Analysis of Variables in the Determination of Lambda/k-factor of Construction Insulations

摘要

The building community has long used the lambda or k-factor obtained using test methods such as ASTM C518 to specify the insulation requirements for buildings. There have been many publications which discuss the impact of sample preparation on the estimation of long term thermal performance for building insulation materials. Sample preparation is not the only test variable in this procedure. Limited works have been published on the impact of other test variables such as the temperature difference across the test specimen (ΔT), or changes in sample thickness to mention a few, have on lambda or k-factor. Why be concerned about the other variables? In reality there are very few buildings in the world which will be exposed to only a single mean temperature of 75°F. Insulation materials standards vary on the specified ΔT between the hot and cold plate when testing the material for thermal performance. Yet specifiers and architects rely on the reported thermal performance of insulation materials to choose these materials and define the quantity necessary in the design of buildings in a variety of geographic regions without understanding the impact of these differences. Do these reported values allow them to accurately specify these materials? With the advancement of thermal measurement equipment, it is now possible to test the insulation performance of materials under a variety of conditions which more represent the exposure in the field. The focus of this work is to understand the impact of varying several variables in the thermal conductivity measurement procedure and their effect on estimating the thermal performance for a variety of building insulation materials. This information will be critical to truly understand and accurately specify insulation materials.