Thermal performance of biofacade with natural ventilation in the tropical climate

Abstract

Facade and roof greenings enhance thermal comfort in building environment both indoor and outdoor by reducing heat transfer to and from buildin envelope. They shade buildings from solar radiation, absorb solar radiation for photosynthesis and evapo-transpiration, reduce solar reflection and re-radiation to atmosphere. Green façade and roof has been included as one of major green building evaluation criteria for many sustainable cities in the world nowadays. This research aims to study the use of climbing plants as vertical shading devices, "biofacade", for naturally ventilated building with windows facing west. Blue trumpet vine (Thunbergia grandiflora) was selected due to its fast growth and consistently full leave coverage. Two experiments were carried out to compare air temperature of a room with biofacade and a room without. Natural ventilation were added to both rooms and the thermal performances were compared. It has been found that biofacade performance increased when room air velocity was high from the case with natural ventilation. The room air temperature was reduced from outside ambient air temperature to the maximum of 9.93 °C, with an average of 3.63 °C during day time (9:00 a.m. - 8:30 p.m.). When air velocity was low, the temperature difference had maximum of 6.72 °C, average of 0.91 °C lower than normal room. At night (9:00 p.m. - 8:30 a.m.), however, biofacade had slightly higher air temperature than normal room and outside ambient air in both cases. Unexpectedly, leaves of the selected climbers did not obstruct wind when cross ventilation was provided and air velocity inside room with biofacade was higher than room without biofacade especially in the daytime. Besides, in tropical climate, air behind leaves always maintain lower temperature than ambient air temperature, which is different from research in temperate climate where air behind leaves can sometime obtain higher temperature. From the 2 experiments, the room temperature with biofacade reduced significantly but still could not reach comfort zone (22-28 °C) during the day time. However, the application can be recommended to use for pre-cooling the fresh air-intake of air conditioning systems, so it can help reduce cooling load efficiently. © 2011 Published by Elsevier Ltd.