Kumar Kumaran

Interlaboratory comparison of hygric properties of porous building materials

The precision of methods used for the determination of hygric properties of porous building materials was investigated. The study was performed in the framework of the EU-initiated HAMSTAD-project. Six laboratories measured the selected hygric properties of three porous building materials. While the most measured properties show acceptable agreement, yet, it was found that some of the existing standards or commonly accepted measurement methods need improvement. Most striking were large variations in the results of the vapour transmission tests performed in accordance to the existing European Standard.

Assessment method of numerical prediction models for combined heat, air and moisture transfer in building components: benchmarks for one-dimensional cases

The standardised Glaser method for calculation, prediction and evaluation of moisture performance is considered as rarely applicable. The present state of knowledge, analytical as well as experimental, concerning heat, air and moisture demands updating of standards. This paper presents five numerical benchmark cases for the quality assessment of simulation models for one-dimensional heat, air and moisture (HAM) transfer. In one case, the analytical solution is known and excellent agreement between several solutions from different universities and institutes is obtained. In the remaining four cases, consensus solutions have been found, with good agreement between different HAM models. The work presented here is an outcome of the EU-initiated project for standardisation of HAM calculation methods (HAMSTAD WP2).

A Comparison of Different Techniques to Quantify Moisture Content Profiles in Porous Building Materials

Several advanced non-destructive techniques are available to measure the evolution of content profiles with time, allowing the analysis of unsaturated flow and the determination of the moisture diffusivity of porous building materials. The reliability of six different techniques is investigated: the NMR-technique, the MRItechnique, the γ-ray attenuation technique, the capacitance method, the X-ray projection method and the TDR-technique. All of them were applied to measure the moisture content evolution during free uptake experiments on two building materials. Considering the limitations of some of the techniques, a good overall agreement is obtained. The work presented is an outcome of the EU-initiated HAMSTAD-project.

Determination of the liquid water diffusivity from transient moisture transfer experiments

The Boltzmann transformation method is used to determine the liquid water diffusivity from moisture content profiles as measured in a capillary water absorption experiment. An inter-laboratory comparison for analyzing the reliability of the determination method showed that the inaccuracy in the liquid water diffusivity is caused by scatter in the transformed data and by uncertainty in the boundary conditions at the intake surface and ahead of the steep moisture front. A methodology is proposed based on (1) the evaluation of the validity of the diffusion approach, (2) a simplified handling of the boundary conditions, (3) smoothing of the scattered data and (4) the evaluation of the quality of the determined liquid water diffusivity. For HAM (Heat-Air-Moisture transport) calculations values of the liquid water diffusivity for moisture contents higher than the capillary moisture content are disregarded. The liquid water diffusivity can be described by an exponential function limited at a lower moisture content bound. To describe the moisture diffusivity including liquid water and water vapour transports, a new parametric description of the moisture diffusivity is presented, which shows sufficient flexibility both in the hygroscopic and overhygroscopic ranges. When permeability is calculated from diffusivity, the permeability should monotonically increase with decreasing capillary pressure. In the hygroscopic region it should coincide with the measured water vapour permeabilities.

Effect of Surface Temperature on Water Absorption Coefficient of Building Materials

Water absorption coefficient of a material governs the liquid moisture movement into it. In the case of various components of a building envelope, in particular exterior claddings, this is one of the most important hygrothermal material properties that needs to be assessed to determine the overall moisture management strategy. In different geographical locations, components of the building envelope, in particular the surface of the exterior cladding, are exposed to various temperature regimes. However, the effect of various temperature regimes on the water absorption coefficient of common building materials has not been adequately investigated. This study looks at the water absorption characteristic, determined through water absorption test, of three commonly used building materials (i.e., eastern white pine, red clay brick and concrete)at four temperature levels at the surface of the material, ranging from 3 to 35° C. A clear surface temperature effect on water absorption coefficient and derived liquid diffusivity value is shown in eastern white pine whereas changing the surface temperature shows no effect on the water absorption characteristic of red clay brick and concrete.

Effect of Exfiltration on the Hygrothermal Behaviour of a Residential Wall Assembly

The hygrothermal behaviour of timber frame wall is analysed using a steady-state calculation method and a two-dimensional heat, air, and moisture transport computer model. The conditions associated with exfiltration of warm and humid indoor air are examined. The physical quantities investigated included the amount of moisture accumulated in the wall cavity during the heating season and the heat loss across the wall. Several interesting correlations between moisture accumula tion in a cavity and parameters such as leakage rate, vapour permeance characteristics of the exterior boundary, additional thermal resistance offered by an exterior sheath ing, and indoor humidity level emerge. These correlations show the advantage of us ing the analytical methods in deriving design guidelines for building components. The results from the analysis are used to identify and quantify various parameters that govern the performance of air barrier systems.

Biological damage function models for durability assessments of wood and wood-based products in building envelopes

A durability assessment system that links an advanced computer model for structural and hygrothermal analysis with damage functions is currently being developed. The computational system has different modules that calculate the different structural and hygrothermal responses of wall systems. Outputs of these modules are input to the module of damage function models to calculate damage, performance and service-life of building envelopes. Details of biological damage functions implemented in the damage function module of IRC’s durability assessment system are presented. The biological damage functions trace deterioration in wood materials subjected to hygrothermal loads that favor fungal growth. The developments of the models are based on recent biological experimental data from the literature. Equations to calculate various parameters in the model are presented and the application of the developed models is demonstrated using air leakage of warm and humid indoor air in a typical wood-frame construction in Ottawa.ZusammenfassungDerzeit wird ein System zur Beurteilung der Dauerhaftigkeit entwickelt, das ein fortschrittliches Computermodell für die statische und hygrothermische Berechnung mit Schadensfunktionen verbindet. Das Computersystem besteht aus verschiedenen Modulen, mit denen die verschiedenen statischen und hygrothermischen Eigenschaften eines Wandsystems berechnet werden. Die Ergebnisse dieser Module dienen als Eingangsgrößen für das Schadensakkumulationsmodell, mit dem die Schädigung und die Lebensdauer von Gebäudehüllen berechnet werden. Die biologischen Schadensfunktionen, die in das Schadensakkumulationsmodell des IRC Systems zur Beurteilung der Dauerhaftigkeit implementiert wurden, werden detailliert beschrieben. Die biologischen Schadensfunktionen bestimmen Schädigungen im Holzmaterial, das Pilzwachstum verursachender Belastung ausgesetzt war. Zur Entwicklung der Modelle werden aktuelle biologische Versuchsdaten aus der Literatur hergenommen. Gleichungen zur Berechnung verschiedener Parameter im Modell werden dargestellt und die Anwendung der entwickelten Modelle wird anhand der Konvektion von warmer und feuchter Innenraumluft durch eine typische Holzrahmenkonstruktion in Ottawa aufgezeigt.

Correlation Between Water Vapor and Air Permeability of Building Materials: Experimental Observations

Two fundamental properties of building materials that influence the hygrothermal performance of building envelope systems are water vapor permeability and air permeability. The driving forces for water vapor and air transmission through building materials are, respectively, partial water vapor pressure and total air pressure differentials. The theoretical similarity of the driving forces would suggest the possibility of a relationship between water vapor and air permeability. During past two decades, researchers at the National Research Council of Canada—Institute for Research in Construction have compiled a database of measured air permeability and water vapor permeability properties of building materials commonly used in North America. This material properties database was examined to identify the degree to which air permeability and water vapor permeability of the building materials might be functionally related. The database was segregated into categories for different material types. An approximately linear relationship could, within some categories, be observed between water vapor permeability and air permeability. There were however approximately as many categories within which no relationship between the parameters was apparent as there were categories within which functional relationships between the parameters were apparent. Within categories where functional relationships were apparent, the form of the relationships generally depended on the mean relative humidity at which water vapor permeability was measured. In most cases, a definitive functional form of the relationship between water vapor permeability and air permeability could not be established.

Sorption and Thermal Properties of Insulating Mortars with Expanded and Vitrified Small Ball

Expanded vitrified small hollow ball (EVSB), made from a special type of perlite mineral is one of the recently developed materials in China. It is widely used as a cementitious thermal insulating mortar for building envelope construction in hot-humid areas of southern China. However, EVSB is a porous material sensitive to environmental moisture. The thermal insulating property of the EVSB mortar is dependent on its moisture transport and storage characteristics. In this study, hygroscopic sorption properties of EVSB mortars have been investigated in comparison with those of normal expanded perlite particle (NEPP) mortars. The Brunauer, Emmett and Teller specific surface area and the Barrett, Joyner and Halenda pore size distribution, as well as the scanning electron microscope micromorphologies of the mortars were assessed. It was observed that EVSB mortars had lower moisture sorption capacity than NEPP mortars when the relative humidity (RH) was higher than 70 % because of its lower total pore volume. The addition of water-repellent admixtures in the mortar decreased the moisture sorption capacity of EVSB mortars but still maintains the same physisorption isothermal characteristics. It is also evident that the thermal conductivity values of both NEPP and EVSB mortars increased rapidly when RH is above 90 %. However, the increased rate of thermal conductivity of NEPP mortars was apparently higher than that of EVSB mortars. It is hoped that finding from this study will help to develop a better understanding of the in situ thermal performance of the EVSB mortar used for the building envelope construction in hot and humid areas of southern China.

Moisture Management of EIFS Walls— Part 1: The Basis for Evaluation

The Canadian approach to design accepts the presence of some con struction deficiencies and calls for a multiple-line of defense Until now, such a design has been based on the qualitative assessments rooted in experience, i.e., tradition, and involved little integration with the newly emerging analytical tools, e.g., advanced hygrothermal models. The relation between the design and climatic conditions acting on a building is not well established. Research should be undertaken to clarify the rela tionship between climate and the moisture performance of a given wall assembly, i.e., to enhance the predictability of moisture performance for different wall assemblies when constructed with some deficiencies and exposed to a given climate. To improve the correlation between climatic conditions and design practice, mois ture management of a building envelope must involve the flow-through principles. The flow-through approach is, however, much more difficult than the currently used approach with barriers. The flow-through approach requires performing computer calculations of moisture balance of all layers of the wall with regard to heat, air and moisture transport over an entire year. This is the critical element of the integrated moisture management strategy. Four papers are being written to facilitate the use of analytical tools into EIFS wall