Improved assessment of outdoor thermal comfort: 1-hour acceptable temperature range

Abstract

Transient acceptable temperature range (ATR) is the temperature range that is acceptable by over 80% of the respondents in an outdoor thermal comfort survey. The determination of this range requires the respondents to state whether the thermal environment is acceptable at the time of the interview. However, it takes time for thermal strains to develop in the human body and the assessment of transient acceptability may overestimate thermal comfort. Transient ATR can be very wide (>40 °C), carrying limited value to landscape design and urban planning. An improved thermal acceptability assessment should account for a possible exposure time of outdoor activities. This study proposes a novel assessment of outdoor thermal acceptability: 1-hour thermal acceptability. It requires the respondents to state whether it is acceptable to stay at the interview site for one hour. This predictive assessment was tested against the transient assessment in Hong Kong by a whole-year questionnaire survey with 830 respondents. The 80% 1-hour ATR were 22.6–25.4 °C air temperature, 17.0–31.9 °C PET (70% acceptability) and 19.0–33.0 °C UTCI. They were more reasonable and realistic than transient ATR: 7.4–34.9 °C air temperature, −5.8–45.7 °C PET (70% acceptability) and 4.4–42.4 °C UTCI. The 1-hour ATR has the potential to be adopted as an outdoor thermal comfort standard.