There are a few about, but its not really relevant.. mines are hot because of the mining that goes on. It takes a lot of energy to mine and it heats up the mines a lot. However I don't have a mine to extract the waste heat from, just some land which isn't enough or a bore hole if I can be sure it will still be working in 20 years time or use air which is what the original question was.. how do air sourced heat pumps compare to ground sourced ones?
And you accuse other people of being stupid.
How do explian the elevated temperatures in abandoned workings?
MBQ
Just you ATM, because you appear to be so.
Elevated above what? Obviously any elevation is a result of energy input but without knowing just exactly what you are being vague about means its impossible to answer in a time frame where I care.
A quick google search shows plenty of evidence that mines *cool down* whilst being actively worked due to the ventilation systems, compressed air from the surface used in machinery, and cooler water flowing down from shallower workings.
There are already working heatpumps around the world including Scotland taking heat from the flood waters in abandoned workings that can reach tens of degress C, depending on depth and local geological conditions.
One article may imply (I'm not sure) that coal fields are associated with areas of heightened geothermal activity and maybe cannot be directly compared with rock caves.
MBQ
snipped-for-privacy@r24g2000yqd.googlegroups.com...
Above surface temperatures, what else do you think?
Abandoned working quickly flood, unless the pumps are kept running to protect nearby hydraulically connected operational mines. There is no further energy input and the water reaches thermal equilibrium with the surrounding rock.
MBQ
messagenews: snipped-for-privacy@r24g2000yqd.googlegroups.com...
Well they aren't in summer and they are in winter, are youy sure that is the question as the answer seems a bit obvious.
How long after? To what depth into the rocks? How many years was the mine operating? What's the thermal conductivity of the rock? What mining technique was used? Where is the mine? All change the answer, as I said you are far too vague to expect an answer in the timescales before I get bor
Wrong. They are hot because the earth is hot.
Otherwise the cold ground would take heat OUT of the mines wouldn't it?
It does not.
Otherwise it wouldn't be worth doing. Not for coal anyway/
There are in fact studies to use flooded mines in silesia, that have been closed for 20 years, to extract heat from.
But first, get an education. And understand basic O level physics. Or is that degree level physics these days? Probably.
Above surface ground temperatures., or indeed temperatures a few meters down.
messagenews: snipped-for-privacy@r24g2000yqd.googlegroups.com...
They are.
and they are in winter, are youy sure that is
Well not to you apparently.
A mile down, an abandoned mine is certainly hotter than any english summer day.
Explain that.
Mole plough? (Or drain plough, or mole plow, or mole drain plow....)
They have to be cooled. I went down one that was in fact not working at that time. Saturday.
It was insufferably hot, and the rock was hotter than the air.
Thank god for ventilation, which kept it below 30C.
Dont confuse dennis with facts.
Its just the same in a gold mine. Or any other mine.
England is hardly an area of high geological activity these days.
Neither is S Africa, where many gold mines are. 50C or more there without cooling.
The rock is too hot to touch.
Or Australia. Essentially the FACT is that it gets hotter as you go deeper wherever you are.
In some places where there is geological activity, it gets hotter a LOT faster, that's all.
Thank Alan (and to others who answered). The James moleplough would seem ideal but that manufacturer is unfortunately on the other side of the world.
Attempts to search e-bay for mole plough persistently timed out so I don't know if there are any for sale (or indeed for hire) at present.
AFAIK all deep caves are in mountainous regions and are probably comparatively close to ground surface for much of the system. The deepest quoted has been dived to a depth of 45m which point is apparently just 66m above sea level.
Past changes in sea level mean there is a possibility at least for the cave to be several hundred foot deeper but I would have thought bottoming that depth is well beyond the capacity of cave divers.
Easy..
(mantle temp - 20C ) / crust thickness will give you the temp gradient assuming a steady state. This means that the temp goes up as you go deeper until you start to change things by e.g. drilling a hole or mining.
However the actual amount of energy flowing through the crust is minimal so extracting it will cool it quickly. What it means is you can't get much high grade energy out of the ground unless the rocks are very fractured and you can get it from a large volume. Try extracting heat from the top 100 mm of 300 mm deep glass fibre insulation in a roof to get an idea. When you put the thermometer in it will read higher than the external temp but you won't get much energy out and the temp will drop rapidly.
If you want maths try this..
Mantle about 900C call it 1000C. crust depth about 10000m temp rise about 1000/10000 C/m now google for the R value of the crust and workout how much energy you actually get for a m2.
Its different in the top few hundred feet as the energy also comes from the sun and this is only possible if the ground is cooler as the depth increases as heat energy flows from hot to cold. IIRC its about 13C in the top 10m in the UK.
Diesel is quite a good energy storage medium so I'd need a bit of convincing that the amortisation of a battery plus the charge discharge conversion losses could be worthwhile. If the power source is free then maybe a different matter.
I might use a small battery to absorb peaks and react to changes in demand but principally I would be looking at two gensets sized 2:1 and try and run them intelligently to keep the conversion up in the 30%+ region. We made the mistake with our chp unit of listening to the users insistence of having electric kettle and the photocopier. Still it was worth doing to get some heat recovery, which was not possible with the previous air cooled genset.
I wonder how efficient sine wave inverters are now but modulating the generator speed to stay in a sweet spot, rectification and reforming to
230V 50Hz is an attractive idea.It looks like gas prices are on a downward trend but even so we don't hear much about the little Stirling grid connected gensets which gave 1kW(e) and
9kW(t) that British Gas hyped and then dumped. So I think home generation of electricity from fossil fuels cannot beat grid prices.AJH
tell that to the successful GS heta pumps operating out of flooded mines.
I don't have to, its basic physics and I am sure they understand it.
Explain why the geothermal power stations in Greenland have to keep finding new sources of heat? PS they don't use the heat escaping from the core by conduction just to give you a start.
Oh dear this seems to be turning into a usenet name-calling contest. Anyway, I can't find my original reference to the Southampton project but here's a good link I found while looking around:
It agrees with the view that heat is extracted faster than it is replaced: "Because of this, accessing that heat is considered to be "heat-mining"; i.e., once used, it is only be replaced on geological times-scales. It is thus not "renewable", as are volcanically-active sources of geothermal energy." and goes on to give an expected life of: "The present borehole has a life of about 20 years".
To go back to one of the original questions which started this debate, it does indeed look as if GSHP is another non-scalable renewable - fine in small quantities but doesn't work if lots of people do it.
No, thats geothermal heat.
which is sustainable a lowish levels of output.
Normal heat pumps that don't go below 100m rely on solar input to the ground around them to recharge the subsoil every year.
WE only wandered off into geothermal because Dennis insisted that mines don't get hot as they get deep. And trhen pretended that if they did, it was because people worked in them, and then made some other excuse to try and preserve his façade of being something more than a complete moron who knows next to bugger all about anything.
Average insolation of the UK is a couple of hundred watts per square meter.
You can easily heat a room of a square meter with a couple of hundred watts. Ergo there is more than enough solar energy coming in to stay warm. The problem is utilising it.
wide flat and not to deep is cheap.
But deep is as good, just expensive.
yes if everybody does it, everybody will be less efficient, but the actual heat produced is a small fraction of what is falling on even an urban situation, AND that heat all leaks back to the air anyway, which is (partly) why cities are in general 2C hotter than the country side surrounding them. Which will reduce heat loss from the ground.
Plus of course cities need aircon, and with a borehole type situation, its perfectly possible to charge up the subsoil in summer. Some scandinavian schemes do this.
Well *I* have provided with you with the real physics involved in what you think is true but as usual you just ignore them and pretend that I don't have a clue.
You even chose to argue about stuff where I was in agreement with you, like the energy from the boreholes coming from solar heat and not from heat conducted from the core.
Then you decided I was calling you a liar because I agreed with you that mines were hot.
AFAICT you just argue even if the other party is agreeing with you even if that isn't often.
So we will try it again so you can argue more on a point by point basis.
The crust will obviously have a higher temp the closer it gets to the mantle as the mantle is @ 500C - 1000C (approx) just as any insulation has a temp gradient between the hot and the cold side. This does not mean the heat is useful as the insulating properties stop you extracting it at a useful rate.
An abandoned mine will over the years return to the same temp gradient as the surrounding rocks.
A working mine will have forced cooling and large amounts of energy input from the work in progress, the balance of the two will determine the temp and has nothing to do with the depth below ground and more to do with economics and what you can get away with.
The geothermal energy as extracted in places like Iceland comes from a different mechanism and is primarily there because of volcanoes and comes from cooling magma not the crust. No geothermal systems have drilled through to the mantle to extract heat and there aren't likely to be any in the near future which is why the UK is not going to be able to use geothermal for power generation.
We are in agreement that the heat you can extract from GSHP in the UK comes from the Sun. Therefore it is a *fact* that you can only extract a finite amount per sq m and it is a *fact* that if there are too many boreholes in the area they will fail to provide the returns that one borehole would. It is also a *fact* that ground temps will be lower where such a system is installed and may effect the local environment unless alternatives to letting the sun warm the soil are employed.
The problem is capturing and storing it for when its actually useful. Using it at the time it arrives is easy.
So here you stating the answer to the original question without anything to back it up at all.
And now you are contradicting yourself, a 200 m2 surface collector is never shared by others and is unaffected by those around it.
A borehole may well be shared as you probably wouldn't have used one if you had the land area to put in a surface collector.
So a borehole is not as good in some situations.
This is the point of the question in the first place! I.e. how does GSHP compare to ASHP, which you have had zero input on and just keep throwing in irrelevancies to argue about.
So lets think that through..
The amount of energy from the Sun is probably lower in cities due to pollution.
What may happen in cities is the solar energy hits walls, roofs etc., these have a much lower thermal mass than the ground and will rise in temp faster than the ground, this could lead to a rise in air temps in a city and a fall in the overall amount of energy getting into the ground.
Funny, I said that (not the Scandinavian bit though).
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