Building sol-air temperature calculation model and research prospects

Achieving building energy conservation and carbon reduction requires accurate calculation methods and reliable basic parameters. Evaluating the thermal effects on building exterior surfaces is a fundamental aspect of thermal engineering, energy conservation, and low-carbon design. The current national standard, “Code for Thermal Design of Civil Building” (GB50176-2016), adopts a constant outdoor thermal effect model for thermal insulation design under continuous indoor heating in winter, and a non-steady model for naturally ventilated buildings in summer. This approach categorizes the main thermal effects in winter and summer, simplifies the thermal design of building envelopes, and promotes improvements in thermal performance and energy efficiency. In recent years, increasing demands for energy efficiency and carbon reduction have driven continuous improvements in the accuracy of building thermal effect models. For instance, in regions with strong solar radiation, non-steady thermal effects must be considered even in winter. Additionally, the emergence of zero-energy and zero-carbon technologies has introduced new factors influencing the thermal behavior of building exteriors. For example, advanced radiant materials have changed surface absorption and reflection properties, while integrated photovoltaic components affect both radiative and convective heat transfer. These developments have rendered traditional thermal effect models inadequate. Sol-air temperature is a key parameter for characterizing thermal effects on building exteriors. It serves as the boundary condition for evaluating the thermal performance and energy consumption of building envelopes, and the model’s accuracy directly influences the precision of thermal and energy-saving calculations. In the context of energy conservation and low-carbon development, it is essential to revisit sol-air temperature models and develop approaches that account for emerging technologies and diverse design requirements. This paper first traces the development of the sol-air temperature concept from the heat balance equation of exterior surfaces and clarifies its physical significance. It systematically compares domestic and international sol-air temperature models, analyzing their accuracy and applicability. Simplified models typically neglect long-wave radiation and are suitable for design purposes, though they lack precision. In contrast, more detailed models consider various radiative effects but often rely on parameters only available post-construction, limiting their practical application. Key factors affecting the accuracy of sol-air temperature models are then summarized, including mechanisms related to solar radiation intensity, solar radiation absorbability factor, surface heat transfer coefficient, and long-wave radiation. Finally, in response to evolving energy-saving and carbon reduction demands, this paper proposes a research outlook for sol-air temperature modeling. This includes optimizing summer insulation design in cold regions using sol-air temperature, extending its application to winter conditions in areas with abundant solar radiation, and updating key parameters such as solar radiation absorbability factors and surface heat transfer coefficients to improve model precision. Moreover, it is necessary to further consider the influence of urban environments and photovoltaic-integrated building envelopes on sol-air temperature. An integrated approach that combines steady-state and non-steady-state thermal effects is also recommended to establish a unified model capable of supporting thermal design under diverse seasonal and operational conditions. This paper offers a reference for updating and broadening the application of sol-air temperature models.