Vertical Green Wall Research Articles

The Impact of Coverage Forms of Exterior Vertical Greening Walls on the Thermal Environmental Benefits of Buildings in Hot and Humid Regions

Architectural vertical green walls can mitigate the urban heat island effect, provide shade and cooling, reduce energy consumption, improve a microclimate, and increase indoor comfort. However, an excessive pursuit of high coverage may diminish the benefit ratio and adversely affect ventilation and lighting. Field measurements were conducted in the hot and humid Guangzhou area to investigate the thermal benefits of external vertical green walls with varying green coverage and diverse layouts, encompassing effects such as shading, insulation, cooling, and humidification. Analyses were conducted using ENVI-met, orthogonal experiments, and SPSS to quantify the moderating effects of planted green coverage (PGC), leaf area density (LAD), and air interstitial layers on the environmental thermal benefits. The results indicated that the cooling and humidifying effects of 100% PGC and 75% PGC were comparable and superior to those of 50% PGC, yet 75% PGC outperformed 100% PGC in terms of indoor humidification. Among the layout modes, the horizontal layout was the most effective for cooling and humidification, followed by the point layout, with the vertical layout being the least effective. A global sensitivity analysis revealed that PGC had the greatest impact on wall cooling and outdoor humidification, LAD significantly influenced humidification, the width of air interstitial layers had a minor impact, and the two architectural vertical greening design ratios of 75% PGC × 4.60 LAD and 75% PGC × 2.70 LAD were particularly effective for cooling and humidification. Incorporating horizontal or point-like layouts can enhance façade design diversity while preserving the desired environmental thermal benefits, thereby contributing to the overall aesthetics of a building.

Green horizons: Exploring the potential of vertical green walls

The term “Green walls” also known as vertical gardens or living walls has emerged as a promising solution to combat the environmental challenges posed by rapid urbanization. This review explores the concept ornamental, plant choice suitable and benefits associated with green walls in urban settings. Utilising vegetation to cover vertical surfaces, green walls offer several benefits to the environment, society and economy. They contribute to improved air quality, noise reduction, energy conservation and biodiversity enhancement. Vertical greenery allows for the utilization of unused wall surfaces, creating green areas without occupying valuable ground space, which is often scarce in urban environments. Additionally, green walls offer aesthetic appeal, promote urban agriculture and create opportunities for community engagement. However, their implementation requires careful consideration of factors such as structural integrity, irrigation and maintenance. Despite these challenges, green walls offer a sustainable and innovative approach to enhancing the quality of urban life while mitigating the negative impacts of urban development on the environment. The current emphasis highlights the significance of green walls as an effective tool in sustainable urban planning, underscoring the need for further research and their integration into urban planning practices.

Vertical Green Wall Systems for Rainwater and Sewage Treatment

Rainwater and sewage are important pollution sources for surface water bodies. Vertical greening systems (VGSs) are extensively employed for these wastewater treatments due to the green and sustainable characteristics, as well as their high-efficiency in pollutant (organic matter, nitrogen, and phosphorus) removal. At present, more and more VGSs are designed with green buildings, serving city ecosystems. This study provides an overview of different kinds of VGSs for rain and sewage treatment, emphasizing their types, design, mechanisms, selection of plants, and growth substrate. Plants play a crucial role in pollutant removal, and different plants usually obtain different efficiencies of water treatment. Climbing plants and ornamental plants with fast growth rates are priority selections for VGSs, including Canna lilies, Jasmine, Grape vine, Boston ivy, Pittosporum tobira, Pelargonium australe, Mentha aquatica, and Lythrum salicaria. The substrate is the most critical part of the VGS, which plays an important role in regulating water flow, supporting plant growth, promoting biofilm growth, filtering pollutants, and adsorbing nutrients. The single substrate either has a blockage problem or has a short holding time. Therefore, a number of studies have mixed the substrates and integrated the advantages of the substrates to form a complementary effect, thereby improving the overall purification efficiency and stability. Novel substrates (sand, spent coffee grounds, date seeds, coffee grinds, reed-based, etc.) are usually mixed with coco coir, light-weight expanded clay, growstone, or perlite at a certain ratio to obtain optimum treatment performance. Moreover, plants in clay show more significant growth advantages and health statuses than in zeolite or soil. Operating parameters are also significant influences on the treatment performance. This review provides theoretical and technical support for designing sustainable, environmentally friendly, and cost-effective VGSs in treating rainwater and sewage.

Assessing vertical green walls for indoor corridors in educational buildings and its impact outdoor: A field study at the universities of Canada in Egypt

Developing Green Walls (GW) within the architectural realm involves integration of diverse functions to optimize the indoor performance of the GW, and outdoor in campus buildings. The methodology is fundamentally rooted in the selection and fulfillment of strategic incorporation of additional function-based GW design to various performance aspects through contextual design solutions. This approach is particularly crucial in the education sector, on utilizing GW to educate students as occupants in integrating gardening, ecology, botany, and beyond in their studies for decreasing the environmental pollution for new generations, to feel by environment indoor in accomplishing way for sustainability perceptions.The aim of the study is to assess the effective resources influencing vertical green walls needed for educational buildings to reduce the effect of indoor heat, to upgrade its air quality, simultaneously decreasing noise pollution to avoid the energy consumption. The Educational GW should be accessible easily, either by installing them naturally in accessible locations with appropriate heights or by designing the facilities to increase the student's integration with GW natural environment that will reflect on their academic progress and health. The study aims to assess the effect of green wall installation in the universities of Canada in Egypt campus in the heat gain reduction, energy consumption, CO2 emission reduction by using the Design-Builder simulation program to measure the effect of green wall installation in corridors and inner courtyard at the hottest period of the year (August 2:00 p.m.) and how it can decrease the cooling loads by 10.95 %:19.14 %, heating loads by 4.8 %:12.94 %, CO2 emission by 13 %:28.43 % and the monthly electricity bill by 35:41.5 % measuring the vertical greening cost in relative to short and long period as a needed sustainable technology to reduce building demand significantly.

Prediction Models for the Plant Coverage Percentage of a Vertical Green Wall System: Regression Models and Artificial Neural Network Models

(1) Background: The expansion that most cities have been showing for more than half a century has also brought with it an increase in the density of buildings, most of the time at the expense of green areas. This has led to negative effects, such as overpopulation of cities, rising urban temperatures, pollution of water, air, soil, and others, affecting daily urban life. As a result, specialists from different fields form multidisciplinary teams are looking for solutions to counteract these effects. The subject of visible facades has registered an increased interest among researchers in recent years because they can represent a viable solution that can contribute to increasing the degree of urban comfort. However, for such a system to be effective, it is necessary that the plants used grow and develop harmoniously and ensure the best possible coverage of the facade. The aim of this research is to find an adequate mathematical model that can predict, with a high degree of accuracy, the percentage of plant coverage of a green wall system, which is positioned in the city of Iasi, northeastern Romania. (2) Methods: The models used for this purpose were a multiple linear regression model (MLR) and a model based on a feed-forward artificial neural network (ANN). Four independent variables (soil temperature, soil moisture, week of the year, and cardinal wall orientation) and the interaction between two variables (soil temperature and week of the year) were used for the multiple linear regression model. Artificial neural networks were also trained to estimate the percentage of plant coverage in the analyzed system, and the network with the best mean squared error performance was chosen in doing predictions. For both MLR and ANN models, we constructed confidence intervals for the degree of plant coverage of the system (PCP) for a set of observed values. In the case of the ANN model, the confidence interval was derived via the bootstrap method, which is a resampling with replacement technique used to generate new samples from the original dataset. To the best of our knowledge, the derivation of confidence intervals using a combination of neural networks with the bootstrap method has not been used before, at least for predictions in horticulture. (3) Results: The ANN employed here consisted of one input layer with four neurons, one hidden layer with five neurons, and one output layer with one neuron. The comparison showed that the confidence interval obtained using ANN has a shorter length (and thus it is more accurate) than that obtained by the multiple linear regression model. The choice of the experimental module façade had a significant influence (of magnitude 1.9073) on the plant coverage percentage. An increase of one unit in soil humidity will determine an increase of almost 5.1% in plant coverage percentage, and an increase of 1 °C in soil temperature will determine a decrease of almost 1.21% in plant coverage percentage. The choice of the experimental module façade had a significant influence (of magnitude 1.9073) on the plant coverage percentage. (4) Conclusions: Although both methods showed to be useful in making predictions, the ANN method showed better predictive capabilities, at least when the performance is measured by the mean squared error. This fact may be useful when predicting the percentage of plant coverage of a green wall system with a higher degree of accuracy, in the case of organizing outdoor exhibitions or other similar projects.

Optimizing Shading and Thermal Performances of Vertical Green Wall on Buildings in a Hot Arid Region

Due to global concerns about energy issues, global warming, and urban quality, vertical greening systems (VGS) are receiving more attention in construction and design research. Therefore, VGS has become part of building envelope design as a passive technique for saving energy in building sectors. The current study aimed to investigate shading and energy performances of VGS in buildings in hot climate regions and to optimize VGS design as a building design element. The study was conducted through simulation and field experiments in a student housing building at a university campus (Irbid, Jordan). Field measurements were taken to assess the thermal effect of the green wall and daylight performance as well as the efficiency of the typical green wall design configuration. Furthermore, a methodology for accurately representing green walls was established and used. Both simulation and experimentation demonstrated that the thickness of the air cavity and the percentage of foliage coverage can have a substantial impact on the performance of the green wall system. Results showed that green wall systems are effective natural sunscreens and shading systems. A green wall helped to reduce the exterior wall surface temperatures by a range of 6 to 11 °C compared to the base case of the wall without a VGS on different days. In addition, it decreased the interior surface temperature of the investigated southern façade by an average of 5 °C compared to the base case. Green wall design configurations for hot climate regions, such as Jordan, will help designers to use the VGS as a design element. Our findings indicate that GW could help to improve the thermal and daylight environment and thus the results could be taken as indicative for GW wall design in other areas or buildings.

Assessment of the Thermal Performance of Vertical Green Walls Using Overall Thermal Transfer Value Based BIM Simulation Method: Case Study of Residential Buildings in Sub-Tropics

Construction of multifunctional building envelopes using vertical greenery walls (VGW) has emerged as a sustainable green technology to improving cooling efficiency. To attaining the desired level of building cooling performance, VGW and overall thermal transfer value (OTTV) of the walls are useful design factors. The study aims to revise the current VGW evaluation, considering the decreased heat flux due to thermal efficiency of wall construction based on OTTV values. To achieve this, OTTV based Building Information Modelling (BIM) simulation method was proposed using Autodesk-Revit and DesignBuilder simulation based on EnergyPlus. Six wall compositions with various OTTV values of south facade for residential buildings located in sub-tropical in cooling season, were evaluated. The findings demonstrate that in the presence of a green system, a good OTTV value of the exterior walls is required for optimal performance, to keep the space within set point of cooling for long time during the cooling season. The comparisons between the bare walls and the VGW have demonstrated a great variation due to the different OTTV reached up to 6.57% and 18.44% reduction in indoor air temperature. The best combination of VGW resulted a maximum of 1.2°C reduction in indoor air temperature, with number of hours (within 28°C or less) were higher by 2506h, representing 85.59% of the overall number of hours (2928h). Overall cooling energy saving is found as 103.3kwh, representing 13.63% of the total of energy saving, and decreased the heat gained by 38.82%, representing 61.51kwh reduction during cooling season compared to base wall.

Biochar from raw and spent common ivy: Impact of preprocessing and pyrolysis temperature on biochar properties

Hedera helix L., the common ivy, is an excellent evergreen climbing plant to be applied in vertical green walls to improve urban ecosystems. These green walls need to be trimmed regularly, yielding a biomass stream, which could be promising as a renewable feedstock for biochar production and the extraction of valuable chemicals. The potential of raw and spent (extracted) common ivy as a biochar feedstock was evaluated using slow pyrolysis at different temperatures: 400, 550 and 700 °C. Biochars produced at 400 °C showed a high carbon, nitrogen and ash content, while still having residual surface functionalities. These biochars are therefore interesting to be applied as soil fertilizer. Additionally, it was found that the impact of different green extraction processes (ethanol extraction versus steam distillation) before pyrolysis on the biochar properties was generally positive. Ethanol extractions increased biochar yields and the fraction of inorganic nutrients. Furthermore, ethanol extractions increased the carbon sequestration potential compared to raw ivy. Steam distilled biochar exhibited a very high carbon content (83 %), biochar stability (97 %) and aromaticity (100 %). Steam distillation did not affect the carbon sequestration potential. In conclusion, this investigation affirms common ivy as a promising feedstock for pyrolysis based biorefinery processes.

Vertical green walls for noise and temperature reduction – An experimental investigation

The abundance of heat-trapping asphalt and concrete, smog, and heat emitted from buildings and vehicles is one of the major reasons for the prevailing high temperature, air and noise pollution in cities. Incorporation of green wall in buildings is considered to be an effective method to reduce temperature and mitigate environmental pollution. This study investigated and compared the performance of two types of climbing green wall (CGW) and paving green wall (PGW) vegetation for temperature and noise reduction. Besides, the biological characteristics of Parthenocissus tricuspidata and Sedum lineare Thunb were also analyzed to substantiate the temperature and noise reduction performance of these plants. The results revealed that, the average temperature reduction by CGW and PGW were 4.9% ± 1.3% and 16.6% ± 7.4%, respectively, under no irrigation condition, and 18.4% ± 9.4% and 23.8% ± 8.7%, respectively, under irrigation condition. The noise reduction by CGW in high (75–80 dB), medium (50–55 dB) and low (30–35 dB) sound pressure level was 12.4, 7.5 and 5.7 dB, respectively, and 15.6, 9.3 and 7.0 dB, respectively, by PGW. The results demonstrated that green wall has an excellent effect on buildings toward temperature and noise pollution reduction.

THERMAL PERFORMANCE EVALUATION OF GREEN LIVING WALLS IN COMPOSITE CLIMATE

Purpose of the study: Due to high solar radiation and extreme heat gain in composite climates, the envelope or the façade of the building becomes an essential part to modulate the heat transfer and temperature in the indoor environment. A passive sustainable approach to tackle heat gain is by adopting green living facades as the exterior skin. The objective of this research is to identify the potential of green living walls in modulating temperature and relative humidity in the composite climate of India.
 Methodology: This research is based on data collection in the form of a Case Study. The paper evaluates the difference of variation in temperature and relative humidity of two façade samples of the same building, one with a “green living facade” and one without it.
 Main Findings: The research aimed to justify that a green living facade may act as a passive strategy for composite climates. The result demonstrated that there is a significant temperature reduction between the ambient air temperature and indoor room temperature. The result also showed a notable change between ambient air temperature and the gap between the green living façade and the surface of the wall.
 Implications: Significant drop in indoor ambient temperature in composite climate may save energy for cooling or heating demands.
 Application of this study: This is a pilot study in order to carry out the main study for a similar application in order to categorize this as a passive sustainable façade strategy.
 Novelty/Originality of this study: The study is one of its kind attempt to investigate the impact of vertical green walls on thermal comfort in the composite climate of India.

Performance of spider plant (Chlorophytum comosum) in modular vertical green walls under various media and nutrients

An investigation was carried out to study the performance of various media and nutrients for spider plant (Chlorophytum comosum) in modular vertical walls under vertical green walls in the Department of Horticulture, Annamalai University, Annamalai Nagar (Tamil Nadu) during 2018 to 2020. The experiment comprised of four media viz., coco peat, greenosil, perlite and vermiculite and their combinations and two nutrients viz., foliar nutrition (Grosure NPK 19:19:19 and @ 1% twice (30 and 90 days after planting)) and fertilizer stick (Greenstix sticks were inserted to the modular containers @ one per container at 30 and 90 days after planting). Results revealed that, among the media, plants grown under vermiculite showed better performance in exhibiting maximum values for plant height (24.9 cm), number of leaves (21.6), leaf length (23.8 cm), leaf width (2.43), leaf area (30.9 cm2), shoot weight (15.1 g plant-1), root weight (3.4 g plant-1), biomass (18.4 g plant-1), size index (24.7 cm), and visual quality (9.08). However, among the nutrients, plants inserted with fertilizer stick recorded highest values for plant height (20.9 cm), number of leaves (18.8), leaf length (20.9 cm), leaf width (2.21), leaf area (30.2 cm2), shoot weight (14.8 g plant-1), root weight (3.24 g plant-1), biomass (18.1 g plant-1), size index (22.5 cm), and visual quality (8.49). compared with foliar nutrition. The interaction between media and nutrients was significant and plants grown under vermiculite and containers inserted with fertilizer stick showed superior performance in exerting maximum values for all the characters than other treatment combinations.

Investigation thermal comfort in urban environmental centres by combining traditional and modern principles

Traditional cities have been able to provide thermal comfort to their residents through the use of simple physical principles related to the movement of air from cold areas high-pressure represented by a cold air gathering focal like the basements and the middle courtyard and shaded alleys to hot areas low-pressure such as large urban open courtyards that exposed to sunlight. However, due to the industrial revolution, The Urban development has deteriorated the traditional urban fabric, and it’s environmental components, which provided urban fabric with thermal comfort reasons, have disappeared, and a modern urban fabric has emerged that does not take environmental considerations and thermal comfort into account. Here, the research tries to suggest a planning urban style that combines the Principles of architecture and traditional planning with a modern ideas that are appropriate for the times, achieving new urban centers within the city capable of providing thermal comfort to its occupants and creating an urban environmental vision to revitalize traditional urban areas by using vertical green walls.

Optimization of media and nutrition for foliage plants grown under modular vertical green walls

An investigation was carried out to study the performance of various media and nutrients for three foliage plants viz., arrow head plant (Syngonium podophyllum), boat lily (Tradescantia spathacea) and spider plant (Chlorophytum comosum) grown under modular vertical green walls. The experiment comprised of four media viz., coco peat, Greenosil, perlite and vermiculite and their combinations and two nutrients viz., foliar nutrition (NPK 19:19:19 and @ 1% twice (30 and 90 days after planting) and fertilizer stick (Greenstix sticks were inserted to the modular containers @ one per container at 30 and 90 days after planting). Results revealed that, among the media, plants grown under vermiculite showed better performance in exhibiting maximum values for plant height, leaf area, shoot weight, root weight and visual quality in all the three foliage ornamentals. However, among the nutrients, those plants inserted with fertilizer stick (N2) recorded highest for plant height, leaf area, shoot weight, root weight and visual quality in arrow head plant and spider plant. However, maximum values for plant height, leaf area, shoot weight and visual quality in boat lily were recorded under the treatment N1 (Foliar nutrient) except root weight. The interaction between media and nutrients was significant and plants grown under vermiculite and containers inserted with fertilizer stick showed superior performance w.r.t. all the characters in arrow head plant and spider plant, whereas, in boat lily, plants grown under vermiculite and plants sprayed with foliar nutrients showed better results.

Parametric Study of an Earth-Air Heat Exchanger Assisted by a Green Wall for Passive Cooling in Hot Climates

Cooling of buildings during summers in hot climates is an important issue for architects and builders and in terms of energy consumption, residential and tertiary buildings are among the highest consumers. This paper presents a numerical study, focused on a new design for a passive cooling system that uses an earth-air heat exchanger (EAHE), which was assisted by a green wall/air heat exchanger (GAHE) in hot climatic conditions. The tubes buried in the ground and the shadow of a vertical green wall offer considerable advantages for saving energy. The depth of the pipes in the ground was calculated by taking into account the physical properties of the soil. A parametric study was carried out by taking into account the pipe diameter, pipe length, pipe depth in the ground, and the velocity of air in the pipes. The vertical pipe in the green wall allowed a significant additional drop in the air temperature at low air velocities or small pipe depths in the ground. This means that shorter pipe lengths can be used in the earth-air heat exchanger to keep the air outlet temperature of the same order. For an earth air heat exchanger assisted by a green wall operating in hot climates, the design and operation parameters recommended are; pipe diameter 120 mm, length of the buried pipe 4 m, depth in the ground 30 m and air velocity 1 m/s.

The impact of urban green infrastructure as a sustainable approach towards tropical micro-climatic changes and human thermal comfort

Green infrastructures such as living walls are technological solutions to replace the declined greenery at urbanized environment and also reliable applications for thermal regulation in buildings through insulation effect and escalates the energy use efficiency. Thermal comfort and local climate are spatiotemporally variable. The existing research gap should be addressed by evaluating the performance of vertical green walls in tropical condition. In this study, thermal performance, relative humidity (RH) and CO2 concentration were quantified for basic three types of green infrastructures; such as (T1) living walls, (T2) indirect green façades and (T3) direct green façades located in Colombo metropolitan in Sri Lanka. An in-situ experimental study was conducted considering temperatures at 1 m and 0.1 m distance in front of the green walls, inside the foliage, air gap and external wall surface comparatively to adjacent bare wall control. Three case studies per green infrastructure within Colombo metropolitan area were purposively selected. Simultaneously, RH and CO2 concentration at 0.1 m in front of the green and bare walls were measured for the performance quantification. The internal thermal comfort simulation and occupants’ satisfaction questionnaire survey was executed to assess the green infrastructure performances. The study revealed that vertical greenery systems were highly effective on external wall surface temperature reductions at 1100 h–1500 h time zones. T1 and T2 accounted for superior temperature reduction in the range of 1.61 °C–1.72 °C through the façade relative to the distance than T3. Maximum temperature reduction compared to the bare wall control was obtained for the T1 (0.28 °C–8.0 °C) followed by T2 (1.34 °C–7.86 °C) and T3 (1.34 °C–6.64 °C). Averaged RH increment (1.6%–1.81%) and CO2 reduction (0.63%) occurred near green walls at day time compared to control. An average 28 °C simulated indoor temperature circumstantiate the indoor thermal comfort. 58% and 89.5% occupants’ were satisfied with thermal and visual comfort respectively, thus emphasizing façade greening as a sustainable approach on micro climatic changes and human thermal comfort.

An experimental method to quantitatively analyse the effect of thermal insulation thickness on the summer performance of a vertical green wall

Green façades and walls greatly contribute to reducing solar gains and dispersion through the building envelope. This implies a lower energy load for both heating and cooling and the mitigation of thermal conditions in outdoor areas. Despite this, more studies are needed regarding the influence of these systems on the thermal behaviour of insulated façades. In this manuscript, we report the results of experimental research carried out on a vertical green wall in a continental Mediterranean climate. The main goal of the research is to establish a thickness above which the behaviour of the green façade becomes isothermal and its performance do not improve. To this end, we analyze and evaluate the effect of insulation thickness on the energy performance of a green wall using a new methodology called green façade optimization (GFO). Comparing the simulations to experimental data, collected in a full-scale experimental box during the summers of 2011 and 2012, allowed the model to be validated. The results show that a green wall acts as a passive cooling system when the façade is moderately insulated, up to an insulation thickness of 9cm, above which more insulation becomes redundant and inefficient.

Quiet environment: Acoustics of vertical green wall systems of the Islamic urban form

The development of sustainability has made the application of green concepts to cityscapes and urban design mandatory and has popularized the installation of vegetation on external street walls. Introducing greenery on external building elements is beneficial to the environment, reducing the heat impact experienced in “urban heat islands” and enhancing an area's visual effect. The popularity of such green systems has necessitated the assessment of their acoustic characteristics and their impact on long-distance noise propagation. These effects become important in hot climates, where the topology of the dense urban texture gives building walls larger areas than exposed streets, thereby amplifying the effects of the former's acoustic characteristics on noise levels. Considering the resultant sound level at a particular location between buildings as the contribution of several remote sources, a simplified computer model based on energy exchange is developed in this study. Owing to the complexity of the urban landscape, buildings are assumed to be an array of rectangular blocks. The computer model is used to investigate the effects of the installation of street vertical vegetation on long-distance noise propagation, as well as those of the geometric parameters of the dense Islamic urban texture on the resultant noise levels.