Went to visit a self build, they had geothermal

[CalvinHobbes]

And explained in our climate it works better than air source, which is better suited to warmer climes. Is this true? I thought GT was more expensive to run too. Internal temp was 20. 

[ProDave]

So in the UK, just how deep do you have to go to get useful geothermal?

[Nick Thomas]

Eden project are at ~5km, bless 'em: https://www.edengeothermal.com/the-project/drilling-and-operations/

 

That's "proper geothermal" though, a ground-source heat pump can do alright with a ~50-200M vertical well, depending on where you are and whether you go open or closed loop.

 

https://www.bgs.ac.uk/geology-projects/geothermal-energy/ has a brief overview of different technologies and a couple of shiny maps.

[eandg]

For geothermal you surely need scale and a heavy load for it to be viable. I have been told that in Denmark they run pipes up to 30km from geothermal mines to get heat to population centres. 

[saveasteading]

The experts in the ground source industry now advise caution. And also admit that the ground needs warming again from solar or water movement.

So nowadays, clay boreholes  needs warming from solar arrays in summer.

 

Near me they used 40m boreholes into clay. Half of the installations work , half have been replaced by air source.

[Nick Thomas]

@saveasteadinginteresting, thanks. That's because the house pulls heat out of the ground faster than it can be naturally replenished, I guess?

[saveasteading]

54 minutes ago, Nick Thomas said:

  pulls heat out of the ground faster 

Correct. If the ground was porous sand/gravel with a flow of groundwater then the cooled water would be replaced by warmer. In heavy clay or rock there is no significant replenishment and it gets cold then freezes.

[IanR]

On 12/02/2023 at 19:53, CalvinHobbes said:

And explained in our climate it works better than air source, which is better suited to warmer climes. Is this true? I thought GT was more expensive to run too. Internal temp was 20. 

 

There is often confusion, even within the industry, with regards geothermal and ground source. The terms are starting to become interchangeable, but I remember when Geothermal required at least a 500m borehole, and probably more, to get down to rock that was being heated by the earth's core, rather than solar energy. Unless you happen to have a hot spring emerging on your plot, when you could go without the borehole.

 

Ground source is of course absorbing energy from the ground, or water that is heated by the sun. Typically GSHPs have lower day-to-day running costs, but are much more to install and a little more to maintain. With the demise of RHI, I can't see there ever being a cost benefit of GSHP over ASHP.

 

3 hours ago, Nick Thomas said:

That's because the house pulls heat out of the ground faster than it can be naturally replenished, I guess?

 

Only if the ground arrays are incorrectly sized, which does seem to be the case with a reasonable number of early installs.

[jamieled]

19 minutes ago, IanR said:

There is often confusion, even within the industry, with regards geothermal and ground source. The terms are starting to become interchangeable, but I remember when Geothermal required at least a 500m borehole, and probably more, to get down to rock that was being heated by the earth's core, rather than solar energy.

+1 to the depths required, particularly in the UK.

 

The key difference that I'm aware is that gshp will still need some sort of heat pump to get useable temperatures, whereas geothermal operates between about 100 and 300 degrees Celsius and so doesn't need one.

[saveasteading]

3 hours ago, IanR said:

Ground source is of course absorbing energy from the ground, or water that is heated by the sun. 

Thus, slinky pipes underground are near the surface.  The ground warms and stores heat in summer, but loses it in winter. Hence the newish acceptance of force heating the ground, using solar panels, in summer. 

Power therefore needed all year.

[SteamyTea]

19 hours ago, IanR said:

There is often confusion, even within the industry, with regards geothermal and ground source

Yes, and it cost us a fortune when they decided to heat the Jubilee Pool with geothermal energy.

They still claim it is, but I had a heat pump.

May as well have fitted a WSHP as all the plumbing is already there.

 

I would have to look at my old text books, but seem to remember that radioactive decay gives out very little energy, on average. Something like 60 to 100 mW/m² at the Earth's surface.

Solar is 250W/m² on average.

So all but a tiny fraction of a percent is solar energy in a domestic geothermal installation.

 

Like hydrogen in the universe, there is a lot of radioactive decay in the Earth.

Just that nearly all of it is not accessible.

 

[Nickfromwales]

On 12/02/2023 at 19:53, CalvinHobbes said:

And explained in our climate it works better than air source, which is better suited to warmer climes. Is this true? I thought GT was more expensive to run too. Internal temp was 20. 

Did they have true geothermal or the geothermal intake for ventilation? 
 

https://www.gogeothermal.co.uk/products/mvhr-awadukt/awadukt