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Determining variations in air temperature and mean radiant temperature (MRT), two primary environmental parameters directly linked to thermal comfort, can be challenging. The ease and effectiveness of both measurement and simulation are quite different for determining air temperature and MRT. We review these challenges and present an experiment demonstrating how these differences in complexity and resolution can lead to challenges coupling these variables, whose effect on thermal comfort is interdependent. Bearing these challenges in mind, we measured and simulated the air temperatures and MRTs inside a radiantly heated high bay laboratory space. We found the spatial variation of the MRTs to vary by 5 ° C at the elevation of 1.3 m, which is much larger than the variations observed in air temperature. The variations in measured air temperature were up to 2 ° C. This calls for improvement to current tools and methodologies for measuring and simulating the radiant environment, particularly at locations closer to the exterior envelope where hot and cold surfaces affect both air temperature and MRT. It is important to improve the evaluation techniques for MRT, as we observe its spatial variation to be much greater than that of air temperature, while its measurement is limited and usually ignored in practice. • Simulated and modeled air and mean radiant temperatures distributions. • Used angle-factor-based MRT characterization when modeling 3D MRT. • Demonstrated rarely-captured spatial MRT variation in an indoor environment. • Discussed existing limitations in using Ta to evaluate indoor thermal environment. • Showed importance of integral indoor environment sensing and monitoring. [ABSTRACT FROM AUTHOR]

Mean radiant temperature is central to our understanding of the radiant heat exchange between the human body and surrounding environment. This paper will present a review of the concept's evolution including its qualitative definition, methods of quantitative evaluation and corresponding challenges. In the process, this review suggests that more effort needs to be invested in addressing the geometric complexities of radiant heat transfer in research into MRT; the ASHRAE definition is broad and is liable to simplification, and research which uses the definition relies on a variety of simplifications, often without acknowledging the degree of geometric complexity which exists in reality. Existing means of obtaining an estimate of mean radiant temperature range from direct measurements using globe thermometers or net radiometers, to computational simulations, and are widely used for studies within indoor and outdoor environments. Previous literature studying the correlation between air temperature and MRT has found equivalence ratios, the relative importance of convection to radiation, ranging from 0.71 to 1.4, however, it is often assumed to be 1.0 in current research practices. We also identified a rapid increase in the usage of MRT in biometeorological studies during the last ten years on top of the increased usage in indoor environment sensing and modeling in light of recent developments in heating and cooling systems. Recent efforts to include the short-wave component in indoor MRT characterization have shown an increase in cooling capacity of radiant floors from 32 to 110 W/m2; significantly decreasing peak energy demand. • We have expanded the conclusion section with both numerical conclusions and expanded discussions on the limitations of existing MRT usages. • Included new citations that covers the latest development of MRT research and standardization effort (ASHRAE Standard 55-2017, for example). • Adding new illustration of the MRT as a concept in relation to the human body geometry. • Expanded review on how indoor MRT variations due to shortwave radiation are characterized [ABSTRACT FROM AUTHOR]