Living wall for outdoor air biofiltration - precedents?

Katie,

For what seems like decades the "Living Wall" people (Nedlaw and others) have claimed that they can place a mat of plants at the return air grille of a recirculating HVAC systems and let plants do their magic.  Very pretty, but I was told we should budget $100/sf for the system + 10% per year for paying someone to replace plants that die.  The more I looked into them the less I was convinced that they were a good idea given that we live in a world of imperfect maintenance.   There seemed to be plenty of opportunity for a damp mat of plant matter to become a host for all kinds of things that you wouldn't want people to inhale.  It seemed safer just to not have VOC-emitting materials inside the buildings to begin with and use a simple MERV13 filter (at both the outdoor air intake and in any reciruculating air systems) to handle particulates etc. 

I'd be happy to hear of anyone who found these systems to be something other than attractive but expensive.

Long time ago, I attended a lecture by CASE, and they had an example using plant based filteration system.. not sure whther there is anything beyond this research installation, but pretty cool concept..  https://www.case.rpi.edu/research/psacii  

The science suggests that indoor plants do help with air quality, but the impact is unfortunately too small to be significant.  Here is a literature review of the impact on VOCs (summary), and here is a study of the impact on particulate matter.  They both suggest an absurd amount of plants (1-100 plants per square foot of floor space!) would be required to have a similar impact on air quality as with the typical cycling of outdoor air + filtration in an HVAC system.  In other words, plants are far too slow at cleaning to keep up with how frequently indoor air is exchanged with outdoor air. The above studies are only for VOC and PM; maybe the benefits for other air pollutants (like CO2) are greater.  However, whether or not there are meaningful impacts on air quality, biophilic design does have a meaningful impact on occupant wellness, so more living walls please!

I wrote an article on Nedlaw years ago, and the consensus at the time was as Z suggested. They are attractive but their IAQ impact is questionable.

Not exactly an answer to your specific issue -- but I love this book and plug it whenever I can: "How To Grow Fresh Air", by Dr. Wolverton, who has specific researched studies on how different plants filter air for different chemicals. Not all plants perform the same cleaning function, so you need to be choosy about which you install. It also describes light and water requirements. A great book, written for humans. Harry