As we know, green walls greatly improve the outlook of the office, shopping centre, school or hospital. They suppress sounds and improve the air quality of a building. But what is the actual effectiveness of such a wall? What substances are really filtered from the air? And is it possible to give a green wall a boost for extra effect? These were the questions that were investigated in both a Swedish and a Dutch study.

In May 2015 a group of researchers from the university of Linköping in Sweden investigated how a special system for vertically planted walls works. For the study they developed a wireless network with sensors, allowing them to gauge humidity and temperature. They also applied sensors for measuring three elements you would rather not have in the air:

  • Carbon dioxide (CO2)
  • Volatiles that evaporate easily and can damage the health of people and are bad for the living environment. Volatiles are all around us; they can be found in paint, glue, wall-to-wall carpeting, furniture, plastics and cleaning agents. One of these volatiles is formaldehyde. This poisonous gas harms people and animals and can be found in chipboard, MDF and textiles. It also evaporates when you burn gas, wood or tobacco;
  • Small particles like hair, dust, pollen and organic particles.

The test arrangements

The tests took place in a closed-off area, with a humidity of 55 to 67%. The temperature ranged from 22 to 28 degrees centigrade. The plants weren’t placed in soil, but in insulating material that was kept moist automatically. Underneath the planter a fan was placed that could fan the air past the plants at various speeds.

The results

Carbon dioxide levels decline
It is known that plants absorb carbon dioxide during the photosynthesis process. However, we didn’t yet know the effect of a four by two metre green wall on carbon dioxide levels. The absorption of carbon dioxide wasn’t a speedy process. It would take 36 green walls to compensate for the amount of carbon dioxide one person exhales during 24 hours. It took about 13 hours to decrease the amount of carbon dioxide in the test room by 50% with fan blowing air at speed 2.

Volatiles are quickly dissolved
The green wall appeared to be succesful in absorbing volatiles. If a built-in fan was used, the effectiveness was even greater. The concentration of formaldehyde went down by 50% in 48 minutes with a very high fan speed (5). With a slow to medium fan speed this took 90 minutes and without ventilating this took no less than 6.5 hours. Using a fan at the highest speed proved to be eight times as effective as not ventilating.

Small particle concentration brought down rapidly
The wall was very effective in absorbing small particles. These were brought down by 50% at fan speed 5. Using fan speed 2, this took about 2.5 hours; without ventilating: 6.5 hours. The results showed that the fanning at the highest speed could speed up the effect by 11 times.


Green wall with fan boosts the indoor climate
The Swedish research team drew the conclusion that the green wall was effective in both absorbing volatiles like glue and formaldehyde as well as particulate matter. The built-in fan increased the absorption by 8 to 11 times, at fan speed 5. So it is recommended to use a fan to improve the effect of a green wall. If ventilating is used, the green wall effectively works as a huge vacuum cleaner that is able to absorb harmful substances. Any existing ventilation system is easily beaten!

Humidity increases as well
In the closed-off area the green wall increased the humidity of the air up to 100%. This means the wall was also effective in humidifying the air. This makes the system very suitable for spaces with a dry climate. It could improve the indoor environment of these spaces for human use.

What does the study reveal?

This study shows that it is possible to enhance the natural properties of plants, making green walls more effective and active. This way they will become an essential part of the climate control system in a building. In fact these kind of systems can be used in all situations where there is a need for a more healthy indoor climate, such as offices, schools and hospitals. Most people spend around 90% of their time indoors, often in poorly ventilated, unhealthy places. Lowering harmful substances in the air around them will have a direct positive effect on their health and wellbeing. Furthermore, plantwalls have a noise tempering effect. Poor acoustics are also widely reported to have a negative impact on people’s wellbeing. As such, living walls can be helpful in bringing down the costs for absenteism in organisations.

Dutch initiative

This kind of research and development can contribute to new innovations such as a Dutch concept that was presented during the international Trade Fair in November 2015. This prototype was based on smart ventilation, special sensors that measure the concentration of volatiles and, of course, a green wall with carefully selected absorbing plants. The objective is to develop a system that can guarantee to clean the air by gauging the air quality and, if necessary, uses active ventilation to let air pass through the plants. Several parties such as Van der Tol Hoveniers, Nieuwkoop de Kwakel, FloraHolland, Waterdrinker, Stichting Innovatie Glastuinbouw and Into Green have cooperated in this project.

Meanwhile in Canada

Also based on scientifc research, Canadian company Nedlaw Living Wall has developed a plantwall system with active biofiltration. See more here