Conference Paper
Proceedings of BSA Conference 2024: Sixth Conference of IBPSA-Italy
Simulation Tests for the Determination of the U-Value of Walls by Using Response Factors Theory with Noisy Boundary Conditions
Simulation Tests for the Determination of the U-Value of Walls by Using Response Factors Theory with Noisy Boundary Conditions
Maja Danovska, Davide Cassol, Ivan Giongo, Alessandro PradaDOI: https://doi.org/10.13124/9788860462022_60Abstract: The thermal behaviour of buildings’ opaque components is still one of the most important aspects in the overall energy performance of a building. In the framework of the reduction of greenhouse gas emissions and global energy consumptions, the optimization of the walls’ composition can lead to more sustainable and highlyefficient buildings, both for new and existing constructions. One of the parameters describing the thermal performance of a building’s wall is the thermal transmittance or U-value. The determination of the U-value is usually done through analytical methods according to the Standard UNI EN 6946, especially when components are characterized by simple geometries and uniform layers. However, when such a hypothesis does not stand anymore, experimental procedures in controlled environments must be adopted, e.g., climatic chambers. Stationary methodologies, like the ones suggested either by the standard UNI 1934 or the UNI EN ISO 8990, are extremely accurate and reliable, but the main drawback is the long-time procedure required, especially for highlyinsulated walls with larger thicknesses. To overcome this issue and to save both time and energy required to run the experiment, techniques based on the response factors theory have been recently gained interest with the aim of finding an alternative methodology to the standard timeconsuming one, without compromising the accuracy of results. The simple application of a triangular temperature solicitation at one side of the wall, allows the determination of the thermal response of the wall in time, as well as, the assessment of the U-value, within a significant shorter time. Besides, such dynamic methods are capable of considering also the thermal capacity of the wall, which also influences its thermal performance. Nevertheless, the technique relies on very strict experimental conditions, e.g., high signal to noise ratios. For this reason, this work investigates the effect that noisy boundary conditions, in terms of temperature, have on the determination of the thermal transmittance of walls. To do this, simulation tests in dynamic regime were developed in a COMSOL Multiphysics® environment. By applying multiple levels of noise to the boundary conditions, simulations are run and results in terms of perturbated heat fluxes and computed U-values are analysed. Results are then compared to the reference U-value obtained through a steady-state simulation. The main outcomes of this research can lead to practical guidelines for an alternative experimental technique aimed at measuring thermal transmittances of opaque buildings’ components in controlled ambient conditions. Pages: 495 - 502 Paper: