Heat pump Theory
The basic Thermal principle behind the heat pump.  

Warning!!! In this section we are going to discuss the thermal heat pump theory and air conditioner … so if you are not a geek please leave…

In order to better understand how the heat pump works you might want to know about heat pump theory and air conditioner theory.

Temperature & Heat

It is a common mistake to confuse temperature with heat even though they are two different things. Just because an object has a higher temperature doesn’t mean that it has a greater amount of heat than an object with a lower temperature.

Heat is the thermal energy that an object can contain. The heat must have a source. For example, the Sun emits radiant solar energy which will warm a rock or a swimming pool. Or the source can be fossil fuel which is burned to cook your steak on the gas grill. Heat can be measured in standard units- BTU. But in reality heat or energy is the force of life- we can’t create it from nothing nor can we destroy it .

Only for the sake of simplifying things and to understand the heat pump theory, I will give an example: (engineers and physicists will hate me)

Assume you have 1 gallon of water and it has 1,000 BTU in it (BTU is the amount of heat, and is the acronym for British Thermal Unit). Also, you have 2 gallons of water and it has the same 1,000 BTU. Which water has higher temperature? You said the 1 gallon of water- yes, you are correct because the amount of heat is contained in a smaller object.

Heat Pump Theory

Another quick example: which has more heat your body, or the ocean? You said the ocean and you are correct. Even though it has a lower temperature than your body the ocean has more heat because the heat is contained in a very large object. But in your body the heat is contained in a relatively small object. Assume the ocean has millions of BTU but it has millions and millions of pounds of water so each 1 pound of water might have only 1 BTU. In your body you might have only 1,000 BTU but you are only 150 lb (my wife will love me if I am that skinny) so each pound of your body has 6.66 BTU- so your body has a higher temperature but less heat.

OK we've got the picture, let’s move on…

No… No… we don’t want anyone to hate us so we will give the scientific definition of Temperature.

“The average energy in each degree of freedom in the particles in a system”

The Laws of Thermodynamics

Thermo what? “Thermo dynamic” means in Greek the “movement of the heat”.and in order to understand the heat pump theory we have to understand those laws There are four laws that control that movement but we really need to know two.

The Zeroth Law of Thermodynamics

First- why do they call it Zeroth? Because it was understood fully only after the 1st law was invented- crazy right? Well it says,

“The heat moves from the Higher Temperature Object to the lower Temperature One”

Not from the higher heat to the lower heat but from the higher temperature to the lower temperature- remember the difference between heat and temperature. So when you jump into the ocean in January you will freeze your butt off, because all your body heat will move to the ocean and leave you in the cold even though the Ocean has more heat than you …..

The 1st Law of thermo Dynamic

This law says the “Heat can’t be created from nothing nor can it be destroyed. We can only transform it from one form to another”.

In layman’s terms you can’t have a fire without a fuel.

3rd and last principle (I promise)

The Temperature- Pressure Relationship

This one is easy- well kind of. If you pressurize a gas, you will increase its temperature. The reason is simply that you will decrease the volume, without adding or removing any heat. Remember the first example of the single gallon of water with 1,000 BTU and the 2 gallons of water, also with 1,000 BTU and how the single gallon had a higher temperature?

Heat-pump Temperature-Pressure relationship

In this Example Container A contains a gas and the temperature of that gas is 80 F and the pressure is 10 PSI (pounds per square inch). Next we pressurize (compress) it as shown in Container B. The volume of the gas goes down. The pressure goes up (because we have increased it) and the temperature goes up because the heat has nowhere else to go. Heat is not added or removed- but since it is in a smaller volume of gas the temperature of that gas goes up.

And if you depressurize the container the gas will expand and you will drop its temperature.

I hope I didn’t bore you to death-

But that’s it! Now you can have a better understanding of how the heat pump works .




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