N.M.M. Ramos

Can moisture buffer performance be estimated from sorption kinetics

This article describes the research on the moisture buffering effect of building materials. A set of experiments on samples of current building materials are conducted under transient conditions of relative humidity (RH). The results obtained are then analyzed using kinetics models. The experimental settings are based on the moisture buffer value (MBV) test method currently under study by Nordic researchers. The main result from these tests is the MBV number that can be used to characterize the moisture buffer performance of a material or a system. The application of kinetics models to the experimental results is explored and several parameters are retrieved. A proposal for the use of these parameters is presented and its practical use is discussed.

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.

Application of different transient sorption methods to evaluate moisture diffusion coefficients of building materials on the hygroscopic range

Typically, moisture transport coefficients are determined either by stationary measurements, as standard cup set-up and modified cup method, or by dynamic measurements, as the means of the type t rule in the initial phase of adsorption processes, logarithmic procedure in the end stage of adsorption processes, the half-time method, the moment method, and the hybrid 1-term method. The aim of this work was to test the usability of the five dynamic calculation methods to define the moisture diffusivity in the hygroscopic range of different building materials. The results obtained were compared in order to evaluate the discrepancies between the different calculation techniques. Advantages in time saving using each experimental technique were compared with the feasibility of each process. Two commonly used building materials are considered in the study, gypsum board and gypsum plaster, for adsorptive measurement of the moisture diffusivity at three different temperatures in three different relative humidity ranges.

Anomalous Diffusion during Water Absorption in Porous Building Materials – Experimental Evidence

The sorption and transport of water in two porous building materials, clay brick and autoclaved aerated concrete, was studied in detail. The evolution of the distribution of liquid in the porous medium was analysed in terms of the Boltzmann transform method and anomalous diffusion equation proposed by Küntz and Lavallée [1]. The apparent moisture diffusion coefficients of water were determined from the total water profiles using a modified Boltzmann-Matano analysis, and a good agreement with literature values was found. The application of anomalous diffusion model to building materials indicates that the previous 1/ 2 t relation is not entirely accurate to estimate the volume of absorbed water. This result has particular relevance for evaluating the durability of building structures.

Hygrothermal Performance and Degradation of Gypsum Houses in Different Brazilian Climates

This work consisted of two main lines of research: one of a literature review and other of simulation. In the first part, a modular constructive system based on gypsum blocks is presented. This constructive system reduces the manpower considerably, the time of execution and the final costs of construction. However, the durability assessment should be analysed but first its implementation and performance along the country must analysed.In this work a preliminary experimental characterization of the thermal conductivity, vapour permeability and water absorption coefficient of two different samples of gypsum plasters from the northeast Brazil (plaster pole of Araripe, Pernambuco) was performed. The experimental and analytical procedures followed either international standards or well-established methodologies, supporting the analysis of gypsum walls hygrothermal behaviour. The measured properties were adopted as inputs to hygrothermal simulation software and the analysis of gypsum based exterior walls was conducted for different climate zones and exposure conditions. The study demonstrates the durability issues that may arise in each location, due to differences in hygrothermal action.The other simulation part included hygrothermal advanced modelling, using the EnergyPlus software. The numerical results carried out allow a discussion over the interior comfort and durability of this modular constructive system. In this paper, the computer simulation model and the results of a parametric analysis of the dwelling performance on the eight climatic regions defined in Brazilian regulations are presented. The model was validated using the in situ measurements of air temperature.

Durability of Interior Renderings in Schools: Optimization of Envelope Insulation for Mitigation of Mould Growth Risk

A high standard education is, nowadays, a clear objective for any modern society. In Portugal, the retrofit of educational buildings has an enormous relevance as demonstrated by the “Program for Retrofit and Upgrade of High Schools”. Educational buildings specific characteristics such as high occupancy rates and high amount of time children spend in classrooms make them a special case compared to other buildings. Mould growth on envelope surfaces is frequently observed in these buildings, reducing the expected durability of renderings and coatings. The present work consisted of two main lines of research: one of simulation and other of optimization. The simulation part included modelling of Interior Surfaces Temperature, Indoor Air Temperature and Relative Humidity variation, before and after a hypothetical retrofit process. Optimization techniques were applied in the definition of insulation thickness to be numerically tested in the “after retrofit” scenario. The objective was to minimise insulation thickness in each building element of the envelope. The constraints were derived from the control of surface temperature values that would result in mould growth risk.

Drying Kinetics of External Thermal Insulation Composite Systems (ETICS)

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. In this work we analyse the drying kinetics of External Thermal Insulation Composite Systems (ETICS) using a first-order and a second-order drying kinetic models to describe mass transfer phenomenon. The results show that the second-order kinetic models described well the drying process studied. The application of kinetics models to the experimental results was explored and several parameters were retrieved. A proposal for the use of these parameters is presented and its practical use is discussed.

Optimisation of Envelope Insulation for the Retrofit of an Educational Building

This paper presents ongoing work for the definition of an optimal design strategy for retrofitting educational buildings. The term “optimal design” refers to the selection of different retrofitting solutions to ensure an energy efficient building that can be developed which will not compromise hygrothermal comfort, indoor air quality, health and durability. In this paper, a selection model of thermal insulation thickness of envelope elements is developed, aiming the control of surface condensation and upgrade of hygrothermal comfort. The mathematical formulation of this model leads to a nonlinear program with linear objective function. The software Gmas/Minos was chosen to solve the optimization problem and to develop a calculation program to solve this specific application. The software Energy-Plus developed by the US Department of Energy was used to simulate hygrothermal performance of the building, providing results for a comparison with the developed simulation tool. The paper presents an example of an optimal design problem for a specific classroom of a retrofit educational building.

Concentration Dependent Diffusion in Building Materials – Application of Different Methods

Moisture is an important factor when analyzing the behaviour of building elements and materials. A deeper knowledge on moisture transport under transient conditions of environmental air temperature and humidity is required. In this experimental work, the measurements of moisture diffusion coefficients, w D , of three different types of building materials commonly used in Portugal (gypsum plasterboard, gypsum plaster and gypsum+lime plaster) were obtained for different values of temperature and relative humidity. The results obtained were in good agreement with the values found in literature and show that the increase in temperature resulted in an increase in the diffusion coefficient and an increase in relative humidity (54% to 69%) resulted in a decrease in w D .