Saturday, February 23, 2008

Living Walls: Indoor Filtering

New Vegetated Architecture, moving to the indoors. This post was borne of images from the Cambridge Civic Administration Building in Toronto, featuring a large indoor living wall very reminiscent of the project at Guelph-Humber. This gives us the opportunity to get into depth regarding the function of indoor walls (and indoor vegetation by default) to provide climate modification via 'vertical filters' (one of the VegArch typologies).

From World Architecture News on the Cambridge Building: "Features of the building include a four-storey atrium which will act as an interior public square during the winter months. The atrium also features a green wall bio-filter which is a component of the indoor air quality systems and is an element of the sustainable design strategy for the building."

:: images via WAN

So how do these things work? For some answers, the first stop is a company that evolved from the research of Dr. Alan Darlington on the Guelph-Humber project, Air Quality Solutions, and specifically their Naturaire® Systems.

:: images via Air Quality Solutions

Their site offers the most detailed account of some of the scientific processes at work to provide air quality benefits by the use of indoor plants. In addition, the also have a pretty good library of research. A summary of the process (all quotations from the AQS site):

1. The process involves a hybrid of two technologies: "... biofiltration, the use of biological systems of beneficial microbes to break organic pollutants down their benign constituents and phyto-remediation, the use of green plants to facilitate the remediation or reclamation of contaminated soils or water."

2. Unlike mechanical filters which clog or saturate, plants are self-rejuvenating: "Because the pollutants in the air are broken down to their benign constituents, there is nothing to accumulate in the system."

3. Because of the variability of indoor contaminants,: "Microbial species diversity is a key parameter. To maximize diversity, an indoor biofilter must provide many different microbial ecological niches."

4. This is where planting comes in, offering a: "...complex ecosystem which infers operational stability and, in contrast to conventional biofiltration, ecosystem diversity which may promote the degradation of a broader range of contaminants."

5. Plants are beneficial in other ways, by a variety of means. These include, a high surface area ratio, they are regenerative, can actively break down microbes versus merely filtering - both in vegetation and roots, accumulate airborne pollutants and dust, and provide a CO2 sink via photosynthesis.

:: images via Air Quality Solutions

Why would you implement a project such as this, aside from the obvious aesthetic benefits? The quality of our indoor air has degraded to the degree that poor air quality is fourth on a list of 31 environmental threats in the US, according to the EPA. According to Air Quality Solutions: "It is estimated that nearly 25% of US residents are affected by poor indoor air quality, either at the workplace or the home. Indoor air pollutants can be as diverse as toxic chemicals emitted from building materials and furnishings, combustion pollutants like carbon monoxide and toxic particles, and biological contaminants such as moulds and bacteria."

:: Dr. Darlington, I presume? - image via Treehugger

The final technical issue is sizing, which varies depending on the system, contaminant load, and level of cleaning, but works by the following rule of thumb: "Given most residential and office conditions, a ratio of at least 1 to 100 for the area of the biofilter to floor area to be treated will give desired affect. Given typical operating conditions, this will mean that one square metre of biofilter will treat 100 square metres of floor space (or 1 square foot of biofilter will treat 100 square feet of floor space)."

Below is a simplified diagram of a circulating indoor system, with pump, and fan providing flows throughout the aparatus:

:: images via Manhattan Plant Experts

The type of plants matter, for starters, check out Treehugger's list from NASA of the top 5 indoor cleaning plants, (fyi: peace lily, bamboo palm, English ivy, mums, gerbera daisies). Yikes, I may stick with bad air if that's my choices.

And applications vary as well, to high-tech, small-scale solutions working on similar principles, such as the Bel-Air, "...a mini mobile greenhouse that continuously inhales the space-polluted air, forces it through three natural filters (the plant leaves, its roots, and a humid bath) before ejecting it, purified."

:: Bel-Air - image via Core77

So the multiple benefits together help to justify the cost of implementation. Natureaire has developed two 'systems', Natureaire Supreme - in 'classic' or 'custom'. This always kind of scare me a bit as off-the-shelf nature (read green roof 'systems') is never something I've been too comfortable with. But the idea of a system, or at the very least, some viable precedents with proven track records, makes me feel that we will soon be seeing more of these proposed and built throughout the world.

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