Electricity Saving Tips For Homes And Offices

Ideal Air Conditioner temperature for electricity savings

By on September 22, 2014
This article is also available in these languages: hi Hindi

Buying an air conditioner once considered a sign of luxury, is now becoming quite common in India. Many urban homes are equipped with air conditioners in one or more rooms. But everyone who owns an air conditioner knows that it comes at the cost of increasing electricity bills. Although cooling does take a lot of electricity but taking effective steps can surely get it down. One of the main things that can help is maintaining the right temperature for the air conditioners.

Air Conditioner Temperature

How does an air conditioner work?

For most people, air conditioner just throws cool air at the temperature one sets it at. But does it really work that way? In fact air conditioner during cooling process, takes the indoor air, cools it  by passing it through evaporator coil and throws it back in the room. It is quite opposite to how our good old air coolers used to work. Air coolers used to take outside air, cool it with water and throw it in. But air conditioners just work on internal air.

How does the thermostat work?

If you set the thermostat at 18oC (64.5oF), does it mean that the air conditioner will cool the room faster than if set at 25o(77oF)? No. The thermostat just checks the temperature of the air inside the room and stops the compressor when the temperature reaches the desired level. This means that the compressor will work longer if the temperature is set to a lower level, i.e it will work more and use more electricity if temperature is set to 18oC (64.5oF) than if it is set to 25oC (77oF). This is because it will take less time for air to reach to 25oC (77oF) than 18oC (64.5oF) as the compressor is working with the same power or wattage.

What happens when the compressor stops?

The air conditioner just blows the fan when the compressor stops and thermostat reaches the desired temperature level. At this stage the electricity consumption is only for the fan which is running and not for the compressor. The compressor will start again when the thermostat detects that the temperature has increased again from the levels that are set. Compressor is the most electricity consuming component of an air conditioner.

What factors impacts electricity consumption of Air Conditioner?

There are 4 factors that influence the electricity load:

1) Indoor air temperature

2) Outdoor temperature

3) Thermal insulation of the room

4) Temperature setting of the air conditioner.

If the difference between temperature desired and indoor/outdoor temperature is huge, then the air conditioner will need lot more electricity to cool the indoor air to desired temperature as the compressor will run for longer duration. If the temperature is set at 18oC (64.5oF) and the outdoor temperature is 38oC (100oF) then the electricity required will be lot more than when thermostat temperature is 24oC (75oF) and outdoor temperature is 38oC (100oF). As per study by ACEEE (American Council of Energy Efficiency Economy), increase of each oC can save 3-5% of units consumed. This can considerably bring down the units consumed per month in the electricity bill.

What is the ideal temperature that should be set on thermostat?

Having said that, increase in temperature does not reduce the comfort level. In fact as per ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers), the ideal temperature for thermal comfort is between 23.5oC (74.3oF) and 25.5oC (78oF) in summers (depends on several factors as listed on wikipedia). Thus setting the temperature to 24oC (75.2oF) saves on electricity bill and provides good comfort. Using ceiling fans along with air conditioners can additionally help in increasing the thermostat temperature.Air Conditioner Temperature Infographic

Does “Quick Cool” option in Air Conditioners help?

Setting an air conditioner to quick cool sets it’s temperature to 18 or 16 oC (64.4oF or 60.8oF. This means that the compressor stops only when indoor temperature reaches this level. But while coming down from 35 or 40 oC (95oF or 104oF) it would have surely crossed 24oC (75.2oF) which is a comfortable temperature. So using “Quick Cool” option does not help because more electricity is used to get the temperature down to 18oC (64.5oF) whereas compressor would have stopped in between if the temperature was set to 24oC (75.2oF) thereby consuming less electricity.

How do old air conditioners without thermostat work? 

Old air conditioners without thermostat have high, medium and low cool options. As we learnt earlier that compressors of air conditioners work in binary mode (either they are on or off), an air conditioner without thermostat does not control air temperature. The high, medium and low options just changes the air conditioner fan speed. High means that air conditioner will throw more air and low means that the fan speed will be slow. The options do not change the temperature of the room, nor do they change the electricity consumption. 


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There Are 69 Comments

  1. Bhanoji says:

    Let me explain why the inverter technology air conditioners not having star rating….

  2. Prasanth KR says:

    Which is the best option for Air conditioner- Swing or Fan?

    • Abhishek Jain says:

      Both serve different purpose. Swing helps in throwing the air in all directions. Fan blows the air. If you are seated at one place, you can off the swing. Keeping fan speed low will decrease electricity consumption but you do not feel cool enough when you don’t get air. So if you use ceiling fan then you can keep AC fan speed low. But if you do not use ceiling fan, keeping fan speed to high is better.

  3. Vivek Thaker says:

    Hi Abhishek,

    I am living in 2BHK tenement at Rajkot city, Gujarat where pick summer temperature is 45c. I am going to purchase two split ac for bedrooms further detail of my bedrooms and query here bellow.

    # Bedroom 1: Size 8’ X 9’, Ground floor with open terrace and three sides cover, 15sq ft. window in west no direct sunlight on window.

    Occupancy: Single person

    Usage: 2Hrs. Day time and 4-5Hrs. at night

    #Bedroom 2: Size 8’ X 11’, First floor with open terrace and three sides cover, 10sq. ft. window in east balcony no direct sunlight on window.

    Occupancy: 2 Adults and 1 Child

    Usage: 7 to 8 Hrs. Night use only

    Query

    1. Does 0.75 or 0.80Ton ac is ok for bedroom 1.
    2. 3 Star, 5 Star or Inverter, Which ac is more efficient for my usage.
    3. Please suggest few options with model no.

    Do take your time.

    Thanks.
    Vivek Thaker
    [email protected]

  4. shyam says:

    Hi Abhishek,

    I am living in Delhi, bought Hitachi RAW KUD 1.5 ton 3star window Ac in the beginning of May 2014 to fix into my room which is located on the top floor(3rd floor) of the building having 1 sun facing wall , i was quite satisfy with the performance of my AC during the extreme session of May & June despite consuming more electricity…..12-14 units per night ..

    just 3.5 months over and we are sitting in month of August, where the average temperature of Delhi is 30 to 31 degree, sudden i have noticed a change into the performance of my AC, now it takes too much time to spread the chilling into the room, some time its compressor takes more than 1 hour to cut off … though i have set the temperature on 25 Degree…..

    please advise …

    regards
    Shyam

    • Abhishek Jain says:

      Hi Shyam,

      It sounds like manufacturing defect. It should not happen this way. You should call up Hitachi and register a complaint for this.

    • Charanpreet says:

      Hi Shyam,

      In Delhi month of August is very humid as compared to May and June, And High Humidity effects the air conditioning very badly. As during dehumidification, water vapors present in air releases the Latent heat and changes to liquid form. This Latent heat again increases the air temperature. So in humid environment compressor of air conditioner will be working much much more for decreasing the temperature by same range, than it was working earlier when it was less humid.

  5. Jamey says:

    What differences does location of thermostat have on energy consumption? More directly mine is in the corner of a short hallway.

    • Abhishek Jain says:

      Hi Jamey,

      Thermostat should be located away from direct sunlight/windows. It should be on the interior wall and it should be located where natural room air currents–warm air rising, cool air sinking–occur. There should be no furniture around it that blocks movement of air around it.

      • Jamey says:

        I am thinking of moving the thermostat out of the hallway into the family room wall next to the hallway. It’s the biggest room, no corners. As it is now the return is sitting right under the thermostat; if I move it I think the return could still move air past it coming from the family room which is centralized in the house. Good idea?

        • Abhishek Jain says:

          Hi Jamey,

          I am not able to visualize properly. However as long as the thermostat is not covered and it gets to sense the room temperature properly, keeping it in the family room will be better as it will work according to the temperature in the family room.

  6. Josepha says:

    what is usually the temperature of the air emitted from the AC? as i am suspecting the the air coming out of the wall unit is not cool as it should be. thanks

    • Abhishek Jain says:

      Hi Josepha,

      It will depend on the cooling capacity of the air conditioner. Cooling Capacity is the rate at which the AC can remove heat from air. If this rate is more than the rate at which the air gains heat from outside, then the AC can reduce the temperature of air as much as you want it to (that is what the thermostat controls).

      Hope this helps.

    • Abhishek Jain says:

      If you feel that the air coming out of your AC is not cool enough, then it means that its cooling capacity has reduced and the rate at which it is removing heat from the room is lesser than the rate at which the air in the room is gaining heat.

  7. Anumakonda Jagadeesh says:

    Excellent. Yes. Air conditioning consumes much of power mostly in Cities. According to one study in Mumbai out of 2700 MW Consumption Air conditioning share is 1000 MW !
    Dr.A.Jagadeesh Nellore(AP),India

  8. Karyn M. Bruce says:

    My husband keeps changing the thermostat all day long. When we go out, he sets the thermostat at a higher temperature (from 76 to 80). When we come home, it goes back down. When he go to sleep, it goes up. When I get too hot, I change it to make it cooler in the house. When he sees that, he sets it higher again. I believe that this constant change in A/C temperature affects the electric bill. Does it?

    • Abhishek Jain says:

      Hi Karyn,

      It will depend on the temperature outside. In winters if you keep temperature high, then heating will take a lot of electricity. In summers if you keep temperature low, then cooling will take a lot of electricity. Frequent change does not impact electricity bills, but the temperature difference between the room and the outside does.

  9. Usman says:

    Hi. I have two rooms.One is of 160square foot and the other 170 square foot. I am currently using a 1 ton A.c.I have installed a ventilating fan 250mm in the wall between the rooms which transfers cold air from one room to another. The thing is that the other room’s temperature becomes moderate, better than outside temperature but it does not cool.There is still a marked difference in temperature between the room containing the A.c and the one being controlled by the fan. I wanted to know if shifting to a 1.5 ton A.C would increase the cooling in the room controlled by the ventilating fan ?

    Kindly let me know.
    Thank you.

    • Abhishek Jain says:

      Hello Mr Usman,

      AC works very differently from an air cooler. Cooler takes air from outside, cools it and throws it inside. Whereas working of AC is very different. It does not take any air from outside, in fact it takes inside air, cools it and sends it back. The tonnage or cooling capacity of AC depends on the total amount of air inside a room. If the room is small you need smaller capacity, if room is big, you need bigger capacity. And that is also why it is always recommended to keep the doors and windows of the room closed while using AC because any amount of extra hot air from outside will increase the load on AC which will either result in extra electricity consumption and/or in inadequate cooling.

      The sizing is done not just based on size of the room but also on several other factors like: number of people, number of appliances in the room, etc as everything adds to heat in the room. It also depends on city where you live in as some cities are hot and some are cooler. Now 1 ton AC is small for 160 sq ft room even in cities like Mumbai where temperature is not high but humidity is high. And what you are trying to cool is 160+170=330 sq ft. And 1 ton AC will never ever cool 330 sq ft space. Even 1.5 ton AC would not work.

      The most ideal setup would be to have individual AC in each room for their individual size.

      • Usman says:

        Hey Abhishek,
        Thanks for your reply.
        I have installed 1.5 ton A.c . Its working very well . The thing is even if i keep the temperature at 28degrees,it gets very cold and i have to use a blanket.I want to know should I switch to a 1 ton A.c since I dont think a 1.5 ton A.C would be used to its full capacity. And whether a one ton A.c would be a cheaper option bill wise? I am using the 1.5 ton A.c at a higher temperature fluctuating between 26 to 30 degrees.
        The room dimensions are the same.160sq foot and a 170 square foot room linked together by a ventilating fan in between them.
        Thank you.

        • Abhishek Jain says:

          One ton AC will certainly use lesser electricity as compared to 1.5 ton AC. It will also not cool as much as what a 1.5 ton AC does.

  10. JACKSON KOMBAN says:

    hello Abhishek… appreciate your article.. I own 1 ton Godrej *** AC, by reading your article i keep temp @ 25 nowadays i wanted to know about the ideal mode and fan speed… the AC is installed in my bedroom say a standard family bedroom.the different modes are FEEL COOL DRY FAN & HEAT we often keep it in COOL MODE. the different fan speeds are AUTO HIGH MID LOW we often keep it in AUTO. are these ideal settings or should i change them. what you suggest ?

    • Abhishek Jain says:

      Hi,

      It truly depends on what keeps you comfortable. You should certainly derive the convenience that you need from your AC. 24-25 degrees is a good setting to keep. If you can keep it higher than that without being uncomfortable, nothing like it. Also looking at the number and kind of modes in your AC, it is better to keep it in cool mode. Dry mode would be good if you have high humidity. Also same for fan, if you are comfortable with low fan speed, then you can use that, however low fan speed will not circulate the air much, and if you are using a ceiling fan, then it would be good (as you can reduce AC fan speed as well as can increase AC temperature which can reduce your electricity bills).

  11. Buddhika says:

    can save energy by reduce air conditioner capacity for same heat load?

  12. prabu says:

    Thanks Abhishek for good article. Im living in chennai. My room is around 12X10sqft and located in first floor, direct sun light on roof and one side of wall, Im using 1ton LG split AC. Usually I used it during night time only, normally temperature will be around 34 – 38 deg. I have switched off swing mode in AC and have allowed to flow air in single direction directly to me. I always keep temp in 29 or 30 with energy saving mode enabled and fan speed is below normal. Is this good for power saving and AC? Whether I need to keep AC in swing mode, also I need to decrease temperature? What about fan speed? Please advice to save power and which is good practice for AC.

    Thanks in advance,
    Prabu

    • Abhishek Jain says:

      Hi Prabu,

      First thing that is important is your comfort. You should derive the comfort you need from the AC. 24-25 is good for body’s thermal comfort. If you are comfortable at 29-30 then that is certainly better for saving electricity. Certainly if the flow of air is directly towards you, then you will feel more comfortable. If you put it in swing mode then the air will not flow in your direction and you may not feel that comfortable. Even for fan speed: the electricity consumption is higher at higher speed and lower at lower speed. But your comfort is primary. Else AC will not solve its purpose. So I think whatever you are doing now is good enough. Additionally what you can do is get a reflective white paint applied on the roof top or get something like XPS (Extruded polystyrene) board put on ceiling. This will reduce the heat in your room. Try to put some sun film on windows that do not reduce light but reduce heat. You may also use thermal insulating wall paper. Do check our section on insulation: https://www.bijlibachao.com/save-electricity/insulation

  13. Khaled says:

    Thanks Abhishek for the nice write-up. My question is related to savings when the AC is in heating mode not cooling mode. Does the equation above work. If for example outside is 12C and temp is 24, now I set it to 20, the savings will be around 41%?

    • Abhishek Jain says:

      It should work in heating mode as well. However the savings will be (4/12)*100 or ((24-20)/(24-12))*100 so about 33%.

  14. ravi s says:

    In my office i am comforatble ac temp is 28 degree, but some told that if i put 28 degree ac may damage since comprosser will work minimum. it is correct. And sugest me 28 degrees ideal degree.

    • Abhishek Jain says:

      The compressor will have lower life if there is frequent switch on and switch off. And that will happen when you keep it too cold. So there should be no problem at 28. If you are comfortable with your AC temperature at 28, then it is the best. Below 24 should be avoided.

  15. MEENA says:

    Hi Abhishek

    i have bought LLOYD LS13A5LN AC 1 TONE 5 STAR , BUT its fan is not running at low fan speed .Please advice me there is problem in AC. it is just 2 day before installed. what you suggest , ? i should go for replacement ? tell me more thing to check, so i come to know its working properly or not.

    regards

    meena sharma

    • Abhishek Jain says:

      You should contact Llyod customer support and ask for inspection and replacement. Its fan should have options to run at high, medium and low speeds. It certainly looks like a problem. Does it not have option to run at low speed or it does but it is not changing to it?

  16. deep says:

    Is case if air conditioner is off but it’s switch remains in.so does the electricity bill comes

    • Abhishek Jain says:

      in some cases yes. Old ACs had 4-5 watts of standby power consumption. New ACs are much better (especially the split ACs). But yes it does consume electricity if switch is not off.

  17. Madan says:

    Hi Abhishek
    Nice article i have 0.75 Ton blue star ac, my room is 10×10 feet in second floor. My problem is whether i set any temperature, ac come to room temperatur then decreases temperature but never reach to my setting in remote . Is there anything wrong with ac or it is not sufficient for room. I am
    Iiving in new delhi.

    • Abhishek Jain says:

      You need 1 ton AC if your room does not get direct sunlight on walls or ceiling. If you do get sunlight then it would need 1.2 ton.

  18. Mohit says:

    Sir does split ac bring air from external environment ?
    If we keep room close will it suffocate?
    I have a voltas 1.25 ton ac.

  19. Sanjay Chandelia says:

    Hi, I have gone through most of your articles and they have been a deciding factor in purchase of my AC. Initially i had shortlisted Godrej 1.5T, 5 star AC but after reading your articles i went for Sharp AX-XP13PHT 1.1 Ton Invertor AC.

    My question is whether i will be able to recover my spendings. I live at Delhi, my room size is 9X12, height about 10Feet, middle floor, no direct sunlight, I run this at around 26-27 C.

    What would be the per hour unit consumption?

    Thanx and Regards.

    • Abhishek Jain says:

      As per my calculations, you need 1 ton AC for your room or 0.75 ton inverter AC. Even 1.1 ton inverter AC would work good. Electricity consumption should be about 0.6 to 0.7 units per hour max.

  20. arunkumar says:

    If we turn on Air conditioner compressor will (on) immediately or it will take some time (seconds or minutes). which one is correct? Please suggest.

  21. sanjay singhal says:

    Dear Sir,

    now a days, i am feeling less cooling from My window AC (1.5 T, Hitachi) in comparison to when it was new. How can i check the system is healthy.

    • Abhishek Jain says:

      How old is your AC? There is a concept of derating and with time the ACs derate and their cooling capacity decreases. But should not be a lot.

  22. tarun says:

    As u said ac will set 25 degree in less time than 18 degree its ok.and compressor stop, But as soon room temperature increases for say 26 degree or to 19 degree. Compressor starts it will take both same time to reduce 1 degree temp. So it vill consume same time same power.

    • Abhishek Jain says:

      It should consume same power and same time to reduce 1 degree temperature. However the room will get from 18 to 19 faster and it will be slow in going from 25 to 26. As the heat flow rate will be directly proportional to the difference between outside and inside temperature. So the compressor cycle will be more frequent at setting of 18 than at 25. So in a longer duration, power consumption will be more at 18 degrees.

  23. nida subhan says:

    Hii abhishek,
    Mai jan na chahti ho ki agar compressior per pani gir jae ya zyada garmi ho to hum pani daal sakte hain ac mai koi probblam to nahi hogi

    • Abhishek Jain says:

      problem तो नहीं होनी चहिये. infact अगर AC के आस पास काफी गर्मी है तो पानी ज़रूर डालना चाहिए , उससे AC अच्चा चलता है. वैसे भी बारिश के दिनों में AC पर पानी गिरता है.

  24. Suresh says:

    I brought Samsung split AC 1 ton 4 years before since now i never seen my AC temp reduced less than 26 after running continue 9 to 10 hrs, most of the time it will touch the Temp max 28 after running 4-5 hrs.
    1. My room temp will be 34 -35
    2. My ODU is kept directly face to sunlight
    3. The ODU and IN-DU is just attached by the same wall, but inside and outside
    4. What mode has to be kept in summer season

    What should i do get a cooling air?

    Thanks,
    Suresh

    • Abhishek Jain says:

      Which city are you located in and what is the size of your room? From your response it seems one of the wall is directly facing the sun, does the roof also exposed to sun or do you have more floors above the room?

      • Suresh says:

        Abhishek, First thanks for your reply. I am from chennai, we stay in first floor there is no building above and side. My room window and door is fully enclosed with glass not wooden door so the sunlight directly fall to my room. size of my bedroom is small coarsely i can say 12×15. considering my room size i brought 1ton.

  25. tapan says:

    Sir pl suggest. i bought a new 1.5t window ac and after installation set temp to 23 c.
    from the night of the installation if find
    1) compressor takes about 5 minutes to start after switching on the ac till then the lcd display shows “UP” (installation person said it happens for the first day only)
    2) in the middle of the night again the compressor was off and only fan running for a long time . the lcd display again shows “UP”. and room was not cool.
    Is this the first day blues or a defective unit pl advise
    Thanks

    • Abhishek Jain says:

      Hello Mr Tapan,

      It sounds like a defective piece, as the compressor should not go off at Night. Can you check if it is running in the right “mode”? Make sure it is in cool mode.

  26. meenal says:

    I have 1.5 ton ac how much bill will come if i set it at 13 degree celsius

  27. raza says:

    Hi, I wanted to know how much average time a room ac takes to achieve a set temperature from the time it is switched on, assuming set temperature was 24 degrees.

    • Abhishek Jain says:

      Depends on room size and in general on the heat in the room and heat outside. However if you have sized your AC properly, it should not take more than 15-20 mins.

  28. Rishabh says:

    Hi,
    I am looking for an air conditioner which is power efficient as well as should have a good performance at the times when there is high outdoor temperatures..
    I concluded to go for an inverter ac of 1ton..

    The thing which is confusing me is operating temperature of compressor. In my city temperature hits 48 sometimes 49 in peak summer.. But all good brands (general, daikin, mitsubishi, etc) gives operating temperature till 46.. I have seen only hitachi claiming it is designed to work on 52…

    I this condition, how significant is this criteria while choosing the right one or is hitachi the only option left for me?

    • Abhishek Jain says:

      Hi Rishabh,

      Typically if the temperature is very high around the outdoor unit and there is direct sunlight on it, the efficiency of condenser goes down. To a certain extent it will try to work by consuming more electricity, but if the temperature goes really high, the compressor stops working and the air does not get cooled. However you can avoid that situation by making sure that the ODU does not face the sun directly and is in a place that has a good shade or is surrounded by plants that keep the temperature around the ODU cooler. So if you go for a model which has operating temperature of 46, you will have to take care in placing the ODU in a place that is cooler as compared to outside and does not get any direct sunlight.

  29. saialuka says:

    we have 1.5 ton 3 star a.c during night time temperature changes automatically from 22c to 24,25,26c gradually is thi normal in energy saving mode.

    • Abhishek Jain says:

      Well if temperature increases, it will certainly save energy. Unless it is causing any discomfort, it should be good. Every brand has different kind of energy saving modes. In some ACs, the AC actually switches of completely for some time in energy saving mode and restarts automatically after some time.

  30. amjad says:

    What is the ideal position for remote setting for Electricity saving. there are three options 1- Auto 2-Cool 3-Dry. I have Panasonic Inverter, Econavi Split AC.

  31. Abhishek Jain says:

    It will depend on your temperature setting more than the option setting.

  32. ASMA says:

    plz help me ,i want to know that .the thermostat is in every AC’s??? i have Sabro Split Ac but its compressor is not turning off when room temperature is maintained.Where is problem????

  33. Abhishek Jain says:

    Hi Asma,

    All ACs have thermostat. So either your AC is smaller for your room or certainly there can be a technical problem.

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