Multi-objective optimization of rural residential envelopes in cold regions of China based on performance and economic efficiency

Building envelope renovation solutions are critical to building performance and post-renovation economics. Building renovation is easier to carry out if the impacts of building envelope renovation solutions on building performance and post-renovation economic efficiency can be foreseen and a more sustainable and efficient renovation design can be achieved. This paper explores the optimal design of building envelope renovation using genetic optimization algorithms and statistical analysis methods, taking the performance of the renovated building and the economic efficiency of the renovation solution as the starting points. In Qingdao, a cold region of China, a survey was carried out on typical rural areas in seven regions. The selected design variables include the external wall and roof insulation material type(TWall, TRoof), external wall and roof insulation thickness(δWall, δRoof), type of window construction(TWc), and area radio of the window to the wall(WWR). Minimization of total building energy consumption(E) and renovation cost(COSTRE) and after renovation maximization of the combined incremental cost-benefit ratio over a 20-year life cycle(CICBR20-year life-cycle), effective natural daylighting illuminance(UDI), and percentage of time spent in indoor comfort(PTC) were considered in the optimization of the envelope. The results show that in cold regions, different envelope renovation solutions affect the optimization objectives to different degrees; changing the south-facing window-to-wall ratio(S_WWR) has a bigger effect on E, PTC, and UDI; and choosing different TRoof has a bigger effect on COSTRE and CICBR20-year life-cycle. Renovation of the selected typical rural residence with the optimal solution results in an energy-saving rate(Re) of 53.08 %, an increase of 940.86 h/year in annual indoor comfort hours(HIC) and 377.00 h/year in annual effective natural lighting hours(HUDI).