Effect Of Thermal Bridges Research Articles

Numerical assessment of thermal bridging effects in 3D-printed foam concrete walls

Abstract Integrating smart technology and advanced materials in the construction industry has revolutionized traditional building practices, enhancing efficiency, sustainability, and overall performance. Researchers and professionals in the construction sector have shown significant interest in three-dimensional concrete printing (3DCP) for automating structural engineering tasks. Despite its potential as a sustainable solution to modern construction issues, there is a lack of research on the thermal insulation performance of three-dimensional printed concrete (3DPC) building envelopes, and the potential for integrating foam concrete (FC) to enhance energy efficiency has not yet been studied. This paper presents a numerical analysis examining how different infill geometries affect the thermal performance of 3D-printed foam concrete (3DPFC) lattice envelopes. Six lattice structures were designed with identical thickness, height, length, and comparable insulation areas. The effects of the contact (intersection) area of webs with the interior face shell, webs, and infill rows on the thermal performance of granularly insulated envelopes were studied. The effectiveness of insulation was also established. The findings indicate that the thermal transmittance of 3DPC envelopes correlates directly with the contact area of the webs and the interior surface, with U-values ranging from 0.151 W m2·K to 0.652 W/m2·K. Notably, the absence of direct connections between exterior and interior surfaces enhances insulation efficiency, with double-row structures achieving up to 94% insulation efficiency. However, when there is a direct connection between the two surfaces, the thermal performance of these envelopes is mainly affected by the contact (intersection) area of the webs with the interior face rather than the number of webs. By integrating foam concrete and double-row walls, this study demonstrates an innovative approach to reducing thermal bridging and improving energy performance in 3D-printed construction. The results offer novel insight into optimizing the thermal behavior of 3DPC systems for sustainable building practices.

Experimental study on thermal bridge effect of steel-concrete-steel tunnel elements under fireproof board insulation schemes

Steel embedded parts welded on the surface of steel-concrete-steel tunnel elements serve as thermal bridges in tunnel fires. Their influence on temperature field and macroscopic thermal damage of steel-concrete-steel structure were investigated through fire tests, and their heat transfer forms were analyzed. Then, a thermal bridge disposal scheme was proposed and examined. The results show that steel embedded parts significantly cause an increase and an uneven distribution of steel shell temperature in tunnel fires. As time exposed to fire increases, the extent and range of these influences grow. Thermal bridges raise the average temperature by 45.2 % inside the steel-concrete-steel structure, worsen the unevenness of temperature distribution in horizontal and vertical directions. Thermal bridges worsen surface macroscopic damage, lengthening cracks by more than 32.5 % and widening them by more than 22.6 times. Within a distance of 30 cm from the embedded part, heat provided by embedded parts accounts for over 79.9 % of the steel shell's total heat, and heat conveyed along the steel shell through thermal conduction accounts for over 53.7 %. GX-3 high-temperature adhesive is an effective method for thermal bridge treatment. These detailed findings offer new insights into the design of fire insulation schemes for the steel-concrete-steel structure.

Thermal insulation performance of non-load-bearing light gauge slotted steel stud walls

Light gauge steel stud walls have been widely used in buildings as load-bearing members. But if used as non-load-bearing walls, more rows of perforations can be placed on stud webs and then the thermal bridge effect can be reduced. Experiments on six non-load-bearing light gauge slotted steel stud walls were conducted using a calibrated hot box. The temperatures of the steel studs and gypsum plasterboard were monitored for subsequent analysis of thermal bridging. The effects of parameters (number of rows of perforations, stud web height, and the ratio of window area to wall area) on the insulating capacity of the wall were identified and analyzed. Thermal transmittance decreases by 18.5% and 29.6% for specimens with 3 and 7 rows of perforations in comparison with the specimen without perforations, while it decreases by 29.8% and 42.7% respectively for 150 mm and 200 mm thick walls compared with that of the 100 mm thick wall. However, thermal transmittance increases obviously for the wall with a window opening relative to the wall without a window opening, reaching 14.7% in this test since more studs are placed around the window opening. A three-dimensional finite element (FE) model of the wall was developed and validated against experimental results, and then was used for parametric studies. A general method of calculating the thermal transmittance of the light gauge slotted steel stud wall was suggested based on the experiment and the FE model results, which can consider influences of wall thickness, web perforations, window openings, and thermal properties of materials.

Insulation performance evaluation of stone-finished exterior insulation systems with insulation frames for green remodeling of concrete exterior walls

This study aimed to evaluate the thermal bridge reduction effect of insulation frames applied to a stone-finished exterior insulation system, which is commonly used in green remodeling projects. The insulation performance of the exterior walls and the energy performance of the building in a baseline case in which an existing steel pipe frame was applied were compared with those in cases alt 1 and alt 2, which included application of double- and single-wired truss-shaped insulation frames, respectively. First, a three-dimensional steady-state heat transfer simulation was conducted for the exterior wall-floor joint of the model building, and the effective U-factor was obtained. Next, mock-ups were constructed and the U-factor was tested to verify the insulation performance of cases alt 1 and alt 2. The heat loss decreased as the effective U-factors of alt 1 and alt 2 decreased by 19.0 % and 19.7 %, respectively, compared to the baseline case, according to the heat transfer simulations. In the mock-up test, the U-factors of alt 1 and alt 2 were similar to design U-factor, indicating almost no heat loss caused by the thermal bridges. Notably, the U-factor of alt 2 was 2.4 % lower than that of alt 1. Finally the energy performance of the entire building was compared through dynamic building energy simulations by reflecting the thermal bridging effect. The annual heating and cooling energy use of alt 1 and alt 2 were 2.5 % and 2.6 % lower than those of the baseline case, respectively, confirming the energy-saving effect of reducing thermal bridges.

Thermal bridging effect enhancing heat transport across graphene interfaces with pinhole defects

Interfacial thermal conductance (G) is of critical significance to the efficient thermal management of two-dimensional (2D) material devices. Despite the importance of defects engineering in tuning G, the mechanisms of heat transport across defective graphene interfaces remain unclear. In this study, we have identified and demonstrated the origins of the enhanced heat transport across pinhole defective graphene through our ultrafast pump-probe measurements and molecular dynamics (MD) simulations. In prior work, the enhanced G across defective graphene interfaces was commonly attributed to the improved overlap of phonon density of states (DOS) or interfacial coupling strength. We, however, observe a remarkable 2.5-fold increase in heat conduction and a distinctly different temperature dependence of G for defective graphene with the same superstrate and substrate material, compared to pristine graphene. In contrast, interfaces with different superstrate and substrate materials show only minor changes (<15%) in thermal conductance after introducing defects in the graphene layer. Through careful analysis of our MD simulations for various defective graphene interfaces, we conclude that, contradictory to common beliefs, it is the formation of direct contact thermal bridge, instead of the improvement in the phonon DOS overlap or interfacial coupling strength, that has a decisive effect and promotes heat transport across defective graphene interfaces. The differing impacts of the thermal bridge on G of defective graphene sandwiched by layers of the same and different materials are primarily attributed to the varying coupling strength between the substrate and superstrate. Our work provides important insights and physical understandings of the mechanisms of heat conduction across defective graphene interfaces.

Thermal analysis of the window-wall interface for renovation of historical buildings

Due to the long time since their construction, some old buildings have experienced a decline in performance and do not meet contemporary requirements. Retrofitting methods, as opposed to demolition and reconstruction, are considered a more cost-effective and energy-efficient approach, particularly applicable to historical buildings with conservation significance. Exterior windows account for a significant amount of heat loss within the building envelope, but it is a challenge to improve its performance while retaining the historical appearance of the building when retrofitting. In this paper, a new design of the window-wall interface structure was proposed, which facilitated the incorporation of additional thermal insulation materials and mitigated the thermal bridge effect at the joint between the window frame and the wall. Comparative analysis with existing window-wall interface structures revealed the superior thermal performance of the proposed structure, with less heat transfer as well as smaller surfaces at risk of condensation. The structure was first implemented in a renovation project in Nanjing, providing an innovative approach for future exterior window renovations of historical buildings.

Experimental and Numerical Assessment of the Thermal Bridging Effect in a Reinforced Concrete Corner Pillar

This paper discusses experimental and simulated data regarding the thermal bridging effect in a reinforced concrete corner pillar, which belongs to a building dating back to the 1980s and located in Southern Italy. The thermal field determined by the concrete pillar corner has been evaluated, introducing an experimental procedure based on both direct measurements and indirect observations of the inner superficial temperature by means of thermal imaging techniques and surface temperature probes. Moreover, indoor and outdoor air temperature and relative humidity were measured to provide suitable boundary conditions in the numerical simulations, performed with a commercial software tool widely used in Italy based on 2D finite element techniques. The experimental measurements show that, at more than 50 cm from the corner, the surface temperatures become almost constant, meaning that the thermal bridging effect becomes less evident. However, the surface temperature in the corner is around 1.5 °C lower than in the undisturbed flanking walls. In terms of local heat flux, the discrepancy between simulations and measurements is below 3%. Finally, this paper verifies the effectiveness of External Thermal Insulation Composite System (ETICS) renovation in reducing the thermal bridging effect of the corner pillar. The results also include the calculation of the linear thermal transmittance with a series of relations available in well-known atlases for thermal bridges and show that these relations are more reliable in the case of uninsulated pillar than for the insulated one.

Effect of thermal bridges on the energy performance of Chinese residential buildings

Thermal bridges may represent up to 50 % of the building's envelope area and may increase the energy consumption of buildings by up to 30 %, however their impact is often not taken into account adequately in China. In this study, the energy performance of a typical two-story residential building under four different Chinese climate zones is investigated using WUFI Plus program in terms of annual heating and cooling energy demands. Several typical thermal bridges were taken into consideration. Two methods were used to evaluate the effect of thermal bridges on the building energy performance, the simplified method commonly used in China and the dynamic 3D modelling method, and were compared to do not consider thermal bridge. Also, two different types of building envelope, brick wall and aerated concrete wall, were used to evaluate the effect. The results show that by taking into account the thermal bridges, the annual heating energy demands of residential building increase 21.2 %, 24.8 %, 27.8 %, and 16.6 % under the four Chinese climate zones. Therefore, attention should be paid in the building envelope design to reduce thermal bridges. Compared to the dynamic 3D modelling method, the simplified method underestimates annual heating and cooling energy demands.

Thermal analysis of tubular daylight guidance system on an insulated flat roof with overlying soil

As an emerging passive daylighting technology, tubular daylight guidance systems (TDGSs) are increasingly used in low-energy buildings. However, TDGS may become a thermal bridge to increase indoor air conditioning load. To avoid an increase in total energy consumption, the thermal analysis of a flat roof section with a TDGS is simulated using CFD in this work. Additionally, the simulation compares the heat transfer performance of a conventional TDGS with eight different designs TDGS that contain additional glass unit. The findings show that TDGS has a thermal bridging effect on an insulated flat roof with overlying soil. The additional glass unit in the middle of the conventional TDGS with diameter 500 mm decreases its overall heat transfer coefficient by 53 %. Further, the same thickness of glass is divided into 4 layers and evenly distributed inside the TDGS with diameter 500 mm, which can reduce the total heat transfer coefficient of the conventional TDGS by 67 %.

Ensuring the Energy Efficiency of Buildings through the Simulation of Structural, Organizational, and Technological Solutions for Facade Insulation

The article presents ways of selecting effective designs and technological and organizational solutions for the bonded thermal insulation systems of complex-shaped facades based on thermal field and flow modeling using the SolidWorks Simulation Xpress 2021 software and experimental–statistical modeling using the Compex program. Determining optimal insulation parameters at the design stage will help eliminate the negative effects of thermal bridges at balcony junctions and reduce the cost of implementing bonded thermal insulation systems for facades with complex shapes. It has been established that the most effective approach is to insulate not the entire perimeter of the balcony slab, as required by normative documentation, but rather to insulate a sufficient portion of the exterior wall, which is equal to 750 mm, with a 30 mm insulation thickness on top of the slab and 50 mm beneath it. This insulation technology is economically feasible for modern multistory buildings with nonstandard volumetric and architectural solutions, constructed using frame–brick, frame–monolithic, or monolithic schemes without thermal breaks between the balcony slab and the monolithic floor slab, with open-type balconies, bays, or uncovered loggias.

Research on evaluation methods for thermal bridge treatment measures for building envelopes

Along with the promotion of low-carbon and zero carbon buildings such as ultra-low energy buildings, near zero energy buildings, and zero energy buildings, there is higher and higher demand to the thermal performance of building envelopes. Thermal bridges have a crucial impact on the thermal performance of building envelope structures. In order to achieve the goal of energy conservation and carbon dioxide reduction in building structures, it is necessary to conduct refined calculations and evaluations on thermal bridge treatment measures. In this paper, three thermal bridge treatment measures evaluation methods from different dimensions are presented: evaluation method based on reduction degree of thermal bridge effect, evaluation method based on carbon dioxide emissions from thermal bridges, and evaluation method based on technical economy of thermal bridges.

Analysis of Thermal Bridges with an Automated Framework using BIM

In response to increasingly stringent energy performance requirements for buildings, the need for energy-efficient construction becomes ever more important. Although new construction technologies have emerged, thermal bridges are still common in new and especially in to-be renovated buildings. To facilitate analysing the effect of thermal bridges this paper investigates the development of a method to automatically integrate their effect into energy simulations. The developed workflow starts with integrating thermal bridges into Building Information Modeling (BIM) software. Subsequently, the thermal bridges are exported to the open source format Industry Foundation Class (IFC). Finally, a conversion of the IFC file to a readable file for the energy simulation software Modelica, using the ifc2modelica tool is shown. Furthermore, it investigates the impact of thermal bridges on different key performance indicators (KPIs) for both renovation and new build cases. This research aims at efficiently integrating thermal bridges in energy simulations during early design stages. The foundation for a BIM-library for standard thermal bridges has been developed, allowing an easy integration in existing BIM models with good simulation results.

Heat transfer characteristics and thermal insulation optimization of buried ductile iron heat-supply pipeline

ABSTRACT This study investigates heat transfer in a ductile iron heat-supply pipeline and develops a mathematical model through a comparative assessment of different techniques. The goal is to accurately describe non-steady state heat transfer in buried pipelines. A high-precision model is established by considering assumptions, equations, boundary conditions, calculation domain, geometry, and grid number. Calculation time is reduced, and accuracy is improved, providing a foundation for optimizing the thermal insulation layer. ANSYS software is used to simulate and optimize the thermal insulation of the pipeline. Results show a maximum error range of 1.20% to 10.20% with consistent temperature trends, verifying the model’s accuracy. The heat-affected zone of the thermal bridge is evaluated and optimized, and preventive measures are proposed to reduce the impact of heat bridges in joint areas. The study also compares nodular cast iron pipes with conventional steel thermal pipes under the same conditions. It reveals that the economic thickness of the thermal insulation layer for nodular cast iron pipes increases from 31 mm to 39 mm due to the thermal bridge effect, which is significant.

RC-Network based thermal bridge calculation method for transient heat transfer analysis of multidimensional building envelope details: A frequency response analysis-based method

Thermal bridges have a significant impact on the overall energy performance and thermal comfort of buildings. Proper accounting of thermal bridge effects through model coupling leads to more accurate predictions of heating and cooling loads and narrows the performance gap between the design and the actual energy consumption of buildings. In this paper, a dynamic thermal bridge calculation method is introduced in a frequency domain to transform a broad range of multidimensional building envelope assemblies to thermally equivalent RC-Network simple models. RC-Network model with three resistances, four capacitances, and internal and external surface resistances at the ends is found to represent multidimensional thermal bridge assemblies more accurately with minimal computational time. The method is applied for the simulation of diverse two- and three-dimensional thermal bridge details of lightweight and mass constructions exposed to hourly varying sol–air temperature boundary conditions, and the results are compared to reference solutions obtained from transient finite element modeling of the original thermal bridge details. The highest RMSE of the proposed RC-Network model for the lightweight and mass construction details are 0.12 W/m2 and 0.37 W/m2, respectively. The low RMSE values reaffirm the good performance of the method and its appropriateness for the calculation of hourly heat flux through multidimensional thermal bridge details.

Seismic behavior of autoclaved aerated concrete masonry walls reinforced with glass-fiber geogrid

Reinforcing horizontal mortar joints with steel bars can improve the seismic performance of autoclaved aerated concrete (AAC) masonry walls. Nevertheless, the diameter of steel bars can require a large thickness of the mortar joints, which in turn results in the thermal bridging effect. Glass fiber geogrids (GFGs) can be employed to replace steel bars to reduce the thickness of mortar joints, and thus can mitigate the thermal bridging effect. Despite considerable advancements in understanding the mechanical performance of GFGs in masonry walls, their effect on the seismic performance of AAC walls remains unknown. Therefore, this study investigates the effect of different GFG configuration rates on the seismic performance of AAC masonry walls using reciprocating load tests. Furthermore, the effect of different vertical compressive stresses on the seismic performance of GFG-reinforced AAC masonry walls was studied via comprehensive finite element simulations. The test results show that the ultimate load-bearing capacity and ultimate displacements of the wall specimens were enhanced as the GFG configuration rate increased, approaching that of benchmark specimens reinforced with steel bars. On the other hand, the cracking and ultimate loads, along with ultimate displacements of GFG-reinforced AAC masonry walls were significantly improved compared to those of the unreinforced AAC masonry walls. It was also evidenced that the crack formation, failure mode, ductility and energy dissipation capacity of the specimens simulated through the finite element method were highly comparable to that of experimentally tested specimens. Accordingly, the vertical compressive stresses were in the range of 0.1 MPa ∼ 0.6 MPa, while the seismic performance of GFG masonry walls was improved with the increase in vertical pressure. The results of the current study confirm that embedding GFG in horizontal mortar joints can delay the cracking of AAC masonry walls and improve their seismic performance. Ultimately, an empirical equation was developed to calculate the seismic shear strength of GFG-reinforced AAC masonry walls.

A promising approach of caved vacuum insulation panel and investigation on its thermal bridge effect

Vacuum insulation panels (VIPs) are excellent adiabatic materials widely applied in various field. Unlike conventional insulation materials, VIPs cannot be trimmed on-site to desired dimensions, necessitating the pre-designing panels to specific sizes. The impact of cavities on VIPs was investigated by numerical and experimental methods in this study. Five cavity shapes for VIPs were involved, that is: circular, equilateral trigonal, equilateral quadrilateral, equilateral pentagonal, and equilateral hexagonal. The variations in thermal insulation performance of VIPs with cavities of different shapes but equal perimeter (124 mm, 500 mm) and equal area (2826 mm2, 6192 mm2) were investigated. The results shew that, the presence of cavities caused sharp reduction of thermal insulation performance of VIPs. VIPs with circular cavities exhibit the lowest effective thermal conductivity (ETC) and thermal bridge effect. For equal perimeter case, the adiabatic performance decreased with increase in the number of sides and corner points. For equal area, VIPs with equilateral quadrilateral cavities exhibit the highest thermal insulation performance among VIPs with polygonal cavities. This work provides valuable insights into optimizing VIPs design for enhanced thermal performance and energy efficiency in various applications.

Evolution Law of Structural Form and Heat Transfer Performance of Thermal Insulation System.

Building thermal insulation and energy conservation have become urgent problems in the field of civil engineering because they are important for achieving the goal of carbon neutralization. Thermal conductivity is an important index for evaluating the thermal insulation of materials. To study the influence of different porosity levels on the thermal conductivity of materials, this paper established a random distribution model using MATLAB and conducted a comparative analysis using COMSOL finite element software and classical theoretical numerical calculation formulas. The thermal conductivity of composite materials was determined based on a theoretical calculation formula and COMSOL software simulations, and the theoretical calculation results and simulation results were compared with the measured thermal conductivity of the composites. Furthermore, the influence of the width of the gaps between the materials on the heat transfer process was simulated in the fabricated roof structure. The results showed the following: (1) The thermal conductivity values calculated using the Zimmerman model were quite different from those calculated using the Campbell-Allen model and those calculated using the COMSOL software; (2) The thermal conductivity values calculated using the theoretical calculation formula were lower than the measured data, and the maximum relative error was more than 29%. The COMSOL simulation results were in good agreement with the measured data, and the relative error was less than 5%; (3) When the gap width was less than 60 mm, it increased linearly with the heat transfer coefficient. The heat transfer coefficient increased slowly when the gap width was greater than 60 mm. This was mainly due to the thermal bridge effect inside the insulation system. Based on these research results, a thermal insulation system was prepared in a factory.

Optimization of Thermal Bridges Effect of Composite Lightweight Panels with Integrated Steel Load-Bearing Structure

In order to maintain the quality of construction for nearly zero energy buildings and to reduce the pressure on construction workers with the addition of the need for faster and simpler structures, the use of cavity-insulated LSF (lightweight steel frame) panels is increasing. Requirements for performance quality, quality of life, and low energy consumption have led to the need for closer examination of heat transfer through building elements. Due to the impact on increased heat losses, thermal bridges can cause structural damage due to the increased risk of water vapor condensation on the interior surface. In this paper, numerical heat transfer analysis with the optimization of thermal bridges for LSF cavity insulated walls was made in order to reduce the overall transmission heat losses. The effects of different cavity insulation materials (mineral wool and polyurethane foam) on overall heat transferred through the building elements were analyzed. Additionally, in order to reduce the effect of thermal bridges caused by the steel frame structure, the PVC spacers between the steel and sheathing panels are introduced into calculation models. Lastly, additional layers of insulation were added on the internal and external sides of the LFS panels in order to minimize the effect of thermal bridges and maximize air tightness. Combinations of all three setups were made for wall–window, ceiling–wall, wall–floor joints for the numerical calculation. For each setup, the temperature distribution and overall heat transferred through the building elements were calculated. Different thermal bridge designs have a significant influence on the overall heat transfer, and by choosing the optimal design, the transmission heat losses can be reduced by up to 67%.

Slotted lightweight steel sections for thermal improvement of building envelopes

AbstractThin‐walled steel sections are used as substructures in multi‐shell constructions of metal facades to create space for thermal insulation. They transfer parallel and vertical loads acting on the outer cladding into the load‐bearing system. Thus, they penetrate the layer of thermal insulation and form a thermal bridge. The resulting thermal losses can be e.g. compensated by higher insulation thicknesses or the change of material selection, but both options usually come along with an increased demand of material and additional costs. By inserting slots in the webs of the steel sections the thermal bridge effect can be reduced. The use of one‐piece substructures enables a faster and thus more cost‐effective installation compared to classic two‐part substructures consisting of a bracket and mounting rail system. Although linear components initially exhibit a greater thermal bridge effect, due to the prolongation of the heat flow through slotted webs these can be thermally improved. However, the insertion of slots weakens the section, which requires the consideration of its load‐bearing behaviour. The improvement of thermal behaviour and the reduction of the load‐bearing capacity is investigated in ongoing research. First results show that both thermal and structural requirements of building practice can be achieved by the investigated slotted steel sections.

Thermal performance and sustainability assessment of refrigerated container with vacuum insulation panel envelope layer at different design forms

The thermal performance of vacuum insulation panel envelope layers at four design forms are explored by computational fluid dynamic. The design arrangement form 1, design arrangement form 2, design arrangement form 3 and design arrangement form 4 have the same coverage percentage of vacuum insulation panels. The insulated performance of the VIP envelope layer is impacted by the thermal bridge effect and the polyurethane distribution. The key parameter W, which affects the thermal bridge effect, is found. As the W value decreases, the thermal bridge effect also decreases. For the operation time of 3600 s, the carbon emission of the envelope layer at the four design arrangement forms are 819.9, 426.8, 407.1 and 340.3 g CO2, respectively. And the average heat flux of the four design arrangement forms are 0.995, 0.518, 0.494 and 0.413 W/m2, respectively. Based on the sustainability assessment, the design arrangement form 4 is the best design form for small and medium-sized refrigerated containers. If the size of the VIPs could be customized, the W value will be equal to 0 and the heat leakage caused by PU gaps can be avoided which can enhance the insulated performance of small and medium-sized refrigerated containers.