Experimental study on the thermal performance of building external window greenery in a subtropical climate

•The window greenery system reduces the radiative heat transfer through the window by 88 %.•The heat flux at the bottom wall adjacent to the window garden is reduced by 29 %.•The heat flux regression model through the bottom windowpane of the window garden is proposed.•The equivalent heat transfer coefficient for the exterior wall adjacent to the window garden is estimated.•The window greenery system cools the nearby outdoor air by 1.0 ℃.