Say, for instance, "one" didn't have access to such a sizeable "garden" as you've got for your system . . . is there a break point where a ground heat pump isn't really viable?
Only we've got a south facing garden, on a pretty steep slope, and it's a funny shape, but size wise, best guess 40 yards by 40 yards, would a system like this be viable
And how the hell do you bury pipes 4' into the ground, please tell me you didn't hand dig them in, surely, or was that part of the installation by a company?
And, super cheeky I realise, but would you be prepared to give an indication of cost and / or break even time . . . a simple Fuck Off HV is a perfectly acceptable answer btw
A ground source array of 40x40 yards could power a ground source heat pump of about 15kW output (ballpark) (possibly less depending on just how weird a shape), which is fairly decent and exceeds the requirement of most houses - whether it would be sufficient for yours specifically would depend on the energy requirements of your house of course.
You can use boreholes instead of horizontal trenches as well, which massively reduces the ground area required, but is more expensive to install.
To dig the pipes in you get Danny and Steve to come by with their 5 ton diggers and dig ten 60m by 1.2m deep by 1m wide trenches, 3m apart, in a sort of fan pattern. The pipes are then laid as 10 loops, running up one edge of the bottom of each trench and back the other - so it’s 1m between the flow and return of each loop, and 2m to the next loop - this is so you don’t freeze the ground!
Cost was about £5k for the digging, £15k for the equipment, and £5k for the labour. Breakeven - well, lots of ways of looking at it. The simplest would be just assuming that all heat and hot water was powered by direct electricity. For an estimated annual requirement of 22MWh (which is what it’s estimated at - haven’t actually finished renovating it yet) the cost differentials per year are something like:
At 30p/kWh and COP of 5.4(!): saving of about £5.5k/year.
At 30p/kWh and COP of 4(more realistic): saving of about £5k/year.
At 50p/kWh (where it looks like it will be in autumn) and COP of 4: saving of about £8k/year.
So 3 to 5 years or so, on those figures.
However of course on purely cost grounds you’d not use electricity as your primary energy source, so that’s not really fair. Oil-fired heating is standard round here, so would be a fairer comparison pound for pound. It would have cost about £5k to install an oil boiler and tank etc, so the cost difference to use would be £20k vs the £25k cost of the gshp.
Heating oil is currently about 10p/kWh, so actually cheaper than gshp at COP of 4 and 50p/kWh electricity (12.5p/kWh), so one would never break even. Who knows what the price of oil (which isn’t subject to the energy cost cap I believe) will be at that point though? If it doubles from here (and it’s already very high historically) then one would get an annual saving of about £1,500, so about 13 years. But trying to guess relative oil and electricity prices 13 years into the future is a fools game anyway!
Also - there are govt grants and paybacks for installing low-carbon systems including gshps. How much one gets (paid quarterly over 7 years) depends on a complex calculation based on the energy requirements, energy savings, insulation level of the house and other things - I have applied for it, but don’t know yet how much I’m going to get. It could theoretically be as much as £30k - which would of course make the whole thing free (making a profit in fact!). We shall see.
And of course the main point here, really, is to de-carbonise the energy requirements of the house; the comparisons with heating oil above therefore are missing a term which expresses how much ‘value’ to put on that. I think it’s extremely important and am therefore willing to pay somewhat over the odds to help achieve it (and recognise that I’m very lucky to be in a position to be able to choose so - but it’s the people who can who have to for all our sakes).
When I find out what the govt contribution is going to be I will update here.
Had it about ten years now & it's still working fine, although various parts are starting needing replacing. Our heating & hot water costs about a third of a conventional gas or oil system.
so you end up chasing your tail. 
