Thermal performance of vertical greenery systems (VGS) in a street canyon: A real-scale long-term experiment

Abstract

Outdoor vertical greenery systems’ (VGS) thermal aspects have been intensively studied in recent years; nevertheless, real-scale long-term experiments are scarce in the literature, and little is known about the thermal effect of VGS in street canyons. An experiment on east–west-oriented real buildings in street canyons was conducted for 31 months, analyzing the thermal performance of two VGS technologies using sensors and a thermal camera. Energy saving was assessed and an allometric model was used for carbon sequestration estimation. We present time series analyses of the diurnal and seasonal cycles of the outdoor and indoor environments with respect to bare walls street canyon. Daytime cooling in the middle of the canyon 10 m from the VGS persisted for 59.4% of the time in summer and 79.4% in a heatwave, while heating persisted for 73.9% of the day in the winter. The cooling effect was more efficient in higher temperatures and was stronger 1 m near the VGS. The surface temperature of the sunlit VGS was cooler by an average of −3.8 °C in the summer and −6.8 °C in a heatwave and was slightly warmer during the winter. The average indoor summer cooling effects were greater on the south-facing orientation (air −1.57 °C; wall −1.31 °C), while the winter warming effect was greatest on the north-facing orientation (air 2.67 °C; wall 1.6 °C). The yearly energy-saving performance due to air conditioning was 8.9%. The CO2 sequestration potential (140 kg/year) was negligible compared to the CO2 emissions that were saved from air conditioning (∼9 tons/year).