Coordinated energy-environmental-economic optimisation of building retrofits for optimal energy performance on a macro-scale: A life-cycle cost-based evaluation

Given that energy-efficiency policies focus on meso- or macro-scale interventions, it is imperative to establish a macro-scale evaluation approach for building retrofits to support policymaking in building energy conservation, management and sustainability. This study applies the generic idea of optimising the energy, economic and environmental outputs to propose a facile framework for evaluating the prospects of building retrofits on a macro-scale. Here, an extensive optimisation approach integrating life cycle cost evaluation and an environmental assessment is formulated, involving coordinated on-site survey, modelling and data analytics. The model framework is corroborated by a case study analysis focused on identifying the optimal retrofit solution for lowrise office buildings in Shanghai. Simulation results show that modifications in occupancy regime, improvements in natural ventilation, heating and cooling systems, cool roofs insulation and installation of renewable energy systems (such as geothermal and solar/photovoltaics) are the basic retrofit measures for a macro-scale intervention to attain maximum life-cycle benefits. Individually, an estimated investment cost for each retrofit project varied within RMB 1 - 5 million with a payback period < 13 years, depending on the building characteristics. Overall, an investment estimated at RMB 1.7 billion (with a payback period of 6 years) is required to achieve 80% energy reduction with a carbon dioxide savings of - 243 Gg-CO2/yr. In summary, this study provides a guidance framework for stakeholders to evaluate investments on retrofit projects, including existing and prospective ones.