Table of Contents
Advertisement
Operating Principles
This section contains an overview of the operating
principles of the Thermafit™ TACW modules equipped with
Danfoss MCX controllers.
Refrigeration Circuits
The refrigeration cycle makes use of a shell-and-tube
evaporator design with refrigerant evaporating on the shell
side and water flowing inside tubes having enhanced
surfaces.
The compressor is a two-stage oil-free variable speed
centrifugal magnetic bearing type. The magnetic bearings
allow the compressor to operate without the use of oil for
lubrication, which reduces energy losses due to friction and
increases the heat transfer efficiency of the chiller. A
variable speed drive on the motor allows the compressor to
operate much more efficiently at partial loads.
Condensing is accomplished in a shell-and-tube heat
exchanger where refrigerant is condensed on the shell side
and water flows internally in the tubes. Refrigerant is
metered through the flow system using an electronic
expansion valve that maximizes chiller efficiency at part
load. Microprocessor-based unit control modules provide
for accurate chilled water control as well as monitoring,
protection and adaptive limit functions. The "adaptive"
nature of the controls intelligently prevents the chiller from
operating outside of its limits, or compensates for unusual
operating conditions, while keeping the chiller running
rather than simply tripping due to a safety concern. When
problems do occur, diagnostic messages assist the
operator in troubleshooting.
Refrigeration Cycle
Evaporation of refrigerant occurs in the evaporator that
maximizes the heat transfer performance of the heat
exchanger while minimizing the amount of refrigerant
charge required. A metered amount of refrigerant liquid
enters a distribution system in the evaporator shell and is
then distributed to the tubes in the evaporator tube bundle.
The refrigerant vaporizes as it cools the water flowing
through the evaporator tubes. Refrigerant vapor leaves the
evaporator as saturated vapor.
The refrigerant vapor generated in the evaporator flows to
the suction end of the compressor where it enters the
ARTC-SVX007A-EN
motor compartment of the motor. The refrigerant flows
across the motor, providing the necessary cooling, then
enters the compression chamber. Refrigerant is
compressed in the compressor to discharge pressure
conditions.
Immediately following the compression process the oil-free
refrigerant vapor enters the condenser. Baffles within the
condenser shell distribute the compressed refrigerant
vapor evenly across the condenser tube bundle. Cooling
device water, circulating through the condenser tubes,
absorbs heat from this refrigerant and condenses it.
As the refrigerant leaves the bottom of the condenser, it
enters an integral subcooler where it is subcooled before
traveling to the electronic expansion valve. The pressure
drop created by the expansion process vaporizes a portion
of the liquid refrigerant. The resulting mixture of liquid and
gaseous refrigerant then enters the Evaporator Distribution
system. The flash gas from the expansion process is
internally routed to the compressor suction, and while the
liquid refrigerant is distributed over the tube bundle in the
evaporator.
The TACW chiller maximizes the evaporator heat transfer
performance while minimizing refrigerant charge
requirements. This is accomplished by metering the liquid
refrigerant flow to the evaporator's distribution system
using the electronic expansion valve.
Compressor
The compressor uses two impellers on a single, high-
speed, rotating shaft. The rotating shaft and impeller
assembly is the only moving part in the compressor.
The compressor has a fully integrated variable-speed drive
with soft start. The variable-speed drive allows the
compressor to be highly efficient, especially at partial load
and the soft-start feature reduces start-up stress.
The single shaft rotates within magnetic bearings. This
unique feature reduces friction, adding to the overall high
efficiency, and eliminates the metal-on-metal contact of
conventional bearings. This, in turn, allows the chiller to
operate without the need for lubricating oil. Eliminating
lubricating oil eliminates the need for several ancillary
components required to support the oil system (e.g., oil
pumps, oil heaters, oil separators, and oil filters).
17
Advertisement
Table of Contents
