Seasonal Changes in Indoor Thermal Conditions and Thermal Comfort in Urban Houses in the Warm–Humid Climate of India

Cities in India experience distinct seasons, including summer, winter and monsoons. the understanding of thermal comfort within modern houses throughout the different seasons is pivotal for determining a passive design strategy for residences, towards carbon neutrality. Long-term investigations were conducted within five typical houses in the warm–humid climate of Kharagpur, India, spanning three seasons from July 2023 to July 2024. These included air temperature (AT), relative humidity (RH), indoor wind speed and globe temperature for calculating standard effective temperature (SET*). The SET* was used in thermal comfort evaluation, focusing on the cooling effects of elevated wind speeds. The results showed that indoor ATs were well stabilized among the houses, ranging from 27 to 32 °C in monsoon, 20 to 23 °C in winter and 30 to 32 °C in summer on average, due to the effects of high thermal mass structure with relatively small openings. Overall, both the house-wise differences (1–2 °C) and diurnal differences (0.5–3 °C) were much smaller than the seasonal differences. It was found that the resultant indoor operative temperatures (OTs) did not fall within the required comfort levels during the summer and monsoons, whereas those of the winter months met the required standard. The current modern Indian houses of high thermal mass structure prevented flexible adaptations to the dynamic seasonal changes as well as changes within a day. The occupants tended to reduce the SET* by increasing the wind speeds with the assistance of mechanical air circulation, thus reducing the perceived AT by 5 °C in summers. Separate design strategies should be adopted seasonally and in different parts of the day, to maintain a thermally comfortable environment for the occupants.