Deconstructing the complex jargon behind the energy ratings of air conditioners


The summer is finally here, and there is no escaping it, except for the time you are cocooned in an air-conditioned (AC) room. However, choosing an AC that won’t amp up your power bills or cause environmental distress takes some homework. The thumb rule is to check any appliance’s energy ratings, which mostly show up as a neat line-up of stars on the shiny label. With every AC technician and electronics-store attendant harping on the number of stars on the appliance, it is important to know exactly what these stars mean. Knowledge, after all, is power, and quite literally in this case—because knowing what they mean will translate into more savings on your power bills.

The Indian government’s Bureau of Energy Efficiency has introduced a new star-rating method called the Indian Seasonal Energy Efficiency Rating (ISEER). This is the ratio of total heat that is removed from a room to the total energy consumed in doing so. Simply put, the more the stars on the label, the lesser the units consumed by an AC to cool a room. And more power saving means less damage to the environment.

The following table (valid right up to 31 December 2019) gives you an idea of how this ratio is measured in terms of stars:




2.50 – 2.69


2.70 – 2.89


2.90 – 3.09


3.10 – 3.29




So how do the stars and the ratios translate into savings on your power bill? Let’s first understand the fundamentals that are used to gauge power consumption. The standard assumption is that an AC runs for eight hours a day, 25 days a month for eight months a year:

8 x 25 x 8 = 1,600 hours  

Suppose you choose a 1 tonne AC with a five-star rating. The units on the energy label are likely to be given as 453.35. This means that the AC consumes 453.35 units in one year (a time span of 1,600 hours, as calculated above).

Therefore, to calculate the units consumed per hour, you divide the units given with the hours of AC usage in a year:

453.35/1600 = 0.28 units per hour  

Considering that the average cost of electricity is Rs 6/unit (will vary by location), the cost of running the five-star AC for one hour is:

6 x 0.28 = Rs 1.68

Now compare that with a three-star AC with a 1 tonne capacity with the units on the energy label given as 759. This means that the AC consumes 759 units in one year (or 1,600 hours). Therefore, units consumed per hour in this case will be:

759/1600 = 0.47 units/hour

As the average cost of electricity is Rs 6/unit, the cost of running a three-star AC for one hour is:

Rs 6 x 0.47 = Rs 2.80

This means that there is a 66.6 per cent increase in savings if you opt for a more energy-efficient variant (or a five-star AC over a three-star one).


AC remote with ‘24’ written on the screen

Even after you’ve selected your AC, there are simpler ways to get more out of it:

Stick to 24°C
The compressor in an AC has to work harder to achieve a lower temperature, say of 18°C. It therefore needs to consume more power to reach that level of cooling. Comparatively, it would need a lot less electricity to achieve a comfortable 24°C. (Very often, a ‘pleasant’ temperature setting is all that we need instead of a ‘cold’ one.) So be sure to use your AC judiciously.

Look for a vigilant display panel
There are ACs with advanced features that display the consumption figures of electricity while the AC is on. These serve as good reminders to switch off the AC when you see the figures escalating.

Want to up the game? Try an inverter AC
An AC with inverter technology has a variable speed compressor that enables it to adjust its power output to precisely maintain room temperature. It also cools the room faster as it has a high power start-up.

Ensure you are choosing the right tonnage  
A tonne basically refers to the heat capacity of a tonne of melting ice over a period of one day. Essentially, this means that a 1.5 tonne AC can remove enough heat to melt 1.5 tonne of ice in a day. Therefore, the bigger the room, the bigger the tonnage of AC that you will require. Fortunately, the websites of most AC manufacturers these days help you calculate the required tonnage for your room and is typically based on the room’s length, breadth and height, the number of occupants and the size of the glass windows, among other variables.

So when you step out to buy that perfectly suited AC to cool down the heat-baked days, choose wisely. After all, being forewarned is being forearmed.

With inputs from Sachin Trivedi, founder, Bicon Consulting, empanelled as an accredited energy audit company with the Bureau of Energy Efficiency; Santosh Salian, product group head, air conditioners, Godrej and the staff of Croma store, Juhu, Mumbai.


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