Vacuum insulation works in the same way as a thermos flask. The thermos flask uses a vacuum between two glass walls in order to prevent heat travelling by conduction and silver on the walls to reflect radiant heat travelling as infra red light.
Vacuum insulation is made from a silicon/carbon material in a packet made from metallised plastic. It looks like a foil bag but ordinary kitchen foil would conduct too much heat. Hundreds of these bags would be fitted into the wall, the roof or the floor that was being insulated. The silicon/carbon material is full of tiny holes called nanopores. These holes are so small that you could only see them under an electron microscope. It makes it hard for gas molecules to conduct heat as they can’t move around. The air is sucked out to create a partial vacuum in the foil bag – this doesn’t have to be a complete vacuum. The quality of insulation this produces is enormously powerful – 20 mm of vacuum insulation can be equal to 120 mm of conventional PIR board (which is good expensive stuff) or 300 mm of mineral wool or polystyrene (which is ordinary cheap insulation.)
What are the main problems associated with vacuum insulation? One is the cost. This is exceptionally good insulation but it’s difficult to make so it’s expensive. Another problem is that in spite of all the modern science that goes into making this product as leak proof as possible it does leak. It leaks air, it leaks water vapour, and if other insulation is used alongside it this will also produce gases itself. If the building you create is around for a hundred years the little bags of insulation won’t contain a near vacuum by then, there’ll be other things inside as well. The other problem with vacuum insulation is that it isn’t very strong. Modern insulation designed specifically for a ground floor can stand up to anything. Vacuum insulation really can’t. If it’s used in a ground floor it has a rubber crumb mat above and below to protect it from footfall and an extra waterproof layer underneath to protect it from water vapour. It’s a delicate thing and requires careful design. You can’t just shove it in the floor of a bus station and assume that it will be all right with a big bus driving across it. Some modern insulation really does have this kind of physical strength.
What do I think of it? It’s one of those products that the SAP assessor knows is really fantastic and that his customer knows is really expensive. It also requires extra design considerations because it is quite fragile, is unusually sensitive to water vapour and it would deteriorate over a very long period of time. A few other things would convince me. Will the price of this product ever come down? If it did I would be more likely to use it. How easy is it to replace the insulation? If my great grandchildren are troubled by soaring energy bills as their vacuum insulation finally fails, would it simply be a question of the builder removing the plasterboard from the wall, pulling out the old insulation and putting new insulation in? Most manufacturers will tell you, yes, it does deteriorate, it just doesn’t deteriorate very much. Another concern of mine would be how many decades do I get out of it before anyone notices that it’s failing? Replacing the insulation might be all right if it really only needed to be done once a century, maybe just about acceptable if it needed to be replaced every fifty years, but really terrible if it required replacement every twenty five years or even ten years. I don’t know how long it lasts because it hasn’t been around that long. If it lasts a reasonably long time and becomes quite cheap I think we’ll use it a lot.
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