Abstract

While energy codes in India have introduced increased thermal insulation in the building envelope, this paper finds evidence that increased insulation may not be appropriate for naturally ventilated affordable housing built across India. Energy consumption in buildings is expected to increase with forecasts of 230 million new urban housing units by 2047 (MoHUA, 2019), and an 11-fold increase in demand for Room Air Conditioners (RACs) by 2037–38 (IEA, 2018). The residential code introduced in 2018 prescribes Residential Envelope Transmittance Value (RETV) for cooling-dominated climates. Common construction practices like concrete shear walls and conventional brick walls usually fail to meet these criteria, prompting the need for porous masonry blocks or additional layers of insulation. Despite the projection in RAC ownership, market penetration rates are expected to be below 50% by 2040, and the predominant modes of cooling are likely to be natural ventilation assisted with ceiling fans. This study evaluates the thermal comfort in naturally ventilated apartments in four Indian climate zones for the effects of additional insulation in wall assemblies to achieve lower RETV. A calibrated Energy Plus model of a residential building in Aurangabad, Maharashtra, India was used, and the alternatives were simulated under future weather conditions. Indoor operative temperatures were assessed for India’s adaptive thermal comfort model for 80% acceptability. Results show that non-insulated walls provide 3-4% more comfort hours compared to insulated walls, suggesting that lower RETV may not benefit naturally ventilated buildings. This study provides critical evidence to revisit current ENS requirements, which require RETV less than 12 W/m². It also question the assumption that reduced conductive heat transfer universally translates to improved thermal comfort. The critical evidence provided by this study needs to be considered before India’s policymakers and financial institutions create mechanisms that scale up increased thermal insulation in the large naturally ventilated stock of affordable housing that is going to be built in the next 15 years.