Evaluating the impacts of condensate-irrigated vertical greenery systems on façade thermal performance, microclimate, and energy efficiency

Vertical Greenery Systems (VGS) have increasingly been recognized for their urban cooling potential, both in reducing façade heat gain and in cooling the surrounding microclimate. Prior studies have focused almost entirely on the plant and structural features, such as vegetation coverage, growing media, and shading, leaving the temperature of the irrigation water unexamined. Yet a lower irrigation-water temperature could itself enhance cooling, and in air-conditioned buildings a cold source is already available. As humid air passes over the cooling coils, moisture condenses into cold water, which is usually discarded or used for landscape irrigation. This study explores Condensate-Integrated VGS (CIVGS) in two stages: controlled field experiments that compared the CIVGS against a conventional VGS and a bare wall, followed by an ENVI-met simulation framework we devised to model its cooling effect. Relative to the conventional VGS, the CIVGS reduced daytime façade heat flux by about 73% and cut cooling power consumption by 21.1%, while lowering near-façade air temperature by about 1°C at 0.8 m from the façade under an ambient temperature of 30°C. The simulation framework uses a regression-based residual correction, validated through leave-one-out cross-validation, that reduced the mean absolute errors of simulated surface and air temperatures by approximately 45% and 40% respectively while preserving their temporal patterns. By establishing irrigation-water temperature as a key driver of VGS cooling, the findings and the modeling framework in this study could help designers treat HVAC condensate not as waste but as a cold irrigation source that enhances VGS cooling.