TED just posted a talk by Kamal Meattle, a researcher in New Deli where he studies methods for improving indoor air quality.  It is well worth the 4 minute investment of time, especially for anyone who is concerned about volatile chemicals inside their homes.  According to him, a common houseplant, the money plant, can remove most volatile chemicals (including formaldehyde) from living spaces.  His research was done in office buildings where phenol formaldehyde adhesives (fiberboard furnishings) are widely used.

http://www.ted.com/index.php/talks/kamal_meattle_on_how_to_grow_your_own_fresh_air.html

And, according to him, it would be possible for a completely sealed environment (possibly even SIPS with relatively little air replacement) to sustain human life with the three plants that he discusses.  He doesn't discuss humidity, though in his air conditioned environments, humidity probably isn't much of a concern - but in most homes it might be more problematic.

I love house plants and will have a ton of them in my house when we are done. Do you think it's possible I could get away without having an HRV in my SIP/EIFS house with enough plants? My original plans called for a HRV or HRV+HEPA, but my budget is starting to spiral out of control and my lender thinks that building green has something to do with the colors I choose for paint and could care less about the DX Geo, Solar or other plans I originally made.

If you have a code compliance issue, an inspector may be reticent to sign off on a system that depends on a home owner keeping all of the house plants alive. You also might not want to trust the health and safety of your family to your ability to keep the plants alive either. On the other hand, any ventilation system is dependent on a mechanical apparatus which might be equally prone to failure.

If you do want to pursue the house plant solution, then make sure that you have all of the information that you can get, and maybe contact Kamal Meattle (his contact info is at TED). He would probably jump at the opportunity to support an effort like this. I would think that it would make a great subject for a book, and he might lend his credibility just for the opportunity to publish.