Maintainability of Indoor Green Wall in Singapore

Introduction

With 80% of the time spending indoors, it becomes more and more important to ensure our indoor environment is a healthy space. This is even more necessary as buildings become increasingly air-tight and ventilation systems become closed-loop as people rely increasingly on air conditioning in the summertime. This closing up of the buildings comes at a price indoor air quality reduction due to emissions from various sources indoors and nowhere for them to go with the window closed.

The term "building ecology" has been coined to describe the interaction between building environments and their occupants. A healthy building is one that does not adversely affect the health of its occupants or the larger environment and an integral factor in this interaction is the indoor air quality of a building or home.

As we all know, plants are the lungs of the earth. They produce the oxygen that makes life possible and absorbs the toxic contaminants. And the color green can relax your eye muscle and comfort your eyes after a long period of working. Therefore, greenery performs essential functions indoors with the same efficiency as a rain forest in our biosphere. In past research, it shows that indoor greenery is the best filter of common pollutants such as formaldehyde, ammonia, and benzene. Thousands of poisonous chemicals could be released by furniture, carpets, and building materials, and induced in the ventilation system, and ventilated everywhere in the building, causing respiratory problems and allergic reactions called Building Syndrome. 

An effective greenery system based on air improvement technique has been shown to be a green wall. Air is drawn through a porous wall kept constantly wet and covered with mosses and ferns, removing low levels of indoor air pollutants. An example of green walls is shown here is Changi Terminal 4 in Singapore.

Integrating plants into the office environment has proven to be an effective, inexpensive, flexible, and aesthetically pleasing bio-filtration system that is self-sustaining as long as the plants are maintained adequately. Not only do they improve the atmosphere of any indoor environment, but they also help improve productivity, health, and overall well-being of employees or your family.

Numerous green wall technologies have appeared over the years but can be defined as three main categories: hydroponic systems, modular boxes, and cable and wire-rope net systems. Green walls are self-sufficient vertical gardens that are attached to the exterior or interior of a building. They differ from green facades in that the plants root in structural support, which is fastened to the wall itself. The plants receive water and nutrients from within the vertical support instead of from the ground. This fundamental denotation includes many different methods. 

1) Hydroponic Systems

A-frame is made, simply as vertical beams or, for larger projects, as a latticework. For exterior green walls that are exposed to the elements, it is possible to use either aluminum, galvanized steel, stainless steel, or some other non-rusting metal. It is firmly attached to the building or structure. Waterproof panels are then fastened to it. For interior green walls, wood beams are used for framing as no moisture is able to go behind the waterproof panels. Wood is cheaper and also more sustainable than metal. However for the tropic, such as Singapore, wood is a limited material for construction. And the weather is humid over the whole year. Hence, the metal frame should be more acceptable applying in Singapore.

Two layers of material are stapled to the waterproof panels. The material is generally made up of recycled synthetic fibers that are spun into a non-woven matrix. Plants are placed between the two layers of material in hand-cut pockets. Soil is removed from around the roots, and some companies use an inert substrate, such as perlite or vermiculite, in its place. 

Depending on a number of factors, the time needed for irrigation is anywhere from three to five times per day with intervals lasting for about one to three minutes. The factors dictating how much watering is required include the exposure of the wall, what season it is, and what types of plants are chosen. Even a south-facing green wall in the hot summer months would still require less water than urban parks and traditional landscaping. This is because the watering is targeted to the roots of the plants as opposed to watering the ground around them as well.

a) Advantages

• The ability to use an extremely large diversity of plants. The system closely mimics how plants grow in nature meaning that thousands of species have been proven to thrive on this type of green wall. Having access to such a variety allows for endless possibilities in design and no limitation of artistic freedom. This system is better for people interested in more than simply covering the wall with greenery, as it has a greater aesthetical appeal.
• The roots of the plants are free to grow throughout the entire green wall and are not confined to limited space.
• As they grow they form a tight matrix and thus with time the strength of the system actually increases.
• This makes it possible to integrate shrubs, bushes, and even trees in addition to ground covers and smaller vegetation. Plants are able to grow to their full potential in this system.
• Use such a diversity of plants is that pests rarely become a problem. Mono-cropping is a common practice in agriculture these days, but a major problem with it is the fact that most pests target a single crop - potentially spelling disaster. However, when there is a diversity of plants, it is more difficult for the pest to establish and wipe out an entire crop. Weight is a very important aspect to consider when integrating a green wall onto a building façade. Being hydroponic makes this system by far the lightest on the market. In fact, it is over 10 times lighter than common modular box systems, weighing in at a mere 4 pounds per square foot. Modular green wall companies claim that having a box makes it easy to replace if the plants die or get a disease but in hydroponic systems, they tend to thrive and do not have to be replaced very often. If they do need to be changed, it is quite easy and done plant by plant instead of as a full panel.

b) Disadvantages 

• This system is more appropriate for permanent applications, as it is not modular. However, some companies offer smaller hydroponic living walls that are portable. Integrated into one convenient system is a reservoir, pump, and everything required to keep the plants thriving, all on wheels. Some companies offer these as natural, breathing dividers for offices, retail stores, hotels, trade shows, advertising campaigns, movie sets, and others.

2) Modular Boxes

There are two main variations of the modular box technology, outlined below. 

The first is the true box system, utilizing an empty square container made of plastic, metal, or some other material. This is filled with coco-coir, rock/mineral wool, peat, or some similar substrate. The number of plants used in a single box can range from six to fifteen, depending on the size of the species and type of box used. Most plants are added as plugs. Layers of plastic, fabric, mesh, and/or metal bars cover the boxes to hold everything in place. The sizes of the boxes vary widely depending on the manufacturer but generally are about one square foot and a few inches thick. 

The second variation uses plastic or metal trays containing multiple slanted cells. These are filled, usually with soil, and then planted. The slanted cells help to keep the plants in place and facilitate irrigation. The water drips through the back of the panels. This technique is slightly more complex than hanging potted plants on a wall as each cell can be thought of as a small pot. These systems usually can be placed side by side and stacked to add height.

a) Advantages

• Modular box systems are the most appropriate for temporary installations.
• The individual boxes are easy to install, replace, and remove.
• Kits are available for purchase online making them great for DIY projects.
• Best for growing short seasoned food crops such as lettuce. This is because they are not as permanent as the hydroponic systems and can be easily replanted panel by panel.

b) Disadvantages 

• The main problem is that the space available for root development is limited to a few cubic inches. Therefore, only ground covers and small plants can be used. This severely reduces diversity, which in effect limits the freedom of design and the potential to recreate natural ecosystems. The overall effect tends to be boxy, squat, and geometrical - not something nature would create. With the true box systems, the panels must be pre-planted and slowly tilted to a vertical position in order for the plants to properly adjust to the new Peat-filled metal mesh boxes, planted and ready to be hung. The process can take anywhere from one to six months. This potentially can increase the price as more infrastructure is required to prepare the panels prior to being hung.
• A drawback to the tray system is that, because the plants cannot firmly take root in the plastic/metal cells, they can easily be washed out or removed when there are heavy rains or strong winds. If soil is the chosen substrate, the dirt can fall out; this being problematic, especially for interior installations. Modular boxes can weigh up to 30 pounds per square foot. This is a substantial difference when compared to 4 pounds per square foot for hydroponic systems.

3) Cable and wire-rope net systems (Climber System)

Flexible steel cables are used in a variety of configurations to create support for vines. Connectors hold a pattern of cables in tension off the surface of a building and can be adapted to attach to almost any surface or structure. This mostly two-dimensional solution relies on the structure of those plants that twine, either at the stem or from a leaf structure. Twining vines might only require a single vertical cable element for climbing. Plants that climb with the aid of leaf tendrils or are scramblers that use hooks or thorns are most adaptable to a rectangular structure with closer supports. These systems can also be used in combinations with various rods or intermediate members that create a variety of surfaces and may add integral structural support. Wire nets can be created from cable elements and are usually custom-designed for a specific installation.

a) Advantages

Cable systems are: 

• Lightweight, can cover large surfaces, and have flexibility in design.
• Easy to ship, but may require installers with specific knowledge of the product being specified.
• Ease of construction and replacement as well as the economies of scale of repeating patterns.

b) Disadvantages

• The metal-made cable exposed to direct sunlight might be heated up, which would affect the growth of the climbing plants.
• The high temperature might scare climbers and reduce the climbing height.
• The size of the planter box will limit the amount of space in which plants can spread their roots into the soil.

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