City trapped in a solar oven

Climate-incompatible buildings that fuel excessive use of air- conditioners not only add to the energy needs of cities but also create temperature hot spots

By Avikal Somvanshi
Last Updated: Tuesday 07 July 2015

City trapped in a solar oven

ON June 7, the demand for electricity in Delhi touched an all time high of 5,654 MW. The power available to the city was 5,300 MW. The grid could not cope with the demand, resulting in large-scale load shedding.

A few aspects make this seemingly ordinary event noteworthy. First, the peak demand almost always coincides with extreme temperature conditions. But this year’s heat wave was not the most severe the capital had seen, according to the meteorological department of Indira Gandhi International Airport. This indicates there are other factors aggravating summer temperatures.

The demand peaked because of the relatively recent trend of using air-conditioners April-May onwards. This was noted by state government-owned power transmission firm Delhi Transco last year when the demand peaked in June. Earlier it would peak in July-August when the ACs would be switched on for the first time to counter the humid monsoon months that render desert coolers ineffective. One of the main reasons behind the early use of ACs is the modern buildings which, more often than not, are incompatible with local climate. Urban landscape and pollution, which do not allow heat to dissipate after the sunset, aggravate the problem.

Energy-intensive cooling options

ACs, which are fast becoming the most common solution to the problem of summer heat, account for 28 per cent of the total monthly electricity consumption in Delhi during summers. According to an estimate by the Bureau of Energy Efficiency, Delhi, ACs are responsible for 60 per cent of Delhi’s peak electricity demand. A study published in 2011 by the Indian Statistical Institute, Delhi, says that the rise in temperature from 30°C to 31°C increased demand for electricity by 3.2 million units in 2009, compared to only 1.2 million units in 2000.

ACs not only consume more electricity, they also heat up the surroundings. According to a study done by the University of Tokyo in Taipei City, Taiwan, the heat discharged from ACs was responsible for raising temperatures by 0.5°C to 2°C during evenings (7 pm to 2 am). Ninety per cent of households in Taipei City have ACs, while the figure in India is three per cent.

The study by the Tokyo university also found that the construction material and architecture of the building, and the location of AC exhaust inside the building, affect the temperature. Installing the compressor unit of split ACs in balconies instead of the roof affects the air temperature more and causes an increase in power consumption by up to 11 per cent.


“Our house used to be comfortable even during peak summers, with cool breeze coming from the windows,” recollects RavindraBhan, a landscape architect living in Defence Colony, Delhi. But his neighbours have now installed ACs with the compressor units facing his house.

“The house has now become hot, as the windows catch the AC exhaust. We have been forced to seal the windows and install ACs,” he says.

Most modern buildings are dominated by western architectural styles. Excessive use of glass, concrete, flat roofs and large windows not only heat up the outdoors, but transfer heat to the interiors. Without electricity, such buildings become a solar oven. “The faith in modern scientific solutions to achieving comfort has side-stepped local building wisdom, and cooling comfort is increasingly delegated to technical experts, potentially with primarily commercial concerns,” says Karin Lundgren of Thermal Environment Laboratory, Lund University, Sweden.

Shift in usage dynamics

Last year when Delhi Transco noted a sudden increase in peak demand for electricity on three consecutive nights in May, officials found it unusual as industries, shops, offices and malls are closed during night. This year, the weekly peak power demands were observed on weekends, with the record breaking demand reported on a Saturday. These upsurges in power demand indicate that the residential sector has upstaged the commercial sector in usage of ACs in Delhi. A study done by Kanvic Consultancy Pvt Ltd in 2012 also says that the residential sector has overtaken the commercial sector in purchase of ACs in India.

A study by the Lawrence Berkeley National Laboratory, US, estimated India would need to construct 300 coal-fired power plants of 500 MW each by 2030 just to run ACs in the country. The study assumes that AC ownership would rise to 47 per cent of urban household from the current three per cent, as stated by the National Statistical Organisation in a 2012 report. In China, AC penetration went from zero to 100 per cent in 15 years (1997 to 2012).

If India sees a similar boost, the crisis could get very severe.

The Associated Chambers of Commerce and Industry of Indiasayssale of ACs in the National Capital Region has increased 40 per cent from last year, while the increase in sale of coolers has been 15 per cent. This has been attributed to rising household income. Having grown accustomed to ACs at their workplace and cars, people now perceive ACs as a necessity.

Not only have people started using ACs from April, most of the time the thermostat is set at 18°C-19°C. As per the National Building Code of India-2005, 25°C to 30°C is the thermal comfort range for humans, with the optimum temperature being 27.5°C. One of the reasons behind the need to set the temperature so low is that people wear clothes unsuited to the weather. Maintaining low temperatures makes ACs guzzle even more energy.

Studies have shown that for every degree decrease in the thermostat setting, there is an energy consumption rise of three to 10 per cent.

The government tried addressing the problem of excessive power consumption by enacting the Energy Conservation Act in 2001. But the efforts have been insufficient and ineffective. The sharp growth in sale of ACs and the real estate sector also have overwhelmed such attempts.

To promote ACs with higher efficiency, the Bureau of Energy Efficiency has been running a rating system since 2006. Still the average efficiency of ACs sold in India is one of the lowest in the world because the rating system is not rigorous. A five star-rated AC in India would get just 2.5 stars in Australia. In India, effectiveness of ACs is tested at 35°C while the outdoor temperatures are over 45°C.

The government drafted the Energy Conservation Building Codes (ECBC) in 2007 to lay down guidelines for energy use in commercial buildings. But these are still not mandatory and not a single ECBC-compliant building has been constructed in the country.

ECBC guidelines are quite lenient too. They do not cap AC usage and allow 60 per cent area of a building’s facade to have glass. Use of too much glass in facade traps heat. The guidelines do not even define temperature and humidity standards.

“Ideally, ECBC should specify the optimal thermostat temperature range to curb power consumption by ACs,” says RajanRawal, coordinator, Centre for Advanced Research in Building Science and Energy at CEPT University, Ahmedabad. With the residential sector becoming energy-intensive, the scope of ECBC needs to be expanded.

Social reality

When Japan ran into a major power crisis after the Fukushima disaster in 2011, the government ordered that no AC in the country should run below 28°C and people should dress accordingly. Such measures can go a long way in putting a check on energy demand.

It is evident that the current crisis has been precipitated by a very small section of our society that has become accustomed to air-conditioners. Of six urban households in India, five still consume less than 100 kWh electricity in a month. An average AC will consume that much electricity in less than a week.

What the government needs to do is to ensure that urban plans and architecture curb formation of heat hot spots. It has to fix and implement ECBC guidelines to stop buildings from turning into solar ovens. Real estate developers should adapt buildings to changing climate conditions so that the occupants are not dependent solely on climate-control devices. ACs should be the last resort.

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  • Excellent. Do most of the

    Do most of the developing countries need air-conditioning at all? Traditional houses with cross ventilation and Mud offer promise. Only thing is we have to modernise the traditional systems. There is Rocky Mountain Institute's Zero Energy House, Mud houses in Rajasthan (India).

    The Eastgate Centre in Harare, Zimbabwe, typifies the best of green architecture and ecologically sensitive adaptation. The countryÔÇÖs largest office and shopping complex is an architectural marvel in its use of biomimicry principles. The mid-rise building, designed by architect Mick Pearce in conjunction with engineers at Arup Associates, has no conventional air-conditioning or heating, yet stays regulated year round with dramatically less energy consumption using design methods inspired by indigenous Zimbabwean masonry and the self-cooling mounds of African termites!
    Termites in Zimbabwe build gigantic mounds inside of which they farm a fungus that is their primary food source. The fungus must be kept at exactly 87 degrees F, while the temperatures outside range from 35 degrees F at night to 104 degrees F during the day. The termites achieve this remarkable feat by constantly opening and closing a series of heating and cooling vents throughout the mound over the course of the day. With a system of carefully adjusted convection currents, air is sucked in at the lower part of the mound, down into enclosures with muddy walls, and up through a channel to the peak of the termite mound. The industrious termites constantly dig new vents and plug up old ones in order to regulate the temperature.

    The Eastgate Centre, largely made of concrete, has a ventilation system which operates in a similar way. Outside air that is drawn in is either warmed or cooled by the building mass depending on which is hotter, the building concrete or the air. It is then vented into the buildingÔÇÖs floors and offices before exiting via chimneys at the top. The complex also consists of two buildings side by side that are separated by an open space that is covered by glass and open to the local breezes.
    Air is continuously drawn from this open space by fans on the first floor. It is then pushed up vertical supply sections of ducts that are located in the central spine of each of the two buildings. The fresh air replaces stale air that rises and exits through exhaust ports in the ceilings of each floor. Ultimately it enters the exhaust section of the vertical ducts before it is flushed out of the building through chimneys.

    The Eastgate Centre uses less than 10 percent of the energy of a conventional building its size. These efficiencies translate directly to the bottom line: EastgateÔÇÖs owners have saved $3.5 million alone because of an air-conditioning system that did not have to be implemented. Outside of being eco-efficient and better for the environment, these savings also trickle down to the tenants whose rents are 20 percent lower than those of occupants in the surrounding buildings.


    Dr.A.Jagadeesh Nellore(AP),India
    E-mail: anumakonda.jagadeesh@gmail

    Posted by: Anonymous | 6 years ago | Reply
  • One of the effective ways to

    One of the effective ways to break this heat island effect is to convert the concrete jungle Delhi right now is into a somewhat greened city, through citywide promotion of rooftop vegetation and green buildings, which consume lesser energy (and water too) on the whole and somewhat compensate for the so closely spaced buildings.
    Though the implementation of the same is a completely different problem I think.

    Posted by: Anonymous | 6 years ago | Reply
  • Hi Avikal, Nice compilation

    Hi Avikal,
    Nice compilation and analysis. The ECBC codes by BEE and GRIHA by TERI and LEEDS system should be acompanied by the financial assessment of the projects. It is not suffice to say that all buildings must use these codes but also how much added cost involved in it
    (See :
    Moreover, there hasn't been systematic research in Indian context on the impact of climate change and extreme events on the electricity demand in the cities other than Delhi (ISI study ( See :

    It will be interesting to investigate the correlation between decrease in thermal comfort temperature with the introduction of ACs.

    Posted by: Anonymous | 6 years ago | Reply
  • Dear Ayush, Fiscal incentives

    Dear Ayush,

    Fiscal incentives to adopt ECBC are not needed, it is suppose to be a base standard for efficiency and developers must adhere to it. It is no different from fire-safety norm or seismic safety standard in spirit and law. You should not confuse ECBC with GRIHA or LEED ratings which are tools to determine best in business and are by no stretch minimum benchmark which ECBC is. One gets these ratings by demonstrating doing much better than the minimum benchmark.
    Yes there are not enough studies to correlate climate change and electricity demand in Indian cities and we surely need more.
    Effect of decreasing thermal comfort temperature due to introduction of AC is pretty well researched globally and even in India. It has a direct correlation to energy consumption, various studies have pitched an increase energy consumption of ACs in range of 3-10 per cent for every degree drop in set-point from 27 degree centigrade. You can read more about it in the article done by my colleagues

    Posted by: Avikal Somvanshi | 4 years ago | Reply
  • Excellent article

    I'm actually getting a brief revision of your presentation during my Agenda for Survival course 2015. It's really necessary that we discourage the practiseof installing ACs and focus more on building designs that would be self reliant in cooling itself and not making it hotter for other buildings as well at the same time.

    How is the rating of ACs done in India and why is it below par to the international standards?

    Posted by: Rohan Dekate | 4 years ago | Reply