Electricity Saving Tips For Homes And Offices

How Does an Air Conditioner Work – A layman’s explanation

By on August 12, 2016

Whenever working of an air conditioner is explained, it is explained by detailing how a system with the condenser, compressor and evaporator works. Although the explanation is technically absolutely correct, but many people find it hard to understand. No wonder we at Bijli Bachao get a lot of questions from people asking various things like: “Can I use my AC to cool two rooms?”, or  “Why is it taking so much time for the temperature to come down?”, or “Why is right sizing of an AC so important before making a purchase?”. It is quite valid that people ask these questions because they are not able to visualize how an Air Conditioner works.

Now physics explains the basis of how various things in this world work and the best thing about physics is that many of its laws work very similar at the sub-atomic level as well as at the scale of the universe. Just like the interaction between sub-atomic particles is similar to the interaction between planets and stars, similarly, heat energy (or heat transfer) works in very similar ways to potential energy (or mass transfer). We will use this basis to explain Air Conditioning in very basic terms.

The Analogy

Analogies always make things simpler to understand and easier to visualize. And here also we will use an analogy to explain the concept. To understand an Air Conditioner, just imagine a big tank full of water. This tank is open to atmosphere and it is getting water from multiple sources:

  1. Rain is filling it up.
  2. Someone has opened up a tap on top of it.
  3. Etcetera (will leave to imagination :) ).

Bring Down and Maintain Height

Now the task at hand is to maintain the “water level” of the tank, for which you install a tap at the bottom of the tank.

Why at the bottom? Because the pressure of water is maximum at the bottom for the water to flow out fast.

Why does water flow out fast at the bottom? Because the height of water creates a pressure difference causing it to come down in case the tap is opened.

Connecting to the Original Problem

Now let’s connect the illustration above to situation in air conditioning:

  • A room or space to be air conditioned is similar to the tank illustrated above.
  • The heat in the room is analogous to the water in the tank.
  • The tank is getting water from various sources. Similarly, a room gets heat from external sources like: “Heat from Outside the room through the walls”, “Hot air flowing in”, “Sunlight coming in from windows”, “People in the room”, “Appliances in the room”, etc.
  • Just like we need to maintain the height of water in the example, we need to maintain the temperature in a room.
  • The tap used at the bottom of the tank in the example above is analogous to “Air Conditioners”.

Myth Busted: Air Conditioner does not generate cooling, it removes heat from the room and throws it outside. It is just like a tap as shown above.

Condenser, Compressor And Evaporator

(Source: Wikipedia)

(Source: Wikipedia)

An Air Conditioner has 3 components:

  1. Evaporator (in the indoor unit of a split air conditioner): It is a heat exchanger coil that takes heat from the room and moves it outside. It is shown as number 3 above. The heat is absorbed by the refrigerant and in turn, the air inside the room becomes cool.
  2. Compressor (in the outdoor unit of a split air conditioner): It compresses the hot refrigerant gas into a hot liquid refrigerant which is ready to exchange heat from outside (the room).
  3. Condenser (in the outdoor unit of a split air conditioner): It is a heat exchanger coil that throws the heat collected from the room (by the refrigerant) outside the room.

In this whole process, a key role is played by the refrigerant which gets compressed from gas to hot liquid at a high pressure in the compressor, changes to cool liquid in the condenser, gets sprayed in the evaporator and absorbs heat (from the room) and gets converted into gas again ready to get compressed.

Bottom line: Just like a tap takes water from the tank and throws it outside. An air conditioner takes heat from the room and throws it outside.

What’s the role of Thermostat?

As we mentioned above, the height of water in the tank is analogous to temperature in the room. Now imagine you have a sensor that controls the tap and shuts it on/off when the height is maintained. A thermostat does a similar job, it shuts off the compressor when the desired temperature is achieved.

How to explain the difference between Inverter Technology and Fixed Speed Air Conditioner?

If we take the same analogy, a fixed speed air conditioner is one where the tap is either completely open or completely closed. So water (or heat in our case) is flowing out at full speed or not flowing at all.

Inverter technology air conditioner is similar to a tap where you can control the flow rate. You can either slow down the flow of water (or heat in our case) or increase the rate of flow, depending on how much you need.

Obviously, you can get more precise water level when you have more control over flow rate. Similarly, you can get more precise temperature control when you have variable heat flow.

What is Cooling Capacity of an Air Conditioner?

We talk about tons of air conditioning or cooling capacity in watts. It is analogous to flow rate in our analogy.

1 ton Air Conditioning = 12000 BTU/hr or 3517 cooling watts

This is the rate of taking out heat just like a tap will have a flow rate in liters/min. The more the flow rate, the faster the tank will empty. Similarly more the tonnage or cooling capacity, faster the AC will cool.

A bigger tap will empty the tank faster, similarly, a bigger AC (more tonnage) will cool a room faster.

Why is right sizing of Air Conditioner important?

Imagine you put a super big tap for the tank. Water will pour out of the tank at a super fast rate. You will find it very difficult to maintain the right height, especially if you cannot control the flow rate.

Or if the tap is too small, it will not be able to bring down the height of water and the tank will keep getting filled.

Similarly, an oversized AC can cool really fast, but then if you have a fixed speed oversized AC, then it will have difficulties in maintaining the right temperature as it is either on or off. By the time thermostat senses the right temperature, it would have become cooler. So it results in over cooling.

In the case of Inverter Technology AC, you still have control over flow rate and thus the rate of extraction of heat will slow down as the thermostat senses that the temperature is closer to the one desired.

If AC is undersized, then it will not cool the room because there is too much to take out.

Can an AC be used to cool two connected rooms?

This case is analogous to asking, can my tap empty two connected tanks. Yes it can, but then the tap has to be bigger. Similarly, an AC can cool two rooms, but then you need a bigger AC that can handle the heat for both the rooms.

Why do you need to keep a room completely closed while air conditioning?

Imagine if your tank gets connected to a river, which is like an infinite flow of water. There is no way a tap can maintain the height of water in such case. Similarly, keeping a room open while air conditioning is like leaving it open to an infinite source of heat. There is no way an air conditioner can maintain the temperature of a room if the room is left open.

Why is my AC taking so much time to bring down the temperature?

This is one of the frequently asked questions that we get: My AC was able to bring down the temperature from 32 to 25 degrees in an hour, but it took 6 hours to bring it down further to 22, why is that?

To explain this, just imagine water flowing out of a tap from a tank. As the height of water decreases, the flow rate of the tap decreases. So much so that when height nears the bottom, you have to tilt the tank to make it flow faster. This is because the height defines the pressure with which water will flow out.

Similarly, the rate of heat flow also depends on the temperature levels we are trying to maintain. Cooling will be faster when you try to get it down from 32 to 25 degrees. But it will be much slower from 25 to 22 degrees.

Most ACs are designed in such a way that if the AC is right-sized, it should be able to bring down the temperature of the room to 25 degrees (which is a very comfortable temperature) in a reasonable time (say about 1 hour). Temperature below 25 are quite chilly and if you really want to achieve temperature sub 25 really fast, then you need to go for an oversized air conditioner.


With this post, we tried to explain the concept of air conditioning in a simple way. We hope that this helps you visualize how it works. If in future we get questions that we can connect to this analogy, we will keep adding those to this page. Do let us know your feedback/questions in the comments below.

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If my room temperature is 80 degree Fahrenheit and I turn on the ac and set temp to 74 degree Fahrenheit and outside temp is 104 degree Fahrenheit. what is the impact on electricity bill and the electricity consumed?
whether the energy is consumed more in this situation.

Abhishek Jain (Mod)

Electricity consumption will depend on the heat load in the room and energy efficiency of the air conditioner. To give you an analogy, if someone asks: I want to lift a box by 3 ft, how much energy will be used? You cannot give an answer without knowing the weight of the box and the efficiency of the machine lifting it. Similarly, difficult to say without knowing the heat load and efficiency of the air conditioner.

Also is energy consumed more or less depends on the temperature difference. You will need more energy to lift a box by 6 ft as compared to lifting it by 2 ft. In your case the temperature difference is 6 fahrenheit. Energy consumption will be more if the temperature difference is 12 fahrenheit and less if it is 2 fahrenheit.


Hi... I am looking for solar vapour absorption system for domestic application [2500 square feet approximately], centralised air conditioning. Is there any company in India which does the same? For night time, I am planning for switching over to normal electricity/bio-gas mode, as the case may be.


Hello mr Jain. I have a problem which i would like to present here.

I recide in kochi, kerala. Recently i brought a 1 ton inverter AC of reputed company. Room size is 130 sqft, well insulated. 2 adult and child. Nominal heat load.
Set temp to 26 deg, mode cool, fanspeed1. From day 1 i have been observing that discharge air is very cool. By morning it was felt very chilly,all the items in room are very cold, including floor tiles. It has been the same even when i set temp to 29 deg. Yest i did some experiment by recorning the temperatures. I set temp as 28 deg, room ambient temp was recorded as 32. But the discharge vent temp was 14 deg. Later the ambient temp reached 28 deg still the discharge vent temp was in 13-14 deg. In the morning i was alarmed to see the discharge vent temp as low as 8 deg.

As it is an inverter ac i understand the compressor is always on and is managed by adjusting speed and flow rate. But this is some malfunctioning.

Kindly advise way ahead.

Abhishek Jain (Mod)

Looks like the thermostat is not working properly. I would suggest you to call the customer care and ask them to send an engineer to check the thermostat of the AC.


Sure. Already initiated the service request. Will update status post visit.

Meanwhile, the temp sensor of indoor unit is working fine. In fan mode the temp was even changing gradually from the set temp, verified by measurements.

Planning to do an energy consumption measurement. I presume the unit is continously working in full load.

Thanks for the response.

natarajan parameswaran

Inverter AC Model 3CNH12TAFU - 3 means 3 star BEE rate, C means cool only likewise...explain the full abbreviation so that we know the exact meaning for the model we choose pl...

Abhishek Jain (Mod)

Hello Mr Natarajan,

It is extremely difficult to explain the naming convention of various brands. There are a few patterns that you can see looking at the AC type, etc, but not a whole lot of information. Certainly a inverter AC model from Bluestar that starts with 3 or 5 and this number represents star rating. C after the number represents cooling only and H is hot and cold. Model number ending with U is copper condenser and X is aluminium condenser. 12 is 1 ton, 18 is 1.5 ton and 24 is 2 ton. T is the series, like P, N and C as well. But I am not sure what NH stands for or AF stands for.


Dear sir
I have samsung MAX(G) AS183UGF 1.5 Ton 3 Star Split AC with power consumption of 1870 watt.From last two days it create problem and technician suggest go for gas filling.As it consume more power can i go for new ac.It is 6 year old model.In adverse condition it work well but my only concern is power bill.The avg temp of my city 35 to 40 with use 8 hour a day.Also humidity is other factor along with depreciation of ac unit.please suggest best option.

Abhishek Jain (Mod)

Hi Mudit,

Gas replacement costs would not be too high. But your AC is certainly old and not very energy efficient. It will be good to replace the AC as you can get options that can reduce your power bill.



Thanks for your valuable post on understanding AC working process.

I am planning to buy 1.5 ton 5star inverter ac. I need an ac that is corrosion resistant and energy efficient and cheapest & best in this class.

Abhishek Jain (Mod)

I'm planning to buy a 1.5 ton 3 star inverter AC with copper coil but hardly any option with this combination is available in the market, can you suggest any model? Thanks in advance.

Abhishek Jain (Mod)

You can get a lot of options:

Hitachi RAU318AWEA or RAU318EWEAS (Flipkart Link: http://fkrt.it/E~nGo!NNNN ) or RAU318KWEA (Flipkart Link: http://fkrt.it/9ZpBJTuuuN )
Daikin FTKH50 (Flipkart Link: http://fkrt.it/E~D7e!NNNN )
or Blue Star 3CNHW18CAFU (Amazon Link: http://amzn.to/2lCcTks )


Thanks a Million Abhishek for your valuable inputs. It was great
to get a response that quick.

Thanks & Regards,

Kersi D. Cooper


Hello Bijli Bachao team,

I want to buy 2 AC’s for my
residence. I stay in Bandra(W), Mumbai. There is no direct sunlight on my flat
as I live on the 1st Floor.

The sizes of my rooms are

Hall 18x11x10

Bedroom 18x10x10

I have zeroed in on Mitsubishi Inverter Split Ac.

For Hall MSY – GK 18 VA (1.5 Ton)

For Bedroom MSY
– GE 13 VA (1 Ton)

I have 4 queries.

Are Mitsubishi AC’s totally Imported as their
prices are way above from the rest.

Do both the above models have Copper condensers?

If possible kindly give me the Official
Mitsubishi Showroom & Service Centers contact address & telephone

Your personal comments on the above models as
far as Mitsubishi Quality and after sales service specifically of the above 2

Abhishek Jain (Mod)

Here is my response:

1) There are 2 mitsubishis: Mitsubishi Heavy Industries and Mitsubishi Electric. Both are imported.

2) MHI mostly has copper condensers but Mitsubishi Electric has mixed models. You have to check the model specifications. Mitsubishi Electric has not mentioned about the two models on their website ( http://www.mitsubishielectric.in/air-conditioners/msy-ge-gk-series.php ). Typically if it is aluminium, they mention Multi Flow Condenser in it. So I assume it is copper, but I am not sure.

3) You should get the details on their website: http://www.mitsubishielectric.in/air-conditioners/room-air-conditioners.php

4) Mitsubishi's Product Quality is great however I cannot comment on their service as service is location specific. If they are in your area then your local dealers can give you better feedback.
As far as energy efficiency of these two models is concerned, the EER numbers of both these models are excellent, so they are certainly very energy efficient.


Hello Bijli Bachao team,

Kudos to all the work you have done to come up with all these information. I have learned a lot from your articles. The calculator that tells the capacity of the a/c for a specific room is another huge advantage to us,the readers.

However,I am trying to learn more about ground-source heat pump a/c (geothermal a/c) and water source heat pump a/c. As in the companies that provide these in India,it's initial cost,maintenance cost and routine. My search here,didn't yield any result. Can you guys post an article on ground-source heat pump a/c (geothermal a/c) and water source heat pump a/c,please? Or share the link,if you have done that already? Any information would be helpful.


Abhishek Jain (Mod)

Hi Avinash,

We have tried covering appliances that are more in demand (and have high impact on electricity consumption) and that is why you do not see much on other things. Heat pump itself is something new in India and the ones that are popular in market are the ones that run on electricity. Currently, we have not done any research on Geothermal heat pumps. So it will be difficult for me to help you out.


Hi Abhishek sir can you explain me the difference between three phase ac and single phase ac i mean merits and demerits which is better in terms of power consumption and maintanance

Abhishek Jain (Mod)

Electricity consumption depends on the appliance and not on type of connection. For electricity consumption you need to know the wattage of appliances. For more info on three and single phase, you can read this: http://www.bijlibachao.com/electricity-bill/what-are-single-phase-and-three-phase-connections-and-how-to-choose-between-the-two.html


Single phase AC requires a single phase connection. Three phase AC will require a three phase connection.
3 phase AC is a rare sight for domestic purpose as it requires additional complexity due to three phase connection.
Good things about 3 phase AC
1) 3 phase AC induction motor is more robustas they need no capacitor (Single phase motor need a capacitor to start and run as single phase can't generate an effective starting torque, the capacitors fail somerimes) and are often made more efficient than single phase motors.
2) The load is equally distributed in 3 phases. So each phase has to carry 1/3rd of rated load. Suppose the AC draws 12 amp current at peak load. Then each phase will carry ~4 amp current. So wires of each phase carry less current and needs lesser thickness.
3) If you have 3 phase connection then a 3 phase AC allows an even distribution and load among 3 phases.
Difficulties you will face
1) Needs a knowledgeable electrician to make connection for your AC
2) The fixed meter charge for 3 phase connection is generally higher than single phase connection.
3)You need even voltage distribution among 3phases. If the difference is high or any of the phase loss power then AC will stop functioning or even malfunction. So you need magnetic relay operated motor starter for your AC which will automatically disconnect, if any of the 3phases loss power.

In Industrial environment 3 phase AC is more preferred as it evenly distribute load amongst 3phases. For domestic purpose a single phase AC is more preferred because of the availability of single phase power points. There is not any huge difference regarding efficiency or service life of both types of ACs. Both types of ACs require routine maintenance.
If you are looking for an energy efficient AC for domestic purpose then look for inverter AC with higher ISEER value.

Abhishek Jain (Mod)

Interesting. I didn't think of it this way. I thought he was asking about alternating current (AC) and not Air Conditioners :) .


Oh! I thought maintenance and consumption are related to machine and not the system. Yeah, he was probably asking about power distribution system.


Dear Sir .

I would like to know the diffrenec between Single Inverter ACs and Dual Inverter ACs . Recently i saw online companies like LG and Panasonic launched Dual Inverter Split AC Models .i would like to know whether Dual Inverter AC Models more Energy efficient than Single Inverter AC Models .

Its very Confusing .

Also which Brand is better in terms of Highest Energy Saving in Dual Inverter Technology ACs with Maximum Features .

Also is sharp planning to launch ACs again in india with similar kind of tecnologies .

Thanks & Regards

Raaj K

Abhishek Jain (Mod)

I would say do not look at the type "Single" or "Double" inverter if you are concerned about the energy efficiency. The most important thing to look at is the ISEER on the BEE label. If there is no BEE label, then look and compare the EER of the models. "Inverter" is just used in the compressor, which certainly makes it energy efficient. But energy efficiency is not dependent only on the compressor, but on the whole design which includes condenser and evaporator design as well (and also on the refrigerant). The whole system energy efficiency reflects in ISEER or EER.

So do not get confused, just compare the ISEER numbers and the one with higher value is more energy efficient.

Also energy efficiency is different for different models, so one cannot say that one brand is more efficient than other. You have to compare models. Top most efficient models are listed on our website on this link: http://www.bijlibachao.com/top-ten-appliances/best-air-conditioner-ac-window-split-hitachi-lg-carrier-samsung-electricity-consumption-tonnage-in-india.html

The data on this link is purely based on energy efficiency data available from BEE. It does not include any personal bias that we have for various brands.


Dear Sir .

I would like to know the diffrenec between Single Inverter ACs and Dual Inverter ACs . Recently i saw online companies like LG and Panasonic launched Dual Inverter Split AC Models .i would like to know whether Dual Inverter AC Models more Energy efficient than Single Inverter AC Models .

Also which Brand is better in terms of Highest Energy Saving in Dual Inverter Technology ACs with Maximum Features .

Also is sharp planning to launch ACs again in india .

Note : - Sorry to write this question out here .But i think you should answer this question on your website in AC section .May be in october lot of people might come up with this question Since AC purchase Desicion is confusing after this new dual inverter technology has launched .You decide where to answer .

Thanks & Regards



Hello Abhi,

I just wanted to inform that ,i was purchased Daikin AC 1 TON 5 star 2015 Model, i have been using more than 1 year for the past. while operating AC continuously more than 1 hour . i am getting some stink smell , later if i reduce the AC temperature it goes away. what would be the cause ?
can you suggest. for ex:starting 26 temp with 1 hour getting good air,after getting some annoying smell and then i just reduced like 24 it goes away like that happen every day,kindly suggests the solution on this.

Abhishek Jain (Mod)

Foul smell comes when the AC is short cycling (or the compressor is switching off too quickly without being able to remove humidity properly). This typically happens when the AC is big for the room. The heat load may be less and AC would be bigger.

So when you keep the AC at 26, the amount of heat to be removed is so less that the compressor switches off very quickly. This results in in effective removal of humidity and thus it results in foul smell. When you keep it at 24, the amount of heat to be removed is more and thus the compressor runs longer and also removes humidity effectively and does not create a foul smell.

Looks like your room is quite small and the AC is quite big for the same.


What u recommend?...whats the best temperature to maintain to avoid smell?

Abhishek Jain (Mod)

With the same AC to avoid the smell you need to keep it at 24 (as you have observed). Also, please make sure that you get the AC serviced. Any mould or bacteria inside the indoor unit should get cleaned properly. Try to see if you can increase the temperature after cleaning.


very good knowledge, thank a lot.....................


ac uses


I am planning to purchase Voltas 183 Cya 1.5 Ton 3 Star Window AC, for commercial purpose. Now I want to know -
1. How is the cooling performance of this AC
2. In terms of energy efficiency, how is the performance of this AC
3. How is the maintenance cost and durability of this AC In long term (10-15 years)
Kindly Suggest.

Abhishek Jain (Mod)

Hello Mr Shikhar,

Window ACs are the least efficient of types available in market and on top of that you are choosing for a BEE 3 star rated window AC. We do not recommend going for anything less than BEE 5 star rated window AC (because we do not recommend going for less than BEE 3 star rated split AC). On top of it you are on a commercial connection where both usage and tariff will be high. So, I would not recommend going for this AC.


Dear Sir, I am using hitachi 1.5 ton zunoh 300 AC, I am experiencing foul smell from indoor unit.have complained to hitachi several times but they are not able to figure out the problem.I am sure the water passage is clear and dust is removed from AC. But still the smell is there , especially bery bad smell when temp set above 24 degree with high fan speed.we are not able to sleep.:(

I lost trust with hitachi service.hope i can get help from you. What could be the reason for those foul smell ? What should i ask the service engineer to check particularly ? Kindly help.

Abhishek Jain (Mod)

Hello Mr Anand,

One of the common reasons for bad smell is when AC is not able to remove humidity properly. Along with removing heat, it also removes humidity. When the hot air of the room comes in contact with the refrigerant in the evaporator, it losses humidity (which gets collected as water and is drained outside). But if the AC is too big for the room, then the compressor cycles are short (room gets cooled very quickly). In that case humidity removal is not very effective and it leaves bad smell.

What is the size of your room (length, width, height) and which city are you in? Also does any of your walls or ceiling directly faces sun?

My guess is that 1.5 ton AC may be big for your room.


Thanks for very fast reply . I have 10 x10x 10 roof top room. Other than roof no walls are directly expose to sunlight. Living in chennai. And earlier we had samsung 1.5 ton ac , no smell observed when using it.

Abhishek Jain (Mod)

1.5 ton sounds quite big for a 10x10x10 room in chennai. This is the only reason I can think of. I am not sure why your previous AC did not have the smell. Because even that is big. Did you get your AC cleaned properly? I hope there are no clogs in the drain or accumulation on the evaporator coil (indoor unit).


Hi abishek, yes am servicing ac every 3 months. I will check the coils , water drain massage after they clean it. It looks clean. Smell increase when we keep the temp as 26,27 ,28 ... Degree if we keep as low as from 24 degree the smell disappears . I agree with your explanation of dehumidification. Is there anything specially i need to check ji ?

Abhishek Jain (Mod)

When you keep the temp as 26,27,28 the compressor does short cycles, from that I mean, the compressor runs for very short time because heat to be removed is very less. When you keep it at 24, the compressor runs for decent amount of time and thus it is able to remove humidity. So clearly the problem is that of oversizing. You need a smaller AC. 1 ton would be good.


Thanks a bunch abishek.just a final question.that odour smell harmfull to us ?

Abhishek Jain (Mod)

It will be better to get rid of it. If it is not comfortable then it is certainly harmful.


Okay abishek. Thanks a lot for your guidance.


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