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The increasing demand of reducing energy consumption in buildings has led to the implementation of insulation material in roof assemblies to reduce heat gain through the roof. This paper investigates the thermal performance of reflective insulation and radiant barrier systems in a gable roof assembly by using computational fluid dynamics (CFD) simu...
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... ensure that the results obtained by CFD simulation are acceptable, the CFD results must first be validated against some of the empirical results obtained by field test conducted by Teh et al. (2017). Due to limitations in conducting the field experiment, the RSI values obtained from CFD simulation and experimental measurements can only be compared against available data which are shown in Table 5. Figure 10 shows a comparison between the predicted RSI values using FloEFD and the measured RSI values for various configuration in different phases. ...Similar publications
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... For previous researchers' survey, the efficiency of the roofs amount from 15 % to 35.7 % across varies climatic, including temperate, dry-hot, tropical, and hot-humid. Furthermore, the application of cool roof technology can potentially have reduced the range of roof temperature from 1.4 to 4.7 • C. Ashhar and Lim [9] presented a comprehensive investigation into heat load conduct of reflect insulation and radiant bar in a gable roof joining. Experimentally conducted test cabin under outside circumstantial environments. ...
This study investigates the impact of roof inclination on heat loss and gain within interior spaces, emphasizes its importance for enhancing building energy efficiency. By employing a systematic methodology to evaluate performance under varying conditions. The optimization of thermal performance is crucial for reducing energy consumption and improving comfort in buildings. The investigation begins by altering the roof angle in multiple configurations, focusing specifically on the southern orientation during winter to maximize daytime heat gain and the northern orientation during summer to minimize heat gain. This analysis is conducted for two distinct geographical locations: Miskolc, Hungary (moderate climate), and Baghdad, Iraq (hot climate). The study is conducted using the Hourly Analysis Program (HAP) to calculate thermal loads, as approved by a carrier company. The results are subsequently verified. The second part of the work contains simulation using ANSYS and comparison to the HAP results. After identifying the optimal roof angles for each location, simulations were performed to analyze the thermal behavior of the most effective models. The results indicate that the heat gain entering the building through the ceiling from the optimum roof is 29.393 W/m², while the heat loss is 24.43 W/m². To further enhance thermal performance, Trombe roofs were implemented. Adjustments to the Trombe roof design, with a height of 0.25 m and width 0.05 m of the channel positioned at 90° parallel to the effective roof surface. These modifications resulted in a 45.78 % reduction in heat gain through the ceiling during summer and a 10.8 % reduction in heat loss during winter.
Additionally, the application of glass wool insulation was analyzed. By insulating the northern side in winter and the southern side in summer, heat loss through the ceiling decreased by 14.4 %, while heat gain was reduced by 19.85 %. These findings demonstrate the effectiveness of optimized roof inclination and supplementary thermal strategies in improving energy efficiency across diverse climatic conditions. The novelty of this work lies in its thorough approach to judging optimal roof angles and complementary strategies, providing insights and results that go beyond previous efforts in literature.
... Base on the above improvements, RCMs have good application prospects in reducing building energy consumption when installed on the surfaces of building envelopes [20][21][22]. Mandal, Yang [23] proposed the use of scalable roof white paints for radiative cooling in buildings. Different from other spectrum-selective materials, the new paints have broadband thermal emittance ( ~ 0.95). ...
Besides highly reflecting solar energy, the spectrum-selective radiative cooling materials (RCMs) dissipate heat to outer space especially through the atmospheric window (e.g., 8–13 μm) and achieve sub-ambient temperature under direct sunlight. Not only potentially contributing to Earth’s heat rebalance, the daytime radiative cooling technology but also presents promising applications to building facades as a passive ‘zero-energy’ cooling method. Although there has been a large amount of radiative cooling materials developed recently due to the wavelength scale photonic material design, the wide application of radiative cooling materials to buildings faces challenges, including the barriers of scalable manufacturing and the lack of industry acceptable simulation tools for designers and engineers. Deliberating the major impacting factors such as moisture variation in atmosphere, this study designed a systematic strategy of incorporating spectrum-selective radiative cooling with whole-building performance simulation by developing a new long-wavelength radiation spectrum integral module (LRSIM) suitable for being built into the state-space model, like the DeST tool. Reduced-scale controllable experiments have validated the accuracy of LRSIM, giving < 3% deviation for the spectrum-based long-wavelength radiation calculation. Subsequently, experimental results from full-scale model houses were utilized to further validate the DeST tool embedded with LRSIM for building application of spectrum-selective radiative cooling materials. Indoor air temperature deviation < 1 °C was observed between the simulated and measured data, indicating the compelling prediction power of the integrated tool for radiative cooling modeling. Simulation analysis to a single-story commercial building at six locations around the world has shown energy-saving potential of 14–42% for an example radiative cooling material. Different from other customized plug-in integration, the experimentally validated DeST with built-in LRSIM will provide architecture designers and application engineers a general-purpose and easily-usable tool for promoting adoption of radiative cooling technology in buildings.
Reflective and insulative composite coatings are a new energy-saving material with high solar reflectance and extremely low thermal conductivity for buildings. The optimization and impact of high solar reflectance and low thermal conductivity on the insulating capacity of walls remain uncertain. This work investigates the dynamic thermal performance and energy efficiency of a reflective and insulative composite coating in regions with hot summer and warm winter. A simplified thermal resistance-heat capacitance model of an exterior building wall is established to predict thermal performance. The dynamic temperature and heat flow of the wall are predicted to reduce heat loss through the interior surface of the wall and compared to the conventional coating. The specific impact of the thermal conductivity and solar reflectance of the coating on the heat loss is further investigated to minimize heat loss of the wall. This research shows that the composite coating shows better performance on adjusting outdoor climate change than the other coating. Compared with cement, it reduces the maximum temperature of the exterior surface of the wall by 7.45 °C, and the heat loss through the interior surface of the wall by 38%. The heat loss is reduced with the increase of solar reflectance and the reduction of thermal conductivity. The results can provide a useful reference and guidance for the application of reflective and insulative composite coating on building exterior wall to promote their energy-saving use on building envelopes.
The use of reflective insulation as roof insulation has become increasingly popular in Southeast Asian countries. It is proven to be effective at reducing heat gain through the roof and building energy consumption, as well as improving indoor thermal comfort. The present work is divided into three sections: field measurements of the thermal performance of reflective insulation in Malaysia, Computational Fluid Dynamics (CFD) analysis of reflective insulation in a gable roof system, and techno-economic analysis of roof thermal insulations for a hypermarket under the equatorial climate of Malaysia. Reflective insulation has proven to be an effective type of roof insulation for buildings in Southeast Asia, where the predominant heat flow direction is downward. Measured thermal resistance (RSI values) of roof assemblies with reflective insulations showed results in the range from 2 to 3 m2·K/W. A ceiling heat flux reduction of 80% was obtained for roofs with reflective insulation as compared to uninsulated roof attic. A validated CFD model showed that increasing the reflective air gap from 25 to 100 mm increases the RSI value of the roof assembly by 26%. Besides that, increasing the roof pitch from 30° to 45° increases the RSI value of the roof assembly by 30%. The techno-economic analysis showed that small bubble aluminum foil has the highest life-cycle savings and internal rate of return, as well as the shortest payback period. Although it does not yield the lowest annual cooling energy consumption, it is the most cost-effective type of insulation to be used as roof insulation under the hot and humid climate of Malaysia.
Global energy use shows that cooling and heating are responsible for the highest energy use in buildings. The trend in building energy consumption has been steadily increasing and is expected to continue to rise significantly in the future. The application of reflective foil in the form of reflective insulation and radiant barrier as a roof thermal insulation system is a potential means of reducing cooling energy in buildings, especially in the tropics. It is proven effective in reducing the heat gain across the roof and can enhance indoor thermal comfort. This paper reviews the thermal performance of reflective insulation and radiant barrier as a roof insulation system. Moreover, this paper also discusses and analyses various types of thermal performance test methods such as laboratory equipment, indoor test rig, field measurement, computational fluid dynamics, and building performance simulation. This paper also discusses several factors such as emissivity value, air gap thickness, weather, and climatic conditions on the thermal performance. Dust accumulation and prevention methods will also be discussed.
