Why AC is rated in Ton and not in kW?

Generally, the electrical appliances in households are rated in watt or kW, but this is not the case with air conditioners and refrigerators. Why air conditioners (AC) and refrigerators are rated in Ton and not in kW? Let’s discuss the reason.

Along with the main question, you will also get to know about few more interesting topics as:

What is British Thermal Unit (BTU)?

How to convert Ton into kW?

How to calculate power consumption of AC?

Why AC is rated in Ton instead of kW?

Before the invention of AC, people were using ice cooling method to keep their room and food fresh during summer days.

The vendors bring ice from glaciers, ponds and other colder region and then sell it to local people. The weight of ice was done in terms of Ton.

Ton is a unit of weight and 1 Ton is equal to 2000 Pounds.

People put the ice in their room and the ice absorbs the heat from surroundings and melts itself. This makes the room temperature lower than before.

Just like the weight system, there is a unit for temperature also which is called BTU (British Thermal Unit).

What is British thermal unit?

The heat required to increase the temperature of one pound of  water by one degree Fahrenheit is one BTU.

A matchstick burn out to release around one BTU of heat. To melt one Ton of ice in a day, it has to absorb 12,000 BTUs of heat per hour.

When Wills carrier invented air conditioner, he kept the rating system of air conditioner in tons just like the ice cooling system, because both serves the same job which is removing the heat from room.

The rating system of refrigerator is also in Tons because of the same reason. The function of refrigerator is removing heat from the items kept inside it.

If you have a 1 Ton AC then it means that it will remove 12,000 BTU of heat per hour.

If you have 2 Ton AC then it will remove 24,000 BTU of heat per hour.

I hope that now it is clear that “why AC is rated in Ton and not in kW” and  “what is BTU”.

How to convert Ton in kW?

Before going to conversion of Ton in kW, we must see some relations.

1 Ton = 12000 BTU/hour

Here’s the reason for why one ton is equivalent to 12,000 BTUs per hour:

1. One ton of ice, when it melts, absorbs 144 BTUs of heat energy per pound (since 1 BTU is the amount of heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit).

2. There are 2,000 pounds in a ton, so 1 ton of ice absorbs 2,000 pounds × 144 BTUs/pound = 288,000 BTUs when it melts.

3. Since there are 24 hours in a day, the cooling capacity of 1 ton of ice per hour is 288,000 BTUs ÷ 24 hours = 12,000 BTUs per hour.

I hope it is now clear that why 1 Ton is equal to 12000 BTU?.

Now the second relation is,

1 Watt = 3.412142 BTU/hour

1 watt is equal to approximately 3.412142 British Thermal Units (BTU) per hour. This conversion is commonly used when comparing electrical power (in watts) to heat energy (in BTUs). So, if you have a device that consumes 100 watts of power, it is generating heat energy at a rate of approximately 341.2142 BTUs per hour.

Now, we can do the conversion of Ton into kW.

1 Ton = 12000 BTU/hour

1 Watt = 3.412142 BTU/hour

So, 1 BTU/hour = 1 watt / 3.412142

       1 BTU/hour = 0.2931 watt

And, 1 Ton = 12000 / 3.412142

                = 3516.8528 watts

To make it in kilowatts, multiply with 1000.

                = 3516.8528 x 1000 = 3.5168528 kW

So, 1 Ton = 3.516 kW

Now, we can say that cooling capacity of 1 Ton AC can be written as 3.516 kW.

Power consumption of AC

The standard formula to calculate power consumption of an AC is

              Cooling capacity / EER  = Power consumption

Here, EER is the energy efficiency ratio which means that how efficiently a cooling system can convert the electrical energy to cooling power.

A higher EER value indicates that the air conditioner is more energy-efficient because it can deliver a greater amount of cooling for a given amount of electrical input power.

Let us take an example,

If we have given a 2 Ton AC which has EER of 3.5 and cooling capacity of 7032 watts then,

Power consumption = 7032 / 3.5 = 2009.14 watts or 2 kW.

Hence, this AC will consume 2kW per hour.

Now, instead of 3.5 EER we take 4.5 EER. Let’s see the change in power consumption.

Power Consumption (in watts) = 7032 watts / 4.5 ≈ 1562.63 watts

So, with an EER of 4.5, a 2-ton air conditioner would consume approximately 1562.63 watts, or approximately 1.56 kilowatts, when running at its rated capacity.

That is why the star rating plays very important factor along with the correct size of an AC while buying it. You can also read more such interesting topics here,

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