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# Why tonnage and not KW or BTU's. No question just an observation.

#1
07-28-19, 06:44 PM
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Join Date: Sep 2013
Location: United States
Posts: 9,006
Why tonnage and not KW or BTU's. No question just an observation.

I often wondered why A/C is sized in terms of tonnage. Does not seem intuitive. So a little bit of GOOGLING turned up these definitions. Still does not seem intuitive. Why not just use BTU's or KW as is?

1)
Why is AC rated in tons?
A ton is the cooling capacity of an air conditioning system. One ton is equal to the amount of heat required (288,000 Btu) to melt one ton of ice in a 24-hour period. A one-ton air conditioner is rated at 12,000 Btu per hour (288,000/24). ... Typical residential central heating systems provide up to 5-tons of cooling.

2)
Why AC rating is in Ton?
Why AC rated in Tons, Not in kW? ... Quantity of heat is termed in Tons means if an air conditioner is able to remove 1000 kilocalories of heat or 4120 kilojoules or 12000 BTU of heat in an hour that AC rated as 1 Ton of AC because 1000 Kilocalories or 4120 kilojoules or 12000 BTU equal to one Ton of heat.

So why not just say an A/C unit is rated at 12K BTU for 1 ton or 36K BTU for a 3 ton? It's just a term, but the term ton, one thinks of a ton of bricks or a truck that weighs tons. Our confusing language!

#2
07-29-19, 07:10 PM
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Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 13,633
On the same line, what is a BTU. Yes, I know it is a British thermal unit but for the definition "The amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit." makes no sense as there is no time reference. It would make more sense to say: defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit in one minute. Otherwise, you can take a candle and wait for a long time for the water temp to rise one degree.

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