Star rating of AC means how efficient the AC is in converting electricity to cooling air and is based on the Energy Efficiency Ratio (EER) for cooling. The earlier BEE Star Ratings were for normal fixed speed Air Conditioners and this could not be applied to Inverter ACs which are variable speed machines. In 2015, Bureau of Energy Efficiency (BEE) started a new Star Rating standards for Inverter Air Conditioners.
The earlier BEE Star Ratings was based on the EER (Energy Efficiency Ratio) calculated by the simple formula of,
EER = Output Cooling in Watts ÷ Input Electric Watts.
The earlier EER Star Rating was a very easy and definite Star Rating based on just 2 variables, the output cooling and input watts. But this same EER Star Rating could not be used for Inverter ACs where a 3rd variable comes into play, that is the speed of the compressor which results in different efficiency ratios depending on the speed of the compressor.
When the inverter AC works at a slower speed the tonnage rating of the inverter AC goes down and when it speeds up, the tonnage rating of the inverter AC goes up. So, for example, a 1.5 ton inverter AC operating from say 10% to 150% of the nominal inverter AC capacity, becomes a 0.15 ton to 2.25 ton AC, depending on the speed of the compressor. Because of this ability of inverter AC to vary its AC ton according to needs, it makes inverter ac running cost so low that inverter ACs become the cheapest AC to run in India.
Therefore, to have a uniform Star Rating which could be applied to all types of air conditioners, The Indian Bureau of Energy Efficiency (BEE) has come up with a new Star Rating system for Indian Air Conditioners called ISEER (Indian Seasonal Energy Efficiency Ratio). How the ISEER Star Rating works is that it is based on the annual cooling output of an inverter AC divided by the annual consumption of electricity of the inverter AC based on the different outside average seasonal variation of temperatures across the whole of India. Hence, what the new star rating of inverter ACs mean is that it is the total annual cooling in watts of the inverter AC divided by the electricity in watts it consumes in a year and it takes into account the outside temperatures during the different times of the year. This is because an AC requires more power to cool a room when the outside temperature is more, for example inverter AC uses more power when outside temperature is 45 degrees C than when it is 30 degrees C.
The new ISEER star rating calculation involves both an annual temperature profile and an assumption of the average usage pattern of an inverter AC. The ISEER assumes that an Air Conditioner will be used for 1600 hrs throughout the year. The annual outside temperature profile is obtained from the weather profile of 54 cities across all regions of India and is from 24 to 43 degree C.
The efficiency of Air Conditioners have been steadily improving in India. For example a 5 star rated AC of 2010 became a 3 Star AC in 2015 and this same AC will only be a 1 Star AC when the new ISEER Star Rating is implemented in 2018. The ISEER star rating is not mandatory to be mentioned by manufacturers on inverter AC units for the time being, but will become mandatory from 1 January 2018. But leading inverter AC makers in India have already started implementing it on a voluntary basis. From 1 Jan 2018, all air conditioner units sold in India, both inverter and non-invertor ACs, must display prominently on the AC unit and its packaging the ISEER label with a Star Rating.
Many are curious as to how much more monthly electric bill you can save by buying a 5 star inverter AC instead of a 3 star inverter AC. We have a dedicated on the savings possible with a 5 star inverter AC instead of a 3 star inverter AC.
More details of ISEER star rating methodology can be seen at the official BEE white paper on ISEER rating
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