A procedure set to construct the optimal energy saving retrofit strategy for old residential buildings in China

A key strategy for lowering emissions and reducing the effects of climate change is to execute energy-saving retrofits in residential buildings. Despite extensive research on different retrofit pathways for building energy efficiency, the current retrofitting of the aged housing stock in China is still constrained by several factors, including occupant willingness, government financial situation, and low energy prices, so retrofitting projects are almost entirely government-led and most of the solutions of existing studies are not applicable. Therefore, a comprehensive optimization framework for low-budget compliance retrofit strategies in the Chinese context is urgently needed. In order to fill this gap, this study established a set of procedures for developing an optimal energy-saving retrofit scheme in old residential buildings in Nanjing city. The results showed that the optimal scheme can reduce 18.52% of residential building energy consumption in five central districts of Nanjing City, and the total energy saving is about 260.43 GW h. The study also showed that improving wall insulation and heating, ventilation, and air conditioning systems were the most efficient retrofit measures but came at a high cost. Setting a reasonable air conditioning target temperature was further identified as the most cost-effective retrofit measure. This study provided a mechanism for district-level retrofit planners to formulate a strategy that may take the performance of retrofitting on the environment and the economy into account while still adhering to code requirements.