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Author Topic: Heat Pump bore holes  (Read 5773 times)
henry
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« on: June 25, 2006, 03:02:57 PM »

Hi my next project is to install 2 of ivans 9 kw heat pumps only I have a small garden and would therefore need vertical bore holes. Any suggestions as to how many holes depth and width to accomodate these two pumps. Thanks H
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Ivan
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« Reply #1 on: June 25, 2006, 03:19:24 PM »

We don't have any experience of utilising boreholes. One option would be to pump water direct from one borehole and after passing through heatpump, back into another. in this case they have to be at least 10m apart.

You can lay your ground source heat pipes vertically, but i don't know the details, unfortunately. you might get some info from a web search or by talking to a heat pump installer. if you find any useful info, please post on the forum.

ivan
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henry
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« Reply #2 on: July 03, 2006, 04:42:14 PM »

Ivan i am still looking at trenches or boreholes for my heat pump system however i am having trouble locating pipe for the venture.Is it stocked by yourselves if so how much is it a metre or could you put me in contact with a supplier thanks.Ps any problems with delivery time of heat pumps thanks H
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henry
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« Reply #3 on: July 10, 2006, 01:45:38 PM »

Having done some "digging" around I have established that the the ground pipe used for the heat pumps is 32mm od mdpe black pe 80 or pe 100 spec.Apparently 1 mtr of pipe should produce 30 watts of energy.Does anyone know the following.If the pipe is laid in a "slinky"ie coiled and linked form, standing up vertically thereby using 5mtrs of coiled pipe for every mtr length ,would that 1 mtr of ground produce the watts or would it be the pipe ie 5mtrs x 30 watts =150.Or am i expecting too much from the ground. H   
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Ian
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« Reply #4 on: July 10, 2006, 08:54:42 PM »

Henry - The simple answer is that the 1 metre of pipe will give you a realistic heat transfer of 30 watts. Therefore, if you coil it into a helix such that 5 metres of pipe occupies only 1 metre , then the pipe has a potential heat transfer of 5 x 30 watts.

However... (you knew that was coming didn't you !). This is where the rest of nature kicks in. The greatest heat transfer occurs when the heat differential is the greatest. The ground may be a good absorber of the sun's energy (which is why we are using is as a source of heat) but it is a lousy heat transfer medium generally.

So the efficency of the ground loop has very little to do with the thermal properties of the plastic pipe and a lot more to do with the material it is sunk into. If the ground cannot conduct heat to the pipe quicker than the pipe conducts it away then it does not matter how much pipe you have.

I think you are asking too much of the ground in your example. But if you were to put your helix into a large pool of water (preferably flowing) I would have thought that would be quite OK - because water is a far better conductor than dry soil.

If the ground in which you sink your helix is reasonably wet in the winter (and I am talking about 2 metres down), then you can look to get a little more than 30 watts per metre - say, 30 - 40 watts. If the ground is bone dry like dry sand, then you must expect to derate to, say 10 - 20 watts per metre. Rock is pretty good at heat transfer but you have to have a good thermal contact between pipe and rock to maximise the transfer.

Whilst "the ground" can be considered to be an infinite heat pool, a finite amount of ground in which a pipe runs is not and is subject to the thermal conductivity of the medium itself.

It is never simple is it ?

I hope this helps.

Regards,
Ian
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mtimm
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« Reply #5 on: July 11, 2006, 08:15:41 AM »

When running ground loops the recommendations seems to be that each pipe should be at least 1 meter from the next because as Ian stated the ground is not a good heat transfer medium.

If the pipes are too close together during times of high heat requirements and low heat replenishment (the winter) the temperature of the ground where you are drawing the heat from can drop drastically and take a very long time to recover. Leading to reduced efficiency of the heat pump.

The problem then becomes the cost of laying the pipes and even more so the space required I have seen stated that a 1600sq ft bungalow would require almost a Ĺ acre for sufficient heat. I donít know how accurate this is or what pipe is used for the calculation.
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henry
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« Reply #6 on: July 11, 2006, 12:33:44 PM »

Thanks for the info ,yes I agree its never that simple,I dont have a very large garden and the thought of boring down towards Aus is not an option. I may have to do a small test bore first to see if I have a wet" bottom". The pond is out of the question nearest water is the Thames. I may have to dump the heat pump and consider another energy source.Perhaps a wind generator to compliment the P.V's. H Cheesy
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mtimm
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« Reply #7 on: July 12, 2006, 07:14:18 AM »

There are air too water\ aerothermal heat pumps available but as with most things there is a question over how efficient they are. But dont require large ground area or bore wells.
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henry
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« Reply #8 on: July 12, 2006, 02:48:14 PM »

I am determined not to give up on the ground source heat pump. I have again been digging around and found ice energy in oxford.They are the agents for a swedish company called IVT.This company has patented a ground collector system which according to their brocures is tried and tested.They are part of the Bosch group.The collector is a  system of pipes 32mm o/d 18 in total 2mtrs high and 1.5 mtrs wide the pipes are connected in a manner where it enters one end leaves the other having travelled the length of the panel which is a total of 40 mtrs of pipe. They estimate that I would need 10 of these panels either vertically installed at a depth of 3 mtrs or horizontal at 1 mtr.Has anyone any thoughts on this idea.I am considering making the panels and tying them up to Ivans 5k heat pump. Undecided  H
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blue
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« Reply #9 on: October 13, 2006, 12:03:23 AM »

Hi Henry,

For the Ground loop, try geothermal supplies ltd of Nuneaton. You can get a thermo loop and borehole grout.

Gary. 
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henry
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« Reply #10 on: October 20, 2006, 02:40:14 PM »

Thanks Gary i will give them a look H
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