Navitron Renewable Energy and Sustainability Forum

HEAT PUMPS & Geothermal Energy => Heat Pumps => Topic started by: Edislaw on April 01, 2015, 08:03:55 AM



Title: Recharging the ground
Post by: Edislaw on April 01, 2015, 08:03:55 AM
The B&ES recommend that, "If possible it is beneficial to recharge the ground in summer." preferably using a simple pumped rather than heat pumped system an  give as an example "circulating water around an underfloor heating system and (indirectly) passing that heat into the ground".

I have read elsewhere that reversible heat pumps are not MCS approved. Since a heat pump uses electricity whichever direction it is pumping using it to recharge the ground must serve to reduce the CoP. I see, however, that there is benefit to be gained from returning energy not being used in the home to the ground. Is it fanciful to direct solar energy from a PV array to a heat store and set up a loop which circulates the hot water produced but not required for heating or domestic purposes to the ground?

Does this mean that the correlation between ambient temperature which leaves the ground temperature in Southern England two or three degrees higher than that in Northern Scotland indicates that the ground is capable of storing heat at higher temperatures? Extrapolating that thought, if recharging the ground could raise the temperature by ten degrees then a system with a maximum running temperature of 45 degrees could then run at 55 degrees? Alternatively, if the system only needs to raise temperature from 20 degrees to 45 degrees does that mean it could run more efficiently and reduce costs?


Title: Re: Recharging the ground
Post by: gravelld on April 01, 2015, 09:30:14 AM
It has been done, also using solar thermal. Check out the Peveril Solar House. Also see Tony Cowling's house which doesn't use a heat pump.


Title: Re: Recharging the ground
Post by: biff on April 01, 2015, 09:54:43 AM
Errr,
   I will keep an eye on this thread. We used to have some very exciting debates on this same subject,
   Bearing in mind that different soils have different compositions and different water contents  and the water can be rising and falling and consequently spreading out to surrounding areas.
   We had one champion of this same idea and,,and,, we need to be careful folks. freeeze
                                                             Biff
   Sorry Gravelld, but that one is out of order,!! very far out of order.


Title: Re: Recharging the ground
Post by: Tigger on April 01, 2015, 10:13:44 AM
Ha ha, oh yes, I remember that thread  exhappy:


Title: Re: Recharging the ground
Post by: A.L. on April 01, 2015, 10:34:44 AM
hello and welcome,

- using a circulating pump to cool a house with ufh is possible and if the house is also heated by a gshp then it would be sensible to dump the heat with the groundloop. I would not attempt on a domestic scale to raise the temp of the ground with summer heat above its natural level with the intent of storing the heat for winter use. The heat losses are too high and the financial gains insufficient.

- Tony Cowlings house is a serious attempt to build a (almost) no heat house http://www.tonyshouse.cowlings.org.uk/ (http://www.tonyshouse.cowlings.org.uk/)

- IMHO The Peveril Solar House is a publicity stunt.


Title: Re: Recharging the ground
Post by: gravelld on April 01, 2015, 10:42:49 AM
Sorry, I actually didn't include the link in the first draft of my post because I was aware of some "beef", then reconsidered because I was trying to be helpful.


Title: Re: Recharging the ground
Post by: biff on April 01, 2015, 10:48:51 AM
No Problem,
           I was thinking it might have something to do with today,s date, :hysteria
                  Not a bother, :crossed
                                    Biff


Title: Re: Recharging the ground
Post by: Tigger on April 01, 2015, 11:23:53 AM
Err, yep, I was also aware of the date and thought someone was possibly having a larf......


Title: Re: Recharging the ground
Post by: gravelld on April 01, 2015, 11:29:49 AM
LOL! Good point.

While we're at it, what do people think of roof mounted turbines...?  :crossed


Title: Re: Recharging the ground
Post by: dhaslam on April 01, 2015, 11:34:02 AM
and don't forget  the  old favourite

http://www.bbc.com/news/uk-england-york-north-yorkshire-29126161


Title: Re: Recharging the ground
Post by: bxman on April 01, 2015, 01:05:43 PM

Hi

Welcome to the forum

If you have not yet got your Heat pump         have a look at Earth Tubes  they cool your house at the same time as recharging the ground  apart from that I know nothing  but suspect the additional costs may not justify the benefits never the less keep up the research and hopefully we will all  learn something.
 best of  luck   
cheers  Patrick


Title: Re: Recharging the ground
Post by: phoooby on April 01, 2015, 02:32:30 PM
A Sainsbury's not too far from me has just put a system in to store heat from fridges and use it to heat the store. They had a big drilling rig in the car park for some time; gives the locals a idea of what fracking is about!. Was there yesterday and all that is now visible is a few large manhole covers and some new tarmac where the pipes run into the store. All they need now is a roof covered in PV to power it all.

http://www.basingstokegazette.co.uk/business/11799564.Sainsbury___s_is_installing_ground_heat_pumps_at_its_Kempshott_store/


Title: Re: Recharging the ground
Post by: dhaslam on April 03, 2015, 01:09:28 PM
Rocks are not very good insulation, it takes 65 metres of limestone to equal one metre of polyurethane.    It would be better to  build an well insulated tank under the car park.       


Title: Re: Recharging the ground
Post by: Fionn on April 03, 2015, 01:42:00 PM
I think the decrement delay of the limestone would also work in it's favour though.


Title: Re: Recharging the ground
Post by: Nickel2 on April 03, 2015, 06:31:09 PM
Doesn't work with ASHP's though. I've been putting heat into the surrounding atmosphere for years, but none of it seems to have come back in a useable form.


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor 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?


Title: Re: Recharging the ground
Post by: Fionn on January 26, 2016, 09:22:11 AM
What's an ORC?


Title: Re: Recharging the ground
Post by: marshman 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


Title: Re: Recharging the ground
Post by: biff 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


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor 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
 


Title: Re: Recharging the ground
Post by: biff 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


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor 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 :) .
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.



Title: Re: Recharging the ground
Post by: Stuart Ian Naylor 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?


Title: Re: Recharging the ground
Post by: titan 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.


Title: Re: Recharging the ground
Post by: biff 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


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor 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.


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor 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?


Title: Re: Recharging the ground
Post by: biff 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


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor 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


Title: Re: Recharging the ground
Post by: titan 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.



Title: Re: Recharging the ground
Post by: dhaslam on January 29, 2016, 01:19:14 PM
Storing heat extra seasonal heat underground only works on a large scale.     The system at Drakes Landing in Canada seems to work  even though they have a lot of water from snow melt in spring.   Their system may work  because the snow melt occurs  when there is already strong spring sunshine.    However in the British Isles   the ground is usually wet from about October through the winter so heat dissipates fairly quickly.   One thing I have found this year  is that the warm ground water  is heating the  bottom of the  seasonal store  quite well, the drain around the bottom of the store is  working in reverse  because  of the  flood water seeping into it.   The temperature in the store is fairly stable    by using a combination of rising heat from under the store and limited input from the solar panels.   The base are of the store is only  about 50 sq metres.    

If you are going to store seasonal heat it is best to have a   fairly small  but very well insulated heat store.   Water is good to store heat because you can  apply low temperature heat in winter without cooling the water above.    

I don't think that  a seasonal store  is a complete replacement  for  a ground loop even though I don't have a ground loop at present.     It is really only practical where a ground loop isn't possible.  
There is a benefit in having a warm source in  that heat pump,  output is increased by up to 50% with very little  extra electricity,  but with mild winters ground loops will work quite well.  They just need to be deep enough and  large enough to keep source input temperature high through the winter.        

http://www.sciencedirect.com/science/article/pii/S1876610215002398


Title: Re: Recharging the ground
Post by: biff on January 29, 2016, 02:41:36 PM
Indeed they have Titan,
                  Just like the wood pellet boilers. i am delighted that you have installed your own GSHP and that you understand it and that you can fix it and tweak it when you see fit, but wait for it,,There are loads of others who seem to be happy with their lot but some how, I keep meeting these quite sensible folks who have taken me through the whole process and explained why they are unhappy. The installers are UK registered and not local'.I look upon this as a new version of "Stone Soup". I am very aware that some of the better educated moderators are rather pleased with their GSHPs but again,that has not been the story here. Maybe it is the soil mechanics, maybe it is the installers fault, Perhaps the soil in some places works better. I just don,t know but I have seen the money spent and it will take a long long time to ever see it back. Not everyone is scientifically minded and able to work these things out which harks back to the renewable energy motto which should be, "Keep it simple."
                                                                          Biff
  NB, One little phrase kept cropping up among the folks that I had spoken to, "We thought it was going to be cheap to run or run itself for nothing"  so maybe it was oversold,?


Title: Re: Recharging the ground
Post by: marshman on January 29, 2016, 04:30:08 PM
Indeed they have Titan,
                  Just like the wood pellet boilers. i am delighted that you have installed your own GSHP and that you understand it and that you can fix it and tweak it when you see fit, but wait for it,,There are loads of others who seem to be happy with their lot but some how, I keep meeting these quite sensible folks who have taken me through the whole process and explained why they are unhappy. The installers are UK registered and not local'.I look upon this as a new version of "Stone Soup". I am very aware that some of the better educated moderators are rather pleased with their GSHPs but again,that has not been the story here. Maybe it is the soil mechanics, maybe it is the installers fault, Perhaps the soil in some places works better. I just don,t know but I have seen the money spent and it will take a long long time to ever see it back. Not everyone is scientifically minded and able to work these things out which harks back to the renewable energy motto which should be, "Keep it simple."
                                                                          Biff
  NB, One little phrase kept cropping up among the folks that I had spoken to, "We thought it was going to be cheap to run or run itself for nothing"  so maybe it was oversold,?
Biff,

I think the problem with GSHP is that they are a) sometimes oversold b) often poorly sized c) often have inadequate ground collection loops and finally d) most people do not understand that they need to run at low output temperatures to maintain efficiency. In my opinion they should only ever be used to drive under floor heating and never radiators no matter how oversized they are.

I had my system installed in December after much thought and investigation and yes I think you are right Biff about the gamble part. The groundloops on my system were a gamble as we are on a shingle bank with pockets of clay. However after discussions with the installer and numerous test holes we decided to grossly oversize the loops as an insurance policy - the extra cost was not huge once the machinery was on site.

In terms of complexity my system is less complex than if I was able to have a gas boiler. On the heating side there are no zone valves, no ther,mostatic valves, no mixer valves and no internal thermostats, timers etc and a just one single circulating pump. It is an unvented system so totally sealed with little chance of contamination. The Hot water is a conventional vented system.  As to running cost,s well at the moment (and I accept it is unusually warm but we have had one cold spell) the running costs are only 25% of the predicted costs from the manufacturer/installer and 50% of my own calculations. Yesterday for instance where the early morning outside temp was 2 deg C and it only rose to 7 deg C the system used 9kWh of electricity (a proportion of which was supplied by the PV). The most ever used in a 24 hour period when it was -3 deg C outside  was 21.6kWh. The inside temp of the house was steady at around 20 deg C, 24 hours a day.  The house, well its a large  old detached farmhouse, about about 250 sq m in total and its in a very exposed position.

The heatpump itself is no different inside than a freezer in terms of bits to go wrong, and they seem to last a long time. Maintenence is virtually zero, keep an eye on the levels and clean the filter every once in a while, thats it.

So as with most things if used in the right situation, properly installed by someone who knows what they are doing and cares enough to do a good job, they do deliver the promise. I am still amazed at the performance of mine - the only complaint I have is that the domestic hot water gets too hot!

So don't be so hard on them. It's no different to solar PV installs where the installers are stupid enough to install in unsuitable locations where there are issues of shade - or as in another recent thread where they expected the sun to be in a different place. I looked at wood pellet boilers and was put of by seemingly endless threads on forums about problems with reliability, jammed feeds,  sooted up sensors, broken fans etc. Yet I am sure there are perfectly good installations where the owners are very happy. As with many things you often only hear of the complaints.

Oh, you are right about the ground being chewed up to install the loops, still in trouble with the other half over that bit of miss information - "it'll just be a few scratches across the grass dear, soon grow over" Whoops! ;D

As to the the original topic of the thread, I don't think it will happen. Any difference a "recharge" system will make will be minimal.  As far as I can work out ground loops tend to be around 200m to 300m long ( I stand to be corrected on that). Now my system (10kW pump) pumps liquid at the rate of around 7 litres per minute around each loop (I have four so a total of 28 to 30 litres per minute). On a normal pipe of 32mm internal diameter this equates to around 7 m per minute (1m of pipe holds roughly 1 litre of liquid. So it takes between 30 and 40 minutes (very roughly) for the liquid to make one circuit.  My heat pump - and again I don't know if this is typical but I would think it is, runs for 20 to 30 minutes and is then off for around 90 minutes. This obviously varies with temperature but is a good average.  This means the liquid in the loop just about makes one circuit per heating cycle. I have monitored the incoming "brine" temp during a normal 20 minutes heating cycle and it stays fairly constant, there is some variation as the pipe runs through shingle and clay (clay is around 9.5 degC and the shingle seems to be around 8.5 degC), However, on a longer cycle where the heat pump goes on to heat the domestic hotwater tank, the runtime can be nearly an hour if the tank is cold. Then I notice the in coming "brine" temperature starts to drop as the liquid starts its second trip round the loop. I assume this is because the plastic pipe is not a particularly good conductor of heat and the liquid takes time to "heat up" which it does during the off time of the pump. My point is this, if as the O.P. said, the idea is to enable shorter loops to be used then this effect will get worse. If you halve the loop length then the temperature drop from the start to the end of the run could well be several degrees, depending on the run time. This will have an effect on the power consumption of the heatpump and could well overide any gains made by any recharging that may, or may not, occur. To make matters worse - if you rely on solar thermal for the heat source for the ORC pump - then on the days when you need the heat the most in the house you will have the least heat input into the ground. As I alluded to above, one of the keys to an efficient and effective GSHP install is a good ground collector, if space is too tight for one then don't fit it - simple. The expense and complication of trying to fit some other system - what ever it is - will not in my opinion have any benefit. At best it will make a compromised system slightly less so.  As Biff said - keep it simple! (all just my opinion).

Roger


Title: Re: Recharging the ground
Post by: stannn on January 29, 2016, 05:38:01 PM
That's a well written and very informative post Roger. :)
Stan


Title: Re: Recharging the ground
Post by: biff on January 29, 2016, 06:41:54 PM
Brilliant post Roger,
                 And it has given me plenty to think about.You have explained it better than anything I have read before.
                                                        Biff


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor on January 29, 2016, 11:55:36 PM
About the only thing I can add, is often the energy of the brine pump is not part of the CoP rating.

Brilliant Post Roger, exactly what the thread needed.

Also found a really good document that contained an eye opener for me, the soil/ trench conditions can effect pipe length by up 50%.
http://www.gshp.org.uk/documents/CE82-DomesticGroundSourceHeatPumps.pdf which is just a great general document

Ignore the ORC and recharging angle as your post surprised me as I had a hunch it was mainly due to the poor thermal conductivity of the ground and never really thought about the plastic pipe itself.
I guess there is always going to be a temperature difference on the first total loop exchange and this is brilliant information.
You stated the ground substrate type, you have the length of coil. If we had temps on extended use of the brine much of that info could be used.
(http://s7.postimg.org/vkoapoep3/Ground_Conductivity.jpg) (http://postimg.org/image/vkoapoep3/)
PE100 Thermal conductivity, W/m–K, DIN 52612 0.38

I was just interested as to be honest I don't even know what the exit temperature of the brine loop is from the GSHP.

From reading I knew you can get localised freezing and overuse can actually seasonally reduce ground temperature, but there doesn't seem to be any figures out there.

Also to be honest I am slightly confused on trench depth as most geological surveys say the UK is a pretty constant 10-12'C at a depth of 15m.
When it comes to GSHP literature often it is said constant 10'C at a depth of 10m but strangely often state a minimum trench depth of 1 -2m in slinky configurations.

Often the 1 - 2m is quoted and use this an an example http://www.kensaheatpumps.com/the-technology/heat-sources-collectors/surface-soil/slinkies/

Roger made a good call by oversizing the system as what the manufactures seem to state seems to be dangerously optimistic.

(http://s8.postimg.org/nmm8yi8fl/Ground_Temp.jpg) (http://postimg.org/image/nmm8yi8fl/)

I think you are right to some respects as the trench requirements for GSHP would seem to be under specced and some of the shallow trench / slinky installs are not much more than a ground solar collector.
The fact that they advise to keep trenches at least 3m apart whilst giving a minimum of 1m depth just doesn't make any sense in my book especially with the nature of heat.
But interesting thread and started to actually talk about figures and installs which is really, really great.    


I started to collect what I could on the thermal conductivity on various ground substrates.
http://www.geothermal-energy.org/pdf/IGAstandard/WGC/2010/2952.pdf
http://www.minersoc.org/pages/Archive-CM/Volume_33/33-1-131.pdf
http://pubs.usgs.gov/of/1988/0441/report.pdf
 


Title: Re: Recharging the ground
Post by: todthedog on January 30, 2016, 07:59:24 AM
What a cracking post Roger.


Title: Re: Recharging the ground
Post by: davec on January 30, 2016, 10:42:27 AM
Quote
... As I alluded to above, one of the keys to an efficient and effective GSHP install is a good ground collector, if space is too tight for one then don't fit it - simple...

Or you can always go downwards... consider a borehole: big collector, small footprint.

Quote
... some of the shallow trench / slinky installs are not much more than a ground solar collector...

Most of the illustrations seem to show ground temperatures as 'seasonal' to -20m, then ~10deg to -100m, then increasing at around 2deg per 100m. However, the heat available in any volume of ground seems to depend very much on region and soil / rock / ground-water conditions, i.e. there is no reliable broad-brush rule; you need to do the geology and, as Roger says, err on the big side while the kit is on site.

DaveC.


Title: Re: Recharging the ground
Post by: billi on January 30, 2016, 11:26:13 AM
Is it   over £10000  for GSHP to install ?

http://www.energysavingtrust.org.uk/domestic/ground-source-heat-pumps

Quote
Costs, savings and financial support
Costs

Installing a typical system costs around £11,000- £15,000. Running costs will depend on a number of factors including the size of your home and how well insulated it is.


I do not understand why so expensive ...





Title: Re: Recharging the ground
Post by: Fionn on January 30, 2016, 11:35:19 AM
Well the pipe is about €2/metre in Ireland Billi.
The pumps are in the 5k ballpark and the balance is civils and installation /commissioning I guess.


Title: Re: Recharging the ground
Post by: biff on January 30, 2016, 11:39:21 AM
I still say that a lot has to do with the soil and how it retains or repels the heat.
     I take on board everything that Roger has written and will hold my anti-GSHP rants in check in the future. Yes there is a place for such systems but some means of checking the soil or subsoil is essential to eliminate the gamble side of it.
    Around here, the bog is seen as a type of refrigeration . Indeed we have many cases of bog butter being discovered,some as old as 3,000 years and up to 100lbs in weight, in good condition.
  Then the lakes that dot these bogs are so cold that diving below 6ft will leave you numb in the grip of a frozen vice,unable to move a limb but just float to the top and wait to the top layer warms you up and this in mid summer. I know this because as kids we would set out to swim these lakes and visit the small islands in them. So you could feel like a dip, find that the water was quite acceptably warm and dive in only to discover that it was ice cold 4ft below the surface but we had all been well warned and knew not to panic and also keep an eye out for each other. Back then,we were never out of the water. Rivers ,lakes and the Sea and tales of Huckleberry Finn. We grew up with it and learned from it and luckily we all escaped our narrow squeaks.
  So I know it is dam,d cold below the surface here. I am not making excuses for my ignorance on the subject but a lot of our houses are built on the bog and deep black peat is all around. Now in many ways this is a good thing because the house owner would not have far to go to cut the turf for the fire. But it is dam,d cold a few feet down and getting heat out of that lot other than the fire,is a mystery to me.
 So maybe it is possible that the unhappy customers ,got the pipework wrong, got the soil wrong, got the whole installation wrong and were oversold the lot but the bottom line was,they were not happy.
                                                                                  Biff


Title: Re: Recharging the ground
Post by: Fionn on January 30, 2016, 12:01:11 PM
Hi Biff,
From an Irish perspective heat pumps in the early days were sold by a lot of less than proficient installers that didn't understand how to size or install them themselves. Furthermore they were installed in the wrong type of house and end users were not sufficiently informed as to how best to operate them.
HPs are at their most efficient when the temperature difference between the source (ground or air) and destination (house is minimised).
As has been mentioned this means underfloor heating is the best option. The surface area is so great that acceptable heat output can be realised with flow temps as low as 30 degrees.
Now this is all well & good but I believe the following issues have been encountered in early installs in Ireland:
1. Ground loops undersized - the installer cuts the length to boost profits or cut out the competition.
End result is that the incoming flow temperature drops & efficiency decreases -> bigger bills.
2. Poor insulation and/or air tightness in the house - heat pumps are generally set up to maintain a constant temperature in the house 24/7. If your house build isn't up to scratch & you try to increase your flow temps for a blast of heat when you come home you'll be left poor & cold!

Overall I really like the concept but nowadays with the high levels of thermal performance available in houses I think the capital is perhaps better spent on insulation & air tightness. At near passive levels a small air source unit may make more sense even if they don't last very long.

Finally it can be hard intuitively to understand that there is heat in that bog or freezing lake. We think of anything less than our body temperature as having no heat in it. In truth everything above absolute zero has heat energy in it.
If you get 1kg of beef from the butchers fridge & put it in the freezer when you get home, a portion of the heat in it can be felt a while later in the coils of the freezer. That same energy will have to be replaced by the air in your kitchen a few weeks later when you thaw it out for your dinner!


Title: Re: Recharging the ground
Post by: dhaslam on January 30, 2016, 12:45:08 PM
The pipe I used  was 1.5"  hydrodare ducting and cost  €186  euro for 150 metres, it is a bit thinner than the equivalent water pipe.   The leads to the heatpump are  3/4"  qualpex.  The connectors  were  between the  hudrodare were 27€ each.     I am only using 150 metres total collector for a 3kW  but it seems to be adequate  even when the  source temperature is similar to ground temperatures at present.         


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor on January 30, 2016, 07:44:34 PM
The loop once installed should be of PE100+ pipe and if vertical maybe even higher rated pipe should be sourced as the depth and pressure increases.

The pipe loop install is guaranteed for 50 years and is expected to last 100 and yeah it is expensive, but in that sense compare it to the cost of 3 or 4 Solar PV installs over that time.

http://www.gshp.org.uk/documents/CE82-DomesticGroundSourceHeatPumps.pdf is a great source of infomation.

Quote
Information on the thermal properties of the ground is needed for determining the length of heat exchanger required to meet a given energy load..
Most important is the difference between soil and rock, as rocks have significantly higher values for thermal conductivity. The moisture content of the
soil also has a significant effect as dry, loose soil traps air and has a lower thermal conductivity than moist, packed soil. Low-conductivity soil may require
as much as 50 per cent more collector loop than highly conductive soil. Water movement across a particular site will also have a significant impact on
heat transfer through the ground, and can result in a smaller ground heat exchanger. A geotechnical survey can be used to reduce the uncertainty associated with the ground thermal
More accurate information can result in a reduction in design loop length and easier loop installation. The British Geological Survey (http://shop.bgs.ac.uk/georeports/) has an on-line service offering simple, or more
detailed, GeoReports giving information on local ground conditions relevant for ground source heat pumps. (A basic GSHP report suitable for a domestic application currently costs £50 – and is available online.)
For large schemes where multiple boreholes are required, a trial borehole and/or a thermal properties field test may be appropriate.  

A shallow trench especially the slinky type is a seasonal heat store that is recharged by the sun. Its probably why we get quite a few posts of problems north of the border.
Generally with shallow trench systems much can be ascertained by grabbing a spade and digging a test pit, high water content can be very beneficial, water flow can carry that heat away.

You seem to have a combination of bad and worst case soil Roger where clay is great stuff when not dry, but the shingle could be very prone to water flow.
Seems like your intuition got it perfect though :)

As for the OP in terms of shallow trench system we are already recharging the ground. I thought I would mention as it occurred to me in terms of cost that a secondary pipe could be used to dump waste heat.
I was just looking at ORC systems which have a cold loop which is dumped to air in all cases I know. It just occured to me that the 45'C waste heat could be dumped into a GSHP loop as its waste heat and otherwise going into the atmosphere.
Also the colder return of a ground source loop would be beneficial to the efficiency of the ORC.
Maybe its just a matter of divertor valves / heat exhanger where brine loop and pump is shared between the two for extra economy.

Roger many thanks for your brilliant post, I do disagree though as an ORC and GSHP are extremely complementary products as dumping that waste heat is the primary concern of the ORC. Returning colder than air temps is a Brucie bonus. So is any increase in seasonal or daily ground temp for the GSHP is also a bonus irrespective of 'recharging' efficiencies.
I would never suggest using a solar array to capture premium high quality heat and dump it into a heat store as poor as the ground. That would heat a dedicated heat store that is insulated and capture heat around an area of 150'C.
Its very similar to Biffs gasification thermal store but specifically a daily recharge, supplied by a low cost oversized solar thermal collector array.
As far as I know we have never had a panel that is suitable as designs have always been hampered by focus on direct temperature use and water.
The ORC solves a problem of stagnation and the heat capacity limits of the thermal store and the GSHP is there for when the sun don't shine or when the useful capacity of the heat store has been exhausted.

The biggest benefit of a Medium temperature solar thermal generation system is its energy profile that is delayed by several hours from collection and its a hugely complementary system to PV and is the only way to balance solar energy without the need of extremely expensive and short life electrical storage.
Its that generation offset and ease of short term storage that makes that energy extremely cost effective, but like PV needs much investment to gain economies of scale.
Also its capacity in terms of heat is way in excess of PV with heat being 85% of domestic energy use, 40% of overall.  



Title: Re: Recharging the ground
Post by: billi on January 31, 2016, 07:12:43 AM
Quote
The biggest benefit of a Medium temperature solar thermal generation system is its energy profile that is delayed by several hours from collection and its a hugely complementary system to PV and is the only way to balance solar energy without the need of extremely expensive and short life electrical storage.
Its that generation offset and ease of short term storage that makes that energy extremely cost effective, but like PV needs much investment to gain economies of scale.
Also its capacity in terms of heat is way in excess of PV with heat being 85% of domestic energy use, 40% of overall.  

Ok ,  lets talk about those cost   of PV  , battery   and a heatpump   (without install)

A 40 kWh  battery costs £2000
A 10 kW PV          costs £12000
An Aquarea 6kW    costs £2500
HC Monoblock ASHP


The ASHP  COP is over 2.5  , so that 40 kWh  battery can deliver  (when cycled down to 50% DoD)  50 kWh  of heat  about 3000 times  so 150000 kWh  so this then means the stored energy in the battery is costing about .... under 2 p

The PV is  delivering  on average  over  10 kWh in winter in the UK  per day makes 25 kwh heat a day  (with a CoP of 2.5)


the average  UK  household consumption per year on gas is about  12,400kWh   or devided by CoP of 2.5  about 4960 kWh heating/hotwater  electricity need    ( for the whole year !!)

Quote
In the period between November 2014 and October 2015, the annual average dual fuel customer bill in the U.K. was £1,326 as can be seen in the table below (source: Ofgem).

http://www.thegreenage.co.uk/how-much-energy-does-my-home-use/  

Offer   a fair trade selling surplus PV (FIT)  or/ and  charge  the electric car 

.....







Title: Re: Recharging the ground
Post by: Stuart Ian Naylor on January 31, 2016, 08:50:26 AM
Keeping with what I have been writing about and its GSHP as ASHP apart from you choosing it because it has a lower CoP can not utilise the solar dumping that I said could be optional. (Also to be honest not a fan of ASHP, in the UK at least, not really a big fan of GSHP. But when the sun don't shine you have to have a contingency or as a system it doesn't work)

What I will say before you get to price is how long will that battery work for? Is 40Kwh storage enough for worst day scenario's? Is 10Kw PV enough to supply this? Also with capacity loss over time what level do we overspec to?

Would be good if someone could use real heat requirements run off electricity only and the required spec for the worst (coldest day) which unfortunately has the least solar energy available.

As that is the problem as much of the cost is based on expected length of life and specifying against worst day scenarios.

The GSHP really shouldn't be part of the comparison as a solar thermal system can capture enough heat as in terms of heat it is massively more efficient in capture than PV.
But even then maybe we should have a backup and irrespective of PV or Thermal either add the cost of the GSHP or don't put it into the comparison.

The recharging the ground thread was purely about GSHP and that waste heat of some sort could recharge the ground to a certain level.
I used an ORC as the ORC cold loop and GSHP brine loop are extremely compatible, but it was just an example of recharging the ground with waste heat and not a specific solar thermal example.

Solar thermal could also run without an ORC and just dump summer excess, or be curtained.

So I think we need to state clearly what we are making a comparison on.

Then also state expected life time and maintenance as with 10 year thermal fluid changes and 20 year tube replacements its going to last similar to a GSHP collector pipe 50 - 100 years as its just pipe.

So are we going to compare the two systems over a 100 year period and match it to the structure they are incorporated into?

As yeah this would be a really good exercise as both systems have perishable items that need to be taken into account.    

What you think? Do you think that would be a better comparison or is the expected life expectancy of housing @ 100 years too short?


Title: Re: Recharging the ground
Post by: billi on January 31, 2016, 11:10:28 AM
Stuart ,  i  guess its  not possible or granted  to heat a home with those 10 kW PV  that i mentioned , it was just a  calculation    to compare  the costs towards a typical GSHP install price

Quote
The GSHP really shouldn't be part of the comparison as a solar thermal system can capture enough heat as in terms of heat it is massively more efficient in capture than PV.
But even then maybe we should have a backup and irrespective of PV or Thermal either add the cost of the GSHP or don't put it into the comparison.

I see that differently , cause PV replaces  fossil fueled  electricity  during the summer  and paired with a heatpump  more efficient than a  solar Thermal  idea


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor on January 31, 2016, 11:54:54 AM
We all see things differently and this is why I see solar thermal as a complementary option.

SRB Energy managed .64MWh/m2 with there solar.

Solar thermal with available space and our low insolation levels can still heat a home and not require electricity in the winter, whilst providing generation with summer excess.

PV is just not efficient enough per m2 irrespective of how cheap it gets, because of regions of low insolation.

Most of our energy usage is heat and it seems perverse to change light (heat) into electricity to make heat, or at least blinkered that the non heat energy (15%) in someway is doing something to replace fossil fuels.

Its just a shame we never had a panel that was really suited for anything more than simple small DHW installs.

A more commercial, elevated temperature collector would not be much more than what is available and could provide much difference.
The biggest thing is the simplicity to store heat over short durations and release that energy several hours from collection. That is a huge advantage with solar thermal and complements PV by providing a much wider usage spread.
That is of huge value, but never really fitted the bolt on consumer appliance world that is PV dominated.  


Title: Re: Recharging the ground
Post by: dhaslam on January 31, 2016, 12:52:46 PM
The GSHP really shouldn't be part of the comparison as a solar thermal system can capture enough heat as in terms of heat it is massively more efficient in capture than PV.
But even then maybe we should have a backup and irrespective of PV or Thermal either add the cost of the GSHP or don't put it into the comparison.
[/color]

In a combined PV/GSHP  system the energy from PV is mostly used just to extract heat from the source.     Thermal panels on their own will not heat a house on their own  but PV is  slightly better in  low light conditions so in combination with a heat pump it would be close to  being  practical for off grid systems.  Of course there would be a large surplus  of unused electricity in summer.   

Probably a better option is  Solar thermal system with  moderate heat storage capacity.  With my present panels  the heat store should start to gain temperature in mid February, previously it was the end of February.   If I had ten of the same vacuum tube panels instead of three  the store would probably gain temperature in mid January.      However it is hard to predict whether the  store would be hot enough for direct underfloor heating.     That is why I opted for a mixed system of heat pump and smaller number of panels.      The heat pump cost was  the same price as five panels.     


Title: Re: Recharging the ground
Post by: billi on January 31, 2016, 01:02:00 PM
Quote
SRB Energy managed .64MWh/m2 with there solar

 1 m2  PV    or approx  220 watt  is  producing  in  central Europe  about 220 kwh  per year  multiplied by pessimistic CoP of 2.5 of the ASHP heatpump    is then  .55MWh/m2


And the price is similar  per m2 including the heatpump on the PV part


If i stay at my suggested 10 kW  PV  ....  and i still can decide  to use those surplus units to charge  a battery , an electric car , the national grid ,  my TV  and if i have nothing better to do then  the ground

Billi




Title: Re: Recharging the ground
Post by: davec on January 31, 2016, 02:44:25 PM
Quote
...
Would be good if someone could use real heat requirements run off electricity only and the required spec for the worst (coldest day) which unfortunately has the least solar energy available.

Would the numbers in http://www.navitron.org.uk/forum/index.php/topic,21987.0.html (http://www.navitron.org.uk/forum/index.php/topic,21987.0.html) help at all?



Title: Re: Recharging the ground
Post by: Bodidly on January 31, 2016, 03:19:20 PM
Not read everything but hows about a polytunnel to recharge the ground? Simple and guaranteed to work to some extent.


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor on January 31, 2016, 06:07:34 PM
The GSHP really shouldn't be part of the comparison as a solar thermal system can capture enough heat as in terms of heat it is massively more efficient in capture than PV.
But even then maybe we should have a backup and irrespective of PV or Thermal either add the cost of the GSHP or don't put it into the comparison.
[/color]

In a combined PV/GSHP  system the energy from PV is mostly used just to extract heat from the source.     Thermal panels on their own will not heat a house on their own  but PV is  slightly better in  low light conditions so in combination with a heat pump it would be close to  being  practical for off grid systems.  Of course there would be a large surplus  of unused electricity in summer.  

Probably a better option is  Solar thermal system with  moderate heat storage capacity.  With my present panels  the heat store should start to gain temperature in mid February, previously it was the end of February.   If I had ten of the same vacuum tube panels instead of three  the store would probably gain temperature in mid January.      However it is hard to predict whether the  store would be hot enough for direct underfloor heating.     That is why I opted for a mixed system of heat pump and smaller number of panels.      The heat pump cost was  the same price as five panels.    

Sort of agree with you as it is possible to heat a solar capture optimised home with solar PV as an average family home could have 120m2 of capture area. Yeah south aligned mono pitch roof, 3 storey single aspect homes are not everybody's cup of tea. But totally using a south face of wall and monopitch roof in conjunction with passivhaus construction, you could :)

But yeah the reality is monopitch 3 storey single aspect buildings are as likely as passivhaus and are as likely as mass solar thermal adoption.

Where I totally disagree with you is that solar PV is more efficient than solar thermal at low light levels. As this is where my real beef is at, its not that solar PV are a bad technology, its just the energy profile of the source is a really bad profile which is a bad fit on lifestyle.
My beef is mainly with what have been atrocious solar thermal designs that are probably much worse than PV because at low light there is probably little or no heat difference.
The whole assumption of water/glycol heat carrier in a direct heat application for the purposes of DHW has created a market of a certain type of solar thermal panel only.
Doesn't mean other types where not possible and generally what happened was the worst type of red tape. Rather than an open market rewarding renewables by results we had government officials create an approved technology list.
Absolute disaster for innovation and it got even worse as even on the approved technology list FiTs where tiered and technology wasn't even.
Access to list meant you needed adoption and the paradox was you couldn't get adoption because there was no FiT from being on the list.

Ritter solar did a panel that came near and Navitron have that which is actually better but still has its feet stuck in the waters of DHW.

SRB Energy have a panel that can use low light and I use that and a quote from them that its not Solar Thermal that is bad in low light just conventional design.
Quote
The collector is particularly indicated for areas with low solar irradiation, as in Central Europe, where the fraction of diffused light is large and conventional solar collectors provide a reduced performance.
   


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor on January 31, 2016, 06:26:14 PM
Not read everything but hows about a polytunnel to recharge the ground? Simple and guaranteed to work to some extent.

To be honest recharging the ground and using the ground as a heat store with a polytunnel could be a great idea in terms of effectiveness. It is being used as a heat source and can be recharged, so I don't see why not.

Bore holes are extremely expensive and again maybe its economies of scale that should of been invested in.

Horizontal trench systems are already being recharged by the sun and I guess your poly tunnel would decrease the area needed or increase CoP and make a great area to grow in.
Not a bad idea at all, but in high density housing situations like much of the UK maybe not.
In the small area's widely available we are talking bore holes or systems pre build that run under the structure and surrounding space. Not everybody has 400m2 spare in one patch or neighbours that will tolerate polytunnels .

But yeah poly tunnels over a GSHP horizontal loop would work and that is a fine sustainable idea for those with the space and lack of shading to do it.

In the recharging the ground thing I was just trying to bring attention, that waste heat could be used to recharge a ground loop.
Maybe reduce size requirements so cheaper horizontal systems could operate with less area.


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor on January 31, 2016, 06:39:21 PM
Quote
...
Would be good if someone could use real heat requirements run off electricity only and the required spec for the worst (coldest day) which unfortunately has the least solar energy available.

Would the numbers in http://www.navitron.org.uk/forum/index.php/topic,21987.0.html (http://www.navitron.org.uk/forum/index.php/topic,21987.0.html) help at all?



You have got a great vertical bore hole where the constant earth temperature is doing a great job.
I was looking at the horizontal cheaper systems that seem to have much more problems.
Would seem your system is extremely well specified but guess waste heat could be dumped there is it was available for short term localised recharging.

I really do think vertical bores are superior because of the constant background temperature and the GSHP is geothermal rather than the horizontal solar versions.
Only downside with deep vertical is the pressure of the static head and reduction in the possible life expectancy of the piping, which fingers crossed will be much more than 50 years.

Could do with a bodged job where the bore is too shallow and localised freezing and seasonal effects are being observed.


Title: Re: Recharging the ground
Post by: davec on January 31, 2016, 09:06:59 PM
Quote
...the GSHP is geothermal rather than the horizontal solar versions.

Nope, it's still solar, unless you go very far down. The heat is conducted in from the volume of soil / rock / water surrounding the collector so the more conductive the material, the better it is for GSHP because it recovers quicker. I suggest this 'good' rock might be just as keen to conduct in the other direction, thus dissipating any extra heat you inject from your recharging the ground thing.


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor on January 31, 2016, 09:52:24 PM
Below 10m is geothermal as it is constant irrespective of seasonal air temp or as years pass by. So its the temperature of the geology and not the above environment (Unless climate change or distance to the sun...). Well GSHP sources say 10m, geological sources say 15m.
Deeper you go, it just gets hotter, but only 2.6'C per 100m.

Yeah good rock is a better conductor than dry soil, but for daily localised waste heat recharges a certain amount will be recaptured in CoP.

I was thinking more along the lines of systems that are very dependent on solar recharge such as horizontal where pipe lengths could be decreased.
Its possible and not sure of what extent as it is dependent on time of recharge to extraction and amount with all the nasty calculations of ground thermal conductivity thrown in.

Both are possible.

https://shop.bgs.ac.uk/GeoReports/examples/modules/C011.pdf


Title: Re: Recharging the ground
Post by: marshman on February 01, 2016, 11:34:51 AM
Thank you all for the comments on my last post. I'm not an expert by any means but am learning fast! As with anything new I like to understand what is going on - I was obsessed by the output from my PV for many months - noting daily production vs temperature, wind etc. The novelty does wear off eventually when something new comes along :), Hopefully the same will apply to the GSHP. Thing is there's so much more to look at and measure!. This thread has certainly revealed quite a lot to me and I think I will soon start another thread with my findings.

Biff carry on speaking as you find, it keeps everyone honest and "on their toes" and guards against any new clothes the emperor may get!, I find your posts interesting and thought provoking because I can see they are mainly based on your own practical experience. It would be good to find out why some of those  GSHP installs you have been told perform so poorly, you never know the installers may have been really incompetent and in some cases it just maybe the system hasn't been set up correctly.

Anyway after my initial post I have been thinking and doing some basic measurements - at this stage they are crude and I have decided I need to make a multi channel data logger for temperatures and also power recording.  Below are displayed 2 graphs. The first shows incoming "brine" temperatures on a normal 20 minute (ish) heating run of the heat pump. I did 3 runs yesterday - the first was normal with all four loops open (1200m of ground collector), second was with 2 loops closed off (600m) and last was with three closed off so only 300m of ground loop.  The flow rate through the heat pump was consistent at around 30 litres per minute - needed to keep the delta (temperature drop across the heat exchaner) to 3 degrees.  So for four loops flow rate in each loop is just under 8 litres per minute, two loops around 15 litres per minute in each loop, and the single loop a whopping 30 litres per minute. I verified this a) by monitoring the delta (brine in to brine out temp difference) and b) by looking at the crude flow indicators on the loops. The results are very clear to see:


(http://s12.postimg.org/x5aatxuu1/gshp_loop_length_compare.jpg) (http://postimg.org/image/x5aatxuu1/)

With all four loops there is little temperature drop. This I would expect as 300m (1200/4) of loop at just under 8 litres per minute takes over 30 minutes for the liquid to make a circuit - longer than this cycle. With two loops the flow rate is doubled and you just start to see the brine temperature drop as the liquid completes a complete circuit. The dramatic one is on the single 300m loop where the fast flow rate means the liquid completes nearly 2 circuits. The final brine temperature was 6.1 deg C. There are two things to note here, a) shorter loops have less liquid or "capacity" and the pipe is a poor conductor so takes time to "recharge" so less capacity means the temperature will drop more quickly and b) I think the faster flow rate through a single loop reduces the time the liquid is in the loop hence the time for the ground to warm up the liquid. A couple of quick conclusions here - 1) more capacity (bigger diameter pipes?) and b) slower flow rates (may be several shorter loops?) could improve things on marginal installs without actually increasing the loop length.

Second observation was a long run with all four loops where the GSHP was also heating the domestic hot water tank.



(http://s11.postimg.org/wls2wl073/gshp_long_run_1200m_cop.jpg) (http://postimg.org/image/wls2wl073/)

This was a bit rushed and the graph starts after the pump had been running for about 15 minutes heating the house. The  Pink line on the graph is the output temperature from the heat pump, It dips as it switches from heating water to heating the house and then jumps as it switches back to heating water. The interesting thing to note here is how the power consumption increases with rising output temperatures. At the end of the cycle the power consumption has increased from 2.5kW to 4.1kW a massive 64% increase.  Most of the time driving the underfloor heating the maximum temp is less than 40 deg C. (Today with an outside temp of 10 deg C the maximum is 35 deg C, and then only for a few minutes before it switches off).  If you have a system driving radiators then flow temps are far higher and the efficiency will suffer massively. One other thing to note is that even after an extended run where the liquid is on its second circuit the incoming brine temperature doesn't show the  drops shown in the other graph on the "short" loops. This can only be down to the lower flow rates in the individual loops, another reason for having multiple loops.

COP figures are usually quoted under specific conditions such as 0 deg C brine, 35 deg C flow etc. In many ways they are like the EU fuel consumption figures for cars. I am sure a heatpump can be optimised to perform really well at one set of temperatures. Change anything from these standard conditions, i.e. lower input temp or demand higher output temp and all bets are off!

On the topic of the thread I think the most cost effective way to improve GSHP installs and performance is to a) get the ground loops right and b) ensure you have an efficient heating system that runs at a low temperature. Anything else like methods of recharging the ground on a daily basis, or erecting poly tunnels is just an expensive distraction from getting the basic right. It is interesting to ponder these things as sometimes good thing come out, but in this case I think the extra cost and complexity (a poly tunnel doesn't last for ever!, and laying extra pipes costs money as would any scheme to use the same pipework but with some valves and clever plumbing).

On the second point above regarding flow temperatures for the heating. The original design for my Under floor heating called for flow temperatures around 46 deg C. BUT and it is a big BUT, the assumption was the heating would be used in the conventional way, i.e. on a timer and on for a time in the morning and a few hours in the evening. By making it run 24 hours a day the temperatures required to keep the house warm drop massively, right now the water circulating around my floor is 25 deg C. Once every 1 1/2 hours or so the GSHP heats this back up to 35 deg C (or so depending on the outside temp). So by moving away from the mind set of timers and having the heating on just in the evening the already good match of underfloor heating can be made better and higher efficiencies achieved. This is with the proviso that the house is well insulated and relatively draught free - which we all know (or should know) anyway.

When I get some more accurate figures I will start a new thread, please bear in mind the graphs above are a bit rough and ready.

Roger



Title: Re: Recharging the ground
Post by: Mikel on February 01, 2016, 12:30:21 PM
Roger,

Thanks for your very interesting posts.

I am uploading an image for yesterday's heating from our GSHP. Just a test as I haven't done this before.

(http://s14.postimg.org/5e0ff243x/image.jpg) (http://postimg.org/image/5e0ff243x/)


Title: Re: Recharging the ground
Post by: billi on February 01, 2016, 01:29:25 PM
Quote
On the topic of the thread I think the most cost effective way to improve GSHP installs and performance is to a) get the ground loops right and b) ensure you have an efficient heating system that runs at a low temperature. Anything else like methods of recharging the ground on a daily basis, or erecting poly tunnels is just an expensive distraction from getting the basic right. It is interesting to ponder these things as sometimes good thing come out, but in this case I think the extra cost and complexity (a poly tunnel doesn't last for ever!, and laying extra pipes costs money as would any scheme to use the same pipework but with some valves and clever plumbing).


I quite agree on  that , that one can overdo it ....  i mean  of how much  kWh electricity for a GSHP per year do talk about in a  modern home ?  Usually they have a CoP of over 4  


What i do  like is combining it with solar thermal panels   and i know one install here in Ireland  intalled in a big renovated  farmhouse  15 years back
The heatpump senses  where to take the heat from , when the solar-collector delivers a higher temp , then the heatpup uses that first , if it falls below the temp of the soil-collector  then  switches over
I installed the pipe inder a 400 m2 Swimming pond

There are fieldtests of more modern version of this idea  that proof   a CoP of over 5.5

PVThermal hybryd panels would be a class act for that idea  ,   as well for Water based heatpumps  and Airsource heatpumps

Billi

Idea like this http://www.solar-bazaar.com/menuis/Wiosun-PV-Therm-Datasheet.pdf


Title: Re: Recharging the ground
Post by: Mikel on February 01, 2016, 04:08:39 PM
In view of the fact that Roger is beginning to post some actual data and the various comments about not using heat pumps with radiators, I hope you won't mind if I post some of our actual performance for our GSHP working with oversized radiators.

Our property is a bungalow of hybrid origin. It was originally a 1984 2-bed timber-framed bungalow extended in 2006/7 by the previous owners to give a 4-bed bungalow. Total floor area 145 sq.m

We have replaced one bedroom to create a dining room which involved knocking down one internal wall. We have installed a ground mounted PV system, 5.7 kW solar thermal panels on the SSE facing roof and GSHP with 3*40m slinkies laid horizontally 1.2m wide, 1.2m depth. The GSHP does both heating and hot water to 50C. The hot water tank (new) is 305L.

We had a very long discussion with our installer on the pros and cons of slinkies versus continuous loop versus borehole. Our installer was strongly of the opinion that provided the ground collector was correctly sized then it didn't really matter which method was used from the heat performance perspective. The installer advised that boreholes were very much more expensive and slinkies avoided the need to join pipe work underground.

The GSHP and solar thermal system was completed in March 2013.

In January 2014, we joined a DECC sponsored trial of heat pump control systems. This meant that we had an electricity meter put on the heat pump, a heat meter installed on the heat pump and various temperature sensors put up around the house. There were a number of modifications made to the heat pump (made with the agreement of the manufacturer so that there would be no issue with warranty).

In August 2014, we would in a wood burner in the lounge, with prior consultation of the organisation running the trial.

So how does this all work in practice?

For the first year we set the room temperature to 18C and total GSHP electricity consumption was approximately 1600 kWh. For the second year, I set the room temperature to 0.5C above that which gave rise to complaints!! This has turned out to be 17C. GSHP electricity consumption for the second year is about 1400 kWh.

A major reason for the drop in electricity consumption for the second year has been this milder winter. For example, GSHP daily electricity consumption for Dec 2014 was 10.09 kWh and for Dec 2015 6.45 kWh.


The overall figures for electricity consumption for domestic hot water are:

2014
GSHP 179 kWh
Immersion 100 kWh (16 times at once per week to heat to above 60C to control legionella)

2015
GSHP 224 kWh
Immersion 94 kWh (15 times at once per week)

We find that we begin to use the GSHP regularly for DHW from about the fourth week in October until mid/late Feb and the Immersion for a similar period.

So how do the CoP figures work out?

It is not worth quoting figures for the CoP outside of Nov-Mar as the use becomes much more intermittent and there appears to be a pump running on occasion during the day over the Spring/Summer/early Autumn months even when the heat pump is not on and consumes between 0.1-0.3 kWh/day. We have put this down to some wiring with the solar thermal system being  on the same circuit as the GSHP electricity meter.

Since March 2014, the trial control system has been in operation. We had about one month of data under the original control system, which gave a CoP of 3.2. I haven't bother to quote the CoP for Mar 2014 because it was  right at the start of the trail.

2014-5 Monthly CoPs

Nov 2014 3.59
Dec 2014 3.50
Jan 2015 3.46
Feb 2015 3.47
Mar 2015 3.46

2015-6 Monthly CoPs

Nov 2015 3.52
Dec 2015 3.57

I don't think these figures are bad for a radiator system although I would expect an underfloor system to perform even better.

Incidentally, there was one week in November 2015 when we just used the heat pump for DHW. The CoP for that week was 2.98.

and now for some pictures

This was yesterday's run and the effect of the wood burner is quite noticeable (after 6pm)


(http://s22.postimg.org/gsst7e8nx/image.jpg) (http://postimg.org/image/gsst7e8nx/)


And this was for the 28th January. We had been away for a few days and this shows how the house heats back up.



(http://s8.postimg.org/ap8zrumch/image.jpg) (http://postimg.org/image/ap8zrumch/)


And this shows a month of heating

(http://s10.postimg.org/yibr0nst1/image.jpg) (http://postimg.org/image/yibr0nst1/)


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor on February 01, 2016, 05:42:38 PM
Thought I would post this as the elevated temps of DHW can cause problems with CoP output.

http://www.kensaheatpumps.com/new-hybrid-gshp-engineered-by-kensa/

Quote
Kensa’s twin compressor Hybrid heat pump harnesses the properties of two separate refrigerants in its compressors to deliver heat outputs similar to those provided by Kensa’s Standard models, along with hot water temperatures typically produced by their High Temperature models.

Its great to get some figures and some brilliant data being posted. I am confused slightly to the figures we are getting as I thought there would be an initial sharp drop in temp and then a noticeable leveling of brine input temp.
What I expected is the static loop has stood still for some length of time and its at the same temp as the geology.
Its pretty damn cold at the moment so maybe a continuous run for 3 or 4 loop circuits, might give more resolution, have a Bali theme night or something :)

Would be good if you copied what the PV guys do and maybe post your monthlies from a group of GSHP enthusiasts. If you can in any way simulate local freezing by extended use, please do.     


Title: Re: Recharging the ground
Post by: Fionn on February 01, 2016, 06:05:34 PM
Great data Mikel, nice to hear that the oversized radiators are proving effective.

Ian, The stable input temperature just indicates that the ground loop is more than sufficient for the heat demand on it.


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor on February 01, 2016, 08:30:57 PM
Great data Mikel, nice to hear that the oversized radiators are proving effective.

Ian, The stable input temperature just indicates that the ground loop is more than sufficient for the heat demand on it.

Marshman, Roger :) posted some mega details, that actually confused me.
What he did by deliberately cutting off loop sections was absolute gold in terms of info.

I said it earlier but if we got data from a bodged GSHP that returned data of freezing characteristics, then actually that would be really useful, even if a bit upsetting for the owner.

The brine cooled solar PV system Billie showed is a renewable symbiotic relationship where the cold and heat are shared and simultaneously benefit both systems.  

ORCs and Sterlings are the same and recharging the ground is very possible in a certain manner especially if instantaneous or of a short duration between charge and extraction.


Title: Re: Recharging the ground
Post by: mike7 on February 02, 2016, 12:57:41 AM
Below 10m is geothermal as it is constant irrespective of seasonal air temp or as years pass by. So its the temperature of the geology and not the above environment (Unless climate change or distance to the sun...). Well GSHP sources say 10m, geological sources say 15m.
Deeper you go, it just gets hotter, but only 2.6'C per 100m.
Probably it matters not a cuss, but the reason it's constant at 10m or so is because that's deep enough to damp out the seasonal variations. If the seasons were longer you'd have to go deeper to find a steady temperature. The reason it is 10'C or so is because that's the average surface temperature over a year, allowing 0.26'C for the geo bit.
 
Staying in nerdmode, if the temp gradient is 2.6'C/100m and the conductivity is 3W/mK, geothermal heat will be escaping to the surface at 0.072 W/m2, which means 14000 m2 per kW. Phew - that's slow!. No wonder the world is still hot inside. You'd need a lot of borehole for true geothermal, so I'd say a real life one is mostly solar and only with a significant bit of geo if its really deep.

...And another thing.  The effectiveness of ground heatstores is dependent more on the diffusivity of the ground, or conductivity divided by the heat capacity per cube, rather than just the conductivity alone.


Title: Re: Recharging the ground
Post by: billi on February 02, 2016, 03:57:24 AM
Great data Mikel, nice to hear that the oversized radiators are proving effective.

Ian, The stable input temperature just indicates that the ground loop is more than sufficient for the heat demand on it.

Marshman, Roger :) posted some mega details, that actually confused me.
What he did by deliberately cutting off loop sections was absolute gold in terms of info.

I said it earlier but if we got data from a bodged GSHP that returned data of freezing characteristics, then actually that would be really useful, even if a bit upsetting for the owner.

The brine cooled solar PV system Billie showed is a renewable symbiotic relationship where the cold and heat are shared and simultaneously benefit both systems.  

ORCs and Sterlings are the same and recharging the ground is very possible in a certain manner especially if instantaneous or of a short duration between charge and extraction.


I would honestly like   to have a better translation program .....    but this did not work  and they talk about an Ice storage idea with a CoP over 4  and the overall over 5.5   with the hybrid solar thermal  connected  and this all with system losses  excluded

http://www.agenda-energie-lahr.de/Ph2_SolarWP-GOT.html    paste it in guugle tanslate  , perhaps it makes more sense then


But i follow that since years and    perhaps  therfore i am a PV fan boy   cause its black, cheap and  works better if cold down by a heatpump 


Regards Billi


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor on February 02, 2016, 07:54:08 AM
Below 10m is geothermal as it is constant irrespective of seasonal air temp or as years pass by. So its the temperature of the geology and not the above environment (Unless climate change or distance to the sun...). Well GSHP sources say 10m, geological sources say 15m.
Deeper you go, it just gets hotter, but only 2.6'C per 100m.
Probably it matters not a cuss, but the reason it's constant at 10m or so is because that's deep enough to damp out the seasonal variations. If the seasons were longer you'd have to go deeper to find a steady temperature. The reason it is 10'C or so is because that's the average surface temperature over a year, allowing 0.26'C for the geo bit.
 
Staying in nerdmode, if the temp gradient is 2.6'C/100m and the conductivity is 3W/mK, geothermal heat will be escaping to the surface at 0.072 W/m2, which means 14000 m2 per kW. Phew - that's slow!. No wonder the world is still hot inside. You'd need a lot of borehole for true geothermal, so I'd say a real life one is mostly solar and only with a significant bit of geo if its really deep.

...And another thing.  The effectiveness of ground heatstores is dependent more on the diffusivity of the ground, or conductivity divided by the heat capacity per cube, rather than just the conductivity alone.

I think its important to distinguish between vertical and horizontal GSHP coils. If it is geothermal or not is a bit of a pint half full argument as the average seasonal air temp is pretty constant or otherwise we get a bit panicky and call it climate change.
Deep bores => 15 - 200m+ can be said to have a constant ground temperature. Horizontal =< 15m follow the above air temperatures.
That is really important as the bore loop can be used to provide cooling to renewables to increase their efficiency. This differs from any previous seasonal heat store that used the used the bore for extracting warm energy which isn't that efficient.
So its important to differentiate between Vertical and Horizontal in design and data capture and Geothermal and Solarthermal pretty much describe what is going on with vertical and horizontal bore loops.

Ground source heat pumps work, they need long lengths of pipe and the depth of this pipe provides some very predictable temperatures over prolonged extraction periods.
You can see it works because ground source heaters works. Where it all goes wrong is when we start looking any further than the localised mass around that tube.

I think a separate thread for you GSHP owners would be interesting and extremely informative. I am using Geothermal and Solarthermal as a distinction as when posting datasets that info is important.
That way if you really wanted to get Geeky and do some calculations on the ground structure knowing depth is very important.
I am really not sure about Slinkies as because of the loops there is a much bigger mass of brine m2.
Reading through the other thread there is a debate about Slinkies and maybe that should be included in datasets.

Because of the information posted here you can go through and see that a GSHP has much effect on the ground in close proximity to the piping.
What effects it most is heat flux and time of use and there is a fine balancing act needed for pipe length.

That system Billi posted with the chilled PV is a direct system with the shortest amount of time and in terms of "recharging" is the most efficient in the "recharging" process.
The cold heat from the GSHP directly cools the PV system this is fed into the ground in a ground loop of appropriate size.
In summer because the ground is cooler than air even with the GSHP off (which is prob the norm) it receives cooling and bonuses in efficiency.
When the GSHP is on it has a huge direct cooling effect and the heat from the PV has a lot of brine mass over a small PV area and is very effective for both systems.

Roger posted some great info that over short periods of time you can effect the collected brine temperature and this can be mentioned in hours.
The longer you extract for in hours reduces the flux between brine feed and localised mass after a while the effect is diminished.
If you can freeze it for a few hours, you can heat it for a few hours and short term cycles of a few hours are possible.

You can get effective results for a few hours and in terms of usage profile that is quite a reasonable fit.
The recharging the ground argument always gets derailed when either the recharge camp start talking about huge quantities over extensive periods. Or the anti camp start quoting figures other than localised mass in terms of a couple of hours.

Now if we had a extended dataset of 12 hours continuous run on say something like the one Roger supplied on the 1,2,3 loop capacity of the system the argument could be settled.

The figures you quoted Mike have a limited effect on the recharge cycle if its of a short duration.
   


Title: Re: Recharging the ground
Post by: davec on February 02, 2016, 08:08:23 AM
Quote
Probably it matters not a cuss, but...

Applause for diffusivity!


Title: Re: Recharging the ground
Post by: Stuart Ian Naylor on February 02, 2016, 11:06:49 PM
Great data Mikel, nice to hear that the oversized radiators are proving effective.

Ian, The stable input temperature just indicates that the ground loop is more than sufficient for the heat demand on it.

Marshman, Roger :) posted some mega details, that actually confused me.
What he did by deliberately cutting off loop sections was absolute gold in terms of info.

I said it earlier but if we got data from a bodged GSHP that returned data of freezing characteristics, then actually that would be really useful, even if a bit upsetting for the owner.

The brine cooled solar PV system Billie showed is a renewable symbiotic relationship where the cold and heat are shared and simultaneously benefit both systems.  

ORCs and Sterlings are the same and recharging the ground is very possible in a certain manner especially if instantaneous or of a short duration between charge and extraction.


I would honestly like   to have a better translation program .....    but this did not work  and they talk about an Ice storage idea with a CoP over 4  and the overall over 5.5   with the hybrid solar thermal  connected  and this all with system losses  excluded

http://www.agenda-energie-lahr.de/Ph2_SolarWP-GOT.html    paste it in guugle tanslate  , perhaps it makes more sense then


But i follow that since years and    perhaps  therfore i am a PV fan boy   cause its black, cheap and  works better if cold down by a heatpump  


Regards Billi

After having some terrible results pasting the link into google translate did a good enough job https://translate.google.co.uk/#auto/en/http%3A%2F%2Fwww.agenda-energie-lahr.de%2FPh2_SolarWP-GOT.html

Yeah nothing wrong with PV and the reason I reopened a dead thread is that generally the recharging concept looked at being the primary heat source.
I have read enough reports and followed seasonal heat sources from when they where initially posted on here.

Mike is right about the diffusivity as its extremely hard to store quantity over extended periods of time.
But be it PV, ORC, Sterling, GSHP efficiencies can be increased and just a couple of degrees can make a lot of difference.
The diffusivity of the mass near the brine loop can be seen in Rogers results where I guess if he runs for long enough with all three coils the same downward slope in heat collected will be shown.
Never had a long enough run on that coil loop to see when its affected.

It does look like you can change the temperature of the ground of a small localised mass near to the pipe by a couple of degrees for a couple of hours.
When you get two renewable technologies sharing the same ground loop with opposite effects of freezing and heating you can double up on the "recharging" efficiencies.
You can't expect much more than a couple of degree's that will last longer than a couple of hours, but you can.

Solar PV is cheap and it allows enthusiasts to quickly and easily generate CO2 free energy.
Currently Solar PV converts at approximately 16% whilst low tech Solar thermal can reach 70%.
That is really important for areas of low insolation as PV needs four times the space to produce the same amount of energy as SolarThermal.
Its just a shame that practically all solar thermal panel systems had a sole purpose of heating a singular heat store (cylinder) and this often limited the size to an extremely small area.
Also its a shame the solar thermal was also exclusively a direct heat system where collected temperature was heating temperature as this limits the amount of heat stored in a certain area.

I have a building shape that is my ideal solar optimised UK building, its a 3 storey single aspect terrace with a mono pitch roof that provides a good average living space.
8m wide, 10m to the rafters and 4m in depth with a 35' monopitch roof giving another  8m x 5m area. Its just some silly theoretical of a house totally cladded by solar panels on the south aspect.
With a total of 120m2 collection area where solar PV = 120m2 * 1kwh * 16% (area x average solar * efficiency) = 19.2kwh
Solar thermal = 120m2 * 1kwh * 70% (area x average solar * efficiency) = 84kwh.

Now that is based on some silly solar optimised house where walls and roof are completely clad and this is the huge problem in the UK domestically as many of us have extremely limited space applicable for any type of solar.
Solar thermal is still much more likely to produce usable energy levels seasonally on the average available space and create a summer excess, whilst looking at the Dec/Jan PV results this isn't so.

I am still a big fan of Solar Thermal coupled to a daily heat store (not of the ground type) coupled to an ORC backed up by a GSHP.
The heat store acts as a buffer where generation time is delayed by a couple of hours which helps massively in balancing.

Solar PV in areas of low insolation is a really great consumer renewable but for bigger commercial and community concerns its returns are not great and much less than Solarthermal / ORC or Solarthermal / ORC / GSHP systems in terms of space available.

Bugs me we never got the right type of panels and innovation / investment was so skewed to a singular type of solar technology whilst maybe a more appropriate complementary technology was available.
Having a generation lag between a solar PV and solar thermal PV makes for a much better UK solar profile. Much of the skew has been caused by having approved technologies rather than rewarding recorded energy profiles of a more open market.

http://repository.tudelft.nl/assets/uuid:2e17121a-d138-4c14-bf1f-421799602beb/PhDTesis_ECasati.pdf


Title: Re: Recharging the ground
Post by: billi on February 03, 2016, 03:27:00 AM
in the end  or better on the long run     PV 

what a success  story   ,


 sure thermal solar as well  , not a doubt


But   if people  here report  of about 1400 kWh  electricity  for the whole house heating  whistle x 0.17pence .......................... bike:


So 200 -£300  per year    even if its more 




Why should i charge the ground   ?  and not the Grid with Units ?




Title: Re: Recharging the ground
Post by: Stuart Ian Naylor on February 03, 2016, 05:40:51 AM
If we don't get a balance in generation profile like germany we could very well end up where the grid charges us.

There might be a few homes that only use 1400 kWh electricity for whole house heating.

The average UK home isn't really changing much with the majority of new builds being the EPC rating C (which I totally disagree with)

https://www.ovoenergy.com/guides/energy-guides/the-average-gas-bill-average-electricity-bill-compared.html

Recharging just helps make other processes more efficient to lessen the grid charge to you, whilst helping with balancing because of delayed energy storage.

In solar thermal it is only the waste heat in the cooling process that recharges the ground, but as a CHP system is massively more efficient over PV alone.

If we all adopted PV with maximised coverage we would have huge problems in balance, cost and storage.

Its fine to point at a singular system and state what it does alone is fine and dandy, but for it to work as a whole for the UK it ain't going to work and we need diversity.

Complementary systems to PV are not better ways of doing things but have equal importance because diversity of energy profile.

Non centralised heat grids in CHP combinations are far more efficient and there are many technologies that can radically make difference in conjunction with PV.

Anything that can bring balance with storage costs at the moment has high value and worth more than a unit that can not.   


Title: Re: Recharging the ground
Post by: dhaslam on February 03, 2016, 11:37:02 AM
It seems that that of buildings tested in England and Wales  two thirds  are below level C.    However what seems to happen is that the  less well insulated houses are heated to a much lower temperature.      In  a larger proportion of houses are new  and proportionately more self builds   

http://www.lcea.co.uk/epc-ratings-explained/

In Ireland a larger proportion of houses are new  and proportionately more self builds.  One half are C or better    and only one quarter worse than D.

http://www.seai.ie/Your_Building/BER/BER_FAQ/FAQ_BER/General/BER_Statistics.html

However what seems to happen is that the  less well insulated houses are heated to a much lower temperature. If that wasn't the case the heating cost for older houses would be  astronomical.    I doubt if anyone in old farm houses spends  €8000 per annum on heating.   The usual thing is a few  loads of turf costing  less than €1000 per annum.           

http://www.seai.ie/Your_Building/BER/Your_Guide_to_Building_Energy_Rating.pdf


Unfortunately the energy ratings don't mean very much because they mix up the  heat requirement with the heat source 


Title: Re: Recharging the ground
Post by: marshman on February 03, 2016, 09:17:36 PM
Nice lot of data Mikel. Unfortunately I don't have a heat meter fitted, I now wish I had for my own curiosity. (another project!).

Good to know that your system works well with radiators. It sounds as though your installer, like mine, realised the importance of correct ground collector sizing.

I didn't see it in your post but do you run your system 24/7 or is it on a timer?  Also is there a room stat to control the temperature?

Mine runs 24/7 and the temperature inside the house is remarkably constant apart from a mild uplift if we light the wood burner - which my wife finally admitted the other night was more for the nice effect of the flames rather than because she was cold! See graphs below (last 3 days recorded by my weather station) - indoor temp is in maroon on the bottom graph.

(http://s10.postimg.org/yopzyjfol/curr72hourgraph.jpg) (http://postimg.org/image/yopzyjfol/)

I love the relatively quick response of your system after you came back from holiday. My place would probably take the best part of 24 hours to stabilise due to the enormous thermal mass - but then again that's probably why the internal temp stays fairly constant.

One last question. Do your CoP figures come from the monitoring system or have you calculated them from the heat meter reading & electricity meter?

Roger


Title: Re: Recharging the ground
Post by: burble61 on February 03, 2016, 09:36:56 PM
Nice lot of data Mikel. Unfortunately I don't have a heat meter fitted, I now wish I had for my own curiosity. (another project!).

Marshmans Christmas prezzie sorted!


Title: Re: Recharging the ground
Post by: Mikel on February 04, 2016, 03:53:56 PM
Roger, thanks for your comments. I'll provide short answers and more informative answers to your questions.

You asked:

"One last question. Do your CoP figures come from the monitoring system or have you calculated them from the heat meter reading & electricity meter?"

The figures are calculated from the electric and heat meter readings.

You asked:


"I didn't see it in your post but do you run your system 24/7 or is it on a timer?  Also is there a room stat to control the temperature?"

The short answers is : Yes, yes and yes!!  I'll explain.

When originally installed we had a timer fitted and weather compensation turned on and no room thermostat. We generally don't need any heating on during the day living in West Cornwall unless it is very damp. I didn't see much point in putting the timer on for the DHW, as we are at home during the day and can operate it manually to benefit from the solar thermal system.

When we opted for the DECC sponsored control system trial, they made a number of additions to our setup as follows:

Their communication box was connected to our router and various sensors and meters setup to send data to the communication box;
Four temperature sensors were installed, one in the lounge, one outside of the kitchen, one in another hallway and one in the guest bedroom;
One temperature sensor is designated as the control sensor. Originally this was in the lounge but designation was moved to the hallway sensor when the wood burner was put into the lounge;
Electricity meters were fitted to the heat pump and to the main meter;
A heat meter was fitted to the heat pump;
Additional parts were installed on the heat pump (all done with the agreement of the manufacturer and does not invalidate the warranty);
The heat pump was wired so that it could be switched from trial mode to original mode minus the weather compensation;
A wireless enabled timer/scheduler was installed;
Control software updates could be applied remotely to the heat pump;
A copy of the monitoring data is sent to me weekly and I use this to calculate the CoP.


So how does this operate in practice?

Whilst we have set a daily and weekly timed schedule with differing temperatures set for In, Out and Asleep, in practice the only variables from the user's perspective that control the system are the temperature setting and the holiday times. The control software would initially learn how our property responds to heating and then it selects the best method for achieving the set temperature (best method also includes an overnight heating time for those to be able to benefit from a lower tarrif) and it also takes into account the external temperature and the forecast temperature. It also brings the house back up to temperature for when we return from holiday.

One very significant difference between this trial control system and the original is that the heat pump tends to run continuously for longer periods and up to quite high flow temperatures (45-50C) with the trial system. Originally, it would cycle about 5 times an hour with lower flow temperatures.

In terms of measured performance, the calculated SPF for RHI purposes comes out at 3.1. I have data for Feb 2014 only under the original system and that gave a CoP 0f 3.2 and under the new system we are regularly getting between 3.4-3.5 plus the heat pump is cycling far fewer times.

I did originally start to record the incoming and outgoing temperatures to the ground loop but now only look at these occasionally (last week during a mid-run the incoming temp was 10.7C and the outgoing 3.1C).

It was interesting to see your graphs. I do not record any weather data. We are only a few miles from a Met Office station that records local weather.

Mike


Title: Re: Recharging the ground
Post by: marshman on February 04, 2016, 08:38:32 PM
Interesting reply Mike, thanks.

My system as I said runs 24/7 and has no internal thermostat, just relies on the outside sensor and some "magic" in the controller. Interesting your original set up cycled so frequently. I'm sure there are settings in my controller to prevent a restart within xx minutes of the last run, currently set to 20 mins I think.  Currently the outside temp is 7 deg C and it is running about 20 minutes every 1 1/2 hours, max flow temp is 38 deg C.  The house sits at a constant temp 24/7, though I am considering a night set back as there is a set of contacts I can easily connect a time clock to on the pump, but not sure how much, if anything that will save.

I have decided that I do need (well OK I don't need but I would like!) a heat meter more out of curiosity than anything else.

Also I note your pump only gets you DHW up to 50 deg C. This is the only niggle with my system. The heat pump controller has no setting for the maximum hot water temperature, it just gets it as hot as it can - usually around 56 deg C - which is a) a bit too hot for my liking and b) not that efficient, I suspect the CoP drops to a little over 2 when it is above 50 deg C. ( I have the auxiliary heater disabled).

1 more question, what make and size is your pump?

Roger




Title: Re: Recharging the ground
Post by: Mikel on February 05, 2016, 10:31:00 AM
Roger, you asked

"1 more question, what make and size is your pump? "

Kensa 10kW single phase, single compressor installed March 2013.

Kensa are just down the road from us and I am fortunate to know one or two people there. I checked with them over the frequency of cycling and was told that was quite normal.

The image below is for yesterday's heating. You can see the effect of the wood burner in the evening. We would also prefer to be a bit cooler overnight but that doesn't seem easy to control as we also like to get up to a warm bedroom. Like you, it appears that the system is at its best keeping a constant temperature.


(http://s10.postimg.org/ekx08u02t/image.jpg) (http://postimg.org/image/ekx08u02t/)

Mike


Title: Re: Recharging the ground
Post by: linesrg on October 16, 2016, 08:09:59 PM
Good Evening All,

I think this is the most appropriate place to post this as the main query relates to recharging the ground.

The gas valve on our 14year old trusty Micromat bolier has given up the ghost and we are looking towards getting a GSHP system fitted.

One of our local specialists has been round and I’m currently waiting on a quote from them. They are recommending a CTC Ecoheat device.

I want to integrate this with the AL4720 ET panels I bought off Navitron. I bought three of these panels as they were being sold at a good price at the time (2012) although I wasn’t entirely sure whether I would use all three or not.

After discussing the best use of the ET panels with the representative who came round and following this up with background reading off the internet I see there is an add-on module (from CTC) which would allow the integration of two of these panels and would divert excess hot water back through the ground loop.

Given the discussion in this thread about the benefits of putting heat back in to the ground I can’t see there is agreement as to the benefits of this although given different ground conditions it would be impossible to have a one answer fits all solution.

On the one hand I could have what would appear to be an excess of panels in the summer but on the other hand all three panels in the depths of winter could produce more ‘hot’ water to go in to the Ecoheat ‘heat store’. As I have already paid for the panels it seems to make sense to fit all three?

As the CTC device appears to store various bits of information it may be possible to determine the value after running the system for some time?

I’d appreciate the thoughts of the forum.

Regards

Richard


Title: Re: Recharging the ground
Post by: biff on October 16, 2016, 09:02:58 PM
Hi Richard,
    As you know, CTE is a brilliant scientist, lecturer and inventor. He has gone all out to make this Charge the ground business work.
  Yet somehow, I think that we would have to be on the same wavelength as CTE to get the necessary satisfaction,
   That is the problem and the only way we can go on the same wavelength is to sit in on his lectures.
   Personally, I am not in a hurry. I know when i have met more than my match.
   I have already beaten the laws of physics once and luckily, did not need to supply any witnesses or affidavits .
   but pumping heat into the ground without any form of containment would be a step too far for even me.
                                                               Biff
   


Title: Re: Recharging the ground
Post by: dhaslam on October 17, 2016, 11:27:51 AM
Horizontal collectors are  usually between one and two metres below the ground.    The insulating effect of the ground means that it takes a few months for the air temperature to  penetrate.    Heavy rain will speed up the process.      There would probably be   little residual heat  retained  from one day to the next  so  it won't   benefit much  but  won't do any harm either.  Sixty tubes  will only produce significant surplus in sunny summer weather, the tank stores 223 litres which is a good fit for  the three panels. 

The situation is much different for vertical  collectors, they get very little heat from the surface  and  depend  more on  ground water  so they would benefit from heat returned in summer.   In North America where there are large seasonal temperature variations  most systems are used for both heating and cooling.


Title: Re: Recharging the ground
Post by: skyewright on October 17, 2016, 12:42:22 PM
Horizontal collectors are  usually between one and two metres below the ground.    The insulating effect of the ground means that it takes a few months for the air temperature to  penetrate.    Heavy rain will speed up the process.
For a few years I ran soil temp sensors at 100mm, 300mm and 1000m.

Without going back to check the data in detail, my recall is:

100mm had a clear daily variation (sort of Sine curve like, but obviously not so regular!), closely tied to what was going on at the surface with little delay (just a few hours).

300mm had a clear, though moderated, daily variation, but related to what happened yesterday.

1000m had hardly any daily variation and took a week to notice a change in trend at the surface.

Heavy rain, especially after a dry period (i.e. the ground suddenly becoming wet) could have a much faster effect on the deep temperatures.