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This study proposes a new method to accurately evaluate the overall building envelope thermal performance considering the window–wall correlation, providing a new tool for building thermal design. Firstly, a non-stationary room heat transfer model is established based on the Resistance-Capacity Network method. The influence of solar heat gain through the windows on the heat transfer process of the walls in the actual environment is considered, and the room's integrated thermal resistance and integrated heat capacity indexes describing the overall room thermal resilience performance are proposed. Then, a field research test is conducted around Lhasa to obtain the local dwelling information, climate conditions, and indoor thermal environment. Numerical simulations using EnergyPlus are made to verify the effectiveness of the indexes in describing the overall building (maximum difference within 3.67% MBE and 2.92% CVRMSE) based on the field test results. Finally, the proposed envelope thermal performance index is used to analyze the local residential buildings around Lhasa. The results show that the lack of consideration of window–wall correlation has led to the failure of a local newly built building's actual envelope performance to meet the design requirements. These findings could help to develop the thermal design method of the building envelope. [ABSTRACT FROM AUTHOR]

This study makes a breakthrough out of the original thermal design idea which is mainly aim to improve thermal insulation performance of building wall, putting forward thermal design method of building wall to consider solar energy utilization and insulation simultaneously. Firstly, a day is divided into daytime and nighttime, and the expressions of indoor heat gain through the wall during such two periods are derived respectively according to the harmonic response method. The weighted sum of daytime and nighttime heat gain, then, could be used as the evaluation index of wall thermal performance. Taking this index as objective function and wall thermal resistance as well as heat capacity per unit wall area having the corresponding thickness of the thermal resistance as variables, a method for determining the optimum wall thermal resistance and heat capacity is proposed. Finally, for the room without heating measures in Lhasa area, using the typical weather data in winter as input conditions, the optimal matching curve of wall thermal resistance and heat capacity taking into account both the effect of solar energy utilization and insulation is calculated, so are the optimal value of them under different indoor temperatures (0–12 °C, interval of 2 °C). The results show that, in Lhasa area, the south wall has great potential to improve indoor thermal environment by using solar energy. From the perspectives of wall's "carrier" role of utilizable climatic resources, the higher thermal insulation performance doesn't always bring better results. [ABSTRACT FROM AUTHOR]