know about them but have zero practical experience, so maybe I should of started a new thread.

Just picking some brains and some practical experience with trench GSHP with daily recharges. Its the laws of physics and how members can eloquently relay those limits has me back on the navitron forum asking a few polite questions.

Not the Tolkien type but like Biff says Organic Rankine and not the most efficient thing in the world, but when its Summer excess and stagnation an ORC couples quite happily to a Solar Thermal array.
Its bit like a Sterling with a hot and cold side and many simply dump heat collected on the cold side to air.

Dumping heat into trench GSHP all boils down to the thermal conductivity of the sub soil and if your loop is too short the temp will not be a constant 12'C as the GSHP will cause localised freezing.
Like a fairly modest GSHP can require a overall trench area of 400m2 and there ain't many of of who have that in the back garden.

So forget the ORC but keep that cold loop on a back burner, forget seasonal stores and move to daily recharges.
Come to pick your brains about practical findings in trench thermal conductivity and how much daily localised heat you could dump and what reductions in overall area you could expect bearing in mind the reality of the laws of physics.

Stuart
 
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biff
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« Reply #20 on: January 27, 2016, 09:44:23 AM »

Good morning again Stuart,
                      I am sure we will all be glad to help you and impart what ever little knowledge we have.
I have to admit that I never heard of ORC before until Roger pitched it in. So already I have gained something from this thread.
  However, your whole quest is governed by the suitability of the soil or subsoil. It is a gamble and then the soil can flood and the water can absorb the hard won heat. wackoold
 GSHPs have pretty hefty running costs and you don,t really know how it is going to turn out until you take the gamble.
 If you have energy to spare in the form of heat,then heavily insulated tanks of fluid are a plausible route to take. You will know exactly what you are dealing with.
Gasifying boilers that burn meter lengths of wood and heat 2,000 gallon thermal stores are something that I have been keeping an eye on this past 3 years. Despite the size and the cost involved this system is very effecient and reliable. The boiler can shut down after 6 to 8 hours and the thermal store is still supplying heat to houses and offices for 48 hours afterwards. The beauty of this system is that the timber and wood that keep the system running are free. Small hopper fed domestic gasifying boilers are now on the market but i don,t know a lot about them.
      If you were lucky enough to sit over a large vein of 2mm limestone chippings, Then you might just get some return from pumping hot air or piped fluid through them. (Now there is an idea)
                                                                   Biff
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Stuart Ian Naylor
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« Reply #21 on: January 27, 2016, 03:08:00 PM »

Cheers Biff.

Doesn't matter about the ORCs and keeping with the thread title "recharging the ground" keeping away from seasonal and purely from looking the angle of reducing trench area of a GSHP.

I don't really want to stray far away from relatively normal trench loops and just try to get any practical experience on localised ground freezing problems. As if you are down at a constant 10'C level and via the use of slinkies, shallow trenches, water flow or just not enough surface area you can struggle to get that constant temperature back.
So around the tube you are reducing the heat energy and if you can do that as a short term heat store another tube applying heat can do the reciprocal.

I will post some links to some new products that might be of interest to Ivan and others as its only lately Micro ORCs have been available in some choice.
Orcs generally are excellent for converting waste heat like say a heat exchanger in the exhaust flue of your boiler, Biff Smiley .
Might be of interest to Ivan and others so if product URLs are taboo have a gander and if a mod would delete the below.
I do think in terms of solar thermal and the problems of summer stagnation a Micro ORC can generate off summer excess and solve a lot of problems with oversized collector arrays.
They are still a cottage industry, no economies of scale and I really think they should become another part of the renewable toolbox and hopefully attain economies of scale.
I have kept the list to "Micro" Orc systems and actually I think the below is about it, in terms of market.

http://www.eneftech.com/index.php
http://www.cogenmicro.com/index.php?select=24
http://www.kaymacor.com/
http://www.enogia.com/product.html
 
Anyway back to trench GSHP and all the things that can effect and just general discussion on what causes low CoP.

« Last Edit: January 27, 2016, 06:36:06 PM by Stuart Ian Naylor » Logged
Stuart Ian Naylor
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« Reply #22 on: January 28, 2016, 01:21:57 AM »

Just to restart this one again as there seems to be some assumptions that some sort of seasonal ground heat store implementation is planned.

I mentioned ORC as I am a fan of Solar / ORC cogeneration like some of the above products I mentioned. I am also a fan of heat pumps but I am aware the ground coverage of trench systems is quite large, bore holes can be quite expensive.

The ORC is one type of generation that produces waste heat via the cold loop that is of little quality. Waste heat is exactly that and again nothing magical but with sensible laws of physics applied it could be used to reduce trench area and bore area. Waste heat from many applications can be used but it did occur to me an ORC has a cold loop that could be a heat pumps hot loop. Extremely close compliments at least.

The thermal conductivity of the ground has much effect on extraction by the heat pump and the same restrictions will apply when dumping waste heat into that ground.

It isn't seasonal or in anyway a conventual heat store but there should be able to help maintain CoP levels with smaller collection circuits.
How much smaller and what sort of heat flux input you would need on a daily recharge, I was wondering if you guys could throw up some guesstimates?
« Last Edit: January 28, 2016, 04:53:00 AM by Stuart Ian Naylor » Logged
titan
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« Reply #23 on: January 29, 2016, 10:18:10 AM »


 GSHPs have pretty hefty running costs and you don,t really know how it is going to turn out until you take the gamble.


You keep trotting this old chestnut out. Running costs depend on the dwelling energy requirement nothing to do with the heat pump which is around the same cost to run as a gas boiler.
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biff
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« Reply #24 on: January 29, 2016, 10:45:48 AM »

Gas boilers take 8kw,?
               Big brute if a unit the size of an american fridge, the whole place dug up to sink pipes and a room devoted to clocks,dials and manifolds. to be told that the running costs are astronomical,The Unit itself @ 8kw minimum,refused to switch off and the guy trying to find enough renewable energy to run the bally thing...Oh he had a modest 4 bed bungalow of about 1600sq feet.
     Old cherry,? don,t think so but I believe the same customer find it a rather bitter modern one to swallow.
  I am no GSHP expert but ,like wood chip boilers ,they have got a bad name around here.
                                                               Biff
« Last Edit: January 29, 2016, 11:01:18 AM by biff » Logged

An unpaid Navitron volunteer,who has been living off-grid,powered by wind and solar,each year better than the last one.
Stuart Ian Naylor
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« Reply #25 on: January 29, 2016, 10:55:32 AM »

I am getting somewhere near and managing to get some data on soil thermal conductivity.
http://www.geothermal-energy.org/pdf/IGAstandard/WGC/2010/2952.pdf

Again like you say it is very dependent on workload and rating.

Personally if I was investing in a GSHP and they said we will not know until its up and running, I think I might find another installer.

I presume the pro's take a few soil cores and check ground feasibility as best they can.
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Stuart Ian Naylor
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« Reply #26 on: January 29, 2016, 10:59:21 AM »

Gas boilers take 8kw,?
               Big brute if a unit the size of an american fridge, the whole place dug up to sink pipes and a room devoted to clocks,dials and manifolds. to be told that the running costs are astronomical,The Unit itself @ 8kw minimum,refused to switch off and the guy trying to find enough renewable energy to run the bally thing...Oh he had a modest 4 bed bungalow of about 16sq feet.
     Old cherry,? don,t think so but I believe the same customer find it a rather bitter modern one to swallow.
  I am no GSHP expert but ,like wood chip boilers ,they have got a bad name around here.
                                                               Biff

With a CoP of 4 what are you heating Biff?
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biff
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« Reply #27 on: January 29, 2016, 11:11:02 AM »

I do not have a GSHP Stuart,
                   I just listen to what the new owners tell me. Perhaps it is installed wrong. Perhaps the ground is totally unsuitable or maybe these folks got units far too big for their houses.
  But it looked very like a 2 steps forward and 3 steps backward scenario. It did seem like a lot of pain for very little gain.
 You could never even  begin to compare a gas boiler set up with a GSHP.
 I am only going by the feedback from the folks that went to the trouble of fitting them.
                                                                       Biff
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Stuart Ian Naylor
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« Reply #28 on: January 29, 2016, 11:20:08 AM »

A GSHP is very comparable to a boiler in terms of heat output.

If it is drawing 8kW with a CoP of 4.0 that should be throwing out about 32kW of heat which is like having 10 3 bar electric fires on.
The ones that I have seen that are the size of an American fridge are either commercial grade or the ones that have an internal cylinder as some do but are a bit thinner but tall.

The main thing is the trenches or bores, as that is a massive difference, but the rest are comparable as that is the whole point of a GSHP.

Imperial (ft 3) meter calculation
Present reading - Previous reading = Total kWh used
Total units used x 1.02264 (correction factor) = Corrected consumption
Corrected consumption x 2.83 = Cubic meters
Cubic meters x Calorific Value (CV on your bill) / 3.6 = Total number of kilowatt hours used
 
Metric (m3) meter calculation
Present reading - Previous reading = Total units used
Total units used x 1.02264 (correction factor) = Corrected consumption
Cubic meters x Calorific Value (CV on your bill) / 3.6 = Total number of kilowatt hours used
« Last Edit: January 29, 2016, 11:44:09 AM by Stuart Ian Naylor » Logged
titan
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« Reply #29 on: January 29, 2016, 12:28:59 PM »


  I am no GSHP expert but ,like wood chip boilers ,they have got a bad name around here.
                                                               Biff

Have they ? there are quite a few people who post on here who are very satisfied with their heat pump systems. The example you gave is quite clearly a poorly designed and installed system as are many others. I designed and installed my system. My unit is  8kW and measures 55x55x90cm , not much different to a boiler, it heats and provides dhw for a 300m2 house and over the last three years since installation has averaged around 2000kWh  or  300, the average UK gas bill for 2014 was  735.

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