Abstract
Stationary and dynamic heat and mass transfer analyses of building components are an essential part of energy efficient design of new and retrofitted buildings. Generally, a single constant thermal conductivity value is assumed for each material layer in construction components. However, the variability of thermal conductivity may depend on many factors; temperature and moisture content are among the most relevant ones. A linear temperature dependence of thermal conductivity has been found experimentally for materials made of inorganic fibers such as rockwool or fiberglass, showing lower thermal conductivities at lower temperatures. On the contrary, a nonlinear temperature dependence has been found for foamed insulation materials like polyisocyanurate, with a significant deviation from linear behavior. For this reason, thermal conductivity assumptions used in thermal calculations of construction components and in whole-building performance simulations have to be critically questioned. This study aims to evaluate how temperature affects thermal conductivity of materials in building components such as exterior walls and flat roofs in different climate conditions. Therefore, experimental conductivities measured for four common insulation materials have been used as a basis to simulate the behavior of typical construction components in three different Italian climate conditions, corresponding to the cities of Turin, Rome, and Palermo.
Highlights
In 2010, buildings accounted for 32% of total global final energy use, 19% of energy-relatedGreenhouse Gas (GHG) emissions, 51% of global electricity consumption, 33% of carbon emissions, and an eighth to a third of F-gases emissions [1]
In the European Union (EU), important efforts have been put into energy policies and different directives have resulted in recent years
This paper focuses on one particular aspect that may affect the performance of building insulation materials—temperature dependence of thermal conductivity—and how the approximations used in calculation tools may affect performance estimates
Summary
In 2010, buildings accounted for 32% of total global final energy use, 19% of energy-relatedGreenhouse Gas (GHG) emissions, 51% of global electricity consumption, 33% of carbon emissions, and an eighth to a third of F-gases emissions [1]. In 2010, buildings accounted for 32% of total global final energy use, 19% of energy-related. Space heating shows the highest share of total primary energy consumption, equal to 32%. In commercial buildings as well, space heating dominated consumption with a 33% share of the total primary energy consumption [1]. There is much evidence that improving energy efficiency practices in the existing building stock will be crucial for energy sustainability at the EU level [5]. This strategy is even defined as the “new start” for the Energies 2018, 11, 872; doi:10.3390/en11040872 www.mdpi.com/journal/energies
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