Modeling solar radiation on a human body indoors by a novel mathematical model

Solar radiation affects occupant comfort and building energy consumption in ways that have received relatively little attention in environmental design and energy simulation. Direct, diffuse, and reflected irradiation on the body have warming effects that can be equated to increases in the mean radiant temperature (MRT) of the occupant's surroundings. A simplified occupant-centered model (SolarCal Model, i.e., SC Model) has recently been adopted in ASHRAE Standard 55, followed by a comprehensive simulation procedure combining detailed roomand manikin geometries using the Daylight Coefficient Model (DC Model). This paper presents an intermediate-level mathematical model (the HNU Solar Model) capable of rapid annual calculations of the MRT increases. Both the room and occupant geometries are simplified but consistent with those of the SC Model. Novel strategies of the calculation include a sky-annulus fraction, virtual body shadow, and equivalent window. Modeled results are compared with those simulated by the DC Model using Radiance software, which is assumed to be accurate. The differences in the Delta MRT by diffuse, direct, and reflected solar radiation are usually less than 1, 2, and 0.5 degrees C between the DC and HNU Solar Models, respectively. For a given occupant position indoors, the HNU Solar Model only needs 5 s to obtain the annual Delta MRT, while the DC Model needs about 7 min. The HNU Solar Model provides a simple and practical way to evaluate indoor environments at the room scale, to design fenestration, and to predict set-point changes in annual energy simulation of HVAC systems.

Automated summary

Solar radiation has a significant impact on occupant comfort and building energy consumption, but it has been relatively overlooked in environmental design and energy simulation. Recent developments have led to the adoption of simplified occupant-centered models, such as the SC Model, and comprehensive simulation procedures like the DC Model. The HNU Solar Model presented in this paper offers a quicker alternative for calculating annual increases in mean radiant temperature (MRT) compared to the DC Model, making it a useful tool for evaluating indoor environments and designing fenestration in HVAC systems.