> If you look at > http://www.panaceauniversity.org/index2.html , search > Peter Davey, look in the PDF linked, you will find all you > need to > know to make one. Without having looked, if it effectively implements a heat pump then it can achieve some gains. If it doesn't then it can't. The maximum theoretical gain of a heat pump is (Th-Tc)/Tc in absolute units, say degrees Kelvin. If you start at 20 C and end at 99C (for reasons covered below) then Tc =~ 293 K and Th =~ 392 K and deltaT = 79K. So max COP = 293/99 = just under 3. In practice you'll be lucky to get anywhere near that much. Anything that claims that much or more is snake oil. I used 99C as it is BELOW boiling so there is no issue with phase change of water etc. FWIW people HAVE implemented Stirling cycle like heaters/coolers using acoustic methods. The trick is to achieve compression and expansion at the right physical points. Gargoyle Pulse tube and thermoacoustic for some refs. Heating by a much smaller delta can be much more productive - which is why there is a market for heat pumps. For an eg 20C delta at 300K in you get a max theoretical COP of 15. Much much less in practice but enough to support the heat pump industry. Russell -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist