Outdoor Test Research Articles

Tree rings-inspired 3D solar evaporator fabricated by rolling polypyrrole decorated waste cotton fabric for efficient desalination

Interfacial solar steam generation (ISSG) has drawn considerable interest as an emerging technology for seawater desalination. However, designing simple and cost-effective solar evaporators with high salt resistance and impressive evaporation rates remains a significant challenge. Inspired by tree rings, a three-dimensional (3D) solar evaporator (PPy-RWCF) was fabricated by rolling polypyrrole-decorated waste cotton fabric (PPy-WCF) into a cylinder. The synergistic effect of polypyrrole (PPy) and interstices within the waste cotton fabric (WCF) allows the PPy-RWCF to absorb around 99.00 % of sunlight. The PPy-RWCF, with an exposure height of 3 cm, achieves an excellent evaporation rate of 2.36 kg m−2 h−1 under 1-solar intensity. Besides, the vertical water channels within PPy-RWCF allow rapid solution transport, enabling it to withstand 20 wt% brine with an evaporation rate of 2.05 kg m−2 h−1. Prolonged outdoor desalination testing has demonstrated that a 1 m2 PPy-RWCF can generate approximately 10 kg of freshwater daily. This study proposes a sustainable approach to the development of solar evaporators utilizing WCF for desalination of high-salinity water.

Bioinspired Diffuse Reflectance Coatings for Fabric-Based Radiative Coolers

As global temperatures rise due to anthropogenic climate change, thermal comfort becomes an increasingly critical area of research. While most buildings are equipped to cool and heat their interiors, this process is very energy intensive; a smarter approach is to enable personal thermal management using clothing and textiles. In particular, we are interested in the ability to use textiles and clothing to cool bodies in extreme heat, both to maintain comfort and prevent deaths in urban deserts due to heat stroke. One innovative category in this realm is radiative coolers—surfaces adept at manipulating light to passively regulate temperature. These coolers achieve sub-ambient surface temperatures by selectively reflecting or refracting sunlight wavelengths (200nm-2.5µm) while emitting infrared light (8-13µm). This unique capability allows them to maintain cooler temperatures, even when exposed to direct sunlight and the open sky. Coatings facilitating this cooling action typically consist of a porous media filled with refractive gaps, requiring specific substrates and custom production processes, thereby limiting their applications. Furthermore, the necessity of low light transmission presents issues in creating fabrics that radiatively cool while still retaining high breathability and durability. In this study we present a method whereby an optically active coating comprised of a mixture of CaCO3 and BaSO4 microcrystals was applied to multiple fabric substrates to create a radiative cooler. Through the use of photoinitiated chemical vapor deposition (pICVD), a 5 µm thick layer of a hydrophilic polymer polyhydroxyethyleneacrylate (pHEA) was deposited on the fabric substrate. Subsequently, through serial immersion in solutions containing Ca and Ba ions and solutions containing CO3 and SO4 ions, inorganic microcrystals were grown directly on the surface of the fabric. These microcrystals formed with a large polydispersity, endowing the coating with excellent reflective properties in the solar spectrum. Mie scattering calculations confirmed that the CaCO3 and BaSO4 microcrystals were primarily responsible for scattering. Further simulations using finite difference time domain software revealed, surprisingly, that surface-immobilized crystals provided the highest reflection efficiency, indicating that composite fibers with embedded particles are not as efficient. Upon outdoor testing, the device showed a cooling ability of 8°C compared to an uncoated fabric, achieving a maximum cooling of 4°C below ambient temperature. Washing and durability testing of the coating found no degradation in the material's performance, affirming its resilience and long-term effectiveness.

Enhanced hydrophilicity and stability of carbon-based aerogel with assembling of halloysite nanotubes and silica fibers for efficient solar seawater evaporation and desalination

Solar vapor generation has emerged as a sustainable technique for seawater evaporation and desalination. Integrating high hydrophilicity, strong light absorbance, good salt resistance, fast water transfer and good structural stability simultaneously in one evaporator at low cost for achieving cost-effective evaporation and long-term utilization is highly desirable but still challenging. Herein, an eco-friendly and low-cost aerogel (CSH) with natural chitosan, halloysite nanotubes and silica fibers was prepared by freeze-casting, which was then carbonized to construct a robust aerogel (cCSH) as evaporator. The cellular structure of cCSH aerogel with microchannels enables fast water transfer and rapid salt dissolution, the carbonized chitosan favors enhanced light absorption, the halloysite assembled on the walls endows the aerogel with excellent hydrophilicity, and the silica fibers penetrating the multilayer guarantee good structural stability. As expected, the prepared evaporator (cCSH200) exhibits remarkable evaporation rates of 2.49/7.20 kg·m−2·h−1 under one/four sun, respectively, exceeding most biomacromolecule-derived aerogels. Besides, it displays outstanding salt resistance, wastewater purification ability and long-term cycle stability. Outdoor test further substantiates the admirable evaporation performance, long-term durability and enormous application prospect of the cCSH200. This work affords a low-cost tactic for the development of efficient evaporator for solar-driven seawater desalination and wastewater treatment.

Fabrication of passive cooling fabric as thermal management curtain for building energy-saving

In the past years, a great deal of attention has been paid to passive cooling envelope materials or smart windows to cope with the increase in building energy consumption due to global warming. However, combining curtains with passive cooling could enable on-demand thermal management based on its dynamically adjustable characteristics. Herein, a superhydrophobic passive cooling cotton fabric with low thermal conductivity (0.0342 W/mK), high solar reflectivity (0.9280) and high infrared emissivity (0.9698) was obtained by wrapping the cotton fabric with a porous SiO2/poly(vinylidene fluoride-hexafluoropropylene) composite coating via solvent exchange phase separation and sanding. The superhydrophobic passive cooling fabrics realized an average of 10.3 °C cooling during the daytime and showed impressive passive cooling performance relative to the pristine cotton. Notably, the superhydrophobic passive cooling fabric demonstrated superior daytime cooling and nighttime insulation performance during outdoor testing and energy consumption simulations compared to commercial curtains. Therefore, superhydrophobic passive cooling cotton fabrics as curtains allow for reducing the energy consumption in building thermal management and broadening the practical application of radiative cooling materials.

Self-Cleaning Solar Mirror Coatings: From the Laboratory Scale to Prototype Field Tests

In this study, a low-cost, scalable and robust process is proposed as an innovative method for coating solar mirrors with a self-cleaning, transparent in the full solar range and versatile material based on auxetic aluminum nitrides, previously obtained at the laboratory scale. This work presents the scaling-up of the fabrication process from the laboratory to prototypal scale and the preliminary results of outdoor self-cleaning solar mirror field tests in the demonstrative concentrating solar power (CSP) plant ENEASHIP located in Casaccia (Rome) ENEA Research Center. Prototypes with a size of 50 × 40 cm have shown stability in external conditions: no coating degradation occurred during the test campaign. Their washing restores the initial reflectance affected by soiling and the self-cleaning performance allows for the utilization of a reduced quantity of water for cleaning operations with respect to the uncoated glass of back surface mirrors. A similar self-cleaning AlN coating could be utilized on other solar components affected by soiling, such as the glass envelopes in heat-collecting elements, PV panels and other parts where a self-cleaning performance combined with an optical one is required.

CuS and polydopamine-modified polyvinyl alcohol foam for steady interfacial solar desalination of high saltwater

Interfacial solar desalination generation (ISDG) presents a promising solution for obtaining freshwater from seawater. However, developing solar evaporators with robust salt resistance using simple methods to ensure consistent desalination performance remains a major challenge. In this study, we engineered a solar evaporator (CuS-PDA-PVAF) by modifying polyvinyl alcohol foam (PVAF) with polydopamine (PDA) and CuS using a straightforward solution immersion method. The incorporation of PDA and CuS enhances the sunlight absorption capability of PVAF to approximately 98 %, resulting in an evaporation rate of 1.44 kg m–2 h–1 under 1-solar intensity. The CuS-PDA-PVAF solar evaporator leverages the macroporous structure and excellent hydrophilicity, enabling it to withstand 15 wt% saltwater while maintaining a steady evaporation rate of about 1.17 kg m–2 h–1. Outdoor tests confirm that a 1 m2 CuS-PDA-PVAF can generate approximately 5.6 kg of freshwater daily. This solar evaporator, designed simply and resistant to salt, possesses substantial potential for alleviating freshwater scarcity.

Turning trash into treasure: Integrating waste MXene sediment with bagasse into photothermal composite aerogel for efficient solar-driven interfacial evaporation

Solar-driven interfacial evaporation (SDIE) technique holds significant potential in addressing the global freshwater scarcity issue. Using waste resources to construct an evaporator is the promising choice for SDIE with low energy consumption, low cost, and sustainability. Herein, an aerogel photothermal evaporator composed of waste MXene sediment (WM) and bagasse-derived cellulose was demonstrated. WM was a mixture of outstanding light absorption and photothermal conversion. Cellulose served as the skeleton. Besides, the ordered vertical microchannel array within the aerogel evaporator (WM/BCA) was successfully fabricated using a super-frozen ice crystal as a template during the directional freeze process. The excellent photothermal characteristic of WM and the unique microstructure of aerogel endowed the high light absorption, superior hydrophilicity, rapid water transport, and salt reflux of composite evaporator. Benefiting from the above advantages, the optimal sample (WM/BCA-3) demonstrated excellent water evaporation, desalination ability, and long-term stability. Furthermore, the effect of aerogel evaporator size on evaporation was investigated. The evaporation rate was enhanced to 2.03 kg·m−2·h−1 (deionized water as source) with 94.5 % solar efficiency through the reduction in diameter of the aerogel evaporator, while an increase in the number of aerogels facilitated an improvement in vapor yield. Finally, an outdoor test exhibited the practical application potential of composite aerogel in freshwater production. This work presents a promising approach to constructing and optimizing an efficient solar-driven interfacial evaporator using waste materials.

Comparative Assessment of the Durability of Glass and Polymer Mirrors for Concentrated Solar Thermal Technologies

This paper describes experimental work that has been carried out to assess the durability of glass and polymer mirrors against erosion and soiling phenomena. Both outdoor and indoor tests have been performed and the results show that polymer mirrors are quickly degraded in comparison to glass. Soiling deposition has been simulated using a soiling test rig developed for laboratory use. Results show that polymer mirrors, due to their high roughness and their surface energy properties, can accumulate more soiling on their surface generating a higher drop in specular reflectance compared to glass mirrors. Contact cleaning processes have also been simulated on polymer mirrors and the results show that using a hard brush, even at low speed with rotational motion, causes significantly more degradation than a soft brush.

Water-efficient evaporative cooling by sunlight-reflective radiative-cooling nanofibers

Evaporative cooling, which has the highest potential for energy transfer, is not sustainable without sufficient water. Here we present the membrane that can be used to protect the moisture from unnecessary evaporation. The membrane is composed of nanofiber non-woven fabric that is breathable and has high solar reflectance and high infrared emissivity for water-efficient evaporative cooling applications. The membrane prevents moisture from evaporating unnecessarily by blocking solar absorption and efficient thermal emission. Specifically, the membrane is composed of ∼400 nm diameter polyurethane fiber, which has a high MIE scattering effect on solar radiation (∼2500 nm wavelength), resulting in over 95% solar reflectance as well as over 95% of total infrared (IR) emissivity and IR transmittance at 50 g/m2 of membrane. In addition, it has sufficient breathability of over 16 mg•cm2•hr that the maximum evaporative cooling is about 100 W/m2. Twice the cooling time and 3 °C cooler surface by tandem of radiative cooling were confirmed in outdoor test of wet fabric covered with nanofiber membrane compared to wet fabric without membrane. This scalable and flexible membrane is applicable where the thermal cooling without energy consumption is required for net-zero energy consumption.

MODEL TESTING WITH WOOD MATERIALS IN INDOOR AND OUTDOOR USE

Wood is a natural material that is easy to find and can be used for building materials. A large number of types of wood causes errors in the selection of wood based on its use. This study aims to determine the reactions and changes that occur in the wood used in the model. This study used an experimental method carried out on wooden models through two indoor and outdoor placements. Indoor testing was carried out by placing the model in a closed room with an average room temperature of 24-33°C for 14 days, while outdoor testing was carried out by placing the model in an open space for 7 days. From the results of the analysis carried out, wood materials can be used indoors and outdoors. However, several factors related to wood’s type, nature, and quality must be considered. Some types of wood require special care such as coating the wood so that it can be used optimally outdoors.From these experiments, it can be concluded that wood has several types, and we must know the characteristics of wood according to its use.

Transforming waste polystyrene foam to carbon on zeolite for efficient solar water desalination

Solar-driven water evaporation was well-proven to be a sustainable technique for seawater desalination by using renewable energy. In this technology, carbon material is preferably chosen as a photothermal conversion material due to its excellent stability and corrosion resistance. However, the applicability of carbon-based materials was constrained by their poor mechanical strength and the high cost. In this paper, carbon coated sands and zeolites were prepared by using waste polystyrene foam (white pollution) as carbon source and this waste utilization method greatly reduces material costs. The solar-driven water evaporation device was fabricated by confining these carbon-coated composites in the PVA hydrogel. Owing to the superior light absorption (over 96 %) and good hydrophilicity for water transfer, the carbon-coated sand and zeolite exhibited maximum evaporation rate of 1.51 and 1.24 kg m−2h−1 under 1 sun illumination, respectively. In outdoor test, the maximum water collection rate was 0.92 kg m−2 h−1. It is possible to create an effective and environmentally beneficial solar interfacial water evaporation system with this approach.

Cellulose Metamaterials with Hetero‐Profiled Topology via Structure Rearrangement During Ball Milling for Daytime Radiative Cooling

AbstractPassive radiative cooling is a zero‐energy consumption approach, which can dissipate heat to outer space by emitting infrared radiation through the transparency window. Traditional cooling materials, such as photonic films, metafabrics, and polymer foams, still suffer from complex preparation processes and high costs. In this work, it is reported that natural cellulose can be converted into a “green” optical metamaterial by rational structure reconfiguration at the micro/nano level via scalable ball milling technology for efficient daytime radiative cooling. Specifically, fine‐tuning the shearing kinetics in the mechanochemistry process, cellulosic optical metamaterial (COM) with ≈98% solar reflectivity and ≈0.97 infrared emissivity has been successfully achieved, which can break through the theoretical value of photonic crystals as well as the conventional synthetic optical materials. The COMSOL simulation reveals that the excellent optical properties of the cellulose metamaterial are explained by the “confined scattering” effect caused by the rearranged heterostructure at the micro/nano level. Outdoor tests demonstrat that the COM‐based coating exhibits a daytime radiative cooling efficiency of 5.7 °C in hot Nanjing. Meanwhile, the COM can be produced into different scattering materials via spray coating, freeze casting, and solution casting technology. This study will facilitate the development of scalable and sustainable optical metamaterials for mitigating energy consumption.

Modifying a mini drone for remote drug delivery for wildlife medicine

Remote drug delivery is an essential tool for administering medication to wildlife. However, the conventional method, the dart gun, has limitations in terms of injection distance, posing risks for operators. This study aimed to modify a mini drone equipped with a dart syringe and delivery system for use with large wildlife. A commercial mini drone was modified to release a syringe dart using a vertical gravity-based delivery system. The performance of the drone and delivery system was evaluated based on accuracy to the target and penetration ability through pig skin. The evaluation compared a dart with or without a plastic shell, with tests conducted both indoors and outdoors. The results indicated that the higher the drone's flight, the more the dart tended to deviate from the target. In outdoor tests, a syringe dart without a shell showed greater accuracy than a dart with a shell. Regarding penetration ability, only a dart without a shell had a 100% success rate at a maximum height of 5 metres, with an overall statistical difference (P = 0.01). In conclusion, this study represents the first scientific validation of using mini drones for remote drug injections that could be used in large wildlife medicine.

Dual-functional tunable emitter with high visual transparency for energy saving and information encryption

Achieving thermal radiation regulation is attractive in the field of thermal management and information security. However, maintaining high visual transparency simultaneously is a challenging task, but it holds vital importance for applications such as smart windows and multispectral information encryption. Here, we designed and fabricated a multilayer film based on thermochromic material vanadium dioxide (VO2) with high transmittance (62.1 %) in visible region and excellent emissivity regulation (0.3) in mid-infrared region. Besides, quantities of energy saving simulations among 85 administrative districts in the United States and China and outdoor tests in Shanghai were done to verify the performance in different climates for the application of energy saving smart window. Furthermore, by taking advantage of its high transmittance in visible band and emissivity tunability in mid-infrared band, VO2-based multilayer film has demonstrated the enormous potential application for information encryption through a proof-of-concept validation. By presenting the novel strategy to achieve independent multispectral regulation, this work offers a solution for multidisciplinary fields including green buildings, adaptive multi-scenes camouflage and other information security.

Excellent self-cleaning surface achieved through the synergistic effect of superhydrophilicity and photocatalysis of PVDF-TiO2-HAP coating

With the increasing demand for living environment, high-performance self-cleaning coatings have become an urgent need in the development of new building industry. Herein, a TiO2-HAP-PVDF self-cleaning coating was successfully developed using a facile precursor mixing method, where porous hydroxyapatite (HAP) was used to facilitate the adsorption of pollutants, TiO2 served as photocatalyst to decompose pollutants, and polyvinylidene fluoride (PVDF) served as adhesive to combine TiO2 with HAP. Owing to the synergistic effect of superhydrophilicity and photocatalysis, the TiO2-HAP-PVDF coating displays outstanding self-cleaning performance. Furthermore, the as-fabricated coating attached to aluminum veneer not only resists mechanical abrasion such as rainwater, sand flow and sandpaper, but also exhibits good stability in the extremely temperatures from -196 to 150 °C, as well as in strong acid and alkaline solutions, and even presents satisfactory performance after 8000 hours of outdoor service test. These merits open exciting possibilities for the industrial application of self-cleaning coating.

Validation Scores to Evaluate the Detection Capability of Sensor Systems Used for Autonomous Machines in Outdoor Environments

The characterization of the detection capability assumes significance when the reliable monitoring of the region of interest by a non-contact sensor is a safety-relevant function. This paper introduces new validation scores that evaluate the detection capability of non-contact sensors intended to be applied to outdoor machines. The scores quantify, in terms of safety, the suitability of the sensor for the intended implementation in an environmental perception system of (highly) automated machines. This was achieved by developing an extension to the new Real Environment Detection Area (REDA) method and linking the methodology with the sensor standard IEC/TS 62998-1. The extension includes point-by-point and statistic-based error evaluation which leads to the Usability-Score, Availability-Score, and Reliability-Score. By applying the principle in the agricultural sector using ISO 18497 and linking this with data from a real outdoor test stand, it was possible to show that the validation scores offer a generic approach to quantify the detection capability and express this in a machine manufacturer-oriented manner. The findings of this study have significant implications for the advancement of safety-related sensor systems integrated into machines operating in complex environments. In order to achieve full implementation, it is necessary to define in the standards which score is required for each Performance Level (PL).

Performance evaluation of PUC7‐based multifunction single‐phase solar active filter in real outdoor environments: Experimental insights

AbstractThis paper presents a novel architecture to enhance the performance of grid‐connected photovoltaic (PV) systems through the introduction of several key novelties. Firstly, a packed U‐cell seven‐level (PUC7)‐based single‐phase solar active filter is implemented, offering a comprehensive solution for harmonics mitigation, reactive power compensation, and efficient power extraction from the PV source, while facilitating the injection of real power into the grid. Secondly, the p‐q power injection algorithm is modified to accommodate the extraction of solar power from the PV generator to the grid, simultaneously addressing the need for harmonic current injection to improve power quality. This modification ensures dynamic performance by extracting reference current with harmonic content and solar power information, thereby enhancing the system's overall efficiency. Lastly, the proposed architecture undergoes real outdoor testing, validating its performance in various key aspects including maximum power tracking, reduction of total harmonic distortion in comparison with previous work, operation at unity power factor, and testing the effective operation of the multifunction feature. These contributions collectively demonstrate the effectiveness of the proposed system in enhancing power injection quality and reactive power compensation under real outdoor conditions of PV systems connected to the grid.

Design and fabrication of porous three‐dimensional Ag-doped reduced graphene oxide (3D Ag@rGO) composite for interfacial solar desalination

Solar-driven interfacial desalination technology has shown great promise in tackling the urgent global water scarcity crisis due to its ability to localize heat and its high solar-to-thermal energy conversion efficiency. For the realization of sustainable saline water desalination, the exploration of novel photothermal materials with higher water vapor generation and photothermal conversion efficiency is indispensable. In the current study, a novel 3D interconnected monolithic Ag-doped rGO network was synthesized for efficient photothermal application. The Ultraviolet–Visible-Near Infrared (UV–Vis-NIR) and FTIR analyses demonstrated that the controlled hydrothermal reduction of GO enabled the restoration of the conjugated sp2 bonded carbon network and the subsequent electrical and thermal conductivity through a significant reduction of oxygen-containing functional groups while maintaining the hydrophilicity of the composite photothermal material. In the solar simulated interfacial desalination study conducted using 3.5 wt.% saline water, the average surface temperatures of the 3D material increased from 27.1 to 54.7 °C in an hour, achieving an average net dark-excluded evaporation rate of 1.40 kg m−2 h−1 and a photothermal conversion efficiency of ~ 97.54% under 1 sun solar irradiance. In the outdoor real-world application test carried out, the surface temperature of the 3D solar evaporator reached up to 60 °C and achieved a net water evaporation rate of 1.50 kg m−2 h−1 under actual solar irradiation. The 3D interwoven porous hierarchical evaporator displayed no salt precipitation over the 54-h period monitored, demonstrating the promising salt rejection and real-world application potential for efficient desalination of saline water.

Investigation of the effect of dimensional and non-dimensional parameters on the performance of pitch-varied staggered arranged dimple solar air heaters

In this study, the efficacy of a single pass, single glazed, five different types of absorber plate incorporated solar air heater (SAH) was experimentally examined in outdoor test conditions on alternative days. The experiment was carried out for flat plate solar air heater (FPSAH) and staggered arranged dimple imprinted absorber plate solar air heater (SDPSAH) maintained at four different pitch ratios (Pt/Pl: 1.0, 1.11, 1.25, and 1.67) by varying the air mass flow rate (ma) from 0.01-0.05 kg/s (corresponding Re range: 1971.66–10466.45). The results show that the performance of both FPSAH and SDPSAH improves when the ma increases. For the tested range of ma, SDPSAH outperforms FPSAH regardless of pitch ratio. SDPSAH, with a pitch ratio of 1.25, on the other hand, has a greater air temperature difference, efficiencies, heat removal factor, collector efficiencies, and averaged Nusselt number (Nuavg) while having a lower global heat loss coefficient and top loss. The Nuavg of SDPSAH at a pitch ratio of 1.25 is 1.01–1.17, 1.16–1.24, 1.26–1.57, and 1.44–1.88 times higher than SDPSAH at pitch ratios 1.0, 1.11, 1.67, and FPSAH, respectively. The higher averaged friction factor (favg) of 0.0443 is attained for SDPSAH at a pitch ratio of 1.25 due to the presence of the largest number of dimples. The ηth and ηd of SDPSAH at a pitch ratio of 1.25 are 34.5 and 35.5 % higher than those of FPSAH. The global heat loss coefficient of SDPSAH at pitch ratios 1.11, 1.0, and 1.67 is 1.05–1.84, 1.09–2.15, and 1.11–2.92 times higher, respectively, than that of SDPSAH at a pitch ratio of 1.25.

Cooling characteristics of thermochromic powder modified sand fog seal on asphalt pavement in summer high-temperature environment

Reversible optical response can occur in thermochromic materials with temperature changes, which has great potential in the field of pavement temperature regulation. The thermochromic sand fog seal (TP-SFS) was proposed in this study, which has the functions of pavement repair and temperature control. In this study, different types (red, blue, black) and contents (0 %, 2 %, 4 %, 6 %, and 8 %) of thermochromic powders (TP) were used to prepare TP-SFS. Secondly, the cooling characteristics of different TP-SFS was explored from the perspectives of temperature change rate, cooling temperature, and temperature gradient, based on the designed indoor and outdoor multi-cycle illumination test. Then, the prediction model of the outdoor cooling effect was proposed. In addition, the conservation and environmental benefits of different TP-SFS were calculated according to the empirical formula. It is found that after spraying TP-SFS, the heating rate of pavement decreases and the cooling rate increases. The cooling effect at 2 cm depth of the pavement sprayed with TP-SFS is the most significant, and the temperature gradient of the pavement is reduced. The cooling temperature of the pavement increases with the increase of TP content. In the outdoor environment, the more obvious cooling effect occurs as the process of pavement temperature increases and decreases. Additionally, the reliability of the designed indoor test is high, and the cooling effect of TP-SFS in outdoor environment can be well predicted according to the proposed model. The results of empirical formula calculation show that TP-SFS has a significant effect on delaying rutting development and alleviating urban heat island effect.