Rethinking building energy performance gap: a workflow for bridging measured, modeled, designed, and optimized strategies – a review with real-world examples

The significant gap between a building’s predicted and actual energy use, known as the energy performance gap (EPG), remains a persistent barrier to achieving decarbonization goals. Conventional analyses often attribute this gap to single causes, such as operational faults or modelling inaccuracies, failing to capture the interplay of issues across the building lifecycle. This paper introduces a structured diagnostic workflow designed to deconstruct the EPG by systematically examining four lenses of performance: As-Operated, As-Modeled, As-Designed, and As-Prescribed Intended Performance. The workflow is demonstrated through a detailed case study of a large healthcare facility. The analysis reveals that an observed 48% overconsumption of natural gas was not a simple operational error but is symptomatic of a cascading discrepancy. The workflow traces the issue back to its source, demonstrating how a suboptimal design (Lens 3) was inaccurately represented in a simplified energy model (Lens 2), which in turn failed to predict the inefficient operational reality (Lens 1). The key contribution of this work is developing a robust, diagnostic method that allows stakeholders to move beyond merely quantifying the EPG to identify its distinct root causes in design, modeling, and operation. This approach provides a more granular understanding of the problem, enabling targeted and effective mitigation strategies to EPG.