Higher star ratings do mean greater efficiency — but variations exist within the same-star appliances
ISEER gives a more realistic picture than older rating methods
Electricity use assumptions (1,600 hrs/year) might not match real behaviour
Regional differences like Chennai vs Bengaluru aren’t reflected in one national label
Looking to purchase a new air-conditioner? The first consideration is usually the tonnage, followed by energy efficiency. But how does one truly assess efficiency? By the star rating, perhaps? A higher star rating does indicate better efficiency and greater energy savings. But the real question is, how much?
For most buyers, checking the star label is the extent of the evaluation. More stars equal more efficiency. While this is broadly true, the label provides deeper insights that are often overlooked. For those who are energy-conscious, it is worth taking a closer look at what the rating really conveys.
The Bureau of Energy Efficiency (BEE) has developed a search and compare tool, where one can compare products such as air-conditioners, LED (light-emitting diode) lamps, fans, televisions, pumps and heaters. It is a simple tool that provides product information and allows the user to apply filters such as brand and model to reach the most apt product for themselves.
Let us explore this in terms of a room air-conditioner. Let us say one wishes to enquire about a 1.5-tonne variable-speed split room air-conditioner. A plethora of options appear with different star ratings. One may then refine the search by choosing, say, a 3-star rating. Again, many options appear, but all within the same rating. It becomes clear that even within a single category, other factors make a difference. Let us decode them and understand how they have evolved.
India began regulating AC energy efficiency in the 2000s. In 2009, BEE introduced a star-rating system based on the Energy Efficiency Ratio (EER), which measured an AC’s cooling output against its power input under fixed conditions: 35°C outdoors, 27°C indoors and 50 per cent humidity. This method ignored seasonal variations in temperature, so it did not reflect real energy use. An AC, for example, works harder at 40°C than at 35°C.
To address this, BEE introduced the Indian Seasonal Energy Efficiency Ratio (ISEER) in 2015, making it mandatory in 2018. ISEER rates ACs using Indian weather data, considering outdoor temperatures between 24°C and 43°C and the number of hours each temperature typically occurs. Since about 65 per cent of the year in 54 major cities sees temperatures above 24°C, ISEER provides a more accurate and realistic measure of AC energy efficiency than the earlier EER method.
The label also mentions the electricity consumption of an AC (kilowatt-hour per year or kWh/year). For this, it is assumed that air-conditioners run for about 1,600 hours per year for cooling.
There are several things a person should be aware of to understand this data further.
Variations exist within a star category and that also impacts the energy consumption. The ISEER is a wide range analysis by Delhi-based think tank Centre for Science and Environment (CSE) found. Within a 3-star rated variable speed room, split air conditioner, the ISEER range varies between 3.7 to 4.38.
Consequently, the energy consumption difference annually could also be around 180 units. Assuming a per unit charge of Rs 4.5, this could mean a consumption difference of over Rs 800 annually. Assuming a higher unit rate at Rs 6.65 per unit, the value comes close to Rs 1,200.
In 4 star rated appliances of the same category, the ISEER ranged between 4.12 to 4.99, an annual energy consumption difference of around 132 units (Kwh) annually. A difference of roughly Rs 600 (@ Rs 4.5/unit) to Rs 877.33 (at the rate of Rs 6.65/unit)
In the 5-star category, the ISEER difference was between 5 and 5.85. An operation cost difference of roughly Rs 580 annually (at the rate of Rs 4.5/unit) to Rs 861.4 (at the rate of Rs 6.65/unit).
CSE’s analysis averaged out the energy consumption within each category. For a 3-star category, it came out to 1008.33, for a 4-star it came out to 902.8 and for a 5-star it came to around 740 kWh/year. Hence the energy savings could range from around Rs 1,200 to Rs 1,800 between a 3 and a 5-star AC.
A 2024 survey by Prayas (Energy Group), a non-profit in Pune, found that the median price difference between a three-star and five-star 1.5-tonne AC is `7,000’. This means that a 5-star AC can pay for itself in 4 to 6 years.
The figure of 1,600 hours is an estimate of how long, on average, a household air conditioner in India runs each year. To arrive at this number, weather data from across the country is studied to see how many hours in a year the outdoor temperature stays above 24 degrees Celcius.
However, dwelling deeper, one realises that about 1,100 of these 1,600 hours have been calculated when the outdoor temperature is at or below 30°C. In most cases, people will be using air conditioning when the temperature is above 30°C. This implies that the annual energy consumption value will differ a lot with the user behaviour and can be much less than 1,600 hours if the user is more conscious.
The star-ratings are the same across the country; however, it becomes clear that this needs to be questioned. A place like Chennai will experience far more hours over 30°C than Bengaluru will. Hence a rating based on a 1,600 hours usage across the year does not capture the regional variations, which will also depend on the climate and humidity levels in the region.
To solve this, India could borrow the solution implemented by Australia and New Zealand. Instead of having a single national rating, they have developed one for three distinct climate zones across the two countries. This system is known as the zoned energy rating label. It highlights how different climatic conditions affect an AC’s energy efficiency and performance. The label shows a zoned energy rating label for air conditioners which demonstrates the annual energy consumption of each product separately for the three climate zones.
The star rating on an AC shows how energy-efficient it is, but it is only a guideline. Within the same star category, actual energy use can vary depending on the ISEER value, which can mean a difference of several hundred rupees a year in your electricity bill.
The “kWh/year” number on the label assumes the AC runs about 1,600 hours annually, but this is only an average: If you use the AC less, or mostly when temperatures are higher than 30°C, your real consumption will likely be lower.
It is important to remember that the rating is the same across India, even though hotter cities like Chennai will see more AC use than cooler places like Bengaluru; hence, regional variations in the AC performance can be expected.