The reduction potential of energy consumption, CO2 emissions and cost of existing urban residential buildings in Hangzhou city, China

China has become the second largest emitter of CO2 in the world. As one of the largest energy consumers, urban residential buildings are required to reduce energy consumption. However nearly all existing urban residential buildings in the Hot Summer and Cold Winter Region of China were built with poor thermal quality. Increasing a building's energy performance has proven to be very helpful in alleviating the pressure of energy shortages and in reducing CO2 emissions. After analyzing the climate of the region, the economic development and existing urban residential buildings of Hangzhou city, one typical building is selected as a case study. Six rational renovation plans, based upon the national and regional standards, are advanced after analyzing their feasibility in simulations and in practice. The energy saving effects of the plans are analyzed using the feedback coefficient method, the reduction of CO2 emissions by a simple LCCO2 method and the costs by a simple LCC method, all for a 40-year residual life span. Based upon these results a suitable plan is developed. The results show that the renovation of existing residential buildings, through the thermal insulation of their building envelopes, is very beneficial in reducing energy consumption and CO2 emissions.