[Closed] ground source heat pumps

sharkbait,

Im pretty sure mine is cheaper than oil now, although when I did the original sums when I was specifying it, it was, on paper, going to be a bit more expensive in the short term, but oil price inflation has already taken oil ahead of biomass since then, only 2 years ago.

Last figures I worked out are here:
http://singletrackworld.com/forum/topic/biomasssolar-eco-experts-advice-sought-stoner#post-2959506

if you use the average kWh consumption figure and british gas tarif structures, the weighted average cost of gas fuel is about 4.9p/kWh. At 90% efficiency for an A rated combi, that's a real heat generation cost of about 5.5p/kWh

My pellets cost about £259/tonne, with an energy density of about 4.9kWh per Kg, 5.2p/kWh
At 89% efficiency in my pellet boiler, thats 5.8p/kWh.

With heating oil prices at around £300/500 litres and oil energy density of 10kWh/litre, oil boilers are a little more efficient at around 92%, so cost comes out at 6.5p/kWh

Those calcs rather surprise me. When I first did these figures 18 months ago, gas was loads cheaper, and oil was the second cheapest - something like 3.5p gas, 4.4p Oil and 5.5p wood.

What I missed out from that calc is the log cost. If I burn logs, my finger in the air estimate is that it costs me around 3.5-4p/kWh.

30m is quite a way, but my neighbour has his biomass boiler in an outhouse about 10m from his scullery where the pipes come into the house and distribution manifold. I saw him install the insulated pipe work and it's big stuff, something like 75mm thick (160mm+ dia) of armourflex insulation around a 28mm flow and return, in a plastic conduit. Not cheap stuff but Im assuming it's got excellent thermal characteristics.

The capital cost of my install was about £10k for the boiler and thermal store and another £2k for the solar thermal that did myself. I currently do not have any RHI payments becuase my particular boiler does not have MCS certification. This is because there's some uncertainty on how the govt want to treat log boiler efficiencies. You can more easily find certificated pellet boilers (the pelletmaster by woodviking is the sister unit of my big biotriplex thing and is certified) and that would give you an RHI income to offset the capital expense.

You dont necessarily need a thermal store, it just makes addition of solar thermal easier. If you were just going to use the pellet boiler all year round you could rely upon the tank in the boiler alone.
https://sites.google.com/site/woodviking2010/pelletmaster

the pelletmaster has a 220L tank and an indirect coil in it so you can use it for potable indirect DHW and as well as radiators and UFH if you have it. That boiler is about 5-6k + installation cost. You'll need to research how much the RHI might be worth I havent done it for ages.

If you're interested in the woodviking models, Id be happy to introduce you to a very excellent installer based in the south west, or the UK rep who I know quite well.

There are plenty of plastic underground heating mains available which are pre insulated.
Uponor springs to mind.

The life span quoted for them worsens the higher the temperature you put through them and if you can do it in a full length with no fittings underground is a better solution. Note "quoted"

I wouldn't even entertain metal pipes underground however well protected but I know there are welded systems out there that work fine.