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TRG-TRC005-EN 25
period three
Evaporators
notes
four rows for the downstream section. This is an attempt to ensure near-equal
loading of the two coil sections when both are active.
A second concern involves the control of superheat. The cooler temperatures
leaving the upstream section of coil hamper the ability of the downstream
section of coil to provide adequate superheat.
Row-split coils are generally not recommended for comfort-cooling
applications. When applied, they require careful coil selection, expansion valve
sizing and selection, and control.
The capacity of a shell-and-tube evaporator is primarily controlled by the
unloading or cycling of compressors. However, as with a finned-tube
evaporator, it also uses an expansion valve to control the flow rate of
refrigerant through the evaporator and ensure the proper amount of superheat
in the system.
A shell-and-tube evaporator may also contain more than one liquid refrigerant
circuit, each served by one expansion valve.
Shell-and-Tube Evaporator Control
refrigerant
refrigerant
vapor
vapor
liquid
liquid
refrigerant
refrigerant
expansion
expansion
valve
valve
shell-and-tube
shell-and-tube
evaporator
evaporator
Figure 37