Open spaces in Hong Kong are in short supply and they are often underused due to the adverse climate, especially in hot and humid summer. This is a missed opportunity that can be otherwise realized to promote health and social interactions for local communities. The high density urban environment makes the condition worse by raising the urban heat island effect and leaving planners with fewer mitigation options. This study aims to test the hypotheses that an unfavourable thermal environment disrupts the use of outdoor open spaces; if yes, whether such disruptions differ by age groups. On-site measurement and computer simulations were conducted in three open spaces in public housing estates in Ngau Tau Kok, Hong Kong. Thermal conditions were assessed using the Universal Thermal Climate Index. Occupant activities were recorded, together with a questionnaire survey. Results showed that an open space purposefully designed for breeze and shading was 2.0°C cooler in Universal Thermal Climate Index compared with the other two. It attracted more optional/social activities, higher frequency of visits, and longer duration of stay. The elderly activities were more susceptible to disruptions from heat stress compared with younger groups. Elderly activities largely diminish when ambient thermal environment exceed 39°C in Universal Thermal Climate Index. Findings have implications to design and retrofitting of open spaces in order to maximize their use.

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In many dense cities, urban heat and the interaction of buildings with their immediate urban environment emerges as a pressing issue due to growing urban heat island effect and climate change. Informed evidence based design decisions to mitigate heat stress becomes a priority for urban planning and design practitioners. The aim of the study is to develop informed design and development decisions using computer simulation tools concerning urban microclimate performance. In this study, academic researchers have worked with industrial partners in an urban renewal project in Hong Kong’s high density urban area. In-house developed simulation software such as CityComfort+ and HTB2-Virvil were applied to assess urban microclimate conditions and risks of pedestrian thermal stress throughout key seasons. Simulation results were provided as feedback to project designers and managers at early stage, allowing timely design modification to improve performance while maintaining code compliance and design and fiscal priorities. The procedure is iterative until performance attributes converge. Preliminary results show that the informed design can deliver significant microclimate benefits compared with “business-as-usual scenarios”. By shaping building mass, orientation, and strategic placement of shading and vegetation, the improved design is expected to reduce summer-time outdoor heat stress by 1°C measured in UTCI equivalent temperature, thus bringing the average conditions for the hot season into the “comfort zone” for the local community. Energy simulation can predict overall energy demand and the potential for renewable energy supply at an urban scale. The simulation-designer workflow shows promising potentials to improve urban microclimate performance of design outcomes and the potential for zero carbon urban blocks. The early-stage action, forward-looking partnership, and computing efficiency of the simulation tools are the keys.

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