Comparison of Thermal Conductivity Measurements of Building Insulation Materials under Various Operating Temperatures

In harsh climates, utilizing thermal insulation in the building envelope can substantially reduce the building thermal load and consequently its energy consumption. The performance of the thermal insulation material is mainly determined by its thermal conductivity (k), which is dependent on the material's density, porosity, moisture content, and mean temperature difference. In practice, the k-value is normally evaluated at 24 degrees C (i.e., k(24)) according to relevant ASTM standards. However, when placed in the building envelope, thermal insulation materials can be exposed to significant ambient temperature and humidity variations depending on the prevailing climatic conditions. The objective of this study is to assess and compare the effect of operating temperatures on the k-value of various insulation materials commonly used in the building envelope. The k-values for seven categories of insulation materials (i.e., fiberglass, wood wool, mineral wool, rock wool, polyethylene, polyurethane, and polystyrene) are measured at different mean temperatures using an automated heat flow meter. Some preliminary measurements are reported for the purpose of assessing the impact of k-value variation on envelope-induced cooling loads (Budaiwi et al. 2002). In this study, comprehensive measurements, comparison, and analyses of results are presented and discussed. These underline the k-value degree of sensitivity ((Delta k/Delta C)/k(24)) of various insulation materials with rising operating temperature. This would allow designers to better evaluate the thermal performance of building envelopes leading to a more realistic thermal assessment and energy requirements of buildings.