Heat Losses Caused by the Temporary Influence of Wind in Timber Frame Walls Insulated with Fibrous Materials.

Piotr Kosiński,Przemysław Brzyski,Zbigniew Suchorab,Grzegorz Łagód

doi:10.3390/ma13235514

Abstract

The paper presents the results of research concerning three fiber materials—mineral wool, hemp fiber and wood wool—as loose-fill thermal insulation materials. The analysis used the material parameters determined in previous works conducted by the authors, such as thermal conductivity and air permeability in relation to bulk density. These materials exhibit open porosity; thus, convection is an essential phenomenon in the heat transfer process. The paper aimed at conducting thermal simulations of various frame wall variants which were filled with the above-mentioned insulation materials. The simulations were performed with the Control Volume Method using the Delphin 5.8 software. The studies accounted for the effect of wind pressure and the time of its influence on a wall insulated by means of fiber material with a thickness of 150 as well as 250 mm. The simulation enabled us to obtain such data as maximal R-value reduction and time to return to equilibrium after filtration for the analyzed materials. The study proved that heat transfer in these insulations strongly depends on the bulk density, thickness of the insulation and wind pressure. The decrease in R is reduced as the density increases. This results from the decreased air permeability characterizing the material. Wind washing causes lower R reduction than air filtration in all models. The greater the thickness, the longer it takes for the models to return to the equilibrium state following air filtration (and wind washing). This period is comparable for air filtration and wind washing. Hemp fibers were characterized with the strongest susceptibility to air filtration; in the case of wood wool, it was also high, but lower than for hemp fibers, while mineral wool was characterized with the lowest.

Highlights

Lightweight external walls made in timber frame construction should be designed as wind-resistant.Thermal insulation should tightly fill the space between the elements of the construction and the outside should be covered with the wind barrier
This paper presents an analysis pertaining to the thermal parameters exhibited by a timber frame wall which was insulated by means of mineral wool, wood wool and loose hemp fibers
The effects of wind pressure and the time of its influence on a wall insulated by means of fiber material with a thickness of 150 mm as well as 250 mm were investigated in the conducted research

Summary

Introduction

Lightweight external walls made in timber frame construction should be designed as wind-resistant.Thermal insulation should tightly fill the space between the elements of the construction and the outside should be covered with the wind barrier. A wind barrier prevents outdoor air infiltration through natural or forced convection in the thermal insulation. This air barrier should be permeable enough for water vapor to pass through in order to avoid condensation inside the wall construction, which—in turn—would lead to additional heat losses and corrosion processes that may cause microbiological degradation of timber elements as a consequence. Timber frame constructions are insulated with, i.e., hemp–lime composite, which covers the structure and reduces the thermal bridges [1,2]. Fiber materials, such as mineral wool, wood wool and hemp fiber, are most often used for insulation purposes, either as loose-fill thermal insulation materials or in the form of mats/slabs. A review of studies [4]

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