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Characteristics of infrared sky radiation in the United States
Abstract
A new algorithm has been developed for calculating the thermal radiant temperature of the sky. It is based on a simple empirical and theoretical model of clouds, together with a correlation between clear sky emissivity and the surface dewpoint temperature. Hourly sky temperatures have been calculated based on typical meteorological year (TMY) weather data sets. A summary of the results is presented for calculations made at 193 TMY sites within the continental United States. The results are displayed in the form of monthly contour maps, histograms, and graphs for the purpose of determining regions of the country in which the radiative cooling of buildings appears to be a promising heat rejection strategy.
... Specifically, a CF value of 0 represents a clear-sky scenario, whereas a CF of 1 signifies an utterly overcast sky. In 1984, Berdahl and Martin [42] introduced a sky emissivity correlation based on the cloud sky fraction ( f cloud ), which can be compared to the Kasten and Czeplak correlation [41]. An f cloud index of 0 represents a clear-sky condition, while a value of 1 represents an overcast sky scenario. ...
... Specifically, a CF value of 0 represents a clear-sky scenario, whereas a CF of 1 signifies an utterly overcast sky. In 1984, Berdahl and Martin [42] introduced a sky emissivity correlation based on the cloud sky fraction ( ), which can be compared to the Kasten and Czeplak correlation [41]. An index of 0 represents a clear-sky condition while a value of 1 represents an overcast sky scenario. ...
... On the other hand, the "TRNSYS Simulation Studio" was used for modeling the environment in terms of climatic conditions, and sky temperature was computed by applying both the specific "Type 69" (widely used as a standard component of the library and based on the Berdahl and Martin [42] formulation for computing the emissivity of the sky and thus the sky temperature) and the assembly function to insert the equations shown in Table 1 The outcomes from all the considered approaches were analyzed and compared. Figure 3 shows the flowchart of the applied methodology. ...
Since the beginning of the 20th century, many studies have focused on the possibility of considering the sky as a body characterized by an apparent temperature, and several correlations to quantify the apparent sky temperature have been proposed. However, the different models were obtained for specific meteorological conditions and through measurements at specific sites. The available models do not cover all locations in the world, although the evaluation of the sky temperature is fundamental for estimating the net radiative heat transfer between surfaces and the sky. Here, experimental data logged from a regional micrometeorological network (in Italy, within the Lazio region) were processed and used to identify an empirical model for the estimation of the sky temperature in the Mediterranean area. Data relating to atmospheric infrared radiation were used to compute the sky temperature, aiming at identifying a direct correlation with the ambient temperature. Climatic data acquired during 2022 were processed. The proposed correlations were compared with other models available in the literature, including the standard ISO 13790. This study proposes an annual-based direct correlation in its initial phase, demonstrating a superior fit to the measured data compared to well-known direct empirical models from the literature. Subsequently, quarterly-based correlations are introduced further in a secondary phase of the work to improve the model’s adaptation to experimental observations. The results reveal that quarterly-based correlations improve goodness-of-fit indexes compared to annual-based and well-known direct empirical correlations. Finally, a detached building was modeled via a dynamic code to highlight the influence of different correlations on annual energy needs.
... A small correction to compensate for altitude is noted in multiple publications from Berdahl and Martin as Δε p = 0.00012(P station 1000) where station pressure P station is given in millibars (Berdahl, 2021;Martin & Berdahl, 1984a). This correction is adapted slightly to scale pressure relative to P 0 instead of 1000 mb and to use a non-dimensional constant so that ...
... which is a simplified version ofc 3 P 0 e z/H P 0 ) , where c 3 =c 3 P 0 , and clearly reflects the formulation of Martin and Berdahl (1984a). The value of c 3 is fitted empirically. ...
... Note that the error statistics for LC2019 are artificially poor due to change in power for the water vapor partial pressure term, but also due to the fact that the correlation coefficients in that study were obtained from LBL integration for a plane-parallel, clear atmosphere with modeled profiles of concentration and temperature with no adjustments to empirical ground data. B2021 is found in Berdahl (2021), though it is the result of previous publications and a body of work including Martin and Berdahl (1984a); Martin and Berdahl (1984b). B2021 was originally written as a function of P w , so c 2 was varied accordingly to scale p w . ...
Clear sky emittance models provide critical information for the determination of downwelling longwave irradiance at the Earth's surface. This study updates existing calculations which relate clear sky longwave emissivity with the main (and most variable) greenhouse gas in the atmosphere, water vapor. Impacts of station elevation and data quality control are quantified. Empirical results are used to validate highly resolved spectral models, and the resultant simplified calculates provide accurate estimations of clear sky emissivity without the need for extensive computation. Results show that correlation coefficients are mostly robust to nuanced data processing choices when regressed from sufficiently large data sets (≥10⁴ samples) with the exceptions of altitude adjustment and measurement bias corrections. The empirical results from this study are compared to results from other leading empirical, physics‐based, and hybridized phenomenological models. Correlations for effective clear sky emissivity, transmissivity and optical depth are provided, based on parameterized line‐by‐line (LBL) model results, for the broadband 0–2,500 cm⁻¹ and for seven wavenumber wideband of interest. Results for the (b3) wideband 580–750 cm⁻¹ are particularly relevant because of its disaggregated and combined carbon dioxide‐water vapor contributions. The broadband effective optical depth (δ) of water vapor is found to be δH2O=0.628+54.756pw , where pw is the dimensionless partial pressure of water vapor at the surface. Equivalently, the broadband effective optical depth of carbon dioxide in the presence of water vapor is found to be δCO2=0.269−10.229pw . Processed training data sets are provided as supplementary content for comparative studies.
... Based on Aili et al. [27] and Martin et al. [28], it is considered that under a fully clouded sky, the clouds are closer to the Earth's surface and can be described as a black body. With a partly clouded sky, the cloud base is higher and, therefore, colder. ...
... The emissivity of the clouds is furthermore considered to be close to one, given that clouds consist of ice crystals [29]. T cloud can be then calculated based on [25,28] T ...
This paper investigates the theoretical and experimental cooling performance of textile materials utilizing radiative cooling technology. By applying Kirchhoff’s law, the emissivity of surfaces is determined, revealing that materials with high transmission values can achieve comparable cooling performance to those with high reflection values. Notably, materials exhibiting moderate reflectance and transmittance in the solar range tend to absorb minimal solar radiation, thus offering high theoretical cooling performance. However, practical applications like building envelopes or clothing present challenges due to the impact of background radiation on overall cooling capacity. Despite their intrinsic cooling properties, a significant portion of solar radiation is transmitted, complicating matters as the background can significantly affect overall cooling performance. This study provides a solution that accounts for the influence of background materials. Based on spectral data, various background materials and their impact on different semi-transparent comparison materials can be considered, and cooling performance can be simulated. This enables the simulation of cooling performance for various application scenarios and facilitates comparisons between transparent, semi-transparent, and opaque textile materials.
... ε is the emissivity of bridge exterior surface, σ = 5.67 × 10 −8 W/m 2 /K 4 is the Stefan-Boltzmann constant, θ i is the angle between the bridge exterior surface and the horizontal plane, ε g is the emissivity of ground, and T g is the ground temperature (K). T sky is the effective sky temperature (K) that can be deduced from the following equations [21]: ...
... where T D1 is the air temperature measurement of sensor D1 and C(t) is the coefficient function defined into five segments as follows: With the updated air temperature, the bridge's internal and external thermal boundary conditions can be calculated from Eqs. (20) and (21). The internal and external long-wave radiation are still simplified to heat convection. ...
Heat transfer analysis has been used to calculate the temperature distribution in bridges. Thermal boundary conditions play a critical role in this analysis. However, existing studies on thermal boundary conditions simplify the air temperature inside the bridge deck as uniform, which is not realistic and thus causes inaccurate simulation results. This study proposes a new approach to thermal boundary conditions in the heat transfer analysis of bridges. For the first time, computational fluid dynamics is used to calculate non-uniform air temperatures inside the bridge deck. In addition, non-approximate heat exchange equations for long-wave radiation are also incorporated into the approach. The techniques are applied to the 1377-m main span Tsing Ma Suspension Bridge to calculate the internal air temperatures of a deck segment. Transient heat transfer analysis is then conducted to calculate the time-dependent temperature distribution of the segment. As compared with the field monitoring results, the proposed approach can simulate the temperature distribution of the bridge with an average discrepancy of 0.88 °C and is more accurately than other existing approaches.
... Clouds can significantly impact atmospheric transmittance. This influence can be determined by Eq. (13) [26]: ...
... where H i (km) is the cloud base height for different clouds obtained from weather data file [27], and a constant value (8.2 km) are used for H 0 [26]. ...
The Passive Daytime Radiative Cooler (PDRC) exhibits potential in enhancing building energy conservation due to its high emissivity in wavelength between 8 μm and 13 μm. However, current building energy simulation programs, e.g., EnergyPlus, generally adopt a constant emissivity. To implement the wavelength-dependent PDRC model into EnergyPlus, a roof model was introduced to couple it with EnergyPlus to assess the energy saving potential of PDRC more reasonably. To assess the PDRC roofs, the impact of buildings constructed in different eras, building heights, and climatic conditions in China on building energy saving was investigated. The results showed that more energy was saved in regions with high cooling demands e.g., Shanghai and Guangzhou. Applying PDRC on roofs of buildings constructed pre 2001 in severe cold regions increased building energy consumptions. Furthermore, buildings with well insulated roofs coated by PDRC were not equally beneficial for reducing cooling demands in summer compared to buildings with non-insulated roofs, but heating demands in winter could be reduced. With an increase in building height, the energy saving potential of PDRC roofs was reduced. Therefore, a comprehensive analysis was imperative considering the local climates as well as the building itself when PDRC is to be applied.
... As already mentioned in the introduction, over time, numerous empirical models have been proposed to model the emissivity of the sky [47,48,59,60]. In this study, this quantity is calculated using the expression proposed earlier by Martin and Berdhal [66], and subsequently by Crawford and Duchon [67] and Carmona et al. [60]: ...
... where ε sky,cl is the clear-sky emissivity and C is named "the infrared cloud amount" by Martin and Berdhal [66] and the "cloud fraction" by Crawford and Duchon [67] and Carmona et al. [60]. ...
... Berdahl/Martin [67] added a diurnal dependence on the solar time t in hours to describe the observed difference of the effective emissivity between ε clear-sky during daytime and nighttime. Furthermore Berdahl/Martin [68] have also incorporated a dependence on the altitude of the observer, which is correlated with the atmospheric air pressure p atm at the position of the observer in hPa: ...
Rapidly rising global temperatures and the intensification of the urban heat island (UHI) effect necessitate new, energy-efficient solutions to mitigate heat stress in cities. Passive radiative cooling (PRC) offers a highly promising, low-energy pathway to achieve sub-ambient temperatures by reflecting incoming solar radiation while emitting long-wave infrared radiation through the atmospheric infrared window. This review summarizes key aspects of PRC and its role in reducing UHI impacts. Furthermore the fundamental physics of heat transfer and radiative heat exchange, including the materials properties such as solar reflectance and thermal emissivity which are correlated with the figures of merit, temperature drop below ambient temperature and cooling power. A comprehensive classification of current PRC materials is presented based on both structural architectures and physical effects. Additionally an overview on measurement techniques are employed to determine the performance of PRC materials, focusing on the key performance indicators. For this purpose in-field as wells as laboratory measurement techniques are introduced and opportunities in standardizing testing protocols are highlighted. Finally, future research directions are outlined, focusing on novel material development, theoretical advancements, scalable fabrication processes, and integration strategies within urban infrastructures. These innovations are important for enhancing building energy efficiency, reducing urban heat stress, and promoting sustainable urban development in the face of climate change.
... The sky temperature (T sky [ • C]) and emissivity (ε sky [-]) -considering no cloud coverage (clear sky), are determined according to references [32], using the relations: ...
The European Union's ambitious goals to reduce carbon emissions and improve energy efficiency has highlighted the importance of renewable energy technologies like solar collectors. Buildings, responsible for a significant share of the EU's energy consumption and greenhouse gas emissions, can benefit from solar collectors integrated with thermal energy storage systems to optimize both heating and cooling. This study investigates how the integration of nano-enhanced phase change materials (nePCM) into a transpired solar collector (TSC) can improve thermal energy storage and efficiency. To explore this, an experimental setup was constructed and tested under real conditions. This study evaluates a transpired solar collector (TSC) integrated with nano-enhanced phase change materials (nePCMs) for thermal energy storage. Experimental results revealed plate temperatures exceeding ambient by up to 20 • C and nighttime outlet air temperatures raised by 2-3 • C. The system achieved an average efficiency of 50 %, validated by a mathematical model (MBE: 3.13 %, RMSE: 3.86 %). This demonstrates the potential of nePCMs to enhance solar energy storage and efficiency under real-world conditions.
... TRNSYS Type 15, a component for weather data processing, is used to calculate the sky temperature. Type 15 calculates the effective sky temperature based on the model from Martin and Berdahl (1984). Table 1 provides the parameters of unglazed PVT collectors used in this study. ...
As building electrification is recognised as an important opportunity to reduce greenhouse gas emissions, the integration of solar energy and heat pump represents a promising solution towards net-zero carbon buildings. This paper presents a hybrid multifunctional solar-assisted heat pump (SAHP) system that can provide space heating, space cooling, domestic hot water, and onsite electricity generation. Photovoltaic-thermal collectors are used for electricity generation, heat collection, and radiative cooling. The system design and controls support fourteen operational modes involving different components. TRNSYS software is used to model and simulate the multifunctional SAHP system. With a 2-m³ storage tank and 30-m² PVT collectors, the multifunctional SAHP system has a seasonal performance factor of 2.7 in Baltimore and 3.7 in Las Vegas. The onsite electricity generation can cover 53% of the building’s electricity needs in Baltimore and 83% in Las Vegas.
... Suichi et al. [25] developed a daytime radiative cooler and achieved a lower atmospheric radiation exchange during low cloud cover. The results of experiments and simulations carried out in Singapore and Sydney demonstrated that the parameters such as precipitable water vapour (PWV), sky temperature, and cloud cover of the location affect the performance of the radiative cooling system [26,27]. The radiative cooling potential is also affected by the temperature variance in the sky and the intensity of solar radiation, which are crucial factors [28]. ...
Radiative cooling is one of the passive methods of cooling by exchanging radiative heat between a surface and the cold universe through an atmospheric window (8 to 13 µm). The effectiveness of radiative cooling depends on the optical properties of the surfaces and the local meteorological conditions. It is essential to determine the local cooling potential to implement radiative cooling strategies. In this research, India’s annual and seasonal average radiative cooling potential was computed for 437 locations from meteorological data and the map has been developed to meet the energy-efficient cooling requirements of the Indian Cooling Action Plan (ICAP) 2019 and to fulfil the targets of Sustainable Development Goals (SDG). The results show that most locations in India have a cooling potential between 60 to 140 W/m2. The minimum area required for radiative cooling to meet India’s cooling demand is also evaluated. These results will help disseminate radiative cooling technologies in India to achieve ICAP and SDG targets.
... The indoor temperature is set by a thermostat and is assumed to be homogeneous and constant throughout the heated space made of the ground floor and the first floor. Cooling (Martin and Berdahl 1984). The indoor and outdoor convection algorithm are TARP (Walton 1983), which corresponds to convection variability based on temperature difference. ...
... A warm-up is performed for each simulation, with a maximum of 150 warm-up days. The sky temperature model chosen is Berdhal-Martin [33]. The indoor and outdoor convection algorithm are TARP [34], which corresponds to convection variability based on temperature difference. ...
The energy consumption of buildings is usually different from that predicted at the design stage. To measure the performance gap between designed and as-built buildings, it is possible to measure the actual Heat Transfer Coefficient, which characterizes the thermal performance of the building envelope. The actual reference method for measuring this coefficient is the co-heating test, which consists in comparing the heat input into a building against the air temperature difference between inside and outside the building. However, the use of this method is limited to a certain period of the year when weather conditions allow a sufficient temperature difference, while avoiding heating the building to temperatures that could damage it. This work proposes to extend the period of validity of co-heating tests by using an equivalent outdoor temperature. This equivalent outdoor temperature allows to take into account impact of solar radiation and sky radiation which have a larger impact in hotter periods. This paper explores and demonstrate the feasibility of this new method from an experimental campaign and from numerical simulations run in a summer period. It extends the co-heating feasibility period, throughout the year for the coldest climates and between seasons for the warmest climates. The results from the experimental campaign agree with the simulated data results.
... Cooling or heating needs are determined by EnergyPlus. The sky temperature model chosen is Berdhal-Martin (Martin and Berdahl 1984). The indoor and outdoor convection algorithm are TARP (Walton 1983), which corresponds to convection variability based on temperature difference. ...
Discrepancy between designed and as-built building performance can be quantified by a Heat Transfer Coefficient measurement. A reference method for measuring this coefficient is the co-heating test. However, the use of this method is limited to certain weather conditions. This work proposes a new method, complementary to the co-heating test, to be performed in summer or in hot climates, called the co-cooling test. This method consists in cooling the building instead of heating it. This article presents a numerical setup to prove the feasibility of the co-cooling test, determining ad-hoc linear regression models. To better account for solar gains, an equivalent outdoor temperature is used. In the cases studied, the simple linear regression method using an equivalent outdoor temperature enables the Heat Transfer Coefficient to be determined with errors below 10 %.
... Several authors suggested that the temperature recorded with thermal cameras depends on topography [58,69,73] in outdoor conditions, where significant amounts of energy radiated by the sky and surrounding ground are reflected by the target [74]. In particular, T REFL is mostly influenced by the radiation contribution of the cold sky ( Figure 4), characterized by temperature values between −65 • C and −55 • C on clear days [60,75]. This contribution appears to be stronger in flat topography, resulting in a cooler apparent temperature [74]. ...
The reliable in situ quantification of rock mass fracturing and engineering quality is critical for slope stability, surface mining and rock engineering applications, yet it remains difficult due to the heterogeneous nature of fracture networks. We propose a method to quantify and map the slope-scale geomechanical quality of fractured rock masses using infrared thermography (IRT). We use the Mt. Gorsa quarry (Trentino, Italy) as a field laboratory to upscale a physics-based approach, which was developed in the laboratory, to in situ conditions, including the effects of fracture heterogeneity, environmental conditions and IRT limitations. We reconstructed the slope in 3D using UAV photogrammetry, characterized the rock mass quality in the field at selected outcrops in terms of the Geological Strength Index (GSI) and measured their cooling behavior through 18h time-lapse IRT surveys. With ad hoc field experiments, we developed a novel procedure to correct IRT data in outdoor environments with complex topography. This allowed for a spatially distributed quantification of the rock mass surface cooling behavior in terms of a Curve Shape Parameter (CSP). Using non-linear regression, we established a quantitative CSP-GSI relationship, which allowed for the CSP to be translated into GSI maps. Our results demonstrate the possibility of applying infrared thermography to the slope-scale mapping of rock mass fracturing based on a physics-based experimental methodology.
... The total tilted surface irradiation is an output of the weather type of TRNSYS and is calculated by first obtaining beam and diffuse radiation on a horizontal surface from total radiation based on the relationships developed by Reindl [66], and transposed to the tilted surface through the Hay and Davies' model [66]. The effective sky temperature (T s ) is instead calculated as a function of the ambient temperature, air humidity, cloudiness factor of the sky, and the local air pressure, according to the algorithm described in mathematical reference of TRNSYS software [67,68], while the ground temperature (T g ) is calculated according to the Kasuda's relationship [69]. The Leaf Area Index (LAI) value was assumed according to data obtained by LAI measurements carried out on Jasminoides species by Convertino [65]. ...
... is instead calculated as a function of the ambient temperature, air humidity, cloudiness factor of the sky, and the local air pressure, according to the algorithm described in mathematical reference of TRNSYS software [67,68], while the ground temperature (Tg) is calculated according to the Kasuda's relationship [69]. ...
Please cite this article as: Detommaso M, Costanzo V, Nocera F, Evola G, Evaluation of the cooling potential of a vertical greenery system coupled to a building through an experimentally validated transient model, Building and Environment (2023), doi: https://doi. Abstract Despite several studies showed that Vertical Greenery Systems (VGSs) have relevant thermal benefits at urban and building scales, researches devoted to investigate the benefits of a green facade through detailed transient thermal simulations are scarce. Furthermore, a study comparing the effectiveness of different plant types is still missing. The present paper aims to fill such gaps by studying the effectiveness of a green façade to improve the thermal behaviour of a well-insulated lightweight building in the Mediterranean area, as well as the perceived indoor thermal conditions, based on both on-site experimental measurements and dynamic thermal simulations with a novel Type in TRNSYS validated through the monitoring campaign. To this aim, two identical full-scale prefabricated modules were installed and monitored at the University Campus of Catania (Italy), differing from each other because one of them hosted a climbing plant species in its west façade. The validated numerical model was then used to appraise the cooling effect of the green façade with two different plant species commonly used in Mediterranean countries (Trachelospermum Jasminoides and Hedera Helix namely). Results show that Hedera helix ensures the best performance when the foliage layer is at an intermediate state of its growing process, while under full foliage development the species investigated show almost the same performance. The incoming heat flux can be strongly attenuated, showing a quite flat daily profile, while the peak value of the internal and external surface temperature of the wall can be reduced by up to 1.6 °C and 10.5 °C, respectively.
... Sky CB is mostly covered by cloud. [45] The reflection properties of sky CB are related to snow-water-ice reflection in general [46,47] without considering other parameters related to interference of sky background. Sand, stone, water (sea), and water vapor reflection have been considered for earth surface reflection of sky. ...
Visible and near infrared spectra of “sixteen materials for textile coloration/finishing/patterning” such as titanium dioxide, calcium oxide, aluminum, tin metal, tin oxide, iron powder, boron carbide, magnesium powder, carbon black pigment, titanium carbide, isolan black 2S LDN, isolan orange, telon blue A 2R, telon red A 2R, telon violet 3R, and telon yellow A 2R; and ‘nine materials of combat backgrounds (CBs) such as dry leaves, green leaves, tree bark-woodland CB; water-marine CB; sand-desertland CB; stone-stoneland CB; snow-snowland CB; sky CB; and ice-iceland CB (DGTWSIB) are obtained by Fourier transform infrared spectrophotometry and colorflex EZ spectrophotometer. A method of ‘Monte Carlo cross validation’ was applied for spectral simulation in visible and near infrared spectrums through experimental data information. The characterized reflection spectra of zero reflection (ZR), low reflection (LR), high reflection (HR), and HR–LR (HLR) materials are coalesced and simulated for camouflage materials design and textile applications against multidimensional CBs, DGTWSIB. The reflections of aluminum, titanium dioxide, calcium oxide, tin metal, tin oxide, and iron powder are irradiated as HR materials. Oppositely boron carbide, magnesium powder, carbon black pigment, and titanium carbide are illuminated as LR materials. Consequently, the mixing principle of HR and LR materials are also classified as HLR materials. Spectral properties of CB materials are also depicted as ZR materials against selected CBs. Spectral signal of ZR, LR, HR, and HLR materials are identified as more expedient camouflage materials for concealment of target signature than six selected synthetic dyes such as Isolan Black 2S LDN, Isolan Orange, Telon Blue A 2R, Telon Red A 2R, Telon Violet 3R, and Telon Yellow A 2R. The reflection spectra of ZR, LR, HR, and HLR materials are simulated and correlated against DGTWSIB in visible and NIR spectrums. Simulated spectral signals are considered for camouflage materials design and camouflage textiles formulation against DGTWSIB combat location, the CBs are mostly practiced by defence professional. Furthermore, the reflection principle of camouflage textiles coloration/finishing/patterning has been accumulated under spectral signal of DGTWSIB, camouflage materials and synthetic dyes, synthetic dye–metal and synthetic dye–pigment combination. Therefore, depth analysis and graphical results of ZR, LR, HR, and HLR materials are the potential findings for selection of camouflage materials, right development of camouflage textile products, and camouflage assessment of hyperspectral imaging for defence protection in the entire spectrums of UV–Vis–IR. This optical parameters of ZR, LR, HR, and HLR materials have also applications to the materials community of multidimensional branches of material research.
Graphical abstract
... Sky CB is mostly covered by cloud. [43] The re ection properties of sky CB are related to snow-water-ice re ection in general [44,45] without considering other parameters related to interference of sky background. Sand, stone, water (sea), water vapour re ection have been considered for earth surface re ection of sky. ...
Visible and near infrared spectra of "sixteen materials for textile coloration/ nishing/patterning" such as titanium dioxide, calcium oxide, aluminum, tin metal, tin oxide, iron powder, boron carbide, magnesium powder, carbon black pigment, titanium carbide, isolan black 2S LDN, isolan orange, telon blue A 2R, telon red A 2R, telon violet 3R and telon yellow A 2R; and 'nine materials of combat backgrounds (CBs) such as dry leaves, green leaves, tree bark-woodland CB; water-marine CB; sand-desertland CB; stone-stoneland CB; snow-snowland CB; sky CB and ice-iceland CB (DGTWSIB) are obtained by Fourier transform infrared spectrophotometry and color ex EZ spectrophotometer. A method of 'Monte Carlo cross validation' was applied for spectral simulation in visible and near infrared spectrums through experimental data information. The characterized re ection spectra of zero re ection (ZR), low re ection (LR), high re ection (HR) and HR-LR (HLR) materials are coalesced and simulated for camou age materials design and textile applications against multidimensional CBs, DGTWSIB. The re ections of aluminium, titanium dioxide, calcium oxide, tin metal, tin oxide and iron powder are irradiated as HR materials. Oppositely boron carbide, magnesium powder, carbon black pigment and titanium carbide are illuminated as LR materials. Consequently, the mixing principle of HR and LR materials are also classi ed as HLR materials. Spectral properties of CB materials are also depicted as ZR materials against selected CBs. Spectral signal of ZR, LR, HR and HLR materials are identi ed as more expedient camou age materials for concealment of target signature than six selected synthetic dyes such as Isolan Black 2S LDN, Isolan Orange, Telon Blue A 2R, Telon Red A 2R, Telon Violet 3R and Telon Yellow A 2R. The re ection spectra of ZR, LR, HR and HLR materials are simulated and correlated against DGTWSIB in visible and NIR spectrums. Simulated spectral signals are considered for camou age materials design and camou age textiles formulation against DGTWSIB combat location, the CBs are mostly practiced by defence professional. Furthermore, the re ection principle of camou age textiles coloration/ nishing/patterning has been accumulated under spectral signal of DGTWSIB, camou age materials and synthetic dyes, synthetic dye-metal and synthetic dye-pigment combination. Therefore depth analysis and graphical results of ZR, LR, HR and HLR materials are the potential ndings for selection of camou age materials, right development of camou age textile products and camou age assessment of hyperspectral imaging for defence protection in entire spectrums of UV-visible-IR. This optical parameters of ZR, LR, HR and HLR materials have also applications to the materials community of multidimesional branches of material research.
... where σ is Stefan-Boltzman constant, Tcell is the PV cell temperature, and Tsky is the effective sky temperature given as a function of dew point temperature, cloud cover, atmospheric pressure, and time of the day. The effective sky temperature is calculated using the Martin and Berdahl (1984) correlation. The PVT modules used in this simulation have an area of 1.45 m 2 , electrical effiecincy of 13.6%, heat removal factor ( ) of 0.6, and heat loss slope ( ) of 15 (W•m -2 • K -1 ). ...
... The results showed that the values calculated by Idso and Jackson's formula were in good agreement with those calculated by the model. Martin et al. [26] proposed a new algorithm to calculate the temperature of thermal radiation from the sky. The results of the calculations performed at 193 TMY sites in the continental United States were summarized. ...
In this paper, an experimental rig of a prefabricated temporary house (PTH) was first established. Then, predicted models for the thermal environment of the PTH with and without considering long-wave radiation were developed. Next, the exterior-surface, interior-surface and indoor temperatures of the PTH were calculated by using the predicted models. The calculated results were then compared with the experimental results to study the influence of long-wave radiation on the predicted characteristic temperature of the PTH. Finally, the predicted models were used to calculate the cumulative annual hours and the intensity of the greenhouse effect of four different climate cities (Harbin, Beijing, Chengdu, Guangzhou, China). The results showed that: (1) the predicted temperature values of the model considering long-wave radiation were closer to the experimental results; (2) the effect level of the long-wave radiation on the three characteristic temperatures of the PTH from big to small was: exterior-surface temperature, interior-surface temperature, and indoor temperature; (3) the long-wave radiation had the greatest impact on the predicted temperature value of the roof; (4) under different climate conditions, the cumulative annual hours and the intensity of the greenhouse effect considering long-wave radiation were smaller than those without considering long-wave radiation; (5) the duration of the greenhouse effect considering and ignoring long-wave radiation varied significantly with the climate region, and that in Guangzhou was the longest, followed by Beijing and Chengdu, and that in Harbin was the shortest.
... The sky temperature shows the widest differences between the programs. There are two main algorithms used to calculate the sky temperature: Clark and Allan (Clark 1978) and Martin and Berdahl (Martin 1984). Both these algorithms start with an empirical relationship for the clear sky emissivity based on the dew point temperature, but Martin and Berdahl further applies correction factors for the time of day and the elevation of the site. ...
The demand for space cooling and heating has surged with the development of technology, posting a global challenge that requires sustainable thermal management solutions. Spectrally selective thermal radiation management stands out as a particularly promising approach due to its zero-energy consumption feature. This review first examines the specific scenarios where thermal demand applies and evaluates the theoretical energy-saving potentials of radiative cooling (RC), solar heating (SH), and dynamic radiative cooling (DRC) technologies. Subsequently we outline the operational principles and recent progress in various innovative research areas. Additionally, we explore the broad prospects of spectrally selective thermal radiation management in addressing urban heat island effects, advancing green energy initiatives, facilitating water desalination, and improving energy effectiveness across diverse applications. This review identifies major challenges and emerging opportunities for future research, offering an in-depth guide to advancing the frontiers of sustainable thermal management technologies.
With growing demands on energy supply across the world, combined with increasing concern about environmental sustainability, there is a rising need for innovative cooling methods. Traditional active cooling systems are effective yet very energy-consuming and contribute a lot to environmental degradation. Passive radiative cooling technologies represent promising alternatives for reducing energy consumption and mitigating heat accumulation, especially in urban areas. this study focused on four single-layer configurations of varying percentages of SiO2 coated on aluminum substrates in radiative cooling performance evaluation. It evaluates the effect of radiative cooling processes on the temperature of these coatings compared to the ambient conditions and the uncoated aluminum substrate. Numerical simulations using COMSOL Multiphysics have been used to assess their cooling performances, with experimental validations under a humid climate. For instance, in Rabat, Morocco in order to see their influences on cooling performance. We conclude that the SiO2 coatings on aluminum reduces the surface temperature between 2.4 °C and 3.15 °C below the ambient air temperature and drop by 1.4 °C to 4.23 °C compared to Aluminum uncoated during night periods. This work, therefore, optimizes passive cooling solutions using SiO2 coatings in humid climates and thereby offering a perspective on environmentally sustainable, energy-efficient cooling technologies.
Amidst the escalating environmental concerns driven by global warming and the detrimental impacts of extreme climates, energy consumption and greenhouse gas emissions associated with refrigeration have reached unprecedented levels. Radiative cooling, as an emerging renewable cooling technology, has been positioned as a pivotal strategy in the fight against global warming. This review examines the theoretical model of radiative cooling emitters and complex practical environment. We first investigate the thermodynamic interactions between environmental factors and the cooling surface, followed by an examination of innovative modulation techniques such as asymmetric/non-reciprocal radiative heat transfer mechanisms. Additionally, we summarize the latest advancements in structural design and simulation methodologies for radiative cooling materials at the device level. We then delve into potential applications of radiative cooling materials in various scenarios including energy-efficient construction, personal thermal management, photovoltaic cooling, and dynamic passive daytime radiative cooling materials with seasonal adaptability. In conclusion, we provide a comprehensive overview of this technology’s strengths and current challenges to inspire further research and application development in radiative cooling technology with a focus on contributing towards energy conservation objectives and promoting a sustainable society.
Due to climate change, population increase and the urban heat island effect (UHI) the demand for cooling energy especially in urban areas has been on the rise and is expected to further increase in the future. Previous conventional cooling systems for buildings like air conditioners are based on thermodynamic cycles that account for a large share of electricity demand while dissipating waste heat and carbon dioxide (CO2) into the environment.
Technologies such as radiative cooling offer a sustainable and energy-free solution by using the wavelength ranges of the atmosphere that are transparent to electromagnetic radiation, the so-called atmospheric window (8–13 μm), to emit thermal radiation into the colder (3 K) outer space. By designing coatings that selectively emit heat through the atmosphere while absorbing less solar heat, cooling below ambient temperatures even during the day is possible.
While previous publications in the field of textile building cooling have focused on specific fiber structures and textile substrate materials as well as complex multi-layer constructions, which restricts the use for highly scaled outdoor applications, this thesis aims to develop a novel substrate-independent coating with spectrally selective radiative properties.
Through the detailed adjustment of coating parameters such as particle concentration, distribution, and size, combined with low-emitting and solar-reflective particles, along with a matrix material emitting strongly in the mid-infrared range (MIR), substrate-independent cooling below ambient temperature is achieved, as demonstrated using three types of fabric typical for membrane and tent construction. Moreover, the coating is designed to be easily applicable, with a low thickness to ensure high flexibility and scalability.
To validate the viability of the developed coating system, outdoor testing is conducted using a tailored measurement setup to measure temperature differences and cooling power under real weather conditions. The results show a median daytime temperature reduction (7 a.m.–7 p.m.) of 2 °C below ambient temperature on a hot summer day. Additionally, a thermal model for textiles is adapted and validated to simulate and calculate the cooling power for different weather scenarios.
This thesis contributes to the advancement of sustainable textile-based cooling technologies, offering a promising solution to address the growing demand for energy-efficient cooling in urban environments.
The energy consumption of buildings is usually different from that predicted at the design stage. To measure the performance gap between designed and as-built buildings, it is possible to measure the actual Heat Transfer Coefficient, which characterizes the thermal performance of the building envelope. The actual reference method for measuring this coefficient is the co-heating test, which consists in normalising the heat input into a building with respect to the indoor-outdoor air temperature difference. However, the use of this method is limited to a certain period of the year when weather conditions allow a sufficient temperature difference, while avoiding heating the building to temperatures that could damage it. This work proposes to extend the period of validity of co-heating tests by using an equivalent outdoor temperature. This equivalent outdoor temperature allows to account for the impact of solar radiation and sky radiation which have a larger impact in hotter periods. This paper explores and demonstrates the feasibility of this new method from an experimental campaign and numerical simulations run in a summer period. It extends the co-heating feasibility period, throughout the year for the coldest climates and between seasons for the warmest climates. The results from the experimental campaign agree with the simulated data results.
To meet the increasing need for outdoor personal thermal management (PTM) since the intensified global warming, radiative cooling (RC) textiles with tunable solar reflectivity and mid-infrared emissivity/transmissivity attributes can dynamically...
This study explores the optical design of a daytime radiative cooler with near-ideal solar reflectance and longwave infrared (LWIR) emittance through materials selection and nanostructuring. Focusing on polymers as a materials platform, we introduce a bilayer architecture, comprising a porous poly(vinylidene fluoride-co-hexafluoropropene) (P(VdF-HFP)) topcoat that serves as a low-index LWIR emissive effective medium, over a nanofibrous, solar scattering polytetrafluoroethene underlayer. This novel configuration yields a superwhite coating with a near-ideal solar reflectance of >0.99, and a blackbody-like near-normal and hemispherical LWIR emittances of ∼0.98 and ∼0.96 respectively. Under humid and partially cloudy sky conditions unfavorable for radiative heat loss, these values enable the bilayer radiative cooler to achieve a sub-ambient of 2.3 °C. Given that the porous polymer bilayer uses scalable fabrication processes and commercially available materials, it holds significant promise for device-scale, as well as building thermoregulation applications.
Radiative thermoregulation has been regarded as an energy‐efficient method for thermal management. In this study, the development of a mechanoresponsive polydimethylsiloxane (PDMS) micro‐nanofiber matrix capable of both sub‐ambient radiative cooling and solar heating is presented, achieved through a core‐shell electrospinning technique. The electrospun PDMS micro‐nanofibers, with diameters comparable to the solar wavelengths, exhibit excellent solar reflectivity (≈93%) while preserving its pristine high infrared (IR) emissivity. As a result, the electrospun PDMS radiative cooler (EPRC) successfully demonstrated sub‐ambient radiative cooling performance (≈3.8°C) during the daytime. Furthermore, the exceptional resilient property of PDMS facilitated the reversible alteration of the structural morphology created by the fiber‐based matrix under mechanical force, resulting in the modulation of solar reflectivity (≈80%). The precise modulation of solar reflectivity enabled reversibly switchable multi‐step radiative thermoregulation, offering enhanced flexibility in addressing varying thermal environments even in maintaining the desired temperature. The findings of this work offer a promising approach toward dynamic radiative thermoregulation, which holds significant potential for addressing global climate change concerns and energy shortage.
Radiative cooling, a technology that lowers the temperature of terrestrial objects by dissipating heat into outer space, presents a promising ecologically‐benign solution for sustainable cooling. Recent years witness substantial progress in radiative cooling technologies, bringing them closer to commercialization. This comprehensive review provides a structured overview of radiative cooling technologies, encompassing essential principles, fabrication techniques, and practical applications, with the goal of guiding researchers toward successful commercialization. The review begins by introducing the fundamentals of radiative cooling and the associated design strategies to achieve it. Then, various fabrication methods utilized for the realization of radiative cooling devices are thoroughly discussed. This discussion includes detailed assessments of scalability, fabrication costs, and performance considerations, encompassing both structural designs and fabrication techniques. Building upon these insights, potential fabrication approaches suitable for practical applications and commercialization are proposed. Further, the recent efforts made toward the practical applications of radiative cooling technology, including its visual appearance, switching capability, and compatibility are examined. By encompassing a broad range of topics, from fundamental principles to fabrication and applications, this review aims to bridge the gap between theoretical research and real‐world implementation, fostering the advancement and widespread adoption of radiative cooling technology.
A robust representation of the radiative properties in complex urban settings is important for accurate estimations of radiant load. Here, we present a new parameterization scheme in the SOlar and LongWave Environmental Irradiance Geometry (SOLWEIG) model that partitions the upper hemisphere into 153 patches. Partitioning of the upper hemisphere enables determination if longwave irradiance originates from the sky, vegetation, sunlit building surfaces, or shaded building surfaces from each patch. Furthermore, a model for anisotropic sky longwave irradiance where emissivity increases with zenith angle is included. Comparisons between observations and simulations show high correlation, with R2 and RMSE for Tmrt of 0.94 and 4.6 °C, respectively, and R2 and RMSE for longwave radiation of 0.89 and 14.1 Wm-2, respectively. Simulations show that mean radiant temperature (Tmrt) can be up to 1.5 °C higher with an anisotropic sky compared to a uniform sky as an effect of higher radiant load on the vertical of a human when sky longwave irradiance increases with zenith angle. In comparisons of simulated Tmrt with the new parameterization and old parameterization schemes, previously overestimated Tmrt under trees (high sky obstruction, sky view factor (SVF) < 0.3) can be decreased by up to 3 °C from more realistic estimations using the patches. Moreover, Tmrt close to sunlit walls (SVF ~ 0.5) is increased by up to 2-3 °C from increased exposure to sunlit surfaces. Concluding, anisotropic sky longwave radiation and directionality of longwave radiation from different sources are important in estimations of Tmrt of humans in outdoor settings.
This chapter details the basis of heat transfer and the basic principles of radiative cooling, including different mathematical and physical descriptions of thermal radiation, infrared sky radiation, solar radiation, and parasitic cooling losses.
The surface temperature of a passive daytime radiative cooler (PDRC) can be lower than the ambient temperature without consuming any extra energy. Thus, the technology of the PDRC has attracted the attention of researchers recently. However, most current studies only focused on the short-term performance of the PDRC during sunny and cloudless days. The influence of clouds and variations of atmosphere total column water vapor on the long-term performance of PDRC have not been investigated in previous research. In this study, a radiative cooling model considering the influence of total column water vapor and clouds was developed for PDRC, and TMY weather data files with total column water vapor were generated for estimating the annual performance of PDRC in five selected major climate zones in China. The results showed that the high total column water vapor would deteriorate the performance of the PDRC. Considering the impact of cloud or not, the difference in potential of achieving sub-ambient cooling during daytime annually ranged from 12.68 % to 43.35 % in five cities, i.e., Harbin, Beijing, Shanghai, Kunming, and Guangzhou. The results also indicated that the selective PDRC always achieved a slightly better performance than the broadband one. Finally, the potential of applying PDRC in five selected cities was estimated. The results demonstrated that the PDRC could yield satisfying performance in Beijing, Shanghai, Guangzhou, and Kunming, with the energy-saving potential of 39.53 kWh/m², 221.40 kWh/m², 435.82 kWh/m², 97.26 kWh/m², respectively.
Reconciling the use of space and the production of low‐carbon electricity is a key challenge in the face of changing human needs. In this context, floating photovoltaics (FPV) is proving to be a key application to colocate energy production with several activities (hydroelectricity and aquaculture). A major benefit of FPV technologies is the reduced module temperature. However, the causes of this thermal observation are still unknown. The density of the distribution of the floaters and the thermal behavior of the waterbody are two postulated roots that show positive correlations with regard to the module temperature. Therefore, there is interest in identifying precise thermal features in the application because the yield surplus promised in FPV technology is based on this cooling effect. This research aims to understand the heat mechanisms that arise in this application in comparison with ground‐mounted photovoltaics (PV). A special framework based on 1‐D thermal modeling and statistical classification of the results by dimensionless related features is proposed. This strategy offers a possibility to differentiate the influence of the thermal modes separately over the module temperature. First, a gain of 20% to 50% in the convective transfers is demonstrated for FPV compared with ground‐mounted applications. Data exploitation associates these gains with the forced convective effects of the wind blowing on the front of the modules. Gains in free convective transfers are associated to the airflow around the module rear face, reducing the phenomenon of thermal buffering. The framework also demonstrates that the emissivity‐based correlations for the radiative boundaries are in good agreement with the radiative phenomena involved in FPV. When convection preferentially cools down the module, the participating media nearby acts as a heat source, warming the installation. Thus, understanding these mechanisms in the FPV application would provide opportunities for improved temperature management through floats or array‐scale optimizations.
Building Performance Simulation (BPS) tools rely on different methods to estimate the downwelling longwave radiation incident on surfaces, which can be expressed as an equivalent “effective sky temperature”. The longwave radiation is calculated using regressions based on the temperature, humidity, and cloud cover. This paper assesses the regressions implemented in 3 popular BPS tools (EnergyPlus, TRNSYS, and ESP-r) using measured data for the downwelling longwave radiation obtained from the SURFRAD network for 2 stations in Illinois and Colorado. Results show that the 3 regressions deliver acceptable estimations of the sky temperature. Differences are relatively small, with CVRMSD values in the order of 10 %. The impact on simulation results is also relatively small but not insignificant compared to other factors, especially in the context of inter-model validation exercises. The effective sky temperature is also required to model other energy systems such as unglazed solar collectors. A simulation of a PV/T collector shows that the useful thermal energy output changes by up to 11 % depending on the regression used.
This report describes a computer code for predicting atmospheric transmittance and the thermal radiation emitted by the atmosphere and Earth from 350 to 40,000 per cm at a spectral resolution of 20 per cm. The program is based on the LOWTRAN 4 (1978) computer code. New altitude and relative humidity dependent aerosol models and new fog models are included in the code. In addition, the new code structure consists of a main program and 19 subroutines. The computer code contains representative (geographical and seasonal) atmospheric models and representative aerosol models with an option to replace them with user derived or measured values. The program can be run in one of two modes, namely, to compute only atmospheric transmittance or both atmospheric transmittance and radiance for any given slant path geometry.
Extensive measurements of the thermal IR radiance of the sky were obtained at 6 U.S. locations: Tucson, AZ; San Antonio, TX; Gaithersburg, MD; St. Louis, MO; West Palm Beach, FL; and Boulder City, NV. Fifty thousand observations were obtained at half hour intervals during 1979 and 1980. Each observation consists of measurements in 7 spectral bands, wavelengths (in microns) of 8.1–13.7, 8.3–9.1, 9.4–9.9, 10.0–11.4, 14.0–15.8, 16.6–21.6 and 6–17 at zenith angles of 0, 20, 40, 60 and 80°. The data have been expressed and presented as apparent sky emissivities. It is shown that the measured spectral and angular sky emissivities can be reliably estimated from a knowledge of the total (global) sky emissivity, using an empirical “sky emissivity” equation. The results are of particular relevance to the performance of radiative cooling systems designed to make use of spectral and/or angular selectivity.
The effects of atmospheric IR radiation must be accounted for in energy budget computations of solar collectors. IR radiation is often parameterized by determining an equivalent sky temperature dependent on surface temperature. Hourly values of IR radiation were computed at eleven stations in the United States in 1971 and 1972 and the equivalent sky temperature obtained. The model used for these computations was verified by comparison with special observations in the Lake Ontario region taken during the International Field Year of the Great Lakes (IFYGL) in 1972. Differences between surface temperature and sky temperature ranged between 5 and 20°C and are a complex function of season (specifically of cloudiness, humidity, and surface temperature) and geographical location.
The effective atmospheric emissivity, F/(T04), where F is the downward radiative flux density and T04 the blackbody flux density at the surface temperature T0, is computed for clear skies and straight temperature and dew-point soundings by means of emissivity integrations. Emissivity data by Jurica and by Staley and Jurica were used, and separate computations made for H2O, CO2, H2O-CO2 overlap, and O3. The effective atmospheric emissivity depends almost entirely on surface vapor pressure, decreases slightly with increasing surface elevation, and is essentially independent of surface temperature. The contribution by CO2 decreases from about 0,19 to about 0.17 as surface elevation increases from sea level to 710 mb. The contribution of overlap is negative and increases rapidly with increasing surface vapor pressure, becoming comparable to the CO2 contribution for very large vapor pressures. Measurements support the computations, but suggest, as has been found before, additional downward flux density from aerosols or from as yet unspecified trace gases.
Dans un article recent cite en bibliographie, Berdahl et Fromberg ont etudie la radiance thermique des ciels sereins et presente des resultats de mesures pour trois villes des U.S.A. sous la forme d'une correlation entre l'emissivite du ciel et la temperature du point de rosee de la surface. On presente ici des donnees complementaires et la formule correspondante amelioree pour l'emissivite du ciel
A test facility designed to measure the amount of radiative cooling a specific material or assembly of materials will produce when exposed to the sky is described. Emphasis is placed upon assemblies which are specifically designed to produce radiative cooling and which therefore offer promise for the reduction of temperatures and/or humidities in occupied spaces. The hardware and software used to operate the facility are documented and the results of the first comprehensive experiments are presented. A microcomputer-based control/data acquisition system was employed to study the performance of two prototype radiator surfaces: 4-mil aluminized polyvinyl fluoride (PVF) and white painted surfaces set below polyethylene windscreens. The cooling rates for materials tested were determined and can be approximated by an equation (given). A computer model developed to simulate the cooling process is presented. (MCW)
The results of a ruby lidar (0.694 micrometre wavelength) and infrared radiometer (10-12 micrometre) study on cirrus clouds are reported for a period covering the autumn and winter months at Aspendale (38oS, 144oE). The lidar and radiometer data have been used to study the temperature dependence of the gross structure and optical properties of cirrus clouds. Well-defined correlations are found between the mid-cloud temperature and cloud depth, infrared absorption coefficient, infrared emittance, backscatter to extinction ratio and ratio of the visible extinction coefficient at 0.693 micrometre to the infrared absorption coefficient at 10-12 micrometre. -from Authors
Measurements of the longwave radiance of the sky were made during the summer of 1979 at Tucson, Arizona; Gaithersburg, Maryland; and St. Louis, Missouri. The global longwave radiation (wavelengths greater than 3 μm) was monitored with a pyrgeometer and the distribution of this radiation in several spectral bands at five different zenith angles was monitored with a spectral radiometer. This paper presents results for the global sky radiation during clear sky conditions. The spectral radiometer was used to calibrate the pyrgeometer and to detect the presence of clouds. The results can most appropriately be summarized in terms of the correlation between the global sky emissivity ϵsky and surface dewpoint temperature Tdp(°C). The global sky emissivity is defined as the ratio of sky radiance to σTa4, where Ta is the absolute air temperature near the ground, and σ is the Stefan-Boltzmann constant. Based on 2945 night-time measurements in all three cities we find with a standard error of estimate of 0.031. A similar relationship with almost identical coefficients holds during daylight hours.
Passive cooling strategies for nonresidential buildings: impact assessment
- C Peterson
- F Mangeng
- W I Roach
- K Whiddon
- Hart
Peterson, C. Mangeng, F. Roach, W. I. Whiddon, and K. Hart, Passive cooling strategies for nonresidential buildings: impact assessment. Lawrence Berkeley Laboratory Report, LBL-14558 (1982).
Passive cooling strategies for nonresidential buildings: impact assessment
- Carroll