Ledger, B.
1999
Canadian Consulting Engineer, August/September 1999
| Researchers are permanently stationed in the Environmental Room in the Canada Life building in Toronto to monitor how well the Breathing Wall System works. The wall, standing 2 metres high by 5 metres wide at the end of an L-shaped meeting room, uses plants and natural organisms to clean the indoor air.
The room was set up four years ago and was developed by Canada Life Assurance/Adason Properties, Genetron Systems and the University of Guelph, with the Mitchell Partnership as mechanical consultants.
The biofiltering system consists of a hydroponic bed, an aquarium, and behind that a vertical scrubber. Life forms, from exotic orchids to duck week, to aphids and angel fish, inhabit the wall and help to absorb pollutants from the air. The room has a 1,250 cfm air handling system in total, with an 800 cfm unit located behind the scrubber, drawing air through the filter. The scrubber consists of five fibreglass panels faced with porous lava rock and moss, and is continually wetted with recirculating water. The room is isolated from the building's main HVAC system and though it has the ability to draw in outside air, the dampers are presently kept closed so that it exists as a contained ecosystem. Lights shining on the plantings, however, give off so much heat they have to be isolated from the system in a separate glass plenum with its own air handling system.
How well is the Breathing Wall working? In a four-week test the researchers subjected it to heavy doses of three common volatile organic compounds (VOCs): formaldehyde, toluene and trichloroethylene (TCE). They found that the biofilter easily removed formaldehyde, as it is a very soluble compound. Toluene levels remained undetectable even though the system was subjected to 10 g of the compound every day. However, it did not cope well with trichloroethylene. One pass through the scrubber removed 10% of the substance, but levels accumulated in the aquarium.
Dr. Alan Darlington, Ph.D. of Guelph University monitors the Breathing Wall and finds that overall it is performing well. He says the key to the success of such biofilters is finding the right balance of life forms. Once that is achieved a system will take care of itself. The only infestation problem they have had in the Canada Life room was with fruit flies which were breeding in a composter. They solved it by moving the rotting vegetation outside. Humidity levels in the room are slightly above the norm, but there is no problem with mould spores.
Biofilter air-cleaning systems might be too cumbersome for the average commercial building, but they have many advantages -- not least that they give the occupants the pleasures of nature first hand. Darlington says biofilters will gain wider acceptance once researchers come up with calculations that show how they save energy by reducing the need to ventilate with outside air. The most likely applications will be in places like the Arctic, although studies are also looking into using such systems in deep core mining. As for size, the rule of thumb is to have one square metre of biofilter per 100 square metres of floor space.
Meanwhile, two of the partners involved in the Environmental Room are helping to develop a modular air biofilter, which is currently at the prototype stage. Guelph University and Adason Properties are working with Crestech and the Northern Centre for Advanced Technology in Sudbury, Ontario to develop a plug-in unit that could be used in any office environment. |
