Groundloops for a heat pump

[linesrg]

Good Afternoon,
I've got my digger driver coming over on Wednesday and I'm trying to get my head around all the seperate jobs I'm wanting him to do for me.
The Navitron site tells me I need around 300mtr of pipe for the groundloops for a 9kW GSHP. Elsewhere I read it may require upto 450mtr. As the pipe is supplied in 100 or 150mtr coils I'm presuming I'll need to use a manifold and create a number of parallel loops? Any suggestions as to a source other than the one guy I can see on eBay? I don't want to oversize the system as this will just increase the ciculating pump power requirements and potentially lead to shortcycling(?).
I also read that the manifold 'should' be located down a manhole and thus I assume I'd need slightly larger supply and return pipes from the manifold back to the GSHP?
I'm not planning on doing anything this week but I am looking to get the pipes down before the farmer sows his barley in Spring.
Comments/ advice appreciated.
Regards
Richard

[welshboy]

This is what I did - for what its worth.
As it was an easy dig 5 trenches each about 35 metres long 4 metres apart.
4 trenches each had about 150 metres laid in slinky (olympic rings cable tied)with the ends returning in the fifth trench.
just wanted to keep the flow returns separate.
All this in 25mm mdpe.
Manifold X 2 made up from
each 2 elbows 3 t's  all in 32mm but reducing to join the 25mm 4 taps( so I could isolate a set.)
32mm flow return to the heatpump 9kw
google found cheap mdpe supplier don't think I can name them but they stock pipe.

[baker]

 hi
 the size of the ground loops will be based on the soil condition
 you cannot over size the system a bit more is good  its better to have the primary fluid temp in ground loop as high as possible
 as the heating season goes on the  bank or energy recovered  from the ground will bring the loop temperature down
 and the cop will also drop the more surface area covered the better
 Slinky are good in wet damp soil
 redial in sandy

[linesrg]

Good Evening,
Given farmers and the like use MDPE pipe fittings and bury them routinely I guess there is no good reason why I can't make up a manifold from 'T' pieces and having tested the system for leaks leave the whole manifold buried in the ground.
I'm also reading about lagging the pipes back from the manifold to the pump.
All comments/ advice still welcome.
Regards
Richard

[baker]

 to bury the manifold is not a good idea
 you will need isolation valves on manifolds to fill and vent  mix antifreeze
 you will need to inspect manifold if you have a problem its a good bet its there
 we insulate the internal pipe work only

[linesrg]

Baker,
OK no problem with the manifold being above ground and adjacent to where I plan to put the GSHP.
My digger driver was here today and has some experience of having done a couple of previous groundloop jobs. Given I have a 10acre field to play with his view was that I could spread say 4 x 100mtr or 3 x 150mtr loops well away fron one another and that he would just rip the ground up with a 300mm backhoe bucket which would take no time at all to do and use less sand to boot (he also suggested possibly using quarry dust???) and that we just lay the pipes singly in each trench. He also suggested using 32mm pipe to reduce back pressure and it only cost about £0.04 per metre more as opposed to the 25mm I was looking at.
All comments/ thoughts invited.
Regards
Richard

[ecogeorge]

Use 32mm pipe.
Go 2m deep - harder than you think in places , make coiled "slinkies" and fix with heavy duty cable ties uses must less trench length. Single uncoiled pipe is an expensive luxury. If your ground is dry / stoney/ free draining  make the   lengths longer. Use equal lengths of pipe on the same manifold for equal flows.
Place pipe in the wetest / boggiest ground you have.
rgds George.

[linesrg]

George,
We live on a clay based soil and the ground can certainly get wet which is why we're getting the digger in in the first place to lay more drainage. Also digging down 1.5 - 2mtrs is no real issue. I could slinky it which is want the digger driver has seen done before but I would rathet take the heat from a large area in the hope I won't see so much of a drop off in performance as the season draws on.
Your comments and others are welcome.
Regards
Richard

[Bodidly]

Hi there

I have a 6kw heat pump with a 200m single loop my ground is fairly wet and i wish i had put more pipe in.I used slate dust from the local quarry (£3ton) but if your ground is not to rocky i would do without the sand.

[Ted]

We have a 12kW GSHP with 800m (8 x 100m) ground loop.  At a depth of 1.5 - 2m all laid in sand - the ground is hard shale at that depth here.  It is also very wet land (underground springs and rain) on a slight gradient so there is plenty of water constantly running through. You don't want water unmoving and stagnating underground in your trenches.

[linesrg]

Ted,

Thanks for your contribution, so basically more is better than less. Taking a similar ratio then I'd be looking at 600mtr rather than 450mtr? No real problem to run 4 x 150mtr loops. Our field is definitely on a gradient (it has a wee burn running down one side and a larger one across the bottom so we know there is no shortage of water!!) and very definitely wet which is why we're now installing more drainage to solve problems from slightly higher up on the top field which has a natural spring line.

Regards

Richard

[StBarnabas]

Our 9kW GSHP was installed by a company so I have no part in the design but has 3x30 metre trenches each with c. 250m of 28mm pipe  laid as slinkies. These run to a central manifold about 20m away from the heat pump. The heat pump is connected to the manifold via 50mm pipe. We have very heavy clay soil normally waterlogged for about 6 months of the year.
Sean

[welshboy]

Use 32mm pipe.

rgds George.

I readily accept that I could be wrong in my layout where I used 32mm flow return to the groundloop manifold and then 25mm slinkies but I reasoned that  for a given flow rate in litres per minute the 25mm pipe would put more surface area in contact with the soil relative to the volume of water carried so there should be a better heat transfer. Another reason was that the pump/valves place a constriction on the pipe so large sizes are really redundant.
Anyway that was my thinking at the time.

[Eccentric Dyslexic]

What temps are you getting from your ground loops during this cold weather chaps?

im getting about7.6c and 8.4c from the loop in the well.

steve

[Richard Owen]

The smaller the diameter of a pipe, the higher the ratio of surface area to volume.

I think you should use as small a diameter pipe as possible for the ground loops.

It will aid heat transfer.

I use 20mm pipe for my 9KW heat pump.

I have a manifold made of T-pieces and 35mm pipe running between the manifold and the heat pump.