Third air-to-root component: a fan
According to Wolverton, a plant’s transpiration process creates a natural convection which acts to bring gases into the activated charcoal at the plant roots, so that the gases would be stored in the charcoal and available to the plant’s root system when needed.
Therefore, Wolverton’s system does not need the capability of a fan, and this has been proven by Kamal Meattle, whose successful use of plants to purify air in an office building in New Delhi has been the subject of a TED talk and is discussed later in this article.
However, Wolverton was able to boost the gas removal from air by a fan, so that fewer plants could be used to achieve an effective level of air purification, and this technology makes the use of plants more practical, to the extent that the great number of plants otherwise required may often be inconvenient to maintain and accommodate.
The fan is the most difficult part of Wolverton’s technology to implement, in that the technology seems to always place the fan below the roots.
However, the bottom placement is not a necessary placement.
Possible fan placements
There have been numerous experiments based on Wolverton’s research. Some experiments appear to have incorporated ordinary fans to circulate air.
1. In Irga’s experiments, a 50 mm (2-inch) fan was used in a 26 x 20 x 30.5 cm (8 x 10 x 12 inch) test chamber (along with temperature and lighting control).
2. Wang used an axial fan, an irrigation device, and a moisture sensor.
A six-inch propeller axial fan was placed in the middle of the chamber to mix the chamber air in an acceptable manner (equivalent air change rate of 20 ACH). The total nominal power of the fans of the DBAFs was 0.75 kW. The fan was utilized 3 minutes after irrigation and continued until the moisture content dropped below the desired level.
It appears the Wang experiments were also carried out in an open building space: “Three Campbell CS616-L water content reflectometers (M.C. Sensors) were buried inside the bed in sequence for accurate moisture content measurement in experiments conducted in the real-world condition:
A programmable logic controller was used to automatically control the operation sequences of the irrigation system and fan.
Do-It-Yourself addition of a mechanical fan
Several types of fans would be able to move air to the bottom of a planter from the top.
1. Squirrel-cage fan: A squirrel cage fan is a centrifugal fan http://en.wikipedia.org/wiki/Centrifugal_fan used to move air or gases. It is sometimes called a blower, and blows air out of a bottom opening. A 1 amp, 12-volt squirrel cage fan, 33 mm (1.3 inches) is very affordable, and with an adapter may be appropriate to mount on a planter.can be found at around $5 as of January, 2015. It is possible to place such a fan at the top of a planter.
2. A CPU fan: This type of fan is used to cool a computer and could possibly be utilized economically.
3. A six-inch clip-on two-speed fan: This type of fan would appear similar to a fan used in Wang’s experimental plant chambers, and is easily available.
4. An aquarium pump< and airstone/b>: By reversing the orientation of the pump, it is turned into a vacuum. It can be attached to an airstone placed in the bottom of an ordinary flower pot. See this setup at this website.
5. Another possibility: A Kickstarter project has been offered using a spin-off of Wolverton technology, utilizing a fan and an inexpensive wall planter. A diagram is provided, without explanation, here.
Click next page to see other factors influencing the plant air filter’s effectiveness.
