Evaluation of the observation methods of outdoor mean radiant temperature in a subtropical city.

The outdoor mean radiant temperature (MRT) has been used as an indicator to characterize radiation in an outdoor thermal environment. To investigate outdoor MRT, the cost-effective and portable black-globe thermometer method has commonly been used, though its shortcomings have been noted, such as limited accuracy and environmental applicability. The objective of this paper is to evaluate MRT estimation results of the black-globe thermometer method and upper and lower hemispheric radiation method through the MRT results of the six-directional radiation method as a benchmark for three open sites with different underlying surfaces in a subtropical city. The hourly diffuse solar radiation model applicable to the subtropical region was further explored through statistical evaluation. Numerous findings were noteworthy: (i) the different values of albedo of the materials of underlying surfaces critically affected the long-wave radiation environment in the corresponding sites, which in turn led to differences in the MRT across the sites; (ii) the Orgill model exhibited the highest accuracy in characterizing the diffuse solar radiation for both hourly and minutely data; (iii) the upper and lower hemispheric radiation method registered significantly lower deviations for the MRT estimation results than the black-globe thermometer method, and (iv) the MRT results with the Orgill model were closer to the benchmark values than those with the measured data. In general, the upper and lower hemispheric radiation method has demonstrated accuracy, cost-effectiveness, and environmental applicability, reflecting its appropriateness for observational studies on subtropical outdoor thermal environments. • Underlying surfaces varied in daytime long-wave mean radiant temperatures (MRTs). • Orgill model outdid empirical models in gauging Guangzhou's diffuse solar radiation. • Upper and lower hemispheric measurements outperformed black-globe thermometer ones. • Despite lacking observed solar data, the model's MRT deviations were not elevated. [ABSTRACT FROM AUTHOR]