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 specifythe insulation requirements for buildings. There have been many publications which discuss the impact of samplepreparation on the estimation of long term thermal performance for building insulation materials. Sample preparation is notthe only test variable in this procedure. Limited works have been published on the impact of other test variables such as thetemperature difference across the test specimen (ΔT), or changes in sample thickness to mention a few, have on lambda ork-factor.Why be concerned about the other variables? In reality there are very few buildings in the world which will be exposed toonly a single mean temperature of 75°F. Insulation materials standards vary on the specified ΔT between the hot and coldplate when testing the material for thermal performance. Yet specifiers and architects rely on the reported thermalperformance of insulation materials to choose these materials and define the quantity necessary in the design of buildings ina variety of geographic regions without understanding the impact of these differences. Do these reported values allow themto accurately specify these materials?With the advancement of thermal measurement equipment, it is now possible to test the insulation performance ofmaterials under a variety of conditions which more represent the exposure in the field. The focus of this work is tounderstand the impact of varying several variables in the thermal conductivity measurement procedure and their effect onestimating the thermal performance for a variety of building insulation materials. This information will be critical to trulyunderstand and accurately specify insulation materials.