It is one way of doingit. I do feel a bit p'd off that I'll get nothing apart from OAP and what I've saved for over the last 40 years, whilst those who've just spent and not saved will get everything given to them.
Off to the pub... :-)
Think about the volumes of earth (and even Earth) involved..
You can scale this up quite a long way, if you drill deep enough. But you're correct that lots of shallow coils or boreholes in close proximity wouldn't work so well.
The US Army heated whole barracks worth of their married quarters by installing ground source heat pumps - but I guess even army housing in the US has lots more space available per house than the little boxes we get over here :-(
A very long time, essentially the heat is coming from below not above...
1m soil temperatures only very slowly follow the surface temperature and even then only by a degree or so. Think caves, they are a pretty constant 55F(ish) all year,
Yes, you are pumping the heat out and you could freeze the soil around the coil/borehole but heat would still be conducted up from below. This is the tricky part of the design, you don't want to freeze the soil if you can help it otherwise heat that you could be pumping out is having to be used to thaw the ice (OK you have already had that heat when you froze the ground but...). The overall rate of heat conduction in from below should not be exceeded (in the long term) by the overall rate of extraction by the heat pump.
The message from "Dave Liquorice" contains these words:
I can't find it atm but ISTR that the last time this subject came up TNP provided figures that showed that solar radiation, even in winter, was the predominant source of heat for ground source heat pumps, or at least those that relied on shallow pipes. Geo thermal energy from deep boreholes is obviously a different ball game but how deep do you need to go before heat from within matches heat from without?
As I said soil temps vary very little at even just a metre down in the UK. The boreholes for a heat pump system will be around 50m deep.
As you say Geothermal is a different ball game and is passive extraction of the heat so you need to go deep enough (or be in the right place) such that your circulating medium is heated to a useful temperature. With a ground source heat pump system you are actively extracting the heat from the ground.
The sun heats the ground and replenishes the heat. It is solar system really.
The ground is a sufficiently large mass that it tends to average to a constant, more or less the average of the yearly insolation minus the average losses. That holds good from about a meter down, to the point at which geothermal energy takes over. Viz permafrost in Siberia, where the deep ground is still frozen even in summer when the top layer is warm bog.
I cant remember the references, but it seems that the average earth temperature is too high to be accounted for by insolation and whatever heat is left in the core..the implication being that the earth is at some level a vast fission reactor anyway, as well..
With respect to heat pumps, ground sourced anyway, that means you need to go down a meter or so, and not expect a huge extraction of last summers heat as it were...there is a definite rate at which you can pull heat out, without freezing the ground round the pipe.
It doesn't really make any difference if you go straight down or horizontally - its the size of the pipe and the soil character that counts. Soggy clay is best, sand or chalk worst.
An interesting thought is that city based air source pumps will in fact make use of the energy 'spilt' out of traffic, and poorly insulated houses. Its pretty true to say that London with in M25 is 2 degrees warmer at night than here in rural East Anglia.
So whilst winter insolation in itself isn't enough to cover the heat input, the soil is enough of a thermal store to have plenty left over from summer.
I saw one Scandinavian design where the air con was actually heating up the soil beneath the insulated house..making a heatbank there as well, and the concrete car park which got nice and hot in summer, covered yet more coils.
IIRC the earths total insolation is about 10-100 times our entire fossil energy usage. So there is plenty of it. In the UK I think it was about
10:1. The problem is the scale of what would be needed to capture it - maybe 20% of UK land area covered in 'renewable technology'. For biofuel the conversion rate is so bad that you need the whole country devoted to growing it, and none for food..However, with respect to heat pumps, consider that at least some of the heat extracted from the ground is replaced by heat escaping from buildings..and heat pumps are about the cheapest way* of picking up solar energy that actually do work cost effectively.
I refer interestsed parties to David Mackays web site and book
Which basically, although that was never his intention as a very committed cycle riding greenie, blows renewable energy out of the water.
Simply on the scale and energy density required. Never mind the actual COST.
If you wnat carbon free pwer, it boils down right now to three things. Much better insulation, heat pumps and nuclear power stations. These are cost effective and capable of doing the whole job at sensible costs. Nothing else is.
I've put my heatpump plans on hold, largely due to three things
1/. The technology is not yet mass market and is bloody expensive.2/. The costs go beyond mere installation of a heat pump, as the whole house heating system is not geared to lots of warm water, but a little very hot water. I would essentially have to replace half the house heating..only the UFH would take the heat pump output successfully- and the hot water tank and radiators and fan convectors would all need upgrading.
3/. Oil prices have crashed to the point where the economics no longer make sense over my expected lifetime.HOWEVER if I were doing a new build, or root and branch refurb, I would definitely go heat pump with UFH everywhere, And super insulation, a gas tight house and heat recovery ventilation.
Anyone know how shallow? We typically have snow cover from November-March here, but I believe GSHPs are still viable (ASHP is out; too cold) - and I doubt there's any solar heating effect in play there.
I believe the criteria's "below the frost line" for the pipework, but I've not seen any data detailing what level that is for different regions. It's on the to-do list to drill some test bores and monitor temps one winter, but I didn't manage to order any suitable sensors this season before the ground froze solid.
Hopefully GSHPs will become DIY at some point - I could happily borrow a Bobcat and go do some digging (and a lot of the expense normally seems to be in the labour), but there's nowhere local to get the parts from, and I don't think the knowledge of what works and what doesn't is quite in the public domain yet.
cheers
J.
They are DIY. The slinkies are fully DIYable. And that is a the bulk of the cost.
In message , Doctor Drivel writes
House prices still rising are they dIMM ?
A mate, CORGI engineer and general plumber has recently done a major refurb of his new (to him) house and done as you suggest (heat pump, UFH, big water tank thing).
He has done his house this way as a sort of test bed re being able to provide that as a solution for his own customers.
I believe he imported the pump from the Far East much cheaper than it would have cost here in the UK.
However I believe he is having (or was having) some teething troubles, mainly around the pump itself (a risk you take bringing that sort of thing in yourself I guess).
Luckily he also installed a conventional boiler at the same time. ;-)
From what I have read here re most of the thermal energy coming from below, would being on top of a hill work against him?
Cheers, T i m
If ground sourced, then if he drilldown deep then no problems. A heat pump where natural gas pipe is available, is a foolish thing to install.
I think he has 3 bore holes but I can't remember how deep (I remember it sounding pretty deep at the time). I think one was shorter than the others because it hit something pretty solid (Underground train tunnel maybe) ;-)
The big snag withheat pumps pretty much no matter the source is the low grade heat they produce, 30 to 40C at the most. Suitable for UFH but not much else so unless you have a suitable UFH system already in place it becomes very expensive to retro fit. New builds or restoration from a shell requiring new floor slabs etc is another matter.
What about the new high efficiency radiators? I know nothing about them, but found these while goggling:
R.
No. The efficiency is proportional to the temperature difference you pump against. 3:1 will generally see temps around 50C. 4:1 its down around 35-40C.
There are two stage pumps that can do better, and optionally fitting an immersion heater coil will net you better temps, but at ever lowering efficiencies.
Suitable for UFH but not
Yup.
They cost the earth to install and cost no more to run. So no gain anywhere.
Maxie, what are you on about? Please focus on the topic in hand. I know you are a known fabulist who is also in a Paddy band, but you must focus. Then your life will be far more complete and meaningful. Yes, Maxie more complete and meaningful. Your life.
Mitsubishi do an air source heat pump that is claimed to operate down to approximately minus 20 degrees centigrade.
Direct link to the brochure pdf:
Cheers,
Sid
In message , Doctor Drivel writes
The fact that you said that they couldn't fall because of the demand. sometime last year
You sad, sad pathetic deluded old fart
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