Phalguni Mukhopadhyaya

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.

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 capillary condensation in wood and the moisture content of red pine

The major purpose of this study is to improve hygrothermal simulation of wood responses to environmental vapor and moisture conditions under high relative humidity conditions. The article first reviews moisture property–related wood microstructures, sorption behavior, the concept of fiber saturation point, the potential for vapor to condense in wood under high relative humidity conditions, the measurement of equilibrium moisture content using traditional sorption methods, and the use of pressure plate test method at relative humidities above 95%. It then summarizes the results of equilibrium moisture content measurements for red pine sapwood at high relative humidity conditions using both sorption and pressure plate methods, with capillary saturation as maximum moisture content. It also discusses a number of wood microstructure and end-use-related factors that could influence the moisture content in service and the measurement of equilibrium moisture content in laboratory. Inconsistencies were found with other equilibrium moisture content data using the pressure plate test method.

Use of the Modified Cup Method to Determine Temperature Dependency of Water Vapor Transmission Properties of Building Materials

This paper describes a modified cup method and its application to investigate the effects of temperature on the water vapor transmission (WVT) properties of building materials. The modified cup method is a simple and versatile technique that allows the user to vary the temperature condition of the test without altering the relative humidity. Two commonly used building materials considered in this study were fiberboard and gypsum board. The five temperature levels under consideration were between 7°C and 43°C. The WVT properties were measured at 50 % average relative humidity. The results obtained from these tests are critically analyzed and reported in this paper. These results demonstrate that there is a steady exponential increase of WVT rate, through both the materials tested, with temperature. However, water vapor permeability (WVP) through the materials shows no significant change due to the variation of temperature between 7 and 43°C. The general observations made in this study confirm that the modified cup method could be used reliably to measure WVT properties of building materials. Detailed analysis of the test results also reaffirms the fact that, for fiberboard and gypsum board, at 50 % average relative humidity condition, the WVP is not dependent on the temperature condition.

Critical Evaluation of Existing Specifications for Polyisocyanurate (ISO) Foam Insulation Boards in Roofing Applications

In North America, more than 50 % of low slope roofing applications uses faced rigid cellular polyisocyanurate (hereafter abbreviated as ISO) board as thermal insulation. Long-term performance of a roof assembly is critically dependent on the ISO characteristics during the service period in various environmental conditions. For this reason, the ASTM C 1289-02, “Standard Specification for Rigid Cellular Polyisocyanurate Thermal Insulation Board,” outlines the physical and thermal property requirements for the ISO boards. However, these requirements are based on the available knowledge, information, and consensus at the time of drafting and balloting of the ASTM standard. Nevertheless, the standard gets updated and revised when more credible data are available that solicits revisions of the current standard. This paper presents experimental results from an ongoing pilot research study that critically evaluates the ASTM C 1289-02 specification requirements for the ISO on three engineering properties: (1) dimensional stability, (2) thermal resistance, and (3) compressive strength. Preliminary results from this study reveal many unknown phenomena, particularly regarding the dimensional stability and compressive strength of ISO boards.

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.

Long-Term Thermal Performance of Impermeably Faced Polyiso Foam Boards: Field and Laboratory Observations

AbstractResearchers at the National Research Council (NRC) Canada–Construction Portfolio in association with the Canadian Polyisocyanurate Council conducted collaborative research activities on the long-term thermal resistance (LTTR) of polyisocyanurate (polyiso) foam insulation with impermeable facers. Polyiso boards are commonly used in building envelope constructions (roofs and walls) in cold regions. The primary objective of the research project was to contribute towards the development of a comprehensive test procedure that could be used to measure the LTTR of polyiso foam insulation products with impermeable facers. As a part of that initiative, a project was initiated in 2001 that consisted of accelerated aging tests using thin slices in parallel with a field investigation in which polyiso boards were installed in a purpose-built test hut at the NRC’s Ottawa campus. The polyiso boards installed in the field were monitored for a period of 6 years and subsequently removed from the test hut and tested...

Preliminary Characterization of Physical Properties of Cross-Laminated-Timber (CLT) Panels for Hygrothermal Modelling

Cross-laminated-timber (CLT) panels are a type of relatively new wood-based structural panel, typically manufactured by laminating three or more layers of lumber together, with each layer rotated 90° relative to the neighbouring layers. This study explored preliminary assessment of the physical properties of a range of specimens for the purpose of initiating generating material property data for hygrothermal simulation of CLT building enclosure assemblies. Three types of five-layer CLT panels (nominally 130 mm thick) were made with Canadian softwood species, including spruce-pine-fir (SPF) from Eastern Canada and British Columbia, and hem fir from British Columbia, all glued with emulsion polymer isocyanate (EPI) as the adhesive applied between neighbouring layers. One type of three-layer CLT (nominally 90 mm thick) commercially manufactured in Europe using European spruce, with polyurethane adhesive, was also tested. Physical properties including density, thermal conductivity, liquid-water absorption, water-vapor permeability, sorption (moisture storage function), and air permeability were measured, mostly based on established international standards. To assess the impact of the adhesive on the hygrothermal properties of CLTs, test specimens used for most tests included at least one layer of adhesive, except those used for sorption tests, which used very small specimens. The properties were expected to mostly reflect the properties of the lumber used for CLT manufacturing. Variations in properties were found among these different CLT specimens; however, it was generally concluded that the differences caused by wood species and manufacturing methods would not be large enough to cause considerable differences in the hygrothermal properties or significantly impact the outcomes of hygrothermal simulation. With small-scale testing and very limited replication this study showed that the water-vapor permeability of CLT generally increased with an increase in relative humidity (RH), and the air permeance of the CLT specimens without visible gaps and checks was negligible.

Long-Term Thermal Resistance of Polyisocyanurate Foam Insulation with Impermeable Facers

Polyisocyanurate (polyiso) foam insulation with impermeable facers is known for its superior insulating properties in building envelope applications. The impermeable facer on both sides of polyiso foam insulation board is designed to increase and maintain the long-term thermal resistance (LTTR) of the insulation. Currently, the Institute for Research in Construction (IRC)/National Research Council (NRC) of Canada, in association with the Canadian Polyisocyanurate Council, has embarked on a research project to develop a standard test methodology that would help to quantify the design LTTR value of polyiso foam insulation boards with impermeable facers. This paper outlines the research project and presents preliminary test results from experimental work. These preliminary results are discussed with a view to developing a methodology that will be used as the basis for a National Standard in Canada for the determination of LTTR of polyiso foam insulation with impermeable facers.

MOISTURE MANAGEMENT PERFORMANCE OF WOOD-FRAME IN-FILL WALL IN SHANGHAI, CHINA

This paper discusses the results of a research project which aimed at determining the hygrothermal (i.e. thermal and moisture) performance of the Canadian wood-frame building envelope construction in the city of Shanghai in China. The performance assessments of the wood-frame walls were conducted using the two-dimensional hygrothermal simulation tool called hygIRC-2D. In this study an in-fill type wall was considered and hygrothermal simulations were carried out for the weather conditions of Shanghai. Investigations were conducted to determine the influence of the vapour barrier, exterior stucco cladding material and different types of sheathing boards on the moisture performance of in-fill walls. Additional simulations were carried out to determine the influence of air leakage on the moisture performance of in-fill walls. The outputs from the simulations were analysed with the help of a hygrothermal response indicator called RHT index. It was concluded that the design of the in-fill wall including a rain...