| Archive for Downsizer For an ethical approach to consumption |
| skyeten |
Wind turbine/ Underfloor heatingI am planning to install a wind turbine on my garage to heat water for my underfloor heating. I am planning to use a hot water cylinder with internal heat exchanger coil linked into the underfloor system, the water in the cylinder would be heated by an immersion type heater element fed from the output from the turbine. The question is would it be more efficient to use an inverter to convert to 240v or use a DC type immersion element ? The distance from the garage to the tank in the house would be about 25-30m. Any ideas/views on this would be appreciated.Thanks |
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| mochyn |
Away from the power side, Coes your water come from the mains or do you have your own supply? I ask because a friend has under-floor heating and the pipes have furred up, msking the system useless. This is because they have a borehole and the water from it has high levels of something that causes furring. Possibly a filter would have prevented this. So think on, lad! | ||
| dougal |
Ummm, effect and cause are being banged together... Any heating system should be recirculating the same fluid through the pipes, underfloor or whatever. There's not much fluid there, a few gallons. The 'fluid' will be mainly water - but it should also have a strong concentration of 'inhibitor' in there, to prevent scaling and corrosion. The source of the water doesn't really matter, as long as the same water goes round and round. There's only a limited amount of minerals in there. The trouble comes when the fluid is changed, and replaced with 'new' water, bringing additional minerals (for scale) and oxygen (for corrosion). Especially if the inhibitor is not replaced. (Like antifreeze, it should be augmented from time to time anyway). It is possible to hire a special pump and buy special chemicals to descale the pipes, boiler, etc. http://www.kamco.co.uk/WhichPumpDescaling.htm Underfloor heating system pipes are *less* prone to scaling up than conventional systems - because they run at lower temperatures. However pipe replacement is a major undertaking. |
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| dougal |
Re: Wind turbine/ Underfloor heating
Hi Skyeten, and welcome to Downsizer. I understand the question regarding distance of low voltage (so high current, high heating loss, high cable cost to minimise) versus high voltage, (so lower current, lower heating loss, cheaper cable but needing a costly inverter bringing its own losses) - but that's very much a matter of the philosphy of your installation versus cost. Certainly, using a DC system just for heat generation you can almost entirely avoid all the complexity of control systems. It can get very simple! But size also matters, and that's where I have serious reservations. 1/ Electrical energy is more valuable than heat energy. So to generate electricity (especially 240v) and just use it for heat, seems somewhat wasteful. 2/ You need a lot of energy for home heating compared to what a wind turbine produces. A 6kw boiler (or heat pump) is a pretty small one - and it will give a solid 6kw 24/7 if required. A 6kw turbine is enormous for a domestic installation - and would only give 6 kw very occasionally. 3/ A heat bank (or thermal store), as described will allow a small turbine to contribute a little to heating. And, I'd suggest that the cost of an inverter would take a long time to pay back on a small system (quite apart from its energy content). However, I don't really see a large system as being appropriately employed directly to heating. 4/ Now, a decent-sized turbine, with a mains-tied inverter, and a system to dump surplus energy (generation exceeding consumption) to the thermal store would be a different matter. And then to drive a heat pump from self-generated electricity might be one route to getting enough heat out of a moderate (rather than gigantic) sized turbine... |
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| TimNeo |
How about a nice big geothermal heat sink powered by your turbine! You can power your heat exchange with the turbine making maximum use of your electrical energy and use the ground for heating...
or am I going mad here = ) You might want to wait a few weeks for it to cool down before digging any 50ft long trenches though... |
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| dougal |
Tim, the thing you aren't doing is considering efficiency.
Conversion efficiency. Every time you convert energy from one form to another, some will be lost, escaping as heat. Basic thermodynamics. One can make machines more efficient, but typically the extra complication has extra costs. Transmission efficiency. This is what Skyeten was concerned about. You leak energy in transporting it. Always. Whether its heat from a wire or the fuel bill from a petrol tanker, there's an energy cost to energy transport. Storage efficiency. You never get out as much as you put in. Different forms of storage have different rates of loss. Even hydro-electric pumped storage has losses due to the frictional viscous losses in the pipes, never mind evaporation and reservoir leakage - and I'm counting pump/turbine efficiency as conversion efficiency. And taking wind energy, converting it into electricity, transmitting it to a 'heat store' converting it to heat, trying to store heat in the ground, trying to recover that heat and 'transforming' it to a higher temperature for use... is going to have an appallingly low overall efficiency. You'll only get back a tiny fraction of what you put in. And with a small 2m (diameter?) wind turbine, you aren't catching much energy anyway. The absolute best thing to do with electric energy is to use the electricity in a worthwhile way, immediately its generated. Storing it as recoverable electric energy is highly desireable, but its expensive, heavy and bulky for the amount of energy that you can store. The 'buzz' about Hydrogen is as a means of *storing* (not generating) electricity. Converting electricity into stored heat is not making the best use of the resource - we know electric storage radiators are expensive heating. But if its the 'best' use you can make of your generated electricity at the time, then it makes sense to trap the heat. |
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| mrutty |
mochyn, it's worth also looking at a sonic clean first and then dougal's chemical clean. The sonic clean in effect shakes the scale lose and is used on normal household water cylinders. You get a rush of crud so you do need the special pump the dougal is pointing to. The chemical clean will then be very effective. |
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| dougal |
Got any more info? It sounds useful... |
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| mrutty |
I can't find details via google because of toothbrush adverts 
Basically any big'ish plumber (size of company not a fat git) will have a ultrasonic unit that you hold against hot water cylinders to de-fur them. These unit work on most pipe work too. |
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| skyeten |
The whole point of the exercise is to reduce my oil bill for the underfloor heating which is about £900 per year and rising. My house is badly designed in that the boiler is close to the bedroom and so has to be shut down between the hours of 10pm to 8am. As you will know this is not the most efficient way to run underfloor heating as the slab cools down and requires a greater input to bring it back to temp. In the winter my oil boiler is running about 8 hours a day constantly, the house is well insulated too !
I thought that a wind turbine running 24 x 7 would supplement the system and during the night would be a lot quieter than a boiler switching on and off. The turbine itself will be mounted on a garage 20m or so from the house. The question is still there --- do I use an inverter to convert to 240v or use a DC water heating element. I may add that I live in a VERY windy site !! Thanks for replies so far. |
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| dougal |
Skyeten - as I indicated previously, the choice between high and low voltage is one of system size and budget.
What turbine are you planning to install? Regarding your existing system, clearly relocating, and working on quieting the boiler would be the prime option - I guess you have reasons for not doing that. But don't overlook the possibility of installing proper sound insulation - it could be the least difficult and most effective option. A job for the pro's though, details really count. If the boiler is not a condenser, and especially if its not recent, replacing it with a more efficient one is likely to pay back in only 5 or 6 years. And you could use noise as one of your selection criteria for the new one. And/or have it installed in another location... To be getting through that quantity of oil, I'd guess that your boiler is at least 20kw (it'll be on a label somewhere on the boiler, or you might track it down online). Compare that 20kw with the 5kw that a 4.8 metre diameter (16 feet across!) turbine on a 14 metre mast in an ideal (ie non-turbulent airflow) site should generate on those occasions when you have 35+ mph winds. But such a turbine installation is likely to cost towards £20,000... ... and is unlikely to fit on your garage roof. http://www.downsizer.net/Projects/A_sustainable_world/Wind_power_to_the_people!/ On the other hand a little marine battery charging whirlygig, a couple of feet across, is only going to generate 1/100 of the heat that your boiler probably does - and the whirlygig only gives even that much is when its blowing a hooley. Other schemes that you might investigate include using a heat bank (or thermal store). Have that fully heated before going to bed, and add a couple of kw from an Economy 7 immersion heater into the heat bank, and you could likely get through the night without the boiler firing. E7 electricity is usually competitive in price with oil - so that's a cheap solution for noise reduction. If you do have a great wind energy site (turbulence-free, and much of the time over 20mph, not just strong when it does blow) then look to generate electricity from it, rather than just heat - which is economically much less worthwhile. Use that electricity to drive a heat pump, and you can multiply the energy that you capture from the wind by a factor of maybe 4... |
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| H.I.S |
\Swift do a system to do what you are trying to do. | ||
| Ben W |
these two statements seem to be contradicting each other, though it is possible that the heat is not making it out of the pipes very well if they are scaled up as previously mentioned. many people have very different ideas about what is good or bad insulation. current building regs are 10" in the loft which very few people have. If you could answer these qs it might be easier to pin down: What is the wall construction? how much insulation in the loft? is the underfloor heating copper or plastic pipe? (plastic doesnt scale to anything like the same degree as copper) does the boiler close down / start up frequently? does the underfloor heating manifold have a temperature gauge on it? how large is the house? what output does the boiler have in KW? Ben |