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  #1  
Old 26-07-2006, 12:40 AM
pat_os pat_os is offline
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Default Horizontal Vs vertical for geothermal heating

I'm looking at putting in a gshp in a new build but am wondering whether it would be better to go with the vertical or horizontal collection method. The vertical is presumably more efficient but more expensive to install but I'm wondering how much more expensive it is. If the horizontal pipes are going to require a digger and driver at ~€30 an hour for a week and the grant for the vertical is 2k more than for the horizontal then would it be worth my while going for the vertical
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  #2  
Old 26-07-2006, 12:47 AM
Sue Ellen Sue Ellen is offline
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Default Re: Horizontal Vs vertical for geothermal heating

Hi Pat,

Welcome to AAM.

Have you had a read of the key post on Ground source heat pump and geothermal heating. There are also some other threads on the same subject but not too sure if any of them will address your question.

Best of luck with the new house.
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  #3  
Old 27-07-2006, 12:07 PM
ipxl ipxl is offline
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Default Re: Horizontal Vs vertical for geothermal heating

Quote:
Originally Posted by pat_os
I'm looking at putting in a gshp in a new build but am wondering whether it would be better to go with the vertical or horizontal collection method. The vertical is presumably more efficient but more expensive to install but I'm wondering how much more expensive it is. If the horizontal pipes are going to require a digger and driver at ~€30 an hour for a week and the grant for the vertical is 2k more than for the horizontal then would it be worth my while going for the vertical
Pat,

I was originally all set to go with a horizontal collector when I just
by chance happened to ask a chap locally about his house build and
heat system choice. He told me that his plumbing expert advised
against GSHP for his site on account of the type of soil (gravelly,marl,
etc). I invested a couple of weeks checking the issues and what
I have found is that amongst the most reliable folks in the know
there seems to be a consensus that horizontal collector is very
sensitive to the soil conditions and because of that one needs to
be wary of installers/suppliers who de-emphasise site survey to
advise on ground conditions before giving the choice of horizontal
versus borehole.

The horizontal collector relies on a sort of replenishing conditioning
of the ground by rainwater/moisture and the heating of the upper
layers (within the first meter to meter & half) of soil.
The "marly" soil it seems loses the moisture conditioning too fast
to boost thermal conductivity of the soil and the other extreme
is if you have very poor drainage as a result of stagnant water.
The latter scenario is very bad news as you have risk of ground
freezing up around collector area.

It seems there are ways to counteract the first case .. eg,... importing sand
and creating drainage channels.. but when you add the cost
of excavation, sand import, drainage channels, refill for such a
wide area of ground you might be well worth exploring the borehole
option now that the grant is available.

My current plans are borehole .. and if the drilling isn't feasible
I'm going to look at wood pellets ... or a condensing oil boiler
(option 3).

-ipxl
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  #4  
Old 27-07-2006, 02:18 PM
pat_os pat_os is offline
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Default Re: Horizontal Vs vertical for geothermal heating

Thanks for that. There is a lot of fill on the site so the soil quality isn't great which was what was making me think about the borehole originally. Have you gotten any quotes on how much the bore hole will be?
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  #5  
Old 27-07-2006, 02:36 PM
ipxl ipxl is offline
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Default Re: Horizontal Vs vertical for geothermal heating

At the moment the keenest quote (from a reliable/well recommended
supplier/installer) is approx 19.2k (including VAT - without SEI
grant allowance). The installers are grant approved so actual
outlay would be approx 12.9k inclusive of drilling & borehole collector
installation and heat pump commissioning. I've to get a separate
quote for the UFH controls & installation in the house itself.

The borehole drilling is subject to hitting bedrock at 6metres and
other small print which I have to read over.
Someone in very recent days mentioned to me that I should also
investigate if there might be a well somewhere on the site because
a water source heatpump can have the most efficient coefficient
of performance (COP) in terms of geothermal.
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  #6  
Old 27-07-2006, 03:06 PM
Jolly Man Jolly Man is offline
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Default Re: Horizontal Vs vertical for geothermal heating

Hi there IPXL, i will be starting my house in the coming months and will be drilling a well, would this be able to double up with the ground source heat pump? ie could i give the lads drilling the well a few extra euros to keep drillling? Or your last comment about the well?
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  #7  
Old 27-07-2006, 03:17 PM
ipxl ipxl is offline
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Default Re: Horizontal Vs vertical for geothermal heating

Hi JollyMan

Interesting that you picked up on my comment regarding a wet well.
The plot thickens. Someone yesterday mentioned to me that our
site might be positioned in a place where there is a high likelihood
of a well. This wasn't the heat pump supply/installer I'm looking at
but a plumber who has associations with another heat pump supplier.
Nice guy but the amount of "multiple fingers in multiple alternative
energy pies" which plumbers seem to engage can be more than
a bit confusing and disconcerting at times.

Anyway - I did take his point. It would be worth checking if there
might be well water source on site. How did you go about this ?
Was there a costly survey ? He mentioned a diviner. Last time I
saw a diviner was about 20 years ago when I was a teenager
watching the Late Late Show and there was a balding country
man going around fields with a willow stick or something similar.

We should compare notes on well water sourced heat pumps.
I'm an ordinary punter and have no affiliation with plumbing
or heat pump suppliers. I'm just interested in getting a decent
COP with the heat pump if we are going down that route.
The horizontal collector principle looked way too marginal and
delicately balanced to be capable of giving a decent long term
return on investment or confidence of paying for itself for
my liking.

-ipxl
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  #8  
Old 27-07-2006, 03:28 PM
Jolly Man Jolly Man is offline
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Default Re: Horizontal Vs vertical for geothermal heating

Its exactly as you said i got a local diviner with the willow branch, she also had a steel chain! If you are drilling a well i know the subcontractor who carrys out the job will survey it for water in the process and is all included in the price! Do you have any indication on the price of the ground water heat pump? I have no idea how all this works so please excuse me if some of this comes across as being clueless!
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  #9  
Old 27-07-2006, 03:31 PM
ipxl ipxl is offline
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Default Re: Horizontal Vs vertical for geothermal heating

No price indications as of yet.
I'll send you a PM.

-ipxl
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  #10  
Old 27-07-2006, 03:56 PM
extopia extopia is offline
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Default Re: Horizontal Vs vertical for geothermal heating

Quote:
Originally Posted by pat_os
If the horizontal pipes are going to require a digger and driver at ~€30 an hour for a week...
Your man should be able to dig out the area in half a day easily. Another half a day to fill it back in. Who quoted you for a week?

AFAIK vertical grids are generally used where there isn't enough room in the garden for the horizontal version. Costlier, as you've discovered.

We went with horizontal, and our soil is of the heavy, wet type. No problems last winter (which was very cold up our way).
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  #11  
Old 27-07-2006, 04:05 PM
ipxl ipxl is offline
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Default Re: Horizontal Vs vertical for geothermal heating

Extopia - You characterize your soil as the wet type. How did things
go in terms of your T-test/percolation test for septic tank/&-or treatment
plant ? We were told we needed raised percolation field which was
to address the poor or non-ideal drainage quality of the soil area
on our land.

I'm not great at understanding the various types of soil morphology
that exists around the countryside but from what I can gather our
subsoil is gravelly/marly. It seems it might dry out quick. I think
the horizontal arrays work best if the rainwater gets a chance to
condition the soil (water being a relatively good conductor of heat)
and also there needs to be ability for water to freely move (stagnant
bog would be bad). We don't have stagnancy issue but it seems to
be the marly subsoil which would probably lower the effective
thermal conductivity of the soil. This is what is pushing me to
investigate either dry borehole or well. We have 1.3 acres of space.
Some installers seem to de-emphasise the soil conditions issue
when it comes to installing horizontal collectors. That concerns
me greatly !

-ipxl
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  #12  
Old 27-07-2006, 04:44 PM
extopia extopia is offline
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Location: Dublin
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Default Re: Horizontal Vs vertical for geothermal heating

Well perhaps that is because it's not really an issue? I've come across the theory myself (elsewhere on this site, actually) but I'm not convinced. Geothermal heat pumps extract only a small amount of heat from the soil, and the theory is that ground temperatures are pretty uniform below a certain depth, regardless of the composition of the ground.

I'm no expert, but our system seems to be working well. I would describe our ground conditions as "heavy."

Re waste treatment - our ground does not percolate well. However ours was a renovation, not a new build, and we opted to continue with the existing septic tank, in the absence of any obvious problems. I would expect to have to install a treatment plant in the future, however.
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  #13  
Old 27-07-2006, 09:22 PM
pat_os pat_os is offline
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Posts: 30
Default Re: Horizontal Vs vertical for geothermal heating

I got the timeline of a week to dig the trenches from another post on aam. I spoke to one supplier at one of the ideal homes exhibitions and he also suggested that if I could source a well on the site that this would be more efficient to take the heat directly I must say though that I ws a bit sceptical of this. Even with research done I had never heard of it before. I have no idea of what is involved in digging a well, is it just a matter of getting below the water table? Prior to all the fill that went in to the site there was a number of small springs there but nothing major and the soil type below the fill is peaty.

Something else I had conidered is locating the collection pipes near to the percolation area of the septic tank. My percolation test results weren't great but passed and maybe a boreholoe nearby would prevent percolation problems and also give some way of collecting the warmer water leaving the septic tank.
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  #14  
Old 27-07-2006, 11:31 PM
extopia extopia is offline
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Location: Dublin
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Default Re: Horizontal Vs vertical for geothermal heating

A vertical collector does not have to be in a well. You can go straight into the ground, water or no water.

However what you were told is correct - siting the collector in a well or a pond or river, if available, is indeed more efficient as the temperatures will always be that little bit higher. As far as I know, it's not necessary for a good system, but more efficient if available on your site.

A week to dig the trenches is a little over the top, unless you have a huge collector area. Mine was pretty standard, about 20m x 20 m (not trenches - we dug out the entire 400 sq metre area). Like I say, a total of about a day to dig and then fill back in.

How would a borehole prevent percolation problems? If your ground doesn't percolate the borehole won't make much difference.

Warmer water leaving the tank? Maybe - but remember the whole idea of ground source heat pump is to collect the 8 degrees (average winter soil temperature at 1m deep), and multiply it using a compressor, then circulate it through your indoor heating system (preferably an underfloor system).
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