ground source: soil, well or 'lake'?

[sam123]

Hi sam

Thanks for that post. My ground loop is  probably too short (1x200m loop) but well insulated house with UFH.

Current temps
outside air 2c
incoming ground loop 2.8c
outgoing ground loop -0.5c
UFH water  26.5c
room  20c

IVT greenline 6 and woodburner off

Beau

That is short ground loop. How deep is it? Is it 40mm pipe?

You can check your "real" ground temperature by circulating ground loop without compressor. My experience is that after 1h30min hour temperature will not get any higher.

I have incoming fluid around 4 degree (with circulation), 210m borehole. It´s very gentle Christamas this year (+1 degree outside), it was like -27 degree last year 

( http://classic.wunderground.com/history/airport/EFJY/2010/12/24/DailyHistory.html?req_city=NA&req_state=NA&req_statename=NA )

[baker]

Hi sam123
love your post big fan of air/ground hp,s
but got some serious compitition with thies air source heat pumps
coming along and taking over
is it time to throw in the towel?
baker

[Solal]

In 1980´s we also buried ground loops too deep. That caused lot of problems,

What type of ground loops? Undersized maybe! Or incorrect  back filling methods!
Are you suggesting  a lack  of the suns energy  recharging the ground  was the cause of these  problems?

If so  where do bore holes get  their energy from  which are drilled  deep   into  the bowels  of the earth?

[sam123]

In 1980´s we also buried ground loops too deep. That caused lot of problems,

What type of ground loops? Undersized maybe! Or incorrect  back filling methods!
Are you suggesting  a lack  of the suns energy  recharging the ground  was the cause of these  problems?

If so  where do bore holes get  their energy from  which are drilled  deep   into  the bowels  of the earth?

Hi Solal

They dig those pipes too deep (and maybe they used too short ground loops with too narrow spaces also) which caused permanent frost around pipes. Ground is pretty good insulation material.

Bore holes are different than ground loops. Bore holes their energy below 5-10 meters from geothermal energy (Earth's molten core). Deeper hole = more heat.

Finland´s deepest bore hole is 2500 meters with bottom temperature of 40 degree celsius.

If you get deeper, you get very high temperature even in Russia ( http://en.wikipedia.org/wiki/Kola_Superdeep_Borehole )

@ baker
Are you planning for "air to air heat pump" or "air to water heat pump"?

cheers, Sam

[Bodidly]

Hi Sam
 Pipe diameter is 32mm external and the depth is between 1 - 1.2m current ground temp is 8.4c. We do not have to worry about the ground not getting recharged during the summer because during periods of heavy rain the ground water sometimes reaches the surface recharging the soil with heat I have seen this happen overnight!

I was wondering about adding another 200m of pipe to my existing ground loop so 1 400m horizontal loop.

We  have not corrected this fault with my system because most of the time we only use it for the hot water this is because we have found are wood burning stove heats most of the house very well but we are using the heat pump at the moment because the downstairs bedroom does not get warmed very well by the stove.

Beau

[CeeBee]

Ivan posted a graph a few years ago (and I can't find it now) that tracked soil temperature at various depths by month...

There's a nice graph on this page of David MacKay's "Sustainable Energy - without the hot air". Read the text alongside the graph for the assumptions and dependence on what type of material the ground is made up.

The adjacent pages - techy stuff on heat pumps - are good reading too.

Anyone got a pointer to a technical analysis of the source of the heat for 'borehole' GSHPs? 'Solal' asked this above, and 'sam123' said "Bore holes their energy below 5-10 meters from geothermal energy (Earth's molten core)". I've not got the data to argue (hence the request), but do they? The above pages from MacKay's book say the energy flux (both in and out in summer/winter) at the surface of the ground is about 5 watts per square meter (and he argues that you therefore won't be able to extract a lot more than this long-term without disturbing the status quo, i.e. freezing the ground). The earlier chapter on 'geothermal' starts here - he says that the upwards heat flux (heat from earth's core, plus a greater contribution from radioactive decay) is about 50 milli watts per square meter, so around 100 times less than the annual in/out due to solar heating at the surface. So aren't borehole (100 meter or so) heat pumps also using the solar energy, but just than it takes a lot longer for the heat to get down there? I know it's not as simple as that - the borehole isn't part of a uniform array of boreholes (usually!) so can also draw heat 'sideways' from the ground.

[Solal]

The Graph on page 6   shows  temperatures for Falmouth  from Geoscience  who are  earth energy  consultants  afaik....
http://gshp.org.uk/documents/CE82-DomesticGroundSourceHeatPumps.pdf

It would be interesting  to have borehole/s  combined with horizontal collectors.  And in summer  circulate  between  the two  lifting the bore hole temp  in summer  and  lifting  the horizontal  collector  temp  in  winter.

[baker]

reality check 
 can some one post the cost to drill  bore hole and a ground loops
and the cost of fees, to get permission /surveys
extra costs for unforeseen problems
skips ,water pump/plant hire,  liners, etc
baker

[titan]

reality check 
 can some one post the cost to drill  bore hole and a ground loops
and the cost of fees, to get permission /surveys
extra costs for unforeseen problems
skips ,water pump/plant hire,  liners, etc
baker

The only way you will get a reasonably accurate estimate for boreholes is to contact a drilling company. I looked at it a while back and around £6000 per borehole was the going rate, that was for the complete job , drilling, pipe installed , grouted and topside completion. I would have needed two boreholes for my 8 kW heat pump. I installed my own ground loops  Rough costs for 500M of 40mm geothermal pipe,  fittings for manifold and  10 days  5 tonne digger hire about  £1,500. I also needed   60 tonnes of dust to 3mm crusher run stone to surround the pipes as the ground was very difficult. I would think you could easily half this time in normal ground. I was seriously considering an ASHP until we had the second winter with long periods of below zero temperatures and quite a few days at -11. I think it would be difficult to make an economic case for boreholes for a normal domestic installation.

[sam123]

Hi Sam
 Pipe diameter is 32mm external and the depth is between 1 - 1.2m current ground temp is 8.4c. We do not have to worry about the ground not getting recharged during the summer because during periods of heavy rain the ground water sometimes reaches the surface recharging the soil with heat I have seen this happen overnight!

I was wondering about adding another 200m of pipe to my existing ground loop so 1 400m horizontal loop.

We  have not corrected this fault with my system because most of the time we only use it for the hot water this is because we have found are wood burning stove heats most of the house very well but we are using the heat pump at the moment because the downstairs bedroom does not get warmed very well by the stove.

Beau

Hi Beau

It is good idea to add second loop to your system. Another 200m loop will do the job. It is pretty much same if you connect it parallel or serial with your existing loop. Problem with your existing loop is that when your GSHP starts, it gets warm (=good cop) warm ground liquid until all liquid has passed your pump first time. Second circulation round will be much colder and so on...ground liquid needs time to suck heat from soil.

With such a short ground loop liquid gets colder and colder, until temperature difference between liquid and surrounding soil grows big enough and temperature is stabilized.

I have two fire places on my house, but there is no economical reason to heat GSHP-house with logs. (As you probably know Finland is covered 77% of it´s area with forest.) Electricity cost nowadays here about 9 pence/kWh (12 cents in €). With GSHP your COP is 3-4 (in UK easily 5 in UFH). Heating kWh is then 2.25 pence with COP 4.

If you buy your logs from free markets here, you get stacked 1m3 wood for £36 ready to burn. You get 1360 kWh/m3 dry pine. Best fire places burns wood with 75% efficiency, normally iron stove 40-50%. Which make kWh price of 3.5 pence.

How much you pay from your logs? If I have free logs (own forest etc.) I would sell them to neighbor, who heats with direct electricity.


@ CeeBee

Here is figures from test-drilling here in Finland:

Vertical axle is temperature and horizontal is depth. Different colours are Finnish places. (you can google-map them)



Swiss research says that bore holes temperature drops 0.5 degree in 50m at 30 years. But link is broken: http://www.geothermie.de/egec-geothernet/prof/0103.PDF

Cheers, Sami

P.S Borehole cost here in Finland like: 28€/m for rock and 55€/m for ground (have to pipe it). Including collectors and fluid assembled (denatured alcohol + water = -15 degree freezing point)

[Bodidly]

Hi Sam

 We live on a small farm and have stated running a small firewood business so the logs are free apart from petrol and sweat you can have a look at lizlogs.co.uk but we don,t ship to Finland.

 I think we would financially  be better off if we just used the GSHP and sold the logs but some how this seems wrong to me but I would be interested in other peoples opinion on this.

If we do extend the ground loop it would probably be in series. Could we do the extra 200m in 40mm or would this cause problems.

Thanks for your advise on this
Beau

[sam123]

If we do extend the ground loop it would probably be in series. Could we do the extra 200m in 40mm or would this cause problems.

Hi

Connecting 32+40mm is not a problem. I´m trying to figure out is it difference which way you connect them?

In bore holes they use sometimes  2x40mm down and 1x40mm pipe up. (cold liquid slowly down and warm liquid fast up to pump).

In ground loop it is probably same. Liquid runs in 40mm pipe  a little bit slower and faster in 32mm section.

Then there is turbulent issue. I have to think about this 

Cheers, Sami
 

[baker]

its already done by the Europeans
The best way to connect the ground loop is
25mm thin wall  /2>3 mm wall pipe     thinner than standard water poly pipe
in 50 meter circuits
to a low loss header type manifolds with  5 >10m long runs of 40>50 mm flow and returns  to heat pump
the idea is to get the most surface area of pipe  exposed to the heat bank
and the thin wall pipe conducts better
 the  long 40 mm runs to the heat pump stabilise the flow and temperatures

[sam123]

Hi
Hi Bodidly

Thought about this...and: I would connect loops in parallel after all. And I would use same 32mm pipe exact length of first loop. If you use 40mm pipe your second loop, you need to assemble a valve to reduce it a bit. Otherwise flowing happens mostly in larger pipe.

200m+200m = 400m is okay with 40mm, but 32mm+40mm in serial have too much flowing resistance and you exceed optimal in/out temperature difference 3 degree, which means that you don´t get most from your pump.

Result: 200m 32mm parallel, or 200m 40mm in parallel with valve to reduce flowing.

Cheers, Sami
 

[sam123]

its already done by the Europeans
The best way to connect the ground loop is
25mm thin wall  /2>3 mm wall pipe     thinner than standard water poly pipe
in 50 meter circuits
to a low loss header type manifolds with  5 >10m long runs of 40>50 mm flow and returns  to heat pump
the idea is to get the most surface area of pipe  exposed to the heat bank
and the thin wall pipe conducts better
 the  long 40 mm runs to the heat pump stabilise the flow and temperatures

Hi Baker

I wouldn´t go that way. In "Scandinavian style" there is ONLY 10bar 40mm pipe with two (2) pipe fittings in warm space. No leaking joints and manifolds. It is always challenging to balance flow rates in multiple loops. I wouldn´t put anything less than 10bar pipe on ground. Hard to imagine nothing worse than dig up your garden in a case of broken pipe.

Playing with manifolds is playing with flow resistance. How to make sure that your ground loop circulation pump is handling it? 40mm pipe has more collecting area and it has more warm liquid waiting GSHP to start etc.

Your system is good for company that installs ground loop. It´s sounds like rocket science and you can charge a lot of money from it.

400m ground loop is dug in one day with 1,5 meter wide excavator bucket. You can assemble two pipes in one trench at the time. Meaning 200m trench for 400m loop. Take biggest excavator to do the job.

 

More pictures from ground loop assembly (two loops, because soil is dry sand): http://puutarha.net/index.asp?s=/tv/tvtulostus.asp?id=1035

There is no need to trying to reinvent the wheel...

Cheers, Sami

EDIT: correct some words and idea (I´m running 210m bore hole, not ground loop)