The influence of oscillating climate conditions during the conventional drying of beech timber on drying time and drying quality has been analyzed. Three conventional drying cycles were carried out as well as nine cycles, in which the oscillations of equilibrium moisture content (EMC), temperature, and their combination were applied. The combinations of two amplitudes (10% or 20%) and two frequencies (3 or 6 h) were used in different test runs. Higher drying quality regarding casehardening was achieved both in runs with oscillations of EMC (gap values 2.2-2.4 mm) and in runs with temperature oscillations (gap values 2.3-2.4 mm) compared with conventional runs (gap values 2.5-2.9 mm). The oscillations of both temperature and EMC did not improve any of the observed parameters.

There are several factors influencing a fundamental property of a wood species, the limit of hygroscopicity of wood (LH) or fiber saturation point (FSP). The effect of temperature upon the limit of hygroscopicity has been mentioned in literature, but has not been precisely quantified. In this paper we have correlated the LHs with temperature of thermal pretreatment, taking also into account the properties of particular wood species, i.e. density and chemical composition. For our investigation we have selected the most important domestic wood species for industrial processing: oak, beech, poplar, fir and spruce. We have determined the limits of hygroscopicity by method of compression strength parallel to grain, for the following temperature ranges of thermal treatments, in dependence of wood species: for hardwoods from 20° to 80 °C and for softwoods from 20° to 90 °C. Our results demonstrate the general decrease of the limit of hygroscopicity with the increase of temperature of the thermal pretreatment of the examined wood species. Mathematical correlations have been evaluated on the basis of experimental data by polynomial regression statistical method. Wood density is another factor examined as influential upon the limit of hygroscopicity. We have determined the decrease of the LH with the increase of wood density, i.e. denser wood species have lower capacity for water adsorption. The differences obtained for the LHs between the examined wood species have been explained in relation to their chemical compositions. Our results indicate that cellulose is the major wood component determining its capacity for water adsorption.

• The infl uence of applying the oscillations of air parameters during conventional drying of beech timber on energy consumption is discussed in the paper

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The research results from an analysis of the influence of conditioning time on case-hardening reduction are presented. The levels of case-hardening and moisture content differences across the thickness on beech and oak lumber were measured before, during, and after conditioning. A relationship between gap, as the measure of case-hardening in wood (ENV 14464), and conditioning time was found; a highly linear relationship also exists between gap and moisture content differences across the lumber thickness. Time analysis showed that much shorter conditioning times were adequate to reach acceptable drying quality than the times currently used. It is shown that the conditioning regimes that use equilibrium moisture content lower than the final moisture content are inadequate to obtain a dried product quality that meets modern European standards.