Use of microclimate models for evaluating thermal comfort: identifying the gaps

Abstract

The study identifies the gap between actual thermal sensation and theoretical comfort calculated through simulated microclimate data in different urban configurations in a tropical, high-density, megacity: Dhaka. The methodology stated here could be applied for evaluating outdoor comfort conditions for future urban areas at an early design stage. To apply the concept of theoretical comfort it is important to understand its limitations and degree of deviation from the actual comfort conditions at real scenarios. This study mainly focuses on traditional and formal (contemporary) residential settlements with different urban-geometry features. On-site climatic measurements were carried out during the hot-humid months and were compared with simulation results calculated through ENVI-met 4. Simulation results were found to have good agreement with actual air-temperature, mean radiant temperature (Tmrt) and relative humidity. In terms of windspeed, the simulated model for a complex traditional settlement did not successfully match with the actual scenarios. However, this does not affect the model competency, because, the area has rather unusual wind pattern due to its location and current arrangements of buildings. The simulated results were subsequently used to calculate outdoor thermal comfort using the PET index in RAYMAN Pro. The calculated theoretical comfort was assessed against Actual Thermal Sensation Votes (ASV) obtained through a thermal comfort survey in the case-study areas. Strong correlation (r=.58) was found between theoretical and actual comfort in the formal settlements, while the comparison with the traditional settlements produced rather weak results (r=.238). This leads to the understanding that theoretical comfort can be a useful tool for comparing between regularly planned sites; however, for complex urban geometry, theoretical comfort can deviate from actual comfort levels recorded, in part due to adaptive behaviour.