Energy Efficiency of Air Conditioners – Explained

Air conditioners have become indispensable and an essential part of life. Home, office, shopping malls, hospitals, and colleges – all rely on air conditioners to make the environment comfortable. Aircons consume a lot of energy, and it is, therefore, essential to understand the efficiency of an aircon. Owning a higher efficiency air conditioner can save annually hundreds of dollars in electricity bills. This article to save money how electricilty bills monthly on aircon consumption.


Efficiency rating of an air conditioner

Air conditioners are rated in stars (or ticks) depending on location. A higher star-rated air conditioner consumes lesser energy to provide the same amount of cooling than an aircon with lesser star-rating.

The government of a country typically decides the star-rating specifications. A threshold is defined for every rating which is the minimum efficiency required to earn that star. The efficiency of aircon is measured as a ratio called the Energy Efficiency Ratio (EER). Higher the EER, the greater is the efficiency of the unit.

We shall have a glance into the working of an air conditioner before defining EER.


Air Conditioner – A heat exchanger

An aircon is a heat pump. It consists of the condenser, the evaporator, refrigerant gas, and the heat exchanger coils. Just like a refrigerator, the aircon pumps heat from the room and vents it off with the ambient air outside.

Energy Efficiency Ratio (EER)

This number indicates how much heat the air conditioner removes from the area to be cooled relative to the energy consumed by it. A higher EER means a better air conditioner

Energy Efficiency Ratio = Heat Removed by the system / Energy consumed by the system

Energy is measured in Joules (J). If an air conditioner consumes 1000 joules of energy to pump out 3200 joules of energy from the room, its energy efficiency ratio is 3200/1000 = 3.2

Since electricity is metered as power consumed, EER can also be expressed as “cooling power”.

Energy Efficiency Ratio = Cooling Power of the AC / Power Consumption of the AC

“Cooling Power” can be understood as the heat removed by the aircon every second. Power is measured in Watts (W), and you may come across this term in the technical specifications of an air conditioner. It reflects the amount of energy removed by the system in one second of operation.

It becomes evident that an air conditioner that provides higher cooling power compared to others, for the same power consumption, is more efficient.


Star Rating Compared

The following data compares the energy consumed by a 1.0-ton air conditioner (based on annual electricity consumption). This data is only for comparison and reflect typical power consumption. Values would differ across different brands of air conditioners.


Typical Power Consumption of a 1.0-ton aircon calculated on an annual usage basis
Star RatingPower ConsumptionPower SavingCumulative Power SavingPower Saving (%) compared to previous star-rated ACPower Saving (%) compared to 1-star rated AC
1-star843 WZeroZeroZeroZero
2-stars800 W43 W43 W5.10 %5.10 %
3-stars747 W53 W96 W6.62 %11.38 %
4-stars645 W102 W198 W13.65 %23.48 %
5-stars554 W91 W289 W14.10 %34.28 %


The data indicates that a 5-star rated aircon consumes 34.28 % less energy than a 1-star rated aircon. Said another way, four 5-star rated air conditioners would consume approximately the same power as three 1-star rated air conditioners. This translates directly to capacity too. These four 5-star rated aircons can provide 4 tons of cooling compared to the 3 tons supplied by the 1-star aircons, for similar power consumption.

It must be noted that a higher star rating also means a more expensive air conditioner. Higher efficiency parts cost more and have newer technology, which means higher cost.


EER – Example

Referenced from:

Consider the Hitachi Toushi 3100S air conditioner. We shall examine the energy efficiency of the 1.0-ton unit. For simplicity, we shall consider the rated capacities instead of maximum capacity. Do you want to know aircon energy saving tips ?

Rated Cooling Capacity (at 100 % load) = 3516 Watts (12000 BTU/hour, or 1.0 ton)

Rated Power Consumption (at 100 % load) = 1110 Watts

Energy Efficiency Ratio = 3516 / 1110 = 3.16

These numbers indicate the power consumed to pump out heat from the room. If you visit the link provided below the table, you will find a number designated ISEER, which represents the “Indian Seasonal” Energy Efficiency Ratio. It considers the reduction in power consumption when the outside air is cooler (spring season compared to the summers).


How to make a purchase decision

Air conditioners are expensive but durable appliances. You should consider your budget and cooling requirements (number of hours of use per day). Tell me more on how big air conditioner is needed. If a higher star-rated aircon has a higher initial cost than the additional electricity consumed by the lower model, you could consider buying the more economical model. This is Return on Investment (ROI) calculation.

An average air conditioner easily lasts eight to ten years when maintained properly. Return on investment considers a shorter time frame. Assuming energy costs would increase over the lifetime of the air conditioner, you would almost certainly save money in the long-run with a more efficient air conditioner.

If you are planning to use the aircon for a short duration, you could save money with a cheaper and lesser rated air conditioner.

Saving electricity means burning lesser fossil fuel. You would help not only your finances but also the planet. We recommend buying a higher star-rated air conditioner since the benefits would certainly outweigh the costs in the long run.



Energy Efficiency Ratio (EER) is a measure of the air conditioner’s efficiency. When comparing air conditioners from different brands, use the formula to calculate the EER. Manufacturers may report EER differently based on their assumptions. However, cooling power and electrical power consumption are reported accurately in watts. A division of those would give you the EER, and that would help compare and decide why aircon you want to purchase.

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