When they said there was a green revolution taking place with mechanical systems, Alan Darlington took them literally. Working on new ventilation ideas in the early 1990s at the University of Guelph in Guelph, Ont., Darlington decided to go back to basic common sense.
"We all know what fresh air feels like, and science tells us that outdoor fresh air is kept clean by natural processes. Vegetation is the key element in those processes."
He decided to investigate whether this same natural air purifying process could be brought indoors. "Strangely, most of us spend 90 percent of our time in an indoor artificial environment."

He began work on moving air through a wall of plants to help condition it. Some things just seem intuitive. But in today's world it's not enough to trust your instincts. It has taken years of research, verification and development, but Alan's company, Nedlaw Living Walls, is now installing plant wall HVAC systems in numerous locations. Forty projects have been completed from coast to coast in Canada and the U.S.? About fifty projects are in development, including some in the UK and in Kuwait.

Living walls improve indoor air quality, save energy and beautify indoor environments. Ideally they are included early in the building design process, and have been for projects where walls are 30 square metres or larger. Among the smaller projects, 60 to 70 percent have been retrofits. They're mostly found in big lobbies and atriums, but the technology is scalable. Projects as small as one square metre have been completed without complication.

How it works

The system uses bio-filtration and phytoremediation as air is drawn by fans through tropical plants, roots and root material into perforated ducts. The clean air is then directed into the existing conventional HVAC system or simply released back into the space. (Online encyclopedia Wikipedia.org describes 'phytoremediation' as "the treatment of environmental problems through the use of plants which mitigate the environmental problem without the need to excavate the contaminant material and dispose of it elsewhere.")
There is no soil used in the wall; plants instead root themselves naturally into a special polyester weave material. The plants survive on water, available light and nutrients. Water is pumped to the top of the wall and falls to the bottom where it is filtered and reused. The plants consume about a cup or two of water per square metre of wall per day. Standard plant nutrients are added once each month as part of a maintenance contract. The contract includes a warranty and is mandatory for the first year.
The system's key vulnerability is if the pump fails and is undetected for 48 hours or more. In such a case the plants would die, creating an expensive remedy. Larger installations are routinely specified with a back-up pump, and users are coached on visual monitoring. When possible, pumps and fans are monitored by building control systems. When the pump is functioning normally 90 percent of the plants survive in a given year.
Living walls utilize fairly common tropical house plants such as Philodendrons, Ivy, and Ficus. Outside Canada native plants are used as most countries do not permit plant importation.
Because microbes do the work, plants must be able to support microbe life, must take to the soil-free polyester and must be able to survive site-specific conditions, light sources, temperature and water conditions.

Installation

Installation is completed in two phases. The first phase includes the ductwork, mechanical systems and growth media. This can take several weeks and in a new building is usually recommended at rough-in. The second phase is the planting of the vegetation after any heavy construction is completed. This can take up to two weeks.

Indoor air quality

"Many customers care more about indoor air quality than about energy savings," says Darlington. "There is plenty of good research to support improved employee performance, reduced office ailments, absenteeism and turnover when indoor air improves."
The system removes 40-60 percent of the toxins, dust and spores in a single pass through 'the wall, ' providing a highly viable solution to air quality challenges. "Some thought that because we use plants the system would create airborne spores. In fact it reduces spores, dust, and most importantly, toxins..."
Air is actively drawn through the root zone where highly specialized microbes degrade pollutants such as formaldehyde and benzene into their benign constituents of water and carbon dioxide.
In order to achieve recognition under Leadership in Energy and Environmental Design (LEED) Canada, the system was challenged in a series of tests for efficiency against odours and a host of volatile organic compounds such as toluene, ethylbenzene, xylene, acetone and others.

Energy savings

The Living Wall can also save energy. This is especially true with the recommended installation configuration that feeds directly into the HVAC system. Less fresh external make-up air is required because fresh internal make-up air is available. In many parts of Canada (not B.C. so much), where there is great variance between cold and hot temperatures, this reduced need makes a difference in terms of energy usage. Most Living Walls use up to 85 percent less energy than conventional methods during periods of peak load. Average energy savings are on the order of 50 to 60 percent.
Although the system's lights, pumps and fans consume electricity, usage is fairly modest depending on the size of the plant wall. Grey water can be and has been used. Lighting costs are further reduced when Living Walls are located in atriums and beneath skylights. If not, total energy usage is 120 watts per cubic metre of plant wall. Most of this is for lighting.

Odour control

Living walls are also effective for controlling odour. In one case the system was installed in the paint shop of an automotive plant. It effectively eliminated between 60 and 80 percent of odours, but over time it became less effective.
"We learned a lesson there. We installed the wall near where there was an acetylene tank. The biocides became airborne and began wiping out our microbes. Still, the client remains satisfied," remarked Darlington.
There is probably no science to prove that a wall of plants makes a more beautiful environment for most of us, or results in better quality of life. You'll just have to take Darlington's word for it; or trust your instincts.

A living wall brings comfort – in a number of ways – to what might otherwise be a sterile indoor environment.

Alan Darlington takes "green design" literally.

Incorporating a living wall requires little deviation from traditional HVAC duct design.

Workers plant greenery into a special polyester weave material.