I see Croydon is fitting ground source heat pumps to heat a 44 unit high rise. Amongst other things, they say it'll cut the costs of maintaining the current storage heaters.
I thought storage heaters were pretty much maintenance free. And GSHPs required annual monitoring of their relatively complex electronics and piping to make sure they continue to work as designed.
Any insights?
You need an acre or so of land with the proper soil type or a serious borehole for ground source heat.
The deep tubelines are warm even in the depths of winter. I'm surprised no-one has tried to harness that for heating. Not that would help Croydon, the underground doesn't go there.
Electric night storage heaters are indeed maintenance free from an operating point of view and AAFAIAA require no annual safety checks.
As with all electrical installations in public buildings, periodic checking of the electrical systems is required.
If the nsh's are ancient running repairs may be needed from time to time. e.g replacement heating elements or thermostats.
The cost of ground source heat pumps and the installation of hot water pipe and radiator systems will be considerable.
The maintenance costs of the heat pumps is an relatively unknown at present but in my experience will be more than considerable.
AIUI the main benefits of the scheme is lower running costs for the tenants and a relative reduction in the Council's carbon footprint.
Am I being thick here, but is not the result of taking heat from the ground to heat a building going to make the ground cold until it presumably gets so cold no more heat can get in fast enough to keep heating the building? Brian
Yes which is why I mentioned it, unless they have a secret volcano in Croydon nobody is aware of? Brian
I think that trying to cool down the Earth would probably require more of a heat exchanger than a tower block.
You just need to exchange heat over a suitably large area and temperature gradient.
Cheers
Dave R
Yes its the area, but if you put it under other peoples land that could be an issue. Does anyone remember the idea of putting a rock store under your patio when you put up a conservatory? Brian
The heat is renewed by the sun, rainfall, groundwater and geothermal heat. Depending on how deep the pipes are buried and the nature of the ground. Around 50m pipe is needed per KW
Back in the 1970's the CEGB started research programmes on renewables, including solar PV, wind, wave, and what was called at the time "hot rocks". The latter involved drilling reasonably deep bore holes, maybe a kilometer or two, into known "warm spots", one of which is in the Southampton area, convenient for the (long gone) Marchwood laboratories that had the lead in this work. IIRC they were in effect using fracking to increase the useful heat transfer surface area. They were basically pumping water down one hole and up another to harvest low grade heat suitable, I think, for district heating. (Certainly you don't get the sort of quality of steam that they have in Iceland which will run steam turbines). I think they might also have been thinking about running power turbines using gases such as ammonia or methane.
My recollection is that they found they could get about 50 years worth of useful energy before they had cooled the rocks off significantly. There is, of course, a fairly uniform temperature gradient of the order of 30 deg C per km and a heat flux of about 0.1W per square metre.
I think this is why ground source heat pumps are normally associated with a reasonably sized "field" per house, because they are mainly collecting solar (and air) heating rather than true geothermal.
It's interesting to speculate that if, some time in the future, we get small modular reactors that can be sited in urban areas, perhaps heat pumps could provide sensible district heating from their waste heat. At least in the domestic market we use something like three times as much thermal energy as electrical, so it is not a bad match for water reactors with ~ 30% thermal efficiency (at least in the heating season).
As I understand it some badly designed ground sourced systems in the UK did take too much heat from the ground. The ground will recover but its how long it takes. A day or two is not enough so as the weather gets colder and there is more demand on the system the system become less efficient. Instead of putting 1kWh in to get 5kWh out it starts getting closer to 1:1.
Assuming that the tower block hasn't got enough land to lay the pipes horizontally then boreholes will be used. 10kWh will require maybe 2 off
100m of boreholes. However this is a 44 unit dwelling requiring many such boreholes.
Also in Cornwall, drilling down into granite:
The way it works is that summer sun heats the earth and winter heat pumps cool it. You probably need an area somewhat larger than the total floor area you are trying to heat...
The problem with boreholes is that over a period of time the heat is NOT replenished.
geothermal use of (flooded) mines results in abouyt 10 years before the mine is too cold to be of use.
Perhaps there are potential enviroment issues. The greenies are worried about ground water pollution with fracking but what about when one of these boreholes gets to an age where it starts failing and releases whatever fluid/antifreeze they are pumping around the system?
Fast flowing water tens or hundreds of metres underground may be supplying a local river and any contamination may be seen in the local waterways almost immediately. Fast flowing underground water may also indicate unstable ground that may cause a borehole and associated pipes to shear horizontally.
Please research how fracking works.
I know how fracking works but I'm not sure how many of the fracking protesters do.
Why would anyone want so much rock? It's horribly sticky and it rots your teeth.
Bill
From the above, it seems you do not
None., Key up theit bottoms wind em up and watch them protect your oil and gas business from new competition.
>Ahe there is that of course, you need to get the specification right for heat storage purposes, and then run water pipes through it to take the heat away. Brian
Did the CEGB have any input into the scheme apart from that it was a convenient organisation who had a site where the borehole could be drilled? A mate worked there in the labs during that period until the Power station and labs were closed so I must remember to ask him next week . I always thought it was the Department of Energy and some European money that was behind the project. Neither Marchwood or the Southampton Boreholes produced the expected results with temperatures much cooler than anticipated due to the level of where hot water was to be found being hit nearer the surface than expected. Marchwood was just abandoned . Southampton well head for many years was left in situ in a small compound in the middle of the car park that served Toys r Us , it looked quite comical as there was an information board that bore the information about this wonderful new technological enterprise but the effect was destroyed as the well head had been hidden from view by a Six by Four garden shed of the type that is bought as a flatpack in B and Q and probably was.
The Department of Energy having given up Southampton City Council stepped in and restarted the project and got investment in a company they have an interest in to progress a district heating scheme which has been running for over 2 decades now. The hot rather than scalding hot water is augmented by gas to bring it up to the temperatures needed.
I suppose the finances are a bit like Concordes,the research and development cost of the borehole having been spent by someone else and lost using it subsequently because it was there makes the scheme viable to operate .
GH
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