| Non-motoring > Geothermal heat pumps | |
| Thread Author: Armel Coussine | Replies: 11 |
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New Mon 22 Mar 10 22:59
Geothermal heat pumps - Armel Coussine
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Does anyone know anything substantive about these? A geothermal system is proposed for our upcoming house extension, and a brisk internet trawl can't find a word to say against it so it seems a good idea. Oddly, the government seems to offer more generous subsidies to the less efficient air-sourced heat pump system than to ground-sourced ones. Does anyone have any experience of this newish technology first used in the forties I think? Or know anything about subsidies and cutting the cackle over them? |
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New Tue 23 Mar 10 07:57
Geothermal heat pumps - L'escargot
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| www.ecovisionsystems.co.uk/residential/heat-pump-grants.asp |
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New Tue 23 Mar 10 08:32
Geothermal heat pumps - Dog
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| This geezer knows all about that sorta stuff Sire ~ www.newhousefarm.tv/ |
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New Tue 23 Mar 10 09:15
Geothermal heat pumps - Dave
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They're reasonably popular here in Sweden. Most use a bore hole, but you can also run pipes into a nearby lake, or horizontally into a mountain. The big problem is obviously the capital cost. Plus, of course, you still need to use electric to run the compressor. Effectively, by having a slightly warm medium, you can use that as the heat source for the pump. It's the same as a air/air heatpump, or air conditioning unit, except instead of having air moving over the outside unit, you have the warm medium (usually some form of liquid). The advantage here is the temperature of the medium is quite high compared to the outside air temperature in winter. As a result, they're more efficient during the winter. The efficiency is measured by the COP value, usually something like 3 or 4 to 1. The COP value is measured with a source temp of 7 degC, so for a ground source pump you will always get this. But with air/air, this doesn't happen in the winter (here), so they struggle to get 1/1 for a few months. I looked at this last year when I was reviewing my overall heating requirements. In the end I stuck with wood and a small air/air pump for emergencies or if I'm away. To get the best from the pump I mounted the outside unit in the cellar, so it's always fed with air at 8-10 degC. Heating is of particular interest to almost everyone here, so there is always plenty of indepth comparisions and tests being done. As there's very little gas, for those that are responsible for their own heating ie. not living in flats supplied with communal heat, it's always an important consideration. The method of heating also has a big effect on house values. From looking at the details, with the geothermal it's a very difficult calculation. There's a high initial cost, but lower running costs if you only have electric like here. Then there's the potential increase in house value (here). But.. they are more complicated, and obviously have a finite lifespan, typicially reckoned here to be 10 years. There is also the problem of getting someone to fix it when it goes wrong, or more importantly, has the knowledge, spare etc. And obviously part of the initial cost, won't have to paid for again. As far as I can see, if you're not planning on selling the house (here) in the near future, it's hard to see a payback time within the 10 year lifespan. Plus, of course, still laying yourself open to the vagaries of electric prices. |
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New Tue 23 Mar 10 09:43
Geothermal heat pumps - Dog
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| This may be of interest ~ www.naturalnews.com/027550_wind_turbine_renewable_energy.html |
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New Tue 23 Mar 10 10:11
Geothermal heat pumps - captain grimes
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Times columnist Matthew Parris wrote a couple of interesting pieces about his own installation for his Derbyshire farmhouse - though at that time (2/3 years ago) it didn't appear economically enticing and he was advocating greater subsidies. www.timesonline.co.uk/tol/comment/columnists/matthew_parris/article1624021.ece www.timesonline.co.uk/tol/comment/columnists/matthew_parris/article3054310.ece |
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New Tue 23 Mar 10 11:55
Geothermal heat pumps - Dave_
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>> Does anyone know anything substantive about these? Geothermal heating and Ground Source Heat Pumps are two different things, in a domestic dwelling I assume we are talking about the latter. Geothermal energy is usually only used in parts of the world where the earth’s crust is thinner, or where the average temperature is lower than in the UK, such as Iceland. There is, however, a geothermal power station operating in Southampton which draws hot water from an aquifer some 1,000 metres underground. As some of you may know, I’m going for a complete change of career and am currently studying for a Level 2 NVQ in Plumbing. We're currently in the middle of the Environmental Awareness module, which covers solar powered hot water heating systems, solar photovoltaics, biomass, wind, wave and tidal power, CHP (combined heat and power) and ground source heat pumps. As the UK government is keen to promote initiatives which help to conserve energy and reduce waste, I’m hopeful that enough installation and maintenance work should be around over the next 20-30 years to make it worth my while. The plumbing and “green” energy workshop at my college is one of the best equipped in the country and has installations of all of the above both for training and demonstration purposes, except for wave and tidal power as we are about as far as you can get from the sea in the UK. An extract from my textbook on Ground Source heating: Ground Source Heat Pumps transfer heat from the ground into a building to provide space heating, and, in some cases, to pre-heat domestic hot water. They operate on a similar basis to a fridge – but in reverse. For every unit of electricity used to pump the heat, 3-4 units of heat are produced. As well as ground source heat pumps, air source and water source heat pumps are also available. There are three important elements to a GSHP: 1. The ground loop – This is comprised of lengths of pipe buried in the ground, either in a borehole or a horizontal trench. The pipe is usually a closed circuit and is filled with a mixture of water and antifreeze, which is pumped around the pipe absorbing heat from the ground. 2. A heat pump – This has 3 main parts: the evaporator, similar to the device in the cold part of your refrigerator, takes the heat from the water in the ground loop the compressor moves the refrigerant round the heat pump and compresses the gaseous refrigerant to the temperature needed for the heat distribution circuit the condenser gives up heat to a hot water tank which feeds the distribution system 3. Heat distributing system – Consisting of underfloor heating or radiators for space heating and in some cases water storage for hot water supply. At my college the ground loop is sunk into a 30m deep bore hole, but it is also possible to lay the pipe (approx 200m length for an average house) back and forth under the lawn, much in the style of football pitch heating pipes. The average temperature 600mm below ground in the UK is around 6°C all through the year. It is not yet cost-effective to retro-fit GSHP heating in the UK, however in new-builds and extensions where the garden and the internal floors have not yet been laid and where the standard of insulation is much greater, the additional cost of installation can be absorbed into the overall construction cost. In terms of payback it is best to view the GSHP as part of an overall package of energy-saving measures, rather than a bolt-on bill-cutting solution. Of course there is the added benefit to the environment from using a renewable energy source. Hope this helps ;-) Dave TD Last edited by: Dave_TD {P} on Tue 23 Mar 10 at 11:56
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New Tue 23 Mar 10 14:12
Geothermal heat pumps - Dave
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Regarding the air/air pumps (just regular air conditioners optimised for running in reverse), there has just been a thing on TV about them. All the major manufacturers (Sanyo, Toshiba, Mitsubishi etc.) have been making some rather grand claims in their adverts about electricity cost savings. Some are saying savings of 'up to 80%'. Because they don't really give any savings when the outside temperature starts to get much below zero, plus the outside part also needs regular defrosting using an electric element, it seems that some of the claims have been exagerated a little. They also fail to point out that out of the total electric useage, not all of it goes towards the heating of the house directly, as there's other things like hot water, lights, cooking etc. Considering this winter at least, the max temp in many parts of the country didn't go above zero for over 3 months, and for pretty long periods of time never went above -10, so there are no benefits at all with these pumps. Much cheaper to just buy electric wall heaters, plus there's not much to go wrong with them. As a result, the consumer department have launched an investigation into the claims. People have complained that after installation, their electric bill hasn't dropped from £200/month to £40/month. |
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New Tue 23 Mar 10 18:42
Geothermal heat pumps - Mapmaker
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Dave>>To get the best from the pump I mounted the outside unit in the cellar, so it's always fed with air at 8-10 degC. Errr, so you're sucking heat out of your cellar to put it into the living room. I hope your cellar is well insulated from the rest of the house, otherwise it's all completely pointless... Ground source heat pumps generate what they call "low grade" heat. i.e. the hot water in your radiators will be at about 40 degrees. They therefore only really work with super-insulated modern buildings, and with underfloor heating. Otherwise, I'm told, don't bother. |
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New Wed 24 Mar 10 12:49
Geothermal heat pumps - RichardW
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"Ground source heat pumps generate what they call "low grade" heat. i.e. the hot water in your radiators will be at about 40 degrees. They therefore only really work with super-insulated modern buildings, and with underfloor heating. Otherwise, I'm told, don't bother." Indeed, the higher the high side temperature goes, the worse the coefficient of performance gets, so the more energy you have to put in to 'pump' the heat from outside to inside. Also got to consider that electricity is twice the price of gas, and you only use 1/3 of it, so the cost is only reduced by 1/3 - say £200 a year optimistically - this is going to take a long time to offset the capital investment. And the overall efficiency (taking into account generation and transport of the electricity) is probably worse than mains gas. Might be an advantage if you're off mains gas I suppose, or you can generate your own electricity. We've got air / air heat pumps in our offices here, and they all froze up this winter, so we had to run them on A/C for a while to melt the ice outside! |
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New Wed 24 Mar 10 13:27
Geothermal heat pumps - Tooslow
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I can't add anything but can anyone answer a question please? How does this work upstairs? We use oil, no gas out here, and the price is going up & up. I had a brief look at ground source heating but was put off by the idea of ripping up the floor downstairs to put in underfloor heating and could not get to the bottom of how you heat upstairs. There were passing references to "oversize radiators" but nothing substantial. I'm pleased to say that a ridiculous amount of loft insulation plus cavity wall insulation has resulted in a lowest ever fuel consumption despite a horribly cold winter. Thanks, JH |
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New Wed 24 Mar 10 14:14
Geothermal heat pumps - Dave
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| For new build here, the usually go underfloor. But on the old houses I've seen it works the radiators in the normal way, and also supplies domestic hot water at up to 65 deg, so they must be cranking a bit more heat out of the pumps. |
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