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Radiant systems are an energy-efficient method for providing cooling to building occupants through active surfaces. To assess the impact of the radiant environment on occupants in space, we develop a ray-tracing simulation, which accounts for longwave radiation. Thermal radiation shares many characteristics with visible light, and thus is highly dependent on surface geometry. Much research effort has been dedicated to characterizing the behavior of visible light in the built environment and its impact on the human experience of space. However, longwave infrared radiation's effect on the human perception of heat is still not well characterized or understood within the design community. In order to make the embodied effect of radiant surfaces' geometry and configuration legible, we have developed a Mean Radiant Temperature (MRT) simulation method, which is based on a ray-tracing technique. It accounts for the detailed geometry of the human body and its surrounding environment. We use a case study of a pavilion built with an envelope consisting of active cooling panels in Singapore. Using measured data for the surrounding surface temperatures in the pavilion, we explore the impact of both the active panels and the surrounding passive elements and thermal environment on a person's radiant heat exchange in different postures. The reflectivity and emissivity values of different surfaces are taken into account, and the ray-tracing process allows for multiple-bounce simulation. The model accounts for both longwave and shortwave radiation, and the simulation results are compared with field measurements for validation. The results are expressed both numerically and as spatial radiant-heat-maps. These show a variation of up to 11°C in MRT across the space studied. Furthermore, a digital manikin is used to assess the impact of the radiant cooling panels across the human body. The results show a 10°C variation in radiant temperature perceived by different regions of the body in one position. The findings reveal a significant heterogeneity of radiant heat transfer that current analysis methods typically overlook for both architectural space and the geometry of the human body. [ABSTRACT FROM AUTHOR]

It is widely accepted that most people spend the majority of their lives indoors. Most individuals do not realize that while indoors, roughly half of heat exchange affecting their thermal comfort is in the form of thermal infrared radiation. We show that while researchers have been aware of its thermal comfort significance over the past century, systemic error has crept into the most common evaluation techniques, preventing adequate characterization of the radiant environment. Measuring and characterizing radiant heat transfer is a critical component of both building energy efficiency and occupant thermal comfort and productivity. Globe thermometers are typically used to measure mean radiant temperature (MRT), a commonly used metric for accounting for the radiant effects of an environment at a point in space. In this paper we extend previous field work to a controlled laboratory setting to (1) rigorously demonstrate that existing correction factors used in the American Society of Heating Ventilation and Air-conditioning Engineers (ASHRAE) Standard 55 or ISO7726 for using globe thermometers to quantify MRT are not sufficient; (2) develop a correction to improve the use of globe thermometers to address problems in the current standards; and (3) show that mean radiant temperature measured with ping-pong ball-sized globe thermometers is not reliable due to a stochastic convective bias. We also provide an analysis of the maximum precision of globe sensors themselves, a piece missing from the domain in contemporary literature. [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]