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Author Topic: Pipe for underground collection array  (Read 5251 times)
rogermunns
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« on: February 08, 2011, 05:30:22 PM »

I intend using 25mm MDPE pipe for my underground array, which I'll be doing in the Spring. It will be used with my WRB09 HeatPump.

What's the general opinion about this choice? Several years ago I bought 500m of this but will need more. So should I buy more the same?

I've got a fair bit of land and the intention is to lay out the pipe at about 40cm centres over 250sq.m. or so. Something like that.
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titan
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« Reply #1 on: February 08, 2011, 06:00:45 PM »

I am sure you will get a selection of answers but I am using 40mm mdpe pipe so will have a larger volume of brine in the loops  than 25mm or 32mm pipe  Polypipe make the one I have bought it is sold for ground arrays and has a slightly thinner wall thickness for better conduction. Just about everything I have read about ground array spacing calls for a 1 metre minimum spacing.  I will be using two loops of 250 metres ( no joins) at 3 metre spacing and at 1 metre depth. The manifold will be the highest point where the purge and vent connections will be.
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sam123
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« Reply #2 on: February 08, 2011, 06:19:07 PM »

I intend using 25mm MDPE pipe for my underground array, which I'll be doing in the Spring. It will be used with my WRB09 HeatPump.

What's the general opinion about this choice? Several years ago I bought 500m of this but will need more. So should I buy more the same?

I've got a fair bit of land and the intention is to lay out the pipe at about 40cm centres over 250sq.m. or so. Something like that.

25mm is a bit thin. Too much flow resistant. I would make two loops from it. Length depends how many kWh your house need to kept warm.

We you use here 40mm 10bar pipe with 1,5m spacing. Depth 0,7-1,2m. 0,7m in Southern part of Finland and 1,2 on North. In UK you have regulation? for minimum depth of 1 meter? If not, I would let loops to max. 70cm depth.

Cheers
Sami 
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Baz
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« Reply #3 on: February 08, 2011, 10:13:51 PM »

I'm rather surprised by this low depth. I thought 6ft was more the order to escape the seasonal variation.
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Countrypaul
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« Reply #4 on: February 08, 2011, 11:10:32 PM »

Is this difference is depths due to different environmental conditions?
In scandinavia there may be little benefit in going more than 70cm down (how deep is the soil layer for example), where as in the UK there may be benefits in getting heat out of the ground lower down. For example how does the rainfall compare and the water table?

I ask only because I am interested (not enough depth before I hit rock in the garden to put GSHP pipes in.

Paul
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baker
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« Reply #5 on: February 08, 2011, 11:18:01 PM »

Hi
what are the soil conditions wet/dry
25mm thin wall for 9kw in medium soil approx 800m
100m loops to manifold   40mm flow /return to heat pump 10m each  resistance should be OK
and check flow rate through pump and fit appreciate brine pump
the more pipe surface area you have and the smaller diameter the more efficient your loop will be
adding extra loops can keep the brine temperature up getting better cop.s
their is a small increase in pump power con sumsion    
happy digging
john
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knighty
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« Reply #6 on: February 08, 2011, 11:47:44 PM »

if you still use the same pump, then it should use less power ?

if there are more loops, there should be less resistance to flow and so less pump power used ?

personally... I'd cover as large an area as physically possible... it's a one off cost which should make a big difference to the efficiency of the system and the amount of power used/running costs for years to come ?
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rogermunns
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« Reply #7 on: February 09, 2011, 10:07:51 AM »

Paul

I too am in a rock situation. About 30cm of heavy clay then rock. But it is a soft-ish limestone at first, hardening up at half-a-metre.

But I am lucky, in that my garden slopes @ 10% down away from the house. I am going to scrape off the 'topsoil', install the loops in some sand, then make a raised bed about a metre deep, compacting it as well as I can. This is gonna involve about 15 lorry-loads of topsoil.

I also intend putting extra pipe down there so I can pump some solar-heated water into the ground during Summer / Autumn.

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welshboy
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« Reply #8 on: February 09, 2011, 10:42:56 AM »



I also intend putting extra pipe down there so I can pump some solar-heated water into the ground during Summer / Autumn.


You may be interested in the following graph which I think came from a Toddington road test storing heat underground.
Please forgive me If I got that wrong.
The interesting bit is the difference in temperatures at the shallower depths.
Perhaps somebody can advise but I seem to recall that temperatures in the top 20cm of soil is also reasonably high in the summer months.
If I was starting again I would put out two arrays - one deep for the winter and one shallow to pump surplus surface heat deep down. Presumably in the shoulder months it would be possible to just use the surface array when it is a higher temperature than deep down.

More on this in the post by Ivan showing another graph in this thread
http://www.navitron.org.uk/forum/index.php?topic=5880.0


* navitron6j.JPG (22.99 KB, 356x478 - viewed 833 times.)
« Last Edit: February 09, 2011, 10:50:06 AM by welshboy » Logged
welshboy
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« Reply #9 on: February 09, 2011, 01:07:26 PM »

Map of UK ground temperatures can be found here
http://www.metoffice.gov.uk/climate/uk/averages/19712000/e3/7.gif

The 7 on the end means July

http://www.metoffice.gov.uk/climate/uk/averages/19712000/e3/5.gif
5=May

http://www.metoffice.gov.uk/climate/uk/averages/19712000/e3/9.gif

9=Sept etc
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sam123
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« Reply #10 on: February 09, 2011, 02:54:51 PM »

Is this difference is depths due to different environmental conditions?
In scandinavia there may be little benefit in going more than 70cm down (how deep is the soil layer for example), where as in the UK there may be benefits in getting heat out of the ground lower down. For example how does the rainfall compare and the water table?

I ask only because I am interested (not enough depth before I hit rock in the garden to put GSHP pipes in.

Paul

Hi Paul

That 70cm can be a bit deep in UK. Only reason for digging loop to ground is our seasonal permafrost. AND you loose some "heat storage" capacity above the loop if you dig it only 30cm deep.

If you dig your loop deeper than necessary, it takes more time at Spring to recover. If you dig it only 30cm.  It will recover early, but at winter you get less heat from it. 70cm-100cm works for sure in UK also. But less than 70cm is not tested in Finland.

Summertime is not problem (less heat needed, and sun is hopefully shining).

You can check conditions from South of Sweden from Swedish forum: http://www.varmepumpsforum.com/

It translates very nicely to English via google. South Sweden is about same latitude as Scotland.

Cheers
Sami
« Last Edit: February 09, 2011, 02:56:53 PM by sam123 » Logged
baker
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« Reply #11 on: February 10, 2011, 08:56:53 AM »

Hi
rock@30cm
its bore holes for you @2 to 3 k each
will need two @60m deep to do it
why not fit a air source heat pump will be more efficient
ground source heat pumps is old technology now
if you have a lake or river ok
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skyewright
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« Reply #12 on: February 10, 2011, 10:21:48 AM »

The interesting bit is the difference in temperatures at the shallower depths.
Perhaps somebody can advise but I seem to recall that temperatures in the top 20cm of soil is also reasonably high in the summer months.
Hardly long term scientific evidence, but attached is the last year as recorded by soil temp sensors I have at 100mm, 300mm and 1000mm. The bars show daily variation.

Here at least the average and trend at 300mm is much closer to the one at 100mm than at 1000mm (typically 300mm reacts to "yesterday", but 1000m takes around 7 days to notice a change in trend at the surface).

N.B. I don't have a Heat Pump, or a Heat Store, this is just "nature"...


* soil-year-to2011-02-10.png (15.79 KB, 1000x500 - viewed 788 times.)
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Regards
David
3.91kWp PV  (17 x Moser Baer 230 and Aurora PVI-3.6-OUTD-S-UK), slope 40, WSW, Lat 57 9' (Isle of Skye)
Baz
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« Reply #13 on: February 10, 2011, 10:59:08 AM »

That is really valuable information which should be more widely appreciated. It shows that autumn heating will be considerably more efficient due to the stored heat from summer and probably all installations should be provided with a small shallow loop for summer DHW use which would be cheap as the trench is already dug.
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welshboy
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« Reply #14 on: February 10, 2011, 11:50:52 AM »

Yes Valuable info. Particularly interesting as it is from such a high latitude -on par with Aberdeen.

This map shows the temperature further south  is a bit higher.

http://www.metoffice.gov.uk/climate/uk/averages/19712000/e3/7.gif
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