The summer season reminds us the need of Air Conditioner (AC) due to the ever increased temperature. While using the Acs both our body and mind are getting cool and relaxed due to the controlled atmosphere around us. But when we get the electricity bill, mind getting totally disturbed with high amount billed. Really what mistake happened here, didn’t we choose the right AC for our use. There is no need to suffer all around the summer heat when we get an inexpensive and energy efficient ACs, But choosing the right one is the real fact behind this.

There is few little things to remember before choosing the right AC and some technical terms that specifies the right AC for our use.

Let’s start with Technical Specification:

What Size AC we Choose : Tonnege (TON)

We ask to the retailer that we need 1 ton or 1.5 ton AC. Is that all? What is Ton. It doesn’t mean the weight of the AC, The ton means “the amount of heat removed by the air conditioner in one hour”. And this is measured by BTU aka British Thermal Units. When the higher BTU means higher cooling rate. One ton is approximately equivalent to 12,000 BTU/h or 3.5 kW.

ie, 1 ton = 12000BTU/h                     1.5 ton = 18000BTU/h                     2 ton = 24000BTU/h

Now we check the factors to take for calculating the tonnage of AC the we need. It is based on some factors like room size, city of use, number of people in room, number of appliances in room, etc. Other than the said factors, season and chances of direct sun light too room etc are need to be calculated. And all this is not easy. So whenever we choose the tonnage, we have to keep the peak summer day in mind and choose accordingly.

Efficiency of the Air Conditioner

The efficiency means the input and output ratio. ie, how much power the AC take and how much it cools the room. The efficiency of the AC is defined by the following factors.

  1. Indian Seasonal Energy Efficiency Ratio or ISEER (Previously EER)
  2. Coefficient of Performance or COP

The Indian Seasonal Energy Efficiency Ratio aka ISEER means the Amount of heat removed per hour/ power consumed. Ie, ISEER = BTU/hr/watt

Here it means that, Higher the ISEER value means Higher the Efficiency (ie, Higher the amount of heat removed per hour per unit of power consumed = High Efficiency)

The Coefficient of Performance aka COP means The amount of heat removed in Watt/ Power consumed in Watt. And Higher the CoP means Better Efficiency.

1kWh = 3412 BTU     ;     1W = 3.412 BTU/hr     ;     ISEER = 3.412 x COP


New energy rating system has been applied to AC in terms of ISEER which is based on indian climatic conditions. Earlier, the calculations of energy efficiency ratio (EER) was based on US climatic zone conditions which is completely different.

BEE Star Rating

Bureau of Energy Efficiency (BEE) with the objective of progressively improving the efficiency of Room Air Conditioners (AC) and transforming market towards better energy efficiency standards has brought in Star labeling of ACs. Since 2010, BEE has mandated air conditioners as a mandatory-labeled appliance under Energy Conservation Act and since then air conditioners cannot be sold without star label. BEE continuously tightens the standards such that, the Star-5 in 2010 became Star-3 in 2015 and will become Star-1 in 2018 as per new ISEER methodology. The weighted average Energy Efficiency Ratio (EER) of AC has increased from 2.6 in 2006 to 3.26 in 2015, which is an increase of 25% in efficiency due to tightening of standards. Now as per latest notification, from January 2016, Star-2 is the least efficiency level to be sold in the market, hence variation in power consumption is compared between Star-5 (most efficient) and Star-2 (least efficient) air conditioners.

As per the label, higher the star rating means higher the efficiency. Latest revised star rating with effect from 1st January 2018 is shown below.

One important thing to be noted here is that ISEER is given by W/W (which is also the same as COP) whereas we have defined ISEER by BTU/hr/W. Hence, ISEER in BTU/hr/W = 3.413 * ISEER in W/W

BEE has revises the start rating of air conditioners from time to time. Hence, a 5 star AC in the previous year may become a 3 star AC the next year after revision of rating takes place. You may recognize the validity of the label from the ‘label period’ section printed on the label.

Inverter Air Conditioner

The Inverter technology that concerning the electro motors of the compressors. An Inverter is used to control the speed of the compressor motor time to time. It is introduced in Japan. The inverter technology works like an accelerator a vehicle. When compressor needs more power, it gives it more power. When it needs less power, it gives less power. With this technology, the compressor is always on, but draws less power or more power depending on the temperature of the incoming air and the level set in the thermostat. The speed and power of the compressor is adjusted appropriately.

Benefits of Inverter Air Conditioner

Buying a Inverter AC is little bit costlier than normal ACs. But recurring energy bills make it worth it.

  1. At least 30% – 50% cheaper to run as it consumes less power
  2. Far quicker to achieve desired temperature
  3. The start up time is reduced by 30%
  4. Much quieter
  5. No temperature fluctuations, maximising comfort level
  6. No voltage peaks from compresso

The Advantage of Inverter Controll

Inverter vs Non-Inverter air conditioner

Non inverter or Fixed speed air conditioning deliver a fixed amount of power via a fixed speed. This means the compressor has to stop and start to maintain the desired room temperature. Inverter air conditioning system, varies the speed of the compressors, delivering precise cooling or heating power as required. So the consumption of energy will be less in Inverter ACs that Non-Inverter Acs.

Power Consumption of Inverter and non inverter air conditioners

0.75 ton 1 ton 1.5 ton 2 ton
1 Star AC (mostly non Inverter)
627 843 1246 1648
2 Star AC (mostly non Inverter) 596 800 1184 1626
3 Star AC (mix of Inverter and non Inverter)
542 747 1104 1448
4 Star (mostly Inverter) 464 645 945 1293
5 Star (mostly Inverter) 450 554 840 1113
Annual Electricity Consumption (Units or kWh for 1600 hrs) based on data from BEE

From 2018 onwards the Inverter ACs also getting star rating and it is merged in to the star rating segment of 3 Star to 5 Star