Thermal Bridges In Buildings Research Articles

Thermal bridges in buildings of consolidated contexts in high-altitude cities. Case study: Ambato, Ecuador

This research work has been centered on the study of thermal bridges in the urban area of the city of Ambato, this city is located at an altitude of 2570m with an average temperature of 15°C throughout the year, the construction systems used in the study area mostly consist of a layer of material either clay brick or concrete block and exterior and interior finishing’s. The objective is to diagnose the points where thermal leaks can be found in consolidated environments and to provide possible solutions in different construction elements. The methodology used is based on a mixed study, which analyzes the urban context, the buildings present, the construction materials used, their relationship with the current climate of the area and the quantification of latent temperatures for further simulation. The results were obtained through a calculation software where the diagnosis and the improvement plan were simulated to increase the ambient temperature of the houses from 15-17°C to the range of 20-24°C within the comfort temperature range for interior spaces. This study concluded that it is possible to significantly improve the thermal performance of buildings in consolidated contexts with specific interventions.

Impact of an Innovative Solution for the Interruption of 3-D Point Thermal Bridges in Buildings on Sustainability

During the design of the external cladding, it is possible to use different materials and compositions. One of these possibilities is also a ventilated facade, which consists of a supporting structure, a thermal insulation, a supporting grid, an air gap for ventilation and a cladding layer. The construction of the supporting grid in the ventilated facade must be mechanically anchored into the supporting structure of the external cladding. This mechanical anchoring causes 3-D point thermal bridges in the external cladding itself. Therefore, the aim of this work is to assess and analyze the influence of these 3-D point thermal bridges on transmission heat losses through the external cladding. A Finite Element Mesh analysis has been used for this analysis. Different types of external cladding compositions were modeled in the simulation program, and the effect on the heat transfer coefficient was determined. In addition to the analysis of the existing anchoring systems, an innovative solution has been suggested that is more economical and easier to implement. The results show that the application of anchors and their number impacts significantly on the thermal properties of the envelope. The difference between the anchoring element with a thermal insulation pad and the patented method is minimal. This is a 1.29% difference. The last variant was a proposal (patent) that the anchoring element is only plastic-coated and thus its thermal engineering properties are improved, which is manifested mainly in heat conduction but also from the radiant point of view, as plasticizing the emissivity changes. Compared to the perimeter cladding without the ap-plication of an anchoring element, the heat loss increases by 29.37%. In addition to the energy savings, there are also financial savings. While the plastic pads costs about EUR 0.3, the plastic coating (patent) represents a price of around EUR 0.03. If we had a building with 10,000 m2 of wall area where 6 pieces of anchors per 1 m2 are applied, the savings would be EUR 16,200. Such savings are already significant. The conclusion of this work is that these point thermal bridges have a significant impact on the overall transmission heat loss coefficient and therefore they have overall heat demand and energy demand.

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.

Analytical Mathematical Modeling of the Thermal Bridge between Reinforced Concrete Wall and Inter-Floor Slab

The evaluation of thermal bridges in buildings, following the UNI TS 11300-1:2014 standard, must be carried out with finite element analysis or through the use of atlases compliant with the UNI EN ISO 14683:2018. The paper illustrates the development of an analytical tool to determine the internal linear thermal transmission coefficient (ψi) for the thermal bridge between concrete wall and inter-floor slab, neglected in the main existing catalogs or atlases. This type of thermal bridge is relevant in multi-story buildings, and is typical of public housing districts built between the 1960s and 1970s throughout Europe by means of industrialized systems. Considering energy requalification, due to their low energy efficiency, these buildings require adaptation to the standards imposed by law, and this thermal bridge, which has a high percentage incidence on the total heat losses, cannot be overlooked. From the survey of a representative number of such buildings in Italy, three different technological solutions were examined, with dimensional variations in the individual technical elements and the related functional layers. The combination of these variables resulted in 216 different case studies. The analysis of the existing atlases and catalogues has demonstrated their inapplicability for the selected case studies. For each one of these, ψi was calculated, using off-the-shelf software. The correlation of the data made it possible to determine an analytical mathematical modeling process to assess heat losses due to the analyzed thermal bridge. The validity of this mathematical formula was verified by recalculating the typologies investigated, reaching an error evaluated by means of the mean square deviation equal to ±4%.

Improving the detection of thermal bridges in buildings via on-site infrared thermography: The potentialities of innovative mathematical tools

The detection of thermal bridges in buildings is one of the key points to be taken into account in energy saving procedures during refurbishment works. Passive infrared thermography (IRT) has been applied for years to detect thermal bridges by referring to the International Organization for Standardization (ISO) 6781:1983. However, the successfulness of this norm is strongly affected by the detection accuracy of the thermal imprint produced on the facade by a conductive material called as “defect” in this work. The drop shadow effect, also produced by the surrounding environment on the facade under inspection, plays indeed an important role during the defect evaluation procedure since it can mask/modify the natural thermal evolution due to diffusion.Many real-life signals acting in the space physics domain exhibit variations across different temporal scales. This work presents an application of a new multiscale data analysis method, the Iterative Filtering (IF), which allows to describe the multiscale nature of an electromagnetic signal working in the long-wave infrared (LWIR) region. IF appears to be a promising method minimizing the influence of the shadows projected on the facade under inspection; subsequently, it allows the optimization of the detection of thermal bridges via sparse principal component thermography (SPCT) technique. The latter inherits the advantages of PCT allowing more flexibility by introducing a penalization term.Here is shown how the accuracy of the defect detection increases after the application of the IF mathematical procedure. Results are discussed on the basis of a couple of case studies referring to dissimilar buildings. Finally, a signal-to-noise-ratio (SNR) comparison with raw data is added to the discussion of the results.

Thermal-based analysis for the automatic detection and characterization of thermal bridges in buildings

There are several techniques for the performance of energy studies in buildings, where infrared thermography is widely used for the study of the composition of the envelopes, to find faults in the building materials and in the composition of the envelopes with influence on their thermal behaviour, as well as to detect areas with humidity. Common thermographic building interpretations are performed by a human operator, which involves a high level of subjectivity and mainly relies on the expertise of the operator.With the aim at minimizing this subjectivity and maximizing the accuracy of the inspections, this paper presents a procedure for the automation of thermographic building inspections mainly focused on thermal bridges. The procedure, in addition to detecting the thermal bridges by their geometric characteristics and their temperature differences with the surroundings, includes the computation of the thermophysical property of linear thermal transmittance of each candidate to thermal bridge, thus implying their characterization in addition to their detection. With this addition, together with a previous process of rectification of the thermal images analysed, the accuracy of the detection of thermal bridges regarding existing methodologies is improved in 15% considering the false positives and negatives obtained in each methodology.

The Effect of Thermal Bridges on Energy Balance of Wood Frame Houses

In compliance with the today’s trend of designing sustainable and energy-saving architecture, it is necessary to firstly solve the factors influencing the energy balance. In this respect, the thermal bridges in buildings constitute a crucial factor. In case of their occurrence, the use of construction and insulation building materials is significant for finding the solution. The aim of this paper is to analyse the thermal bridges in buildings constructed on the basis of light constructions. The subject of analysis was an implemented wood frame house with common sandwich construction, designed in a low-energy standard. The house analysis is divided in theoretical and experimental part. The house in question has been directly exposed to dynamic boundary conditions. In order to analyse the thermal bridges, critical details have been selected methodically, verified by thermography. The experimental and theoretical results were compared by the simulation method for calculating critical surface temperatures. Both the measurements and results show how attention shall be paid to this issue at the project stage already. With increasing demands for overall energy balance of buildings, it is necessary to exactly define the critical details and consider the thermal bridges in the project documentation already.

Infrared Thermography Assessment of Thermal Bridges in Building Envelope: Experimental Validation in a Test Room Setup

Thermal infrared imaging is a valuable tool to perform non-destructive qualitative tests and to investigate buildings envelope thermal-energy behavior. The assessment of envelope thermal insulation, ventilation, air leakages, and HVAC performance can be implemented through the analysis of each thermogram corresponding to an object surface temperature. Thermography also allows the identification of thermal bridges in buildings’ envelope that, together with windows and doors, constitute one of the weakest component increasing thermal losses. A quantitative methodology was proposed in previous researches by the authors in order to evaluate the effect of such weak point on the energy balance of the whole building. In the present work, in-field experimental measurements were carried out with the purpose of evaluating the energy losses through the envelope of a test room experimental field. In-situ thermal transmittance of walls, ceiling and roof were continuously monitored and each element was characterized by its own thermal insulation capability. Infrared thermography and the proposed quantitative methodology were applied to assess the energy losses due to thermal bridges. The main results show that the procedure confirms to be a reliable tool to quantify the incidence of thermal bridges in the envelope thermal losses.

Study of the Mechanical Behavior against Horizontal Forces of Self-Supporting Facades

The brick façades are one of the most used façades in the current architecture. This typology is used during centuries, but still relevant today. The conventional way to build a brick façade is supporting the outer sheet on the slabs of the building. In buildings with these conventional façades have appeared stability, insulation and sealing problems.The self-supporting façade appears to solve these problems easily. This type of façade can solve more easily thermal bridges in buildings, which is an optimization of energy consumption. To resist horizontal forces façades need anchors between the two sheets or between the outer sheet and the structure. The current standards in Spain do not define the arrangement of the anchorages between the exterior sheet and the inner sheet of the enclosure. This paper studies the influence of the inner sheet in self-supporting façades. The transmission of horizontal forces between the two sheets of the façade is analyzed in detail, in order to check whether the inner sheet assists in the stability of the outer sheet. Different models of façade have been simulated to compare their results using the finite element method.

Transient modeling of high-inertial thermal bridges in buildings using the equivalent thermal wall method

The method of the equivalent thermal wall has been employed for modeling the transient response of high-inertial thermal bridges. A new strategy is presented in order to adjust the thermal properties of the equivalent three-layered wall, which takes into account the temperature distribution across the thermal bridge in a steady-state heat conduction scenario. Two different thermal bridge topologies created by the junction of a vertical wall and an intermediate or a ground floor slab are analyzed with this method, and its feasibility for the implementation in building energy simulation tools is discussed: if the thermal bridge is not considered, an underestimation of 25% in the heat flux across the bridge is predicted. If the thermal bridge is modeled but its thermal inertia is neglected, a time-delayed heat flux response is retrieved. Conversely, the simulation based on the equivalent wall method provides a response nearly identical to the actual dynamic performance of the thermal bridge.

A Study on the Architectural Application of Aerogel

As the building energy saving is more and more important, high-performing insulation like aerogel will be required in buildings to improve their thermal environment and to save building energy. This study conducted the literature survey on the aerogel blanket and presents the architectural application considering its high-insulating property. If aerogel is applied to a building as an envelope insulation, its thickness could be reduced to as half as that of existing insulation such as polystyrene foam board or glassfiber. Currently, aerogel is largely used as a thermal breaker in thermal bridges in buildings. It is still too expensive to be used as a main insulation of whole building envelopes. Thanks to the advantages of aerogel blanket such as low thermal conductivity, broad temperature range for use, excellent water repellent property and fire resistance, easiness of moving and applying, it has much possibility in the respect of its building application.

Thermal bridges in buildings as a result of urban transformation

The paper analyzes the deterioration of energy performance in buildings and construction defects caused by thermal bridges resulting from changes taking place in urban planning, for example in Vojvode Stepe street in Belgrade. The transformation of the urban matrix done over the last 50 years coupled with a time lag in implementation, resulting in partial sequences to completed buildings, has left a number of free side walls (gable ends), which are exposed to temperature influences. In some cases, these walls are adequately heat-treated, but in many others (especially in existing buildings) they are not, causing increased heat loss mould growth, leading to construction damage, and health risks to users. This paper presents a methodology for testing the risk of condensation in a specific example, using the computational support of T Studio software, intended for 2D calculations of thermal bridges, with an emphasis on contact temperature in the interior, relative humidity, and a term that is new to us: Temperature factor.

A quantitative methodology to evaluate thermal bridges in buildings

The use of multi-layer walls with high thermal resistance values is widely used to reduce heat losses in buildings during wintertime. Nevertheless, it is extremely important to treat also weaker components of the envelope such as doors, windows and all the various thermal bridges, otherwise the efforts in increasing walls thermal resistance can be vanished.If the improvement of the thermal performance of windows and doors has reached a significant development and a high level of standardization, the same is not true for the corrections related to thermal bridges, which therefore require a specific analysis in the design phase.Thermal bridges, of whatever nature, are therefore a crucial point in the energy analysis of the building envelope. The analysis on existing constructions can be performed on site with thermographic techniques that describe in first approximation the qualitative energy performance of the building and put in evidence the main heat losses.The paper proposes a methodology to perform a quantitative analysis of some types of thermal bridges, through simple thermographic surveys and subsequent analytical processing. From the simple measurement of the air temperature and the analysis of the thermogram, the thermal bridge effect can be estimated as a percentage increase of the homogenous wall thermal transmittance. This term is obtained without further information on the structure of both the thermal bridge and the stratigraphy of the wall.The analytical methodology – which was validated with experimental and numerical analyses – is described and the results of surveys on different types of thermal bridges are reported. This method represents a quick and effective tool to define the actual heat loss of high-insulation buildings and to evaluate the benefits in treating thermal bridges.

Energy and cost evaluation of thermal bridge correction in Mediterranean climate

In the cold climate of continental Europe the correction of thermal bridges in buildings is a mandatory issue, as in these areas they produce not only heat losses but frequently also condensation and mould growth. In mild Mediterranean climate thermal bridges also cause an increase in energy consumption, but usually do not present condensation effects. In Italy, the current regulations for new buildings only recommend but do not impose the thermal bridge correction, which usually needs extra costs during construction and refurbishment phases. This paper presents a study on the effects of thermal bridges for two building types (terraced houses and semi-detached houses) and three current envelope solutions in Italian climate, which may be considered representative of mild Mediterranean climate. The buildings are characterised by reinforced concrete frameworks and clay block walls; the thermal performance of the envelopes complies with Italian regulations for new constructions. In a first step the impact of thermal bridges on both heating and cooling energy demand is studied; then the economic convenience of correcting such thermal bridges is assessed by calculating the discounted payback period referred to the additional costs of construction and refurbishment.

Application of modal analysis to modelling of thermal bridges in buildings

It is shown, in the example of a thermal singularity of a building (outer wall/slab/ terrace junction), how a model of the dynamic behaviour of two-dimensional thermal systems can be obtained by spatial discretization and by investigation of eigenmodes. Corrected spectral reduction allows a considerable decrease of the order of these models while maintaining a good accuracy. The thermal bridges of a whole building can then be included in computer codes.