The Concept

Gleaned from an idea in one of the eco friendly books Here, the concept is to use the power of the sun to heat up rocks which in turn warm the air around them. Then use convection to duct the air into a building for free underfloor heating. It requires absolutely no input of energy apart from the sun so it is completely free and eco friendly. I think the French know it as a "duct canadien".

Site

We had an ideal situation in the outhouse as there was no floor so putting in a duct was not a problem. The area infront of the building slopes away and faces directly south.

Step by Step Line it with tin Fit glass and let it shine

• Find a way of getting a 2"-4" duct into the building under where the floor is gonna go and make sure that it is inclined up into the building from where the box will be situated. We found the duct in a skip. We routed the duct under the door step and dug a shallow trench to the box site which meant that we could easily alter the gradient of the duct.
• Find a sheet of plate or toughened glass (coffee table top or a big glass shelf would do).
• Make a wooden box to fit so that the glass forms the "lid" of the box. On the basis that it is easier to make a box to fit the glass than cut the glass to fit the box. We used off cuts from planking the roof.
• Make a hole in the box to accept the end of the duct. This should be pretty near the top i.e. at one end near the glass lid.
• Make other holes in the other end of the box to let air in.
• Line the box with tin. We used corrogated iron as we had some and didn't want to spend money.
• Put the box in position on an incline (exit duct higher than the inlet holes).
• Fill with rocks so that air can still circulate. We grabbed rounded rocks out of the stream bed.
• Fix on the glass lid.
• Wait for the sun to shine.

We laid the concrete floor in the building such that the duct came up through it just inside the door. This could then be fitted with a closable grill if required. We battened the concrete and laid a pine floor so that the warm air then flows under the wooden floor.

Another idea is to fit the box with a wooden cover. If you want to turn the heating off just close the cover.

Refinements

• Paint the rocks black to absorb more solar heat
• Using lots of small rocks is good if you want then to heat up quickly
• Using larger rocks acts a bit like a storage heater – they still heat the air after the sun has gone
• Using a double layer of glass makes the box more efficient, similar to the concept of double glasing

Generally getting lots of research done on eco stuff. Regarding solar PV pannel, we are currently looking at alternatives to incorporating them in the roof. This has advantages aesthetically. Also it allows for expansion easily and potentially offers us further rainwater capture for water (if we go down that route).

Many thanks to Matthew and Esther Phillips for their information sharing on the eco front. They have sent through a couple of links which are really useful:-

http://www.kyocerasolar.de/products/solar_faq.html which is an easy read FAQs on photo voltaics.

http://www.naturalinsulation.co.uk/cms_items/20060607164406.pdf  which is the result of research paper about making buildings 'breathable' and why it's better all-round than the modern technique of trying to envelop buildings in impermeable barriers. This is especially important for old buildings with their stone walls without damp-proof courses. Like ours! Be warned this is not an easy read unless you are a boffin. Still not sure what meaning to take out of that one.

Thanks also to Mark & Lauren who added a comment to the previous post with a couple of useful links to pages of links. I will plough through them but I am impressed with this site purely for its numpty proof, plain speaking information.

http://www.navitron.org.uk/

Next steps for us is to work out what power we need to generate and how, then identify what implications that has for the roof design so that we don't end up having to alter the roof after we have built it. Just seems like everything needs to be considered in detail before you start anything. The biggest nightmare is establishing where to start as there seems to be so many variables.

Happy New Year to all! 

Essentially we are starting with a very solid but basic shell of a building with no power, water, sewage, post box and most of a roof. The intention is to fix it up in such a way that it can be self sufficient once the roof is fixed. For us this is quite a challenge and has meant we have done some research en route already. This we propose to share in this category. We know that we will have to do loads more and no doubt we will have to overcome a few issues as well.

In documenting these and also identifying sources of information and support, then hopefully it will become a valuable resource for others attempting similar projects. Immediate thinking includes use of:

• Solar power using Photo Voltaics
• Wind power
• Water Power (using the stream)
• Heat Sink (need to learn loads on this one)
• Thermal mass
• Solar heating (hot air)
• Solar heating (water)
• Composting toilets
• Filter / Reed beds (not sure the climate will make this a feasible option)
• Carbon footprints