Effect of building re-entrant shape on performance of air-cooled condensing units

Provision of split-type air-conditioners in high-rise residential buildings has become fashionable in Hong Kong. Building re-entrants are most popular for placing the outdoor condensing units. Heat energy dissipated by these condensing units induces a buoyant airflow. Inadequate displacement of air may lead to an elevated temperature environment at the re-entrant, which could significantly affect the condenser performance at the upper floors and subsequently result in a degradation of the overall capacity and efficiency of the air-conditioners. In recent years, some innovative building designers go for sustainable housing design. Re-entrants of various shapes thus evolve. One of their concerns is whether these various shapes would incur more difficulties in the airflow and thereby, would intensify the condenser heat dissipation problem. This paper describes some investigations on different re-entrant shapes making use of the computational fluid dynamics (CFD) techniques together with an energy evaluation model. The results show no evidence that the new re-entrant shapes will have adverse effects in comparison with the conventional design.