Determining overall heat transfer coefficient (U-Value) of wood-framed wall assemblies in Canada using external infrared thermography. (15th July 2021)

• Record Type: Journal Article
• Authors: Mahmoodzadeh, Milad; Gretka, Voytek; Hay, Katie; Steele, Casey; Mukhopadhyaya, Phalguni
• Is Part Of: Building and environment. Volume 199(2021)
• Publication Date: 2021-07-15
• Subjects: Wood-framed wall -- External infrared thermography (IRT) -- U-value -- Clear wall -- Parallel path -- Region of interest (ROI) -- Vignetting; Buildings -- Environmental engineering -- Periodicals; Building -- Research -- Periodicals; Constructions -- Technique de l'environnement -- Périodiques; Electronic journals; 696
• DOI: 10.1016/j.buildenv.2021.107897
• Languages: English
• ISSNs: 0360-1323

Abstract

Abstract: Quantitative thermography is considered as a reliable method to measure the thermal transmittance U-values of opaque building envelopes. Previously developed external infrared thermography (IRT) methodologies mainly focused on comparison of measured U-values with nominal U-values of wall assemblies in European construction. This study attempted to develop an external IRT method to determine clear wall U-values, where the impacts of repeating members (studs) were considered. The proposed method was compared with two established practices in Canada, namely the parallel path method and 3D thermal simulations. The IRT measurements were conducted on a conditioned at-scale insulated wood-framed wall structure. Besides the importance of environmental conditions on the thermal images, two thermal imaging artefacts were assessed and discussed, including nonlinear characteristics of infrared (IR) camera focal array, a.k.a. non-uniformity corrections (NUC) and vignetting. The results demonstrated that the location of the region of interest (ROI) plays a key role in U-value measurement due to the vignetting effect and colder thermal bridges at corners. It was also found that NUC should be considered during the survey. Furthermore, U-value measurement with IRT in the best-case scenario (depending on the location of ROI) deviated from nominal U-values by 6.25%–25.00%. The clear wall U-value results with IRT were validated with three-dimensional (3D) finite element analysis software, Siemens NX, which differed by −11.53%–10.00% (in the best case scenario). Additionally, the clear wall U-values obtained with parallel path method were comparable with simulation values for walls without highly conductive materials such as metal. Highlights: External infrared thermography (IRT) was performed to quantify the U-value of three insulated wood-framed wall assemblies. Effects of the thermal anomalies such as studs on the U-value measurement were assessed. Impacts of thermal imaging artefacts on the U-value measurements such as non-uniformity corrections and vignetting were analyzed. Results were validated with two accepted industry methods; 3D simulation tool (NX) and parallel path method. External IRT could be considered as a rapid and reliable tool for quantification of wood-framed wall thermal performance.