A new methodology for the in-situ measurement of thermal transmittance and thermal capacity of opaque walls: Thermal Decoupling Method (TDM)

• A new method for the in-situ measurement of both thermal transmittance and capacity. • This active method measures thermal properties by heating the wall, avoiding edge effects. • Effective for both insulated and non-insulated walls with varying features. • Shows lower errors than existing methods in theoretical thermal property evaluations. • Achieves errors below 5 % across almost all analyzed scenarios and wall conditions. Improving the energy efficiency of buildings requires precise measurements of the thermal transmittance and thermal capacity of walls. However, existing in-situ methods often struggle with limited applicability under varying climatic conditions and challenges related to edge effects, particularly when using temperature-controlled boxes. This study introduces a novel methodology that addresses these limitations by offering a compact, portable solution capable of accurately measuring these thermal properties under diverse environmental conditions. The proposed apparatus consists of two temperature-controlled chambers, heat flux meters, and temperature sensors. The innovation lies in the ability to eliminate edge effects through the decoupling of heat flux contributions associated with boundary transmissivities, allowing for reduced apparatus size compared to traditional active systems and the flexibility to operate in any climatic condition, a significant advantage over passive systems. The results are obtained simulating different wall configurations under both winter and summer conditions, using a dedicated calculation code. Results show that the method achieves high reliability, with errors consistently below 5 % for most wall types, with the exception of some heavyweight walls. The methodology outperforms traditional methods, such as the HFM-Average Method and SHB-HFM, especially in terms of accuracy and applicability across various wall configurations. This study provides a more flexible and practical approach to in-situ thermal property measurement, with significant implications for building energy efficiency and retrofitting projects.