Plant based ventilation systems

What do you think this is?

If you said a CO2 generator for a green house, that’s correct.  Plants thrive with added CO2.  What do they do with it?  According to climatecentral.org, “In a process called “photosynthesis,” plants use the energy in sunlight to convert CO2 and water to sugar and oxygen. The plants use the sugar for food—food that we use, too, when we eat plants or animals that have eaten plants — and they release the oxygen into the atmosphere.”  So plants take up CO2 and release Oxygen, and humans release CO2 and need Oxygen.  It sounds like the perfect synergy–perhaps plants should be in every environment where there are humans.

It turns out that, similar to disco and the Rubik’s cube, this thinking has been around since the 70s.  Bill Wolverton, PhD, a scientist who worked for NASA at the time, first documented in the early 70s the beneficial affect that plants can have on indoor air quality.  His work was focused on closed environments constructed solely with artificial materials, such as the Skylab space station.  He also discovered that much greater gains in indoor air quality were realized when the air was actively circulated through the plants rather than simply passively placing the plants in the indoor environment.  His team’s research led to a greater understanding of indoor air quality in buildings.  Though he, and others, have been working on developing plant based ventilation systems for the last 40 years, they are not well known or widely employed.

Human being produce CO2, and human beings can be found in large concentrations in offices and similar buildings, so it’s a building code requirement that outside air be brought into the indoor environment so that the air is safe and healthy to breathe.  There are other compounds of interest when indoor air quality (IAQ) is discussed, but CO2 is the main element that code required ventilation is designed to mitigate.  On a recent office building job of mine, about 26% of the size of the HVAC equipment was to account for ventilation loads, i.e. the additional cooling load that the air conditioning system sees in order to bring in outside air and cool it.  Ventilation is also typically responsible for a third of the cost of the energy used in operating the HVAC system.  So a plant based ventilation system could not only add interest and beauty to the the indoor environment, the cost could be offset by the costs associated with HVAC based ventilation systems.

At the University of Technology Sydney, Australia, and Junglefy, a commercial venture to bring the research to market, a group has developed a plant based ventilation system, called the Breathing Wall, which removes 80% of CO2, 95% of CO and PM<10 and a majority of VOCs from the air (see http://www.junglefy.au).  It also happens to be seriously attractive.  Here it is:

This system has tiny fans behind the plants which draw ambient air in through the back, pass it through the root system and out through the leaves.  Research has demonstrated that it’s the root, soil, bacteria biome which clean the air.  Though plants will clean the air if passively placed in a room, by creating their own air circulation around themselves and drawing CO2 and VOCs down toward the root system, this process is much more efficient if ventilation is forced across the root structure.

Another plant based ventilation system has been developed by a joint research effort by SOM, an architecture firm, and Rensselaer Polytechnic Institute.  This system has been deployed at New York city public building.  A cut away of the system, showing how the air circulates through it, is shown below.  This system uses Pothos as the plants–a plant which is “impossible to kill”, according to the developers.  This has been true in my experience, and I have also found that it not only lives but thrives in the typical underlit, underventilated office environment.

Using a system like this commercially would face a number of hurdles, including getting the HVAC engineer on board with trying it, getting a code variance to use it, and the education of the Owner and Owner staff on maintenance.  However, the potential gains for the building occupants are huge and multi-faceted.  If the technology were ever employed on a grand scale, that is, if every new building used a system like this instead of mechanical ventilation, the potential energy savings would be enormous.