Passive Cooling Strategies in Greening Existing Residential Building in Hot Dry Climate： Case Study in Bahrain

This paper will present several passive-cooling technologies and design features that can be adopted to reduce building heat gain without the need of excess energy consumption. A typical residential unit will be selected as case study and a three basic passive cooling strategies were selected to enhance the building envelop, as well as using appropriate shading devices and green roofing system that prove to be a good environment quality improver. IES energy simulation software will be used to evaluate the performance of the building. The study revealed a number of significant findings in reducing the energy consumption and enhancing the tenants＇ thermal comfort. American Society of Heating Refrigerating and Airconditioning Engineer （ASHRAE） standards specially via improving the performance of building envelop because it is the interface between internal and external environment. Moreover, improving the building envelope has recorded that overall energy and chiller energy consumption can be reduced up to 10.8% and 21.6% respectively, Therefore, it is anticipated that further reductions can be achieved via applying more passive cooling strategies. Finally, it could argue that the results of this paper will not only be applicable to Bahrain but also many countries that have similar climatic and environmental context.

Green Affordable Social Housing: A Survey-Based Passive Cooling Design, with Focus on Jakande Housing Estate in Lagos, Nigeria

With rising health risks escalating from temperatures in the Global South, the shortage of essential indoor cooling is frequently seen as a dimension of energy poverty and human wellbeing. As a result, this study assessed ventilation and passive cooling in Jakande, Lagos Housing estate to design social housing that integrates proper cross ventilation and cooling. A total of 1215 housing units in the estate were used for the sampling frame. Based on the survey, the authors proposed an analytical housing design equipped with urban greenery that allows for free air movement with minimal thermal discomfort. The design methodology aids continuous cooling within the housing envelope and also improves aesthetics and landscaping within the environment.

Numerical Study of Mixed Convection in a Photovoltaic Trombe Wall Channel Coupled with a Solar Chimney Integrated into a Building for Habitats Passive Cooling

The solar chimney can generate airflow through the living space of the building to provide cooling. Hence, solar energy represents the best renewable, environmentally friendly source of energy that can be used for heating and cooling of houses. The present paper reports the numerical study of the performance of the mixed convection in the associated hybrid Photovoltaic/Thermal chimneys integrated into building for natural habitat ventilation. The front side glass plate of the chimneys is heated by a non-uniform daily solar radiation flux. Air is considered to be the cooling fluid. The stream fucntion-vorticity formulation with a finite difference numerical discretization solution scheme has been adopted. The system of algebraic governing equations is solved by Thomas algorithm method. The aim of the present paper is to study and to predict the dynamic fields and particularly of the mass flow rate of the air thermosiphon drawing in the associated hybrid Photovoltaic-Thermal chimneys integrated into a building for passive cooling in the habitats. The effects of the governing parameters, namely Reynolds number (30 ≤ Re ≤ 200), Rayleigh number (103 ≤ Ra≤ 105), the integrated chimney width on the fluid flow and the heat transfer characteristics, are studied in detail. The local Nusselt number, streamlines, isotherms, PV cells electrical efficiency and the outlet velocity at the top of the channels are the results represented versus the above controlling parameters.

The Combination Effect of Night Ventilation and Thermal Insulation on Passive Cooling of Buildings in Baghdad

An experimental investigation of passive cooling buildings has been carried out for a typical summer days extended from July to December of Baghdad in Iraq. Six independent chambers were designed and constructed for different roof constructions. Night ventilation has been applied to study the possibility of reducing air temperature in buildings by testing different air changes per hour extended from 5 to 30. Measurements outside chambers including air temperature; relative humidity and solar radiation were achieved, while surface temperature and air temperature inside the chambers were recorded. The results show that the air temperature can be decreased with a range from 3 ℃ to 6 ℃ when using 50 mm polystyrene. This decrease can further be lowered by 2 ℃ to 4 ℃ if night ventilation of change per hours in buildings is allowed. The reduction in air temperature can be reduced to 5 ℃ by combination of external night ventilation and white paint.

Engineering particles towards 3D supraballs-based passive cooling via grafting CDs onto colloidal photonic crystals

Particle engineering has opened the floodgates to material science in both fundamental and application field. However, covalent interactions have not yet been adequately designed in the particle engineering for functional colloidal photonic crystals(CPCs). Herein, we achieved covalent coupling between carboxylrich poly(styrene-acrylic acid)(P(St-AA)) monodispersed colloidal particles and amine-rich carbon dots(CDs) based on an feasible and universal particle engineering strategy. The designed CDs-grafted P(St-AA)monodispersed colloidal particles initiate a hydrogen bond-driven assembly mode and ensure the construction of large-scale crack-free CPCs. Moreover, the CDs equipped with selective broad-band absorption capacity could improve the saturation of structural colors for high-visibility CPCs. Furthermore, an injectable photonic hydrogel(IPH) is developed to design CPC supraball hydrogel via integrating the CDsgrafted P(St-AA) CPC supraballs with supramolecular hydrogel. Combining superior flexibility, sufficient self-healing capacity of supramolecular hydrogel with visual optical information of our CPC supraballs, a cyclically reversible coding and decoding system was developed. Meanwhile, we firstly demonstrated the novel strategy of 3D supraballs-based passive cooling. The designed 3D CPC supraball hydrogel presents nearly full observation angle reflections behavior and excellent water evaporation capacity and achieves3.6 ℃ temperature drops, showing the application advantages in 3D thermal management. This work not only provides a new insight for manipulating optical properties of CPCs, but also demonstrates an easyto-perform platform, as well as indicates the direction for the promising application of CPCs.

Low-energy-consumption temperature swing system for CO_(2) capture by combining passive radiative cooling and solar heating

Temperature-swing adsorption(TSA)is an effective technique for CO_(2) capture,but the temperature swing procedure is energy-intensive.Herein,we report a low-energy-consumption system by combining passive radiative cooling and solar heating for the uptake of CO_(2) on commercial activated carbons(CACs).During adsorption,the adsorbents are coated with a layer of hierarchically porous poly(vinylidene fluoride-co-hexafluoropropene)[P(VdF-HFP)HP],which cools the adsorbents to a low temperature under sunlight through radiative cooling.For desorption,CACs with broad absorption of the solar spectrum are exposed to light irradiation for heating.The heating and cooling processes are completely driven by solar energy.Adsorption tests under mimicked sunlight using the CACs show that the performance of this system is comparable to that of the traditional ones.Furthermore,under real sunlight irradiation,the adsorption capacity of the CACs can be well maintained after multiple cycles.The present work may inspire the development of new temperature swing procedures with little energy consumption.

Integrated radiative and evaporative cooling beyond daytime passive cooling power limit

Radiative cooling technologies can passively gain lower temperature than that of ambient surroundings without consuming electricity,which has emerged as potential alternatives to traditional cooling methods.However,the limitations in daytime radiation intensity with a net cooling power of less than 150 W·m^(−2) have hindered progress toward commercial practicality.Here,we report an integrated radiative and evaporative chiller(IREC)based on polyacrylamide hydrogels combined with an upper layer of breathable poly(vinylidene fluoride-co-trifluoroethylene)fibers,which achieves a record high practical average daytime cooling power of 710 W·m^(−2).The breathable fiber layer has an average emissivity of over 76%in the atmospheric window,while reflecting 90%of visible light.This IREC possesses effective daytime radiative cooling while simultaneously ensuring evaporative cooling capability,enhancing daytime passive cooling effectively.As a result,IREC presents the practicability for both personal cooling managements and industrial auxiliary cooling applications.An IREC-based patch can assist in cooling human body by 13℃ low for a long term and biocompatible use,and IREC can maintain the temperature of industrial storage facilities such as oil tanks at room temperature even under strong sunlight irradiation.This work delivers the highest performance daytime passive cooling by simultaneous infrared radiation and water evaporation,and provides a new perspective for developing highly efficient,scalable,and affordable passive cooling strategy.

A newly designed BIPV system with enhanced passive cooling and ventilation

Nowadays,the application of renewable energies such as solar energy in the building sector has increased notably considering the adverse impacts of climate change on human life;hence many studies have focused on the application of photovoltaic panels in buildings.In the current study,a 3D computational fluid dynamics(CFD)model has been developed to evaluate the performance of a newly designed building-integrated photovoltaic(BIPV)system.Given the negative influence of overheating on the lifespan and performance of PV panels,their passive air cooling has been studied.Further,the potential of rooftop-mounted solar panels in passive ventilation of buildings by generating natural convective currents has been explored.The developed CFD model takes into consideration the effects of radiation,conduction,and buoyancy-driven natural convective currents generated by solar PV panels which are heated due to the exposure to solar radiation heat flux.The results suggest that applying a high surface emissivity for the part of the roof beneath the PV panels intensifies the natural convective currents which in turn provides better cooling for PV panels with higher cooling effects at higher solar heat fluxes.Up to a 34%increase in the convective mass flow rate and a 3 K decrease in the mean temperature of the panels were attained by modifying the emissivity of roof surface.Such a 3 K decrease in the operating temperature of the PV panels can enhance their efficiency and lifespan by about 1.56%and 21%,respectively.Based on the operating conditions and system characteristics,the BIPV system yielded an air change rate(ACH)in the range of 3-13 which was considered to be highly prevalent in providing the required passive ventilation for a wide range of applications.It was also observed that the flow dynamics inside the building were affected by both the amount of solar heat load incident on the solar panels and the emissivity of the roof surface behind the panels.

Highly Porous Yet Transparent Mechanically Flexible Aerogels Realizing Solar-Thermal Regulatory Cooling

The demand for highly porous yet transparent aerogels with mechanical flexibility and solar-thermal dual-regulation for energy-saving windows is significant but challenging.Herein,a delaminated aerogel film(DAF)is fabricated through filtration-induced delaminated gelation and ambient drying.The delaminated gelation process involves the assembly of fluorinated cellulose nanofiber(FCNF)at the solid-liquid interface between the filter and the filtrate during filtration,resulting in the formation of lamellar FCNF hydrogels with strong intra-plane and weak interlayer hydrogen bonding.By exchanging the solvents from water to hexane,the hydrogen bonding in the FCNF hydrogel is further enhanced,enabling the formation of the DAF with intra-layer mesopores upon ambient drying.The resulting aerogel film is lightweight and ultra-flexible,which pos-sesses desirable properties of high visible-light transmittance(91.0%),low thermal conductivity(33 mW m^(-1) K^(-1)),and high atmospheric-window emissivity(90.1%).Furthermore,the DAF exhibits reduced surface energy and exceptional hydrophobicity due to the presence of fluorine-containing groups,enhancing its durability and UV resistance.Consequently,the DAF has demonstrated its potential as solar-thermal regulatory cooling window materials capable of simultaneously providing indoor lighting,thermal insulation,and daytime radiative cooling under direct sunlight.Significantly,the enclosed space protected by the DAF exhibits a temperature reduction of 2.6℃ compared to that shielded by conventional architectural glass.

Designing radiative cooling metamaterials for passive thermal management by particle swarm optimization

The passive radiative cooling technology shows a great potential application on reducing the enormous global energy consumption.The multilayer metamaterials could enhance the radiative cooling performance.However,it is a challenge to design the radiative cooler.In this work,based on the particle swarm optimization(PSO)evolutionary algorithm,we develop an intelligent workflow in designing photonic radiative cooling metamaterials.Specifically,we design two 10-layer SiO_(2) radiative coolers doped by cylindrical MgF_(2) or air impurities,possessing high emissivity within the selective(8–13μm)and broadband(8–25μm)atmospheric transparency windows,respectively.Our two kinds of coolers demonstrate power density as high as 119 W/m^(2) and 132 W/m^(2) at the room temperature(300 K).Our scheme does not rely on the usage of special materials,forming high-performing metamaterials with conventional poor-performing components.This significant improvement of the emission spectra proves the effectiveness of our inverse design algorithm in boosting the discovery of high-performing functional metamaterials.

Using passive cooling strategies to improve thermal performance and reduce energy consumption of residential buildings in U.A.E. buildings

Passive design responds to local climate and site conditions in order to maximise the comfort and health of building users while minimising energy use. The key to designing a passive building is to take best advantage of the local climate. Passive cooling refers to any technologies or design features adopted to reduce the temperature of buildings without the need for power consumption. Consequently, the aim of this study is to test the usefulness of applying selected passive cooling strategies to improve thermal performance and to reduce energy consumption of residential buildings in hot arid climate settings, namely Dubai, United Arab Emirates. One case building was selected and eight passive cooling strategies were applied. Energy simulation software namely IES was used to assess the performance of the building. Solar shading performance was also assessed using Sun Cast Analysis, as a part of the IES software. Energy reduction was achieved due to both the harnessing of natural ventilation and the minimising of heat gain in line with applying good shading devices alongside the use of double glazing. Additionally, green roofing proved its potential by acting as an effective roof insulation. The study revealed several significant findings including that the total annual energy consumption of a residential building in Dubai may be reduced by up to 23.6% when a building uses passive cooling strategies.

Superelastic Radiative Cooling Metafabric for Comfortable Epidermal Electrophysiological Monitoring

Epidermal electronics with superb passive-cooling capabilities are of great value for both daytime outdoor dressing comfort and low-carbon economy. Herein, a multifunctional and skinattachable electronic is rationally developed on a porous all-elastomer metafabric for efficient passive daytime radiative cooling(PDRC) and human electrophysiological monitoring. The cooling characteristics are realized through the homogeneous impregnation of polytetrafluoroethylene microparticles in the styrene–ethylene–butylene–styrene fibers, and the rational regulation of microporosity in SEBS/PTFE metafabrics, thus synergistically backscatter ultraviolet–visible–near-infrared light(maximum reflectance over 98.0%) to minimize heat absorption while efficiently emit human-body midinfrared radiation to the sky. As a result, the developed PDRC metafabric achieves approximately 17℃ cooling effects in an outdoor daytime environment and completely retains its passive cooling performance even under 50% stretching. Further, high-fidelity electrophysiological monitoring capability is also implemented in the breathable and skin-conformal metafabric through liquid metal printing, enabling the accurate acquisition of human electrocardiograph, surface electromyogram, and electroencephalograph signals for comfortable and lengthy health regulation. Hence, the fabricated superelastic PDRC metafabric opens a new avenue for the development of body-comfortable electronics and low-carbon wearing technologies.

Passive daytime radiative cooling coatings with renewable self-cleaning functions

Passive daytime radiative cooling(PDRC)technology is emerging as one of the most promising solutions to the global problem of spacing cooling,but its practical application is limited due to reduced cooling effectiveness caused by daily wear and tear,as well as dirt contamination.To tackle this problem,we report a novel strategy by introducing a renewable armor structure for prolonging the anti-fouling and cooling effectiveness properties of the PDRC coatings.The armor structure is designed by decorating fluorinated hollow glass microspheres(HGM)inside rigid resin composite matrices.The HGM serve triple purposes,including providing isolated cavities for enhanced solar reflectance,reinforcing the matrices to form robust armored structures,and increasing thermal emittance.When the coatings are worn,the HGM on the surface expose their concave cavities with numerous hydrophobic fragments,generating a highly rough surface that guarantee the superhydrophobic function.The coatings show a high sunlight reflectance(0.93)and thermal emittance(0.94)in the long-wave infrared window,leading to a cooling of 5℃ below ambient temperature under high solar flux(∼900 W/m^(2)).When anti-fouling functions are reduced,they can be regenerated more than 100 cycles without compromising the PDRC function by simple wearing treatment.Furthermore,these coatings can be easily prepared using a one-pot spray method with low-cost materials,exhibit strong adhesion to a variety of substrates,and demonstrate exceptional environmental stability.Therefore,we anticipate their immediate application opportunities for spacing cooling.

Environment-adaptive phase-separation-porous fluorofilm for highperformance passive radiation cooling

Passive radiative cooling is widely recognized as an environmentally sustainable method for achieving significant cooling effects.However,the mechanical properties and environmental adaptability of current radiative cooling materials are not sufficient to maintain high cooling performance in external environments.Here we reported an environment-adaptive phase-separation-porous fluorofilm for high-performance passive radiation cooling.Compared to the homogenous fluoro-porous network with limited scattering efficiencies,we modulated the porous structure of the fluorofilm to achieve a strong emissivity of 95.2%(8-13μm)and a high reflectivity of 97.1%(0.3-2.5μm).The fluorofilm demonstrates a temperature drop of 10.5°C and an average cooling power of 81 W·m^(−2)under a sunlight power of 770 W·m^(−2).The high mechanical performance and environmental adaptability of fluorofilms are also exhibited.Considering its significant radiative cooling capability and robust environmental adaptability,the fluorofilm is expected to have a promising future in radiative temperature regulation.

面向工业化种植的光热管理农膜——机遇与挑战

As indispensable parts of greenhouses and plant factories,agricultural covering films play a prominent role in regulating microclimate environments.Polyethylene covering films directly transmit the full solar spectrum.However,this high level of sunlight transmission may be inappropriate or even harmful for crops with specific photothermal requirements.Modern greenhouses are integrated with agricultural covering materials,heating,ventilation,and air conditioning(HVAC)systems,and smart irrigation and communication technologies to maximize planting efficiency.This review provides insight into the photothermal requirements of crops and ways to meet these requirements,including new materials based on passive radiative cooling and light scattering,simulations to evaluate the energy consumption and environmental conditions in a greenhouse,and data mining to identify key biological growth factors and thereby improve new covering films.Finally,future challenges and directions for photothermalmanagement agricultural films are elaborated on to bridge the gap between lab-scale research and large-scale practical applications.

Porous block copolymer films with self-adjustable optical transmittance and passive radiative cooling

As an energy-free cooling technique,radiative cooling has garnered significant attention in the field of energy conservation.However,traditional radiative cooling films often possess static optical properties and their inherent opacity limits their applications in building such as windows.Therefore,there exists a requirement for passive radiative cooling films endowed with adjustable transmittance.Here we report the porous block copolymer films with self-adjustable optical transmittance and passive radiative cooling.In a result,the film exhibited a high solar reflectance(0.3-2.5μm)of 96.9%and a high infrared emittance(8-13μm)of 97.9%.Outdoor experiments demonstrated that the film surface temperature was 6.6℃lower than ambient temperature,with a cooling power of 104.8 W·m^(-2).In addition,the film’s transmittance can be regulated by altering the polarity of the post-processing solvent,providing an effective approach for regulating indoor light intensity and thermal balance,thereby enhancing the applicability of radiative cooling.

Tuning on passive interfacial cooling of covalent organic framework hydrogel for enhancing freshwater and electricity generation

Developing an efficient freshwater and electricity co-generation device(FECGD)can solve the shortage of freshwater and electricity.However,the poor salt resistance and refrigeration properties of the materials for FECGD put big challenges in the efficient and stable operation of these devices.To address these issues,we propose the covalent organic framework(COF)confined co-polymerization strategy to prepare COF-modified acrylamide cationic hydrogels(ACH-COF),where hydrogen bonding interlocking between negatively charged polymer chains and COF pores can form a salt resistant hydrogel for stabilizing tunable passive interfacial cooling(TPIC).The FECPDs based on the TPIC and salt resistance of ACH-COF display a maximum output power density of 2.28 W m-2,which is 4.3 times higher than that of a commercial thermoelec-tric generator under one solar radiation.The production rate of freshwater can reach 2.74 kg m-2 h-1.Our results suggest that the high efficiency and scala-bility of the FECGD can hold the promise of alleviating freshwater and power shortages.

Springtime Monitoring of Passive Cool Roofs in Subtropical Climate

Passive strategies for acclimatization of buildings have been studied by several authors in many countries, especially the evaporative and radiant cooling techniques. Fiber cement tiles are very common in popular constructions due to their low cost. However, they have over twice of the value thermal transmittance indicated to this bioclimatic zone according to Brazilian guidelines. The objective is to present an alternative to reduce high temperatures on fiber cement tiles. In this paper, the monitoring of passive cooling of roofing during the spring season in a city with subtropical climate is described. Single and combined reflective and evaporative cooling systems were studied in different environmental conditions. Internal surface temperatures of tiles were monitored together with weather variables. Results show a decrease of about 6 ℃, 9 ℃, 10 ℃ and 11 ℃ as compared to the original tiles according to environment conditions and the combined passive cooling techniques. These results allow for the conclusion that the use of passive cooling techniques opens up new possibilities to attenuate the internal surface temperatures of tiles and to consequently decrease the roofing solar heat gain into buildings, thus, providing less air cooling energy consumption.

Decoupled thermal–hydraulic analysis of an air-cooled separated heat pipe for spent fuel pools under natural convection

An investigation of the decoupled thermal–hydraulic analysis of a separated heat pipe spent fuel pool passive cooling system(SFS)is essential for practical engineering applications.Based on the principles of thermal and mass balance,this study decoupled the heat transfer processes in the SFS.In accordance with the decoupling conditions,we modeled the spent fuel pool of the CAP1400 pressurized water reactor in Weihai and used computational fluid dynamics to explore the heat dissipation capacity of the SFS under different air temperatures and wind speeds.The results show that the air-cooled separated heat pipe radiator achieved optimal performance at an air temperature of 10℃ or wind speed of 8 m/s.Fitted equations for the equivalent thermal conductivity of the separated heat pipes with the wind speed and air temperature we obtained according to the thermal resistance network model.This study is instructive for the actual operation of an SFS.

Comparative Study of Two Materials Combining a Standard Building Material with a PCM

Phase change materials(PCMs)have the ability to store thermal energy and make it available at a later stage to keep indoor temperature within a specific range and achieve better thermal comfort in buildings.This study focuses on the performances of materials obtained by combining a standard building material with a PCM.In particular,two different materials mixed with the same PCM are considered under the same climatic conditions.The related thermal behavior is assessed in the framework of numerical simulations conducted with ANSYS Fluent assuming parameters representative of a city located in Europe.The results show that the addition of PCM to concrete and bricks can improve the thermal inertia of the resulting material.