Quantifying Thermal Performance of the Building Envelope - Beyond Common Practice

Abstract

Performance metrics serve as useful tools and indicators for many applications. For the building industry, various metrics exist; typically, these metrics do not assess the whole building performance. Instead, these represent separate components or heat transfer mechanisms of a building like R-value, U-factor/value, and airtightness. The mechanisms defined under these metrics all contribute significantly to the overall thermal performance of a building but will rarely act independently. There are metrics that account for the overall energy performance of a building, such as Energy Use Intensity (EUI). However, these metrics tend to be highly influenced by how the building is operated and used. There are also metrics which provide assessment on a relative basis. These indices are based upon comparison to a baseline, which complicates meaningful metric-based energy analyses. This paper presents a performance metric developed to account for various thermal properties and behaviors of a building. The metric accounts for all the relevant mechanisms that influence heat losses and gains in buildings and is thus directly related to the energy performance. In addition, the metric is designed to comprise air infiltration and allows users to account for workmanship quality, and imperfections of the building thermal resistance due to penetrations and other installations. This paper will describe how the metric can be applied for various building types and in different climates.

Numerical sensitivity analysis of the energy performance of building envelope with dynamic conditions

“…The effective U-value is a way of correcting the steady-state measured material properties, reflecting the actual performance of a construction element in dynamic conditions. The study [5] from Newcastle in Australia emphasizes that the steady-state thermal resistance (R-value) is insufficient to describe the energy performance of a construction element alone. It concluded that the thermal mass is a crucial parameter in the overall energy performance of a house and is the reason for the deviation between steady-state measured U-value and effective U-value.…”