Dynamic Thermal Features of Insulated Blocks: Actual Behavior and Myths

Abstract

Abstract:The latest updates in the European directive on energy performance of buildings have introduced the fundamental "nearly zero-energy building (NZEB)" concept. Thus, a special focus needs to be addressed to the thermal performance of building envelopes, especially concerning the role played by thermal inertia in the energy requirements for cooling applications. In fact, a high thermal inertia of the outer walls results in a mitigation of the daily heat wave, which reduces the cooling peak load and the related energy demand. The common assumption that high mass means high thermal inertia typically leads to the use of high-mass blocks. Numerical and experimental studies on thermal inertia of hollow envelope components have not confirmed this general assumption, even though no systematic analysis is readily available in the open literature. Yet, the usually employed methods for the calculation of unsteady heat transfer through walls are based on the hypothesis that such walls are composed of homogeneous layers. In this framework, a study of the dynamic thermal performance of insulated blocks is brought forth in the present paper. A finite-volume method is used to solve the two-dimensional equation of conduction heat transfer, using a triangular-pulse temperature excitation to analyze the heat flux response. The effects of both the type of clay and the insulating filler are investigated and discussed at length. The results obtained show that the wall front mass is not the basic independent variable, since clay and insulating filler thermal diffusivities are more important controlling parameters.

Numerical Two-Dimensional Steady-State Evaluation of the Thermal Transmittance Reduction in Hollow Blocks

“…Several studies have been conducted to understand the phenomenon of heat transfer in hollow blocks. In an interesting study, Cianfrini et al [6] investigated the impact of insulation filling in hollow blocks and the role played by filling in thermal inertia of walls, and the results showed that for some blocks, a lower front mass can lead to a higher time lag, which is found to describe building performance in the literature. Caruana et al [7] used 10 different techniques and parameters for measuring the thermal performance of the hollow blocks, describing the differences between them and comparing them with the standard.…”