The effect of dynamic albedos of plant canopy on thermal performance of rooftop greenery: A case study in Singapore

Abstract

A field experiment was conducted to study the albedo variations of plant canopy with time for two local species in Singapore. It was found that diurnal albedo variations of plant canopy showed a “M” shape on clear day and did not vary significantly on cloudy day. The maximum fluctuation range of hourly albedo was up to 0.085 and 0.015 on typical clear day and cloudy day, respectively. A dynamic canopy radiation transfer model was introduced in order to predict canopy albedo and was validated against measured data. The results show that the maximum relative error of predicted canopy albedo is less than 10%. Sensitivity analysis based on this model shows that leaf area index, leaf angle, albedo and transmissivity of leaves have significant effect on canopy albedo. Comparing the simulated results of thermal performance between green roof model with and without considering dynamic canopy albedo, it can be found that the dynamic canopy radiation model could further improve the predictive performance of green roof model. Finally, thermal performance of green roof was simulated with and without considering dynamic canopy albedo under different scenarios on typical clear day. The results indicate that significant error of simulation results may occur without considering the variation of canopy albedo caused by plant parameters, especially at noon period when solar radiation is strongest. The findings drawn from this study benefit to improve the accuracy of thermal performance simulation of green roof, and also provide some reference for plant selection in terms of thermal performance.