How the nozzle density and height of mist spraying affect pedestrian outdoor thermal comfort: A field study

Abstract

We explored the effects of mist spraying with different nozzle densities and heights on pedestrian thermal comfort during summer in Xi'an, China. Thermal perceptions of 106 college students in open spaces (sky view factors: 0.598–0.699) varying in nozzle density (4, 6 and 8 nozzles) and height (2.3, 2.7 and 3.1 m) in a 4.5 m2 area were investigated using meteorological variables measured at 1.1 m above the ground and longitudinal questionnaire surveys. Universal Thermal Climate Index and skin temperature were selected to evaluate thermal perceptions and physiology. We found that: 1) Effects of mist spraying on humidification (2.60–7.03%), reducing globe temperature (6.55–15.15 °C) and mean radiant temperature (9.77–31.52 °C) increased as the nozzle number increased from 4 to 8. The effect of humidification declined as the nozzle height increased from 2.3 to 3.1 m (7.03–2.60%). 2) Subjects' thermal sensation vote decreased as the nozzle number increased from 4 to 8, and increased with nozzle height from 2.3 to 3.1 m. 3) ST reduction measured at the forehead (0.45–1.24 °C) and upper arm (0.38–0.95 °C) increased as the nozzle number increased from 4 to 8. Mean ST reduction decreased (0.72–0.53 °C) as the nozzle height increased from 2.3 to 3.1 m with 8 nozzles. 4) The UTCI reduction resulting from adding a nozzle was equivalent to lowering nozzle height by 0.82 m. A model of the nozzle density and height was built to predict when respondents would perceive neutral UTCI in misted environments.