Inferring the thermal resistance and effective thermal mass of a wall using frequent temperature and heat flux measurements

Abstract

a b s t r a c tEvaluating how much heat is lost through external walls is a key requirement for building energy simulators and is necessary for quality assurance and successful decision making in policy making and building design, construction and refurbishment. Heat loss can be estimated using the temperature differences between the inside and outside air and an estimate of the thermal transmittance (U-value) of the wall. Unfortunately the actual U-value may be different from those values obtained using assumptions about the materials, their properties and the structure of the wall after a cursory visual inspection.In-situ monitoring using thermometers and heat flux plates enables more accurate characterisation of the thermal properties of walls in their context. However, standard practices require that the measurements are carried out in winter over a two-week period to significantly reduce the dynamic effects of the wall's thermal mass from the data.A novel combination of a lumped thermal mass model, together with Bayesian statistical analysis is presented to derive estimates of the U-value and effective thermal mass. The method needs only a few days of measurements, provides an estimate of the effective thermal mass and could potentially be used in summer.

A Bayesian Dynamic Method to Estimate the Thermophysical Properties of Building Elements in All Seasons, Orientations and with Reduced Error

“…These models were used to predict the time series of interest (i.e., either the heat flux through the structure or the temperatures on opposite sides) and evaluate the thermophysical properties of the element by means of Bayesian inference (Section 2.3) [6,29,30]. Note that in this paper, the term "predict" is used in its statistical meaning of estimating the value of a random variable rather than as a synonym of forecast, which implies making a prediction of the value of the variable at a given time in the future.…”

“…Lumped-thermal-mass models including between zero and four effective thermal masses-both with and without the explicit incorporation of solar radiation-were developed in this research (refer to [6] for a pure resistive model, to [29] for a model including two effective thermal masses and four thermal resistances without the explicit incorporation of solar radiation (i.e., two thermal mass model, 2TM), and to [30] for all other models). These models may provide a better description of the thermal structure of the building element, such as in the case of more complex structures.…”

“…In-situ measurements facilitate the assessment of the energy performance of buildings in use, in their environment and state of conservation [5]. Such measurements may be used to reduce the uncertainty in estimating thermophysical properties by avoiding the need to infer the construction details, materials, and in-use condition from visual inspection, then estimating thermophysical properties from year of construction and tabulated values [6]. The characterisation of actual energy performance of a building of interest can then be used to inform the retrofitting strategy, or for quality assurance on new builds or interventions on existing properties, or for energy performance assurance, in addition to providing data and insight to inform modelling studies and policy initiatives.…”

Designing an Efficient Mathematical Model for Different Thermal Insulation Material using Group Search Optimization

“…In 2014, P. Biddulph et al [19] have stated how the thermal resistance as well as the effective thermal mass of a wall has been observed with the help of heat flux and temperature measurements. The effect of weather on the U-values was properly examined with the smaller time scale and the considerations related to thermal comfort was made available with the estimation of the effective thermal mass.…”

Estimation of thermal transmittance based on temperature measurements with the application of perturbation numbers

“…The work [22] et al presents the description of in-situ monitoring measurements, using the measurements of temperature and heat flux flows as a more precise measurement of the thermal performance of walls. However, the authors indicated some limitations, as for example the fact that with the use of standard methods, the measurements in winter must be carried out over the time period of two weeks.…”