Towards an improved thermometric method: Convective and radiative heat transfer for heat flux measurement through an indirect approach

Abstract

Actual thermal performance of building walls need to be assessed through on-site tests. Several measurement procedures have been proposed during the last decades. Nonetheless, among them the Thermometric (THM) method has been poorly explored in literature, hence opportunities for improvements can be highlighted. The THM technique is a quite a new and non-standardized procedure for wall thermal characterization, based on the well-known Newton’s law of cooling. This law needs the heat transfer coefficient knowledge and there is no agreement about the value to apply when the THM method is used. In this work, a low-cost experimental apparatus characterized by a heated wooden sample was realized. Sensors were installed to measure heat fluxes through a common heat flux plate. The obtained values were compared with the heat flows achieved via the THM method, where dimensionless groups analysis was performed for computing suitable heat transfer coefficients obtained from data processing. The aim of this work is to lay the groundwork for overcoming the disagreement related to the value of the total heat transfer coefficient in the THM method by proposing and consolidating an alternative approach. The results show that the proposed data processing for the THM method can provide satisfying results in terms of indirect heat flux measurements, showing extremely low percentage differences (ranging from + 1.16 % to + 3.56 %) if compared with the HFM method.