Sustainable space cooling solutions

Climate change is not a phenomenon waiting to happen, it has already happened, global climate experts have warned. Climate extremes like unbearable heat for a longer duration in a year will further increase the demand for space cooling solutions in a residential building during long spells of hotter summer. A "House Owner's Guide to Alternative Roof Cooling Solutions" published by the National Disaster Management Authority (NDMA) provides an alternative to costly mechanical space cooling solutions like having more electric fans and air-conditioners. Apart from involving high upfront cost, air-conditioners also increase electricity bills and are not an affordable option for the majority of households. The rising cost of electricity generation has also led to the steady rise in power tariff for commercial and domestic consumers, which has led to rise in long-term cost of using air-conditioners as space cooling solutions. The NDMA handbook states that roof contributes up to 70% of the heat gain of a building during high temperatures. Solar radiation striking a surface is either reflected, absorbed, or transmitted. Cool roofs through use of reflective materials and techniques, help in reducing heat absorption and improving overall thermal comfort of the building, it explains the rationale behind focusing on cooling the roof to make houses climate resilient. It categorizes the states and regions into different climate zone such as hot and dry, warm and humid (that covers most areas in northeast except Sikkim and large part of Arunachal Pradesh along India-China border), composite, temperate and cold. For hot and dry, warm and humid and composite climatic zones, roof cooling solution suggested is installing bamboo, thatch and palm leaves as secondary roof for reducing the heating effect. Advantages of this solution highlighted in the handbook are that the materials are readily and locally available, light weight and have high insulating capacity and keep the indoor temperature comfortable. But the materials are prone to fire risk which needs to be kept in mind. Two other solutions offered are installation of green net shading and roof mist cooling system on the existing roof. Roof mist cooling system reduces the roof surface temperature by spraying an extremely small amount of water across the roof. Spraying allows to cool the roof as the water evaporating from the surface captures the heat, it explains with a rider that system is unfavourable for areas with water supply problems. Aligning this solution with the central government's flagship programme of Jal Jeevan Mission of providing functional tap water connection to every rural household can widen the base of users seeking to adopt it for roof cooling. Other solutions recommended include heat insulation tiles, hollow terracotta or concrete tiles, inverted earthen pots, puddle clay mixed with chopped straws and cow dung, polystyrene foam depending on availability of material locally to make it cost-effective and suitability in a certain climatic zone. For new homes to be constructed, the NDMA handbook lays emphasis on building orientation, cross ventilation, exterior shading and landscaping such terrace garden. Orientation of the building plays a crucial role with respect to solar exposure and wind direction while properly oriented doors and windows when open provide natural cross ventilation and more cooling can be obtained if air is forced to take the longer path between inlet and outlet, it states, explaining the benefits. As these solutions are based on traditional cultural practice of communities of building houses with locally available materials, panchayats, municipal boards, town committees and city authorities can explore these as a climate-resilient strategy to make the houses comfortable and protected from extreme heat during summer. Disseminating the handbook to beneficiaries of flagship housing scheme- Pradhan Mantri Awas Yojana will enable them to apply the solutions to existing houses or during construction of a new house under the scheme. The handbook can be useful in orienting authorities of educational institutions, government as well as private offices on adopting sustainable roof cooling strategy to make public spaces climate-resilient and comfortableavoiding adding higher electricity cost on account of mechanical space cooling solutions. The latest report of the Intergovernmental Panel on Climate Change (IPCC) reminds the global community that prospects for climate resilient development are increased by inclusive processes involving local knowledge and indigenous knowledge as well as processes that coordinate across risks and institutions. Heat Health Action Plans that include early warning and response systems are effective adaptation options for extreme heat, according to IPCC. The intergovernmental panel sounds cautions that globally, population exposure to heatwaves will continue to increase with additional warming, with strong geographical differences in heat-related mortality without additional adaptation. The IPCC found that most observed adaptation is fragmented, small in scale, incremental, sector-specific, designed to respond to current impacts or near-term risks, and focused more on planning rather than implementation. The NDMA handbook merits serious consideration for implementation in view of the alert sounded by the IPCC.