Influence of clearances on the energy performance of window-type air-conditioners at the same level outside residential buildings

Abstract

Due to the hot and humid weather, the majority of residential units in Hong Kong are equipped with window-type air-conditioners. However, the provisions made in the building envelope design for their installation are often inadequate, particularly in the clearances for intake and disposal of outdoor air for condenser cooling. Consequently, the air-conditioners would consume an unnecessarily high amount of electricity and at the same time output less cooling. The paper describes a study on the outdoor airflow around air-conditioners in residential buildings and the related thermal phenomena. The CFD code FLUENT was employed to predict the airflow patterns in 20 installation configurations of window-type air-conditioners, which embrace different shapes of clearances around the air-conditioners that are on the same story in a building. The results reveal that insufficient clearance spaces could cause a significant increase in the temperature of the outdoor air entering the air-conditioners, which would also be accompanied by a reduction in the airflow rate. The increase in the electricity consumption of the air-conditioners could exceed 45% for the case where the air-conditioners were drawing in the discharged hot condenser air from other air conditioners located at an opposite wall for condenser cooling. The presence of a sidewall, however, could cause the discharged hot air to move quicker away from the air-conditioner leading to a lower entering air temperature to its condenser.