Browsing by Keyword "Heat flow meter method"
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Item Estimation of thermal resistance and capacitance of a concrete wall from in situ measurements: A comparison of steady-state and dynamic models(2023-10-01) Arregi, Beñat; Garay-Martinez, Roberto; Ramos, Juan Carlos; EDIFICACIÓN DE ENERGÍA POSITIVAThere is a growing interest in characterising the thermal performance of building envelopes when exposed to realistic weather and indoor conditions. In this study, data from a full-scale test of four uninsulated concrete panels is analysed using (1) a steady-state model as per the standard average method, (2) a dynamic lumped resistance–capacitance model with a stochastic method, and (3) a dynamic distributed capacitance model based on an analytical solution. These have been favoured over purely data-driven methods, since their physical formulation allows the characterisation of thermal capacity alongside the usual thermal resistance. The models are applied to different data subsets, sampling times and campaign lengths. For the sole estimation of thermal resistance, winter conditions with constant indoor heating allow campaign lengths around 72 h. For a strong indoor-outdoor temperature difference (e.g. 10 °C) steady-state models provide reliable estimates, and lumped capacitance models are found to suit lower temperature differences or less stable conditions. However, for estimating thermal capacity, fluctuating indoor and outdoor temperatures are preferred and only the distributed capacitance model provides consistent estimates for different time steps and data subsets. The present work might be helpful in establishing future guidelines for the use of dynamic methods with physical interpretation, presenting a case study of a simple well-known wall facing a variety of winter and summer conditions. It might also provide a basis for further research, extending the application of these models to more complex multi-layer walls and/or for the assessment of design scenarios including thermal insulation.Item Experimental and numerical thermal performance assessment of a multi-layer building envelope component made of biocomposite materials(2020-05-01) Arregi, Beñat; Garay-Martinez, Roberto; Astudillo, Julen; García, Miriam; Ramos, Juan Carlos; Tecnalia Research & Innovation; EDIFICACIÓN DE ENERGÍA POSITIVA; ECOEFICIENCIA DE PRODUCTOS DE CONSTRUCCIÓNBuilding envelope systems are rapidly evolving, driven by increasingly stringent requirements for limiting energy consumption. Current trends favour lightweight, prefabricated wall assemblies with high levels of insulation, which have been shown to be particularly sensitive to thermal bridging through anchoring and framing elements. This paper presents a self-supporting multi-layer wall component made from bio-based materials, where novel biocomposite profiles are used instead of conventional metallic frames. The thermal performance of the proposed solution is calculated from numerical modelling and characterised through in-situ measurement of a full-scale prototype. For the plane areas of the wall with continuous insulation, theoretical calculations are broadly in line with results from experimental monitoring (7–15% deviation). Additionally, an area along a framing profile was specifically monitored, and it was found that the numerical model overestimated thermal resistance with a deviation of 121%. The presence of air gaps between the rigid insulation and framing elements, linked to the fabrication process of the prototype, was identified as a plausible cause. A subsequent explanatory numerical assessment, considering the effect of such cavities in the numerical model, provided results that are consistent with measurements from the experiment and previous literature. The study aims at demonstrating the insulation levels achievable with the use of novel bio-based materials of low thermal conductivity, and more generally, contributing to a better understanding of the thermal performance of framed lightweight insulated assemblies in service conditions, by monitoring and modelling the impact of thermal bridges and workmanship at framing elements.