Thermal environmental effects and energy saving benefits of various vertical greening systems in high-rise office buildings

Vertical greening offers a promising strategy to mitigate the critical thermal and energy challenges associated with high-rise office buildings. However, quantitative insights regarding the impact of greening coverage and layout configurations on the thermal-energy performance of such buildings remain limited. This study employs a coupled ENVI-met and EnergyPlus to evaluate the effects of varying greening coverage ratios (20%-100%) and layout types (vertical, horizontal) on microclimate regulation, energy conservation, and carbon abatement, specifically quantifying the differences in air temperature (ΔT_a), relative humidity (ΔRH), surface temperature (ΔT_s), energy savings (ES), and carbon reduction (ΔC). Results show increasing coverage enhances cooling and humidifying effects, peaking at 16:00. Horizontal layouts outperform vertical layouts in cooling effects at low-moderate coverage (20%-60%), with differences diminishing at higher coverage. Vertically, maximum façade temperature reduction occurs at mid-heights (36-48 m), while the strongest air cooling is observed in the near-surface layer (0-10 m). Under full coverage, pedestrian-level air temperature reduction (ΔT_a) reaches 0.67 °C, and the façade surface temperature reduction (ΔT_s) reaches 13.88 °C. Energy performance improves with coverage: each 20% increase delivers 101.8 kWh additional daily cooling savings, and carbon emissions decrease on average by 3.1%. While horizontal layouts offer higher absolute benefits, vertical layouts provide greater performance stability. The findings recommend prioritizing east-west façades and mid-height zones, and adopting horizontal layouts under partial coverage — noting that the influence of layout diminishes as coverage approaches saturation. This study provides quantitative evidence to guide the sustainable design of vertical greening systems in high-rise office buildings.