Combined effects of sorption hysteresis and its temperature dependency on wood materials and building enclosures-part II: Hygrothermal modeling

Published Date
September 2016, Vol.106:181–195, doi:10.1016/j.buildenv.2016.06.033

Author 

• Xiaobo Zhang ^a,b
• Wolfgang Zillig ^b
• Hartwig M. Künzel ^b
• Christoph Mitterer ^b
• Xu Zhang ^a,,,

• aInstitute of Heating, Ventilating and Air Conditioning, School of Mechanical Engineering, Tongji University, 200092, Shanghai, China
• bDepartment of Hygrothermics, Fraunhofer Institute for Building Physics, 83626, Holzkirchen, Germany

Received 10 May 2016. Revised 23 June 2016. Accepted 25 June 2016. Available online 27 June 2016. 

Highlights

• •
  Sorption hysteresis should be considered for moisture buffering capacity of surface layer.
• •
  Temperature dependency is of interest for RH variation due to drastic temperature fluctuation.
• •
  Temperature dependent hysteresis is important for analysis of mold growth risk.

Abstract

Hygroscopic materials such as wood and wood based materials have been widely used as insulation and surface moisture buffering materials due to their low thermal conductivity and high moisture capacity. And their hygrothermal performance is mainly dependent on the moisture properties, such as sorption isotherm and water vapor permeability etc. Instead of a univalued function of relative humidity, sorption isotherm of wood materials is not only affected by sorption history, but also temperature dependent. This work is devoted to a better understanding of the effects of temperature dependent sorption hysteresis on moisture transport in wood and wood based materials under ambient temperature and relative humidity variations through experimental investigations and numerical modeling. In part I, the formulated hygrothermal model based on local thermodynamic equilibrium assumption and Frandsen’s hysteresis model are experimentally validated. In this part, the effects of sorption hysteresis and its temperature dependency are investigated under several dynamic conditions through numerical modeling. Hysteresis should be taken into account in determining the moisture buffering capacity, and temperature dependency should be considered to investigate the RH variation in the material when it is subjected to drastic temperature fluctuation. Then heat and moisture transport through a roof assembly under natural climate conditions is further modelled to show the effects of temperature dependent sorption hysteresis in practical applications.

Keywords

Hygroscopic range

Sorption hysteresis

Temperature dependency

Frandsen’s model

Hygrothermal modeling

Wood based materials

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• ∗ 
  Corresponding author.
  
  

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