Thermal performance in buildings with insulated external walls and intermittently operated air-conditioning systems (ACS) is investigated in the lower reaches of the Yangtze River region of China. Because the convective coupling between inner surface and room air makes the exact solutions of heat transfer processes difficult to be obtained when the ACS is switched off, an alternative method, which combines mathematical models and numerical solutions, is developed to analyze the effects of insulation location and thermal resistance on heat transfer of building walls and energy consumption. The investigation is carried out using the climate data of Shanghai over three summer and winter seasons (June 2011-March 2014). The results show that heat dissipation and storage of the wall's inside layer during non-working times are the key factors affecting the transmission loads of the intermittently operated ACS. The energy saving of rooms with inside insulation is at least 18% higher than that of rooms with outside insulation, and inside insulation has a more significant effect on energy savings for south oriented office rooms. In addition, the results indicate that the insulation thermal resistance of 1.0 m(2) C/W is an appropriate value for thermal insulation in this zone. (C) 2017 Elsevier B.V. All rights reserved.