India can significantly reduce the energy consumed by its building and construction sector by promoting contextual cooling mechanisms
These towers inside the NIIT University in Neemrana, Rajasthan, collect hot air from the outside, which is then naturally cooled through underground tunnels and used for air conditioning campus buildings (Photograph: Sugeet Grover; Illustrations Courtesy: CSE Report And Nzeb.In) The building and construction sector has significant energy consumption and carbon footprint. A major share of this is due to space cooling. NITI Aayog estimates that 65 per cent of the energy demand in India comes from space cooling and heating. A warming climate, increasingly frequent episodes of heatwaves and growing access to space cooling are set to bring about a surge in cooling demand in the country.
India is projected to see an 11-fold increase in cooling demand in buildings by 2037-38, compared to the 2017-18 baseline, as per the Union Ministry of Environment, Forest and Climate Change. Recognising this threat, the country in 2019 became one of the first in the world to bring out a Cooling Action Plan (ICAP). It predicts that a potential reduction of around 20 per cent in cooling load could be achieved by 2037-38, through climate-appropriate building envelopes. An additional 30 per cent reduction in cooling energy can be achieved through improvements in cooling equipment efficiency and better servicing and operation and maintenance practices, it adds. The current codes also specify cooling equipment efficiencies but are largely focused on refrigerant-based cooling. Low-carbon cooling has so far gained very little traction.
For decades, the narrative of providing thermal comfort has revolved around heating and cooling, however, factors such as humidity and air velocity also play a part. Just as our personal clothing and food choices vary with the external climate, recognising the cooling technologies appropriate for the conditions in order to provide thermal comfort is the key. An easily relatable example is that of a ceiling fan. It does not reduce the temperature of the air but blows away the heat generated by equipment or human bodies. Another common device used in parts of India is the desert cooler, which apart from cooling also introduces humidity. This is especially useful during the hot and dry months of May and June when cooling and humidity both are required for human comfort. In spite of its utility, chances are that a person from coastal regions would never use a desert cooler. For a humid climate, ventilation and dehumidification could serve the purpose.
These solutions mostly cater to households. However, large-scale spaces also require cooling solutions that are low in energy consumption and are applicable in varying contexts and climatic conditions. There are at least four solutions that could reduce, if not replace, the need for conventional air conditioners in India.
Tapping the earth’s potential
The temperature just 4 m below the Earth’s surface remains relatively constant throughout the year. The Earth can thus work as a heat sink or a heat source depending on the season and requirements. The campus of NIIT University in Neemrana, Rajasthan, has used this to their advantage, wherein ambient air is filtered and passed through 100-m-long tunnels embedded inside Earth. This cools the air without adding humidity. The technology can reduce the temperature of the air by 10-12°C during the start of the summer season (see ‘Earth air tunnel’).
Evaporative cooling is an extremely effective technique that has been in use for centuries in hot and dry conditions. The process involves passing hot air through a medium that is saturated with water. The air transfers heat to the water, causing it to evaporate and turn into vapour. As a result, the air becomes cool and moist, providing thermal comfort. Putting this principle in use, the Indian Institute of Technology (IIT), Gandhinagar has constructed its dining halls with a tower in the middle that is 20-25 m high (see ‘Passive downdraft cooling’). Air enters from the opening at the top of the tower and gets filtered by the dust screen. A fine water mist is generated on top with the help of micro ionisers that convert water into tiny droplets. This mix of cooled air and tiny water droplets, which is denser than warmer air, rushes down the tower. The water evaporates, leaving the air cooled and denser in comparison to ambient air.
Delhi-based non-profit Centre for Science Environment’s Anil Agarwal Environment Training Institute, located in Tijara, Rajasthan, uses an indirect evaporative cooling system where the incoming air stream is cooled using water- carrying pipes. The air, however, does not directly touch the water; it only interacts with the pipes containing it. Heat is exchanged between the air and the water, but the air does not acquire any moisture (see ‘Indirect evaporative cooling’).
While excellent at cooling large spaces, the above technologies are unlikely to ensure thermal comfort in extremely humid weather conditions where both temperature and the amount of moisture in the air pose a challenge. In such situations, the solution lies in filtering the ambient air through a desiccant (a substance that can absorb moisture). Nalanda University in Bihar is currently implementing such a system where desiccant-based evaporative cooler is used to dehumidify the air with help from excess or renewable heat (see ‘Cooling with dehumidifying’). The dehumidified air can then be cooled using evaporative cooling.
(For more details on the technologies, download “The Cooling Web: Calibrating cooling-energy requirements in India” report by Centre for Science and Environment, New Delhi)
This was first published in the 16-31 July edition of Down To Earth
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