Three-dimensional thermography-based method for cost-benefit analysis of energy efficiency building envelope retrofits

Recent research efforts to improve energy modeling and diagnostics for existing buildings have focused on devising methods based on digital photogrammetry or three-dimensional (3D) laser scanning and thermal imagery. Prior research has shown that fusing actual and expected 3D spatiothermal models provide valuable information for analyzing performance gaps. Until now, these methods have primarily focused on detecting and localizing potential performance problems without analyzing their associated cost. A reliable assessment of the cost provides an opportunity to conduct cost-benefit analysis for various retrofit alternatives. It also improves current thermographic inspection which relies on visual detection and qualitative interpretation of thermal irregularities. To this end, this paper presents a new 3D thermography-based method for cost-benefit analysis of energy efficiency building envelope retrofits. The method builds on energy performance augmented reality (EPAR) modeling which generates and fuses actual and expected 3D spatiothermal models using collections of thermal and digital images. In the resulting EPAR models, first detect and calculate the building areas associated with potential thermal degradations, and then explore the as-is thermal conditions of the associated building assemblies at 3D vertex-level. Next, using the historical climatic data and the recommended R-values, the amount of the unnecessary heat transfer through the detected areas and the monetary benefits from their retrofit are estimated. Finally, the expected energy cost savings were balanced against the cost of implementing insulation retrofit alternatives. Experimental results on two real-world buildings and four hypothetical cases with different geographical conditions show potential of the proposed method in reliably estimating the return on investment from retrofitting thermal performance problems.