14-08-2012, 02:48 PM
REFRIGERATION and AIR CONDITIONING SYSTEM
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INTRODUCTION
This section briefly describes the main features of the refrigeration and air conditioning
system.
What is Refrigeration and Air Conditioning
Refrigeration and air conditioning is used to cool products or a building environment. The
refrigeration or air conditioning system ® transfers heat from a cooler low-energy reservoir
to a warmer high-energy reservoir (see figure 1).
Air-Conditioning Systems
Depending on applications, there are several options / combinations of air conditioning,
which are available for use:
§ Air conditioning (for space or machines)
§ Split air conditioners
§ Fan coil units in a larger system
§ Air handling units in a larger system
Refrigeration Systems (for processes)
The following refrigeration systems exists for industrial processes (e.g. chilling plants) and
domestic purposes (modular units, i.e. refrigerators):
§ Small capacity modular units of the direct expansion type similar to domestic
refrigerators.
§ Centralized chilled water plants with chilled water as a secondary coolant for a
temperature range over typically 5 oC. They can also be used for ice bank formation.
Description
Compression refrigeration cycles take advantage of the fact that highly compressed fluids at a
certain temperature tend to get colder when they are allowed to expand. If the pressure
change is high enough, then the compressed gas will be hotter than our source of cooling
(outside air, for instance) and the expand ed gas will be cooler than our desired cold
temperature. In this case, fluid is used to cool a low temperature environment and reject the
heat to a high temperature environment.
Vapour compression refrigeration cycles have two advantages. First, a large amount of
thermal energy is required to change a liquid to a vapor, and therefore a lot of heat can be
removed from the air-conditioned space. Second, the isothermal nature of the vaporization
allows extraction of heat without raising the temperature of the working fluid to the
temperature of whatever is being cooled. This means that the heat transfer rate remains high,
because the closer the working fluid temperature approaches that of the surroundings, the
lower the rate of heat transfer.