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Operating Principles
This section contains an overview of the operating
principles of the Thermafit™ AMC chiller modules design
equipped with Carel c.pCO™ controller.
Refrigeration Circuits
Each chiller module has two refrigerant circuits, each with a
scroll compressor. Each refrigerant circuit includes
compressor suction and discharge service valves, liquid
line shutoff valve, sealed filter drier, liquid line sight glass
with moisture indicator, charging port, and a thermal
(standard) or electronic (with compressor VFD) expansion
valve.
Refrigeration Cycle
Each chiller module uses a brazed-plate evaporator. The
suction lines are designed to minimize pressure drop. The
scroll compressor pressurizes vaporized refrigerant from a
low pressure and temperature to high pressure and
temperature. De-superheating, condensing, and sub-
cooling is accomplished in a fin and tube air-cooled
condenser where refrigerant is condensed in the tubes.
Refrigerant flowing through the system is balanced by a
thermal or electronic expansion valve.
Refrigerant R-454B
Trane believes responsible refrigerant practices are
important to the environment, our customers, and the
modular chiller industry.
Thermafit™ AMC chiller uses environmentally friendly,
class A2L, R-454B refrigerant. R-454B is a zero-ozone
depleting, zeotropic, hydrofluoroolefin (HFO) based
refrigerant blend. It is designed to serve as direct
replacement for R-410A, yet has 78% lower Global
Warming Potential (GWP) (466). R-454B has similar
capacity and has better efficiency to R-410A.
Compressor and Oil System
Each compressor is hermetic, scroll type, and has constant
speed, and there is one on each refrigeration circuit.
An optional variable speed drive is available for use on
standard fixed speed compressors and allows capacity
modulation from 58% to 100% of the compressor capacity.
Condenser and Fans
Air-cooled condenser coils have aluminum fins
mechanically bonded to internally finned seamless copper
tubing. Spacing is 16 fins per inch. Copper fins and an
epoxy, corrosion-resistant coating are available options for
environmentally harsh chiller locations (coastal areas).
The condenser coil has an integral subcooling circuit.
Condensers are factory proof tested and leak tested.
ARTC-SVX008A-EN
Condenser fans are direct-drive, vertical discharge,
maintenance free, and have highly efficient Electronically
Commutated Motors (ECM). These variable speed fan
assemblies varies fan motor RPM to maintain the
refrigeration pressure of the chiller modules and allow
operation of the chiller down to 0°F ambient.
Evaporator
The evaporator in each module is dual circuit, brazed-plate
design, constructed of 316 stainless steel plates and
copper brazing. The fluid connections to each evaporator
uses roll grooved couplings for service convenience and
ease of installation.
Evaporators are insulated with ¾ inch closed cell
insulation.
Heat tracing can optionally be provided on the evaporators
and all fluid components for freeze protection. A factory
installed flow switch is installed on the branch line
discharge of the evaporator (typical).
Free-Cooling Operating Modes
The advantage of optional chiller integrated free-cooling is
the ability to use outdoor air temperatures to assist in
making chilled fluid with or without mechanical cooling.
Determining the operating mode depends on four
temperatures:
•
Ambient air temperature
•
Evaporator entering fluid temperature
•
Evaporator leaving fluid temperature
•
Chilled water setpoint
When the ambient temperature falls to 5°F below the
entering fluid temperature, a three-way valve diverts the
fluid from the internal header to the free cooling coils. If the
free cooling coils do not cool the fluid down to the set point,
the fluid continues to the brazed-plate evaporator for
further mechanical cooling.
Mechanical Cooling Mode
In this operating mode, the ambient temperature is less
than 5°F below or higher than the entering fluid
temperature to the chiller. The free-cooling coils are
bypassed, compressor(s) are operating, and the fans vary
their speed to control head pressure.
Combined Mechanical and Free-Cooling
Mode
If the ambient temperature is 5°F or more below the
evaporator entering fluid temperature, and free-cooling
only cannot satisfy the load, the fluid will continue to flow
through free-cooling coils — reducing the evaporator
entering fluid temperature – and the compressor(s) will
operate to achieve the set point temperature.
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