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To maintain an adequate and economical work environment, modern buildings are as airtight as possible. The upside of being airtight is a limit to the cost of heating or cooling the space while providing a comfortable work space for the occupants. The downside of being airtight is that any pollutants arising within the space — from building materials, activities or the occupants themselves — may accumulate. This accumulation of pollutants can influence the enjoyment, productivity, and potentially the health of the occupants in that space. The principal indoor pollutants of concern to us are VOCs (volatile organic compounds). VOCs arise from many sources, including solvents, building materials, adhesives, carpets, electronic equipment and cleaning fluids.
What’s traditionally done to maintain indoor air quality?
To avoid the build-up of VOCs and other indoor air contaminants, most buildings bring in outside air through a ventilation system to displace a proportion of the inside air. This is the modern equivalent to opening a window.
Why do we need an alternative approach?
During the extremes of summer and winter the new fresh air being pumped in can be far below the quality desired by people in their work environment in terms of temperature and humidity. Consider working at a desk in front of an open window in the middle of winter and you will quickly realize the value of air-handling systems designed to precondition incoming air. Conditioning the introduced air requires substantial energy and therefore represents a significant cost to the operation of the building. The heating or cooling of this new air means the building manager faces the choice of either allowing the operating cost of the building to increase or allowing indoor air quality to decrease. An alternative that allows the maintenance of indoor air quality without the introduction of outside air would avoid the dilemma altogether.
What is the alternative to ventilation?
Rather than introducing large amounts of so-called fresh air from outside, we incorporate into the building itself the features responsible for making outdoor air fresh in the first place. That is, we integrate a complex ecosystem as a biological filter into the building's air-handling system. This removes pollutants from the air, and removes them through normal biological processes.
How do Living Walls work as a biofilter?
Nature has the built-in capacity to adjust to environmental changes. It can repair itself after damage or adapt to exposure from a wide range of compounds. Although the time scale may vary from minutes to centuries, in time a natural ecosystem can repair almost any damage it may sustain. For example, given enough time nature can restore a site contaminated with organic compounds such as VOCs. One reason for this is that, frequently, materials such as VOCs that are toxic to some life are food for others. Most of the biological breakdown of VOCs is done by microbes (bacteria), although higher plants may also be involved. Some pollutant-degrading species are usually present and active in most environments, and the act of introducing the pollutant only increases their relative numbers and/or activity levels. NEDLAW active Living Walls are a biofilter containing such organisms to remove contaminants present in the air at very low concentrations. In essence, we mimic indoors what happens outdoors every day.
What do active Living Wall biofilters look like?
A wall covered in plants, our system is essentially vertical hydroponics. Water from a basin planting is lifted by a pump system to the top and flows back through the interior of the plant wall, circulating through a closed water loop system.
How was it designed to work?
Filtration takes place right in the active Living Wall. Basically, dirty air, drawn in from indoor space, makes close contact with the constantly-flowing water within the wall. Pollutants are moved from air to water — all the while improving air quality. Once dissolved into the water, pollutants are attacked by biological components on the wall itself, and are metabolized into a harmless state.
What breaks down the pollutants?
Although plants are able to remove some VOCs, the majority of the breakdown is done by the beneficial microorganisms present in the system.
If microbes are metabolizing most of the pollutants, why include the green plants?
Green plants are included for a number of reasons: They offer ecological stability to the system as a whole by providing species diversity. They also may be active at removing some VOCs to some degree. Furthermore, the inclusion of plants adds important aesthetic value to the space. Of course, since CO2 is considered an indoor pollutant, green plants, through the process of photosynthesis, offer a means to control it.
Why so much diversity?
Species diversity gives the system ecological stability. This is very important in order to give the ecosystem the power to deal with a broad range of potential challenges in the indoor setting.
Is the system modeled after a particular ecosystem?
Rather than trying to duplicate a particular outdoor ecosystem, active Living Walls are designed for the unique indoor environment. Just as the best place for a Brazilian rainforest is Brazil, the plants used in our walls have been selected for their adaptations to the moderate temperature, humidity and light conditions typically found indoors. Although many are exotic and unusual plants, some are quite common.
Could native plants be used in the system?
Some native plants may be present. However, most native plants would not survive well indoors. Plants adapt to their local climate and, as such, plants from northern climates generally require the different seasons to grow properly. For most native plants to survive indoors, the climate in the wall would have to mimic these seasons, making routine use of the space difficult and its performance irregular.
How long do the plants survive in the space?
We expect about 90% survival of the plants each year; but this is largely dependent on the choice of plants and local conditions.
Are pesticides used in the wall?
We use only methods that can be considered organic to control pests in our walls; we emphasize management practices and biological controls such as predators. So-called pests such as white flies, fungus gnats, spider mites and their respective predator species are necessary, even desirable. They contribute to the ecosystem’s species diversity and ecological stability.
How much maintenance does a Living Wall require?
We carry out scheduled maintenance on our Living Walls every month. Some clients choose more frequent visits based upon their unique conditions.
How good is air quality from an active Living Wall?
The air quality of a space relying almost entirely on active Living Walls is as good as, or better than, similar indoor spaces relying on sophisticated ventilation systems that replace the building air up to six times per hour.
How well does the system work?
During studies at the University of Guelph, very low concentrations of some common indoor pollutants were released into the wall to measure the system’s potential as a filter. The chemicals were formaldehyde, toluene and trichloroethylene (TCE). These were selected to represent the wide range of chemicals, with which the system would need to deal. Formaldehyde is very soluble in water and readily metabolized by bacteria and higher plants. Toluene is slightly soluble and degraded by a select microbial population. TCE is relatively insoluble and resistant to biological degradation.
A single pass through the Living Wall removed up to 80% of the formaldehyde, 50% of the toluene and 10% of TCE. These numbers are incredibly impressive, particularly when you consider that the filter is only 5 cm thick. Concentrations of toluene and formaldehyde in the aquatic system did not increase during the four-week experiment, suggesting that these materials were readily metabolized. TCE levels in the aquatic system initially did increase slightly, but then plateaued, suggesting a possible capability to degrade this compound. Even before the challenge, we knew that two to three percent of the bacteria present had the ability to breakdown VOCs.
What's the difference between installing an active Living Wall and simply putting a large number of plants in your space?
Some suggest that plants may remove VOCs from their surrounding environment. However, there is very little available data to support this claim. Most studies which find any VOC removal with potted plants suggest it is in the potting soil (where the beneficial microbes live), not the green plant, where the breakdown occurs. Others believe that even if plants can clean the air, they could only clean a very thin layer of air immediately around their leaves. When a plant is simply placed on a desk or even in a grouping on a wall, the typical low rates of air movement around it would limit its impact on the air, in the space as a whole. By actively drawing air through a Living Wall, we force pollutants to the root zone where real breakdown can occur.
How large should the Living Wall be for a typical building?
Although there are many factors to be considered, the quickest and easiest estimate for sizing a Living Wall is one square metre of active Living Wall to meet the needs of 100 square metres of floor space. Our design team can work with you to develop more accurate sizing for your particular application.