Found some interesting products from the U.K. The first two use the spiral/tubular heat exchanger that was mentioned in this thread at one point. The last one is really interesting - a passive HRV, apparently just going on the market in the U.K.
Retrovent by Envirovent
HeatSava by Envirovent
http://www.envirovent.com/downloads/...a_brochure.pdf
Ventive Passive HRV System
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