Presence of tall buildings in a city creates poor aerodynamic conditions - wherein these structures are obstacles to natural air circulation by reducing wind speeds. Further, such tall structures create the ‘urban canyon effect’ with temperatures inside the canyon elevated by 2-4°C as the presence of multiple buildings provides multiple surfaces for the reflection and absorption of sunlight
With over 140 deaths and more than 40,000 hospitalisations for heatstroke, according to the Health Ministry's National Centre for Disease Control (NCDC), summer 2024 has seen the most dramatic heatwave yet. It is no longer metaphorical. The heat is actually killing us. And even as extreme climate events become normalised, it is also becoming evident that the impacts of a rapidly warming planet are not faced equally by all.
Cities, for example, often face the brunt of a heatwave. This can be squarely attributed to the Urban Heat Island (UHI) Effect, which is when urban areas have a significant temperature difference from surrounding rural areas due to a lack of green cover and addition of waste heat generated by energy usage into the urban environment.
The geometry and structure of urban areas, in addition to use of materials like concrete only worsen the problem. An Australian study, for example, has shown that use of asphalt concrete in roads and pavements, results in surface temperatures touching 60°C on hot summer days.
A universal response to these high temperatures has been increasing reliance on artificial space cooling through air conditioning. India’s air conditioner market, for instance, has seen an explosion in sales and revenue, and is only projected to keep increasing.
But increased AC usage comes with a catch, a phenomenon that the Centre for Science and Environment (CSE) has aptly called a "Midsummer Nightmare". More AC usage generates not just more greenhouse gas (GHG) emissions but also throws out waste heat into the immediate environment, further warming it.
Sanjay Seth, Senior Director, Sustainable Infrastructure Programme, TERI says that "ACs are not the sole cause for UHI, but taking into account factors like installation location, usage hours and efficiency, can paint a better picture of the role they play. For example, rooftop AC units installed in direct sunlight and in close proximity to each other can reduce system efficiency and exacerbate the Urban Heat Island effect."
The UHI effect is not directly responsible for climate change. But, it plays a significant enough role in personal thermal discomfort; that it becomes necessary to evaluate the role our built environment may be playing in creating conditions which have a human cost.
Housing and Built Environment: Contributors to Space Cooling Demand
Beyond increased AC usage, our housing and built environment may be contributing to the increased need for space cooling as well. This can be attributed to two main factors: one, the way our cities are shaping up with tall skyscrapers and two, increasing use of building materials with poor thermal performance, such as steel, glass, and concrete.
Presence of tall buildings in a city creates poor aerodynamic conditions - wherein these structures are obstacles to natural air circulation by reducing wind speeds. Further, such tall structures create the ‘urban canyon effect’ with temperatures inside the canyon elevated by 2-4°C as the presence of multiple buildings provides multiple surfaces for the reflection and absorption of sunlight. The conditions inside these buildings are worsened by the use of elements like large French windows, that turn homes and office spaces into hotboxes.
Seth concedes that "Currently, there is no replacement that matches concrete's versatility and cost-effectiveness in construction." What then becomes crucial is to incorporate elements that enhance thermal comfort and decrease dependency on artificial cooling.
Elements like building orientation and shading devices can go a long way. Mr Seth's colleague from TERI, Sheen Pandita has some suggestions that can even be applied to existing buildings, "Implementing green roofs and vertical gardens, installing cool roofing materials that can reflect more sunlight, painting exterior walls with reflective paint, outdoor misting systems and maintaining the sealing and insulation of doors and windows."
Lessons from traditional eco-friendly construction
Multiple studies have suggested that low-rise, high-density housing can help reduce the UHI effect by reducing the surface area exposed to heat, helping to manage indoor temperatures better. Traditional vernacular housing offers an example of this. Traditional housing has always been low-rise and high-density, adapting to the environment as part of its design.
Housing in hot and dry regions of Rajasthan and Gujarat have conventionally used elements like shaded courtyards that are deep into the house. These houses are often clustered together, with top floors that often jut out and cover part of the street. 'Pol houses' in the old city of Ahmedabad are a great example of this. Other vernacular building techniques include 'Wardha tumblers' that create air cavities in the roof and ceramic tiles over the roof to reduce solar heat gain.
Some of these principles have been emulated in low-cost social housing projects in India, such as BV Doshi designed Aranya Housing in Indore and CIDCO Housing project by Raj Rewal in Navi Mumbai.
Modern constructions, that have embraced the glass and steel design, need to look to both traditional housing and modern-day passive cooling techniques. Use of passive techniques like building orientation, natural cross ventilation and elements like jalis, climate-appropriate window shading, use of rat-trap bond in walls and central courtyards need to be incorporated.
Looking at innovations in Space Cooling
As the demand for space cooling continues to surge, innovative solutions like District Cooling (DC) present a promising alternative to traditional air conditioning systems. DC systems centralize cooling production and distribute it across multiple buildings, potentially reducing energy consumption by up to 45 percent. Sudheer Perla, MD of Tabreed Asia & Country Manager for India, highlights this shift: "District Cooling can be the missing piece in India's green growth puzzle, especially given that 45 percent of the country’s peak energy demand over the next 30 years will be for cooling."
For new developments, integrating DC at the master plan stage can be advantageous, but retrofitting existing complexes requires a tailored approach. Although challenges such as infrastructure integration and land acquisition exist, DC offers significant benefits, including reduced power bills, lower greenhouse gas emissions, and freed-up space for other uses. In India, examples of successful DC implementation include the GIFT City in Gujarat, and the My Home residential complex in Hyderabad.
What do policies and regulations say?
In 2018, Bureau of Energy Efficiency (BEE) issued Eco Niwas Samhita or Energy Conservation Building Code - Residential (ECBC-R). It set minimum performance standards for a building envelope to limit heat gain. Interestingly, a CSE study found that the parameter used by ECBC-R, i.e. Residential Envelope Transmission Value (RETV), as a proxy for thermal comfort, might be inadequate. Even materials that performed only average in RETV value, can help achieve thermal comfort, if they have a high thermal mass.
There is clearly a need for increased research focussing on building materials with an aim to manage the heat stress on cities. Materials such as autoclaved aerated concrete (AAC) blocks and compressed stabilized earthen blocks (CSEB) have shown promise. Further, Ministry of Housing and Urban Affairs (MoHUA)’s Building Materials and Technology Promotion Council (BMTPC) recommends insulation-based technologies, such as K-Wall Panels and Insulating Concrete Forms.
Ministry of Environment, Forest and Climate Change (MoEF&CC)'s India Cooling Action Plan (ICAP) predicts a crisis of thermal comfort by 2038 in Indian households. ICAP emphasises the use of ‘green walling’ to reduce the demand for artificial cooling and create thermally comfortable housing.
Incorporating innovative solutions like District Cooling (DC) into the policy framework could significantly enhance cooling efficiency. Addressing the integration of DC in both new developments and retrofits, alongside traditional building material research and improved insulation standards, is crucial. Urban planners, builders, and policymakers must collaborate when it comes to understanding this multifaceted issue and implementing strategies to create a more sustainable and comfortable living environment.
A thermally comfortable habitat is the first step towards adaptation in the battle against rising temperatures.