How cities can beat the heat with passive design

The monsoon has brought much-needed relief from a scorching summer, in which the national Capital saw temperatures pushing 50 degrees Celsius. The India Meteorological Department (IMD) had issued red alerts for heatwaves in several states, and cities were panting for cooling solutions. While the clamour for air conditioning units grows louder, an impactful approach to combating such heat exists, rooted in scientific understanding and sustainable principles — passive design.

Marketed as an easy fix, air conditioning systems mask deeper issues like power cuts and global warming. Rising temperatures and reliance on air conditioners (ACs) strain the grid, leading to breakdowns, higher peak loads, and increased fossil fuel demand. This heightens heat exposure risks when passive alternatives aren’t used. Additionally, ACs exacerbate the urban heat island effect by transferring indoor heat outdoors, making concrete areas hotter than green spaces and compromising thermal comfort for those without them. Integrating passive features into buildings decreases reliance on energy-intensive cooling systems, lowers carbon footprints, reduces electricity bills, and addresses climate change by minimising peak loads on air conditioning systems.

Incorporating passive design principles starts right from the beginning of house design, with close attention to factors like massing (the architectural concept that relates to the three-dimensional structure of a building) and orientation (a building’s position in relation to the Sun’s paths and direction of wind). Creating shading through strategic massing and incorporating courtyards are integral aspects. Professional guidance ensures optimal building orientation to maximise airflow and minimise heat gain. Utilising indigenous materials with natural cooling properties enhances sustainability. Retrofitting existing constructions to incorporate these strategies improves thermal comfort and reduces electricity costs.

The insulation forms the foundation for cooler homes. With options from building air pockets to advanced thermal materials available in the market, insulation offers a versatile toolkit for protection. Reflective coatings and lighter hues on exterior surfaces deflect heat while traditional mosaic roof-floors minimise heat absorption. Yet, insulation alone isn’t sufficient. Walls made of high thermal mass materials like clay bricks or autoclaved aerated concrete (AAC) blocks impede heat transfer, enhancing thermal comfort. Modern catalogues of such materials often feature hollow configurations, which allow for the addition of air pockets or extra insulation materials to further optimise performance.

Efficient window design is crucial for balancing daylight and minimising harsh sunlight, promoting natural ventilation, and reducing reliance on mechanical cooling. Historically, courtyard-based layouts offered shaded areas and central vents for airflow, with windows positioned to reduce heat gain. Modern residences often overlook these features, but homeowners can still use shading techniques ranging from traditional chajjas to modern louvers to reduce heat penetration. Additionally, dampened bamboo or reed curtains, or chik blinds, provide effective shading during dry summers. Modern adaptations like modular clay brick louvers offer both functionality and aesthetic appeal.

Planting local, drought-resistant trees significantly lowers ambient temperatures, reducing reliance on ACs and providing essential shade. In urban areas, vertical gardens and green roofs offer compact alternatives to trees. While maintenance is a consideration, automatic watering systems and innovative gardening techniques help address thischallenge.

While deceptively simple, these measures are crucial for maintaining thermal comfort and reducing bills. Passive design effectiveness varies by climate, making it essential to prioritise the right strategies. Engaging architects and sustainability consultants becomes imperative for effective implementation.

Residents can enhance self-reliance and reduce their carbon footprint by transitioning to net-zero housing and leveraging government subsidy schemes for photovoltaic (PV) electricity generation and rainwater harvesting. Programmes like the Indian Housing Technology Mela under the PM Awas Yojana and the ministry of housing and urban affairs provide access to innovative building materials and technologies. Additionally, homeowners can enrol in green rating programs such as SVAGRIHA by Green Rating for Integrated Habitat Assessment (GRIHA) to receive feedback on their sustainability efforts.

Investing in insulation, optimising thermal mass, and fostering natural ventilation may lack the glamour of a brand-new AC unit, yet its enduring benefits for both your finances and the environment are undeniable.

Sanjay Seth is senior director and Sheen Pandita is project associate, Sustainable Buildings Division, The Energy and Resources Institute (TERI). The views expressed are personal