Search

Walls overgrown with plants can have a positive impact on urban comfort and contribute to biodiversity in the city. In particular, quay walls, thanks to their close contact with water, have the potential to be ecologically engineered to encourage the growth of herbaceous plants. Different factors can affect growth of vegetation on walls. This research aims at experimentally investigating the effect of several variables, including quay wall design, building materials and environmental conditions, on receptivity of brick masonry quay walls for herbaceous plants. To this scope, ten quay walls (size 2 m × 2 m x 0.43 m), have been built and placed in a canal in the city of Breda (the Netherlands). The survival and growth of vegetation and the moisture content in the wall were monitored during a period of about 2 years. The results show that the presence of a layer of soil substrate with high capillary suction, positioned in between the masonry cladding and the concrete structure of the wall, has the most relevant positive effect on vegetation growth on the masonry. Mortar composition and irregularities of the wall surface influence bio-receptivity too, but to a less extent; orientation had only a limited effect. Moreover, the strategy of using a mechanically strong bedding mortar in combination with a weaker but more bio-receptive pointing mortar has proven successful at favouring growth of herbaceous plants, while providing sufficient strength to the masonry.

The process of rapid urbanisation is becoming problematic due to the reduction in, and lack of compensation of, previously vegetated areas. With a combination of green roofs and green walls, adopted on a large scale, it is possible to attenuate the urban heat island effect and internal temperatures in buildings. Tall buildings are becoming a common housing type in many cities, and considering the role of external walls in heat gain, it is expected that the combination of green roofs and green walls have great potential to improve thermal performance. As only 1-2% is added to the total stock of buildings annually, the focus should be on the retrofit of existing buildings to deliver maximum thermal benefits. In the present work lightweight, modular vegetated systems were adopted for roofs and walls. Instead of considering only the temperature influence in heat stress, this research adopted the use of heat index that encompasses the combined effect of temperature and relative humidity. For this purpose, the thermal benefits of green roof and green wall retrofit is evaluated in two small scale experiments, where identical prototypes (vegetated and non-vegetated) are compared using block work and timber framed drywall structures for Rio de Janeiro, Brazil and Sydney, Australia, respectively. The results show a different understanding in heat stress evaluation regarding heat index rather than temperature itself, especially under high levels of relative humidity. This evidence demonstrates green roof and green wall retrofit offer a proven role in heat stress attenuation in residential buildings.

Green walls are increasingly being considered as a suitable greywater treatment technology. Nevertheless, until now there have been no clear recommendations for the use of effective lightweight media in greywater treating green walls. Previous studies of potentially suitable growing media have suggested that a combination of perlite and coco coir might be the most effective for these novel systems. However, there is no clear understanding of what proportion of perlite and coir should be used and how different mixes would affect greywater treatment. This work tested the hydraulic and pollutant removal performance of six different perlite and coco coir media mixes in an unvegetated column experiment. The results suggested that there is a point between 2:1 and 3:1 ratios of perlite to coir where the infiltration rate significantly increases, as the result of perlite dominance. As the infiltration rate increases, the mix gets less prone to clogging, but this negatively affects pollutant removal performance, with insufficient time for biological processes. We therefore optimised the mix for effective long-term treatment of total suspended solids, total nitrogen, chemical oxygen demand and Escherichia coli. Unfortunately, total phosphorus removal from greywater was limited for all tested mixes. This study also showed that attention should be given to greywater inflow dynamics and expected daily water treatment capacity; e.g. systems with a lower hydraulic loading were able to use greater proportion of coir in the mix achieving greater water treatment performance, while systems with higher hydraulic loadings require faster flowing mixes with lower coir proportion.

Green facades can represent a sustainable solution for construction of new buildings and for retrofitting of existing buildings, in order to reduce the energy demands of the cooling systems, to mitigate the urban heat island and to improve the thermal energy performance of buildings. Green facades can allow the physical shading of the building and promote evapotranspiration in summer, and increase the thermal insulation in winter. An experimental test was carried out at the University of Bari (Italy) for two years. Three vertical walls, made with perforated bricks, were tested: two were covered with evergreen plants (Pandorea jasminoides variegated and Rhyncospermum jasminoides) while the third wall was kept uncovered and used as control. Several climatic parameters concerning the walls and the ambient conditions were collected during the experimental test. The daylight temperatures observed on the shielded walls during warm days were lower than the respective temperatures of the uncovered wall up to 9.0 °C. The nighttime temperatures during the cold days for the vegetated walls were higher than the respective temperatures of the control wall up to 3.5 °C. The thermal effects of the facades at daytime was driven by solar radiation, wind velocity and air relative humidity. The highest cooling effect of such parameters occurred with a wind speed of 3–4 ms−1, an air relative humidity within the range 30–60% and a solar radiation higher than 800 Wm−2. The long-term experimental test demonstrated that both Pandorea jasminoides variegated and Rhyncospermum jasminoides are suitable for green facades in the Mediterranean climatic area. The results shown in the present research allow to fill the gap in literature concerning the lack of data for all the seasons of the year, in order to obtain a complete picture of the building thermal performance in the Mediterranean climate region.

Microclimate knowledge has been intensively integrated into urban planning and design to improve the buildings’ energy performance and outdoor thermal comfort. To assess the climatic mitigation strategies, numerical modeling is gaining higher relevance. ENVI-met, a microclimate model to simulate the complex surface-vegetation-atmosphere interactions in the built environment, is receiving increasing popularity. This study aims to systematically evaluate the thermal-radiative performance of the ENVI-met model based on its recent updates. First, a field measurement was conducted in a subtropical city. Thermal-radiative parameters were collected besides three green infrastructure (GI) typologies (i.e., green roof, green wall, ground tree) and three corresponding reference sites. Second, sensitivity tests were conducted for the inputs and settings of ENVI-met model, including new radiation module IVS (Indexed View Sphere), meteorological boundary conditions, materials settings, and output intervals. Third, the thermal-radiative performance of ENVI-met was compared among the six measurement sites, three output intervals, and nine microclimate variables, based on four evaluation metrics. The results showed that 1) recent updates of ENVI-met can improve the estimation accuracy, especially with IVS on, radiation forcing, and localized materials settings; 2) ENVI-met was capable of simulating the thermal-radiative performance of three GI typologies simultaneously; 3) mobile measurement can be used for ENVI-met validation, and 4) model evaluation results were sensitive to the metrics. Overall, this study emphasized proper validation for ENVI-met before applications, when full forcing and localized settings are essential. The strengths and limitations of ENVI-met were discussed and implications were provided for model developers and users.

Covering buildings with vegetation systems has been a significant feature of architectural design towards sustainability in recent years. This study reports an investigation on the green wall thermal performance compared to the bare wall on the northern facade of a 2-story residential building in the humid climate of Rasht during summertime. For experimental measurements, temperature and humidity data loggers were used for real-time data collection. Thereafter, an existing building was modeled in EnergyPlus for validation purposes. According to the results, a decrease in temperature and relative humidity was seen in the case of the building with a green wall. It was found that the green wall could drop the indoor temperature by 9% and also decrease the relative humidity level by 32%. Besides, in order to predict the green wall performance in a short time interval, a deep artificial neural network was trained from the experimental data and a 15-day weather dataset was collected and fed into the deep learning model. Moreover, the ENVI-met software is utilized to evaluate the effect of the green wall on the surrounding air. Findings indicated that the temperature in front of the green wall is slightly lower than the part of the wall without the plant. The highest temperate reduction was 0.36 °C at 12 p.m., which is insignificant.

Social change due to COVID-19 has had negative impacts on the mental health of people who live indoors. One of the possible solutions to these problems is to introduce biophilic design. Among the elements of this design, green walls are often favored due to their spatial efficiency. This study investigated the effectiveness of green walls in relieving stress indoors. First, the stress level of the occupants of an indoor space that has green walls was measured. Then their psychological and physiological responses to the green walls were analyzed. To this end, using virtual reality, an experimental condition was set up in which a green wall was installed, and the stress level of the subjects was analyzed based on their state-trait anxiety (STAI), heart rate variability, electrodermal activity (EDA), and electroencephalogram (EEG). Twenty-seven subjects were recruited and the changes in their psychological and physiological responses when their environment changed from a non-green wall condition to a small to large green wall condition were measured. The results showed statistically significant differences in STAI, EDA, the relative alpha power in the parietal and occipital lobes, mental stress, and mental fatigue. Ultimately, the small green wall had a more significant relaxing effect. On the other hand, in the indoor space with a large green wall, the stress level of the residents increased. Thus, when installing a green wall in an indoor space, a small green wall is proposed.

Thermal benefits of tropical climber green walls deserve more in-depth studies. A field experiment was designed in humid-subtropical Hong Kong to assess microclimatic effects of plant species, orientation and weather condition. In-situ measurements of air and surface temperatures of the indoor and outdoor environment were conducted respectively on the northeast and northwest oriented wirerope climber green walls with different air-gap depth. Adjacent bare walls were monitored as experimental controls. Days with sunny, cloudy and rainy weather in summer 2016 were chosen based on field-monitored incident solar radiation. The daytime and nighttime mean temperatures of the sampled days were evaluated statistically by t -test, analysis of variance (ANOVA) and Mann-Whitney U test. The best cooling benefits were realized at external building surface at 3.49, 0.52 and 1.19 °C respectively in sunny, cloudy and rainy weather during daytime. The respective values were 0.78, 0.05 and 0.03 °C during nighttime. Sunny weather featured more substantial external air and surface cooling, but indoor warming was recorded in cloudy and rainy weather. The northeast green wall achieved greater external air and surface cooling than the northwest one respectively by 0.38 and 0.77 °C in sunny weather. However, the northwest green wall registered higher external surface cooling by 0.47 °C at night. These results suggested the importance of research-informed green wall design for effective thermal regulation in urban areas. A deep air gap between the vegetation and the exterior building wall would provide more external surface cooling. Walls receiving higher solar exposure could be prioritized for greening.

© 2017 Elsevier Ltd Indoor air quality has become a growing concern as people are spending more time indoors, combined with the construction of highly sealed buildings that promote thermal efficiency. Particulate matter (PM) is a common indoor air pollutant, with exposure to high concentrations associated with several detrimental health outcomes. Active botanical biofilters or functional green walls are becoming increasingly efficient and have the potential to mitigate high suspended PM concentrations. These systems, however, require further development before they become competitive with industry standard in-room air filters. Whilst the plant growth substrate in active biofilters can act as a filter medium, it was previously not known whether the plant component of these systems played a function in PM filtration. This study thus examines the influence of the botanical component on active green wall PM single pass removal efficiency (SPRE), with a focus on evaluating the air filtration features of different plant species in green wall modules. All tested botanical biofilters outperformed biofilters that consisted only of substrate. Green walls using different plant species had different single pass removal efficiencies, with fern species recording the highest removal efficiencies across all measured particle sizes (Nephrolepis exaltata bostoniensis SPRE for PM0.3-0.5 and PM5-10 = 45.78% and 92.46% respectively). Higher removal efficiencies were associated with increased pressure drop across the biofilter. An assessment of plant morphological data suggested that the root structure of the plants strongly influenced removal efficiency. These findings demonstrate the potential to enhance active botanical biofiltration technology with appropriate plant species selection.

During the last decade, vertical greenery systems are increasing their presence in building designs, providing several urban ecosystem services. One of them is the potential to provide energy savings in buildings, which develops an important role, however, data about its performance during winter periods is still scarce. Therefore, the main objective of this paper is to compare at real scale the thermal performance of two different vertical greenery systems implemented in experimental houses-like cubicles for both cooling and heating periods. A double-skin green facade has been installed in the first cubicle that uses deciduous creeper plants, while the second one is designed with green walls made with evergreen species. Finally, a third identical cubicle without any green coverage is used as reference. Two different types of experiments have been carried out to test the performance of the house like-cubicles. One consists of controlling the internal ambient temperature providing heating or cooling to maintain the desired comfort conditions. On the other hand, to study the thermal response of the construction system, the heating, ventilation and air conditioning system was disconnected and the cubicles were tested under free floating condition. First results showed a high potential for energy savings during cooling season for green wall (58.9%) and double-skin green facade (33.8%) in comparison to the reference system. On the other hand, for heating periods no extra energy consumption was observed for evergreen system. The work partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER), ENE2015-64117-C5-3-R (MINECO/FEDER) and ULLE10-4E-1305) in collaboration with the company Buresinnova S.A (C/Saragossa, 95 Entsol 3a, 08006 BARCELONA). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123) and to the city hall of Puigverd de Lleida. This study has received funding from the European Commission Seventh Framework Programme (FP/2007–2013) under Grant agreement Nº PIRSES-GA-2013-610692 (INNOSTORAGE) and from European Union's Horizon 2020 research and innovation programme under grant agreement Nº 657466 (INPATH-TES). Alvaro de Gracia would like to thank Ministerio de Economia y Competitividad de España for Grant Juan de la Cierva, FJCI-2014-19940. Julià Coma would like to thank the Departament d'Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya for his research fellowship.

In metropolitan cities like Hong Kong, residential buildings are mostly high-rise developments. These buildings do not have external insulation. In sub-tropical regions with mild winter heat loss from buildings in winter is insignificant and hence heat transfer from the interior of the building is low. Heating systems are rarely installed. However, heat transfer through the external facade into the interior is high in summer necessitating air-conditioning for thermal comfort and consuming large amounts of electrical energy. Vertical greenery, installed to the external walls of buildings, has been proved to be a good insulation system. This research studied the feasibility of applying a double-skin green facade, to high-rise residential buildings in Hong Kong in order to reduce energy consumption for cooling in hot and humid summer. The study concluded that substantial energy saving is possible. Further research on the application of vertical green wall systems to high-rise residential buildings is recommended.

Green walls can act as natural thermal regulators, reducing solar radiation on surfaces and providing cooling due to shading and evapotranspiration. Several studies have investigated the cooling effects of a bare wall, in contrast to a vegetated wall, as well as the correlation between temperature reduction and system characteristics. In the present work, we analyze the influence of the orientation of a green wall on its ability to reduce surface temperatures in a Mediterranean climate. Environmental variables such as irradiation and air temperature have been considered. A real-time monitoring system has been used, with a database of three years of measurements. Results show that on average, the control temperature is greater than the green wall temperature with maximum differences of 20 °C in summer and 8 °C in winter in the south wall surface. During the summer, the temperature reduction in the south facade occurs mainly in the central hours of the day, while in the west facade it occurs mainly in the afternoon. Being the summer the most relevant season for the use of green walls, this information is very valuable as it allows the designers to know at what time of day the facade provides a temperature reduction, depending on the orientation.

Covering a building envelope with vegetation provides a solution capable of mitigating the urban heat island phenomenon and its impact on the energy consumption of buildings. Simulation tools to assess the efficiency of such a solution are lacking, especially for green walls. The present research aims to offer a hydrothermal model of green walls and green roofs for implementation in the urban microclimate simulation software SOLENE-Microclimate . To this end, a fast, efficient coupled heat–mass transfer model has been developed. Simulation results are compared with experimental data obtained from the LEEA Laboratory in Geneva for three green wall samples. Aside from the level of uncertainty found for the evapotranspiration calculation, these results confirm that the model accurately characterizes the temperature evolution of all three prototypes. Results also show good correlation between measured and simulated temperatures. The model is indeed able to reproduce water stress and characterize various types of living walls.

Green walls provide an option for reducing the thermal load on buildings, reducing the requirement for mechanised air conditioning and helping to mitigate urban heat islands. The range and extent of benefits can vary with green wall typology. This research investigated green facades utilising wall shrubs and climbing plants to reduce air temperature adjacent to, and surface temperatures of, brick walls. Artificial wall sections were used to provide replicated data sets in both outdoor and controlled environmental conditions. During periods of high solar irradiance outdoors, the presence of live Prunus laurocerasus plants placed against walls significantly reduced air and surface temperatures compared to blank walls, but also in comparison to excised (non-transpiring) plant sections. Largest temperature differentials were recorded mid-late afternoon, where air adjacent to vegetated walls was 3°C cooler than non-vegetated walls. Prunus also provided significant wall cooling in controlled environment studies, but was intermediate in its surface cooling capacity (6.3°C) compared to other species; Stachys and Hedera providing >7.0°C cooling. When evaluated on a per leaf area basis, however, other species demonstrated greater cooling potential with Fuchsia, Jasminum and Lonicera out-performing others. Not only was it evident that different species varied in their cooling capacity, but that the mechanisms for providing wall cooling varied between species. Fuchsia promoted evapo-transpiration cooling, whereas shade cooling was more important in Jasminum and Lonicera. Plant physiology and leaf area/morphology should be considered when selecting species to maximise cooling in green wall applications. © 2013 Elsevier Ltd.

An experimental approach is used to assess the effect of vegetation on the thermal performance of a vertical greening system, which comprised of turf-based vertical planting modules, on an elevated facade wall of a public housing apartment. Despite temperature fluctuations in the various compartments external and internal to a concrete wall, the vegetated cladding reduced interior temperatures and delayed the transfer of solar heat, which consequently reduced power consumption in air-conditioning compared with a building envelope with bare concrete. Vegetation cover led to a different pattern of temperature fluctuations on wall surfaces, which may affect the comfort of occupants even after sunset. The cooling effect which was closely associated with the area covered by living plants and moisture in the growth medium, demonstrated the value of maintaining a healthy vegetation cover beyond visual amenity. Marked variation in moisture distribution along the vertical profile of the growth medium highlighted a concern rarely addressed in planting on ground. Substrate moisture measured at randomly selected locations would underestimate the water stress in some plants and impair their survival.

The aim of the present work is to analyse thoroughly the influence of the orientation and proportion (covering percentage) of plant-covered wall sections on the thermal behaviour of typical buildings in the Greek region during the summer period. As to the effect of construction parameters, the layer position of masonry/insulation has been also considered. The investigation has been carried out using a thermal-network model that adequately simulates the building zone under assumption; its validation was based on experimental results from a recently reported study. The model makes provision for several heat-flow paths in order to take into account the leaf cover on the external wall surface, heat transfer through the surfaces that constitute the building envelope, and natural ventilation. The influence of orientation and covering percentage of plant foliage for walls with different configurations was studied using representative outdoor environmental data for the zone location at a specific time period.

This research involves the study of 8 different vertical greenery systems (VGSs) installed in HortPark to evaluate the thermal impacts on the performance of buildings and their immediate environment based on the surface and ambient temperatures. VGSs 3 and 4 have the best cooling efficiency according to the maximum temperature reduction of the wall and substrate surfaces. These results point to the potential thermal benefits of vertical greenery systems in reducing the surface temperature of buildings facades in the tropical climate, leading to a reduction in the cooling load and energy cost. In terms of the lowest diurnal range of average wall surface temperature fluctuation, VGSs 4 and 1 show the highest capacities. No vertical greenery system performs well in term of the diurnal range of average substrate temperature fluctuation. By limiting the diurnal fluctuation of wall surface temperatures, the lifespan of building facades is prolonged, slowing down wear and tear as well as savings in maintenance cost and the replacement of facade parts. The effects of vertical greenery systems on ambient temperature are found to depend on specific vertical greenery systems. VGS 2 has hardly any effect on the ambient temperature while the effects of VGS 4 are felt as far as 0.60 m away. Given the preponderance of wall facades in the built environment, the use of vertical greenery systems to cool the ambient temperature in building canyons is promising. Furthermore, air intakes of air-conditioning at a cooler ambient temperature translate into saving in energy cooling load.

There is a rapidly expanding market for green building materials. Such materials are intended to be environmentally friendly, with such characteristics as low toxicity, minimal chemical emissions, ability to be recycled, and durability. In addition, green materials often contain recycled and/or bio-based contents. Consequently, some green materials may undergo significant oxidation with potential for reduction of indoor ozone. In this study, 48-L electro-polished stainless steel chambers were used to study the reactive consumption of ozone by ten common green wall, flooring, ceiling, and cabinetry materials (perlite-based ceiling tile, unglazed ceramic tile, natural cork wall-covering, aluminum tinted cork wall-paper, bamboo, UV-coated bamboo, wheat board, UV-coated wheat board, sunflower board, and UV-coated sunflower board). Ozone removal was quantified in terms of deposition velocity and reaction probability. Ozone removal decreased with time after initial exposure, but for several materials the ability to react with ozone was regenerated after a period of zero ozone exposure. Test materials found to have the highest ozone reaction probabilities were a perlite-based ceiling tile, natural cork wall-covering, and wheat board.

This paper discusses the thermal effect of covering the building envelope with vegetation on the microclimate in the built environment, for various climates and urban canyon geometries. A two-dimensional, prognostic, micro scale model has been used, developed for the purposes of this study. The climatic characteristics of nine cities, three urban canyon geometries, two canyon orientations and two wind directions are examined. The thermal effect of green roofs and green walls on the built environment is examined in both inside the canyon and at roof level. The effects of this temperature decrease on outdoors thermal comfort and energy savings are examined. Conclusions are drawn on whether plants on the building envelope can be used to tackle the heat island effect, depending on all these parameters taken into consideration.

Thermal regulation is a key ecosystem service provided by urban plants. In addition to summer cooling, plants can insulate buildings against heat loss in winter. Research was conducted over two winters using replicated small-scale physical models to simulate heat loss from a built structure and to investigate the insulation properties of plants during cold weather. Brick cuboids were constructed around a water tank maintained at 16 °C and energy use monitored. Covering cuboids with ivy (Hedera helix) reduced mean energy consumption by 21% compared to bare cuboids during the first winter (means of 4.3 and 5.4 kWh per week, respectively). During the second winter, when foliage was more extensive a 37% mean saving was achieved (3.7 compared to 5.9 kWh per week). The presence of Hedera enhanced brick temperatures significantly compared to bare walls. Temperature differences were affected by weather parameters, aspect, diurnal time and canopy density. Largest savings in energy due to vegetation were associated with more extreme weather, such as cold temperatures, strong wind or rain. Under such scenarios green facades could increase energy efficiency by 40–50% and enhance wall surface temperatures by 3 °C. These empirical studies with replicated treatments augment previous research based on urban modelling and data from non-replicated individual buildings in situ. They indicate that planting design requires more attention to ensure the heat saving aspects associated with green facades and shelter belts are optimised. These aspects are discussed within the context of wider urban ecosystem services provided by vegetation, and implications for climate change mitigation.