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Author Topic: Never use a slinky in Scotland?  (Read 13359 times)
skyewright
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« on: March 05, 2015, 10:54:42 AM »

I'm just getting quotes for a possible GSHP system.

One of the firms is talking about using slinkies. Another thinks "straight" pipe is the way to go, indeed they feel "Never use a slinky in Scotland" is something of a rule. They say slinkies may work in the south of England but they don’t work here since they take too much heat from too small an area.  They say they take their lead from the Swedish, where the NIBE heat pumps come, and use straight pipe.

It makes sense to me that straight pipes with at least a metre of separation should be better than slinkies that inevitably have many cross overs even if the loops don't actually overlap (as pictures often show them).

Ultimately GSHPs are extracting solar thermal energy from the ground & we do get less sun here, so it also makes sense that a different approach might be relevant when compared to down South.

Hopefully the pipe is going to be doing it's thing for many years, so best to get it right.

So what does the panel think about "Never use a slinky in Scotland"?
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David
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oliver90owner
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« Reply #1 on: March 05, 2015, 11:12:07 AM »

Ultimately GSHPs are extracting solar thermal energy from the ground 

Are they?
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JonG
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« Reply #2 on: March 05, 2015, 11:23:54 AM »

We wont use them at all, and are based in the North West of England (just south of Manchester). We take a steer from Northern Europe and fit mainly Swedish and Austrian units and none of the manufacturers that we work with will recognise their use. Anecdotally the inclusion of slinkys within the MCS is related to who was/is on the advisory panel and a particular heat pump manufacturer's preference for their usage.

In practice it should be feasible to use a slinky if designed correctly, but originally they were designed to work in smaller areas than horizontals, but MCS requires something like a 3m trench separation now any way so what you lose on length you gain on width. in addition you can dig 2 narrow bucket width slit trenches for horizontals and then put a light bulb on the end to link them with a fraction of the spoil needed for a 1m wide slinky trench.

They are harder to install and increase pumping resistance which then impacts energy consumption and increases the issue of glycol density at lower operating temperature.
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Bodidly
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« Reply #3 on: March 05, 2015, 11:28:52 AM »

I did not want slinkys down here in Devon for the same reasons. Only advantage I see with slinkys is the speed and size of excavations. This becomes a very small part of the cost in the long term. Slinkys presumably make it harder work for the pump as well
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biff
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« Reply #4 on: March 05, 2015, 11:52:36 AM »

I was quite relieved,
                   When a friend, son took our Slinky of our hands. I never got close enough to find out if it was a he or a she. Being a polecat/ ferriet   cross ,it had the most fantastic coat but it was totally without humour or any kind of forgiveness . If it was in bad humour, it would just grab you by the end of the finger and chomp away at it. I had very good hunting dogs at the time. They could get along with anyone who hunted and drove out the game but after Slinky latched on to their noses, they would just have sooner wrung its neck.
  Slinky was the perfect name. My daughter christened it. I flowed across the rocks and seemed to have a dozen legs. The new owner was only 21 and worked and lived locally. He just said, "How nice," dived his hand into the cage and hauled out Slinky by the neck before I had even time to warn him.
 Even when I did tell him that it had a tendency to give very painful bites, he was even more keen. I did have another such animal and it came to a sticky end but Slinky and the new owner got along famously. I was never as glad to see the back of any animal in my life.
                                                                      Biff
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skyewright
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« Reply #5 on: March 05, 2015, 11:58:49 AM »

Ultimately GSHPs are extracting solar thermal energy from the ground
Are they?
Off topic, but...
A really deep borehole might be using "geothermal" energy from the earth's core, but ground loops that are just a metre or two down are primarily extracting heat derived from solar radiation on the surface.
« Last Edit: March 05, 2015, 12:02:23 PM by skyewright » Logged

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David
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dhaslam
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« Reply #6 on: March 05, 2015, 04:54:13 PM »

Heat in the ground moves upward in the winter so  pipe  spread probably helps quite a lot.   It depends on the  system used to lay the pipes, using a mini digger it is probably best to use a long  narrow trench.    If using a large digger it would probably be better to dig out a  large deep  hole   and fill it with coils of pipe, particularly if there is plenty of moisture in the ground.  .   
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« Reply #7 on: March 05, 2015, 05:18:37 PM »

I thought a slinky was one of those kids toys - the extra long springs that can run themselves down stairs?
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biff
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« Reply #8 on: March 05, 2015, 05:33:44 PM »

I found the whole Geothermal concept a bit of a hit and miss affair,
                 When it first came out, I had people asking me about it and asking if it was a worker. So I just said a plain,, "I am not sure , I don,t have any experience of the systems"  or,  "You best get some professional advice I have not met many people that are satisfied with it"
  But I spoke to a few who complained about the 8kw costs of running the system. Then there were those whose ground did not lend itself to the Geothermal mechanics.. Not every ground is suitable. There was big installation money involved in each case..
  Around the same time, Dimplex ( I think) marketed an air version, A big Grey box the size of 2 washing machines was stuck on the back of the house and a couple of heat pumps were housed inside it. I made a point of asking the owner about it and he said it was a very good system. he could not complain and it was trouble free. It did the central heating and the DHW. I expected the running costs to be very high but the guy said it was not as dear as oil.
   Around that same time pellet boilers were getting a very bad name and getting dumped after 2 years in operation.
  So it is hard to know. I got the impression after a while that Geothermal was a bit like stone soup with a heat pump being the stone.
                                                                                                 Biff
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Nickel2
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« Reply #9 on: March 05, 2015, 05:43:28 PM »

I had the water-main to the house renewed a few years ago with blue plastic pipe instead of rusty-brown. The blokes that did the job had a 'mole' thing that ran on compressed air.
They dug a hole then put the mole into one face of it with a spirit level on top. Turn on the air and 'donk-donk-donk-donk'- etc away it went, pulling the air-hose behind it. Five minutes later, it appeared in the next hole 25 feet away. BT rope attached to blue pipe, pipe pulled through from end to end and connected. Nice clean water again, no more lawn-puddles.
This was done over 4 holes, about 20 yards altogether.
My point is; would it be a viable proposition to use a mole, rather than digging out tons of soil? With the agreement of neighbours, it would be possible to do this over a large area without disturbing the peace and harmony at ground level.
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skyewright
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« Reply #10 on: March 05, 2015, 06:16:25 PM »

Thanks all. Glad to see that the consensus is strongly with straight pipe.
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David
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biff
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« Reply #11 on: March 05, 2015, 06:52:49 PM »

Sounds like a very good idea N2,
                               I wonder why no one has ever thought of that before. Maybe the mole is expensive. It must be because it would be impossible to pull the pipe through in one continuous  length. It could be done but then again the pipe might trap air if the mole was forced to drop below a big rock .
  It would be a real headache if you did manage to get almost there and then find that the mole could not complete the job, then have to bring in the digger. I guess the digger is the surest way of getting it done the right way.
                                                             Biff
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Nickel2
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« Reply #12 on: March 05, 2015, 07:01:29 PM »

Probably right about the rock Biff. I haven't got any rock near me though, it's all alluvial stuff: 0.5m brown soil, 50mm yellow running sand, then green-sand and gravel as far as the centre of the earth. I'd imagine my back garden would be ideal if it was big enough, the water-table is 0.5m down.
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24V 400 Ah battery. (4x200Ah FLA)
EpEver STI1000-24-230 pure sine inverter
Of course it'll work. (It hasn't caught fire yet).
stannn
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« Reply #13 on: March 05, 2015, 07:39:45 PM »

There are videos on youtube of the utility mole described by N2. It has also cropped up previously on this forum.
http://www.navitron.org.uk/forum/index.php?topic=10424.0?iframe=true&width=90%&height=90%

I have always wondered about using a mole plough on a tractor to insert the ground-source piping. Sure enough, the following extract mentions that method being used.

 always good to learn. Paul, Nick, Garry and myself spent Friday afternoon being shown around the Rhyg estate near Corwen. Always good going to places with renewables and good coffee. Overall I was impressed with the business approach to investment but also project management and kit selection. The new farm shop and cafe on the A5 gets 500,000 visitors per annum but only costs £6 per day to heat. This was due to a combination of new build, good design and a well thought through ground source heat pump. It was the first installation I had seen which mole ploughed the ground collector in. As was explained to us trenching is half the price of bore hole and mole ploughing is half the price of trenching. But you do need a lot of room eg 600m pipe for a 12kw heat pump system. One of the larger heating systems seen on the day (22kw GSHP) even had a new 7kw Francis hydro feeding power direct to the heat pump…sweet! we had a lot to learn and a lot to share. It’s good to look over the hedge as Patrick Begg calls it to see what others are doing. No such thing as a new idea…better to share and learn.

1.2 to 1.5 metres is quite deep but just requires bigger equipment.
Stan

http://ntenvironmentalwork.net/2014/04/27/looking-over-the-hedge-how-do-other-estates-manage-renewables/
« Last Edit: March 05, 2015, 07:48:22 PM by stannn » Logged

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« Reply #14 on: March 05, 2015, 07:47:13 PM »

Ground temperature is the average of the local temperature, in Greece the ground is 18 degrees here in the UK the ground is 10 degrees. All at about 1 meter deep. Soil is very bad at transmitting heat it takes months to change even 1 degree. Dare I mention heating your ground loops in the summer hysteria hysteria
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