Investigation of the thermal insulation performance of fibrous aerogel samples under various hygrothermal environment: Laboratory tests completed with calculations and theory

Ákos Lakatos

doi:10.1016/j.enbuild.2020.109902

Abstract

Insulation materials are mainly porous or fibrous materials. Therefore, the presence of moisture can easily cause problems inside the materials, and in the whole building structure. For correct calculations of heat and moisture transfer problems in building applications, practitioners need design values. Design thermal values are deduced and calculated from declared values which are reached from laboratory measurements. This is the case for both insulation and building materials. If the design environments are different from those where the declared values should be used, the data have to be changed to the relevant conditions. There are standards giving suggestions on how to calculate the design values of thermal insulation materials, however, their database and tables are insufficient regarding the values of the super insulation materials. In this paper, a calculation method will be presented so as to specify the design thermal conductivities of a glass fiber-reinforced aerogel. The calculation method is based on measurement results, where the lambda values were measured treating the samples in a humid environment. As a result, the moisture conversion coefficient for the thermal conductivities is obtained after measuring the humid thermal conductivities of materials. Moreover, a new calculation method will also be presented to estimate the vapor absorption coefficient from humidity measurements. Furthermore, the effects of ice and freeze on the thermal conductivities of the aerogel samples are characterized, too. The thermal conductivities were measured in a Holometrix type heat flow meter, while for the wetting a Venticell 111 type drying apparatus and a Climacell 11 climatic chamber were applied. Moreover, the cooling treatment was executed in a freezing room. In addition, new theory for the thermal conductivity was given, for moist/frost insulation materials.

Highlights

In the European Union, the energy use of buildings counts for about 20 to 40% of the entire energy consumption [1,2,3]
One way to reduce these unwanted phenomena is the application of thermal insulation materials on the walls
In order to see the possible effects of frost as well as ice in the thermal conductivity of the aerogel samples two different measurement rows were done independently from the results presented above

Summary

Introduction

In the European Union, the energy use of buildings counts for about 20 to 40% of the entire energy consumption [1,2,3]. The above-mentioned energy use goes together with about 30% greenhouse gas emission. One way to reduce these unwanted phenomena is the application of thermal insulation materials on the walls. It is said that the commercially available ones have excellent thermal conductivity values with approximately 0.017 W/mK. They are porous materials having small density and with pores and cells on the nanoscale. Due to their fibrous structure, moisture might have a substantial reduction effect in the thermal resistance.

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Conclusion