# Do Living Walls Really Contribute to Clean Air? Apparently, Yes.

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When faced with a choice between simple technologies and complex ones, I like the simple and easy. Living walls seem to me to be needlessly complex; that is why I prefer the green façades by Edouard François to Le Mur Végétal of Patrick Blanc. So when a big living wall was installed in an Embassy Suites in Chicago, and when designer and project manager Denise Eichmann said "This green wall provides clean oxygen indoors, equivalent to 16 fourteen-foot-tall trees," I did the math and concluded that 7.17 times as much Carbon dioxide is created powering the thing as is absorbed by it. Boy, was I wrong.1. Living walls use a lot less power than I thought.

Irrigation controllers never constantly run. All irrigation controllers run on very low power in-between watering events just to keep their clock and schedule running. Think of it like a DVD player with a clock on the face, it only really uses power when it's playing a DVD, the power required to see the digital clock in between uses is very very little. The only energy used during the down-time is a small amount of energy drawn to run the computer real time clock (RTC) that is on the circuit board of the controller and some further energy required to power the circuits for the alarm monitors. When the controller is not actuating valves, it uses 50mA @ 5V, 365 days a year, 24 hours a day. When the RTC actuates a watering event (once a week for 1 hour for this wall), the irrigation controller then draws further power to physically open the water valves on the wall (which have a solenoid coil resistance of 38 Ohms). The watering event power draw for this wall is 0.3A @ 24V for 1 hour every week x 2 valves (one per side).

Here are his power calculations:

Real Time Clock - 0.02192 kWh / year.

Watering Events - 0.7488 kWh / year.

TOTAL = 0.77072 kWh / year.

2. Chicago isn't powered only by coal.

Commenter Geoffrey tells me that Chicago gets 60% of its power from nuclear plants and less than a third from coal. This significantly drops the proportion from coal:

Total from coal: 0.77072 kWh / year * .33 = .091433 KWh/year from coal, * 2.3 pounds of CO2 per KWh = .210 pounds of CO2. Per Year. And we calculated that the wall was sucking up 1.709 pounds of CO2 per day, or almost 3,000 times as much CO2 as is produced powering the wall.

Chad's number for electrical consumption sounds awfully low to me, and as we noted before, the calculation for the amount of CO2 that the wall was sucking up is probably high, but nonetheless I have to conclude that the living wall is absorbing a lot more CO2 than is emitted making the power that runs it. A lot more.

I will be a lot more positive about living walls in the future, they really are more than just green eye candy.

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