AC-SVX003A-EN
75
product offering. The fan impeller is a bladed-shrouded fan
made from heavy-duty molded plastic.
Standard units will start and operate between 32 to 105°F
(0 to 40°C) ambient.
The unit controller calculates optimum fan speed for
maximum efficiency based on compressor load and
outdoor air, resulting in high IPLV values
Evaporator
Evaporators are configured as follows:
• Tube-in-shell heat exchanger design, constructed from
carbon steel shells and tubesheets.
• Internally and externally finned seamless copper tubes
are mechanically expanded into the tube sheets.
• Designed, tested, and marked in accordance with the
ASME Boiler and Pressure Vessel Code for a
refrigerant side working pressure of 200 psig.
• Water side working pressure 150 psig.
• Water connection design:
– Standard: Grooved for Victaulic style pipe
couplings.
– Optional: Flange style connections.
• Waterboxes include vent, drain. and fittings for
temperature control sensors. Available pass
configurations:
– 150 to 330 ton units: 2 or 3–pass
– Units larger than 330 tons: 1 or 2–pass
• Insulated (3/4 inch closed cell).
• Evaporator water heaters with thermostat are provided
to protect the evaporator from freezing at ambient
temperatures down to -20°F (-29°C).
• Factory installed flow switch is installed on the supply
water box in the evaporator inlet connection.
Free-Cooling Operating Modes
The advantage of optional chiller integrated free-cooling is
the ability to utilize outdoor air temperatures to assist in
making chilled water when appropriate. The unit controls
direct flow through or around the free-cooling coils to
optimize chiller efficiency. Determining the operating mode
depends on four temperatures:
• Ambient air temperature
• Evaporator entering fluid temperature
• Evaporator leaving fluid temperature
• Chilled water setpoint
Table 27. Free-cooling operation
Component Mechanical Cooling
Combined Mechanical
and Free-Cooling
Free-Cooling Only
Fan Control Valve Control
Ambient Air Greater than Fluid Less than Fluid Less than Fluid Less than Fluid
Compressors On — Modulating On — Modulating
Off Off
Fans
On — Modulating On — Modulating Modulating
15%
Free-Cooling
Coil Flow
Off 100% 100%
Modulating
Mechanical Cooling Mode
In this operating mode, ambient temperature is the same or
higher than the temperature of the fluid entering the
evaporator. Free-cooling coils are bypassed, compressors
are running, and the controls modulate compressors and
fans to meet cooling load at optimum efficiency.
Combined Mechanical and Free-Cooling
Mode
If the ambient temperature is below the evaporator entering
fluid temperature, and free-cooling only cannot satisfy the
load, the controls modulate compressors and fans to meet
the remaining cooling load at optimum efficiency. Fluid will
continue to flow through free-cooling coils, reducing the
evaporator entering fluid temperature.
Note: Depending on load, one or both circuits may engage
mechanical cooling.
Free-Cooling Only Mode
In this operating mode, free-cooling is enabled and capable
of meeting the cooling load without the need for
mechanical cooling. As ambient falls below the
temperature at which full load capacity is provided by free
cooling only (or as the load drops), capacity control is
accomplished by fan control and control valve modulation.
If ambient (or load) continues to drop, valve control
provides modulation between free-cooling coils.
Operating Principles
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