Principles of operation, critical points
There is a significant technological background behind the most advanced green wall systems, from design and sizing to the operation and maintenance of the wall. In this section, following a brief introduction to the differing technologies, detailed information is provided on the greenwall.pro green façade module, with a downloadable application guide at the end.
The roots are planted in soil with the foliage being trained onto the wall.
From a technological perspective, the climbing systems are interesting as different technologies exist for holding and leading the foliage, from wooden trellises to professional stainless wire systems. It is very important for the technology (sizing and quality of the parts) to be of a high standard, especially when using plants producing a considerable amount of foliage. From a technological perspective, the quality, durability and choice of options of the structural elements carrying and leading the foliage, as well as those required for fastening, tightening and bracing them, are of relevance. There are several good systems on the market, however, a thorough overview is needed to be able to select the best option for a given task. Water supply and drainage does not necessitate special technological solutions here.
The plants are not rooted in the ground, but in a typically large volume horizontally positioned planter that is positioned at various heights. Due to the large volume, the most important technological question is of a structural nature, including that of the planter, the sizing of the framework and the connection to the facade. Providing solutions for even water and nutrient supply per stories and the closed-circuit excess water drainage (per level or in a flowing trough system) is not a simple task either, especially as the horizontal orientation results in the top line of planters getting water from natural rainfall. This leads to differing growth and presentation between the top and bottom planters.
It is a monolithic system, where the plants are planted into pockets cut into felt material fixed to a watertight board and the plant do not root in the felt itself. One of the most important technological questions is managing the waste drainage. The system is rather wasteful with water due to its design, with the irrigation water flowing down in an uncontrolled way on the surface and on plant parts, therefore for the drainage and collection of the large quantity of the excess water a separate large capacity system has to be constructed at the bottom of the wall and above doors and windows. In many cases the water is being taken out from the system by the leaves, which then falls onto the area in front of the wall. The most serious technological problem is the felt material itself: it tears, damages and rots easily with algal growth also a problem. Although the roots of the plants are able to cling to the felt, but if they grow too large there is no guarantee that they will not fall off the surface, taking a section of the structure with them. The fixing of the felt onto the watertight board in most such systems is simply done by staples. The pocket system using man-made fibres is counter-indicated for facades with openings, as the material is synthetic and flammable.
A system consisting of small elements is fixed to a pre-installed framework, where the plants are placed into predetermined openings. All details require precision technology, and if available, the modular systems are suitable, almost without compromise, to create the most varied green façade structures. An especially sensitive area, and with many systems without any solution, is the even water and nutrient supply within the modules, for which each system applies a different solution with more or less success.
The irrigation system for almost all such systems is integrated drip irrigation; the excess water in most cases flows through all of the modules. The greatest disadvantage of this is that from top to bottom the plants receive increasing amounts of water, thus their development is uneven or the lower sections rot or the top dries out. The most advance systems (including greenwall.pro) collects water at every level, preventing flow within the system. An additional problem is that the excess water in all cases also contains nutrients, and exactly those that the plants in a given maturation period do not need (this is why they do not absorb them). This enriched water flows down in a concentration that increases as it approaches the lower parts of the facade. This may prevent the absorption of useful nutrients, which in the long run can lead to deficiency diseases, in more serious cases to the death of the plant.
Fixing technology, framework
In addition to the structural assessment of the carrying surface, technological sizing is also required. Contact corrosion must be avoided; therefore the separation of metal parts with differing electrode potential is necessary.
The background structure can be constructed as a vertical framework, which can be ventilated, however the vent effect has to be taken into account, the scale of which is dependent on many factors. It can be constructed with horizontally positioned boards, which still ventilates but without the vent effect. The background structure, which holds the elements of the green façade, can be made from wood, metal and also plastic. Solutions constructed without a framework are rare and not ideal, as there is risk of condensation. The background structure has to be designed together with the external heat insulation, when using a thicker insulating layer, the spacer brackets need to be sized accordingly.
Wood is inexpensive and easy to work with, although in a wet environment even with the best wood preservative, it will sooner or later decay.
Mass plastics are inexpensive and durable, but are sensitive to UV, in cold weather they become rigid, and are flammable.
Technical plastics and composite materials provide varied opportunities in terms of composition, the disadvantage is that most are flammable and the price often exceeds that of stainless steel or aluminium.
Aluminium is a durable material, however it is expensive and not fireproof.
In case of powder-coated galvanised steel, corrosion resistance cannot be guaranteed, the paint is flammable.
Stainless steel has technically perfect qualities, but the price is relatively high.
Soil is inexpensive, but the condition deteriorates with time, furthermore the quality is rather varied and the considerable weight is a disadvantage when used in a facade system.
Peat substrates initially provide excellent quality, however it also compacts, thus is only usable for one-two years.
The structure of fibrous mineral substrates (e.g. mineral wool) after the second year deteriorates rapidly, and it does not wet evenly vertically, resulting in uneven plant development.
The porous inorganic granulates (e.g. lava grist, clay-granulate, perlite, bulbous glass gravel) have a stable structure, their pH is usually too high, but it can be controlled by setting the pH value of the medium. These materials, in addition to being durable, are also excellent in getting rid of the excess water. Due to their micropores they ensure an even medium-vapour concentration in the macro pores between the granulate grains, providing a perfect habitat for the roots of the plants.
The structure of foams is adequate only for a relatively short period of 2-3 years.
Felt is inexpensive and easy to work with, although the mechanical and hydrostatic characteristics are weak, and there is a tendency for rotting.
The porous boards have excellent drainage, but due to their low microporousity, the root microclimate developing in them is unfavourable (plants dry out easily).
Planar and spatial coordiantion
Scaling and sizing
In the case of climbing systems, following the geometry of the facade is limited, plants will grow in all directions where suitable conditions exist and a surface to cling to can be found. Modular systems provide the best opportunities for these, however, the accuracy of the alignment to the surface differs from system to system.
Wall sizes and their geometry differ from one to another and adjusting the green area to them requires considerable engineering work; the answer to why this is the case will be clear as it is described below. But this engineering work will be to no avail if the system itself is unfit to accommodate the various geometries of the facades. Therefore prior to selecting a suitable system, this parameter requires increased attention. Any of the systems can be used for the construction of a surface shaped as a regular rectangle, however in cases of different geometry or in the presence of openings, many of the systems do not cope well or become increasingly expensive.
If a modular system works with fixed module sizes, the accuracy to follow the facade geometry is implicitly reduced. For example filling a 210 cm wide surface with 60 cm wide modules requires rather significant compromise. The same filled by 20 cm wide modules provides much greater accuracy, while the use of variable module sizes allows complete accuracy. Unfortunately the variation in module size is limited space requirement of the plants, therefore when designing the facade spacing, a good knowledge of the plants used and keeping their needs in mind is of critical importance. If not taken seriously, the precisely crafted pattern will result in plants being unable to reach maturity. For example; although in theory any horizontal facade size can be accurately followed by perhaps 10 cm wide modules, the plants would die in such a small place.
Module size considerations:
1. Economy: a too small module size means more material use and increased labour required for installation. In case of too large modules, the increased weight of each module requires costly framework as well as increasing handling costs if the modules cannot be moved by hand. Most advanced modular systems have standard sizes and cover approximately 0.2 -0.4 m2.
2. Uniformity of water supply: water pressure on a vertical surface typically is supplied by a central booster. This pressure decreases by 0.1 bar per meter and parallel to this the quantity of discharged water through the drip holes will also be proportionally less. This issue can be eliminated with additional equipment, but can become expensive if included vertically every 20 cm or 100 cm. Over and beyond the importance of cost, this is also important as this is the most likely part of the system to fail. That is why it is expedient to select a system with larger modules.
3. Drainage: Technically the best solution is to drain the excess water for each line of plants, this is also rather costly. If the drainage only takes place at the bottom of the lower module, we have to face the problems of water flowing through the modules was described previously. According to this, the advanced modular systems, as a healthy compromise, collect the drainwater every 4-6 plants (positioned above one another).
4. “Lower plant” effect: Within a module, the rooting zone available for the lowest plants are restricted compared to those above them, therefore their development may be somewhat weaker. This would rhythmically show horizontally on the façade.
The ideal module geometry has a vertical orientation similar to the greenwall.pro system.
By default, in order to achieve a unified covered surface, the stem distance of the plants need to be identical. As the vigour of the plants differs from species to species, this also needs to be taken into consideration when arranging the stems. The selected system also needs to manage this. A further requirement is to ensure that the root and foliage living space is the same size for each plant at the edges and around any objects or openings on the facade. When planning the arrangement on the facade, the long-term plant size also needs to be taken into account. These factors influence the design of the whole structure, the size of the modules and the allocation of the irrigation system.
Precise drainage above openings and facade intersections has to be addressed. The plants cannot hang in, unless we deliberately want to use them for shading. In addition to the upper section of the openings, the same requirements have to be taken into account on the side and sills. From a technical construction aspect, the areas under and above the openings are considered as critical sections, as here there is a good chance that the horizontal arrangement of the modules cannot be followed exactly, thus modules that differ from the standard height need to be installed. The reason why it is interesting is because in these cases the required quantity of the irrigation water is different from the other modules, therefore at the water supply points located here, the irrigation water needs to be controllable and individually dosed. In systems using inorganic mineral granulate substrate this problem does not require special treatment.
Signage, logos, cameras, advertising boards etc.
It is preferable not design plantings behind signs or facade protrusions that might reduce the light and subsequent development of the plant. When planting around an object, the mature size of the plants needs to be considered so as not to obscure it, with object fully integrated into the green facade system.
Canopies, terraces, balconies
When constructing a canopy that is enclosed, plants may suffer from a lack of light, or the structure is transparent, the sun may burn the leaves. Overall, a roof/canopy, terrace or balcony that extends above the green facade is more beneficial, as it protects it from sleet and ice.
Negative corners are relatively easy to manage, but in the case of positive corners the construction and use of a corner-closing element or special module is recommended. Few systems allow for special modules, and as a result of reduced rooting zones, the vegetation will not be homogenous. The edges maybe better managed by covering them with another material that already appears on the facade. In certain cases, the main pipelines of the irrigation system also need to be positioned here. Following finer arched surfaces with large modules is not always attractive, the use of a monolithic system or narrower module size is simpler and gives a more attractive result. Any slanting edge can be completely followed by the monolithic systems, while in case of the modular system the solution is to create steps with the units, the scale of which differs and depends on the system. The larger the module, the more “pixelated” the final appearance.
Irrigation and nutrient supply
The irrigation and nutrient supply of green walls uses the well-proven technologies developed for hydroponics adapted to vertical surfaces. Various approaches exist: Irrigation can take place with a single horizontally positioned dripping pipe at the top of the plant wall; this may result in water and nutrient deficiency for the lower plants, or conversely, over watering. Not only is this wasteful, but the large quantity of unused fertiliser also presents a significant environmental pressure. The other extreme model is irrigation with water-delivery-regulation for each plant, this does work in practice and presents unwanted costs and technical risks. As a compromise, the multilevel irrigation became common, in which case the irrigation pipes are located approximately at meter heights, thus ensuring satisfactorily homogenous water distribution and manageable levels of technological devices.
Irrigation of the plants can be carried by connecting the irrigation system into the public utilities system, from a well or by the utilisation of grey water or rainwater. Grey or well water needs to be filtered and treated if necessary. The solution that is most environmentally friendly and best for the plants is the utilisation of the collected rainwater, where an additional appropriately scaled water tank is included in the system. Although available space and costs need to be considered carefully, in this case, in areas prone to flooding or where environmental schemes are in effect, the use of rainwater storage maybe supported.
Nutrient supply to the plants can take place by dosing the irrigation water, the exact regulation of the quantity and composition of the medium falls within the competence of a gardening professional. The technical arrangement for providing the nutrients for the plants can be varied, it can be carried out by a single item of equipment, or in the case of very diverse planting, up to four different injectors can be integrated into the system. (Three are needed for precise dosing of nutrients that cannot be mixed with each other, and one is used to adjust the pH). Two further methods exist for feeding the plants, one is the application of foliar fertiliser (applied by a sprayer onto the foliage), which although suitable for quickly remedying any occasional nutrient deficiency, cannot replace the long-term balanced supply to the roots. The other option is the use of individual slow release fertiliser to each plant, which is a costly and labour intensive process and in many systems practically not possible.
Water drainage, water management
Positioning the structural elements of the drainage system is covered in the section on dimensions, the actual implementation is as varied as the number of existing systems. The majority of even the advanced systems still allow for the drain water to flow through the entire height of the system.
The low point drainage can be resolved by a “leaking pipe” and drainage system at the bottom of the green façade. For design and implementation, see the detail drawing under “Nodes”. To reduce water usage and further improve sustainability, it is advisable to design a recirculation system that reduces the quantity of drainage water and unused nutrients to a minimum. The quality of the recirculated water should be regularly monitored to avoid an excessive increase in the EC value as well as the accumulation of certain nutrients that might prevent the plant from absorbing those that it requires. Beneficially, “tired” mediums are still suitable for the irrigation of other green areas, which is an ideal recycling choice.
Remote diagnostics, remote control
Modern diagnostic systems allow the observation, measuring and regulating of plant conditions by remote control, resulting in a more efficient, timely and secure operation.
Parameters that can be monitored remotely:
• External temperature – frost warning, automatic dehydration
• Soil temperature – initiating soil temperature control
• Soil humidity – irrigation control regulation
• pH and EC value of the medium – aligning medium parameters
• pH and EC value of the drain water - adjusting values
Measuring additional parameters (e.g. absorption of certain nutrients) may also be justified. In general these cannot be tested locally; the soil, foliage or water sample is best tested in an accredited laboratory, which can provide accurate data on the most important parameters necessary for the wellbeing of the plants.
This information can be continuously monitored through mobile communication or internet connection. The cost of these technologies is justifiable in larger installations or sites where access is an issue.
CNC process engineering
The first step in creating a greenwall.pro façade is to produce CAD plans for the exact arrangement of the modules, framework and installation of the services, based on the planting requirements. The next phase is the transcription from the CAD system to a CAM system for parts manufacturing and assembling plans. The parts are laser cut, bored, threaded and pressed with additional CNC programmable machinery. The resulting accuracy greatly simplifies the final assembly, reducing construction time to a minimum. The completed module is a precise and accurately produced product that ensures trouble free on-site construction and subsequent operation.
Fixing technology and frame design
The greenwall.pro system is assembled onto the horizontal stainless steel frame that locates the modules. This can be fixed directly onto the wall surface or onto vertical elements (insulation can be placed between these for example). The horizontal framework is fixed to ensure a corrosion free connection. Gradient drainage is integrated into the system. The frame and the modules are finally connected by a bracket that precisely positions and secures the units, and further reduces on-site works.
The dimensions of the modules are designed to comply with manual handling regulations, in respect of both weight and size. In this way, construction can be quick and without the utilisation of mechanical aids. The geometry of the modules facilitates individual removal, thus in case of plant replacement or maintenance the modules can be simply taken out and replaced. The mounting and dismantling of the modules requires only two fixings, which can be specified with security heads, thus providing protection against unauthorised dismantling.
Fireproofing, fire propagation
Apart from the default plastic front panel, all material used fall into the non-flammable A1 category. The system can also be supplied with a fireproof front panel (steel, ceramics, flame retardant composite). The background structure is sectioned in the basic model by the horizontal elements of the frame that act as firebreaks. It can also be designed as vertically ventilated; in this case, the chimney effect has to be taken into account. With a firebreak design, for vapour control, pressure balanced layers are created by including ventilated gaps between the modules.
The dripping pipe providing irrigation to the modules is integrated into the system and can be checked and maintained from the front without dismantling the modules. Furthermore, the trough system for the draining any excess water is also integrated into the system, as well as the vertical catch-drains, which direct the water to the horizontal main collector positioned at the bottom of the green façade.
Other engineering elements are located separately, under optimal conditions in a space that is protected from the weather. Within reason, this space is independent of the location of the green façade.
Construction optimisation (location, timescales, delivery)
As the complete system can be pre-manufactured and pre-planted, the onsite installation time is very short. Following the positioning of the frame and the engineering units / pipes etc, the planted modules arrive to the sites on rolling “cc” containers. These containers can be easily and quickly handled with each container providing approximately 5 m2 green façade; accordingly, a traditional lorry can transport 215 m2 of completed modules. This ensures, even with construction sites geographically remote from greenwall.pro’s premises, that logistics issues and added labour costs are avoided.
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