AC 101: There Is No Spoon
- September 17, 2015
- Posted by: Core Control
- Category: Tech Notes
Customers want their air conditioners to be pumping out cold air. When it isn’t we get the call – “I don’t have any cold air!” But what if I told you there was no such thing as “cold”? It is more accurate, and can be very helpful when troubleshooting equipment, to think only about heat and the absence of, or transfer of, heat. This is like the Matrix. Cold is the spoon and, as Neo put it famously, “There is no spoon.”
The second law of thermodynamics is behind all that “cold” air our customers enjoy. Heat flows naturally from an object at a higher temperature to an object at a lower temperature. What happened when you were a kid and stood with the refrigerator door open too long? Besides your parents yelling at you? It felt like cold air was getting out.
In fact, hot air was getting in to the refrigerator. Or think about a tea kettle: the “cold” in the water isn’t going into the stove is it? No. Heat is moving naturally from an object at a higher temperature (the burner) to an object at a lower temperature (the tea kettle) and, eventually, the water boils. (Homework! Watch a pot of water boil tonight and really think about what is going on.)
Customers want their air conditioners to be pumping out cold air. When it isn’t we get the call – “I don’t have any cold air!”
So, if a room is hot, say 85 degrees, how do you get it to cool down? To the average person it feels like the answer is pumping in cold air. Actually, the task is to use the second law of thermodynamics and give the heat in the room a colder place to go. From the burner to the tea kettle. From the kitchen into the refrigerator.
This is a challenge, of course, if it is 100 degrees outside. Then heat naturally moves into the 80 degree room making it even hotter! Enter the air conditioner. Through the magic of a compressor (we’ll get to that in AC 102), air conditioners absorb heat inside of a hot building and dump it outside, creating an absence of heat in the room that used to be hot. “Heat sink” is a term you’ll hear for that.
Air conditioners don’t make cold air; they remove heat.
- There is No Cold
- Second Law of Thermodynamics
- Heat Sink