Heat Reflective Coatings Research Articles

Transparent Sol-Gel-Based Coatings Reflecting Heat Radiation in the Near Infrared.

Thin, flat textile roofing offers negligible heat insulation. In warm areas, such roofing membranes are therefore equipped with metallized surfaces to reflect solar heat radiation, thus reducing the warming inside a textile building. Heat reflection effects achieved by metallic coatings are always accompanied by shading effects as the metals are non-transparent for visible light (VIS). Transparent conductive oxides (TCOs) are transparent for VIS and are able to reflect heat radiation in the infrared. TCOs are, e.g., widely used in the display industry. To achieve the perfect coatings needed for electronic devices, these are commonly applied using costly vacuum processes at high temperatures. Vacuum processes, on account of the high costs involved and high processing temperatures, are obstructive for an application involving textiles. Accepting that heat-reflecting textile membranes demand less perfect coatings, a wet chemical approach has been followed here when producing transparent heat-reflecting coatings. Commercially available TCOs were employed as colloidal dispersions or nanopowders to prepare sol-gel-based coating systems. Such coatings were applied to textile membranes as used for architectural textiles using simple coating techniques and at moderate curing temperatures not exceeding 130 °C. The coatings achieved about 90% transmission in the VIS spectrum and reduced near-infrared transmission (at about 2.5 µm) to nearly zero while reflecting up to 25% of that radiation. Up to 35% reflection has been realized in the far infrared, and emissivity values down to ε = 0.5777 have been measured.

NIR reflective lanthanum zirconate (La2Zr2O7) ceramic colorant and its solar heat reflective glaze coatings

Pyrochlore-type rare earth ceramics are ideal for high-temperature coatings due to their exceptionally low thermal conductivity, high-temperature stability, and chemical inertness. To reduce the impact of urban heat island effect, ceramic colorants and coatings made of such materials are now required. The impact of iron oxide chromophore is investigated in this study on pyrochlore type lanthanum zirconate (La2Zr2O7) to make solar heat reflecting ceramic yellow colorant, and the same is then used for creating multifunctional glaze coatings. Using appropriate methods, the impact of iron oxide on the morphological, optical, and solar heat reflection properties of the yellow colorant is examined. The pyrochlore crystal structure and 93% NIR reflectivity of lanthanum zirconate were not impacted by the doping of iron oxide. Additionally, the glaze coating developed from the yellow colorant, surface non-wettability, NIR reflectivity, and tinting behavior were comprehensively examined and presented for the first time. The findings strongly indicated that pyrochlore La2Zr2O7 is a candidate to produce ceramic functional materials and coatings with sustained energy savings. This work opens up fresh possibilities for functional glaze coating applications using the pyrochlore type ceramic materials.

Modelling sustainable transparent metasurfaces for tunable near infrared reflectance

Transparent conducting oxide (TCO) nanodisk metasurfaces on polymer substrates were modelled for high visible transmittance (400–750 nm) of more than 97%. An increase in the nanodisk diameter tuned the resonant wavelength between 840 and 1200 nm based on the transparent oxide material and the plasmonic metasurface geometry. The optical properties of ethylene tetrafluoroethylene (ETFE) and polyethylene terephthalate (PET) polymer substrates were imported for simulating the reflectance, transmittance and near field distributions for a TiO2/Ag/TiO2 metasurface. A high reflectance of 92.33% was observed for a specific three tier titanium dioxide (TiO2)/silver (Ag)/TiO2 geometry at a resonant wavelength of 1130.6 nm. High electric field localisation was exhibited at the resonant wavelength, which was compared at three interfaces, TiO2-air, TiO2-Ag and TiO2-polymer, for varying nanodisk diameters. A red shift in the resonant wavelength was recorded with a change in polymer substrate and nanodisk geometry. The use of fully recyclable polymers and the long-lasting nature of TiO2 can be beneficial for the fabrication of sustainable heat reflective films or coatings.

Effects of load and environment on the durability and anti-skid performance of road heat-reflective coating

• Studied the heat-reflective coating of asphalt pavement. • Systematically studied the durability of heat-reflective coating. • Investigated the effect of anti-skid particles on the cooling performance of coating. • Studied the optimal dosage of anti-skid particles. Reducing high temperature rutting on asphalt pavement is of great importance to improve the quality of pavement engineering and road traffic safety. In laboratory and field tests, this study investigates the cooling performance and optimal dosage of heat-reflective coatings. The temperature-change resistances, water stabilities, abrasion resistances, and skid resistances of six colored heat-reflective coatings were studied. Among the differently colored coatings, the red coating demonstrated the best cooling performance, with a maximum cooled temperature of 13.2 °C. The colored heat-reflective coatings showed good temperature-change resistance, water stability, and abrasion resistance. At dosages of 0.35 and 0.55 kg/m 2 , the heat-reflective coating met the specification requirements of skid resistance; meanwhile, the coating added at 0.75 kg/m 2 achieved the highest cooling performance but failed to meet the required skid-resistance standards. After adding anti-skid particles, the skid resistance was improved while the cooling performance was hardly affected. The optimal dosage of anti-skip particles was 0.3 kg/m 2 .

Design and Experimental Evaluation of Composite Magnesium Phosphate Cement-Based Coating with High Cooling Effect

The application of surface heat reflective coatings is one of the effective measures to solve the temperature disease of concrete structures in sunlit environments. To achieve strong bonding, high durability, and good cooling characteristics, a novel inorganic reflective thermal insulation coating was prepared using magnesium phosphate cement (MPC) as the binder and reflective matrix, and titanium dioxide and glass beads as the reflective thermal insulation reinforcement functional additives. The optimum ratio of the new reflective thermal insulation coating was preferred through laboratory irradiation test, thermal conductivity test, and spectral reflectance test. The results show that MPC itself was a good reflection cooling material, and the surface and internal temperatures of concrete blocks were reduced by 7.6 °C and 6.6 °C, respectively, after using MPC as the cooling coating. When 2% titanium dioxide was added to MPC, the surface and internal temperatures were further reduced by 6.0 °C and 4.9 °C, respectively. On top of this, the surface and internal temperatures of the concrete were reduced by a further 3.9 °C and 2.2 °C when 8% glass beads were added. The bond strength of the MPCTG coating to the concrete matrix reached 2.1 MPa. Finally, the microscopic characteristics and the reflective thermal insulation mechanism of the MPCTG coating were investigated with the aid of SEM, thermo gravimetric analysis, and XRD analysis. The results show that the MPC in the MPCTG coating was well hydrated, and a large number of hydration products encapsulated the unreacted MgO particles, titanium dioxide, and glass beads, forming a dense whole with high reflection and low thermal conductivity, and the coating effectively prevented the entry of radiant heat. At the same time, the MPCTG coating was thermally stable below 70 °C. The magnesium phosphate cement-based reflective thermal insulation coating developed in this study has potential application prospects in concrete structure cooling coatings.

Regulating the albedo and radiation absorption of engineering surfaces for cooling the embankments in high-altitude permafrost regions

Under the influences of global warming and strong solar radiation, the construction of the wide high-grade roads in high-altitude permafrost regions becomes more challenging. To reach the challenges and further improve the thermal-mechanical stabilities of the permafrost embankment, this study proposes a novel cooling embankment structure based on the heat-reflective coatings. The principle is to reduce and regulate the solar radiation absorption by the permafrost embankment surface, thus improving the temperature field of the embankment and preventing uneven settlement and other freeze-thaw damages of the embankment. First, a theoretical-empirical model is proposed to describe the transfer processes of incident radiations on the pavement and slope surfaces. Based on the model, we carry out a systematic study of the main factors influencing the solar radiation absorption of the embankment surfaces and their variation patterns. By analyzing the calculation results, we propose the regulating schemes of the heat-reflective coatings for the radiation absorption balance of the embankment surfaces. Meanwhile, the solar albedo properties of the heat-reflective coatings under different solar spectral are also studied. The results indicate that the heat-reflective coatings can significantly reduce the solar radiation absorbed by the embankment surfaces. It proves that the cooling embankment structure and albedo regulation schemes proposed in this paper are expected to be applied in practical engineering. Finally, we discuss the shortcomings of the current research and the next research plans.

Attenuation pattern of skid resistance of heat reflective coatings under the effect of simulated pavement abrasion

ABSTRACT The cooling performance of heat reflective coatings (HRC) for pavement applications has attracted wide attention. In this study, the cooling performance and bond strength of HRC were investigated and the attenuation pattern associated with the skid resistance of specimens sprayed with different amounts of HRC coating was examined based on four-wheel wear test. Furthermore, an asymptotic model associated with the attenuation of the HRC’s skid resistance was developed for investigating the effects of anti-slip particle gradation and dosage as well as HRC dosage on the skid resistance. The results show that the cooling performance and bond strength of HRC (sprayed amount: 0.8 kg/m2) are 12.4 °C and 1.75 MPa, respectively, and the skid resistance of HRC sprayed with different amounts of HRC was stabilised at approximately 48 BPN after 150,000 abrasion cycles. The attenuation pattern of the skid resistance of the skid-resistant HRC (SHRC) fitted well with the developed asymptotic model, showing a correlation coefficient exceeding 0.99 and an error of less than 5% from the test value. Anti-slip particle gradation (G4), anti-slip particle dosage (0.6 kg/m2) and HRC dosage (0.6 kg/m2) were selected based on the stable value of the skid resistance, and SHRC was developed for pavement applications.

Enhanced near-infrared reflectance and functional characteristics of nano metal oxide embedded alkyd coatings

The main idea of the research is to formulate alkyd based smart coatings with high NIR-reflectance to decrease the cooling load in order to maintain cool comfort in buildings. In addition to the NIR reflectance studies, the physical characteristics of the coating such as glossiness, hiding power, spreading area, volatile organic contents are evaluated. Heat reflective coatings are prepared by ball milling technique utilizing white metal oxide nanoparticles (NPs) titanium oxide (TiO2), zinc oxide (ZnO) and zirconium oxide (ZrO2) as pigments. The x-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) results reveal the prepared metal oxide pigments are of high purity. Bonding interaction between the alkyd resin and the NPs are studied using Fourier transform infrared spectroscopy (FTIR).The spectral reflectance of the prepared coatings are measured using spectrophotometer in the solar spectrum range, wherein ZnO based nanocoatings shows better results. The cool comfort is measured for ZnO nanocoatings in an enclosed glass cabinet and the differences in temperature with respect to exposure to sunlight are highlighted. Finally, a prototype coated with ZnO NPs maintains lower indoor temperature than the commercially available white paint coated model in the order of 2.7 °C.

Lab-Controlled Experimental Evaluation of Heat-Reflective Coatings by Increasing Surface Albedo for Cool Pavements in Urban Areas

Many studies were conducted to find possible strategies for reducing the urban heat island (UHI) effect during the hot summer months. One of the largest contributors to UHI is the role that paved surfaces play in the warming of urban areas. Solar-reflective cool pavements stay cooler in the sun than traditional pavements. Pavement reflectance can be enhanced by using a reflective surface coating. The use of heat-reflective coatings to combat the effects of pavements on UHI was pre-viously studied but no consistent conclusions were drawn. To find a conclusive solution, this work focuses on the abilities of heat-reflective pavement coatings to reduce UHI in varying weather conditions. Within this context, both concrete and asphalt samples were subject to a series of per-formance tests when applied to a heat-reflective coating, under the influence of normal, windy, and humid conditions. During these tests, the samples were heated with a halogen lamp and the surface temperature profile was measured using an infrared thermal camera. The air temperature was recorded with a thermometer, and the body temperature at multiple depths of the samples was measured using thermocouples. The results from these tests show that the effectiveness of the heat-reflective coating varies under different weather conditions. For instance, the coated samples were about 1 °C cooler for concrete and nearly 5 °C cooler for asphalt, on average. However, this temperature difference was reduced significantly under windy conditions. As such, the findings from this work conclude that the heat-reflective coatings can effectively cool down the pavement by increasing the surface albedo, and thus might be a viable solution to mitigate UHI impacts in the city/urban areas.

Durability of a heat-reflective coating on an asphalt pavement

A heat-reflective coating can be used to solve various problems, including rutting and deformation caused by the excessively high asphalt pavement temperatures during summer. However, the durability of the heat-reflective coatings applied to asphalt pavement has not been extensively researched. The colour changes, crack development and attenuation of the cooling performance are studied along with the changes in skid resistance and cooling performance because of wear. Subsequently, the lifespan of the heat-reflective coating is predicted based on the results. This study indicates that the amount of spraying is positively correlated with the cooling performance. After 120 days of aging, a B–A type coating shows no cracks or any decay in performance. When the wear rate is less than 40%, the skid resistance of the coating meets the required specifications and the coating exhibits good cooling performance. The lifespan of the heat-reflective coating is predicted to be one year.

Structure effect of the envelope coupled with heat reflective coating and phase change material in lowering indoor temperature

The building envelopes that integrate heat reflective coatings (HRCs) and phase change materials (PCMs) can block solar radiation from outdoors and have a high thermal inertia, which helps lower the indoor temperature and save the cooling energy costs. However, an inappropriate combination of the two materials could lead to a worse cooling performance. This paper studies the cooling performance of a wall which is coated with the HRC, coupled with a cavity filling the PCM and insulation materials. This work intends to find out the optimal way of integrating the HRC and PCM together to improve the passive cooling performance of the envelope. The effects of the relative positions of HRC and PCM boards on the indoor temperature are studied by comparing 15 combinations of HRCs and PCMs. The results show that the HRC coated on the exterior surface of the wall can block the radiation heat more efficiently than that on the interior surface. An insulation layer between the HRC and PCM is essential to improve the thermal regulation performance of the wall. The insulation layer avoids the fast heat conduction through the PCM and decouples the roles of the HRC as a radiation reflector and the PCM as a thermal storage medium. The thermal conductivity of PCMs, the thickness of PCM layers as well as insulation air gap are also changed to investigate their influence on temperature fluctuations. The RT31/SiO2 (0.09 W/m K) can effectively reduce the indoor temperature by up to 3.6°C compared with the RT31/expanded graphite (EG) (1.25 W/m K). The optimum thickness of both PCM cavity and air cavity are no more than 8 mm. The work provide an insight into the optimal combination of the PCM and HRC in the building envelope for passive cooling.

Influence of Heat Reflective Coating on the Cooling and Pavement Performance of Large Void Asphalt Pavement

To reduce the temperature of asphalt pavement in summer, and alleviate the urban heat island effect, a comprehensive method of combining a heat reflective coating and large void asphalt pavement was proposed. Using the developed coating cooling test equipment, the cooling effect of the coating on a large void asphalt mixture was studied in six different proportions, four different colors, and four different dosages, and the durability of the coating was verified by abrasion tests. Finally, the best dosage of the coating was recommended through an adhesion test of the coating, and a water permeability and anti-skid performance test of the pavement. The results show that the reflectivity of the coating can be improved by adding functional fillers, of titanium dioxide and floating beads, into the coating. The order by reflectivity and cooling effect of the four color coatings was green > red > gray > blue, and the maximum cooling value of the green coating reached 9.7 ℃. The cooling performance of the coating decreased with the increase of wear time, and the rate of decrease was fast, then slow, and finally tended to be stable after 20,000 times wear. The coating reduced the anti-skid performance and the water permeability coefficient of large void asphalt pavement, but still maintained a high level. The green coating with 15% titanium dioxide and 10% floating beads is recommended as the cooling coating for large void asphalt pavement, and its dosage should be controlled at about 0.4–0.8 kg/m2.

Cross-overlapped flat-silver/hexagonal boron nitride for translucent heat-reflective coatings

Multifunctional heat-reflective coatings are increasingly in demand for use in energy-efficient buildings and vehicles, as well as for optoelectronic devices. Conventional heat-reflective coatings (e.g. dielectric/metal/dielectric (DMD)) exhibit poor structural flexibility and combine complex fabrication process of multilayered structures, which hinders their scalable production. Herein, a low-cost translucent heat reflective mechanism is presented using single-coat composite film of flat-silver (flat-Ag) and hexagonal boron nitride (hBN) as an alternative to the multilayered DMD structure. The conversion of grey Ag-nanoparticles into shiny flat-Ag results in significant enhancement (~7 times) in infrared (IR) reflection. The dielectric-hBN layers integrated with flat-Ag improves the visible transmittance and heat-dissipating properties of coatings. The flat-Ag/hBN ink sprayed onto a flexible, transparent, and adhesive substrate of polydimethylsiloxane (PDMS) exhibits excellent IR-reflection (~70%) with ~57% visible transmittance. When irradiated by an IR heat source, the film displays 8.9 ± 0.5 °C lower temperature than those of uncoated surfaces, that results in reduction of the interior air-temperature by 5.4 ± 0.5 °C compared to the uncoated control. This newfabrication process of heat-reflective coatings with structural flexibility and optical transparency has great potentials to be used for thermal management in building and transportation sectors.

Solar Heat Reflective Coating for Sidewalks Considering Cooling Effect, Anti-Skid Performance, and Human Comfort

Abstract The solar heat reflective coating for sidewalks (SHRCS) is investigated in the present article. Compared with the reflective coating for the traffic lane, the reflective coating for the sidewalk has low requirements for abrasion resistance but high requirements for human comfort. Therefore, cooling characteristics, anti-skid performance, abrasion resistance, and sports performance are chosen to assess SHRCS. SHRCS consists of three layers, the bottom layer, the elastic layer, and the surface layer. The materials of the three layers were determined. Particularly, because the surface layer is composed of resin, functional materials, and pigments, the suitable surface resin was chosen from five kinds of resin, and the Taguchi orthogonal array design method was used to determine the optimal mix ratio of the surface layer materials. The in situ test shows that the surface of the road using SHRCS can be cooled by 5.9°C versus the original road surface. The temperature difference of the skin surface between standing on the coated and uncoated road can reach 1.6°C. In the end, the sports performance characteristics of SHRCS, such as the vertical ball rebound, were tested.

Development of Super Road Heat-Reflective Coating and Its Field Application

Heat-reflective coatings, used to reduce the asphalt pavement temperature and urban heat island effect, have a good cooling effect; coating development, however, generally focuses on cooling. This study aims to design a heat-reflective coating with both durability and cooling effect by considering the functions of each component, improving the coating bond strength and abrasion resistance, and conducting laboratory tests and test section verification. The coating developed exhibits bond strength and abrasion resistance 20% and 49%, respectively, higher than those of ordinary coatings. The experiments reveal a cooling effect of red coating up to 10.2 °C, a bond strength of up to 1.20 MPa at 25 °C, and an abrasion rate of up to 25% after 60 min; the cooling effect is basically the same as that for traditional heat-reflective coatings, but the bond strength and abrasion resistance significantly improved. In the analysis of the test section, the cooling effect reaches 7.0 °C, the performance of anti-skid decreases little, and the coating is still usable normally after 4 months.

Dark, heat-reflective, anti-ice rain and superhydrophobic cement concrete surfaces

Antifouling, weatherable, and heat-reflective coatings have much value for solar sheltering of building in summer. In this work, a multifunctional cement mortar mixture was obtained by mixing “cool cold” black pigments with cement, sand, TiO2 nanoparticles and water. After the mixture was mortared on a cement concrete slab, dried at room temperature and treated with fluorine silicon sol, a gray cement concrete layer was obtained. UV–visible-infrared spectrometer confirmed that the layer has obvious infrared-reflective property at 780–2500 nm. Under the radiation of a 275 W and 40 cm height infrared lamp, the surface temperature of the gray “cool cold” cement concrete is about 40 °C lower than that of the carbon black cement concrete, and is about 20 °C lower than that of the ordinary cement concrete, and is only about 1 °C higher than that of the white TiO2 cement concrete. Moreover, all these cement concrete surfaces showed typical superhydrophobic (SH) property and the “cool cold” cement concrete surface further exhibited stable SH properties to both rain and UV radiation, which may allow for self-cleaning performance for the surface and the ability to retain its heat-reflective property over a long period of time. Meanwhile, the “cool cold” cement concrete SH surface exhibited excellent anti-ice rain performance. Because the layer can be easily mortared on the cement concrete substrate, we think it would have great potential for use on building roof and outside walls to reduce air-conditioning energy consumption in the summer.

Analysis on Environmental Thermal Effect of Functionally Graded Nanocomposite Heat Reflective Coatings for Asphalt Pavement

The heat-reflective coating for asphalt pavement is a functional layer applied on pavement surfaces to reduce heat storage in the pavement via reflecting sunlight, thus inhibiting pavement temperature rise. The objective of this study was to analyze the environmental thermal effect of the self-developed reflective coating, namely, functionally graded nanocomposite reflective coatings, for asphalt pavement. The thermal effects of heat-reflective coatings were compared and analyzed based on field tests. A heating model of the atmosphere layer near the road surface was established. Moreover, the influence of urban road temperature on the thermal comfort of the human body was analyzed. Results showed that the radiation heat of all heat-reflective coatings decreased around two-thirds, and the convective heat decreased nearly 50% when compared with the control asphalt pavement, and the temperatures of the pavement itself and the atmosphere layer were lowered. Additionally, the heat-reflective coating improved the thermal comfort of the human body. This indicated that the heat-reflective coating reduced ambient temperate and relieved the urban heat island effect (UHI) as well as improved the environmental thermal effect.

Thermosetting powder coating for asphalt pavement

The high temperature in asphalt pavement during summer accelerates the rutting and aggravates the phenomenon of urban heat island (UHI). One of the mitigation methods is the use of heat-reflective coating (HRC) on asphalt pavement. However, conventional HRC faces some challenges such as poor abrasion resistance, poor skid resistance and environment pollution. In this paper, a new type of coating, named thermosetting powder coating (TPC), was developed for reflecting heat off asphalt pavement. Four types of TPCs, including the polyester powder coating (PPC), modified polyester powder coating (MPPC), polyester/epoxy powder coating (PEPC) and modified polyester/epoxy powder coating (MPEPC) were made. Meanwhile, A type of conventional HRC was chosen as a reference. Performances tests were conducted to evaluate the cooling effect, skid resistance, abrasion resistance, adhesion strength, anti-glare performance and erosion resistance of the asphalt concrete specimens coated by the TPCs or conventional HRC. Impacts on performances of several factors such as resin type, application rate and texture agent were discussed. Finally, the costs of the TPC and conventional HRC were compared. Results indicate that though the cooling effect and anti-glare performances of these two types of coatings are resembled, the skid resistance, abrasion resistance and adhesion strength of the TPC are better than those of conventional HRC. What’s more, the cost of the former is only 0.1 times of that of the latter. Among four types of TPCs, MPPC is recommended to be used for reflecting heat and its optimum application rate (dosage) is 100–150 g/m2.

Indoor and Outdoor Aging Behaviors of a Heat-Reflective Coating for Pavement in the Chongqing Area

AbstractThe indoor and outdoor aging behaviors of a heat-reflective coating were studied regarding the problems derived from aging and reduced cooling effects. A one-year natural exposure test of the coating on a roof and on concrete samples was conducted, and a 28-day xenon lamp aging test on concrete and cylindrical samples was carried out. Surface appearance, infrared spectrum, cooling value, and reflectivity changes in different aging periods were analyzed. The results show that the amount of solar radiation is a key factor in aging. Aging can cause a gradual increase in carbonyl content and thus lead to a decrease in resin light transmittance, given that the carbonyl group absorbs visible light and infrared rays easily. This results in a reduction in reflectivity and cooling value. Reflectivity and cooling value show a linear relationship in the indoor and outdoor aging process. With respect to reflectivity and cooling value, solar radiation has a downward quadratic parabolic tendency whereas xenon l...

Energy Saving Property of Heat-Reflective Coatings on Temporary Buildings

The energy saving of temporary buildings used heat-reflective coatings in cold region has been paid growing attention. Surface temperature and energy consumption were calculated by the temporary office building and factory building in Beijing. The buildings are color steel plate structure in this paper. The roofs and exterior walls of buildings were painted with heat-reflective coatings. The general solar reflectivity of roofs and exterior walls were about 26% and 22%; after the application of heat-reflective coatings the reflectivity increased to about 84% and 72%. Results demonstrated that the roofs have the best cooling effect, with the average surface cooling reaching 23.32°C in summer. The estimated energy savings of roof was about 9.95Wh/m2 per day and the energy consumption reducing rate was up to 67.7% in summer. Considering the energy consumption increased in winter, heat-reflective coatings were only strongly advised to paint on roofs in cold region.