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Tuesday, July 02, 2019

Air Conditioners and the Summer Heat

A report has estimated that there is at least 40 per cent difference between summer and winter afternoon peak and 60 per cent difference in the summer and winter evening peak in cities like Delhi because of electricity demand from ACs.

Delhi’s peak demand has doubled in last 10 years, growing faster than the population of the city. This reflects wider use of AC as primary cooling device in place of desert cooler and fans.

Air conditioners consume 6-10 times the electricity of coolers.

Peak power deficit in India stood at 0.8 per cent and the overall energy deficit remained 0.6 per cent in 2018-19. We may soon be a power surplus nation after a long journey to get there. But in so doing we have been sharply increasing our carbon emissions over the years.

Room air conditioners must be responsible for almost a third of the electricity consumed by homes and offices in 2014-15 as reported by the Central Electricity Authority.

Energy Efficiency Ratio (EER) is calculated as the rated capacity of the system (how much does it cool) divided by its rated total power input. So a 1.5 ton ac which has cooling capacity of 5000 w and uses 1500 w as power input has an EER of 3.3 (5000 divided by 1500).

A minimum EER of 2.7 is allowed in india, given star rating 1. That would be equivalent to a cooling capacity of 4000 w with a power input of 1500 w.

India’s 5 star EER rating starts at 3.3+. Japan’s is double and even china uses ACs rated at 6 EER.

The advert released on 23 March 2015 by Bureau of Energy Efficiency (BEE) showed that the models of Samsung, Godrej, Panasonic, O General, Whirlpool, IFB and Videocon had failed the compliance test. Their 3 star and 4 star Room Air Conditioners (RAC) models could not qualify for even 1 star rating. No reports on compliance have been made public by BEE since the publishing of advert in March 2015.

Tests done recently found that even the highest rated energy efficient AC in our country will perform at two-third efficiency as the outside temperature reaches 50 c. Power consumption will go up by 28 percent while cooling capacity comes down by 20 per.

In fact, Energy efficiency drops by 2.5 per cent for every degree rise in external ambient temperature above 35 degree C. And power consumption rises by 2 per for every degree rise over 35 c. Ability of the ac to remove heat from the room drops by 1.3 per for every degree rise above 35 c.

Tests found that on average, ACs in india deliver only 77 per of their stated cooling capacity even at 35 c ambient temperature. This further decreases by 11 per when the temp climbs to 50 c.

The EER is calculated at about 27 c internal temperature. If the ac is set to achieve a lower temperature inside, then there is a further 2 per drop in EER for every degree of lower temp.

Thus in both situations – when the ambient temperature outside is 35 C but internal temperature that the AC has to achieve has been set at 20 C, the efficiency of the appliance drops by over a third.  And it drops by a third even when the ambient temperature outside is 50 C and the internal temperature to be achieved is 27 C.

Average drop in cooling capacity was measured at 20 per cent when the thermostats setting was lowered from the standard 27 degree C to 20 degree C.

Overall, in both situations – when the ambient temperature outside is 35 C but internal temperature that the AC has to achieve has been set at 20 C, there is a drop in cooling capacity to 70 %. There is a similar drop in cooling when the ambient temperature outside is 50 C and internal temperature to be achieved is 27 C.

There was also a 5% drop in efficiency with 55 % humidity. This is expected to be higher if 90 % humidity were applied.

Dense urban areas and highly commercial areas in Delhi have urban heat island effect with temperatures in these areas higher by 8-11 C compared with the city’s ambient temperature at the time.

For instance average ambient temperature conditions in Delhi in months of April, May and June is about 38 degree C but micro-climate of Connaught Place, central business district in Delhi, during same time would be 46-48 degree C. Also RACs themselves contribute to the heat island by warming up the immediate environment outside.

Tests in Tokyo indicate that raising the air conditioner’s thermostat from 26 C to 28 C and using an electric fan can reduce electricity consumption by up to 22 percent. After the Fukushima disaster when Japan faced major power crisis, Japanese government mandated that all ACs in the country should not run at temperature setting lower than 28 C. It introduced Bush Shirt rule to relax dress code in work place to encourage comfortable clothing.

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