Clean air and thermally comfortable hours are a rare occurrence for residents of Delhi and Chennai, a recent study revealed.
The study conducted by CEPT University in collaboration with climate tech startupRespirer Living Sciences (RLS), revealed that only 3% of the total yearly hours in the national capital feature both clean air and comfortable temperatures. In contrast, the study highlights that residents of Bengaluru enjoy these conditions for the majority of hours throughout the year.
The study found that Delhi residents experience only 259 hours annually—less than 3%—where both clean air and comfortable temperatures are present.
Overall, Delhi experiences thermally comfortable temperatures (TCT) about 2210 hours in a year. Of those, 1,951 of those hours (88%) also coincide with poor air quality (AQI above 150). That leaves just 259 hours in a year, or about 3% of the total annual hours, when residents can enjoy both clean air and comfortable temperatures, conditions necessary for safe and effective natural ventilation.
The TCT is defined using an outdoor temperature range of 18°C to 31°C.
Following the footsteps of Delhi, Chennai also showed a similar trend. It's 88% of comfortable hours were also impacted by air pollution, suggesting that the convergence of climate stress and ambient pollution is becoming more common across Indian metros.
However, other cities in the study showed a more favourable alignment, with Bengaluru reporting over 8,100 hours of acceptable air quality and minimal overlap of poor AQI during thermally comfortable periods. Ahmedabad, while warmer, also provided more usable outdoor conditions than Delhi.
The study demanded a rethinking of the approach to building design. It pointed out that conventional buildings promote sealed, air-conditioned spaces, which no longer meet the needs of urban India. It proposed the integration of Personalised Environmental Control Systems (PECS), which offer localised thermal comfort, filtered ventilation, and occupant-level control.
"PECS work especially well in conjunction with low-energy solutions like ceiling fans and task-based ventilation, which enhance perceived comfort through increased air movement without the energy costs of cooling the entire space,” said Prof Rajan Rawal, a prominent expert in building science sector in India.
Besides PECS, the study introduced another technological sensor-based solution where buildings adapt dynamically to outdoor conditions.
In the wake of climate volatility and rising air pollution, the researchers called for mainstreaming PECS into building codes, urban planning regulations, and public infrastructure guidelines, especially in high-risk geographies like Delhi and Chennai.