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wellington womble
Joined: 08 Nov 2004 Posts: 15051 Location: East Midlands
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Posted: Sat Dec 18, 04 12:39 am Post subject: Re: Building a home - to live in! |
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anneka wrote: |
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We want our home to be as environmentally friendly and sustainable as possible - and cheap to run in the future. We have decided on several things which although making the project initially more expensive to build will reduce running costs and hopefully deliver us the most self sufficient manner of heating and lighting our home.
The structure of the house is timber frame, with an incrediblly high U value (down to masses of insulation) and will have triple glazed argon (don't know if thats good) filled windows.
...We will be running the lighting as long as we can fathom the system properly from batteries which will be recharged by a wind turbine and a small solar panel. The larger solar panel tubes are probably beyond our budget, my MIL has them on her roof and they were fantasitally expensive to buy and install, I don't really think that she will see the return on them in any way other than as a benifit to the environment, I'm not knocking the technology - just the cost. We are also looking at geothermal heating but are unsure about this as we have yet to talk to someone who actually has it - but have family in Sweden where it is common so hopefully all will become clearer.
We will have underfloor heating and a heat exchanger for ventilation (see insulation) - we are undecided as to wether to get a solid fuel range (there is an oil fired range which can do hot water, underfloor heating and cook) - but again we could get these things from seperate appliances cheaper.
Would be extreamly grateful for any suggestions ... |
Hi -
Undoubtedly brilliant insulation is the right priority for expenditure.
But remember that "free" solar gain can be maximised, and heat loss minimised by the basic design using large south-facing windows, and smaller ones on the north.
I'm surprised that you have concluded that windpower and pv (solar electricity generation) are more worthwhile than solar water heating. My reading has suggested that large, cheap (albeit relatively low "effeciency") 'flat plate' solar water heating was quite cost effective - and you can even make your own, see CAT. The vacuum tubes have higher "efficiency" in terms of heat per square metre, but not in terms of heat per �!
I'd think of using solar water heating with a larger than expected (and better insulated) tank. A tall, thin tank gives better "stratification". Thus you can harvest all the heat on offer on good days, and have enough to see you through the odd bad one or two. I'm thinking of this as a means of getting nearly 100% of your water heating for 6/8 months of the year.
Some auxilliary heating is going to be required in winter, (or otherwise the system is going to be excessive for summer).
Just pick the low-hanging fruit!
Underfloor makes a lot of sense, but particularly in a 'solid' floor. Which probably means concrete. This can then act as a giant "storage radiator", spreading daytime solar gain into the evening - and potentially allowing a heatpump system (called "geothermal" but not correctly) to run usefully on off-peak electricity.
Heatpumps are at their most efficient when producing a small rise in temperature. So while you may get a factor of 5x for their efficiency when heating water to 35C for underfloor, it will likely drop to 2x when heating to 65C for hot water (or conventional radiators)...
You can take that efficiency factor, and use it to *divide* the unit cost of electricity to get the cost of your heat.
Running a heatpump primarily on offpeak is pretty good on running costs (and making use of generator output that would likely otherwise go to waste). But it barely makes economic sense compared to mains gas, if that should be available...
With super-insulation, all the heat from cooking and lighting will make a noticeable impact on the central heating requirement. So a smaller, less wildly expensive heatpump can be used.
And don't do anything to improve the "garden" area where the collector would be buried until after its in! (Buried about a metre down, its really using the ground as a solar collector and energy store - true geothermal means going much much deeper for volcanic-type earth's core heating.)
There are special hot water tanks called "thermal stores" which can be used to 'gather' the heat from varoius sources (solar, range backboiler, heatpump,...) and even (although I doubt you should) distribute it at different temps to hot water and central heating. You might want to check them out, but probably a big tank with two or three indirect coils is your answer.
I'm a little surprised that you would opt for "standalone" electricity generation - with lots of faffing with batteries, and a limited output. If you are on mains electricity a "grid connected" system would be so much easier to live with - think of it as using your own, selling the surplus and having the mains to draw from if needed - automagically and without you having to get involved in the problems of energy storage! Unless, of course, you just want to disconnect...!
Just my two-pennyworth, hope its helpful, I'm dead jealous really!
Dougal |
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tahir
Joined: 28 Oct 2004 Posts: 45676 Location: Essex
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tahir
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wellington womble
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