A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required. As a necessary byproduct, refrigeration creates waste heat that must be exhausted to ambient or, for greater efficiency, recovered for heating purposes. Concerns in design and selection of chillers include performance, efficiency, maintenance, and product life cycle environmental impact.
A chiller plant design consists of many pieces of HVAC equipment that are all interconnected by piping to form a chiller plant. This article will look at a water cooled chiller plant design.
The major parts of a water cooled chiller are the compressors, the evaporator heat exchanger (piping circuit #1) and the condenser heat exchanger (piping circuit #2). There are two separate piping circuits in a chiller plant design.
A chiller produces cold water that is typically circulated (pumped) to cooling coils that are inside air conditioning units. This is called the chilled water piping circuit, circuit #1.
The air conditioning unit fan takes air from a room and blows this air across the cooling coil to produce colder air and then circulates this colder air through a duct system to cool the room.
Once the cold water from the chiller cools the air, it becomes warmer, and it must be circulated back to the chiller so that it can become cooler again.
A chiller uses a refrigerant to cool the water, but once it cools the water the refrigerant becomes warmer and it rejects its heat to the cooling tower (or condenser water) piping circuit, circuit #2, so that the entire process can start over.
The chiller can be water-cooled, air-cooled or evaporatively cooled. The compressor types typically are reciprocating, scroll, screw or centrifugal. The evaporator can be remote from the condensing section on air-cooled units. This has the advantage of allowing the chilled water loop to remain inside the building envelope when using an outdoor chiller. In applications where freezing conditions can be expected, keeping the chilled water loop inside the building avoids the need for some form of antifreeze.
There can be multiple chillers in a chilled water plant. The details of various multiple chiller plant designs will be discussed in future sections.
The chilled water flows through the evaporator of the chiller. The evaporator is a heat exchanger where the chilled water gives up its sensible heat (the water temperature drops) and transfers the heat to the refrigerant as latent energy (the refrigerant evaporates or boils).
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