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SYS-APM001-EN Chiller System Design and Control
1
Primary System Components
Chilled-water systems consist of these functional parts:
• Chillers that cool the water or fluid
• Loads, often satisfied by coils, that transfer heat from air to water
• Chilled-water distribution pumps and pipes that send chilled water to the
loads
• Condenser-water pumps, pipes, and cooling towers or condenser fans that
reject heat from the chiller to ambient air
• Controls that coordinate the operation of the mechanical components
together as a system
In most cases, the chiller’s purpose is to make water colder. Some chillers cool a
mixture of water and other chemicals, most commonly added to prevent
freezing in low-temperature applications. Other additives may be used to
modify the properties of the fluid, thereby making it more suitable for its
intended application. For the purposes of this manual, the term water can be
understood to be any such acceptable fluid, with recognition of the diverse
applications in which chillers are used.
The chiller rejects the heat extracted from the chilled water, plus the heat of
compression (in the vapor-compression cycle), or the heat of absorption (in the
case of an absorption chiller) to either the ambient air (air-cooled) or to another
circuit of water (water-cooled). If the compressor-motor is refrigerant cooled,
the chiller also rejects heat generated by motor inefficiency. Air-cooled
condensers use fans to facilitate cooling by the ambient air. Water-cooled
condensers typically use an evaporative cooling tower.
After the water has been chilled, it is distributed via pumps, pipes, and valves
(the distribution system) to the loads, where a heat exchanger—for example, a
cooling coil in an air-handler—transfers heat from the air to the chilled water,
which is returned to the chiller.
Each component of the chilled-water system is explained in more detail in the
following sections.
Chiller
There are a variety of water chiller types. Most commonly, they are absorption,
centrifugal, helical rotary, and scroll. Some reciprocating chillers are also
available. Chillers can be either air- or water-cooled. Major vapor-compression
chiller components include an evaporator, compressor(s), condenser, and
expansion device(s) (Figure 1). This manual discusses the chiller’s evaporator
and condenser and their relationship to the chilled-water system.
For more details on the basic operation
and components of a chilled-water
system, consult another Trane
publication, Chilled-Water Systems, part
of the Air Conditioning Clinic Systems
Series (TRG-TRC016-EN).
Specific application considerations for
absorption chillers are addressed in
another Trane publication, Absorption
Chiller System Design (SYS-AM-13).