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Abstract: Urban heat island can significantly increase the demand for cooling of buildings in cities. This paper investigates one of the main causes of the urban heat island phenomenon, i.e. reduced city ventilation. Two simple Hong Kong city models with relatively complex terrain were considered here under different atmospheric conditions. A 3D RNG k–ɛ turbulence model was used for modeling turbulence effects. The simulation results showed that the influence of thermal stratification can be significant on city ventilation driven partially by thermal buoyancy. When the wind speed is relatively large, the impact of thermal stratification on air flow in city street canyons is minor. When the wind speed is small relative to the buoyancy force, the airflow in the street canyons is dependent on thermal stratification. When there is an adverse vertical temperature gradient, the greater the instability, the stronger the vertical mixing and the greater the flow rate caused by turbulence. The heat and pollutants can easily accumulate under stable atmospheric conditions when there is only a weak background wind or none at all. [Copyright &y& Elsevier]

Abstract: The provision of balcony to the living room of a residential flat offers a number of merits including improved view enjoyment, enhanced ventilation and increased planting space. In addition, a balcony can act as an overhang and provide solar shading as well as electricity saving of the air-conditioning system. This paper reports the findings on the energy and environmental impact due to the provision of a balcony. In this study, a typical residential flat with balcony constructed at the living room was modeled and the energy performance was investigated with the use of the typical weather data set of a subtropical city, Hong Kong. The effects of balcony''s orientation and glazing material of window were also evaluated. It was found that the residential flats facing various orientations (N, E, S, W, NE, SE, SW and NW) can offer substantial energy saving in air-conditioning system due to the shading effect of balcony. The building case with southwest facing balcony and clear glass glazed window gave the highest saving percentage of 12.3% in annual air-conditioning consumption. In terms of cost payback period, the values were estimated as 25.9 years (based on extra construction cost of a balcony) and over 100 years (based on extra purchasing cost), respectively. On the other hand, the energy payback period was 22.4 years for this building case. The provision of balcony to the living room of residential flat was found environmentally feasible in Hong Kong. [Copyright &y& Elsevier]