Flow inside a recessed space outside a high-rise residential building due to heat rejection by one air-conditioner of window-type per story

摘要

Recessed spaces formed by the external walls of adjacent residential flats can be found outside many high-rise residential buildings in Hong Kong. During summer, a large number of window-type air-conditioners could be rejecting condenser heat into such a recessed space at the same time, when a powerful rising hot air stream is formed in this space. This paper describes the findings for recessed spaces of 'l' type for a 30-story building. Inside the recessed space, one window-type air-conditioner is located per one story with its position that corresponds to the minimum dimensions prescribed by the HK-BEAM (Hong Kong Building Environmental Assessment Method) recipes. Prediction of the temperature and flow field in this space is performed by using FLUENT 5.0, a computational fluid dynamics (CFD) code. The development of detailed flow and temperature field inside the recessed space reveals existence of the hot 'Γ' shape bulk air stream together with one strong vortex pair. The mass flow rate and temperature of air inside the recessed space increases and entrainment of fresh air decreases with its height. For the highest condenser units at the inlet to the condenser coils, the temperature elevation of the air increases above 8°C, and its mass flow rate falls up to 40% below its nominal value. For the lowest units, this mass flow rate may be up to 12% higher than its nominal value.