Why Air Conditioner (AC) capacity is measured in tons?

Most of us are using Air Conditioner to fight with summer heat. It makes everyone to feel relaxed in summer. Do you ever observe the specification of air conditioner. You will find that its cooling capacity is measured in ton and not in KW or something else. Why it is in tons?

Welcome to Engineering Master. In this article, we will tell you the answer…


When I was young, I always think that the AC is heavy as it weighs in tons. But today I realized that I was wrong. Air conditioning tonnage has nothing to do with weight. A ton is used to describe how much heat is removing from a room in 1 hour. In earlier times, natural ice is used to cool a room. So, the cooling we get in a room with 1 ton of ice in 24 hours is called as ton of refrigeration.

After that, air conditioners are invented and the cooling capacity of ice is matched with cooling capacity of air conditioners. It means that the cooling effect we get from 1 ton of ice is equal to the cooling effect given by 1 ton of air conditioner. So if we put 1 ton of ice in one room and 1 ton air conditioner in another room (both must have same size), then the cooling effect will be same.

Now we will understand how much heat is absorbed by air conditioner in FPS (British unit) system. In FPS system, 1 ton is equal to 2000 lb (lb is the symbol of pound). Latent heat of ice is 144 BTU/lb (BTU is British thermal unit). This means that when 1 pound of ice starts melting, then it absorb 144 BTU of heat.

So 1 ton of ice or air conditioner absorb 2000×144=2,88,000 BTU of heat in 1 day.

Now we divide the above with 24 to find the absorption of heat in 1 hour. 2,88,000÷24=12,000 BTU/hour. This means that a 1 ton air conditioner or ice absorb 12,000 BTU in 1 hour. Similarly, 4 ton air conditioner absorbs 4×12,000=48,000 BTU heat in 1 hour. Therefore, with increase in ton of air conditioner, more heat absorption takes place and hence it can cool more air.

Different ton of air conditioners are required as the size of a room is not same in all places. So, larger rooms need more ton of air conditioners than smaller room.


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