A new method to assess spatial variations of outdoor thermal comfort: Onsite monitoring results and implications for precinct planning

Abstract

a b s t r a c tResidents wish to have outdoor spaces to enjoy walking, cycling, and other recreational activities, which are often hindered by the unfavorable thermal comfort conditions, especially in the summer. High building densities lower the average wind speed and this intensifies the urban heat island effects at city scale. The conscientious use of building morphology to create local thermal comfort zone at selected spots in a large precinct is becoming a pressing issue for sustainable urbanization. This paper is a proof of concept study via continuous monitoring of the pedestrian level winds and thermal parameters at two sample days in summer, which include instantaneous air temperature, globe temperature, wind speed and humidity. Three outdoor locations at an university campus are chosen and daytime thermal perceptions at the three sites were evaluated using PET (Physiological equivalent temperature). A PET based new index was defined, which is called the thermally-perceivable environmental parameter difference. By analyzing the simultaneous differences of radiant temperature, wind speed and air temperature between the monitored spots, it is shown that it was the wind speed and radiant temperature differences that were making significant differences in thermal comfort. This pilot study clearly indicates that wind amplification combined with shading effects can generate thermally comfortable conditions in the open ground floor beneath an elevated building, even on a sunny, hot summer day in a subtropical city. This finding helps to alert city planners of additional options available in precinct planning to encourage outdoor activities.

Improving pedestrian level low wind velocity environment in high-density cities: A general framework and case study

“…Step 2: based on the obtained basic information, the wind environment at pedestrian level can be obtained by field measurements (Jones et al, 2000;Niu et al, 2015), wind tunnel tests (Du, Mak, Huang et al, 2017;Kubota et al, 2008;Tsang et al, 2012) or computational fluid dynamics (CFD) simulations (Blocken, Janssen, & van Hooff, 2012Du, Mak, Liu et al, 2017;Du, Mak, & Ai, 2018;Tominaga, Mochida, Murakami, & Sawaki, 2008). The field measurements should be conducted for a long time due to the uncertainty and unsteadiness of meteorological conditions (Schatzmann & Leitl, 2011;Schatzmann, Rafailidis, & Pavageau, 1997).…”

“…The results showed that a small gross coverage ratio should be adopted in city planning because a high gross coverage ratio results in low wind velocity at pedestrian level, especially for the detached houses. Niu et al (2015) conducted field measurements in a university campus in Hong Kong, and their findings indicated that local wind amplification could be achieved by utilising an innovative building design (lift-up design). numerically studied the wind environment in idealized high-rise urban areas, and reported that building height variation could improve pedestrian level wind environment.…”

“…Step 4: the low wind velocity environment can be improved by adopting improvement measures such as using the lift-up design to create a void space underneath the building (Du, Mak, Liu et al, 2017;Niu et al, 2015) or adopting openings in building design to guide wind flow through buildings (Fan, Chau, Chan, & Jia, 2017;Yuan & Ng, 2012). The main findings of previous studies on improving weak wind environment by adopting innovative building designs are detailed reviewed in Section 4.…”

Deduction of Optimum Surface Design Factors for Enhancement of Outdoor Thermal Environment in a Micro-Scale Unit

“…Research was conducted on parks and streets to identify the current problems, and improvement plans using green space planning approaches were explored. Changes in the thermal environment were examined by applying various design factors [13][14][15][16][17][18]. Field studies and experiments, surveys of pedestrians, and programs to evaluate the improvement in thermal comfort have been conducted [19][20][21][22][23].…”

The Effects of the Layouts of Vegetation and Wind Flow in an Apartment Housing Complex to Mitigate Outdoor Microclimate Air Temperature

“…Ashie and Kono [19] and Tominaga et al [20] utilized k-ε models to investigate the urban outdoor thermal environment for mitigating the microclimate. Liu and Niu et al [21,22] analyzed the thermal comfort condition underneath an elevated building by using the measured thermal parameters and simulated wind velocity. The sensitivities for a large eddy simulation (LES) model and a delayed detached eddy simulation (DDES) model were tested in an idealized building array by Liu et al [23] and Liu and Niu [24].…”