Influence of air-conditioning exhaust on exterior recessed space

Recessed spaces are essential for high-rise residential buildings in Hong Kong. During the summer, they allow the discharge of heat from residential air-conditioners; throughout the year, they enable natural lighting and natural ventilation. Investigations are reported on the dynamic flow inside a 30-story-high recessed space for different amounts of waste heat (different sizes of cooled rooms) by window-type air-conditioners. Predictions based on a computational fluid dynamics code showed that when waste heat per air-conditioner is R = 2 kW, mechanical cooling is efficient (coefficient of performance, COP ≅ 3.1). However, when the waste heat increases, a buoyant air stream inside the recessed space becomes hotter and more powerful. Condenser units draw hotter air from this air stream, and their efficiency drops. In addition, this air stream strongly obstructs airflows through condenser units and natural ventilation through flats. The usability, efficiency and comfort of buildings will benefit from an enhanced understanding of the dynamic relationships between the configuration of the recessed exterior space, the amounts of waste heat discharged into it and the configuration of internal rooms.