Eva Barreira

Infrared thermography – evaluation of the results reproducibility

Purpose – Infrared thermography is increasingly being used to diagnose pathologies in buildings, such as facade defects. The purpose of this paper is to assess the results reproducibility and the equipment influence on the measurements. To do so, it was defined as case study the assessment of rendering delamination. Design/methodology/approach – Two infrared cameras of different makers were used to detect the presence of defects deliberately created in specimens. The tests were done in the laboratory with a heat source. The defects were detected through a temperature gradient between the zones with and without defect. Findings – With this thermographic imaging, it was possible to identify the defects in the specimen both qualitatively and quantitatively. The results were found to be reproducible in the three cycles performed. The influence of the equipment on the results was of little significance for the quantitative assessment criterion “temperature difference between zones with and without defect”, but...

The effect of nearby obstacles in surface condensations on external thermal insulation composite systems: Experimental and numerical study

External thermal insulation composite systems are, nowadays, quite common in European buildings, used both in new constructions and refurbishment. Unfortunately, external thermal insulation composite systems can have serious problems of biological growth causing the cladding defacement. Studies carried out in recent years allowed understanding the hygrothermal behaviour of external thermal insulation composite systems. It is known that biological growth is due to high values of surface moisture content, which depends mostly on exterior surface condensation. Despite this existing knowledge, there is little information available about the influence of obstacles near the façade on condensation and surface moisture content. In this article, the results of a field test campaign to assess the influence of obstacles on surface condensation are presented. They show that nearby obstacles influence exterior surface temperature during the night and, consequently, surface condensation. Different obstacle configurations have different effects, which may lead to stained patterns on the façade due to differential biological growth rates. The effect of nearby obstacles on exterior surface condensation, revealed during the test campaign, addressed the development of a numerical routine to simulate their influence. This routine can be used with any existing hygrothermal model with the ability to simulate explicitly the radiative balance on the exterior surface. It calculates the increase in long-wave radiation due to the obstacle as a function of its geometry and emissivity of its surface. This extra amount of radiation is added to the atmospheric radiation that is an input of the hygrothermal models. The validation of this routine was performed by comparing simulated and experimental results. An example of the practical use of this routine is also presented in this article, with the calculation of the exterior surface condensation on different façades covered with external thermal insulation composite systems, with and without nearby obstacles, and its comparison with the coating defacement that they actually present.

External Thermal Insulation Composite Systems: Critical Parameters for Surface Hygrothermal Behaviour

External Thermal Insulation Composite Systems (ETICS) are often used in Europe. Despite its thermal advantages, low cost, and ease of application, this system has serious problems of biological growth causing the cladding defacement. Recent studies pointed that biological growth is due to high values of surface moisture content, which mostly results from the combined effect of exterior surface condensation, wind-driven rain, and drying process. Based on numerical simulation, this paper points the most critical parameters involved in hygrothermal behaviour of ETICS, considering the influence of thermal and hygric properties of the external rendering, the effect of the characteristics of the facade, and the consequences of the exterior and interior climate on exterior surface condensation, wind-driven rain, and drying process. The model used was previously validated by comparison with the results of an “in situ” campaign. The results of the sensitivity analyses show that relative humidity and temperature of the exterior air, atmospheric radiation, and emissivity of the exterior rendering are the parameters that most influence exterior surface condensation. Wind-driven rain depends mostly on horizontal rain, building’s height, wind velocity, and orientation. The drying capacity is influenced by short-wave absorbance, incident solar radiation, and orientation.

Thermography Applications in the Study of Buildings Hygrothermal Behaviour

Infrared thermography (IRT) can be defined as the science of acquisition and analysis of data from non-contact thermal imaging devices. The process of thermal imaging has simplified over the years with the availability of efficient, high resolution infrared cameras that convert the radiation sensed from the surfaces into thermal images (Rao, 2008). Thermography literally means “writing with heat”, just as photography implies “writing with light”. The invisible infrared radiation emitted by bodies is converted into temperature and displayed as thermal images, the thermographs. Infrared thermography is a powerful tool for engineers, architects and consultants for use in evaluating existing buildings and structures. Infrared thermography is a fast and reliable tool to assist in identifying potential problems in existing buildings. Infrared thermography offers several advantages in condition surveying. Recent developments in thermography and image processing made the technique a valuable addition to the repertoire of nondestructive testing methods. Thermography is a non-contact, non-destructive technique. While the potential exists, thermography has not yet been utilized extensively in the assessment of monuments and ancient structures. Condition surveys by conventional techniques cannot detect the presence and source of moisture readily, require access to the surfaces, and are expensive and time consuming. On the other hand, IRT offers a rapid method for assessing large surfaces without the need of a scaffold to reach the area under investigation.

Exterior condensations on façades: numerical simulation of the undercooling phenomenon

This article intends to apply existing numerical models of exterior boundary conditions on the simulation of exterior condensation on façades (undercooling phenomenon) finished with external thermal insulation composite systems. The results of three hygrothermal models were compared, regarding the temperature on the exterior surface of a west façade. The climatic conditions from Porto city were used. We analysed in detail how the simulation of the undercooling phenomenon is influenced by the numerical treatment of the radiative balance on the exterior surface. The numerical results show that these programs are useful tools in assessing the exterior condensation on façades and the importance of radiative balance on the exterior surface temperature. However, some differences were observed in the calculated values due to different parameters included in the radiative balance of the models.

Hygrothermal numerical simulation: application in moisture damage prevention

1.1 Background Building pathologies originated by moisture are frequently responsible for the degradation of building components and can affect users’ health and comfort. The solutions for treating moisture related pathologies are complex and, many times, of difficult implementation. Several of these pathologies are due to innovative techniques combined with new materials of poorly predicted performance. The knowledge of the physical processes that define hygrothermal behaviour allows for the prediction of a building response to climatic solicitation and for the selection of envelope solutions that will lead to required feasibility. Over the last five decades, hundreds of building energy software tools have been developed or enhanced to be used. A list of such tools can be obtained in the US Department of Energy Webpage (2007). This directory provides information for more than 345 building software tools for evaluating energy efficiency, renewable energy and sustainability in buildings. The problem of moisture damage in buildings has attracted interest from the early days of the last century, but it was during the past decades that the general topic of moisture transport in buildings became the subject of more systematic study, namely with the development of the modelling hygrothermal performance. In the field of building physics the hygrothermal models are widely used to simulate the coupled transport processes of heat and moisture for one or multidimensional cases. The models may take into account a single component of the building envelope in detail or a multizonal building. In literature, there are many computer-based tools for the prediction of the hygrothermal performance of buildings. These models vary significantly concerning their mathematical sophistication and, as shown Straube and Burnett (1991), this sophistication depends on the degree to which the model takes into consideration the following parameters: moisture transfer dimension; type of flow (steady-state, quasi-static or dynamic); quality and availability of information and stochastic nature of various data (material properties, weather, construction quality, etc.). All the hygrothermal simulation tools presented later in this paper are based on one of the following numerical methods for space and time discretization: a. Finite Difference Methods (FDM) and Finite Control Volume (FCV) methods; b. Finite Element Method (FEM); c. Response Factor and Transfer Function method.

Infrared Thermography Application in Buildings Diagnosis: A Proposal for Test Procedures

The study of hygrothermal behaviour is essential to evaluate the performance of construction components and building envelopes. Most building pathologies are related with temperature action. The use of non-destructive techniques to evaluate a building behaviour may be very useful as there is no need to destroy the building components, which would interfere with the user’s life. Infrared thermography is a non-destructive testing technology that can be applied to determine the surface temperature of objects. This technology has been applied to buildings for a couple of decades, to evaluate the building performance. It has been used to detect insulation defects, air leakages, heat losses through windows, moisture and different “hidden details”. This work evaluates the applicability of thermography to study the behaviour of building materials and building envelopes. A short literature review about thermography principles is presented. It is also showed the effect on the results of some factors that affect infrared thermography measurements. Several applications of infrared thermography to building diagnosis are listed, based on the work published by the scientific community. And finally, three test procedures are described in detailed to detect detachments on wall renderings, to evaluate the thermal comfort of floor coatings and to analyse the wetting and drying processes.

Wetting and Drying of External Surfaces with ETICS Systems

Moisture is one of the most deteriorating factors of buildings. The deteriorating effect of moisture occurs mainly during the drying phase, and appropriate parameters of the drying kinetics are required for the building materials. Environmental factors, such as air temperature and air humidity affect drying. An experimental campaign was performed to investigate the drying performance of External Thermal Insulation Systems (ETICS). Drying kinetics was examined at three air temperatures, four solar orientations and two different air humidities. A first-order kinetics model was obtained, in which the drying time constant was a function of the drying conditions, and the equilibrium material moisture content was described by several different models, such as linear type, power type, exponential type, Arrhenius type and Logarithmic type. The parameters of the proposed model were found to be affected strongly by the material and the drying air conditions.

Water masses surface temperatures assessment and their effect on surrounding environment

The aim of this study was to evaluate the effect of water masses on the surface temperature with direct impact on the surrounding area. Three systems were used for the study: a fully vegetated system (subsurface flow constructed wetland (CW)), a lake with no vegetation and a lake partially vegetated with Lemna minor. Infrared thermography was applied for the different systems analysis, allowing the determination of the surface temperature spatial distribution. In general, the presence of plants and water in the analyzed systems contributed to lowering the surface temperatures when comparing to its surroundings. Differences up to about 22 °C were observed in the temperature between the CW canopy and the surrounding soil, and up to about 19 °C between the lake and the surrounding border. Different plant species (Canna flaccida, Canna indica and Zantedeschia aethiopica) inhabiting the CW were also compared and slightly higher average surface temperatures were observed for C. indica. The above mentioned results are relevant in terms of supporting a strategy for water systems inclusion, for example a lake or a CW, in a site as means of having influence in the surface temperature and to some extent in the heat island effect supporting a sustainable environmental management.

Wetting and Drying Kinetics of Building Materials

Moisture is one of the most deteriorating factors of buildings. The moisture content depends on hygroscopic equilibrium between buildings materials and environment, which is determined by the drying and wetting rate of masonry. So, the moisture content is not only determined by the water that is absorbed by the material, but also by the amount of water that is evaporated under favourable conditions, which is described by the drying process. This work presents the results of an experimental evaluation of the drying kinetics, considering both surface and bulk moisture transfer. Two different specimens were used: External Thermal Insulation Composite Systems (ETICS) to study surface moisture transfer and solid brick to analyse the bulk moisture transfer. For both samples the drying kinetics was assessed considering different environment conditions (air temperature and humidity). Six different first-order kinetics models, available in the literature, were adjusted to describe the drying process and estimate the equilibrium moisture content of ETICS and solid red brick samples. The results point that Hii et al. and Midilli models allow the best fit and that the drying time constant is strongly affected by the moisture transfer phenomenon (at surface or bulk) and by the drying air conditions. It was also estimated the apparent molecular diffusion coefficient for solid red brick samples and its variation with temperature.