A/C Technology Basic Principles

A/C Technology Basic Principles

Physical Principles







The four known states of water also apply to air conditioning system refrigerants.
1. gaseous (invisible)
2. vapor
3. fluid
4. solid







When water is heated in a vessel (heat absorption), water vapor can be seen to rise. If the vapor is further heated through heat absorption, the visible vapor turns into invisible gas. The process is reversible. The warmth is extracted from gaseous water, vapor forms first, then water and then ice.

A - Heat absorption
B - Heat emission

Heat Transfer
Every substance consists of a mass of moving molecules. The fast moving molecules of a warmer substance give off some of their energy to the cooler and thus slower molecules. As a result, the molecular motion of the warmer substance slows down and that of the colder substance is accelerated. This process continues until the molecules of both substances are moving at the same speed. They are then at the same temperature and no further heat exchange takes place.

Pressure and Boiling Point
The boiling point given in tables for a liquid is always referenced to an atmospheric pressure of 1 bar. If the pressure acting on a fluid changes, its boiling point also changes.

For example, water boils at a lower temperature the lower the pressure.

The vapor pressure curves for water and refrigerant R134a show for example that, at constant pressure, reducing the temperature changes vapor to liquid (in condenser) or that, for instance, reducing pressure causes the refrigerant to change from liquid to vapor state (evaporator).







Vapor pressure curve of water
A - fluid
B - gaseous
C - Vapor pressure curve of water
1 - Pressure acting on liquid in bar (absolute)
2 - Temperature in degree C







Vapor pressure curve of refrigerant R134a
A - fluid
B - gaseous
D - Vapor pressure curve of refrigerant R134a
1 - Pressure acting on liquid in bar (absolute)
2 - Temperature in degree C.