Temperature dependent thermophysical parameters of agglomerated wood boards.

In recent years, problems of increased energy consumption and related green-house gas emission impose new demands on building structures. Strict policies require low heat transmission of building envelope and their inbuilt materials. For the precise evaluation of the heat transmission coefficient (HTC) using numerical methods, thermal properties of building materials need to be characterized. Data on the thermal material parameters commonly used in calculations are usually obtained under laboratory conditions, and may by different from the real state of material element, especially in the case of temperature and relative humidity fluctuations of the environment. To increase the accuracy of numerical assessment of HTC, thermal properties of materials at elevated temperatures can be used as raw data for further processing. In this study, thermal properties of four types of wood-based boards (wood agglomerates) at temperatures up to 150 °C were investigated together with their basic structural characteristics. These were measured both before the samples exposure to elevated temperatures and for samples that underwent the thermal treatment. Among the structural parameters of wood-based boards, bulk density, specific density, and total open porosity were analyzed. Parameters characterizing the heat transport and storage were measured using hot-disk apparatus and the samples were placed in the heating chamber. The researched thermal characteristics were evaluated for samples heated up to 150 °C with the 25 °C steps. The examined thermophysical parameters were thermal conductivity, volumetric heat capacity, and thermal diffusivity. Up to 100 °C, increasing trend in the thermal conductivity and volume heat capacity values was identified, which is typical for this type of materials. On the other hand, the thermal diffusivity has decreased with the temperature of samples exposure. After full water release, the thermal conductivity dropped, while volumetric heat capacity still increased in a similar trend. This was partly due to the evaporation of water incorporated in intercellular spaces of wood, and mainly because of the chemical changes of wood-board adhesives. This feature was proved by porosity data, which changed about 1 % of its initial value. Based on the acquired experimental results, the thermal characteristics of wood-based boards obtained by hot-disk method may be suitable to use as raw data for the numerical evaluation of HTC of building elements or the whole building envelopes. [ABSTRACT FROM AUTHOR]