Air Conditioners: A technical approach

In this post we will mostly be using Air Conditioners as a reference appliance. But, the same principle is true for refrigerators, too. However, I am unable to affirm the same with regard to washing machines due to the lack of data on the market for them (and some sense). The three mentioned above are the sole items that I have observed inverter technology in India

I get this question often. Not only from the commoners as well as from experienced technocrats and engineers. The most frequent phrase will be “Just cutting off the cycle of on and off, will not reduce your expenses by more than seven to ten percent. The claims of savings of 40% are just a marketing gimmick.”. I had a lengthy conversation with a friend about this issue this past week, which led to pen this post. I hope this article will to give people a better understanding of how technology like inverters can help conserve energy.Therefore, you won’t see any references in this article. However, this post was written from my personal observations and experience over the past 8-9 years of working on Bijli Bachao and watching the market.

Let’s take a look into Air Conditioners.

Many people inquire: “What is better in the case of a 5- Star AC that will save more energy when compare the 3 Star? or is 5 Star just marketing hype?”. The 5 Star models are more efficient in energy use, and there are many ways for manufacturers to increase the efficiency of air Conditioners. Certain of them (this list is not intended to limit ):

  • It’s using the best refrigerant, which gives higher thermodynamic efficiency.
  • They are increasing or improving surface areas of the heat exchanger (mostly condenser) areas to allow for better energy dissipation.
  • Use better compressors (inverter technology, etc. ).

One of the comments I heard from a man was that companies are producing 5 star inverter ACs, with bigger condensers. This is the reason they are more efficient when compared to non-inverter ACs with 3-star ratings. If manufacturers produce non-inverter ACs that have larger condensers they’ll save money. To a large extent I am not in disagreement that non-inverter ACs can’t be enhanced. However, this article is about proving the benefits of inverter technology and the reasons it is sensible to invest in technology for inverters and not as much on non-inverter technology.

Compiling numbers of Air Conditioners

To see how the numbers compare I’ve taken the data from two models of Daikin which are a bit like each other. Both models are BEE 3 stars, with identical ISEER numbers and technologies. One model is non-inverter while the other model is an inverter. The reason I chose Daikin is that I believe they’re pretty great in terms of being transparent about the numbers. A majority of Japanese brands offer a decent amount of information, however Daikin is the most reliable for information you can utilize to make a choice.

Let’s dive into some math:

Our Scenario – Room 1

The current temperature in the room is 16000 BTUs (at 40°C)

The room is heated at the desired temperature between 8000 BTUs (say roughly 20-21°C)

In the room, heat is circulating (through walls, human or other.) – 4000 BTUs/hr

Therefore, once the additional 8000 BTUs are eliminated, in the steady state the AC must remove 4000 BTUs/hr in order to keep the temperature steady (or to keep the temperature to 8000 BTUs).

Non-Inverter Air Conditioners – Daikin FTL35 (BEE 3 star)

The Cooling capacity for an AC 3350 Watts (or 11782 BTU/hr)

The power consumption of an AC 918 Watts

EER or ISEER = 3350/918 = 3.65

In about 1 hour it will need to eliminate in the first hour 8000 BTUs plus around 2000 BTUs that are generated because of the temperature gradient that is created. Thus, roughly 10000 BTUs have to be removed within the first hour.

Time to run the same amount = 10000/11782 = 0.848 hours or 51 minutes.

Thus, the power consumption is 918 times 0.848 (779 Wh), or 0.779 units

After that, it will have to remove 4000 BTUs/hour. Thus, each hour it will run for 4000/11782 = 0.3395 hours or 20 minutes

Power Consumption per hour equals 918 * 0.3395 is 311Wh, or 0.311 Units.

If the AC is running for 8 hours The total energy consumption is 0.779 * 7 + 0.331 is 2.96 units.

inverter Air Conditioners – Daikin FTKL35 (BEE 3 star)

Cooling Capacity The range of the AC The AC’s Cooling Capacity Range is (Max) 3700 Watts (or 12600 BTU/hr) and (Min) 1070 (or 3650 BTU/hr)

Power Consumption The range of the AC The AC’s power consumption range is (Max) 1200 Watts as well as (Min) 1200 Watts and (Min) 210 Watts.

In the assumption that the variation is linear and runs along an unidirectional line. The relationship between power consumption is described in

y (cooling capacity) = mx (power consumption) + c

then m = (3700 – 1070) / (1200 – 210) = 2.656

and C = 512.12

It is the same as non-inverter AC in the first hour, the AC will remove around 10000 BTUs. Then in steady state it will take away 4000 BTUs/hour (or 1137 watts)

Let’s assume that in the one hour, the speed of operation that is being produced by the AC is at a level that averages 10.000 BTU/hour (or 28,43 Watts).

By using the line formula the power consumption will be

(2843 – 512.12)/2.656 = 877.59 watts

Thus, the consumption of units during the 1st hour equals 877.59 Watts or 0.87759 units. (which is higher than the non-inverter AC’s first hour). If we assume that it behaves linearly.

In the following hours, it must remove 4000 BTUs/hr , or 1137 Watts.

By using the same line formula that calculates the power consumption:

(1137 + 512.12)/2.656 = 235.27 Watts

Thus, the consumption of units after the first hour is 235.27 wh, or 0.23527 units

Total Power Consumption in 8 hours = 0.87759 + 7 x 0.23527 = 2.5244

Total Savings

Non-inverter consumed 2.96 units over 8 hours.

The inverter AC used up 2.5244 units in just 8 hours.

Saves = 0.42552 units equals 15 percent of 2.96

Based on these calculations, simply changing the compressor to an equivalent inverter compressor, you can save 15% on energy consumption over the course of 8 hours.

Why inverter Air Conditioners have better efficiency for less tonnage?

In cooler temperatures the amount of gas pumped is lower. This causes less heat dissipated from the condenser. The condenser stays coolerand it will be less stress to the compressor. The compressor therefore draws less power and is efficient. The condenser is already big.

Important Observations made based on the calculations above

Now , what meaning can you get from the above calculations that you can apply to your decision-making process:

  • The inverter AC is ideal when they come with a large tonnage so that they will meet your cooling needs to the minimum and more.
  • Inverter ACs that are too small are bad and won’t save you any energy. While oversized inverter ACs could be extremely efficient when they are in the large range of cooling capacities (or tonnes) range.
  • It is definitely possible to save energy by using the Inverter AC. Turning it off and on does not assist in reducing your energy consumption. It is best to keep it at a temperature that is comfortable and use it for a long.

Do ISEER numbers of Air Conditioners provide any benefit to consumers?

The ISEER number, or the annual energy consumption of electricity that is presented to you is only intended to compare ACs. It is a useful instrument when trying to make a purchasing decision. However, it is not applicable in the real world because the ISEER you receive from your AC inverter could differ from the one that is described. It is contingent on the conditions under which an inverter AC is operating. In the case of non-inverters ACs, the ISEER does not alter based on the operating conditions. If the inverter AC is large that has a large cooling capacity, you could get a higher ISEER than that stated and for a smaller inverter ACs, the ISEER will be significantly less. Inverter AC with a larger cooling capacity has the potential to provide higher ISEER than an inverter AC that has a smaller range of cooling capacity.

What do we need to do as consumers?

The most crucial thing to do is solicit details. With only a few manufacturers, they don’t offer a lot of data to evaluate. Sure, we have information from BEE which receives test reports from manufacturers that are conducted in the NABL accredited lab, however, this data isn’t enough. The calculation of ISEER is based on power consumption of ACs inverters at 50 and 100 percent capacity. It does not take into consideration the capacity at which the AC is able to run at or the power consumption that it consumes at the capacity. The nature of the inverter AC is so complex that it’s difficult to create a standard apple-to-apple comparison without standardizing the calculation procedure. But, there’s more to it than conventional comparisons that provide additional information. Without getting into complicated calculations, you can simply take a look at ACs with larger cooling capacities. Just ask for that information!


Inverter technology isn’t simply a buzzword. It is extremely effective in ACs and refrigerators. Making the right decision and using it correctly is essential for your energy saving project.

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