Electricity Saving Tips For Homes And Offices

Ideal Air Conditioner temperature for electricity savings

By on April 19, 2015
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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.

Here is a short video for tips to buy the best air conditioner in India


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There Are 90 Comments

  1. iftekhar says:

    i am using llyod 5 star split ac..living in top floor of appartment. setting ac to 28 and keep the fan running will consume more or less.. pl suggest
    and also pl tell me, ceiling fan kept at high speed will consume more when compared to low speed?

    • Bijli Bachao Team says:

      Hello Mr Iftekhar,

      Ceiling fans induce a draft of air which when circulates around our bodies make us feel cooler (because of the sweat that comes out of our body). When used along with AC, it can help us increase the temperature setting in the thermostat of the AC. Increasing the temperature reduces electricity consumption significantly. However when you have a hot ceiling, using a ceiling fan will move the hot air on top towards bottom, and this can increase the electricity consumed by AC. So if you live on top floor, using a ceiling fan would not help. Instead you should use a table fan or pedestal fan with AC rather than a ceiling fan.

      A fan consume more electricity at high speed as compared to low speed.

  2. Tushar Naik says:

    How can fan automatically stop in LG spilt Ac

  3. a v somesh says:

    i baught a split ac 1.5T. we are using this in night time 4 to 5 hours in 28 degrees set point. next day if we can check metre reading, 10 units consumed. actually how many units will take for 4 to 5 hours of using AC. whats the reason? can u give any suggestion?

  4. Ankit says:

    HI,
    I have purchased Voltas 1.5 ton 2 star AC, i live in Lucknow, Ground floor with open terrace and three sides cover, i dont get direct sunlight in my room. my room size is 13×16. how much time will my AC take to cool my room.

    • Bijli Bachao Team says:

      Hi Ankit,
      According to our calculation your room requires 2 tons of cooling. So a 1.5 ton AC is undersized for your room and it will take about 45 mins to cool the room to a comfortable level.

  5. wina says:

    Hi im wina, i want to ask you, if i set low temperature at my remote for example 16 or 17°c my unit will follow but suddenly it came back to 37°c and my room is looks like having a heater than an air conditioner. What should i do? Do u think thay my AC is broken?

    • Bijli Bachao Team says:

      HI Wina,

      It certainly looks like your AC is broken. You should contact the manufacturer’s customer support for the same.

  6. S Taparia says:

    Dear Abhishek,

    Thanks for the nice article.

    I noticed that in my 1.5 Ton AC ( Samsung) which is 5 years old unit, we set the temperature to 24 but after some running it automatically started showing higher temperature on the display i.e. the displayed numbers were increasing from the temperature initially set by us e.g. 25..26..27 ..28 …This is not happening immediately after starting the unit.

    Just wanted to know what could be reason ? Would this need attention of a mechanic.

    Thanks
    S Taparia

    • Abhishek Jain says:

      Well at times some ACs have energy saver or sleep mode which reduces the temperature with time. Which mode are you running your AC on? Is it cool mode?

      • S Taparia says:

        We are not running in energy saver or sleep mode. It is normal in cool mode. In fact, sometimes, immediately after starting the unit, it goes to 30 which is highest possible temperature. I tried switching it off but when switched on again – it went to 30 and it does not allow me to reduce it below 30.

        People who came for regular servicing also could not figure out exact problem.

  7. Ameya says:

    I usually plan to on ac at night use for initial 2 hrs and switch off rest of night and let ceiling fan run.. Is it OK to keep lower temperature in such case like 22 or I’ll run only at 24-25. Or you suggest ac to be on overnight at 24-25

    • Abhishek Jain says:

      Running AC for 2 hours will be more electricity saving as compared to running AC for 8 hours. If you are comfortable with switching off after 2 hours then you should continue with that.

      • Ameya says:

        what about temp.. if i maintain 24 then wil my room get heated quickly as compared to 22? or there wont be much

        • Bijli Bachao Team says:

          Hi Ameya,

          ACs have a standard cooling capacity which means they can remove heat from a room at a fixed rate. So even if you set it to 22 and your room’s temperature is 34 while coming down from 34 to 22 …. it has to cross 24 :) …. so it will always reach 24 before it reaches 22.

  8. Krunal says:

    Hey,
    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. Room size is 12x15sqft. Is there any problem wth compressor or temp sensor ? Also the auto cut off and start time is very short. It shuts and start again very three minutes when temp is set at 26degree.
    Thank you.

    • Abhishek Jain says:

      Hi Krunal,

      Which city are you in? Also which floor are you on (top floor with sunlight on ceiling or lower floor with more floors on top)? An oversized AC can overcool the room. And not just over cool but consume more electricity as well. Short cycle can also lead to bad humidity removal and can lead to bad smell from AC in future.

      • krunal says:

        Hi Abhishek, Thanks for prompt reply. I am from mumbai. I stay on 17th floor. Just one floor above me. Do you think there problem with compressor or temp sensor?

        • Abhishek Jain says:

          Hi Krunal,

          As per my calculation you need about 1.3 tons of cooling for your room. However as you are on 17th floor the temperature at that height in general will be lower even during summers. So may be that would reduce the tonnage requirement to 1.2 ton during peak summer day time. However this requirement is during peak summer day time. During night time the heat is much lesser and thus night time requirement is lesser. Would suggest you to go for an AC power saver as described on this link: https://www.bijlibachao.com/air-conditioners/power-saver-devices-for-air-conditioners.html ….. this company sells the same in Mumbai: http://www.omenergysavers.in/

  9. 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.

  10. 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]

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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.

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