Indoor heat stress and cooling energy comparison between green roof (GR) and non-green roof (n-GR) by simulations for labor intensive factories in the tropics

• WBGT, t sk and t cr of factory workers for both n-GR and GR have significant indoor heat stress impact. • The Green Roof (GR) condition has the biggest temperature attenuation. • GR creates indoor AT 2.5–3.5 °C lower than n-GR construction type. • About 45% indoor environment appears danger level of the factory workers for n-GR during summer. • PHS criteria appears at very high risk level with constraint for n-GR which can be reduced almost 2–2.5 times with GR. • Cooling energy reduction closes to 13% (primary energy) by using GR techniques. This study is based on labor intensive factory, located in Dhaka, Bangladesh which was adversely impacted due to extreme hot conditions. The analysis started with the implementation of green roof (GR) as one of the passive design strategies to reduce indoor heat stress. Impact of indoor heat stress indicated by wet bulb globe temperature (WBGT) and prediction of heat strain (PHS) model for green roof have been evaluated through numerical studies and indoor environmental data of local factory was measured by portable weather station. A factory energy model (by Energyplus and Open Studio) based on one of the surveyed factory’s production space including different activity zones and lab test material’s properties was developed and different roof variables were evaluated. The result indicated that GR has significant contributions on indoor heat stress reduction and substrate indoor temperature decreases (2.5–3.5 °C) with increasing vegetal coverage. It has been also examined the ratio of indoor temperature fluctuation and relatively higher standard deviation (SD) observed for non-green roof (n-GR) condition. For summer, it was also quantified that indoor WBGT and PHS criteria for the workers became 2–2.5 times lower from the high risk level due to the effectiveness of GR.