Effect Of Thermal Bridges Research Articles

Experimental assessment of thermal break strips performance in load-bearing and non-load-bearing LSF walls

A reliable evaluation of thermal behaviour and energy efficiency of buildings depends on the accurate thermal characterization of the envelope components. One of the most reliable methodologies to perform this thermal characterization is the measurements under laboratory-controlled conditions. The thermal performance assessment of lightweight steel-framed (LSF) building components exhibits particular additional challenges related to the strong thermal conductivity contrast between cavity insulation and steel frame materials, which may originate unwanted significant thermal bridge effects. The use of thermal break (TB) strips is one of the most currently used thermal bridge mitigation strategies. It was not found in the literature any experimental campaign for TB strips thermal performance evaluation in LSF elements. In this paper the thermal performance of twenty load-bearing (LB) and non-load-bearing (NLB) LSF walls configurations are measured, using the heat flow meter (HFM) method under controlled laboratory conditions. Three thermal break (TB) strip materials and three TB strip locations in the steel stud flanges are assessed. It was found that the inner and outer TB strips show very similar thermal performances, while double TB strips have a relative significant thermal performance increase. Aerogel was the best performance TB material, exhibiting a substantial improvement relatively to recycled rubber and cork/rubber composite TB strips. Furthermore, the TB strips performance was identical for the evaluated structural (LB) and non-structural (NLB) LSF walls.

Numerical analysis and experimental investigation on thermal bridge effect of vacuum insulation panel

Vacuum insulation panel, composed of a core material and a barrier, is a very efficient thermal insulation material. Compared with conventional insulation materials, the vacuum insulation panel is proposed to achieve a better insulated performance. However, its thermal conductivity will be seriously increased and insulated performance will be significantly decreased since the additional heat is transferred through the barrier; that is called thermal bridge effect. This paper emphasized on effective thermal conductivity to evaluate the performance of vacuum insulation panel. Two criteria, i.e., the linear and point thermal transmittance are introduced to evaluate the comprehensive performance of vacuum insulation panel. A heat transfer model was used to analyze the thermal bridge. Then, a fast and effective method for measuring thermal bridge is presented, which is supported by numerical simulation analysis. The results indicated that thermal bridge not only could increase with the increasing of the mental foil (main aluminum) thickness, but also could exhibit higher heat losses with the reducing of thickness of the vacuum insulation panel. Overall, the effective thermal conductivity of vacuum insulation panel could increase by 110.8% when the barrier contains 10 μm mental foil and the size of vacuum insulation panel is 300 × 300 × 10 mm3. This research provides a reference for measuring the thermal bridge and could also disclose the quantitative behavior of physical parameters in thermal bridge.

Thermal bridge effect of vertical diagonal tie connectors in precast concrete sandwich panels: an experimental and computational study

The purpose of this work was to quantify the thermal bridge effect of vertical diagonal tie connectors in precast concrete sandwich panels (PCSPs). Special interest was in cases where the use of rigid insulation (e.g. PIR) would leave air gaps between insulation boards and diagonal ties, thus intensifying the thermal bridge. A climate chamber experiment using 5 different joint types was performed to gather reference data for CFD model validation. In the experiment, natural convection was observed in joints where no additional insulation was used, i.e. in air cavities. Significantly larger heat fluxes were measured in these cavities compared to insulated joints. The thermal bridging effect was evaluated for a typical PCSP (thermal transmittance without thermal bridges U = 0.11 W/(m²·K)) using CFD software taking into account 3D heat conduction and convection. Simulation results indicate that diagonal ties without adjacent air cavities increased the average thermal transmittance (U-value) of the envelope by 8%, diagonal ties with a 6 mm air cavity – 19...33% and diagonal ties with a 10 mm air cavity – 45...56%. In conclusion, it was found that the joints in insulation caused by diagonal ties affect the overall thermal performance of the building envelope significantly when efforts are not made to fill the air cavities around the connectors.

A new method to estimate point thermal transmittance based on combined two-dimensional heat flow calculation

A well-insulated, airtight and thermal bridge free building envelope is a key factor for nearly zero energy buildings (nZEB). However, increased insulation thickness and minimized air leakages increase the effect of thermal bridges on overall energy efficiency of the nZEBs. Although several more prominent linear thermal bridges are accounted for in the practice the three-dimensional heat flow through vast array of fixation elements, mounting brackets and other point thermal bridges are usually neglected due to time-consuming model preparation routine, lack of input data as well as high number of different thermal bridges that have to be assessed for a single project. In this study a new method was proposed for predicting three-dimensional heat flow and the point thermal transmittance of thermal bridges caused by full or partial penetration of the building envelope with metal elements with uniform geometry in third dimension based on multiple two-dimensional numerical heat flow calculations. A new parameter (equivalent length of thermal bridge) was defined which incorporates the effect of additional thermal transmittance in third dimension when multiplied by the difference of two thermal coupling coefficients derived for two-dimensional cross section. Multiple linear regression model was fitted on database with 102 cases and verified with separate case of window to wall connection incorporating metal penetration at fixation points. The proposed methodology can be useful in general practice where the design team lacks the skills or software tools for conducting detailed numerical analysis in three dimensions.

Energy saving Architecture: Background, Theory and Practice in Kyrgyzstan

This paper for the first time presents a set of background, theory and practice of energy saving architecture of buildings that allows harmonization of appropriate thermal “behaviour” of the building itself with the energy saving behavioural actions of the people in it depending on year-round and daily dynamics of renewable energy of an environment and incoming solar radiation. Energy saving architecture offers a solution to the two-fold task of saving energy and ensuring acceptable internal conditions due to the beneficial influence of natural processes of the building and human behaviour. It is aimed to provide year-round acceptable parameters for the internal microclimate and sanitary-hygiene conditions and to minimize heating, cooling, and ventilation energy consumption. This paper presents the derivation of the formula on the dimensionless indicator of the building’s energy efficient form; its values of the real building forms; examples of solved computational optimization of the location, orientation, and size of the building, and its rooms and thermal envelope components (especially windows and doors). Considerations include issues of minimizing the effect of thermal bridges, especially architectural ones, as well as the structural and operational bridges from the author’s classification. The architectural, constructional, and operational practices are demonstrated by: passive gain and prevention of solar heating; heating and cooling by natural ventilation.

Numerical Simulation and Experimental Investigation on Thermal Bridge Effect of Vacuum Insulation Panel with Cavities

Numerical Simulation and Experimental Investigation on Thermal Bridge Effect of Vacuum Insulation Panel with Cavities

3D Dynamic Simulation of Heat Conduction through a Building Corner Using a BEM Model in the Frequency Domain

This paper sets out a three-dimensional (3D) boundary element method (BEM) formulation in the frequency domain to simulate heat transfer through a point thermal bridge (PTB) at a corner in a building envelope. The main purpose was to quantify the dynamic effect of a geometrical PTB in terms of distribution of temperatures and heat fluxes, which is useful for evaluating moisture condensation risk. The numerical model is first validated experimentally using a hot box to measure the dynamic heat behavior of a 3D timber building corner. The proposed model is then used to study the dynamic thermal bridging effect in the vicinity of a 3D concrete corner. Given the importance of the risk of condensation, this study looks at the influence of an insulating material and its position on the temperature and heat flux distribution through the PTB under steady state and dynamic conditions.

Phase Change Material Used for Masonry Joints to Reduce the Thermal Bridge Effect.

In this paper, a numerical calculation and application analysis of composite phase change material masonry mortar applied to wall parts are performed during the research process. Instead of the conventional “sandwich” phase change material wall, our research group mainly uses phase change materials in the wall parts to build masonry joints to reduce the thermal bridge effect. The influence of masonry joints on the heat transfer of the wall is demonstrated. A quantitative description of the transient heat transfer coefficient is obtained to measure the heat preservation performance of the phase change material wall. Furthermore, the influence of different proportions of phase change materials on the wall heat transfer in different external environments is discussed, supplemented by the influence of the working range and sensitivity on the heat transfer. In summary, the use of phase change materials in the construction of masonry joints is a great innovation for conventional “sandwich” phase change material walls, optimizing the form, the thermal bridge effect and the heat preservation performance of wall parts. The quantitative description of the transient heat transfer coefficient expands the development of wall heat transfer theories. In addition, the conclusions are of great guiding significance for the structure and the phase change material’s blending proportion for the innovative heat preservation phase change material wall.

열교저감방식에 따른 진공단열패널이 적용된 벽체의 열교특성분석

Purpose: The insulation requirements for buildings are being strengthened to make zero energy mandatory. Vacuum insulation panel (VIP) has about 8~10 times better insulation performance than existing insulation and also maintains high insulation performance with a slimmer thickness. However, when VIP is installed on a building wall, thermal bridge occurs. Thermal bridges of VIP itself, thermal bridges due to air gaps between adjacent vacuum insulation panels, and thermal bridges with other building materials that make up the walls. Thermal bridges deteriorate the insulation performance of the building envelope. The purpose of this study is to compare and analyze the insulation performance by designing a wall with vacuum insulation panels and applying a method to improve the insulation performance degradation due to heat bridges. Method: In this paper, thermal bridge phenomenon of the wall was analyzed using Physibel TRISCO simulation program. The walls were designed for VIP encapsulated EPS insulation application walls. The parameters of thermal bridges reduction were set to air gsp seals between VIPs, application of thermal bridge fastener and both. A total of 4 cases were designed. Result: Based on the simulation results thermal bridge effect for wall with encapsulated VIP reduced by 5.2% for Case 1, 7.2% for Case 2, and 13.6% for Case 3. As a result, it was confirmed that the airtight seal between VIPS and the type of connection material affect the thermal bridge of the wall. From the findings in this paper, it is recommended that necessary techniques are adopted to prevent deterioration of insulation performance primarily due to thermal bridges.

Thermal transmittance of lightweight steel framed walls: Experimental versus numerical and analytical approaches

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.

Stereocomplexation of Poly(Lactic Acid)s on Graphite Nanoplatelets: From Functionalized Nanoparticles to Self-assembled Nanostructures.

The control of nanostructuration of graphene and graphene related materials (GRM) into self-assembled structures is strictly related to the nanoflakes chemical functionalization, which may be obtained via covalent grafting of non-covalent interactions, mostly exploiting π-stacking. As the non-covalent functionalization does not affect the sp2 carbon structure, this is often exploited to preserve the thermal and electrical properties of the GRM and it is a well-known route to tailor the interaction between GRM and organic media. In this work, non-covalent functionalization of graphite nanoplatelets (GnP) was carried out with ad-hoc synthesized pyrene-terminated oligomers of polylactic acid (PLA), aiming at the modification of GnP nanopapers thermal properties. PLA was selected based on the possibility to self-assemble in crystalline domains via stereocomplexation of complementary poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) enantiomers. Pyrene-initiated PLLA and PDLA were indeed demonstrated to anchor to the GnP surface. Calorimetric and X-ray diffraction investigations highlighted the enantiomeric PLAs adsorbed on the surface of the nanoplatelets self-organize to produce highly crystalline stereocomplex domains. Most importantly, PLLA/PDLA stereocomplexation delivered a significantly higher efficiency in nanopapers heat transfer, in particular through the thickness of the nanopaper. This is explained by a thermal bridging effect of crystalline domains between overlapped GnP, promoting heat transfer across the nanoparticles contacts. This work demonstrates the possibility to enhance the physical properties of contacts within a percolating network of GRM via the self-assembly of macromolecules and opens a new way for the engineering of GRM-based nanostructures.

Transforming thermal-radiative study of a climber green wall to innovative engineering design to enhance building-energy efficiency

The thermo-regulatory function of building-integrated climber vegetation has been verified. However, there is a need to increase in-situ observation studies on green walls installed on windowed building envelopes. This study presents results of instrumental monitoring of the thermal and radiative environment of a climber-green wall with windows to inspire a more energy-efficient green wall system design. This research is based in humid-subtropical Hong Kong, with reference to experimental controls (without vegetation cover) of a bare wall and a bare roof in sunny, cloudy and rainy weather in summer. The experimental results demonstrated lower short-wave reflectivity on green wall (0.13) than on control bare wall (0.30). Green wall received the thermal influence of long-wave terrestrial radiation as well as sky radiation. On sunny, cloudy and rainy days, the exterior concrete wall surface behind climber vegetation was cooler than control bare wall up to 6.6, 2.3 and 1.2 K respectively, and the posterior air gap shielded by the climbers was cooler than ambient air up to 2.2, 0.8 and 0.4 K. On sunny day, indoor wall surface and air of the green wall envelope were warmer at maximum by 1.4 and 1.3 K respectively, possibly contributed by the thermal bridge effect of the windows. On cloudy and rainy days, however, indoor surface and air experienced cooling by < 2.0 K. The evaluation of the thermal effects of windows on the indoor thermal regime led to the proposal of a rotatable green wall planter system, which could optimize daytime and nighttime thermal benefits by maximizing daytime shading-induced shielding against through-window insolation and nighttime radiative heat loss.

Thermal bridges of metal fasteners for aerogel-enhanced blankets

The use of silica aerogel-enhanced blankets as a thermal insulation material is one of the most promising solutions to reduce the heat loss through the building envelope. Aerogel-enhanced blankets provide exceptionally high thermal resistance, thanks to a thermal conductivity value as low as 0.014 W/mK. However, a challenge in the use of aerogel-enhanced blankets is represented by the way to connect these highly flexible panels to the backing support. This paper describes the effect of mechanical fasteners over the thermal performance of a brick wall covered with an aerogel-enhanced blanket investigated. The effective thermal transmittance of the selected aerogel-enhanced blanket due to the presence of the metal fasteners is evaluated experimentally using a calibrated chamber. The laboratory measurements are also compared with theoretical calculations conducted both for metal and plastic fasteners. Finally, some conclusions about the ways to reduce the thermal bridging effects during the installation of aerogel-enhanced blankets are provided, and the effective thermal conductivity of aerogel blankets considering different materials (plastic or metal anchors) for their fastening are reported.

Distributed Temperature Sensing Monitoring of Well Completion Processes in a CO₂ Geological Storage Demonstration Site.

The Distributed Temperature Sensing (DTS) profiles obtained during well completion of a CO2 monitoring well were analyzed to characterize each well completion process in terms of temperature anomalies. Before analysis, we corrected the depth by redistributing the discrepancy, and then explored three temperature calibration methods. Consequently, we confirmed the depth discrepancy could be well corrected with conventional error redistribution techniques. Among three temperature calibration methods, the conventional method shows the best results. However, pointwise methods using heat coil or in-well divers also showed reliable accuracy, which allows them to be alternatives when the conventional method is not affordable. The DTS data revealed that each well completion processes can be characterized by their own distinctive temperature anomaly patterns. During gravel packing, the sand progression was monitorable with clear step-like temperature change due to the thermal bridge effect of sand. The DTS data during the cementing operation, also, clearly showed the progression up of the cement slurry and the exothermic reaction associated with curing of cement. During gas lift operations, we could observe the effect of casing transition as well as typical highly oscillating thermal response to gas lifting.

State of Knowledge of Thermal Bridges—A Follow up in Sweden and a Review of Recent Research

It is important to minimize transmission heat transfer losses through the building envelope when designing and building energy efficient buildings in heating dominated climates. In such a climate, a large part of the space heating demand is caused by transmission heat transfer losses through the building envelope. Calculations of these losses must be carried out in a correct way to ensure a properly sized heating system and a good indoor climate. Furthermore, underestimating the transmission heat transfer may lead to energy costs that exceed expectations. A Swedish study was published five years ago which concluded that the state of knowledge was low and simplified methods used were not accurate. Five years has passed since the previous study. The purpose of this follow-up is to investigate whether the state of knowledge among Swedish consultants has increased and to review the progress within the international field. The study shows that little has changed in Sweden. The state of knowledge regarding different measuring methods and the effect on thermal bridges is still not satisfying. Furthermore, the review of recent research shows that the relative effect of thermal bridges vary greatly. More guidelines and education/training are needed. Further research should be carried out with a holistic approach where thermal bridges are investigated with varying construction types, energy efficiency of building envelopes and different measuring methods.

Thermal and sound insulation of lightweight steel-framed façade walls

Lightweight steel-framed (LSF) construction has the potential to reach high standards regarding the functional performance of buildings. Despite the benefits of this construction system, the effect of thermal bridges caused by the high thermal conductivity of the steel structure can be a disadvantage. Furthermore, because LSF buildings have low mass and the connections between the outer and the inner sheathing of the walls are usually rigid, provided by steel studs, some acoustic performance drawbacks are also possible. Excessive heat loss or poor sound insulation are related to the external envelope behavior of buildings. Although several studies can be found regarding the influence of the steel frame on the thermal or sound insulation performance of LSF façade walls, the study of this influence from both perspectives at the same time is not widespread. In this work, the influence of the steel frame on both the thermal and sound insulation performance of LSF façade walls is studied. The thermal behavior and sound insulation are assessed using specialized software, namely THERM and INSUL, respectively. With this work it is intended to provide guidelines which can contribute to an effective design of LSF façade walls, considering both functional performances.

Effects of changes in the structural parameters of bionic straw sandwich concrete beetle elytron plates on their mechanical and thermal insulation properties

To develop new, environmentally friendly prefabricated building materials, the effects of individual changes in structural parameters on the mechanical and thermal insulation properties of straw sandwich concrete beetle elytron plates (SCBEPs), i.e., sandwich plates with trabeculae constituting the core layer structure, were analyzed by ABAQUS. In addition, based on the analysis results, the structural parameters were preliminarily optimized. The results revealed the following. 1) The bearing capacity of a SCBEP is mainly controlled by deformation (i.e., the maximum deflection). The two most influencing factors on the deflection are the panel thickness T and the trabecular radius R. In contrast, although the panel area is very large, the influence of changing the panel thickness on the thermal insulation performance ranks only third. This demonstrates that the thermal bridge effect of the concrete trabeculae and edges is the primary limitation on further improvements to the thermal insulation performance of SCBEPs. 2) Based on the effects of individual changes in structural parameters on the performance of SCBEPs and their actual processing and application requirements, the structural parameters of a SCBEP with optimized mechanical properties and thermal insulation properties are determined. 3) Compared with aerated concrete wallboards, the optimized SCBEP has a higher rigidity, more compacted surface and better durability. Compared with straw concrete wallboards, the optimized SCBEP has a higher straw content and better thermal insulation performance. Thus, it provides a new avenue for the development of a new, lightweight wallboard.

Combination of Diagnostic Tools for the Proper Identification of Moisture Pathologies in Modern Residential Buildings

A study of moisture pathologies in a modern residential multifamily building is presented. The housing block was designed under the regulation NBE-CT of 1979 in northern Spain. After the appearance of some moisture problems in the façades, three complementary studies were conducted to analyze the situation of the envelope and diagnose the best improvement possibilities. First, indoor conditions of temperature and humidity of the apartments with moisture pathologies were monitored. During 40 winter days, the occupancy, heating operation, and natural ventilation were analyzed. Second, the inner and outer surface temperatures of the studied façades were measured. Thermal insulation degree, thermal capacity, and thermal bridge effects were measured to assess the risk of interstitial condensation under the real conditions of use. Third, an infrared thermographic survey was carried out, which allowed the detection of irregularities and the assessment of moisture problems. The wrong interpretations, which would have been made if the complementary studies had not been done, are exposed. The key towards the accurate diagnosis was the combination of tools. Finally, some technical solutions based on ventilation or thermal insulation enhancement are proposed as different ways to reduce the high levels of relative humidity indoors and minimize the risk of condensation in the future.

LIFE CYCLE OPTIMIZATION OF A LIGHTWEIGHT STEEL BUILDING: EFFECT OF DIFFERENT INSULATING LAYERS, GLAZING TYPE AND WINDOW SHADING

In recent years, life cycle assessment has become an important tool for determining the environmental impact of materials and products. It is also useful in analysing the impact of a building structure has over the course of its life cycle which includes production of materials, transport, construction, operation, end of life. This paper is intended to provide a life cycle analysis of a building located in Coimbra, Portugal. To achieve the effect of different insulation layers, glazing type and window shading, two different solutions were analysed. In order to compute the thermal transmittance U-values for the walls and roofs, Therm5 software was used, so as to account for the effect of thermal bridges induced by the steel framework. These values were then introduced in the building model, which was designed in the software DesignBuilder, in order to compute the thermal behaviour of the building. Finally, the values of the energy consumption for a period of 50 years were introduced in the life cycle analysis made in the GaBi software. This allowed estimating the impact of both solutions and providing conclusions as to which is the best solution.

Two new methods for the in-situ measurement of the overall thermal transmittance of cold frame lightweight steel-framed walls

The in-situ measurement of the overall thermal transmittance (Uoverall) of lightweight steel-framed (LSF) walls, including the effect of thermal bridges due to metal structure, is a challenge for designers, engineers and energy audits. The present study introduces two methods for the in-situ measurement of the overall thermal transmittance of cold frame lightweight steel-framed walls. The two methods, Representative Points Method (RPM) and Weighted Area Method (WAM), focus on the fast and accurate in-situ measurement of the Uoverall at the central part of an existing LSF wall. The methods combine the analysis of the examined wall using thermal images with the recording and processing of indoor/outdoor air temperature and heat flux. The requirements and the procedure for the employment of the methods on an existing wall are extensively described. The methods concern cold frame LSF walls, however numerical analysis shows that the methods can also be employed on hybrid frame LSF walls. The methods were experimentally validated on a well-known cold frame LSF wall. The results of the in-situ measurements were in a good agreement with the theoretical values, determined in accordance with the international standard ISO 10211 ensuring the validity of methods.