A modified method to measure outdoor mean radiant temperature: Comparison between two-hemisphere method and six-direction integral method

Measurement of the outdoor mean radiant temperature (MRT) is crucial for the investigation and design of outdoor thermal environments. However, the most accurate method for measuring outdoor MRT, the six-direction integral method (SDIM), is expensive and cumbersome. Consequently, the purpose of this study is to propose a modified method (MTHM) for the less costly and more practical MRT measurement. On the basis of radiation measurements in Shanghai, China, the MRT deviation in the two-hemisphere method (THM) was quantified, and its reasons were identified by comparing the radiation and MRT differences between the THM and the SDIM. During the summer in Shanghai, the MRT deviation in the THM is found to be less than 3 °C in the shade and up to 5 °C in direct sunlight. The failure to account for anisotropic sky diffuse radiation is the primary reason for the THM error under direct sunlight. Therefore, the MTHM was generated from the THM by incorporating anisotropic sky diffuse radiation, and it was demonstrated that it could significantly enhance the accuracy and robustness of the MRT compared to the THM. This study will help the outdoor MRT measurement, consequently supporting the outdoor thermal environment planning. •The two-hemisphere method's deviation in the shade is less than in direct sunlight.•MRT deviation in the two-hemisphere method reaches 5 °C during the Shanghai summer.•Deviations of the two-hemisphere method come mostly from sky diffuse radiation.•MTHM can enhance the accuracy and robustness of the MRT compared to the THM.