Why Use BTUs Instead of Power Units for Air Conditioner Capacities?

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In summary: I was just trying to get the point that a conversion was not as simple as stated. The power in watts would be 1200, not 3517.In summary, the conversation discusses the use of BTU as a unit to measure the power of air conditioners, even though it is traditionally used to measure heat value. The conversation also mentions that many people make mistakes when using units, and that AC units are often rated in "tons" or watts. There is also a mention of the Energy Efficiency Ratio (EER) and how it affects the wattage required for an AC unit.
  • #1
pixel01
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In my room there's a small aircon, it is 12000BTU. I know there are some bigger ones which can be 18000 or 24000 BTU.
BTU is a unit to measure heat value, which is similar to calorie or joule. So why do they use a heat value unit to show the power of an aircon, but not a power unit such as kW or horsepower.
Thanks for reading.
 
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  • #2
Well, the writing on the airco is wrong, and there is nothing to discuss about that.
If the correct reading is 12000 btu/h, it would be equivalent to 3517 W.
This indicates the correct units are probably "but/h".
This kind of mistakes is very common, many of them can be found in newspapers or on TV everyday.
People have the biggest problems with electrical energy units: kWh is an abstract concept for most people.
But physicist can have problem with units too sometimes, for example the spectral density of a random signal in W/Hz a real obstacle for some, not to mention the corresponding field intensity!

[leave the political commentary out, lalbatros. -Russ]
 
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  • #3
Now that's more than enough.
Thanks
 
  • #4
That is correct. Simply stating BTU for the units is incorrect. It is analagous to a lot of people referring to the units of pressure as "pounds." Most people just don't know any better and when you try to point it out and that it does matter, you'll get told to get lost pretty quickly.

In most applications, A/C units are rated in "tons." This is a throwback to back when A/C involved putting a big block of ice in a room. The unit of "ton" refers to the heat of fusion of a 1 ton block of ice at 0°C. Today that has carried over to 1 ton = 200 BTU/min or 3.52 kW.
 
  • #5
That conversion does not apply to AC units. That value is dependant on the unit's Energy Efficiency Ratio (EER). EER = Btuh/watts. A unit with an EER of 10 will require 1200 watts/hr to produce 12000 btuh. The higher the EER, the lower the wattage required.

http://www.engineeringtoolbox.com/air-conditioner-efficiency-d_442.html"
 
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  • #6
I think they were talking about converting output heat (rate) to output power, which you can do with the conversion factor. I've worked on a couple of projects in Europe and they express HVAC capacities in watts and energy efficiency ratios in watts per watt. Ie: http://www.toshiba-aircon.co.uk/pdf/residential/high_wall_inverter.pdf
 
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  • #7
russ_watters said:
I think they were talking about converting output heat (rate) to output power, which you can do with the conversion factor. I've worked on a couple of projects in Europe and they express HVAC capacities in watts and energy efficiency ratios in watts per watt. Ie: http://www.toshiba-aircon.co.uk/pdf/residential/high_wall_inverter.pdf

Thanks Russ. Yes, I agree that would be correct for output.
 
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What are BTUs and how do they relate to air-conditioners?

BTUs, or British Thermal Units, are a unit of measurement used to measure the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. In terms of air-conditioners, BTUs are used to measure the cooling capacity of the unit. The higher the BTU rating, the more powerful the air-conditioner is and the larger the area it can effectively cool.

How do I determine the appropriate BTU rating for my room?

The appropriate BTU rating for your room depends on several factors such as the size of the room, the level of insulation, and the climate in which you live. As a general rule, you will need about 20 BTUs per square foot of living space. However, if your room is heavily insulated or located in a hot and humid climate, you may need more BTUs to effectively cool the space.

Can an air-conditioner with a higher BTU rating cool a smaller room?

Yes, an air-conditioner with a higher BTU rating can cool a smaller room. However, it may not be as energy-efficient as using an air-conditioner with a BTU rating that is appropriate for the room size. This is because the larger air-conditioner will cool the room quickly and then shut off, leading to frequent on and off cycles which use more energy. It is important to choose an air-conditioner with the appropriate BTU rating for your room to ensure efficient cooling.

Do all air-conditioners use the same amount of BTUs?

No, not all air-conditioners use the same amount of BTUs. The BTU rating of an air-conditioner depends on its cooling capacity, which can vary based on the type and size of the unit. Window air-conditioners typically range from 5,000 to 25,000 BTUs, while portable air-conditioners can range from 8,000 to 14,000 BTUs. It is important to check the BTU rating of an air-conditioner before purchasing to ensure it is appropriate for your needs.

Can I use an air-conditioner with a lower BTU rating than recommended for my room?

It is not recommended to use an air-conditioner with a lower BTU rating than recommended for your room. This can lead to the air-conditioner working harder to cool the space, using more energy and potentially causing premature wear and tear on the unit. It is best to choose an air-conditioner with the appropriate BTU rating for your room to ensure efficient and effective cooling.

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