Next Article in Journal
A Novel Method for Gas Disaster Prevention during the Construction Period in Coal Penetration Tunnels—A Stepwise Prediction of Gas Concentration Based on the LSTM Method
Next Article in Special Issue
Greenhouse Gas Emissions-Based Development and Characterization of Optimal Scenarios for Municipal Solid and Sewage Sludge Waste Management in Astana City
Previous Article in Journal
Study on the Influence of Population Urbanization on Agricultural Eco-Efficiency and on Agricultural Eco-Efficiency Remeasuring in China
Previous Article in Special Issue
Particulate Matter (PM2.5 and PM10) Concentration of Subway Transfer Stations in Beijing, China
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Sustainability
Volume 14
Issue 20
10.3390/su142012997
sustainability-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Vertical Greening Systems: Technological Benefits, Progresses and Prospects

by
Puyi Wang
1,
Yew Hoong Wong
1,2,3,*,
Chou Yong Tan
1,2,3,
Sheng Li
1 and
Wen Tong Chong
1,4,*
1
Department of Mechanical Engineering, Faculty of Engineering, Universiti Malaya, Kuala Lumpur 50603, Malaysia
2
Centre of Advanced Materials, Universiti Malaya, Kuala Lumpur 50603, Malaysia
3
Centre of Advanced Manufacturing and Material Processing, Universiti Malaya, Kuala Lumpur 50603, Malaysia
4
Centre for Energy Sciences, Universiti Malaya, Kuala Lumpur 50603, Malaysia
*
Authors to whom correspondence should be addressed.
Sustainability 2022, 14(20), 12997; https://doi.org/10.3390/su142012997
Submission received: 21 September 2022 / Revised: 1 October 2022 / Accepted: 4 October 2022 / Published: 11 October 2022
(This article belongs to the Special Issue Green Energy and Sustainable Development)
Browse Figures
Review Reports Versions Notes

Abstract

:
A vertical greening system is becoming increasingly crucial in resolving the energy crisis and environmental problems in a sustainable ecosystem. Researchers have conducted a comprehensive study on vertical greening systems from technology, functional and architectural perspectives. These include ecological, economic and social functions. Most of the current studies emphasize the benefits of vertical greening systems to the environment, while vertical greening technology and its socio-economic benefits receive insufficient attention. In order to study the vertical greening field in depth, this paper comprehensively and systematically summarizes vertical greening technology and functions. Meanwhile, based on the Web of Science (WOS), CiteSpace was used to analyze the relevant literature in the vertical greening field from 2012 to 2022, to explore the hot spots, development status and future trends of vertical greening technology, and to build a knowledge map in the vertical greening field. The research shows that as a low impact development technology, the vertical greening system has received the most extensive attention in the past few years. Air quality, microclimate regulation and energy have always been the focus and hot issues of people’s attention. The future research directions are cooling effect, active system and indoor space. This study is aimed at promoting the future development of vertical greening system technology and providing reference and direction for researchers, planners and developers, as well as individuals interested in future urban and rural planning.

1. Introduction

Industrialization and urbanization have promoted the progress of modern civilization. As the city continues to develop and expand to its surrounding areas, the countryside gradually turns into the city. According to a report from United Nations (UN), the urbanization rate in developed countries is estimated to reach 83% by 2030 [1]. Urbanization has become the general trend of development all over the world. Sustained urbanization can lead to economic growth and social improvement. However, this rapid development leads to environmental degradation and climate change and brings huge pressure on the existing urban infrastructure [2]. Some examples of this include air pollution, rainwater runoff, severe urban heat island effect and biodiversity decline [3,4,5,6]. It also has adverse effects on human and socio-economic development, such as increased physical discomfort and health problems and increased demand for building cooling, resulting in increased energy consumption [6,7,8,9]. Therefore, sustainable measures need to be implemented and incorporated into new and existing development to mitigate the harmful effects of urbanization [6,10].
The demand for various resources, including building developments, land, water and energy, has dramatically increased due to global urbanization. Depending on information from the United Nations Environment Programme, buildings’ construction and maintenance account for around 40% of the world’s demand for primary energy and 33% of its environmental pollution [11]. Therefore, in this case, the implementation of sustainable development methods and plans to transform building components can achieve low-energy buildings [12] and save energy [13]. The burden on the urban environment and climate has been reduced by introducing sustainable green measures and technology [14]. Low impact development (LIDS), such as sustainable green buildings, design and practice techniques, has become the preferred choice for urban construction and planning in recent years [15]. According to the European Research and Innovation Policy Agenda, natural solutions (NBS) are key technologies to improve the sustainability of urban areas [16]. Greening System is the most popular sustainable building form, such as roof greening, wall greening and movable wall, which are often used as an aesthetic feature of architecture. At present, vertical greening technology can not only improve building performance [17] but also be an important measure to beautify the city and achieve sustainable development [18,19,20,21,22,23].
In urban areas, vertical greening does not occupy urban space [24]. In fact, vertical greening uses vegetation to cover buildings, which can bring environmental, economic, social and health benefits. It is an important feature of architectural design for sustainable development [25]. In terms of environment, the urban environment can be enhanced by promoting urban biodiversity [15,26], handling stormwater [27], air quality [28,29,30,31], and mitigating the Urban Heat Island (HUI) [32,33,34]. In addition, a green wall is an alternative form of constructed textiles, which has been well recognized and widely applied worldwide for various wastewater treatments, particularly in green water treatment [16,35]. In terms of social health, it provides aesthetic and therapeutic benefits, improves the city image [21,36,37], reduces noise [38,39], improves the lifestyle of residents, increases architectural value [40] and complements thermal [41] and acoustic protection [42,43]. Economically, cooling can save energy, reduce energy consumption [25,44,45] and prolong the service life of the roof membrane [35,46,47]. The wall greening has greater potential than the roof greening. Because of the limitation of municipal space, the greening degree of the external wall can be twice as much as that of the roof and the ground [24,26,27]. Vegetation can regulate the microclimate climate in winter [28] and summer [29], providing heat preservation and shading [30,32,33] and evaporative cooling effects [34]. Vegetation absorbs a large amount of solar radiation in summer [36], which can reduce the temperature [39] and increase the humidity under the transpiration so that the wall surface temperature is lower than the surrounding temperature [37,39,40,41]. Recent research shows that green systems can improve the thermal performance of buildings [44] and regulate the capacity of heat gain and loss through the basic mechanism of thermal fluid and energy conversion, which enhances indoor thermal comfort, lowers the energy required for building heating or cooling, and results in energy savings [17,42,43,44,46]. Altogether, green walls are a fit-all solution to reduce building energy demand and mitigate UHI and air pollution, providing healthy living conditions. It is the solution to urban environmental sustainability [31,44,47].
As scholars pay more and more attention to all aspects of the vertical greening system, they have conducted research and published papers. So far, some vertical greening system technologies have been proposed, which can help researchers to keep pace with the development of knowledge in this field. This could make it more challenging for researchers to understand their area of study and the current context. It should be noted that the development of knowledge is a dynamic process that involves constant adjustment, enhancement and renewal. Although the vertical greening system has developed rapidly in the industry and research field, there are still many problems to be further improved and strengthened in achieving sustainable development and the optimization and promotion of technology. Therefore, this study systematically analyzes the vertical greening technology and its environmental, economic and social functions by combing the existing literature and helps us to visually and quantitatively analyze the keywords, literature co-occurrence and time zone map in the vertical greening field in combination with CiteSpace software. Help us better discover the existing vertical greening technology, functions, research progress, hot spots and future research directions and trends so as to emphasize the direction for future research in this field.

2. Vertical Greening System

A vertical greening system refers to all systems that can green vertical surfaces. It is related to the selection of plant species, including all solutions designed to plant plants on the wall or in the building [48]. The vertical greening design shall consider the climatic conditions, the structural performance of buildings (structures), morphological layout (orientation, height), plant characteristics, construction and maintenance costs, safety and durability and other factors. Figure 1 is a classification of vertical greening technologies.

2.1. Vertical Greening Technology

In Figure 2, vertical greening technologies are classified as green facades [49] and living walls [50] based on varied vegetation and substrates [51,52]. The former usually refers to climbing plants growing along the wall, while the latter includes materials and technologies supporting more kinds of plants to form uniform growth along the wall. The arrangement is referred to as a green facade when the growth medium is the floor. There are two different kinds: a direct facade, such as a traditional facade, and an indirect facade, such as continuous guidance, modular lattice or double skin facade. The system is known as a living wall or green wall when the growing media is integrated into the building wall [53]. There are two varieties of green walls: continuous green walls that use a continuous panel or geomembrane and flexible green walls that use a tray, container, soft bag or flowerpot. According to the degree of difficulty, the green wall is divided into extensive or dense systems. The green facade is categorized as an extensive system, which is simple to construct and requires teensy future maintenance, while the living wall is classified as an intensive system, which is more complicated in plan and has a higher degree of maintenance [50]. Table 1 lists different vertical greening technologies.

2.2. Components of Vertical Greening

The Figure 3 vertical greening system is mainly composed of vegetation, substrate, supporting structure, irrigation and drainage system, thus forming a complete green ecosystem.

2.2.1. Plants

Plants are an important component of vertical greening systems. They not only provide ecosystem services but also undertake most of the environmental benefits and urban beautification of the vertical greening system [54]. The green wall [35] is made up of climbing plants. At the same time, the modular green wall is manufactured of non-climbing potted plants.
(1)
Climbing plants
Climbing plants are widely used in vertical greening and are economical and practical plants. It can be used for the greening of vertical sides of various walls, retaining walls, bridges, buildings, etc. Climbing plants can be attached to any vertical surface. In some countries, it is common to plant plants on the outer walls of small buildings [53]. It takes about 3–5 years for some species to reach a height of 5–25 meters to achieve full plant coverage [50,55]. In one study, leaf densities of several climbing plants (Hereda helix, Lonicera japonica) and deciduous plants (Parthenocissus quinquefoliate, Clematis SP) were compared after one year. The results showed that Parthenocissus quinquefoliate provided a higher leaf density, and all species were met with muted green [56]. Vertical greening systems generally utilize Parthenocissus and Hydrangea, as well as the evergreen specialty spear and ivy [35]. In addition, winding climbing plants that need endorses, such as metal frames and wires, include Humulus lupulus and Capsis radians. The trailing shrub is usually used in the grid structure, including Forsythia suspense and Pyracantha atalantiodes.
(2)
Shrubs and succulents plants
The new living wall makes vertical greening unrestricted, not limited, allowing more plant species, such as the integration of shrubs, grass and some plants, and some potted plants, such as asparagus, Begonia and Dragon blood tree. Hedera helix and Parthenocissus are the most frequently used plant species [49].
Recently, the modular living wall uses succulent plants instead of perennial plants and shrubs. Drought-tolerant plant species [17] can help to reduce irrigation demand. The maintenance cost of these plant varieties is also quite low, contributing to the system’s weight reduction. However, the surface of succulent plants is flat and suitable for small walls. On the larger wall surface, the use of perennial plants and shrubs can generate more decorative landscapes because these plants are diverse in color, shape and texture. Studies in Japan have shown that [57] shrubs can be supported on inclined surfaces.
(3)
Hydroponic plants
The hydroponic system enables more kinds of plants to grow in different developmental states [58]. In these cases, the vegetation type is chosen according to the required scene, climate and aesthetic effect [59,60], and the appropriate irrigation and nutrition are assisted in achieving the healthy growth and development of plants. Therefore, plant composition: Color, flowering, leaves and morphology are important to plant growth [52]. However, under the concept of sustainable development, vegetation must have low irrigation demand, sufficient water and nutrients for plant growth (such as using local plants), and adapt to local exposure conditions (such as sunshine, semi shading or shading) and the best climate conditions (such as wind, rain, high temperature, drought and frost).

2.2.2. Irrigation

The selection of irrigation type is based on the system type, the plant used (style, size, growth period, root system) and seasonal changes [52]. Modular Green exterior walls and living walls require irrigation systems to provide necessary water irrigation for plant growth. Furthermore, the growth of vegetation can be aided by nutrients, fertilizers, minerals, phosphates, micronutrients or hydroponics substances [52]. The continuous living wall passes through the upper part of the structure and connects to the central irrigation system. For the uninterrupted living wall, the irrigation system makes the water and nutrients evenly distributed along the surface layer. Some living walls in the form of pallets are supported on the top surface of the modules for inserting grooves for irrigation pipes. The tray includes holes on the grooves for pouring the growth medium under the action of gravity [60,61,62,63,64]. In order to allow extra water to irrigate the modules below, the tray’s bottom has drainage holes [52]. Irrigation pipes and joints can be made of a variety of materials (such as rubber, plastic, thermoplastic pipes, silica gel and irrigation pipes), including different irrigation methods (such as drip irrigation, sprinkler irrigation, hole irrigation and pipe irrigation), as well as their distribution and strength, which can meet the irrigation needs of plants.
Some living walls also mentioned approaches for reducing the usage of treated water, such as storing water from building roofs [60], reusing the versus water in the drainage system [65], monitoring the stormwater management demand [60] and controlling the water level, irrigation time and extreme weather conditions by installing sensors [66,67], in order to minimize the wastage. Other than the living wall, whether modular [68,69] or continuous [66,67], it also refers to the installation of a ditch on the basis of the system, the recovery of excess water for storage and re-introduction into the irrigation system. Another strategy is exploited by sensors to quantify nutrient requirements in growth media. This is extremely important to minimize the consumption of nutrients and meet the needs of plants.

2.2.3. Substrate

The substrate is an important aspect of vertical greening systems. In some cases, the choice of substrate will affect the function of the green wall system. Existing studies indicate that the matrix can effectively remove pollutants. Similarly, the efficiency of green wall systems in wastewater purification and pollutant removal is largely impacted by the efficiency and selection of matrix materials [35]. In order to ensure the effective operation of the green wall, appropriate materials are required as the base materials [70]. Recent research has shown that using biochar [71] and alum sludge [72] as materials improves the ability to remove pollutants while also promoting plant growth.
The matrix in the green wall is made up of both organic and inorganic substances [57,64,73], or it has an added element of the inorganic matrix, typically foam, to lessen the weight. The matrix is a crucial component that influences the wall’s steady state and structural load-carrying capacity [35,74]. The physical characteristics of these matrices are used in the majority of green wall designs to achieve porous structure, surface area, uptake capacity and water-holding capacity [35,60,65]. The matrix can be enhanced by using nutrients in plant growth, such as blends of organic and inorganic fertilizers, metal compounds, minerals, plant nutrition, hormones and other additions [64]. According to some modular living wall systems, the geotextile bag is put with the growing medium inside to keep it from going out. These bags can completely bridge the module, granting the insertion of multiple plants [60], or they can bridge the growth media of each plant separately [58,61]. Every plant also requires a fixed front cover to keep the growth medium from slipping off [64].

2.2.4. Structure

Conventional or direct green external walls typically have no supporting framework. They rely on climbing plants’ capacity to adhere to vertical surfaces. However, there is a higher risk of falling when the vegetation is too thick. The “double-layer external wall” forms a certain range of gap between the building surface and the plants as an indirect green exterior wall. The use of support structures prevents vegetation from collapsing. Whether continuous or modular, it can stabilize and sustain the weight of the foliage and increase the system’s resilience to harsh weather influences such as wind, rain and snow.
Most indirect green external wall supporting structures consist of continuous or modular guides [52,63,75]. Climbing plants with thick leaves can be fixed and supported by a steel structure and stretch cable. Smaller spacing between the grid and the steel wire mesh allows for supporting plants with sluggish growth rates [55]. Some indirect green curtain-wall solutions, primarily modular flower racks, have independent supporting structures and pots with substrates inside, which enable pieces to be suspended along the wall at various heights. The modular green wall adopts an arc-shaped grid, which gives the wall a sense of rhythm and three-dimensional feeling [62,75]. A frame is generally included in a living wall to support the components and plants. Through a frame mounted on the wall, the movable wall creates a vacancy between the system and the surface. This frame supports the floor and protects the walls from moisture. The next layer is supported by the bottom and fastened to it with nails. It is shielded from the base by a permeable, flexible and root-resistant shielding layer. After that, the outer mesh layer was installed in cloth bags [66,67] for plant planting.
Modular living walls can take many forms (trays, containers, flowerpot bricks or flexible bags) and require distinct structures. Modular trays are usually composed of multiple interlocking parts and are made of soft materials, such as plastic or metal plates [60,61,62,63,64,73], in order to ensure the continuity of the system. Each component usually includes a side interlocking system for interconnection. These module elements may also include front cover trays and containers forming a grid to prevent plants from falling, which are generally fixed on vertical and/or horizontal frames connected to the surface. The rear surface may include hooks or mounting brackets [52,60,64] for hanging on a frame connected to the perpendicular surface. Multiple plants can be installed in every component of the same sequence using modular containers. They are usually constructed of polymeric materials and, due to their shape and structure, have a significant visual impact on the building exterior.

3. Bibliometric Analysis of Vertical Greening System Research

Scientometrics is a branch of informatics. It quantitatively analyzes the patterns in the scientific literature to find out the latest trends and knowledge structures in the research field [76]. The bibliographic analysis is an approach for quantitative analysis of articles, mainly for objective and systematic analysis of published papers. In 1969, this method was first commonly used in the literature to review evolution and predict upcoming trends [77]. Chen et al. analyzed the field of regenerative medicine using CiteSpace and found the latest development trend in this field [78]. Li et al. utilized by CiteSpace to examine the construction field and build a knowledge map of the building information model [79]. CiteSpace has been widely used in various fields and has achieved good results. However, in the area of vertical greening, there are still few bibliometric studies. This section employs bibliometrics to quantitatively analyze the vertical greening system field, primarily introducing the number of publications, research hotspots and citation evolution in significant countries in this field.

3.1. Methods and Tools

In order to obtain reliable and comprehensive literature data, the Web of Science (WOS) Core Collection Database is involved as the resource. The database is a text file, including the number of variables such as title, author, year of publication, language, abstract, keywords and references. Data collection flow is shown in Figure 4. The search time in WOS is “2012.01-2022.05”, and the theme is “Green Wall”, “Living Wall” or “Vertical Gardens” or “Vertical Green System” or “Biowalls” or “Green Vertical Systems” as the subject, and a total of 547 articles were obtained. To further ensure the rationality of the article, the search results were thoroughly checked, sorted out and some irrelevant sample data was deleted; the search scope was reduced manually. Firstly, irrelevant documents such as meetings and essay solicitations were deleted. Secondly, we deleted some non-academic literature and filtered out less representative record types. Our final sample included 406 original research articles and 43 review articles. Using this database, CiteSpace was used for further analysis and processing.

3.2. Research Status

It can be obviously observed in Figure 5 that the number of publications in the field of vertical greening is increasing exponentially. From 2012 to 2022, the number of documents increased year by year. Specifically, according to the change trajectory of the number of published research papers, three stages can be identified: the first stage (2012–2014) and the gradual rise stage; the second stage (2015–2019) is a stable development period; and the third stage (2010–2022) is a period of rapid progress. In 2021, the number of documents will reach a peak of 98. At this stage, the research results are relatively high and gradually mature. So far, the average number of documents released at this stage is 68, which shows that people pay greater attention to the research of vertical greening. At the same time, it can be predicted that in the near future, the number of papers related to vertical greening will increase rapidly, and new technologies and related strategies will appear.
Figure 6 shows the hot keywords in the field of vertical greening systems in the past decade. The high-frequency keywords are “Urban heat island”, “Thermal performance”, “Energy performance” and “Climate change”, which means that it has been the focus of vertical greening research for many years. “Thermal performance” is the support point of the whole network, which lays the foundation for the stability of the entire network and is the main research hotspot. The second level focuses on “Indoor air quality” and “Life cycle assessment”.
Figure 7 visually shows the evolution process of this field, which is useful for predicting the development trend in the next few years. As shown in the figure, air quality, climate, energy, refrigeration and thermal performance have been the eternal topics in the field of vertical greening in the past 10 years. It has mainly gone through three stages. The first stage (2012–2016) is the initial stage of the vertical greening system, and it began to expand the relevant knowledge and research in this field gradually. With the development of urbanization, the demand for urban heat islands and energy is increasing, resulting in a series of environmental and public health consequences. People gradually increase green spaces through vertical greening, roof greening and tree greening, which can effectively reduce the urban heat island effect and save energy. At the same time, green space also increases the cooling effect of water and wind. Therefore, vertical greening is an effective method to solve the urban air pollution level. In the second stage (2017–2019), with the rise and development of vertical greening technology, many countries have applied it to gray water treatment, indoor space removal of organic pollutants, inorganic pollutants, CO2 and particulate matter, and pollutants in street canyons to improve air quality and achieve good benefits. At the same time, there is a series of international evidence that indoor plants have a direct and beneficial impact on human health, social and mental health and work efficiency. In the third stage (2010 to now), under the background of 2019 coronavirus disease, people have entered the era of user-centered mobile Internet. Vertical greening technology has been continuously improved, and some new technologies have been integrated while solving the problems of air quality, microclimate regulation and energy. We also need to pay more attention to the comfort of user groups.
Figure 8 shows the map of transnational cooperation. On the whole, a collaboration between countries/regions is relatively close. China has the closest cooperation with the United States and Australia. American countries often cooperate with Germany. In China, the research primarily examines and assesses the subtropical external space vertical greening system. Its energy-saving benefits through the simulation and measurement of the vertical greening system. In Australia and Italy, the movable wall system will be used to treat the wastewater from showers and washing basins. Innovative and beautiful living walls can not only be used for household-scale grey water treatment but also provide key comfort and microclimate benefits for our cities [57]. Moreover, there could be further improvements to the technology of removing VOC, CO2 and PM in the indoor space. Plants and substrates in the functional green wall/modular plant biofiltration system can effectively remove indoor PM, especially ferns [59,60].
Figure 9 shows the analysis results of document clustering and timeline from CiteSpace. The documents in the same cluster are highly homogeneous. In the cluster diagram, the warm color represents the research focus in this field in recent years, while the cold color represents the early time of research. The rise, prosperity and decline process of specific cluster research can be clearer with the timeline chart, showing the temporal characteristics of the field. Among them, large nodes or nodes with a red tree ring represent documents that are highly cited or have citation explosion. It can be included that the current distribution fields of vertical greening system research are mainly Clusters # 0, 1, 3, 4 and 6. Among them, # 0, 1 and 3 have highly concentrated nodes with citation bursts, and # 1 is still active; Clusters # 4 and 6 also seem to have the latest publications that cited citations, which are still active.
According to the literature analysis from 2012 to 2022, the research on vertical greening is mainly based on the research on green buildings. The research methods, seasons, plants and matrix types in this field are shown in Figure 10.

4. Functions of Vertical Greening System

Figure 11 is a functional overview of the vertical greening system. The results show that the green wall in the urban environment brings benefits to users (Aesthetic and Psychological), buildings and the surrounding environment (Improving Air Quality, Reducing Heat Island Effect, and Treating Sewage), society (Mitigating Noise) and economy (Energy Conservation).

4.1. Environmental Functions

4.1.1. Regulating Climate

The plants in vertical greening absorb the incident solar radiation through their physiological processes so as to carry out photosynthesis and transpiration and reduce the wall surface temperature [80]; building cooling is achieved through the evapotranspiration process, as the leaves of plants lose water and convert solar radiation into extra heat. This physical process produces what is called “evaporative cooling”. Evaporative cooling of leaves depends on the plant species, and substrate humidity and temperature variations influence it. The impact of a dry environment or wind will increase the evapotranspiration of plants [81]. In addition, plants can also control and modify the wind direction and wind speed. The hot air is caused by convection and rises through the space between plants and buildings, forming a local breeze and alleviating the urban microenvironment. Table 2 is the relevant literature on the cooling effect of vertical greening.

4.1.2. Improvement of Air Quality

Air pollution will directly threaten human health and shorten life spans. With the development and progress of vertical greening technology, vertical greening systems can effectively remove particles in the air.
(1)
Outdoor air quality
According to Table 3, green walls are more useful in removing PM than gas pollutants. By absorbing PM and lowering environmental concentration, plant leaves can improve the quality of outdoor air [57,72,73]. Green walls can provide practical pollutant collection through literature review and summary, enhancing air quality. However, plant species, size, wind direction, leaf area index and humidity all play a role in how much pollution is reduced by green walls. Green walls show better results in collecting fine and ultra-fine particles than coarse particles, and they are more effective at removing particulate matter than gas pollutants. The effects of green walls with different heights and different seasons on decontamination are not significantly different, but the topographic differences of living walls affect the capture of pollutants.
(2)
Indoor air quality
The vertical greening system gradually turns from outdoor to indoor space. Indoor green walls are divided into active and passive forms, which are mainly used to reduce indoor air pollutants [105,106]. The active system has a ventilator that can simultaneously deal with a lot of air pollutants at a low cost while forcing air through the matrix of the vertical greening and the plant rooting system [107,108]. In passive systems, polluted air is simply absorbed and removed by the green wall matrix and plant leaves. The advancement of vertical greening technology is currently moving toward the incorporation of ventilation systems and green walls into building air conditioning systems. Because they increase plant density, are arranged vertically, and allow for the effective passage of polluted air through the matrix, green walls are preferable to pot plants [109]. Recent studies have shown that active green walls have high phytoremediation capacity and can repair a variety of air pollutants. Table 4 shows the relevant literature on indoor vertical greening to remove indoor pollutants.

4.1.3. Sewage Treatment

Vertical greening systems have played a great potential in water savings in urban residential areas. They can not only relieve the pressure on urban sewage treatment plants but also provide water for gardens, green spaces, golf courses and toilets. By implementing these green walls, 40–50% of water can be saved [114].
The principle of vertical greening wastewater treatment has three aspects: physical mode (filtration and sedimentation), chemical mode (reaction and adsorption) and biological mode (removal of pollutants in wastewater through plants and microorganisms in the matrix) because water vertically penetrates down through the matrix. The substrate serves as a surface for bacteria to adhere to while filtering out organic substances. At the same time, they can also serve as the basis for supporting plants [70]. In addition to promoting oxygen transfer to the surrounding soil, which enables microbes to settle and disparage organic contaminants, vegetation offers a suitable environment for microorganisms that capture nutrients from wastewater and degrade organic contaminants [115]. The performance of the wastewater treatment green wall system is determined by major components such as plant selection, fluid load (flow/surface area ratio), water content inside the medium, ambient air quality and ash inflow [35,116].

4.2. Economical Function

The Heating Ventilation and Air Conditioning (HVAC) systems are primarily responsible for indoor thermal comfort and ventilation [117]. The development of the green building concept affects the performance of residents and leads to an increase in energy load. Using a vertical greening system on the building shell is a passive energy-saving technology in buildings and one of the solutions for lowering building energy consumption [118]. It helps to save energy in buildings by providing shade, evaporation and transpiration, heat insulation and wind protection. In addition, it controls heat transfer and reduces the heat load of buildings [53], thereby reducing the power consumption of buildings and effectively realizing the energy saving effect [119]. Table 5 shows the literature on energy saving effect of vertical greening.

4.3. Social Functions

4.3.1. Cultivate Interest

Through its soft and natural characteristics, vertical greening technology eliminates the cold and hard appearance of steel and cement in the urban environment and offsets disharmonious factors such as fast-paced and high pressure in the city. It also promotes people’s optimistic and comfortable form, cultivates people’s interest and promotes physical and mental health [23,36,37].

4.3.2. Beautifying the City

Vertical greening has good ornamental value. It extends the urban landscape from the plane to the three-dimensional, increases the landscape level and effect, and improves the greening coverage. It also weakens the rigid shape of the building, improves the city’s image, and makes its urban space more diverse and friendly [23].

5. Knowledge Graph for Vertical Greening System

The knowledge panorama, knowledge dynamics, and knowledge evolution of the vertical greening field are constructed using the literature measurement method. The knowledge wedge diagram of the vertical greening system is integrated, as shown in Figure 12.

6. Conclusions and Perspectives

This study comprehensively considered and analyzed the vertical greening system, technology and function, combining CiteSpace, and the following results were obtained.
(1) Technology and benefits: Through the analysis of existing vertical greening technologies [124], the advantages and disadvantages of different vertical greening technologies are summarized. Secondly, sewage treatment, air quality, cooling and cooling; economic benefits and remarkable energy-saving effect [125,126,127]; and social benefits have been instrumental in fostering sentiment and beautifying the city.
(2) Research hotspots and development history: This paper uses the keyword co-occurrence analysis function to identify the keywords of the vertical greening knowledge base, among which “Urban heat island”, “Thermal performance”, “Energy performance”, “Climate change”, “Assessment tools”, and other keywords are research hotspots. The evolution of research hotspots has mainly gone through three stages: the initial stage, the rising development and the durable development. Obviously, air quality [128], microclimate regulation and energy issues have traditionally been the focus of attention. At the same time, more attention should be paid to the comfort of the user group.
(3) Research directions in different countries: Due to differences in countries, regions and climates, research priorities are different. In China, it is mainly the energy-saving benefit and evaluation of vertical greening. In Australia and Italy, the living wall system will be used for waste treatment and indoor space application.
(4) Research progress and future directions: The time characteristics of literature clustering and co-cited relationship and the average time of various literature can be concluded that the current research fields of the vertical greening systems are cooling, active system and indoor space.
The unique value of this paper lies in the systematic analysis of the vertical greening field, and the understanding of the current vertical greening technology and benefits, and the use of the quantitative analysis function of CiteSpace to build a knowledge map of vertical greening construction based on keywords, clustering, countries and timelines. To further enhance the vertical greening knowledge map provided by this study, we can conduct pertinent research and regularly update the data.
In future research, green energy (solar energy, wind energy, water energy) will be used to make the vertical greening system form an integrated system construction system of natural energy and natural resources to reduce the consumption of natural resources and energy. In addition, develop more intelligent vertical greening technology to facilitate maintenance [129] and play a greater role, so as to achieve sustainable urban ecological development.

Author Contributions

Conceptualization, P.W., Y.H.W. and W.T.C.; methodology, P.W.; validation, Y.H.W., C.Y.T. and W.T.C.; formal analysis, P.W. and S.L.; investigation, P.W.; resources, P.W., Y.H.W., C.Y.T. and W.T.C.; data curation, P.W. and S.L.; writing—original draft preparation, P.W.; writing—review and editing, P.W., Y.H.W., C.Y.T. and W.T.C.; visualization, Y.H.W., C.Y.T. and W.T.C.; supervision, Y.H.W., C.Y.T. and W.T.C.; project administration, Y.H.W.; funding acquisition, Y.H.W. All authors have read and agreed to the published version of the manuscript.

Funding

This work acknowledges financial support by Universiti Malaya (UM) via Faculty Research Grant (Grant No. GPF060B-2020).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Cui, L.; Shi, J. Urbanization and its environmental effects in Shanghai, China. Urban Clim. 2012, 2, 1–15. [Google Scholar] [CrossRef] [Green Version]
  2. Antrop, M. Landscape change and the urbanization process in Europe. Landsc. Urban Plan. 2004, 67, 9–26. [Google Scholar] [CrossRef]
  3. Shwartz, A.; Turbé, A.; Simon, L.; Julliard, R. Enhancing urban biodiversity and its influence on city–dwellers: An experiment. Biol. Conserv. 2014, 171, 82–90. [Google Scholar] [CrossRef]
  4. Łopucki, R.; Kiersztyn, A. Urban green space conservation and management based on biodiversity of terrestrial fauna—A decision support tool. Urban For. Urban Green. 2015, 14, 508–518. [Google Scholar] [CrossRef]
  5. Berndtsson, J.C. Green roof performance to wards management of runoff water quantity and quality: A review. Ecol. Eng. 2010, 36, 351–360. [Google Scholar] [CrossRef]
  6. Abdo, P.; Huynh, B.P. An experimental investigation of green wall bio-filter towards air temperature and humidity variation. J. Build. Eng. 2021, 39, 102244. [Google Scholar] [CrossRef]
  7. Abdo, P.; Huynh, B.P.; Braytee, A.; Taghipour, R. An experimental investigation of the thermal effect due to discharging of phase change material in a room fitted with a wind catcher. Sustain. Cities Soc. 2020, 61, 102277. [Google Scholar] [CrossRef]
  8. Wang, Y.; Berardi, U.; Akbari, H. Comparing the effects of urban heat is land mitigati on strategies for Toronto, Canada. Energy Build. 2016, 114, 2–19. [Google Scholar] [CrossRef]
  9. Santamouris, M. Analyzing the heat is land magnitude and characteristics in one hundred Asian and Australian cities and regions. Sci. Total Environ. 2015, 512–513, 582–598. [Google Scholar] [CrossRef]
  10. Berardi, U. Sustainability assessment in the construction sector: Rating systems and rated buildings. Sustain. Dev. 2011, 20, 411–424. [Google Scholar] [CrossRef]
  11. Dutil, Y.; Rousse, D.; Quesada, G. Sustainable buildings: An ever evolving target. Sustainability 2011, 3, 443–464. [Google Scholar] [CrossRef] [Green Version]
  12. Quagliarini, E.; Gianangeli, A.; D’Orazio, M.; Gregorini, B.; Osimani, A.; Aquilanti, L.; Clementi, F. Effect of temperature and relative humidity on algae biofouling on different fired brick surfaces. Constr. Build. Mater. 2019, 199, 396–405. [Google Scholar] [CrossRef]
  13. Di Giuseppe, E.; D’Orazio, M. Assessment of the effectiveness of cool and green roofs for the mitigation of the Heat Island effect and for the improvement of thermal comfort in Nearly Zero Energy Building. Archit. Sci. Rev. 2015, 58, 134–143. [Google Scholar] [CrossRef]
  14. Jato-Espino, D.; Sanudo-Fontaneda, L.; Andr’es Valeri, V. Green infrastructure: Cost-effective nature-based solutions for safeguarding the environment and protecting human health and well-being. In Handbook of Environmental Materials Management; Springer: Cham, Switzerland, 2019; pp. 4–5. [Google Scholar]
  15. Zhao, X.; Zuo, J.; Wu, G.; Huang, C. A bibliometric review of green building research 2000–2016. Archit. Sci. Rev. 2019, 62, 74–88. [Google Scholar] [CrossRef]
  16. Boano, F.; Costamagna, E.; Caruso, A.; Fiore, S.; Chiappero, M.; Galvão, A.; Pisoeiro, J.; Rizzo, A.; Masi, F. Evaluation of the influence of filter medium composition on treatment performances in an open-air green wall fed with greywater. J. Environ. Manag. 2021, 300, 113646. [Google Scholar] [CrossRef]
  17. Lundholm, J. Green roofs and facades: A habitat template approach. Urban Habitats 2006, 4, 87–101. [Google Scholar]
  18. Sheweka, S.; Magdy, N. The living walls as an approach for a healthy urban environment. Energy Procedia 2011, 6, 592–599. [Google Scholar] [CrossRef] [Green Version]
  19. GhaffarianHoseini, A.; Dahlan, N.D.; Berardi, U.; GhaffarianHoseini, A.; Makaremi, N.; GhaffarianHoseini, M. Sustainable energy performances of green buildings: A review of current theories, implementations and challenges. Renew. Sustain. Energy Rev. 2013, 25, 1–17. [Google Scholar] [CrossRef]
  20. Zhang, X.; Shen, L.; Tam, V.W.Y.; Lee, W.W.Y. Barriers to implement extensive green roof systems: A Hong Kong study. Renew. Sustain. Energy Rev. 2012, 16, 314–319. [Google Scholar] [CrossRef]
  21. Saadatian, O.; Sopian, K.; Salleh, E.; Lim, C.; Riffat, S.; Saadatian, E.; Toudeshki, A.; Sulaiman, M. A review of energy aspects of green roofs. Renew. Sustain. Energy Rev. 2013, 23, 155–168. [Google Scholar] [CrossRef]
  22. Mazzali, U.; Peron, F.; Romagnoni, P.; Pulselli, R.; Bastianoni, S. Experimental investigation on the energy performance of living walls in a temperate climate. Build. Environ. 2013, 64, 57–66. [Google Scholar] [CrossRef]
  23. Theodoridou, I.; Karteris, M.; Mallinis, G.; Papadopoulos, A.M.; Hegger, M. Assessment of retrofitting measures and solar systems’ potential in urban areas using Geographical Information Systems: Application to a Mediterranean city. Renew. Sustain. Energy Rev. 2012, 16, 6239–6261. [Google Scholar] [CrossRef]
  24. Virtudes, A.; Manso, M. Green façades: As a feature in urban design. ICEUBI 2011. In International Conference on Engineering; University of Beira Interior: Covilha, Portugal, 2011. [Google Scholar]
  25. Daemei, A.B.; Shafiee, E.; Chitgar, A.A.; Asadi, S. Investigating the thermal performance of green wall: Experimental analysis, deep learning model, and simulation studies in a humid climate. Build. Environ. 2021, 205, 108201. [Google Scholar] [CrossRef]
  26. Francis, R.; Lorimer, J. Urban reconciliation ecology: The potential of living roofs and walls. J. Environ. Manag. 2011, 92, 1429–1437. [Google Scholar] [CrossRef]
  27. Schmidt, M. Energy saving strategies through the greening of buildings the example of the Institute of Physics of the Humboldt-University in Berlin-Adlershof, Germany. Forest 2003, 29, 4. [Google Scholar]
  28. Bruse, M.; Thönnessen, M.; Radtke, U. Practical and theoretical investigation of the influence of facade greening on the distribution of heavy metals in urban streets. In Proceedings of the 5th International Conference on Urban Climate and International Congress of Biometeorology, Sydney, WMO/TD–1026, Online, 1 January 1999; pp. 15–20. [Google Scholar]
  29. Pugh, T.; MacKenzie, A.; Whyatt, J.; Hewitt, C. Effectiveness of Green infrastructures for improvement of air quality in urban street canyons. Environ. Sci. Technol. 2012, 46, 7692–7699. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  30. Rahman, A.; Yeok, F.; Amir, A. The building thermal performance and carbon sequestration evaluation for Psophocarpus tetrogonobulus on biofaçade wall in the tropical environment. World Acad. Sci. Eng. Technol. 2011, 76, 86–94. [Google Scholar]
  31. Ysebaert, T.; Koch, K.; Samson, R.; Denys, S. Green walls for mitigating urban particulate matter pollution—A review. Urban For. Urban Green. 2021, 59, 127014. [Google Scholar] [CrossRef]
  32. Santamouris, M. Cooling the cities—A review of reflective and green roof mitigation technologies to fight heat island and improve comfort in urban environments. Sol. Energy 2014, 103, 682–703. [Google Scholar] [CrossRef]
  33. Alexandri, E.; Jones, P. Temperature decreases in an urban canyon due to green walls and green roofs in diverse climates. Build. Environ. 2008, 43, 480–493. [Google Scholar] [CrossRef]
  34. Gago, E.J.; Roldan, J.; Pacheco-Torres, R.; Ordóñez, J. The city and urban heat islands: A review of strategies to mitigate adverse effects. Renew. Sustain. Energy Rev. 2013, 25, 749–758. [Google Scholar] [CrossRef]
  35. Addo-Bankas, O.; Zhao, Y.; Vymazal, J.; Yuan, Y.; Fu, J.; Wei, T. Green walls: A form of constructed wetland in green buildings. Ecol. Eng. 2021, 169, 106321. [Google Scholar] [CrossRef]
  36. Boc, V. Current approaches in metropolitan green infrastructure strategies. Sci. Pap. Ser. B Hortic. 2015, 59, 307–310. [Google Scholar]
  37. Gattringer, H.; Claret, A.; Radtke, M.; Kisser, J.; Zraunig, A.; Rodriguez-Roda, I.; Buttiglieri, G. Novel vertical ecosystem for sustainable water treatment and reuse in tourist resorts. Int. J. Sustain. Dev. Plan. 2016, 11, 263–274. [Google Scholar] [CrossRef]
  38. Yan, F.; Shen, J.; Zhang, W.; Ye, L.; Lin, X. A review of the application of green walls in the acoustic field. Build. Acoust. 2022, 1351010X221096789. [Google Scholar] [CrossRef]
  39. Oquendo-Di Cosola, V.; Olivieri, F.; Ruiz-García, L. A systematic review of the impact of green walls on urban comfort: Temperature reduction and noise attenuation. Renew. Sustain. Energy Rev. 2022, 162, 112463. [Google Scholar] [CrossRef]
  40. Ichihara, K.; Cohen, J. New York city property values: What is the impact of green roofs on rental pricing. Lett. Spat. Resour. Sci. 2011, 4, 21–30. [Google Scholar] [CrossRef]
  41. Wang, Z.; Zhu, Y.; Wang, F.; Wang, P.; Shen, C.; Liu, J. (Eds.) Proceedings of the 11th International Symposium on Heating, Ventilation and Air Conditioning (ISHVAC 2019): Volume I: Indoor and Outdoor Environment; Springer Nature: Berlin, Germany, 2020. [Google Scholar]
  42. Sadineni, S.; Madala, S.; Boehm, R.F. Passive building energy savings: A review of building envelope components. Renew. Sustain. Energy Rev. 2011, 15, 3617–3631. [Google Scholar] [CrossRef]
  43. Wong, N.H.; Tan, A.Y.K.; Tan, P.Y.; Chiang, K.; Wong, N.C. Acoustic evaluation of vertical greenery systems for building walls. Build. Environ. 2010, 45, 411–420. [Google Scholar] [CrossRef]
  44. Al-Kayiem, H.H.; Koh, K.; Riyadi, T.W.; Effendy, M. A comparative review on greenery ecosystems and their impacts on sustainability of building environment. Sustainability 2020, 12, 8529. [Google Scholar] [CrossRef]
  45. Maier, D. Perspective of using green walls to achieve better energy efficiency levels. A bibliometric review of the literature. Energy Build. 2022, 112070. [Google Scholar] [CrossRef]
  46. Renterghem, T.; Hornikx, M.; Forssen, J.; Botteldooren, D. The potential of building envelope greening to achieve quietness. Build. Environ. 2013, 61, 34–44. [Google Scholar] [CrossRef] [Green Version]
  47. Susca, T.; Zanghirella, F.; Colasuonno, L.; Del Fatto, V. Effect of green wall installation on urban heat island and building energy use: A climate-informed systematic literature review. Renew. Sustain. Energy Rev. 2022, 159, 112100. [Google Scholar] [CrossRef]
  48. Newton, J.; Gedge, D.; Early, P.; Wilson, S. Building Greener: Guidance on the Use of Green Roofs, Green Walls and Complementary Features on Buildings; CIRIA: London, UK, 2007. [Google Scholar]
  49. Köhler, M. Green facades—A view back and some visions. Urban Ecosyst. 2008, 11, 423–436. [Google Scholar] [CrossRef]
  50. Dunnett, N.; Kingsbury, N. Planting Green Roofs and Living Walls; Timber Press: Portland, OR, USA; London, UK, 2008. [Google Scholar]
  51. Pérez, G.; Coma, J.; Martorell, I.; Cabeza, L.F. Vertical Greenery Systems (VGS) for energy saving in buildings: A review. Renew. Sustain. Energy Rev. 2014, 39, 139–165. [Google Scholar] [CrossRef] [Green Version]
  52. Manso, M.; Castro-Gomes, J. Green wall systems: A review of their characteristics. Renew. Sustain. Energy Rev. 2015, 41, 863–871. [Google Scholar] [CrossRef]
  53. Seyam, S. The impact of greenery systems on building energy: Systematic review. J. Build. Eng. 2019, 26, 100887. [Google Scholar] [CrossRef]
  54. Ascione, F.; De Masi, R.F.; Mastellone, M.; Ruggiero, S.; Vanoli, G.P. Green Walls, a critical review: Knowledge gaps, design parameters, thermal performances and multi-criteria design approaches. Energies 2020, 13, 2296. [Google Scholar] [CrossRef]
  55. Sharp, R.; Sable, J.; Bertram, F.; Mohan, E.; Peck, S. Introduction to Green Walls: Technology, benefits & design. Green Roofs Healthy Cities 2008, 37. [Google Scholar]
  56. Pérez, G.; Rincón, L.; Vila, A.; González, J.; Cabeza, L. Behaviour of green facades in Mediterranean Continental climate. Energy Convers. Manag. 2011, 52, 1861–1867. [Google Scholar] [CrossRef]
  57. Fukuzumi, Y. Plant Growing Method for Greening Wall Surfaces. U.S. Patent 5,579,603, 3 December 1996. [Google Scholar]
  58. Blanc, P.; Lalot, V. The Vertical Garden: From Nature to the City; W.W. Norton: New York, NY, USA, 2012. [Google Scholar]
  59. Hindle, R.L. A vertical garden: Origins of the Vegetation-Bearing Architectonic Structure and System (1938). Stud. Hist. Gard. Des. Landsc. 2012, 32, 99–110. [Google Scholar] [CrossRef]
  60. Koumoudis, S. Green Wall Planting Module, Support Structure and Irrigation Control System. U.S. Patent 2011/0088319A1, 2011. [Google Scholar]
  61. Urriola, H. Vertical Wall Garden. U.S. Patent 2011/0094153A1, 2011. [Google Scholar]
  62. Laurence, M.; Sabin, R. Plant Wall and Modules for Growing Plants. U.S. Patent 2011/0107667A1, 2011. [Google Scholar]
  63. Yap, T.; Wong, L.; Tan, H.; Lim, H.; Palanisamy, T.; Tan, P.; Poh, C.; Chan, Y. A Plant Housing Device. W.O. Patent 2011/014124A1, 3 February 2011. [Google Scholar]
  64. Sichello, C. Plant Propagation and Display Panel and Assembly. W.O. Patent 2010/031181A1, 25 March 2010. [Google Scholar]
  65. Bindschedler, P.; Lassalle, F. Modular Greening Device for Facades, Walls or the Like. U.S. Patent 7757436B2, 20 July 2010. [Google Scholar]
  66. Corradi, L. Hydroponic Growing System. U.S. Patent 2009/007486A1, 8 January 2009. [Google Scholar]
  67. Bribach, C. Vertical Garden Panel. U.S. Patent 2011/0059518A1, 10 March 2011. [Google Scholar]
  68. Taber, S. Modular Wall Planters. U.S. Patent 2011/0016784A1, 27 January 2011. [Google Scholar]
  69. Huet, P.; Heine, L. Modular Wall Element for Growing Plants and Modular Structure Formed by a Plurality of Modular Elements of the Aforementioned Type. U.S. Patent 2010/0095584A1, 22 April 2010. [Google Scholar]
  70. Yang, Y.; Zhao, Y.; Liu, R.; Morgan, D. Global development of various emerged substrates utilized in constructed wetlands. Bioresour. Technol. 2018, 261, 441–452. [Google Scholar] [CrossRef] [PubMed]
  71. Schulz, H.; Dunst, G.; Glaser, B. Positive effects of composted biochar on plant growth and soil fertility. Agron. Sustain. Dev. 2013, 33, 817–827. [Google Scholar] [CrossRef] [Green Version]
  72. Zhao, Y.; Babatunde, A.; Zhao, X.; Li, W. Development of alum sludge-based constructed wetland: An innovative and cost effective system for wastewater treatment. J. Environ. Sci. Health A 2009, 44, 827–832. [Google Scholar] [CrossRef] [Green Version]
  73. Lee, A.; Sian, G.; Greaves, H. Green Wall System. W.O. Patent 2010/009505A1, 28 January 2010. [Google Scholar]
  74. Prodanovic, V.; Zhang, K.; Hatt, B.; McCarthy, D.; Deletic, A. Optimisation of lightweight green wall media for greywater treatment and reuse. Build. Environ. 2018, 131, 99–107. [Google Scholar] [CrossRef]
  75. Yap, T.; Wong, L.; Yoong, Y.; Tan, H.; Lim, H. Supporting Structure for Green Building Facade. W.O. Patent 2011/016777A1, 10 February 2011. [Google Scholar]
  76. Zuo, Z.; Cheng, J.; Guo, H.; Li, Y. Knowledge mapping of research on strategic mineral resource security: A visual analysis using CiteSpace. Resour. Policy 2021, 74, 102372. [Google Scholar] [CrossRef]
  77. Zhao, R.Y.; Xu, L.M. The Knowledge Map of the Evolution and Research Frontiers of the Bibliometrics. J. Libr. Sci. China 2010, 36, 60–68. [Google Scholar]
  78. Chen, C.M.; Hu, Z.G.; Liu, S.B.; Tseng, H. Emerging trends in regenerative medicine: A scientometric analysis in CiteSpace. Expert Opin. Biol. Ther. 2012, 12, 593–608. [Google Scholar] [CrossRef]
  79. Li, X.; Wu, P.; Shen, G.Q.P.; Wang, X.Y.; Teng, Y. Mapping the knowledge domains of building information modeling (BIM): A bibliometric approach. Autom. Constr. 2017, 84, 195–206. [Google Scholar] [CrossRef]
  80. Kubota, T.; Rijal, H.B.; Takaguchi, H. Sustainable Houses and Living in the Hot-Humid Climates of Asia; Springer: Singapore, 2018. [Google Scholar]
  81. Pérez, G.; Rincón, L.; Vila, A.; González, J.M.; Cabez, L.F. Green vertical systems for buildings as passive systems for energy savings. Appl. Energy 2011, 88, 4854–4859. [Google Scholar] [CrossRef]
  82. Sternberg, T.; Viles, H.; Cathersides, A. Evaluating the role of ivy (Hedera helix) in moderating wall surface microclimates and contributing to the bioprotection of historic buildings. Build. Environ. 2011, 46, 293–297. [Google Scholar] [CrossRef]
  83. Perini, K.; Ottelé, M.; Fraaij, A.; Haas, E.; Raiteri, R. Vertical greening systems and the effect on air flow and temperature on the building envelope. Build. Environ. 2011, 46, 2287–2294. [Google Scholar] [CrossRef]
  84. Wong, N.H.; Tan, A.Y.K.; Chen, Y.; Sekar, K.; Tan, P.Y.; Chan, D.; Chiang, K.; Wong, N.C. Thermal evaluation of vertical greenery systems for building walls. Build. Environ. 2010, 45, 663–672. [Google Scholar] [CrossRef]
  85. Yin, H.; Kong, F.; Middel, A.; Dronova, I.; Xu, H.; James, P. Cooling effect of direct green façades during hot summer days: An observational study in Nanjing, China using TIR and 3DPC data. Build. Environ. 2017, 116, 195–206. [Google Scholar] [CrossRef] [Green Version]
  86. Cameron, R.W.F.; Taylor, J.E.; Emmett, M.R. What’s ‘cool’ in the world of green façades? How plant choice influences the cooling properties of green walls. Build. Environ. 2014, 73, 198–207. [Google Scholar] [CrossRef] [Green Version]
  87. Bolton, C.; Rahman, M.; Armson, D.; Ennos, A. Effectiveness of an ivy covering at insulating a building against the cold in Manchester, U.K: A preliminary investigation. Build. Environ. 2014, 80, 32–35. [Google Scholar] [CrossRef]
  88. Susorova, I.; Azimi, P.; Stephens, B. The effects of climbing vegetation on the local microclimate, thermal performance, and air infiltration of four building facade orientations. Build. Environ. 2014, 76, 113–124. [Google Scholar] [CrossRef]
  89. Susorova, I.; Angulo, M.; Bahrami, P.; Stephens, B. A model of vegetated exterior facades for evaluation of wall thermal performance. Build. Environ. 2013, 67, 1–13. [Google Scholar] [CrossRef]
  90. Jim, C. Thermal performance of climber greenwalls: Effects of solar irradiance and orientation. Appl. Energy 2015, 154, 631–643. [Google Scholar] [CrossRef]
  91. Olivieri, F.; Olivieri, L.; Neila, J. Experimental study of the thermal-energy performance of an insulated vegetal façade under summer conditions in a continental Mediterranean climate. Build. Environ. 2014, 77, 61–76. [Google Scholar] [CrossRef]
  92. Koyama, T.; Yoshinaga, M.; Hayashi, H.; Maeda, K.-I.; Yamauchi, A. Identification of key plant traits contributing to the cooling effects of green façades using freestanding walls. Build. Environ. 2013, 66, 96–103. [Google Scholar] [CrossRef]
  93. Šuklje, T.; Medved, S.; Arkar, C. An experimental study on a microclimatic layer of a bionic façade inspired by vertical greenery. J. Bionic Eng. 2013, 10, 177–185. [Google Scholar] [CrossRef]
  94. Pérez, G.; Coma, J.; Sol, S.; Cabeza, L.F. Green facade for energy savings in buildings: The influence of leaf area index and facade orientation on the shadow effect. Appl. Energy 2017, 187, 424–437. [Google Scholar] [CrossRef] [Green Version]
  95. Currie, B.A.; Bass, B. Estimates of air pollution mitigation with green plants and green roofs using the UFORE model. Urban Ecosyst. 2008, 11, 409–422. [Google Scholar] [CrossRef]
  96. Davies, C.; Lafortezza, R. Urban green infrastructure in Europe: Is greenspace planning and policy compliant? Land Use Policy 2017, 69, 93–101. [Google Scholar] [CrossRef]
  97. Morakinyo, T.E.; Lam, Y.F. Simulation study of dispersion and removal of particulate matter from traffic by road-side vegetation barrier. Environ. Sci. Pollut. Res. 2016, 23, 6709–6722. [Google Scholar] [CrossRef]
  98. Deutsch-Aboulmahassine, E. Modular Wall-Mounted Plant Growing System. U.S. Patent 7627983B1, 8 December 2009. [Google Scholar]
  99. Weerakkody, U.; Dover, J.W.; Mitchell, P.; Reiling, K. Particulate matter pollution capture by leaves of seventeen living wall species with special reference to rail-traffic at a metropolitan station. Urban For. Urban Green. 2017, 27, 173–186. [Google Scholar] [CrossRef]
  100. Weerakkody, U.; Dover, J.W.; Mitchell, P.; Reiling, K. Quantification of the traffic-generated particulate matter capture by plant species in a living wall and evaluation of the important leaf characteristics. Sci. Total Environ. 2018, 635, 1012–1024. [Google Scholar] [CrossRef]
  101. Weerakkody, U.; Dover, J.W.; Mitchell, P.; Reiling, K. The impact of rainfall in remobilising particulate matter accumulated on leaves of four evergreen species grown on a green screen and a living wall. Urban For. Urban Green. 2018, 35, 21–31. [Google Scholar] [CrossRef]
  102. Ottel’e, M.; van Bohemen, H.D.; Fraaij, A.L.A. Quantifying the deposition of particulate matter on climber vegetation on living walls. Ecol. Eng. 2010, 36, 154–162. [Google Scholar] [CrossRef]
  103. Joshi, S.V.; Ghosh, S. On the air cleansing efficiency of an extended green wall: A CFD analysis of mechanistic details of transport processes. J. Theor. Biol. 2014, 361, 101–110. [Google Scholar] [CrossRef]
  104. Morakinyo, T.E.; Lam, Y.F.; Hao, S. Evaluating the role of green infrastructures on near-road pollutant dispersion and removal: Modelling and measurement. J. Environ. Manage. 2016, 182, 595–605. [Google Scholar] [CrossRef]
  105. Kikegawa, Y.; Genchi, Y.; Kondo, H.; Hanaki, K. Impacts of city-block-scale counter measures against urban heat-island phenomena upon a building’s energy-consumption for air-conditioning. Appl. Energy 2006, 83, 649–668. [Google Scholar] [CrossRef]
  106. Kolokotroni, M.; Giannitsaris, I.; Watkins, R. The effect of the London urban heat island on building summer cooling demand and night ventilation strategies. Sol. Energy 2006, 80, 383–392. [Google Scholar] [CrossRef]
  107. Rajagopalan, P. Urban heat island and its impact on building energy consumption. Adv. Build. Energy Res. 2009, 3, 261–270. [Google Scholar]
  108. Dwivedi, A.; Mohan, B.K. Impact of green roof on micro climate to reduce Urban Heat Island. Remote Sens. Appl. Soc. Environ. 2018, 10, 56–69. [Google Scholar] [CrossRef]
  109. Ramakreshnan, L.; Aghamohammadi, N.; Fong, C.S.; Ghaffarianhoseini, A.; Ghaffarianhoseini, A.; Wong, L.P.; Hassan, N.; Sulaiman, N.M. A critical review of urban heat island phenomenon in the context of greater Kuala Lumpur, Malaysia. Sustain. Cities Soc. 2018, 39, 99–113. [Google Scholar] [CrossRef]
  110. Pettit, T.; Irga, P.J.; Surawski, N.C.; Torpy, F.R. An assessment of the suitability of active green walls for NO2 reduction in green buildings using a closed-loop flow reactor. Atmosphere 2019, 10, 801. [Google Scholar] [CrossRef] [Green Version]
  111. Su, Y.-M.; Lin, C.-H. Removal of Indoor Carbon Dioxide and Formaldehyde Using Green Walls by Bird Nest Fern. Hortic. J. 2015, 84, 69–76. [Google Scholar] [CrossRef] [Green Version]
  112. Pettit, T.; Irga, P.J.; Abdo, P.; Torpy, F.R. Do the plants in functional green walls contribute to their ability to filter particulate matter? Build. Environ. 2017, 125, 299–307. [Google Scholar] [CrossRef]
  113. Wang, Z.; Zhang, J.S. Characterization and performance evaluation of a full-scale activated carbon-based dynamic botanical air filtration system for improving indoor air quality. Build. Environ. 2011, 46, 758–768. [Google Scholar] [CrossRef]
  114. Boano, F.; Caruso, A.; Costamagna, E.; Ridolfi, L.; Fiore, S.; Demichelis, F.; Galvao, A.; Pisoeiro, J.; Rizzo, A.; Masi, F. A review of nature-based solutions for greywater treatment: Applications, hydraulic design, and environmental benefits. Sci. Total Environ. 2020, 711, 134731. [Google Scholar] [CrossRef]
  115. Pradhan, S.; Al-Ghamdi, S.G.; Mackey, H.R. Greywater recycling in buildings using living walls and green roofs: A review of the applicability and challenges. Sci. Total Environ. 2019, 652, 330–344. [Google Scholar] [CrossRef]
  116. Fowdar, H.S.; Hatt, B.E.; Breen, P.; Cook, P.L.M.; Deletic, A. Designing living walls for greywater treatment. Water Res. 2017, 110, 218–232. [Google Scholar] [CrossRef]
  117. Kandya, A.; Mohan, M. Mitigating the Urban Heat Island effect through building envelope modifications. Energy Build. 2018, 164, 266–277. [Google Scholar] [CrossRef]
  118. Xing, Q.; Hao, X.; Lin, Y.; Tan, H.; Yang, K. Experimental investigation on the thermal performance of a vertical greening system with green roof in wet and cold climates during winter. Energy Build. 2019, 183, 105–117. [Google Scholar] [CrossRef]
  119. Aflaki, A.; Mirnezhad, M.; Ghaffarianhoseini, A.; Ghaffarianhoseini, A.; Omrany, H.; Wang, Z.-H.; Akbari, H. Urban heat island mitigation strategies: A state-of-the-art review on Kuala Lumpur, Singapore and Hong Kong. Cities 2017, 62, 131–145. [Google Scholar] [CrossRef]
  120. Cheng, C.; Cheung, K.K.; Chu, L. Thermal performance of a vegetated cladding system on facade walls. Build. Environ. 2010, 45, 1779–1787. [Google Scholar] [CrossRef]
  121. Chen, Q.; Li, B.; Liu, X. An experimental evaluation of the living wall system in hot and humid climate. Energy Build. 2013, 61, 298–307. [Google Scholar] [CrossRef]
  122. Perini, K.; Bazzocchi, F.; Croci, L.; Magliocco, A.; Cattaneo, E. The use of vertical greening systems to reduce the energy demand for air conditioning. Field monitoring in Mediterranean climate. Energy Build. 2017, 143, 35–42. [Google Scholar] [CrossRef]
  123. Coma, J.; Pérez, G.; De Gracia, A.; Burés, S.; Urrestarazu, M.; Cabeza, L.F. Vertical greenery systems for energy savings in buildings: A comparative study between green walls and green facades. Build. Environ. 2017, 111, 228–237. [Google Scholar] [CrossRef] [Green Version]
  124. Medl, A.; Stangl, R.; Florineth, F. Vertical greening systems—A review on recent technologies and research advancement. Build. Environ. 2017, 125, 227–239. [Google Scholar] [CrossRef]
  125. Feitosa, R.C.; Wilkinson, S.J. Small-scale experiments of seasonal heat stress attenuation through a combination of green roof and green walls. J. Clean. Prod. 2020, 250, 119443. [Google Scholar] [CrossRef]
  126. Rosasco, P.; Perini, K. Evaluating the economic sustainability of a vertical greening system: A Cost-Benefit Analysis of a pilot project in mediterranean area. Build. Environ. 2018, 142, 524–533. [Google Scholar] [CrossRef]
  127. Ling, T.Y. Rethinking Greening the Building Façade Under Extreme Climate: Attributes Consideration for Typo-Morphological Green Envelope Retrofit. Clean. Circ. Bioecon. 2022, 3, 100024. [Google Scholar] [CrossRef]
  128. Srbinovska, M.; Andova, V.; Mateska, A.K.; Krstevska, M.C. The effect of small green walls on reduction of particulate matter concentration in open areas. J. Clean. Prod. 2021, 279, 123306. [Google Scholar] [CrossRef]
  129. Huang, Z.; Lu, Y.; Wong, N.H.; Poh, C.H. The true cost of “greening” a building: Life cycle cost analysis of vertical greenery systems (VGS) in tropical climate. J. Clean. Prod. 2019, 228, 437–454. [Google Scholar] [CrossRef]
Sustainability 14 12997 g001 550
Figure 1. Classification of vertical greening system.
Figure 1. Classification of vertical greening system.
Sustainability 14 12997 g001
Sustainability 14 12997 g002 550
Figure 2. Vertical greening technology.
Figure 2. Vertical greening technology.
Sustainability 14 12997 g002
Sustainability 14 12997 g003 550
Figure 3. Composition of vertical greening system.
Figure 3. Composition of vertical greening system.
Sustainability 14 12997 g003
Sustainability 14 12997 g004 550
Figure 4. 2012–2022 Document data collection flow chart.
Figure 4. 2012–2022 Document data collection flow chart.
Sustainability 14 12997 g004
Sustainability 14 12997 g005 550
Figure 5. Number of documents issued for vertical greening in 2012–2022.
Figure 5. Number of documents issued for vertical greening in 2012–2022.
Sustainability 14 12997 g005
Sustainability 14 12997 g006 550
Figure 6. 2012–2022 High frequency keyword co-occurrence.
Figure 6. 2012–2022 High frequency keyword co-occurrence.
Sustainability 14 12997 g006
Sustainability 14 12997 g007 550
Figure 7. 2012–2022 Keyword co-occurrence time zone map.
Figure 7. 2012–2022 Keyword co-occurrence time zone map.
Sustainability 14 12997 g007
Sustainability 14 12997 g008 550
Figure 8. The cross-country collaborations visualization map in vertical greening.
Figure 8. The cross-country collaborations visualization map in vertical greening.
Sustainability 14 12997 g008
Sustainability 14 12997 g009 550
Figure 9. 2012–2022 Visualization of the reference co-location clustering network and timeline.
Figure 9. 2012–2022 Visualization of the reference co-location clustering network and timeline.
Sustainability 14 12997 g009
Sustainability 14 12997 g010 550
Figure 10. Review the details of previous studies.
Figure 10. Review the details of previous studies.
Sustainability 14 12997 g010
Sustainability 14 12997 g011 550
Figure 11. Summary of vertical greening system function.
Figure 11. Summary of vertical greening system function.
Sustainability 14 12997 g011
Sustainability 14 12997 g012 550
Figure 12. Knowledge wedge diagram of vertical greening system.
Figure 12. Knowledge wedge diagram of vertical greening system.
Sustainability 14 12997 g012
Table
Table 1. Existing vertical greening technology.
Table 1. Existing vertical greening technology.
TypeClimbingTractionContainerBasinCloth BagPlate SlotModular
IllustrationSustainability 14 12997 i001Sustainability 14 12997 i002Sustainability 14 12997 i003Sustainability 14 12997 i004Sustainability 14 12997 i005Sustainability 14 12997 i006Sustainability 14 12997 i007
CaseSustainability 14 12997 i008Sustainability 14 12997 i009Sustainability 14 12997 i010Sustainability 14 12997 i011Sustainability 14 12997 i012Sustainability 14 12997 i013Sustainability 14 12997 i014
CostLowMediumHighMediumLowLowHigh
PlantSingleMultipleFitMultiple
EffectMediumFineMediumFine
MaintainInconvenientConvenientInconvenientConvenient
Weight (Kg/m2)2.530–6050–10025–5060–12025–50
Tickness (mm)100–200300–500250–400300–500200–500
SubstrateUnlimitedLess limitLimitLess limit
TimeSlowMediumFaster
Table
Table 2. The literature on the cooling effect of vertical greening.
Table 2. The literature on the cooling effect of vertical greening.
Type CountryPeriodPlantReduction TemperatureMethod
Green FacadesGermany [49]Winter Vines Boston Ivy 3°Experiment
England [82]One YearHedera Helix Summer 1.7°–9.5°
Direct FacadeDeflt [83]AutumnHedera Helix1.2°
Indirect Facade Rotterdam [83]H-helix, Vitis, Clematis, Jasmine and Pyracantha2.7°
Living Wall SystemBenthuizen [83]No climbers--
Living Wall SystemSingapore [84]Summer--6°–10°
Direct FacadeChina [85]SummerParthenocissus Tricuspidata2.57°–4.67°
Green FacadesUK [86]SummerHedera Helix, Stachys Byzantina7°
Living Wall SystemUK [87]Winter Hedera Helix 0.5°
Green FacadesUSA [88]SummerIvy0.7°–12.6°
USA [89]SummerParthenocissus Tricuspidata7.9°Simulation
Double-skingreen FacadeSpain [81]All YearWisteria Sinensis5.5°–17.62°Experiment
GreenwallChina [90]SummerPumila, Venusta, Corymbosa2°–5°
GreenwallMadrid [91]Summer --4.5°–8.2°Exp+Sim
Vertical Greenery SystemsSingapore [43]Climber Plants 4.36°Experiment
Green FacadesJapan [92]Bitter Melon, Morning Glory, Sword Bean, Kudzu, Apios3.7°–11.3°
Slovenia [93]Phaseolus Vulgaris
“Anellino Verde”		4°
Spain [94] Parthenocissus Tricuspidata 15–16.4
Table
Table 3. Literature on vertical greening to improve outdoor air quality.
Table 3. Literature on vertical greening to improve outdoor air quality.
RegionTypePlantConclusionMethod
Urban Toronto [95,96]Green Roofs and Green WallsShrubsThe removal rate of PM10 is 1.37 mg/year.Experiment
Road [97,98]Vegetation Barriers--The reduction of pollutant concentration is due to the dispersion and deposition of green walls.ENVI-met
New Street Railway Station [99]Living WallBuxus Sempervirens L., Hebe Albicans Cockayne, Thymus Vulgaris L. and Hebe X YoungiiLiving wall plants have considerable potential in removing particulate pollutants from the atmosphere.Experiment
Road [100]Living WallTwenty species of living wall plantsThe average capture of PM1 particles by the living wall of 100 square centimeters is 122.08 ± 6.9 × 107, PM2.5 particles 8.24 ± 0.72 × 107, PM10 particles 4.45 ± 0.33 × 107.
Road [101]Green Wall Heuchera Villosa Michx, Helleborus × sternii Turrill, Bergenia cordifolia (Haw.) Sternb. and Hedera Helix LThe recovery of PM capture ability of four green wall species after rainfall was studied. Green wall has the potential to capture PM all year round.
Road and Woodland [102]Living Walls Hedera Helix LThe number of particles collected on the front of leaves was more than that on the back, and there was no significant difference in height and season.
Developing Countries [103]Green FacadesVernonia ElaeagnifoliaFor (SO2), the removal rates in dry and wet weather are 1.11 × 10-6 s-1 and 1.05 × 10-6 s-1 respectivelyCFD
Road [104]Green Wall At pedestrian height (1.4 m), green walls are an effective barrier to reduce exposure to pollutants and air quality deteriorates from 4 m.ENVI-Met + Experiment
Street Canyons [29]By planting vegetation in street canyons to increase sediment, street concentrations in these canyons can be reduced by 40% for NO2 and 60% for PM.CFD
Table
Table 4. The literature on indoor vertical greening to remove indoor pollutants.
Table 4. The literature on indoor vertical greening to remove indoor pollutants.
Inorganic PollutantPlantConclusion
NO2 [110]Spathiphyllum Wallisii and Syngonium PodophyllumAverage NO2 clean air delivery rate of 661.32 and 550.8 m3·h−1·m−3 of biofifilter substrate for the respective plant species.
CO2 [111]--The indoor plant wall of 5.72 m2 can reduce the CO2 concentration of 38.88 m3 room from 2000 to 800 ppm in one hour.
1 m2 of active green wall can significantly reduce indoor carbon dioxide.
PM [111,112]Chlorophytum ComosumThe system recorded removal efficiencies were 53.35 ± 9.73% for total suspend particles, 53.51 ± 15.99% for PM10, and 48.21 ± 14.71 % for PM2.5.
VOC [113]Different plant speciesThe significant single removal rates (spres) of toluene and formaldehyde were 91.7% and 98.7% respectively.
Table
Table 5. Literature on energy saving effect of vertical greening.
Table 5. Literature on energy saving effect of vertical greening.
TypeCounryPlantSeasonReduction in Energy Consumption (%)Method
Green WallHong Kong [120]Zoysia japonicaSummer30 W/m2 heat flux reduction.Experiment
Wuhan [121]--2.5 W/m2 heat flux reduction 12% cooling load reduction.
Lonigo, Venice, &
Pisa, Italy [22]		Shrubs, Herbaceous
and Climber 		1.5 W/m2–70 W/m2 heat flux reduction at night.
Genoa, Italy [122]Cistus Jessamine beauty and Cistus crispus26.50%
Puigverd de Lleida,
Spain [123]		Rosmarinus officinalis
and Helichrysum
thianschanicum		Winter 2.96–4.2%
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Wang, P.; Wong, Y.H.; Tan, C.Y.; Li, S.; Chong, W.T. Vertical Greening Systems: Technological Benefits, Progresses and Prospects. Sustainability 2022, 14, 12997. https://doi.org/10.3390/su142012997

AMA Style

Wang P, Wong YH, Tan CY, Li S, Chong WT. Vertical Greening Systems: Technological Benefits, Progresses and Prospects. Sustainability. 2022; 14(20):12997. https://doi.org/10.3390/su142012997

Chicago/Turabian Style

Wang, Puyi, Yew Hoong Wong, Chou Yong Tan, Sheng Li, and Wen Tong Chong. 2022. "Vertical Greening Systems: Technological Benefits, Progresses and Prospects" Sustainability 14, no. 20: 12997. https://doi.org/10.3390/su142012997

APA Style

Wang, P., Wong, Y. H., Tan, C. Y., Li, S., & Chong, W. T. (2022). Vertical Greening Systems: Technological Benefits, Progresses and Prospects. Sustainability, 14(20), 12997. https://doi.org/10.3390/su142012997

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop