The maintenance of the high vacuum within the shell is
important to the proper operation of the plant.
Fan-Coil Assemblies
Fan-coil assemblies (fig. 10-22) use chilled water to
air-condition spaces. These assemblies are known as
spot coolers. The chilled water is piped through the
cooling coils of the units, and a fan forces air over the
coils. Note the chilled water connections, the vent cock
at the top, and the condensate collection tray at the
bottom of the unit.
The condensate collection tray collects the moisture
condensed out of the air. The condensate is generally
piped to the bilge or a waste water drain system. It is
important that the drain for the collection tray be kept
clear. If the condensate cannot drain out of the tray, it
collects and evaporates, leaving impurities that can
rapidly cause the tray to corrode.
SELF-CONTAINED AIR CONDITIONERS
Ships without central air conditioning may use
self-contained air-conditioning units. Naval Sea
Systems Command (NAVSEASYSCOM) approval is
required. A self-contained air-conditioning unit is
simply the type of air conditioner you see installed in
the windows of many homes. All that is required for
installation is to mount the proper brackets for the unit
case and provide electrical power.
These units use nonaccessible hermetically sealed
compressors (motor and compressor are contained in a
welded steel shell). For this reason, shipboard
maintenance of the motor-compressor unit is
impractical. The thermal expansion valve used in these
units is preset and nonadjustable. However, a thermostat
and fan speed control are normally provided for comfort
adjustment.
AIR COMPRESSORS
The air compressor is the heart of any compressed
air system. It takes in atmospheric air, compresses it to
the desired pressure, and moves it into supply lines or
into storage tanks for later use. Air compressors come
in different designs and configurations and have
different methods of compression. Some of the most
common types used on gas turbine ships are discussed
in this chapter.
Before describing the various types of air
compressors, you need to know about the composition
of air and some of the things air may contain. This
discussion should help you understand why air
compressors have special features that prevent water,
dirt, and oil vapor from getting into compressed air
piping systems.
Air is mostly composed of nitrogen and oxygen. At
atmospheric pressure (within the range of temperatures
for the earth’s atmosphere), air is in a gaseous form. The
Figure 10-22.-Fan-coil assembly.
10-24
