Thermal comfort norms
Affordable housing schemes must integrate them
As we get to the hottest months of the year, millions of households are running their ACs 24 hours a day. Between 810 per cent of India’s 300 million households have an air conditioner, but what about the other 90 per cent?
Lowincome families struggle with rising temperatures, unable to afford ACs and are most vulnerable to the effects of extreme heat. Yet surprisingly there are no special guidelines to ensure thermal comfort in the Pradhan Mantri Awas Yojana (PMAY).
Under PMAYU, States and cities offer increased floor space index (FSI), or transferable development rights (TDR) for slum redevelopment and lowcost housing. This promotes dense highrise developments that improve land use efficiency and also increases emissions per unit area. In addition, while the increase in building heights, nonreflective roofs, higher reflectivity of roads and poorly vegetated parking areas create hot air pockets around buildings, the extensive use of cement and steel without proper insulation in the buildings cause higher indoor temperatures and thermal discomfort.
Thermal comfort is a subjective measure of an individual’s satisfaction with the thermal environment, including air temperature, mean radiant temperature, air speed and relative humidity. This has not been given much importance except for token consideration by providing windows for cross ventilation. Even this has become largely irrelevant due to planning that has disrupted wind paths, paved up percolation zones and reduced green cover in cities.
ACS’ ECO IMPACT
While the use of air conditioners achieves thermal comfort they emit fluorocarbons and account for nearly 20 per cent of electricity used in buildings.
Additionally, continuous exposure to an air conditioned environment has been associated with respiratory and skin ailments. Recent observations reveal that the use of airconditioners has increased even in the smallest affordable government housing, where the walls contribute substantially to heat gain.
Indian building guidelines
ACs emit and consume lot of power
focus primarily on space utilisation. There are some parts relating to openings/fenestrations that can be inferred to utilisation of natural light. But there are no other guidelines that directly address thermal comfort — on the contrary many guidelines seem to penalise good thermal practices.
Wall thicknesses are considered within FSI calculations — thicker or cavity walls that would help reduce heat transmission restrict the amount of usable space. The rules for concrete walls, which transfer very high amounts of heat, stipulated a wall thickness of 100mm that was subsequently increased to 150mm. No guidelines take into account sun paths, wind direction or onsite conditions which at times lead to facades that face the direct afternoon sun.
The Centre in its ‘Housing for All’ mission can implement best practices for thermal comfort in buildings. Retrofitting and mitigation by occupants will always be sub optimal, expensive and lead to unforeseen consequences. Simple measures like orientation, alignment of openings to wind paths, use of reflective paint and green roofs can create great impact.
What is needed though is a greater attention to design, new materials and better guidelines. For instance, building codes could mandate adoption of passive design to promote thermal comfort.
In addition, initiatives like the Eco Niwas Samhita codeveloped by the Bureau of Energy Efficiency could be adopted to ensure building envelopes and shaded areas were designed to minimise heat gain.
Monani is Associate Professor & Director, Affordable Housing; Joshi is Senior Researcher and Visiting Faculty, Anant Centre for Sustainability, Anant National University; Sinha, Professor of Economics & Finance, Hult International Business School, London