Comparison of Heat Stress Mitigation of Parasols and Rain Umbrellas

The objective of this study is to clarify the heat stress mitigation of parasols and rain umbrellas. Measurements were conducted at the open space covered with lawn at Daido University in July. Thermal factors were measured under parasols (black/white), rain umbrellas (black/white), and in the sun. UTCI values were derived from the measured thermal environment parameters and MRT calculated from the upward and downward long- and short-wavelength radiation fluxes. The white and black parasols blocked 99.3% and 98.9% of solar radiation, respectively. The black rain umbrella had a solar shielding rate of 95.1%, while the white one had a solar shielding rate of 53.0%, which approximately half of the solar radiation penetrated through the fabric. The downward long-wavelength radiation fluxes under the black fabrics were larger than that of the white fabrics due to the absorption of solar radiation on the fabric surfaces. A strong positive correlation was found between MRT based on the globe temperature and MRT calculated from long- and short-wavelength radiation fluxes. The white parasol had the greatest heat stress reduction, lowering MRT by 18.3 °C, UTCI by 3.7 °C, and WBGT by 1.3 °C. Meanwhile, the white rain umbrella had little reduction in heat stress.