Thermal Bridges Research Articles

Preparation and performance of PEN-OH@BNNS-OH/PEN interlayer dielectric films with superior interfacial compatibility

Polymer dielectric composites featuring great thermal stability, excellent mechanicals, and good dielectric properties have sparked considerable attention. Here, the preparation of hybrid filler was first performed. The hydroxyl end-capped polyarylene ether nitrile (PEN-OH) was synthesized and then hydroxy BNNS (BNNS-OH) was combined with PEN-OH to obtain PEN-OH@BNNS-OH, which is fabricated by ultrasonic combined with applying post-solid phase chemical reaction technology. The aim is to use the -OH interactions of BNNS-OH and PEN-OH to form hydrogen bonds that greatly enhance interfacial heat transport. Next, the post-solid phase chemical reaction is utilized to make PEN-OH crystallize, and its crystals located on the two-dimensional planes of BNNS-OH or between the layers can serve as a thermal bridge. Then, the as-prepared film with 10 wt% hybrid filler displays high thermal conductivity (1.17 W/m.K), 13.67%-fold higher than pure PEN film, boasts outstanding mechanical properties (stress 105 MPa, strain 6%), high glass transition temperature (Tg: 224 ℃), a dielectric constant (4.30 at 106 Hz), together with low dielectric loss (0.007 at 106 Hz). Besides, the film was post-treated to increase the thermal conductivity to 1.77 W/m.K, reach a higher Tg of 263 ℃, reduce the dielectric constant and loss to 3.68 and 0.006 at 106 Hz. Thus, it is suitable as a high-temperature-resistant dielectric material.

Optimum thermal performance of green walls systems and design requirements against heat transfer of conventional external walls of low-rise concrete buildings in hot regions

This paper presents a study on how the thermal performance of conventional external walls of concrete building could be improved against heat transfer in hot regions. 45 buildings were visited to observe the heat transfer from the warmer side of the external wall to the cooler side. The measurements showed that the conventional walls are insufficient because of high indoor temperatures. This study introduced three environmentally friendly scenarios to enhance the efficiency of the concrete wall against heat transfer. In the first scenario, a continuous air layer was added at the middle of the wall to form an aired-concrete wall. In the second scenario, a living green layer was added on the exterior side of the wall to form a living-concrete wall. The third scenario merged the previous two insights to form a living-aired-concrete wall. Thermal models were prepared to conduct thermal analysis. The results showed that the air layer deactivates the work of thermal bridges and improves the thermal resistance of the wall 5 to 15 times. In the aired-concrete wall, the results showed that the minimum depth of the air layer should be at least 6 cm, to secure a convenient indoor environment with indoor temperature not more than 25 °C. Furthermore, the results showed that adding only an outdoor living green layer to the conventional wall is insufficient in all thermal zones of hot regions. Finally, the best thermal performance against heat transfer was found in the living-aired-concrete wall using outdoor Perennials plants and 5 cm middle air layer.

Vacuum Insulation Panel: Evaluation of Declared Thermal Conductivity Value and Implications for Building Energy

Policymakers regularly implement stricter building energy-efficiency codes towards curtailing building energy use. Inevitably, super-insulating materials such as Vacuum Insulation Panels (VIPs) are essential to satisfy such codes. VIPs have been applied to buildings for over two decades now, with many lessons learned. Generally, the thermal conductivity values of VIPs often reported in the literature are the center-of-panel thermal conductivity (λcop) and effective thermal conductivity (λeff), factoring thermal bridges. However, there are other indexes, such as λ90/90 (declared value in the 90% percentile with a confidence of 90%) and λcop,90/90,aged (factoring aging), that increase consistently and reliably in the declared thermal conductivity value for VIPs. These indexes are scarcely computed and hardly reported. The main aim of this study was to examine the different declared thermal conductivity values of VIP-based guidelines, such as draft ISO DIS 16478, and evaluate their implications on annual building energy consumption. The main study constitutes four parts: (1) experimental evaluation of the thermal properties of pristine and aged VIP samples, (2) computation of thermal conductivity indexes, (3) numerical investigation of thermal conductivity indexes based on a reference building, and (4) related building energy implications. The mean λcop for 10 VIP samples was 0.0042 W/(mK) and increased to 0.0073 W/(mK) for λ90/90, bridge, aged. Results show a significant bearing on building energy performance of as much as 2.1 GJ.

Coupling Conduction, Convection and Radiative Transfer in a Single Path-Space: Application to Infrared Rendering

In the past decades, Monte Carlo methods have shown their ability to solve PDEs, independently of the dimensionality of the integration domain and for different use-cases (e.g. light transport, geometry processing, physics simulation). Specifically, the path-space formulation of transport equations is a key ingredient to define tractable and scalable solvers, and we observe nowadays a strong interest in the definition of simulation systems based on Monte Carlo algorithms. We also observe that, when simulating combined physics (e.g. thermal rendering from a heat transfer simulation), there is a lack of coupled Monte Carlo algorithms allowing to solve all the physics at once, in the same path space, rather than combining several independent MC estimators, a combination that would make the global solver critically sensitive to the complexity of each simulation space. This brings to our proposal: a coupled, single path-space, Monte Carlo algorithm for efficient multi-physics problems solving. In this work, we combine our understanding and knowledge of Physics and Computer Graphics to demonstrate how to formulate and arrange different simulation spaces into a single path space. We define a tractable formalism for coupled heat transfer simulation using Monte Carlo, and we leverage the path-space construction to interactively compute multiple simulations with different conditions in the same scene, in terms of boundary conditions and observation time. We validate our proposal in the context of infrared rendering with different thermal simulation scenarios: e.g., room temperature simulation, visualization of heat paths within materials (detection of thermal bridges), heat diffusion capacity of thermal exchanger. We expect that our theoretical framework will foster collaboration and multidisciplinary studies. The perspectives this framework opens are detailed and we suggest a research agenda towards the resolution of coupled PDEs at the interface of Physics and Computer Graphics.

Performance assessment of active insulation systems in residential buildings for energy savings and peak demand reduction

Active insulation systems (AISs) in buildings are envelopes that integrate thermal insulation, thermal energy storage, and controls. Although different designs for AISs have been proposed in the literature, a comprehensive analysis of feasible AISs is lacking. This paper discusses the energy performance, peak demand reduction potential, and performance characteristics of an AIS that uses a concrete wall as thermal mass sandwiched between two solid-state thermal switches (STSs). These STSs change their thermal conductivity using an on/off metal switch to create or break a thermal bridge across the STS. This paper first describes the experimental setup, used to determine the ratio of thermal resistance during R-high (low thermal conductivity) and R-low (high thermal conductivity) states of the STSs. This ratio was then used in whole-building energy simulations to evaluate the performance of AIS walls across different climate zones with/without a freeze timer of 60 min. The timer was added to reduce the number of switches of STSs from one state to another, and hence the energy needed for these switches. Analysis of the switching frequency and interval of STSs, thermal conductivity of walls, impact of wall orientation, and heat transfer through the wall from the use of AIS at different climate zones/locations were performed. The simulation results show that the AIS can achieve energy savings ranging from ∼ 980 to 2,290 kWh in a single-family home with a floor area of ∼ 220 m2 compared with an IECC 2018 baseline. The energy savings was higher in dry climate zones which represent 17% of residential buildings in the United States, compared to humid or marine climate.

Thermal Bridges Monitoring and Energy Optimization of Rural Residences in China’s Cold Regions

With the worldwide dissemination of the “green development” concept and the advancement of China’s new rural construction, the sustainable development of rural residences has gained significant attention within the construction industry. This article focuses on large-scale prefabricated insulation block houses used in China’s cold regions, specifically examining the case of Defa Village in Nenjiang City, Heilongjiang Province. By utilizing thermal imaging cameras, the thermal bridge parts of these houses are detected, and a finite element model is established to optimize the comprehensive heat transfer coefficient of these areas. This optimization is achieved by expanding the insulation layer and implementing low thermal bridge structures, ultimately enhancing the insulation and energy-saving efficiency of the houses. Simultaneously, an energy-saving analysis is conducted based on an optimized enclosure structure scheme, considering seven key design factors that influence building energy consumption: span, depth, clear height, and window-to-wall ratio in all four directions. Through a comprehensive experimental method, the building energy consumption is evaluated, and a scheme with optimal values is proposed. The results demonstrate that the insulation block walls and the main structures with expanded insulation layers and low thermal bridge structures are easier to construct. When compared to the original scheme, the comprehensive heat transfer coefficient of the walls is reduced by 54.82%, while that of the beams and columns is reduced by 97%. Implementing the optimal value scheme leads to a reduction of 66.83% in the building’s overall energy consumption. This research provides valuable guidance for the design and construction of large-scale insulated block rural residences, revealing the substantial potential of rural residences in terms of energy-saving and emission reduction.

A modified support pillar design for a flat vacuum-based solar thermal collectors

Improving the efficiency of low-temperature solar collectors can be attained by decreasing the heat loss from the collectors. The current work proposes an efficient vacuum-based solar thermal collector design with a new support pillar design to reduce the thermal bridge through the support pillars. In addition, the absorber of this collector is isolated from the front and the rear side by a vacuum layer with transparent glazing. The absorption of front and backside ground reflected radiation, possibly achieving the concept of bifacial flat solar thermal collector. The results of the new support pillar are compared with those of stainless steel and glass support pillars under the same conditions. The results showed that using the new support pillar design decreases heat loss from the absorber. At the 6 mm support pillar diameter, replacing the stainless-steel support pillar with the new modified pillar reduces the heat flux through the front glazing from 59.7 W/m2 to 21.9 W/m2 at ASTM boundary conditions.

Measured Impact of Material Settlement in a Timber-Frame Wall with Loose Fill Insulation

Loose-fill thermal insulations in timber-frame structures are designed to provide efficient thermal protection with the ability to fill intricate details. In a previous study, we detected several air cavities formed in timber-framed wall samples filled with loose-fill mineral fiber insulation. This discovery led us to retrofit the walls by adding appropriate insulation, thus enabling us to evaluate the importance of proper amendment. This paper focuses on a wall fragment with an 80 mm high air gap at the top and a 30 mm high cavity in the middle of the wall height. The following paper compares data collected before the discovery and after the replenishment (refill of air gaps with additional insulation), evaluating potential thermal performance improvement. We were able to quantify the impact of these defects on the external wall exposed to realistic conditions. Based on temperature and relative humidity measurements, the results show significant advancement in the middle of wall thickness with an 8 °C and 45% difference. The results show that although this defect did not directly affect the energy balance of the building, it significantly increases the risk of mold growth due to thermal bridging.

Intrinsically modified self-extinguishing fire-retardant epoxy resin using boron-polyol complex

A novel fire-retardant epoxy thermoset, containing boron polyol complex, was prepared and characterised. The fire-retardant additive was a stoichiometric mixture of boric acid and glycerol. Flame retardancy of the epoxy resin was improved by the formation of stable char layer that protected the underlying epoxy from further burning. Phonon transport through the polymer matrix via hydrogen bonding was identified. The hydrogen bonding acted as a thermal bridge for intermolecular phonon transport to gain improved thermal conductivity resulting early char formation. The hydrogen bonding between the complex and the epoxy matrix was demonstrated using Fourier Transform Infrared Spectroscopy. The phonon transport and a high degree of graphitization was confirmed using Raman Spectroscopy. Thermogravimetric analysis was used for polymer decomposition to confirm a char yield of over 20%. Reaction to fire test revealed enhancement in fire retardancy and self-extinguishing properties of the blend compared to the neat epoxy. Cone calorimetry testing confirmed decreased peak heat release rate and total smoke production by the effect of boron compound in the epoxy matrix. Hydrogen bonding, formation of thick stable layer of char at the polymer surface, and a blowing out effect caused by pyrolytic gases escaping to the gaseous phase, were attributed to the improved fire retardancy. This research may find applications in thermal insulation material of electronic circuit boards, coating in aerospace materials, as well as building and construction industries.

Comparison of the Performance of New and Traditional Numerical Methods for Long-Term Simulations of Heat Transfer in Walls with Thermal Bridges

Several previous experiments showed that the leapfrog–hopscotch and the adapted Dufort–Frankel methods are the most efficient among the explicit and stable numerical methods to solve heat transfer problems in building walls. In this paper, we extensively measure the running times of the most successful methods and compare them to the performance of other available solvers, for example, ANSYS transient thermal analysis and the built-in routines of MATLAB, where three different mesh resolutions are used. We show that the running time of our methods changes linearly with mesh size, unlike in the case of other methods. After that, we make a long-term simulation (one full winter month) of two-dimensional space systems to test the two best versions of the methods. The real-life engineering problem we solve is the examination of thermal bridges with different shapes in buildings to increase energy efficiency.

Modelling the Nonlinear Behavior of the Pot Bearings of Railway Bridge KW51

Railway bridge KW51 in Leuven, Belgium, has been monitored since October 2018 with the aim of validating various structural health monitoring techniques. The displacement and strain measurements on the structure show a nonlinear behavior, which is attributed to friction in the pot bearings. This paper describes and validates a methodology that allows the observed nonlinear behavior of the pot bearings to be modeled. This is important for understanding and reproducing the bridge behavior under combined train and thermal loading as in, e.g., virtual sensing applications. To this end, a previously developed detailed linear finite-element model of the bridge superstructure is augmented with nonlinear Bouc–Wen elements, representing the bearings. A comparison between the measured and predicted bearing displacements under train loading shows a significant improvement of the response prediction in comparison with the case where the bearings are modeled as roller supports, as assumed in the design. In addition, it is also shown that the model enables a qualitative description of the thermal bridge response.

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.

Research on a New Plant Fiber Concrete-Light Steel Keel Wall Panel

With the growing worldwide attention towards environmental protection, the rational utilization of rice straw (RS) has gradually attracted the attention of scholars. This paper innovatively puts forward a solution for rational utilization of RS. A rice straw fiber concrete (RSFC) with good physical and mechanical properties and a rice straw concrete-light steel keel wall panel (RS-LSWP) with low comprehensive heat transfer coefficient and inconspicuous cold bridge phenomenon was designed. Firstly, the preparation method and process of RSFC is described in detail. Then, the physical and mechanical properties of RSFC, such as strength, apparent density, and thermal conductivity were tested. Finally, the thermal properties of the four new types of cold-formed thin-wall steel panels were analyzed using finite element simulation. The results show that the RSFC with a straw length of 5 mm, mass content of 12%, and modifier content of 1% is the most suitable for RS-LSWP. The standard compressive strength, tensile strength, and thermal conductivity of the RSFC are 2.2 MPa, 0.64 MPa, and 0.0862 W/(m·K), respectively. The wall panels with antitype C keel have a low comprehensive heat transfer coefficient and the best insulation effect. This study innovatively provides a technical method for the rational utilization of RS, promotes the application of RS and other agricultural wastes in building materials and the development of light steel housing.

Thermal Bridges on Building Rooftops

Thermal Bridges on Building Rooftops (TBBR) is a multi-channel remote sensing dataset. It was recorded during six separate UAV fly-overs of the city center of Karlsruhe, Germany, and comprises a total of 926 high-resolution images with 6927 manually-provided thermal bridge annotations. Each image provides five channels: three color, one thermographic, and one computationally derived height map channel. The data is pre-split into training and test data subsets suitable for object detection and instance segmentation tasks. All data is organized and structured to comply with FAIR principles, i.e. being findable, accessible, interoperable, and reusable. It is publicly available and can be downloaded from the Zenodo data repository. This work provides a comprehensive data descriptor for the TBBR dataset to facilitate broad community uptake.

High intrinsic thermal conductive polymer films by engineered interchain hydrogen bond interactions

AbstractA series of polyvinyl alcohol (PVA) composite films containing different hydrogen bond acceptors 4,4′‐dihydroxydiphenyl (BP), 1,1′‐biphenyl‐4,4′‐diyl dihexanoate (DHB) and benzene‐1,3,5‐triyl tribenzoate (TBB) were prepared by casting method. Due to the existence of strong intermolecular interaction, the highest in‐plane thermal conductivity of the above films is 1.298 Wm−1 K−1, which is about 65% higher than pure PVA films. Fourier Transform infrared spectroscopy (FT‐IR) and wide‐angle X‐ray diffraction (WXAD) demonstrated that the TBB acts as a thermal bridge to enhance the internal interaction force and make the internal structure more regular. Strong molecular contact forces were demonstrated by mechanical tensile testing. The thermal expansion rate of the system was explored through molecular dynamics. Thermal expansion experiments proved that hydrogen bond can effectively reduce the free volume. Molecular dynamics simulations were also performed in this work. The number and density of hydrogen bonds inside different polymers were calculated, and the phonon thermal transport was quantitatively analyzed. The thermal bridge and intermolecular contact force were discovered to effectively restrict the molecular chain's activity and reduce its free volume. The results of the experiments and molecular dynamics reveal that strong intermolecular interactions and thermal bridges can significantly improve polymer intrinsic thermal conductivity.

Thermal bridge assessment at industrial buildings

It is well known that the thermal performance of a building is influenced by the solutions that define the building’s envelope. In the case of industrial buildings, due to the use of different envelope solutions (e.g. sandwich panels, prefabricated concrete panels etc.), the types of thermal bridge details are often different in comparison to those currently found in residential, office and administrative buildings. Thus, several numerical simulations were performed by analysing details of envelope elements identified at industrial buildings, especially the areas prone to intensified heat flow (joint areas, intersections, glazed surfaces, and others.). Therefore, the paper will present the assessment of thermal bridge details for four industrial buildings having various destinations. The effects of two-dimensional heat transfer in envelope elements, such as windows, walls, foundations, roofs and doors, will be evaluated. The impact of the thermal bridges will be measured by verifying to what extent the level of thermal performance of each envelope component meets the thermal resistance requirements, as well as the building envelope ensures the global heat transfer coefficient for each of the studied cases. A series of conclusions and recommendations will be provided for specialists and designers in the building energetics field.

Spatial-temporal evolution principle of temperature field in a high-temperature geothermal highway tunnel

The spatial-temporal evolution principle of the temperature field in a high-temperature geothermal highway tunnel is investigated, which aims to shed light on the thermal damage prevention for the high-temperature geothermal tunnels. Taking the Nige Tunnel, a high-temperature geothermal tunnel of Jianshui (Gejiu) to Yuanyang expressway in Yunnan Province as the research case, the temperature fields of air, lining and surrounding rock covering all the thermal damage grade sections are monitored. Furthermore, the numerical simulation is conducted to simulate the temperature field of the tunnel. The results show that 1) the temporal curve of air temperature inside the tunnel shows a slowly decreasing trend with the decrease of air temperature outside the tunnel. In contrast, the temporal curve of secondary lining shows a rapid increase-rapid decrease-stable-slow decrease trend. The temperature of surrounding rock experienced two stages of natural and slow decline. 2) In the spatial dimension, the temperature in the tunnel is distributed in an “n” shape along the longitudinal direction of the tunnel, and the temperature contour of the surrounding rock is parabolic, with the centerline located at the breakthrough point during the tunnel construction. As time progresses, the region where the temperature field of the surrounding rock decreases gradually develops to the interior. 3) The effect of the sprayed thermal insulation layer is significant: the temperature difference of secondary lining and initial support could reach 20.1 °C; the temperature inside the tunnel then reduces to the standard value. 4) There is no thermal insulation layer in the cable trench of the Nige Tunnel, and the “thermal bridge effect” appears. The cable trench needs a targeted design, and the research of electromechanical heat resistance should be paid more attention.

Rapid-actuating high-Tg shape memory polyimide composites with synergistic “micro-nano” thermal conduction networks

Shape memory polyimide (SMPI) is one of the most promising intelligent materials and has a high potential for deformable flexible electrodes, intelligent thermal management devices, and high temperature active deployable structures, etc. In this paper, silane-modified AlN nanoparticles (M-AlN) are composited with SMPI matrix resin to prepare fast-response high-Tg shape memory composites. Besides, nano-sized AlN and micron-sized Al2O3 are used to construct “micro-nano” synergistic thermal conduction networks, in which the AlN acted as the “thermal conduction island”, and the Al2O3 acted as the “thermal conduction bridge”. The results show that the in-plane thermal conductivity of Al2O3/M-AlN/M-SMPI-2 is 5.99 W m−1K−1, compared with SMPI, its thermal conductivity increases by 91%. In addition, the shape transition temperature of Al2O3/M-AlN/M-SMPI-2 was higher than that of pure SMPI, which was at 426 °C, and the thermal response shape recovery speed is also greatly improved by 433%, which can be used in rapid-actuating and high temperature active deformation structure.

INTEGRATED APPROACH TO ENERGY EFFICIENT BUILDING DESIGNING BASED ON BIM

Problem statement. The design of energy efficient buildings requires compliance with a number of criteria. The use of energy efficient constructions and building materials, the use of energy efficient engineering solutions and high performance equipment can more than halve a building's resource consumption. But it is important to select and define the characteristics individually. A real estate object must therefore, first of all, be designed correctly. Calculated designs, reasonably selected building materials and correct calculations from thermal engineering calculators do not guarantee obtaining a heat-insulating and vapor-insulating envelope without gaps. Due to the complexity of the construction object, it is problematic to identify thermal bridges and take into account weak points without an integrated approach to the design of the future building. The climate, geographical location and terrain must also be taken into account. In order to carefully select the optimal design solution, it is necessary to take a large array of data related to energy efficiency indicators. In classic design systems, such information is not displayed or analyzed. It is very difficult to assess the energy efficiency of the project. The technology of building information modeling, or BIM, makes it possible to radically simplify the task of designing energy efficient buildings. The purpose of the article is to substantiate the use of modern programs based on VIM technologies at the stage of energy efficient building design, to determine the criteria for selecting a software complex that will allow you to perform building simulation, calculate energy efficiency indicators, analyze thermal bridges, visualize the results, and issue a package of working documentation within the framework of one program. Demonstrate a highly detailed three-dimensional model of the building enriched with maximum information: data on the thermal conductivity of building materials and technical characteristics of equipment.

The urgent task of mass construction of «passive houses» in Ukraine

An analysis of energy consumption per m2 of housing showed that in the EU countries the average value of energy for heating is about 95 kWh/(m2) per year, while in Ukraine this value is about 200-250 kWh/(m2) per year. The main mechanisms for reducing energy costs for heating residential premises in the EU countries are shown and the dynamics of this decrease to the level of 15 kWh/(m2) per year is disclosed. The role of the «passive house» strategic building standard (nZEB) as a pioneer in reducing residential energy consumption is shown. Data on the number of "passive houses" built around the world, and data on single houses of this type in Ukraine are given. The urgent task need for the use of the "passive house" standard in Ukraine to reduce the consumption of thermal energy for heating housing, as well as harmful emissions into the atmosphere, has been identified. The topic of availability in our country of local constructive and heat-insulating building materials, technologies and engineering systems was discussed. The basic principles of creating a "passive house", its main digital technical characteristics are listed and it is shown that they are suitable for the climatic conditions of Ukraine. Recommendations are given on the use of structural and thermal insulation materials, special windows, air tightness, mechanical ventilation with exhaust air heat recovery and design of buildings without cold bridges. It has been determined that a "passive house" with simple engineering heating (cooling) systems is more sustainability and anti-crisis. The main methods for calculating a "passive house" are analyzed, the need to involve additional 3D modeling programs is determined to obtain more accurate numerical characteristics of the building and the choice of engineering systems. It is emphasized that the creation in Ukraine of entire eco-settlements from such houses will affect the general increase in the awareness of our society, broad awareness of new technologies and, as a result, the breakdown of the inertia of the entire system and the introduction of new, innovative building codes, which will entail the mass construction of "passive houses”, significant savings in energy resources throughout the country, reducing harmful emissions and improving the quality of life of people.