driveway heat pump

Hello,
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 is!)
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!
Thanks, Stephen.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 08/05/14 17:28, Stephen wrote:

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.

--
Ineptocracy

(in-ep-toc’-ra-cy) – a system of government where the least capable to
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 08/05/2014 17:28, Stephen wrote:

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 08 May 2014 17:48:57 +0100, The Natural Philosopher wrote:

pipe

as

buried

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 scale.
--
Cheers
Dave.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 08/05/14 21:59, Dave Liquorice wrote:

No. you are using summer sunlight.
Look at siberia. PERMAFROST down to several meters.
You need to be a long way down before temps start to rise.
--
Ineptocracy

(in-ep-toc’-ra-cy) – a system of government where the least capable to
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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 ly.
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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..
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

No he's right. The soil temperature is maintained mostly through rainfall seeping into the soil. 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..
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You are right, the technology has improved enormously. I thought about this myself but then I have free wood for heating on the very coldest and windiest of days.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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 local conditions.
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 pretty constant.
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.
--
Cheers
Dave.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Friday, May 9, 2014 9:03:41 AM UTC+1, Dave Liquorice wrote:

My emphasis.

Yes, as the man said, it's coming from sunlight that warmed up the ground in the summer.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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. Brian
--
From the Sofa of Brian Gaff Reply address is active
"Stephen" < snipped-for-privacy@invalid.org> wrote in message
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Friday, May 9, 2014 9:20:40 AM UTC+1, Brian Gaff wrote:

The elevated section of the M4 through Hammersmith & Chiswick has an ice melt system (according to Wikipedia), but its use was stopped due to the energy costs.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Scotland, being a bit colder than England had two well publicised underground heating systems: The Mound in Edinburgh & and SRU pitch at Murrayfield. I've no idea whetehr they still operate.
--
From KT24

Using a RISC OS computer running v5.18
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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 ;)
--
Robin
reply to address is (meant to be) valid
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.