Thermal characterisation of traditional wall solution of built heritage using the simple hot box-heat flow meter method: In situ measurements and numerical simulation

Improving the thermal performance of the historic building stock has the potential to revitalise these buildings and reduce the operational energy share. To achieve that, the first requirement should be to identify and clearly characterise the building stock. However, currently, there is a lack of knowledge regarding the thermal behaviour of traditional wall solutions, and, consequently, energy auditors often use assumptions and simplifications to predict it. Wrong estimations or excessive simplifications may have a severe impact on the thermal behaviour assessment and consequently on the effectiveness of the retrofitting measures. In the scope of buildings thermal comfort and energy efficiency, the thermal resistance of both the external and internal envelope is one of the most relevant parameters for the characterisation of building elements. This work investigates the in situ thermal resistance of a traditional wall solution (“tabique” wall) of a historic building located in the north region of Portugal. The Simple Hot Box - Heat Flow Meter Method (SHB-HFM), based on the procedure described in the standard ISO 9869, is considered in the present study and its applicability to heterogeneous traditional wall solutions is discussed. The importance of controlling the radiative part of the heat transfer onto the measuring sensors is highlighted, and new development to the method is proposed in this paper via the introduction of a baffle inside the SHB. Furthermore, a finite element computer model of the case study was developed in order to ensure that some important premises allowing improving the accuracy of the final results were achieved during the measurement period as well as to enhance the robustness of the obtained conclusions. The achieved results contribute to explore the applicability of the SHB-HFM to highly heterogeneous constructive solutions present in historic buildings, where the traditional HFM method may not be applicable. In addition, this research also aims to better understand the thermal behaviour of “tabique” walls, upon which the available information is scarce. The experimental measurements and numerical simulation results present a good agreement, and an R-value of 0.56 m2 °C W−1 is measured and computed.