Enhanced key performance indicators for energy performance contracts: A proposal for integrating indoor environmental quality evaluation

Abstract

The building sector is a major contributor to energy consumption and greenhouse gas emissions in the European Union. In milder-climate regions, renovation programmes often face additional constraints linked to low baseline energy demand and socio-economic vulnerability. Energy Performance Contracts (EPCs) are a key mechanism for financing retrofits, yet conventional EPC evaluation remains largely savings-driven, which can be insufficient to represent delivered benefits, predominantly where energy use is low and behaviourally constrained. This study proposes an enhanced EPC evaluation framework that integrates Indoor Environmental Quality (IEQ) with energy performance to assess both Return on Investment and Return on Mission. The framework retains energy indicators as essential contractual compliance measures, while introducing a standardised, threshold-based indicator set to evaluate IEQ performance consistently across parameters and spaces. Beyond time of non-compliance, the proposed indicators capture the duration, magnitude, and intensity of noncompliance, complemented by metrics on variability and extreme events to support diagnosis and accountability. The framework is designed for implementation within a Digital Twin environment, enabling continuous monitoring, adaptive threshold alerts, and automated performance visualisation without increasing contractual complexity. Validation in a Portuguese social housing neighbourhood demonstrates that severity-sensitive indicators capture improvements that may be overlooked by time-based indicators, supporting fairer verification of retrofit deliverables. Overall, the proposed approach strengthens EPC appraisal by improving transparency in performance reporting under dynamic operating conditions and aligning contractual evaluation with occupant-centred outcomes, thereby supporting the evolution of EPCs in milder-climate regions toward more mission-driven models that better couple energy efficiency objectives with comfort and well-being.