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.
Shell-and-Tube Evaporator Control
shell-and-tube evaporator
refrigerant vapor
liquid 
refrigerant 
expansion valve
Figure 37
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.
Ashell-and-tube evaporator may also contain more than one liquid refrigerant circuit, each served by one expansion valve.
