Understanding ENVI-met (V4) model behaviour in relation to environmental variables

Abstract

A parametric analysis is carried out to understand how ENVI‐met (V4) responds to the following aspects which form the basis of understanding the model’s behaviour: i) canyon aspect ratio, ii) cloud cover, iii) orientation, iv) wind speed and v) building height variability. The reason for using parametric modelling is that modelling techniques and calculations are made easier as they are applied to simple models and, thus, the process is verified prior to examining the real, complex situations. This is helpful for understanding the links between simple urban form and the resultant environmental characteristics and to determine the model boundary conditions for comparing the real situations. The results of the simulations include: the maximum and average (median) values of air temperature decreases in deeper canyons, but the rate of reduction reduces for canyons with an H/W ratio over 2. The average (median) mean radiant temperature also reduces in deeper canyons, but the trend is not linear. Air temperature is not affected by canyon orientation, whereas Tmrt is significantly affected by canyon orientation as the EW canyon remains exposed to high Tmrt for 8.5 hours while NS canyon is exposed for only 2.5 hours. Windy conditions result in a slightly higher air temperature and a lower Tmrt level compared to still air conditions. Increase in cloud cover has a decreasing effect on air temperature and Tmrt. And finally, the impact of diversity in canyon geometry has little impact on air temperature and Tmrt conditions.