Gori, V; (2017) A novel method for the estimation of thermophysical properties of walls from short and seasonally independent in-situ surveys. Doctoral thesis , UCL (University College London).

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Abstract

This work presents a novel grey-box dynamic method — building on and significantly expanding that presented in Biddulph et al.(1) — to estimate the thermophysical properties of building elements from short monitoring campaigns undertaken at all times of the year. The estimation of thermophysical characteristics of building elements from in-situ measurements accounts for the state of conservation (e.g., moisture) and conditions the structure is exposed to, potentially reducing the performance gap. A family of lumped-thermal-mass models was devised to describe the dynamic heat transfer across building elements. Bayesian-based optimisation techniques (either using maximum a posteriori estimates or a Markov Chain Monte Carlo sampling) were adopted for the identification of the best-fit parameters, their distributions and correlations, and the associated uncertainties. Model-comparison and cross-validation techniques were applied to objectively select the best model at describing the measured data, and to test its ability to generalise to out-of-sample observations. Five walls of different construction and orientation (one housed in a thermal chamber and four in-situ) were monitored to test the ability of the method to shorten the monitoring period and to extend the data collection to non-winter seasons. A two-thermal-mass model (2TM) was selected as best by model comparison in all cases. It was able to account for direct solar radiation on the walls and provided a robust characterisation of the elements surveyed and their thermal structure, while reducing the length of the monitoring period. The systematic errors of the 2TM model were within acceptable ranges throughout the year and its estimates were within the margin of error of the other lumped-thermal-mass models, the average method and literature values. The method developed improves the understanding of the thermal comfort and energy performance in buildings, helping closing the performance gap, and informing tailored retrofitting solutions and space conditioning strategies aiming to reduce energy consumption while improving thermal comfort. (1) Biddulph, P., Gori, V., Elwell, C. A., Scott, C., Rye, C., Lowe, R., & Oreszczyn, T. 2014. Inferring the thermal resistance and effective thermal mass of a wall using frequent temperature and heat flux measurements. Energy and Buildings. DOI: 10.1016/j.enbuild.2014.04.004.

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