The sensitivity of roof surface and envelope insulation in naturally ventilated tropical housing: Case study across three climate zones in Myanmar

The study was aimed to investigate the impacts of the thermophysical property of the building envelopes for the present typical weather and predicted climate scenarios in Myanmar. The objective of this study was to work out the sensitivity of thermal performance of a model by varying levels of envelope u-value, solar absorptivity and thermal emissivity of the roof, coupled with the use of daytime only and nocturnal ventilation. The sensitivity analysis framed with 125 u-value matrices and eight scenarios was carried out to evaluate the impact of material variables on the indoor environment of the model. In total, 3360 dynamic simulations were performed in order to understand the sensitivity of the model to these parameters in three cities of Myanmar: Yangon, Mandalay, and Myitkyina where Koppen climates Am, Aw, and Cwa govern. The findings have found that the logical understanding of adding insulation to the roofs at first is better than adding insulation in walls and floors. In the scenario with high solar absorptivity and high thermal emissivity in the daytime ventilation mode, the overheating period above 32°C was decreased 5.18%, 2.75% and 6.89% of a year in Yangon, Mandalay, and Myitkyina when the roof u-value was reduced from 2.0 to 0.2W/m²K in that scenario. However, a better result could be found in a 24-hour ventilation mode without reducing roof u-value from 2 W/m²K in that scenario. It means the nocturnal ventilation model could decrease more overheating hours than low u-value. On the contrary, the overheating hours were increased when the u-value were reduced in the cool-roof scenarios. It means if the roof has low solar absorptivity and high thermal emissivity "the higher the u-value, the better" could overwrite “the lower the u-value, the better.” Based on the results of all simulations, the nocturnal ventilation becomes more sensitive in future climate scenarios. From this analysis, conclusions are drawn by comparing three insulation types and their characteristic of improving the thermal performance.