Linear Thermal Bridges Research Articles

Determination of core thermal resistance errors of reflective multifoil insulation products measured in a hot box depending on evaluation accuracy of its low emissivity surfaces

The multilayer reflective insulation is relatively new product on a construction market, used as efficient insulation and continuously improved. The thermal resistance of this product has to be determined according to the standard EN 16012+A1 [1], which not defines product's sample installation procedure into a hot box and indicates only rough requirement for emissivity values of surfaces of a tested sample and of adhesive tape for fixing the thermocouples must be similar, but it does not specify allowed differences and its effect on the accuracy of the measurement result. These standard's shortcomings do not ensure reliable and comparable results of the thermal resistance of multilayer thermal insulation. Therefore, a study was conducted and the method for installation and fixing of these products into hot box using frame was created. The influence of the frame on the measured thermal resistance was evaluated as a linear thermal bridge. The research of the influence of the difference between emissivity values of the sample and adhesive tape surfaces on the measured thermal resistance was performed using a calibration standard with known R-value. The research results showed that the linear thermal bridge value of frame was increasing with the increment of emissivity value of adhesive tape. Significant difference between sample and adhesive tape emissivity values can create more than 20% relative difference between both measured and calculated R-values from the known real R-value of the calibration standard. In order to avoid more than 3% relative errors, the limits of difference between emissivity values were set.

Numerical and Experimental Analysis of Heat Flow at Window-to-Wall Interface

External walls have a great influence on the thermal and humidity conditions in buildings as well as on the possibility of reducing energy consumption. While the structural and material aspects of walls and windows are well known, obtaining a tight connection to reduce thermal bridges between the window and walls still poses a significant problem. Therefore, a new window installation system proposed by the authors, eliminating linear and point thermal bridges at the window-to-wall interface, opens a pathway for lowering energy consumption in buildings and increasing thermal comfort and thermal efficiency. To prove the effectiveness of this system, numerical and experimental analyses of heat flow through an outer wall with a window were carried out. The numerical analyses were performed using the TRISCO software package. It was shown that the proposed solution eliminated the occurrence of linear thermal bridges at the window-to-wall interface (a linear heat transmittance coefficient Ψ ≈ 0.007, which meets the requirements of the passive house, was obtained). Thus, heat losses were reduced by nearly eight times compared to conventional installation systems. Numerical calculations were experimentally verified.

A Comparison between On-Site Measured and Estimated Based Adjustment Factor Values Used to Calculate Heat Losses to Unconditioned Spaces in Dwellings

Steady-state methods have been widely used in Europe to analyse the energy performance of low-energy buildings. The accuracy of such methods depends on the assumptions regarding the compensation of non-stationary effects, but also on the input design data, such as the temperature of unconditioned spaces (UnSp). This temperature depends mainly on the thermal characteristics of UnSp envelope, air ventilation rate, temperature of the conditioned spaces and the external environment. External environment varies over time, daily and seasonally, making it difficult to accurately estimate UnSp temperature. European Union (EU) directives stated that the UnSp temperature can be evaluated by the adjustment factor (b) set by EN ISO 13789. However, each Member State may adjust procedures, by proposing simplified approaches, either for new or existing buildings. In this paper the b-values measured on-site in three dwellings were compared to those calculated by EN ISO 13789 as well as those estimated based on simplified procedures, allowed in the regulatory framework of some EU Member States, namely Ireland, Portugal, Spain, France and Italy. The study allowed to conclude that EN ISO 13789 and Irish BR 443 provided similar values. However, if the purpose is to simplify procedures and reduce computation effort, French RE2020 proved to be very effective. The thermal characteristics of the UnSp envelope and air ventilation rate were identified as the parameters that most affect the estimation of the b-value, while thermal losses through linear thermal bridges and the ground do not seem to have a significant impact.

Study of the edge thermal bridging effect in vacuum insulation panels: Steady and unsteady-state approaches using numerical and experimental methods

This study presents an experimental and numerical investigation on edge thermal bridges effects in vacuum insulation panels. For this purpose, an experimental campaign was carried out using a guarded hot plate apparatus to determine the linear thermal transmittance between different types of panel joints assemblies. Numerical modelling under steady and unsteady boundary conditions were carried out and compared with the experimental results. Focusing on a VIP suitable for external thermal insulation composite systems (ETICS), a sensitivity analysis regarding different edge protection materials, thickness and panels dimensions were also carried out and discussed. Additionally, the contribution of the point thermal transmittance of mechanical fixing devices was numerically evaluated. Finally, transient thermal simulations are applied to VIP based ETICS in different support walls.The results allowed for the quantification of the influence of the edge thermal bridging effects on equivalent thermal conductivity, as well as on the overall thermal performance of ETICS walls. The size of the panels, edge material and air gaps between panels are key-factors to be considered for minimizing linear thermal bridges in VIP solutions. VIP based ETICS walls showed high thermal delay when compared with a conventional ETICS wall.

Energetic refurbishment of the historic windows of the listed heritage building Alte Schäfflerei and its influence on the overall energy balance

This study examines compatibility of monument conservation and modernization of historic windows of old buildings on the example of the Alte Schäfflerei (Old Cooperage) housing the Fraunhofer Centre for Conservation and Energy Performance of Historic Buildings at Benediktbeuern monastery. Several historic windows are extended to box-type windows and examined in detail. The calculation of the thermal bridges and the resulting U-values of the windows as well as the linear thermal bridge heat loss coefficients result in a reliable estimation of the thermal behaviour of the box-type windows. Via measurements of the surface temperature and heat fluxes on a box-type window the thermal resistance and heat transfer coefficient are estimated. The heat transfer coefficient is calculated in accordance to DIN 10077 with simple and detailed calculation and compared to the estimated calculation of simplified measurements. The energy efficiency of the whole building of the Old Cooperage is calculated in accordance to DIN V 18599 and shows the rate of heat losses of the windows compared to the overall energy demand of the building. For this purpose, the Old Cooperage is implemented with a hypothetical historic usage in DIN V 18599.

Numerical modelling of point thermal bridge’s impact on the thermal performance of facade systems

Starting with 31 December 2020 all new buildings, as well as existing ones, must comply with the nearly Zero Energy Buildings levels, as defined by each member state. A very important design criteria is the one regarding an accurate assessment of both linear and point thermal bridges of the building envelope. Usually, point thermal bridges are either not considered in calculations or are assessed by using simplified methodology as described by the standard EN ISO 6946/2017. This is due to the modelling and calculation complexity required in assessing them. Therefore, in several situations the impact is underestimated, and the thermal performance results do not offer a clear image of the building’s thermal performance. Thus, the paper focuses on the modelling and simulation of several constructive solutions for façade systems, aiming to identify a correlation between the geometrical and thermal characteristics of fixing components and the thermal performance of the facade. The studied case scenarios include two types of masonry walls, of 240 and 365 mm, that are thermally insulated in various thicknesses using an ETICS system. A sensitivity analysis is also performed to define a correlation between all the components that define the system and the point thermal bridge impact magnitude. The results of the study indicate an increased impact with a direct consequence on the energy performance of the building.

Automatic Detection of Linear Thermal Bridges from Infrared Thermal Images Using Neural Network

Detecting thermal bridges in building envelopes should be a priority to improve the thermal performance of buildings. Recently, thermographic surveys are being used to detect thermal bridges. However, conventional methods of detecting thermal bridges from thermal images rely on the subjective judgment of audits. Research has been conducted to automatically detect thermal bridges from thermal images to improve problems caused by such subjective judgment, but most of these studies are still in the early stage. Therefore, this study proposes a linear thermal bridge detection method based on image processing and machine learning. The proposed method includes thermal anomaly area clustering, feature extraction, and an artificial-neural-network-based thermal bridge detection. The proposed method was validated by detecting the thermal bridges in actual buildings. As a result, the average precision, recall, and F-score were 89.29%, 87.29, and 87.63%, respectively.

Comparative Analysis of the Effect of Different Types of Green Roofs over the Linear Thermal Bridges

During recent years, it appears in the background of global discussions the negative impact resulted from the daily humans’ activities. Taking into account the present surface of the built environment and also the fact that this area will significantly increase shortly, it can be considered that using the buildings to develop new solutions like green roofs. The expanding benefits of a green roof emphasize the key role of this structure in the overall thermal performance of buildings and microclimate conditions of indoor spaces. The main objective of the study is to analyse and to interpret the influence of all three main categories of a green roof on the heat flow, in the thermal bridges developed structurally in buildings. The study based on the structural elements of each type of roof, their thermic characteristics and the principal types of thermal bridges will represent a comparison between the thermal impact of a classical terrace roof and that of the extensive, semi-intensive and intensive green roof. In conclusion, the unpredictable results obtained for the analysed thermal parameters let conclude that the green roof solution in all the three forms has an environmental impact, in terms of both sustainability and aesthetics.

A comprehensive study devoted to determine linear thermal bridges transmittance in existing buildings

The issue of transmittance of thermal bridges in existing buildings has been addressed aiming to achieve correlations able to evaluate the ground-contact thermal bridges. A bi-dimensional steady state FEM model has been implemented to simulate wall-to-floor structural node and then validated in accordance with the EN ISO 10211:2017 standard. Different construction joints have been then simulated for the structural node foundations-vertical elements up to a total of 19 configurations, from which 1700 cases have been derived varying walls and floor stratigraphies and ground properties. Correlations for the linear thermal bridge transmittance have been calculated through regression technique for all the configurations, together with their validity ranges expressed in terms of 95% confidence interval values. Tests performed for more than 1000 practical cases confirmed the accuracy of the proposed correlations. Through those correlations ground contact thermal bridges in existing buildings can be hence analyzed in a simple and operative way, offering technicians in the sector a tool that covers most of the possible situations.

MODELAGEM DE PONTES TÉRMICAS NA ZONA BIOCLIMÁTICA 2: CINCO DIFERENTES ABORDAGENS

Thermal bridges are vulnerable points present in the envelope of buildings and influence the thermoenergetic performance and still bring consequences to the opaque surface such as the favoring in the formation of filamentous fungi. The impacts of thermal bridges and their consideration in calculations of thermal transmittance have been discussed in different parts of the world and in regions of cold climates in Brazil. This work aims to evaluate the impact of thermal bridges of reinforced concrete structure in a residential building in the bioclimatic zone 2, considering five approaches for modeling of thermal bridges in the EnergyPlus computational simulation software. The results show that the type of approach used for modeling in computational simulation influences the energy consumption values of the building. The different models tested showed variations in building energy consumption when comparing the strategies that considered the calculations of thermal bridges with the approach that disregarded this calculation, especially in high insulated buildings, where it was possible to identify differences of up to 13%. The conclusions observed show that the level of insulation of the envelope is one of the factors that interferes in the differences in building consumption between the approaches evaluated for thermal bridges. Keywords: Linear Thermal Bridges, Computer Simulation, Energy Performance

The Influence of Different Facings of Polyisocyanurate Boards on Heat Transfer through the Wall Corners of Insulated Buildings

Polyisocyanurate (PIR) thermal insulation boards faced with carboard, plastic, aluminum, or multilayer facings are used for thermal insulation of buildings. Facing materials are selected according to the conditions of use of PIR products. At the corners of the building where these products are joined, facings can be in the direction of the heat flux movement and significantly increase heat transfer through the linear thermal bridge formed in the connection of PIR boards with facing of both walls. Analyzing the installation of PIR thermal insulation products on the walls of a building, the structural schemes of linear thermal bridges were created, numerical calculations of the heat transfer coefficients of the linear thermal bridges were performed, and the influence of various facings on the heat transfer through the thermal bridge was evaluated. Furthermore, an experimental measurement using a heat flow meter apparatus was performed in order to confirm the results obtained by numerical calculation. This study provides more understanding concerning the necessity to evaluate the impact of different thermal conductivity facings on the heat transfer through corners of buildings insulated with PIR boards.

Comparison of theoretical heat transfer model with results from experimental monitoring installed in a refurbishment with ventilated facade

One of the main points to consider when a building is renovated is the improvement of its energy efficiency, minimizing the heat loss through the enclosures and its heating consumption. Under this scope idea a ventilated facade was designed and incorporated in an educational building located in the city of Burgos (Spain). The main objective of this document is a comparison between the theoretical model of heat transfer across the building envelope separating the environment and the interior space, and the heat intake through a linear regression model with installed experimental monitoring. For this it has been necessary to carry out an exhaustive study of the thermal transmission of each one of the materials that make up the thermal envelope of the building, as well as the linear thermal bridges that can be produced before and after the renovation. In addition, thanks to the monitoring installed in the demonstrator building, the interior and exterior temperatures and the heat consumption of each of the radiators is known. In this way expected and real energy savings have been compared.

Lack of regulation on the energy efficiency in Serbia in terms of the assessment of the impact of thermal bridges

As one of the aspects of sustainable architecture, the energy efficiency of buildings has largely come to life and has found its practical application in modern construction practice. Active action towards the achievement of the adequate energy performance of buildings implies the creation of appropriate regulations, providing basic guidelines for securing energy efficiency in the design and construction of buildings. In that sense, with a dozen years of delay in relation to the introduction of the EPBD, Serbia has adopted its legal regulations regarding energy efficiency in buildings, being in force since 2012. Respecting the basic guidelines of the original directive, the regulations in Serbia were the subject of major changes in relation to the previous ones, making a major shift in the boundaries of the relevant parameters and the basic methodology of calculating the energy performance of buildings. However, in practice, it has been shown that some of the factors that are important for the design and energy behaviour of the buildings have been treated inadequately. This particularly refers to the problem of thermal bridges, whose impact on the overall energy performance of the buildings is too simplified. Consequently, depending on the complexity of the building, the prescribed calculation methodology often yields significantly fewer energy needs than they actually are. By taking the view that the influence of thermal bridges, regardless of their type and character, is treated as an arbitrary magnification of surface transmission loss in the function of magnifying the surface of the thermal envelope, the real impact of both linear and point heat losses is neglected. While the issue of an adequate calculation of linear losses is directly related to the way of designing the building, that is, to the conception of details, the question of the impact of point losses is a consequence of the structure of thermal envelope elements. The paper presents two types of critical cases of thermal bridges: the treatment of linear thermal bridges for which research has shown that their influence can significantly exceed those envisaged by the current rulebook, and the influence of point heat bridges, as seen in the specific case of ventilated façades in which this problem is present.

The influence of polyisocyanurate (PIR) facing on the heat transfer through the corners of insulated building partitions

Prefabricated products made of polyisocyanurate (PIR) thermal insulation material covered with cardboard, plastic, aluminium or composite facings are used for thermal insulation of building envelopes. The facing of these products is selected according to their conditions of use, and the effect of the facing on the declared thermal properties of the product depend only on water vapor diffuse properties of the facing. However, at the corners of the building where these products are joined, facings can be in the direction of the heat flux movement and significantly increase heat transfer through the longitudinal thermal bridge formed in the corner of the building. After analysing the solutions for installation of PIR thermal insulation products on the walls and roof corners of buildings, calculations of the heat transfer coefficients of the linear thermal bridges were made, and the influence of various facings and different structural solutions on the heat transfer coefficient value of the thermal bridge was determined. Aluminium foil facing have the greatest influence, but other facings must also be considered. The structural solutions with the greatest increase in the heat transfer due to the effect of the facing were selected, and the influence to the thermal and air tightness properties of the structural solution when facing is removed were analysed, the stability of thermal properties of the thermal insulation material were analysed as well. Proposals for joining PIR thermal insulation products with heat-conductive facings in the corners of buildings were prepared.

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.

Green roof influence over the characteristics of the linear thermal bridges

Urban heat island (UHI) significantly affects the thermal-energy performance of the buildings. Moreover, urban materials absorb solar and infrared radiation, heat accumulation is dispersed in the atmosphere, a fact which increases air temperature. In this context, green roofs are the most suitable solution to resolve these vital issues. The expanding benefits of a green roof, such as energy saving, thermal insulation, and mitigating heat island effect emphasize the key role of this structure in overall thermal performance of buildings and microclimate conditions of indoor spaces. The main objective of the study is to analyse the influence of extensive green roof on the heat flow, in the thermal bridges developed structurally in buildings where they might replace the classical terrace roof. The influence is analysed through the comparison of the thermal impact of a classical terrace roof and that of an extensive green roof, through thermal characteristics of their components. The first part of the paper presents the structures of each type of roof and their thermic characteristics established and evaluated according to the normative regulation in force. In this context, the classical terrace roof and extensive green roof are examined from a thermic point of view, analysing the parameters of the types of thermal bridges usually met, in order to establish if the extensive green roof might have an influence on the overall heat flow. In conclusion, the unpredictable results obtained for the analysed thermal parameters let conclude that the extensive green roof solution presents a favourable environmental impact, promoting a “beautiful” added value to a building, in terms of both sustainability and aesthetics.

Economic importance of point thermal bridges to buildings with steel casing

Point thermal bridges are usually overlooked, their influence on the building’s energy may be significant. For warehouses, production and wholesale halls, the usual perimeter construction is a lightweight construction with thermal insulation between two sheets. As a thermal insulation in a significant number of cases, PUR, resp. its PIR modification. Recently, however, systems using thermal insulation of mineral wool are preferred. These structures, however, have both point and linear thermal bridges. In this paper, we focus on differences in the heat transfer coefficient calculated more precisely by using the ideal 1D, 2D and 3D model fragments and their comparison with the values reported by some manufacturers / vendors. At the end of the paper, we are devoted to quantifying the economic difference between the "offered" state and the fact determined by a more accurate calculation.

Pipeline in thermal insulation of outside wall

Abstract The paper deals with the pipeline management in the thermal insulation of the perimeter wall. Such a pipeline reduces the thickness of the thermal insulation of the building envelope, deteriorates the thermal insulation properties of the wall and creates a linear thermal bridge. The paper deals with alternatives of gas pipeline placement in the thermal insulation of the perimeter wall. The result is a comparison of alternatives of detail solutions with graphical representation of temperature and humidity of structures, description of critical areas and possibilities of application in practice.

Numerical thermal analysis of the vertical external partition made as the frame thin-walled steel structure

The article presents numerical thermal analysis of the vertical external partitions made in the lightweight steel framing technology. Steel posts that perform the structural role lead to the formation of linear thermal bridges and have a negative effect on the level of thermal transmittance U . Therefore, optimal solutions are being explored for such technologies. One of the solutions is to use perforated Thermo sections. The effect of perforated Thermo sections on energy loss was verified through comparison to the wall made of solid sections. Furthermore, the calculations analysed the effect of linear thermal bridges that are formed on wall connections in the corner. Computer simulation was employed to emphasize the significant differences in the temperature distribution in both analysed wall structures that resulted from constructional solutions.

The Influence of Thermal Bridges for Buildings Energy Consumption of “A“ Energy Efficiency Class

From 2016 energy effieiency class buildings should be designed and built in Lithuania, as their energy consuptions are considerably less comparing with the ones that were built before. In order to meet high requirements of energy efficiency class buildings, not only thermal insulating thickness layer of building's envelopes should be enlarged, not only effective windows and building's energy using engineering systems should be used but also new energy efficient structural and insulating solutions should be made. One possibility to reduce building's energy consumption is to join building's envelopes and units that value of thermal coefficient of linear thermal bridges was smaller in joint places. Moreover, in order to evaluate overall heat losses in these joints more exacly it is required to calculate values of heat transmission coefficients of linear thermal bridges in energy class buildings.The project of semi-detached building was chosen in order to analyse influence of linear thermal bridges for building's energy consumption as there are all kinds of linear bridges wich values must be calculated. Buildings energy efficiency designing program, wich based on EN ISO 13790, was used to calculate building's heat losses. Heat transmission coefficients of linear thermal bridges were calculated using program THERM. Two variations were analysed: building's energy consumptions are close to the lowest point of A class requirements when building's envelopes and joints of units in joint places are the same as they are in currently built houses; and effective energy solutions of building's joints.The results analysis showed that requirements of class can be reached using ordinary solutions for building's envelopes and joint units but if linear thermal bridges are designed like that, it makes 16 % heat losses through envelopes, and it is similar to heat losses through building's walls (17 %), furthermore, it is about 1.5 times bigger than heat losses through roof (10 %) or floors (10 %). Specific heat losses of thermal bridges make 7.80 kWh/m2 per year. The biggest overall heat losses are through walls and windows joint thermal bridges (specific heat losses make 13.55 W/K). Another significant part of heat losses comes from walls and floor joints (specific heat losses make 11.88 W/K).After solutions of buildings with energy effective building's envelopes and joints were analysed it can be stated that overall heat losses decreased about 10 kWh/m2 per year, it is 20 %. Heat losses through thermal bridges make only 3 % of overall heat losses through envelopes, it is 122 kWh/m2 per year.According to results of the analyse general specifications were made for designing building envelopes energy efficient class:The building of class can be designed using ordinary solutions of linear thermal bridges, bigger heat losses through thermal bridges can be covered by increasing thickness of thermal insulating layers and using windows of better thermal bahavior but as a result the costs of building house increase too.When effective solutions of linear bridges are used, the same energy efficiency of the building can be reached using less thermal insulating layers, windows and doors of less thermal behavior if the building of better energy characteristics is designed.The usage of effective structural solutions, also of linear thermal bridges, increases energy efficiency of the building, improves conditions of interior microclimate and makes assumption to decrease additional cost of building house comparing to the ordinary ones. DOI: http://dx.doi.org/10.5755/j01.sace.15.2.15351