Description of system and fundamentals of
operation
System operation description
The YORK Model YK Chiller is commonly applied to large air conditioning systems, but may be
used on other applications. The chiller consists of an open motor mounted to a compressor (with
integral speed increasing gears), condenser, evaporator and variable flow control.
The chiller is controlled by a modern state of the art Microcomputer Control Center that monitors
its operation. The Control Center is programmed by the operator to suit job specifications.
Automatic timed start-ups and shutdowns are also programmable to suit nighttime, weekends,
and holidays. The operating status, temperatures, pressures, and other information pertinent to
operation of the chiller are automatically displayed and read on a graphic display. Other displays
can be observed by pressing the keys as labeled on the Control Center. The chiller with the
OptiView Control Center is compatible with an electro-mechanical starter, YORK Solid State Starter
(optional), or Variable Speed Drive (optional).
In operation, a liquid (water or brine to be chilled) flows through the evaporator, where boiling
refrigerant absorbs heat from the liquid. The chilled liquid is then piped to fan coil units or other air
conditioning terminal units, where it flows through finned coils, absorbing heat from the air. The
warmed liquid is then returned to the chiller to complete the chilled liquid circuit.
Figure 1: Compressor pre-rotation vanes
The refrigerant vapor, which is produced by the boiling action in the evaporator, flows to the
compressor where the rotating impeller increases its pressure and temperature and discharges it
into the condenser. Water flowing through the condenser tubes absorbs heat from the refrigerant
vapor, causing it to condense. The condenser water is supplied to the chiller from an external
source, usually a cooling tower. The condensed refrigerant drains from the condenser into the
liquid return line, where the variable orifice meters the flow of liquid refrigerant to the evaporator
to complete the refrigerant circuit.
The major components of a chiller are selected to handle the refrigerant, which would be
evaporated at full load design conditions. However, most systems are called upon to deliver full
load capacity for only a relatively small part of the time the unit is in operation.
9Model YK (Style H), R-134a and R-513A
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