What is meant by 3 Tons of Air Conditioning?

If the air conditioner cooling our home is a 3 ton unit, what does that mean? Why are air conditioners rated in tons of air conditioning?

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Is air conditioning the same as refrigeration?

So let’s start by talking about refrigeration. Refrigeration is a general term that describes a man made method of cooling a space. In this case, we are referring to cooling your home. An air conditioner performs this function. A larger home needs a larger air conditioner. And a smaller home needs a smaller air conditioner. The common method of measuring different sizes of air conditioners is with the ton.

One ton of ice melting in a 24 hour period

So what is one ton of refrigeration effect? A ton of refrigeration is the amount of heat energy absorbed when one ton of ice melts in a 24 hour period. One ton of ice weighs 2000 pounds. Let’s say your home is cooled by a 3 ton air conditioner. This a/c unit is capable of producing the same cooling effect as a block of ice weighing 3 tons melting in 24 hours. That would leave a pretty big puddle, so we install mechanical refrigeration units (a/c units) instead of using actual ice.

How big is a ton block of ice anyway?

Tons of Air Conditioning represented by a one ton polar bear

Well, a fully grown polar bear weighs approximately one ton. A block of ice weighing the same as an adult polar bear melting in 24 hours produces one ton of refrigeration effect.

For those interested in the technical specifics, the calculation assumes that the ice begins at 32 degrees Fahrenheit. And the melted ice stays at 32 degrees as well over the entire 24 hour period.

One Ton of Cooling versus the British Thermal Unit (BTU)

We can convert one ton of refrigeration effect into British Thermal Units (BTU). For those people more familiar with the BTU unit of energy. We have to know the heat energy released by the melting of one pound of ice (at 32F) into one pound of water (also at 32F). Scientists tell us that this value, called the latent heat of fusion, is equal to 144 BTU/pound.

Taking 2000 pounds x 144 BTU/pound melting over a 24 hour period means that one ton of refrigeration effect equals 2000×144/24 = 12,000 BTU/hr.

If you look at your air conditioner’s model number on the manufacturer’s sticker on the outside a/c unit, you will often find a variation of this BTU/hr rating embedded into the model number. For example, a newer Trane 3 ton air conditioner may have the following model number: 4TTR3036 and then some other letters and numbers will follow. The 36 stands for 36,000 BTU/hr which is a 3 ton air conditioning unit.

Typical sizes for residential air conditioners include the following:

1 ½ ton           18,000 BTU/hr
2 ton               24,000 BTU/hr
2 ½ ton           30,000 BTU/hr
3 ton               36,000 BTU/hr
3 ½ ton           42,000 BTU/hr
4 ton               48,000 BTU/hr
5 ton               60,000 BTU/hr

What does ASHRAE say?

More information can be found relating to air conditioning ratings from the ASHRAE website here. This page lists the top ten things consumers should know about air conditioning. ASHRAE stands for the American Society of Heating, Refrigerating and Air Conditioning Engineers and is an industry standards and publications association for the HVAC industry. ASHRAE currently defines a ton of refrigeration effect in terms of BTU/hr. However, the original definition was in terms of tons of ice melting in a 24 hour time period.

There are some other heating, ventilation, air conditioning, and refrigeration related topics that may be of interest to you. Click here for information on what air filter would be best for your home. There is also information available here on what MERV ratings for air filters mean. If you would like more information on home humidification, refer to this blog. Or on a similar topic, if you have wondered how air conditioners dehumidify, check this blog out. Another option for improving your indoor air quality is to install an electrostatic air cleaner.

Does your home still have one of those older mercury thermostats? Check out this link for more information about them. And do you try to do some of your own maintenance to help keep your furnace and air conditioner running all season long? There are some helpful homeowner maintenance tips at this blog that will help.

Accurate Heating & Cooling can help you with all your HVAC needs. Give us a call today at 402-238-2425.