Abstract
Numerical simulation is widely used in the field of computational building physics for the definition of the thermal performance of building elements. An integral component of numerical simulation using finite elements is the boundary conditions, which, in the case of simulating the thermal performance of a building element, are usually expressed in terms of the external surface temperature as a function of time. The purpose of this study is to examine the effect of the accuracy of the boundary conditions on the thermal performance simulation of building elements. The assumption that the temperature versus time is a sinusoidal function, applied in standard methods, is comparatively assessed with the actual function for diverse climatic conditions using finite elements simulation. The findings of the analysis indicate that the sinusoidal function fails to accurately simulate real boundary conditions. The originality of this study lies within the adoption of a signal reconstruction algorithm, which follows a novel approach by reconstructing the actual temperature versus time signal for the simulation of the actual boundary conditions.
Highlights
Heat transfer problems are, in general, classified as steady state or transient
The purpose of this study is to examine the impact of the sinusoidal temperature boundary condition assumption on the accuracy of the results obtained by numerical simulation for the thermal performance of building elements, and to introduce an improved model for the definition of the boundary temperature
The results indicate that the sinusoidal function defined by the relevant standards for the modelling of the external boundary conditions is the case of an exposed wall in sunny spring conditions, whereas quite considerable differences are accurate for the case of an exposed wall in sunny spring conditions, whereas quite considerable noted for the cases of a non-exposed walls in sunny spring conditions and of exposed walls in sunny differences are noted for the cases of a non-exposed walls in sunny spring conditions and of exposed winter conditions
Summary
In general, classified as steady state or transient. The term “steady”implies no change with time at any point within the medium, while the term “transient” implies variation with time or time dependence. In general, classified as steady state or transient. The heat flux remains unchanged with time in cases of steady heat transfer modelling through a medium at any location, it may vary from one location to another. Concerning the energy performance of buildings, a steady-state calculation gives the correct results on an annual basis; estimates for individual months often have large relative errors [1]. According to the findings of previous studies, a large gap exists between the average values of the calculated and the measured energy in cases where steady-state calculation methods have been applied. The temperature normally varies with time, as well as position. Most heat transfer problems encountered in practice are transient in nature, they are usually analyzed under some presumed steady conditions as steady processes are computationally less expensive to simulate
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