The Experts below are selected from a list of 2499 Experts worldwide ranked by ideXlab platform
Stephen K. Wittkopf - One of the best experts on this subject based on the ideXlab platform.
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summer condition Thermal Transmittance measurement of fenestration systems using calorimetric hot box
Energy and Buildings, 2012Co-Authors: Fangzhi Chen, Stephen K. WittkopfAbstract:Abstract Calorimetric measurement systems are commonly used to determine the Thermal Transmittance or U-value of fenestration specimens, particularly for complex systems with additional external shadings, embedded photovoltaic cells or non-homogeneous patterns. In the past, measurements were mainly performed under winter conditions, where heating of buildings is required, but for tropical climates or summer conditions, where cooling of the building is required, very few Thermal Transmittance data are available, as most of the calorimetric systems were optimized for the winter conditions only. This paper presents a calorimetric hot box (CHB) for summer conditions complying with international standards, but with advanced measurement methodology and uncertainty analysis model. It includes the measurement results of double glazing units and comparison with simulation results obtained with WINDOW and THERM software. The comparison revealed a difference of less than 5% which can be considered negligible as it falls within the accepted uncertainty. Further results from measurements of complex fenestration systems with semi-transparent thin-film photovoltaics embedded into laminated and double glazing units are also presented. Hence, the presented system and method can pave the way for Thermal performance validation of standard and complex fenestration systems necessary for energy efficient buildings in the tropics.
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Summer condition Thermal Transmittance measurement of fenestration systems using calorimetric hot box
Energy and Buildings, 2012Co-Authors: Fang-chung Chen, Stephen K. WittkopfAbstract:Calorimetric measurement systems are commonly used to determine the Thermal Transmittance or U-value of fenestration specimens, particularly for complex systems with additional external shadings, embedded photovoltaic cells or non-homogeneous patterns. In the past, measurements were mainly performed under winter conditions, where heating of buildings is required, but for tropical climates or summer conditions, where cooling of the building is required, very few Thermal Transmittance data are available, as most of the calorimetric systems were optimized for the winter conditions only. This paper presents a calorimetric hot box (CHB) for summer conditions complying with international standards, but with advanced measurement methodology and uncertainty analysis model. It includes the measurement results of double glazing units and comparison with simulation results obtained with WINDOW and THERM software. The comparison revealed a difference of less than 5% which can be considered negligible as it falls within the accepted uncertainty. Further results from measurements of complex fenestration systems with semi-transparent thin-film photovoltaics embedded into laminated and double glazing units are also presented. Hence, the presented system and method can pave the way for Thermal performance validation of standard and complex fenestration systems necessary for energy efficient buildings in the tropics. ?? 2012 Elsevier B.V.
David Bienvenidohuertas - One of the best experts on this subject based on the ideXlab platform.
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towards the implementation of periodic Thermal Transmittance in spanish building energy regulation
Journal of building engineering, 2020Co-Authors: David Bienvenidohuertas, Carlos Rubiobellido, Jesus A Pulidoarcas, Alexis PerezfargalloAbstract:Abstract The recent development of the calculation methodology for dynamic Thermal properties of buildings has opened new possibilities for reducing their energy demand; however, building codes still rely on the traditional static approach. This research aims at filling in this gap by exploring how periodic Thermal properties can be implemented in the Spanish regulatory framework. For this purpose, 2,413 wall typologies were analysed in the two extreme climate zones as per the Spanish regulation pertaining to energy efficiency. Results show that the static U-value itself is not sufficient to optimize the energy demand of buildings, as for a single value of U variations of 4,000 kWh in the energy demand are expected. Regarding periodic variables, decrement factor and time shift were the most effective to minimize the energy demand, along with flexible limitations for the periodic Thermal Transmittance and the time shift. In warm climates, the former can be disregarded if the latter is greater than 15 h. The findings from this study disscuss the applicability of the static Thermal Transmittance and propose a methodology to select and limit periodic variables for the two most extreme climates in Spain.
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automation and optimization of in situ assessment of wall Thermal Transmittance using a random forest algorithm
Building and Environment, 2020Co-Authors: David Bienvenidohuertas, Carlos Rubiobellido, Juan Luis Perezordonez, Miguel Jose OliveiraAbstract:Abstract Reducing energy consumption and greenhouse gases emissions is among the main challenges of building sector. It is therefore crucial to know the characteristics of envelopes. There are experimental methods to determine Thermal Transmittance, but limitations are presented. By using techniques of artificial intelligence, this article solves the limitations of current methods by predicting correctly the Thermal Transmittance value of ISO 6946 and the building period of a wall with monitored data. The methodology used is extrapolated to any country: 163 real monitorings and 140 different typologies of walls have been combined to generate the dataset (22,820 items). The results show the optimal operation of the Random Forest algorithm because both the Thermal Transmittance of ISO 6946 and the building period are determined by using the most common methods: the heat flow meter method and the thermometric method. This study makes progress towards more automatized processes to characterize Thermal Transmittance.
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optimizing the evaluation of Thermal Transmittance with the thermometric method using multilayer perceptrons
Energy and Buildings, 2019Co-Authors: David Bienvenidohuertas, Carlos Rubiobellido, Juan Luis Perezordonez, Juan MoyanoAbstract:Abstract The characterization of building Thermal behaviour is crucial to achieve the low-carbon objectives of the European Union by 2050. In this way, the knowledge of the Thermal Transmittance is being developed as a significant factor of the thermophysical properties of the envelope. In the existing building, the theoretical calculation has several limitations with non-destructive techniques typical of the deterioration of the elements. Many experimental methods obtain therefore more representative results. The experimental method developed in ISO 9869–1 is the most standardized, although it presents limitations in the heat flux measurement. However, the thermometric method obtains the Thermal Transmittance with the surface temperature. This research is focused on the evaluation of the Thermal Transmittance based on ISO 9869–1 (average method and average method with correction for storage effects), but using variables measured with the thermometric method. For this purpose, multilayer perceptrons were used as post-processing techniques. The models were trained by using a dataset of 22,820 simulated tests of representative walls of the building stock in Spain. The determination coefficient was greater than 98% in both analysis approaches. Individual models were also generated for each building period because they significantly influenced the input variables. The results showed that Thermal Transmittance values can be obtained without measuring the heat flux, and the error associated with the use of tabulated values for the total internal heat transfer can be removed. This research would guarantee a high assessment tax of buildings establishing adequate energy conservation measures to improve their energy performance.
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review of in situ methods for assessing the Thermal Transmittance of walls
Renewable & Sustainable Energy Reviews, 2019Co-Authors: David Bienvenidohuertas, Juan Moyano, David Marin, Rafael FrescocontrerasAbstract:Abstract Reducing the energy requirements of buildings is essential in order to address anthropogenic global warming. Among the various factors affecting the energy requirements of buildings, the Thermal Transmittance of the walls is critical in understanding heat loss. It is therefore necessary to assess the Thermal Transmittances carefully in order to develop effective means of energy conservation. Although various theoretical methods and methods using in situ measurements are available for this purpose, the correct use of such methods depends on many factors. In a detailed review of more than 150 publications (scientific papers, congress reports, books, and other documents), the best-developed methods in use by researchers and professionals are analysed. These methods are as follows: the theoretical method, the heat flow meter method, the simple hot box-heat flow meter method, the thermometric method, and the quantitative infrared thermography method. This review is intended to be a useful resource for researchers and professionals in that it covers the fundamental theoretical background, the equipment and material required for in situ measurements, the criteria for installing the equipment, the errors caused by metrological and environmental aspects, data acquisition, data processing, and data analysis.
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applying an artificial neural network to assess Thermal Transmittance in walls by means of the thermometric method
Applied Energy, 2019Co-Authors: David Bienvenidohuertas, Juan Moyano, Carlos E Rodriguezjimenez, David MarinAbstract:Abstract Most of the existing building stock has a deficient energy behaviour. The Thermal Transmittance of facades is among those aspects which most affect this situation. In this paper, the calculation procedure with correction for storage effects from ISO 9869-1 was applied to the thermometric method to determine the U-value. Due to the need for determining the number and type of layers that compose the wall to apply the calculation, a multilayer perceptron has been developed to estimate the U-value. From the different model configurations suggested, the most adequate architecture was the one with 14 nodes in the hidden layer without making transformations in the input variables. Valid results have been obtained by the multilayer perceptron for the case studies analysed from different building periods, with deviations lower than 20% between the measured value and the expected one, varying the test duration according to the Thermal resistance of the wall and the temperature variations. Furthermore, it is not necessary to carry out a data post-processing for the model, so this fact simplifies and hastens the calculation procedure.
Francesco Asdrubali - One of the best experts on this subject based on the ideXlab platform.
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influence of heating systems on Thermal Transmittance evaluations simulations experimental measurements and data post processing
Energy and Buildings, 2018Co-Authors: Luca Evangelisti, Claudia Guattari, Francesco AsdrubaliAbstract:Abstract Nowadays, understanding the actual performance of building components is one of the key factor to achieve energy savings. For this reason, on-site measurements are essential but the boundary conditions during surveys can affect the final results. This can occur during heat flow meter measurements, when the Thermal Transmittance value of a wall can be influenced by disturbing factors, such as the heating system power-on and off. Due to this, the aim of this study is to investigate the influence of these disturbing factors, moving away from steady-state conditions. This research is divided in two main steps: a first critical analysis of data obtained by in-situ measurements and an investigation of how the mentioned disturbing factors can affect the final results, employing a FEM code, where stationary conditions are not respected; a second analysis related to the data post-processing procedures, proposing a new supplementary approach able to exclude heat flow distortions and able to obtain measured U-values closer to the calculated ones, according to ISO 6946. Starting from simulations and on-site measurements, the proposed method was preliminary validated, analyzing actual case studies characterized by heating systems with radiators and obtaining preliminary satisfying results. The simulations allowed to assess a reduction in the difference between the measured and the calculated U-value that goes from +22.1% to +0.7%. Post processing of experimental data with the proposed methodology allowed to significantly reduce the difference between measured and calculated U-values (from +36.9% to −7.6% in the best case study). Starting from the preliminary results, the proposed approach seems to be promising with U-value corrections in accordance with the theoretical ones.
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experimental investigation of the influence of convective and radiative heat transfers on Thermal Transmittance measurements
International Communications in Heat and Mass Transfer, 2016Co-Authors: Luca Evangelisti, Claudia Guattari, Paola Gori, Roberto De Lieto Vollaro, Francesco AsdrubaliAbstract:Abstract Walls Thermal Transmittance value (U-value) is essential to identify the performance of a wall and it is used for the energy labeling procedure. If on one hand the heat-flow meter can measure heat fluxes across its plate giving back the wall's U-value, on the other hand, if air temperatures and wall's inner surface temperatures are measured, it is necessary to set the total heat transfer coefficient value in order to calculate the heat fluxes. Many correlations were developed in scientific literature to quantify the convective heat transfer coefficient and it is possible to distinguish similarity based and experimentally ones. In this paper, the actual total heat transfer coefficients in different case studies were obtained by measuring the physical parameters that are needed to define them. Convective and radiative contributions were separately evaluated and, finally, actual convective heat transfer coefficients were compared with the same coefficients obtained by applying the correlations available in literature and with the constant value suggested by the Standard. The aim of this study is to analyze the differences between the various coefficients values and their influence on the Thermal Transmittance evaluation, in order to better understand the existing correlations and the UNI EN ISO 6946 applicability. This is an initial part of a research which aims to provide an overall more accurate representation of the building behavior, forthcoming developments will deal with the analysis of heat transfer on the outer side of walls.
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Evaluating in situ Thermal Transmittance of green buildings masonries—A case study
Case Studies in Construction Materials, 2014Co-Authors: Francesco Asdrubali, Giorgio Baldinelli, Francesco D'alessandro, Francesco BianchiAbstract:Abstract The determination of the Thermal properties of a building envelope is fundamental for the correct design of energy efficient constructions. Opaque walls can be easily modeled as parallel and homogeneous layers, being characterized by a monodimensional Thermal flux which allows to evaluate the Thermal Transmittance with analytical models. These procedures are well established and they lead to reliable results; however, it is important to verify the actual performance with in situ Thermal Transmittance measurements. This analysis is more important when the wall performance is high, being closely linked to economic assessments. The paper presents the results of a measurement campaign of in situ Thermal Transmittance, performed in some buildings in the Umbria Region (Italy), designed implementing bio-architecture solutions. The analyzed walls were previously monitored with thermographic surveys in order to assess the correct application of the sensors. Results of the investigation show that in situ Thermal Transmittance measurements and theoretical calculated U -value are not in perfect agreement. The mismatch becomes important for monolithic structures such as walls made of Thermal blocks without insulating layers.
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evaluating in situ Thermal Transmittance of green buildings masonries a case study
Case Studies in Construction Materials, 2014Co-Authors: Francesco Asdrubali, Francesco Dalessandro, Giorgio Baldinelli, Francesco BianchiAbstract:Abstract The determination of the Thermal properties of a building envelope is fundamental for the correct design of energy efficient constructions. Opaque walls can be easily modeled as parallel and homogeneous layers, being characterized by a monodimensional Thermal flux which allows to evaluate the Thermal Transmittance with analytical models. These procedures are well established and they lead to reliable results; however, it is important to verify the actual performance with in situ Thermal Transmittance measurements. This analysis is more important when the wall performance is high, being closely linked to economic assessments. The paper presents the results of a measurement campaign of in situ Thermal Transmittance, performed in some buildings in the Umbria Region (Italy), designed implementing bio-architecture solutions. The analyzed walls were previously monitored with thermographic surveys in order to assess the correct application of the sensors. Results of the investigation show that in situ Thermal Transmittance measurements and theoretical calculated U -value are not in perfect agreement. The mismatch becomes important for monolithic structures such as walls made of Thermal blocks without insulating layers.
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Thermal Transmittance measurements with the hot box method calibration experimental procedures and uncertainty analyses of three different approaches
Energy and Buildings, 2011Co-Authors: Francesco Asdrubali, Giorgio BaldinelliAbstract:A large amount of heat loss through building envelopes takes place via inhomogeneous components such as windows, doors, and Thermal bridges. This loss can be approximated by measuring in lab the actual Thermal Transmittance of these components with the use of a hot box. The calibration and experimental procedures can be performed, taking into account three standards for calibrating hot boxes: the European EN ISO 8990; the American ASTM C1363-05; and the Russian GOST 26602.1-99. An experimental setup for testing the accuracy of these standards has recently been created at the University of Perugia; after a measurement campaign for the validation of the test rig, the differences of the approaches were evaluated. Results showed that although the EN ISO 8990 and ASTM C1363-05 are similar in terms of procedures definition, methodology of Thermal Transmittance calculation, and level of uncertainty, the GOST 26602.1-99 differs from the others since it adds individual measurements of the Thermal characteristics of each sample component. The analysis highlighted that the ideal procedure should include the Russian method to define the Thermal behavior of each component under analysis, with a contemporary validation of the global results to be performed with one of the other two approaches.
J J Costa - One of the best experts on this subject based on the ideXlab platform.
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Thermal Transmittance effect on energy consumption of mediterranean buildings with different Thermal mass
Applied Energy, 2019Co-Authors: Eugenio Rodrigues, Marco S Fernandes, Adelio Rodrigues Gaspar, Alvaro Gomes, J J CostaAbstract:Abstract High Thermal mass construction is commonly used to reduce cooling energy consumption during the summer period as a passive design strategy in the Mediterranean region. Although being a generalized design practice, the benefit to the building performance is not fully consensual within the scientific community. This work explores the influence of Thermal Transmittance on the energy efficiency of buildings with different Thermal mass levels. Hence, a statistical comparison of the buildings’ annual energy consumption for air-conditioning is carried out based on two synthetic datasets with high and low Thermal mass and varying Thermal Transmittance for opaque and transparent elements. In addition to climate location, the results demonstrate that Thermal Transmittance has varying impact on the contribution of Thermal mass. The locations presenting such behavior were Marseille (−0.99% to +3.89%), Istanbul (−0.73% to +4.21%), Valencia (−1.31% to +4.97%), Algiers (−2.32% to +3.81%), Malaga (−3.95% to +6.21%), Casablanca (−5.66% to +6.96%), and Tel Aviv (−1.81% to +5.44%). These findings demonstrate that the influence of Thermal mass is more complex than previously thought and levels should be chosen in relation with the Thermal Transmittance value.
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the impact of Thermal Transmittance variation on building design in the mediterranean region
Applied Energy, 2019Co-Authors: Marco S Fernandes, Eugenio Rodrigues, Adelio Rodrigues Gaspar, J J Costa, Alvaro GomesAbstract:Abstract Contrarily to what happens in northern European countries, buildings in the Mediterranean region are prone to overheating. Consequently, it is important to better understand the role that the Thermal Transmittance of the building envelope elements has on air-conditioning consumptions. This paper analyzes the effect of different U-values on building design in the Mediterranean area. 192 000 residential buildings were randomly generated for sixteen distinct locations and the energy consumption was assessed for each. It was found that in northern Mediterranean locations, as U-values decreased, energy consumption also decreased. However, in warmer climates, low Thermal Transmittances tended to significantly increase energy consumption. Hence, the lower the latitude, the higher the U-values should be, in order to prevent increasing the cooling demands. Additionally, geometry-based indexes were correlated with the building’s energy performance. For high U-values, it was found that bigger buildings worsen the energy performance and larger windows tended to improve it. For low U-values, bigger north-facing windows were beneficial. There is an adequate interval of values for which the geometry has a lower impact, which is wider and higher for lower latitudes, thus meaning that not only does the building performance improve but architects are also freer to explore alternative designs.
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Thermal Transmittance of lightweight steel framed walls experimental versus numerical and analytical approaches
Journal of building engineering, 2019Co-Authors: Paulo Santos, Margarida Goncalves, Claudio Martins, N Soares, J J CostaAbstract:Abstract Given the great influence of the Thermal Transmittance of the building envelope on the overall Thermal performance and energy efficiency of the building, it is essential to accurately determine the U-value of the main building envelope elements. Due to the great heterogeneity of the Thermal conductivity of the elements presented in a lightweight steel-framed (LSF) wall, and to the geometric complexity of some steel framed structures, a reliable estimation of the Thermal Transmittance of LSF elements is even more challenging. Indeed, Thermal bridging originated by steel studs must be considered in the assessment of the Thermal Transmittance of LSF walls. In this work, the Thermal Transmittance (U-value) of three LSF walls with different configurations will be investigated based on four different approaches: experimental laboratorial measurements based on the Heat Flow Meter (HFM) method; 3D finite element method (FEM) simulations using ANSYS CFX® software; 2D FEM-based simulations using THERM software; analytical estimations based on the ISO 6946 procedure for building components with inhomogeneous layers. Several verification procedures were performed to ensure the reliability of the results. It was found that a secondary wood stud can mitigate the Thermal bridging effect of the steel frame and improve the LSF Thermal performance, which is more noticeable when there is no Thermal insulation. Furthermore, a good agreement was found between the results of the 2D FEM and the analytical ISO 6946 approaches for the LSF wall with only vertical steel studs.
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laboratory and in situ non destructive methods to evaluate the Thermal Transmittance and behavior of walls windows and construction elements with innovative materials a review
Energy and Buildings, 2019Co-Authors: N Soares, Paulo Santos, Margarida Goncalves, Claudio Martins, Luis Simoes Da Silva, J J CostaAbstract:Abstract The experimental characterization of the overall Thermal Transmittance of homogeneous, moderately- and non-homogeneous walls, windows, and construction elements with innovative materials is very important to predict their Thermal performance. It is also important to evaluate if the standard calculation methods to estimate the U-value of new and existing walls can be applied to more complex configurations, since the correct estimation of this value is a critical requirement when performing building energy simulations or energy audit. This paper provides a survey on the main methods to measure the Thermal Transmittance and Thermal behavior of construction elements, considering laboratory conditions and in-situ non-destructive measurements. Five methods are described: the heat flow meter (HFM); the guarded hot plate (GHP); the hot box (HB), considering the guarded HB (GHB) and the calibrated HB (CHB); and the infrared thermography (IRT). Then, previous studies dedicated to the assessment of the Thermal performance of different heavy- and light-weight walls are discussed. Particular attention is devoted to the measurement of the U-value of non-homogeneous walls, including the effect of Thermal bridging caused by steel framing or mortar joints, and the presence of PCMs or new insulation materials in the configuration of the walls.
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the potential impact of low Thermal Transmittance construction on the european design guidelines of residential buildings
Energy and Buildings, 2018Co-Authors: Eugenio Rodrigues, Marco S Fernandes, Adelio Rodrigues Gaspar, Alvaro Gomes, N Soares, J J CostaAbstract:Abstract European countries impose regulations for low Thermal Transmittance envelopes to improve the buildings’ energy efficiency. However, in scientific literature, evidences are surfacing that such low U-values are affecting the validity of traditional design guidelines. The purpose of this paper is to analyze the implications of lowering the envelope U-values. To achieve this, 96,000 residential buildings were generated, with random geometries and U-values, and their energy consumption evaluated for eight European locations. The buildings were grouped according to the envelope elements’ Thermal Transmittance and the results statistically analyzed. For each group, six geometry-based indexes were correlated with the energy performance. As U-values decrease, the performance variation amplitude was found to reduce, making the geometry less important. However, in warm/moderate climates, low U-values tend to actually increase the energy consumption and also rise the performance variation, meaning that geometry regains importance. In this case, instead of helping reducing the heating demands, solar exposed windows and compact geometries raise the energy consumption. It is concluded that, for each climate location, there is an ideal U-value range for which the energy demand is low and the geometry effect becomes less significant, thus freeing designers to further explore building forms and window designs.
Paulo Santos - One of the best experts on this subject based on the ideXlab platform.
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analytical methods to estimate the Thermal Transmittance of lsf walls calculation procedures review and accuracy comparison
Energies, 2020Co-Authors: Paulo Santos, Gabriela Lemes, Diogo MateusAbstract:An accurate evaluation of the Thermal Transmittance ( U -value) of building envelope elements is fundamental for a reliable assessment of their Thermal behaviour and energy efficiency. Simplified analytical methods to estimate the U -value of building elements could be very useful to designers. However, the analytical methods applied to lightweight steel framed (LSF) elements have some specific features, being more challenging to use and to obtain a reliable accurate U -value with. In this work, the main analytical methods available in the literature were identified, the calculation procedures were reviewed and their accuracy was evaluated and compared. With this goal, six analytical methods were used to estimate the U -values of 80 different LSF wall models. The obtained analytical U -values were compared with those provided by numerical simulations, which were used as reference U -values. The numerical simulations were performed using a 2D steady-state finite element method (FEM)-based software, THERM. The reliability of these numerical models was ensured by comparison with benchmark values and by an experimental validation. All the evaluated analytical methods showed a quite good accuracy performance, the worst accuracy being found in cold frame walls. The best and worst precisions were found in the Modified Zone Method and in the Gorgolewski Method 2, respectively. Very surprisingly, the ISO 6946 Combined Method showed a better average precision than other two methods, which were specifically developed for LSF elements.
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Thermal Transmittance of internal partition and external facade lsf walls a parametric study
Energies, 2019Co-Authors: Paulo Santos, Gabriela Lemes, Diogo MateusAbstract:Light steel framed (LSF) construction is becoming widespread as a quick, clean and flexible construction system. However, these LSF elements need to be well designed and protected against undesired Thermal bridges caused by the steel high Thermal conductivity. To reduce energy consumption in buildings it is necessary to understand how heat transfer happens in all kinds of walls and their configurations, and to adequately reduce the heat loss through them by decreasing its Thermal Transmittance ( U -value). In this work, numerical simulations are performed to assess different setups for two kinds of LSF walls: an interior partition wall and an exterior facade wall. Several parameters were evaluated separately to measure their influence on the wall U -value, and the addition of other elements was tested (e.g., Thermal break strips) with the aim of achieving better Thermal performances. The simulation modeling of a LSF interior partition with Thermal break strips indicated a 24% U -value reduction in comparison with the reference case of using the LSF alone ( U = 0.449 W/(m2.K)). However, when the clearance between the steel studs was simulated with only 300 mm there was a 29% increase, due to the increase of steel material within the wall structure. For exterior facade walls ( U = 0.276 W/(m2.K)), the model with 80 mm of expanded polystyrene (EPS) in the exterior Thermal insulation composite system (ETICS) reduced the Thermal Transmittance by 19%. Moreover, when the EPS was removed the U -value increased by 79%.
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Thermal Transmittance of lightweight steel framed walls experimental versus numerical and analytical approaches
Journal of building engineering, 2019Co-Authors: Paulo Santos, Margarida Goncalves, Claudio Martins, N Soares, J J CostaAbstract:Abstract Given the great influence of the Thermal Transmittance of the building envelope on the overall Thermal performance and energy efficiency of the building, it is essential to accurately determine the U-value of the main building envelope elements. Due to the great heterogeneity of the Thermal conductivity of the elements presented in a lightweight steel-framed (LSF) wall, and to the geometric complexity of some steel framed structures, a reliable estimation of the Thermal Transmittance of LSF elements is even more challenging. Indeed, Thermal bridging originated by steel studs must be considered in the assessment of the Thermal Transmittance of LSF walls. In this work, the Thermal Transmittance (U-value) of three LSF walls with different configurations will be investigated based on four different approaches: experimental laboratorial measurements based on the Heat Flow Meter (HFM) method; 3D finite element method (FEM) simulations using ANSYS CFX® software; 2D FEM-based simulations using THERM software; analytical estimations based on the ISO 6946 procedure for building components with inhomogeneous layers. Several verification procedures were performed to ensure the reliability of the results. It was found that a secondary wood stud can mitigate the Thermal bridging effect of the steel frame and improve the LSF Thermal performance, which is more noticeable when there is no Thermal insulation. Furthermore, a good agreement was found between the results of the 2D FEM and the analytical ISO 6946 approaches for the LSF wall with only vertical steel studs.
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laboratory and in situ non destructive methods to evaluate the Thermal Transmittance and behavior of walls windows and construction elements with innovative materials a review
Energy and Buildings, 2019Co-Authors: N Soares, Paulo Santos, Margarida Goncalves, Claudio Martins, Luis Simoes Da Silva, J J CostaAbstract:Abstract The experimental characterization of the overall Thermal Transmittance of homogeneous, moderately- and non-homogeneous walls, windows, and construction elements with innovative materials is very important to predict their Thermal performance. It is also important to evaluate if the standard calculation methods to estimate the U-value of new and existing walls can be applied to more complex configurations, since the correct estimation of this value is a critical requirement when performing building energy simulations or energy audit. This paper provides a survey on the main methods to measure the Thermal Transmittance and Thermal behavior of construction elements, considering laboratory conditions and in-situ non-destructive measurements. Five methods are described: the heat flow meter (HFM); the guarded hot plate (GHP); the hot box (HB), considering the guarded HB (GHB) and the calibrated HB (CHB); and the infrared thermography (IRT). Then, previous studies dedicated to the assessment of the Thermal performance of different heavy- and light-weight walls are discussed. Particular attention is devoted to the measurement of the U-value of non-homogeneous walls, including the effect of Thermal bridging caused by steel framing or mortar joints, and the presence of PCMs or new insulation materials in the configuration of the walls.