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What is inverter AC how it works

These days you hear so many advertisements talking about inverter AC, inverter fridges and even inverter Microwave ovens. So what is this "inverter" they are all talking about? What is an inverter AC, how does an inverter AC work? What are the advantages of inverter AC technology? We aim to answer all these questions here

Advantages of Inverter AC vs normal AC

The best type of AC to buy in India is an inverter AC, which not only saves electric power cost, but is more silent and comfortable with steady continuous cooling.

A normal AC first over cools the room and cuts off the compressor till the room again gets warm, then it will restart. This constant starting and stopping of normal AC compressor makes the room too cold for a short while and then it becomes too warm. This is does not lead to a comfortable sleep. Also with the AC compressor running at high speeds when it is on, and with the constant restart of the AC compressor, a normal AC consumes a lot of current making a normal AC very inefficient and costly to use.

An inverter AC on the other hand controls the temperature of the room by running the compressor at different speeds, at very slow speed when the room is at the right temperature and speeds up if the temperature starts going up. Thus a room cooled by an inverter AC stays at a constant comfortable temperature enabling a very good sleep. Compare inverter AC vs normal AC, an inverter AC uses 40% less electric power and you get a much better sleep with constant cool temperature. The inverter AC is very silent and lasts much longer than normal AC, because the inverter AC runs at slower speeds and there is no wear and tear of the compressor stopping and starting constantly.

Rather than the stop and start cycles of a normal AC, the inverter AC compressor does not stop running while the inverter AC is switched on. The inverter AC controls the cooling of a room by adjusting the speed of its compressor to suit the cooling needs. Thus the inverter AC will run at very high speed for a short time when the AC is switched on, to cool the room very fast. When the set temperature on the thermostat is reached, the inverter AC compressor slows down with just enough speed to maintain the set temperature by compensating for the heat coming into the room.

To give an example of a 1.5 Ton inverter AC, as soon as it is switched on, its compressor will run at say 150% of rated speed to cool the room fast till the set temperature has been reached and then will slow down to say 10% of its rated capacity which is just enough to maintain the cool room temperature by compensating for the heat coming into the room. This means that the 1.5 Ton inverter AC in our example here will be running as a 0.15 Ton AC most of the time and as a 2.25 Ton AC at the beginning when it is cooling the room very fast. 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.

How does inverter AC work

In an inverter AC, the 50 cycles per second or 50Hz alternating current in our power supply is first converted into a Direct Current DC and then it is reconverted into an alternating current where the frequency is infinitely variable, from say 10 cycles per second or HZ to say 100 cycles per second. This variable frequency enables the main compressor motor of the AC to turn at different speeds. With the fixed 50Hz AC of our electric supply, the compressor motor of normal air conditioner can only turn at one speed, but with a variable frequency, the compressor motor of the AC can run at different speeds, from very low to very high speeds. There are many advantages of the AC compressor to be run at different speeds as explained below.

The problem with the fixed 50Hz power supply is that it will turn electric motors only at only a fixed speed depending on the number of poles. Then you may ask, but we can have our fans running at different speeds without an inverter? Yes true, but the fan speed control is limited and is achieved by the use of changing the number of poles or by changing the voltage which can only have a very limited speed control and is not very efficient.

Since the speed of any electric motor depends on the frequency of the voltage applied to it, so to control the speed of an electric motor, the most efficient way is to control the frequency of the power supply voltage. To achieve this, the AC power supply to our houses has to be first converted into DC and this DC power converted back to AC voltage with the ability to infinitely control the frequency of the AC voltage. The device that converts DC voltage to AC voltage is known as an inverter.


Which AC is better inverter AC or 5 star normal AC

A 5 star normal AC is the most efficient normal AC, but it cannot be as efficient as an inverter AC, because the inverter AC works on a totally different principle. Also inverter ACs have no star rating as yet in India.

The regular AC compressor has only one speed and the cooling is controlled by offing the AC compressor when a set cold temperature has been reached and then restarting the AC compressor when the room heats up and reaches a set temperature. For example, if you set the thermostat in the regular AC to cool the room to 22 degrees, then the AC compressor starts when the room temperature is 24 degrees and stops when the room has cooled to 20 degrees. This is the cycle that repeats itself throughout the period that the AC is on. This is a very inefficient way of the compressor working. The problems with this arrangement are as follows:

  1. When a compressor is running at its full speed it is very inefficient. The relation between efficiency and speed is that efficiency varies inversely as the square of the speed. To put it simply, if the speed is double then the efficiency reduces by a factor of the square of the speed, that is efficiency reduces by 4 times. So, the slower the compressor runs, the more efficient it is.
  2. Start up current in any motor is very high. When a normal AC is on, the compressor starts and stops several times, minutes apart. This start stop cycle consumes a lot of power and is very inefficient.
  3. The temperature in the room is not a constant comfortable level. It is varying between a minimum and maximum temperature of several degrees apart, and the room is constantly changing from uncomfortably cold to uncomfortably hot, with the set comfort temperature zone in the middle of these uncomfortable temperature range.


The graph below shows the room temperature of a normal AC compared to inverter AC

Inverter AC running costs are cheaper and it is more comfortable than regular ACs
Benefits of inverter AC compared to normal AC

Why inverter AC better than normal AC

An inverter compressor in AC solves all the disadvantages of the normal AC and saves more than 40% on electricity bills as claimed by some of the manufacturers. Apart from this the inverter AC is very silent compared to a normal AC and the compressor lasts much longer, because it is never stressed.


When an inverter AC is put on, the compressor starts slowly and picks up speed gradually and reaches a higher speed than a normal AC for a short period to cool the room faster than a normal AC. Once the set temperature of say 22 degrees C is reached, the compressor slows down and has just enough speed to maintain the set temperature of the room. The compressor never stops while the AC is on; it just runs very slowly cooling the room just enough to maintain the set temperature. The variance in temperature in the room will be in decimals, in our example of 22 degrees it may go down to 21.9 and up to 22.1 degrees, which is negligible.

Inverter AC saves Electricity with lower monthly power bill

A normal one ton AC uses on an average about 1.25 units of electricity every running hour. This of course will vary depending on many factors like outside temperature, insulation factor of the room, etc., but 1.25 units of electricity is about the average. The 1 ton inverter AC power consumption per hour would be about 40% less than that of a one ton normal AC. That means the power consumption of a 1 ton inverter AC will be about 0.75 units of electricity. Assuming 8 hours of operation per day, that will be 10 units of electricity per day for normal AC and only 6 units per day for a 1 ton inverter AC.


Thus the monthly power bill for a normal AC, assuming Electricity cost at Rs.5- per unit, will Rs.1,500- per month compared to Rs.900- for a 1 ton inverter AC. Therefore the saving in electricity cost of a 1 ton inverter AC for a month is Rs.600-, and Rs.7200- per year.

In the above example let us say that the 1 ton inverter AC costs Rs.10,000- more than the normal 1 ton AC, then with the monthly electric bill saving of Rs.600 per month, you will have paid off this extra money for the inverter AC in a matter of about one and half years. If you use the inverter AC for 5 years, then you will have saved more money with the inverter AC than the cost of the AC itself.

Apart from the cost savings in the running costs of an inverter AC, you will have a much more silent AC. The room temperature with an inverter AC will be always comfortable without the room becoming too cold for some time and then becoming too warm like with a normal AC.

Best 1 ton and 1.5 ton inverter split AC in India

We have a dedicated page showing all available models of inverter air conditioners available in India and this is the clickable link to it: Best inverter split AC available in India.

One important consideration when buying an inverter AC is the Star Rating of inverter ACs. We have pages explaining what star rating of inverter ACs mean and also how much more monthly electric bill you can save by buying a 5 star inverter AC instead of a 3 star inverter AC.

This is the link to best online deals in inverter AC on Amazon.in



Advantage of buying AC, Fridge, Washing Machine, etc. online

Buying online fridges, washing machines, dishwashers and other major kitchen appliances is now the better option in India, just like it is in the USA and other advanced countries. There are several advantages of buying online. First of all, you get unbeatable bargain prices. Secondly, you get new and genuine products. Other benefits include no interest EMI payments, able to return the product for a full refund if not satisfied, etc.

Just to give you an example, below are some of the benefits Amazon India, the leading global online retailer, offered in India during their last sale. The same deals are not always available, but it is a good idea to check this link to the special offers page on Amazon.in India website.

Amazon India Logo Link to Amazon.in deals


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