Understanding the Energy Efficiency/Star Ratings of the AC’s available in the market is important because an inefficient AC can be quite expensive to run, and nowadays all firms provide this kind of data on their AC/Refrigerator models.
Here is a link to a document on the website of Bureau of Energy Efficiency which lists the star ratings of many AC models available in India:
Here is a link to a document on the website of Bureau of Energy Efficiency which lists the star ratings of many AC models available in India:
The higher the star rating, the better the AC.
Overview of EER and Star Ratings:
AC’s are rated in tonnage for their cooling power. But a tonnage means about 12,000 Btu/hr of cooling capacity. Therefore, 1.5 tons AC corresponds to 18,000 BTU/h. Moreover, a tonnage equals 3.5 kW approx.
Now, the tonnage tells about the output of the AC, i.e., its cooling capacity. But to find out its efficiency, we need find out its power consumption as well. Assuming it to be watts, the EER or Energy Efficiency Ratio is defined as:
The ratio arrived at, by dividing the Cooling Capacity of the Air conditioner, by the electrical power input expressed in Watts. The formula is:
EER = (Cooling capacity in Watts)/Electrical consumption in Watts
The higher the EER, the better the efficiency.
The Bureau of Energy Efficiency arrives at Star Ratings after testing the various models of AC’s available in India. Following is the table used for certifying ACs with star ratings:
Overview of EER and Star Ratings:
AC’s are rated in tonnage for their cooling power. But a tonnage means about 12,000 Btu/hr of cooling capacity. Therefore, 1.5 tons AC corresponds to 18,000 BTU/h. Moreover, a tonnage equals 3.5 kW approx.
Now, the tonnage tells about the output of the AC, i.e., its cooling capacity. But to find out its efficiency, we need find out its power consumption as well. Assuming it to be watts, the EER or Energy Efficiency Ratio is defined as:
The ratio arrived at, by dividing the Cooling Capacity of the Air conditioner, by the electrical power input expressed in Watts. The formula is:
EER = (Cooling capacity in Watts)/Electrical consumption in Watts
The higher the EER, the better the efficiency.
The Bureau of Energy Efficiency arrives at Star Ratings after testing the various models of AC’s available in India. Following is the table used for certifying ACs with star ratings:
Although these limits have been moved up this year (by .2 EER each) the document specified earlier seems to be following this table only. This table, and the rating and labeling is explained in the doc available at http://bee-india.nic.in/Label-launch/Schedule3-RAC.pdf
Let’s take a typical example: a 1.5 ton AC = 5.25 kW = 4.8 kW at 90% cooling efficiency factor having a power consumption of 1900 Watts has an EER of 4800/1900 = 2.53 approx. and would have a star rating of 2 according to the table above.
If compared with a non star rated AC, having an EER of 2.2 for example, and hence an energy consumption of 4800/2.2 = 2182 Watts approx. the difference in electrical power consumption comes out to be about 282 watts (2182-1900). Assuming usage of 8 hours per day for 4 months per year, the total energy consumption comes out to be 8 hrs x 120 days x 282 watts = 270720 Watt hours or 270.72 kW-Hr.
Multiply with rate of electrical unit (say for example it falls in 101-200 units a month range, taking average of Rs. 2.5 per unit), the difference in expenditure comes out to be about 270.72 x 2.5 = Rs. 676.80. ( 1 unit = 1 kw-Hr)
Now, one would have to calculate these savings by putting in the exact values for the AC cooling capacity, the power consumption and the usage. The document specified earlier lists several ACs and their EER and Star Ratings which can be used for this purpose.
After this, one would need to decide if the extra capital expenditure initially, for a higher star rated AC, is justified by the savings in power consumption over the lifetime of the AC. (Playing the devil’s advocate here, because there is also a reason for buying higher efficient ACs regardless of one’s actual usage as it is better for the environment.)
Hope this data helps us in purchasing the right AC.
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