For any given application, the air-conditioning system must have sufficient capacity to remove the quantity of heat necessary to lower the vehicle interior temperature to an acceptable level.
Since heat is a form of energy, it cannot be destroyed. The air-conditioning process is simply one of removing heat from one place and transferring it to another.
The temperature level arrived at is simply the degree of hotness or coldness achieved and is usually measured on the Celsius scale which has two fixed points.
The freezing point of water, that is when it turns to ice, is the lower fixed point.
The boiling point of water, that is when it turns to steam, is the upper fixed point.
When water turns to ice, heat has been removed from the liquid water to bring about a change of state - to a solid.
That is, when sufficient heat is removed from a body of water, its temperature will reduce to 0°C and it will remain at zero degrees until all the water has changed to its solid state - ice.
For water to boil, heat has to be added to the water.
While it is boiling, heat has to be added to it continuously to change its state from a liquid to a vapor.
At standard atmospheric pressure, all the time the water is boiling, its temperature remains constant at 100°C until all the liquid has been transformed.
If the water vapor is contained and the same amount of heat is removed from it, then it will condense back into a liquid.
The greatest quantity of heat movement occurs during these changes of state, while a liquid is boiling and changing into a vapor and when a vapor is condensing back into a liquid.
This is known as Latent Heat.
If a liquid is subjected to pressure, its boiling point is raised. Therefore a higher temperature must be achieved to make it boil and change to a gas.
Subjecting water, in a closed container, to a pressure of 100 kilopascals above atmospheric, will raise its boiling point to approximately 120°C.
Similarly if the pressure in the container is reduced then the boiling point will also be reduced.
Source: CDX Global
