Economizers are mechanical devices intended to reduce energy consumption, Imagine it as a sort of heat exchanger.
They could be divided in two main types, which are internal and external economizer systems. The possibility of energy savings exists both in the chiller itself and in the rest of the chiller system. Because of that modifications of the chiller which are connected with the changes in the vapour compressed cycle are referred to the internal economizers. Whereas the changes in configuration of the chiller system, which helps to save the energy by using cold outside air, are referred to the external economizer systems.
Operating principle economizers can be compared with the opening of the window. This is quite natural idea when the room temperature is higher than the outside temperature. In such a way, letting more air than is needed, the use of mechanical cooling can reduced or even turned off.
An economizer increases the refrigeration effect by further sub-cooling the already sub-cooled liquid by a further 5deg C. The liquid line pipework from the condenser branches off. The one leg of the pipework remains full of sub-cooled liquid. The other branch of pipework goes into an expansion valve where the pressure is lowered and the liquid becomes a cold gas. This gas then passes over the other branched pipe containing the warm high pressure sub-cooled liquid inside the economizer. This cold gas further cools the warm sub-cooled liquid pipe. As a result the gas warms up due to heat extracted from the sub-cooled liquid. This now super-heated gas is diverted back into the suction of the compressor.
The liquid line is further subcooled another 5k without needing to have a bigger condenser and extra condenser fans. It is an economic solution hence the name economizer.