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Photo courtesy Rastegar Property Company
Photo courtesy Rastegar Property Company

by Andrew Chalk

PaperCity reported on April 20th that the tallest ‘living wall’ in North America will be constructed in Dallas on a 26 story condominium tower to be built at 1899 McKinney Avenue (which, claims PaperCity, is in downtown Dallas. It is not, it is in Uptown). The article bubbles effusively about how green this is. The 40 thousand plants in the wall will capture 1,600 pounds of CO2 each year (as well as emitting oxygen).

The author of the article is Megan Ziots, who last year wrote that “There is no authentic Chinese food in Dallas”.

Unfortunately, PaperCity has no sense of context. A one minute Google search would have revealed that the average family car emits six tons of CO2 per year. So, if we assume that all 40,000 plants are in fine fettle, and round up the amount of CO2 captured each year to 2,000 pounds (one avoirdupois ton) then PaperCity’s massive pollution destroyer removes just two months of pollution created by one car each year.

Not a very green result, but at least it is something, you might say. Unfortunately, the savings don’t come free. Those 40,000 plants have to be irrigated. Ignoring the capital costs of building the wall and its irrigation, the irrigation system has to be operated. Assume it is operated for just one hour each week and there is no electricity consumption between watering events (standby mode). Assume also that each of the 26 floors has a separate controller that uses 100 Watts. Then each floor uses 2.4kWh/day, or 124.8kWh/year. For 26 floors that is 3,245kWh. One fifth of that is produced from coal in Texas, and burning coal produces 2.3 pounds of CO2 per kWh. So running the irrigation produces 1,493 pounds of CO2 per year. That sounds close to a wash with the 1,600 pounds of savings, and we haven’t included the cost of plants, nor that they die (one industry estimate was that a plant lasts four years), and countless other things.

All in all, we can’t justify this wall on ‘green’ criteria. Developer, Rastegar Property Company would do better to scrap seven clunker cars a year if it wants to reduce pollution. But keep the wall! Around the world living walls create fantastic ambience in city centers and that is the reason to keep them. Just don’t believe they are anti-pollution devices.

Detail of Patrick Blanc's exterior green wall of the Musée du Quai Branly (image 2012). Courtesy Wikiedia.
Detail of Patrick Blanc's exterior green wall of the Musée du Quai Branly (image 2012). Courtesy Wikiedia.


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