This as many things are relative, of course it will be less effective with dirt or oxidation on it. This because the surface is no longer the surface, it is the dirt. Mixed with a material aluminium could go from its potential emission factor of less than 0.1 to 0.4+, but it is still very much more efficient that most materials that have 0.9 as emission factor. One example is the reflective paint,
http://www.ips-innovations.com/Low-e_Paints/low-e_paints.html (the patent holders site) http://www.radiancecomfort.com/ (licensee in US) This paint inside will give you a 15 to 20% energy saving, dependent on if you use warm air or radiators as heating system. It works in two ways, one is that it blocks losses from the heating system and the other is that it reduces the body's ability to use radiation as cooling method with following possible lowering of room temperature. If the color of the paint would be black it would probably rise the emission factor to around 0.6 and be less effective. But it would still be very much more effective than a traditional paint. So aluminium loses some of its effectiveness if mixed and if the surface is not polished or dirty. It would however still be effective. Regarding air space, you could look at this as a medium also, like any material that you would put in front or behind the aluminium. What happens is that they have different conductivity and emission and this is what determines the effectiveness. I.e. aluminium behind a gypsum board. The gypsum board will in this case have a higher surface temperature than without aluminium and reduce the body's ability to use radiation as cooling method with following possible lowering of room temperature. If you on the other side have air or insulation, you will have a good result. It is however almost always beneficial. Coming to rescue blankets that, where the reflective ones are more effective than insulating ones. The reason is that the body's use of radiation is two times larger than convection. So a reflective folio is more effective than a thick insulating blanket. Adding to this is also that the folio is a humidity barrier and will also a degree reduce the ability for the body to use evaporation for cooling. Since it is of extreme importance to block the fall of body temperature in a victim of an accident, as a result of external or internal bleedings, the reflective rescue blanket is proven to be a real life saver. The principles is also used in modern winter and antarctic clothing. Many applications of the principles have been developed as a result of space research. This philosophies of controlling the body system are valid for all human environments. Hakan At 01:10 PM 9/24/2002 -0400, you wrote: >At 12:10 AM 9/24/2002 +0000, you wrote: > >If we want to make something better, we have to look for a material > >or mixing with a material that give a significant reduction of the > >emission factor for the wall (like aluminium). Maybe straw with > >aluminium mixed in the glue (clay traditionally). I think that > >research should be a little more advanced than only attempt with non- > >traditional materials." > >I am going to ignore the argument portion of this exchange. According to >the research I could find on reflective insulation, which I will admit, >was a couple of years ago, Reflective insulation is only effective as long >as it is still "shiny" (not dirty) and has a space to reflect back >toward. Thus it seemed to me that putting reflective insulation in a >concrete floor, as is recommended by some companies is a waste. Also, if >the reflective insulation is installed in a place it can accumulate dust >or dirt (attic floor) it will eventually become useless unless it is >cleaned. Installing it under the attic roof, over the joist is better, but >still will possibly need to be cleaned eventually. >After all this, I determined a reflective roof to be the best choice for >reflective insulation properties. I could not see that the cost/benefit >ratio of reflective insulation installed in walls was better than using >additional traditional type (cellulose) insulation. >I attended a DOE conference and one presenter stated that if California >had all white or reflective roofs, there would be 100 less smog days a >year. I thought that rather significant and asked why there was not more >reflective roofing available or used. He said that it is an esthetic >problem- people just prefer the look of dark or black roofs. Personally, I >think if people were informed of the potential energy savings, that would >not be the case. >Caroline > > > > > >Biofuel at Journey to Forever: >http://journeytoforever.org/biofuel.html > >Biofuels list archives: >http://archive.nnytech.net/ > >Please do NOT send Unsubscribe messages to the list address. >To unsubscribe, send an email to: >[EMAIL PROTECTED] > >Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ ------------------------ Yahoo! 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