Climate Change Corner
Benefits of Green Wall to Our Environment
Vertical greening also known as green wall, living wall, biowall and green facade, refers to vegetation that grows directly onto a building’s facade or vegetation that is grown on a separate structural system that can be freestanding and adjacent or attached to the wall. Vertical planting is certainly an alternative to roof greenery in a city composed of tower blocks which have high wall to roof ratio, and consequently large potential surface area for greening. The popularity of vertical greenery is growing because current research has shown that incorporating living walls into building design has several benefits.
Building energy benefits
Buildings account for 39% and 71% of total energy and electricity consumption, respectively (U.S. Green Building Council, 2008). A large amount of this energy is used to maintain internal building temperatures through heating and cooling systems. Green wall technology can lower heat absorption of the wall and therefore lower indoor temperature.
Reduction of Urban Heat Island Effect
Vegetation can alleviate urban heat island directly by shading heat-absorbing surfaces and through evapotranspiration cooling. A building envelope is covered with vegetation such as green walls in warmer temperatures, the surrounding air temperature can be decreased which not only leads to energy savings for cooling building interiors but also to the lowering of the urban heat island. Previous study showed that the humid climates of Hong Kong can achieve substantial benefits of a maximum temperature decrease of 8.4ºC with vertical greenery systems in an urban canyon (Alexandri and Jones, 2006).
Carbon dioxide reduction
Green surfaces can play reduce CO² in the atmosphere in two ways. First, carbon is a major component of plant structures and is naturally sequestered in plant tissues through photosynthesis and into the soil substrate via plant litter and root exudates. Second, they reduce energy needs by insulating individual buildings and by mitigating the urban heat island. Research in Canada showed that the reduction in CO² emissions of the green wall included a 15% reduction in CO² generated for cooling buildings and another 2% via CO² uptake by the greenery (Roehr and Laurenz, 2008).
Air pollution reduction
Vegetation removes pollutants in several ways. Plants take up gaseous pollutants through their stomata, intercept particulate matter with their leaves, and are capable of breaking down certain organic compounds such as polyaromatic hydrocarbons in their plant tissues or in the soil (Baker and Brooks, 1989).
From the test carried out by our company with The Open University of Hong Kong and Hong Kong Baptist University shown that green wall system can also remove particulate matter, carbon monoxide, TVOCS, formaldehyde and carbon dioxide in different degree subject to different system.
Since green wall can both be a decorative and functional product. And given the growing popularity of green wall systems in other counties, I envision an increase in usage of green wall technology by designers/ architects in Hong Kong.
Source: The Open University of Hong Kong / Hong Kong Baptist University / InnoGreen Environmental Company Limited joint research: Soilless System for Green Wall Final Report (Phase I), 2011.
This article is contributed by Alfred Tak Kong Lee, Director of InnoGreen Environmental Ltd. with the co-ordination of the Environmental Division.
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