Lets Talk Briefly About Compression and Its Effect to Matters

This page talks more in detail about compression of gases, as an expansion to the fundamentals of how air conditioners work.

Compression, in short, is an act of increasing pressure of gas in an enclosed space. Although solids can be compressed to a very limited extent, similarly for liquids; those are not quite related in our world of air conditioners.


The absolute beginning of understanding compression:

Atom configurationEvery matter, be it solid, liquid or gas are composed of the most basic of all building blocks. Electrons, neutrons and protons. These, will form an atom.

Now, each atom consists of proton/s and neutron/s in its nucleus (analogous to the sun), and electron/s orbiting the nucleus (analogous to planets).

The mass of each building block is in the magnitude of 10-31 kg (for electron), and 10-27 kg for (proton and neutron). I would say, those are extremely light.

Each of these electron, proton and neutron has a specific internal energy in magnitude of 10-19 Joules.

There are a number of possible proton neutron and electron quantities in an atom. Add a few electrons, you’ll have an atom of copper for example. Add a few more, you might have mercury.

Mix two or more different or even same atom types, you’ll have a molecule.

That’s it. Due to different quantity of electrons, protons and neutrons in a single atom or molecule, we’ll have different types of material, from steel to copper, from water to refrigerants. And due to different quantity of these building blocks, we’ll have different internal energy for each material.

If the internal energy of a matter is much much lower compared to the ambient atmosphere, it will be in solid state.

If the internal energy of the same matter is much much higher than the ambient atmosphere, it will be in gaseous state.

Anything in between, it will be in liquid state.

What’s next?


Earth’s condition:

Molecule compressionLet us consider our natural environment, under natural gravitational pull. The pressure and temperature are ambient. This is the phase where things exist naturally. The state at which, we don’t have to put in energy to get air at gaseous state, or gold in solid state.

One of the approved refrigerant for air conditioners is R134a, and it has boiling point of approximately -26 oC (-15 oF) at our atmospheric pressure. Surprise surprise. Refrigerants will be in gaseous state, under Earth’s majority atmospheric conditions.


The need for compressed refrigerant in air conditioner systems:

Manufacturers of air conditioners use refrigerants, since it has an attractive boiling temperature for heat exchange between air that we live in, and the refrigerant.

But, our atmospheric condition will not allow refrigerant to be in liquid state. Hence, we need to compress it enough, coupled with condensing it, to change the state from gas, to liquid. The energy from compression and condensation overcomes the internal energy of the refrigerant. Hence the state is changed from gas to liquid through compression and condensation.

The condition within the compression cycle is no longer ambient. Hence, we have to put in work to compress the gas and reduce the distances between gas molecules.


Concluding with compression and gas laws:

When we talk about gas laws, Boyle’s, Charles’ and Pressure’s law will come into mind.

We have to have a system filled with gas, in an enclosed or restricted space, for these laws to stand.

I am glad to say that air conditioners use compressors connected by a series of tubing and other parts, in a closed loop system. In other words, compression happens in enclosed and restricted condition.

Gas lawsPressure law states that, for a fixed mass of gas (enclosed system), the pressure (p) in bar is directly proportional to the temperature (T) in Kelvin; maintaining the gas volume (V) in m3. This means that heat is provided (or removed) externally to (or from) the system. Volume is maintained, temperature is increased and as a result, pressure increases (the reverse happens for temperature reduction). This application is used in cannons.


Charles’s law states that, for a fixed mass of gas, the volume (V) is directly proportional to the temperature (T) of the gas, maintaining the system pressure. Heat is provided (or removed) externally, and the gas expands (or contracts) in volume. Hot air balloons use this principle to the max!


Boyle stated that, for a fixed mass of gas, the volume (V) is inversely proportional to the pressure applied (p). Hence, volume will decrease as the pressure is increased.

This compression is an adiabatic compression, if no heat is provided or taken from the system externally. Our favourite air conditioners’ compressors use this principle during compression phase. This principle is also applicable in expansion processes.

I have said that adiabatic compression do not take or give heat due to external influences. However, due to collision of atoms or molecules, temperature within the system will rise.

Since air conditioning systems combine compression, condensation, expansion and evaporation, heat is:

  • generated internally through compression

  • taken from refrigerant through condensation

  • received internally through expansion

  • and provided to the refrigerant through evaporation

What I am trying to conclude is, all three gas laws are used in combination by air conditioner manufacturers, to design a suitable air conditioner compressor for you!


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