Here's an interesting question. It's often said that ground source
heat pumps are better than air source heat pumps but the problem is
that you have to dig up a lot of your garden to fit the pipe work. If
you were having a new driveway, would that give you sufficient area to
install the pipe work for a ground source heat pump or would it need
more space than that (though I realise that depends how big your drive
If this could work, what would be involved? Do you just bury the pipe
in the soil and then lay your drive tarmac/concrete/block paving as
normal? Would the weight of the car be a problem or is the coil buried
sufficiently deep that this would not be a problem.
I remember a couple of winters ago, someone posting here that they
wanted to do this in reverse and lay a coil under their drive to melt
snow. Presumably this would require a completely different approach
because I imagine you would need to insulate under the coil to make
sure the heat went up into the drive, not down into the ground, but
the coil would have to be close to the surface to make it effective
but the coil and insulation would have to be able to withstand the
weight of the car.
I seem to remember the person who asked about this being told off for
global warming but he said it was to stop his wife slipping on the ice
and breaking an arm. Just to reassure any critics, these are all
hypothetical questions this time!
It is a thoroughly GOOD idea except of course from the point of view of
icing up your drive to heat the house!
The coil has to go well deep. I think at least a meter.
I think they normally use mini diggers to cut a small trench.
You got it ;-)
I looked into this - I've certainly got the space - you probably need
around 10 sq meters per KW usable heat.
The problem I had was it would be pretty expensive, required on the
limit electricity supply and immersion top up to run my radiators system
that was designed for MUCH hotter water - 79C - than the heat pump could
deliver - typically 45C.
YOu really need to design the whole house plumbing and insulation and
heating fir it. Essentially it is NOT a like for like replacement for a
boiler. You don't get a little scaldingly hot water. You get LOT of
luke warm water.
That means more pipes for UFH, bigger pipes for radiators and bigger
radiators. And a different heat exchange in the DHW tank with probably a
straight immersion coil to top it up to hot enough .
If I were building the house again Id probably do it, but retrofitting
was just too damned expensive, and this renewable nonsense has pushed
electricity prices up so much its no longer as attractive as it was.
(in-ep-toc’-ra-cy) – a system of government where the least capable to
Interesting - I run my condensing boiler at 45/38 most of the time.
The Myson radiator calculator I use oversized the radiators, but in
retrospect, I'm very pleased because I can run the heating at such
a low flow/return temperature.
[email address is not usable -- followup in the newsgroup]
Don't write off air sourced heat pumps.
I fitted one last year to heat (and cool) the conservatory.
Its 5kw and hasn't iced up yet.
Even on full it only lowers the air temp through the outside unit by
about a degree or two so its not going to freeze often in our winters.
If you have solar panels the cooling would be free.
On Thu, 08 May 2014 17:48:57 +0100, The Natural Philosopher wrote:
For the reasons you mention later it's a while since I looked at
ground source heat pumps. But from what I remember the coil of pipe
is a least a metre down and is not far off a metre in dia, so "small
trench" is more like a large trench, total pipe length in the low
hundreds of metres.
Except that you aren't harvesting heat absorbed by the ground from
the radiant heat of the sun but the general warmth in the ground,
ulimately coming from the core. One of the sizing factors is the
thermal conductivity of the local ground conditions. Well draining
sandy soils aren't as good as wet conditions and wet conditions with
water slowly moving through (thus bringing in heat) are even better.
This is what stopped me really exploring GSHPs. I think you can get
two stage ones now that deliver more conventional water temps but
that may be in quantities only sufficient for DHW rather than CH.
Agreed, new custom build I'd look very hard and a *BIG* thermal store
and GSHP. By *BIG* I mean few thousand litres of water capable of
storing enough heat to run the CH for perhaps a couple of days. Or
something that caught my eye the other day using the ground as an
interseasonal (yes interseasonal) heats store but that might not work
on the domestic scale, the article I saw was definitely industrial
On Thursday, May 8, 2014 5:28:23 PM UTC+1, Stephen wrote:
Have a Google for 'snow melt'; external UFH, the Americans use it extensive
It can be done, but I don't see that you'll get a significant advantage in
winter, compared to conventional GSHP. If it works, it will chill the slab
and turn it into an ice rink. It may work in summer, but probably not as we
ll as a conventional solar thermal system.
The last couple of ground source heat pump projects I saw didn't use pipe
but some sort of buried all metal heat exchanger.
I think it was to get round the space to run pipes issue.
There is thepossibility of using a borehole and vertical pipes.
I think this is more costly
If your pipe developed a leak. there might be issues digging it up under the
driveway. Not very likely to leak though.
It might be the black tarmac enabled the heat removed to recover quicker due
to solar gain.
I also suspect the economics have not worked out for some people I know.
Capital cost is high, therefore long payback.
Usually only worth it if mains gas is not available.
Depends on the price difference between gas and electricity.
Little maintenence needed on heat pumps, so another saving there..
No he's right.
The soil temperature is maintained mostly through rainfall seeping into the
Sunlight only effects the top couple of feet.
ISTR sometimes they bury a "wetting pipe" along with the heat recovery
pipe to wet the oil if permeability is too high. It is connected mains
water and turned on manually if the sytem is struggling to maintain output..
On Fri, 09 May 2014 05:40:58 +0100, The Natural Philosopher wrote:
So? We don't have permafrost and do they use surface based GSHPs in
Siberia or borehole based ones?
Agreed you can't pump heat from ice very effciently as ice is a poor
thermal conductor. In fact freezeing the ground is a problem for
badly designed/installed GSHPs
Not that deep it starts to rise before 50 m. At 200 m the ground temp
may well will be in the 15 to 20 C range. It varies greatly with
The 2 m ground temperature in this country is pretty stable, it
doesn't respond to daily solar input only seasonal. With a mean just
above 10 C, which is why once into a cave system the temperature is
OK once you start pumping heat out of an area it will flow in from
warmer places but in winter that isn't going to be the frozen surface
as your heat pump collector shouldn't be freezing the ground around
it or effciency falls through the floor.
Also there is bugger all solar energy available in the winter and
GSHPs still work in the winter so the heat must be coming from
somewhere other than solar gain.
I used to work at a place that had a heated ramp to roof parking. It was
embedded in the actual concrete. It was not that successful though. It was
very patchy and eventually after some five years parts of it stopped working
altogether. I'd hate though imagine how expensive this would be to run
nowadays. The building was demolished in the 90s after a fire.
From the Sofa of Brian Gaff Reply address is active
"Stephen" < email@example.com> wrote in message
Under-soil heating was used in England for football pitches in the 1950s
and is now pretty well the norm in the Premier League.
AFAIK none were DIY'd though - even in the days of sliding tackles which
could've made a start on the trenches ;)
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