Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

Air-Conditioning

Though 30 or 40 years ago air-conditioning

was primarily a luxury found in large vessels,

today more boats and smaller boats have air-

conditioning installed. Air-conditioning units,

of course, cool the air, but they are called

“air-conditioners” rather than “air coolers”

because they also condition the air by reduc-

ing humidity—a critical component in com-

fort. (In large home and commercial installa-

tions, air-conditioners also further condition

the air by filtering it.)

Pumping Heat

Air-conditioning, in fact, does not make cold.

Instead, air-conditioning moves heat from

place to place. On boats, it pumps the heat

from the cabin interior and dispels it into the

water outside. Indeed, air-conditioners are re-

ally heat pumps. Essentially, they all work sim-

ilarly. The compressor changes (compresses)

the refrigerant into a high-temperature vapor

at high pressure. The vapor flows through the

heat exchanger where it loses heat to the

seawater and condenses into a liquid at high

temperature and pressure. From here, the

refrigerant travels to the evaporator (in the

cabin), where it passes though a small orifice.

(The evaporator is in the air handler, which

includes an evaporator coil with metal heat-

transfer fins and blower.) Passing through this

orifice into the evaporator tubes causes the

liquid to expand. Thus, it is transformed into

a low-temperature vapor at low pressure. Heat

from the cabin air blowing over the evaporator

is absorbed by the now cold refrigerant, and

the cooled air is blown back into the cabin.

The refrigerant continues back to the com-

pressor where the cycle repeats.

Freon Anyone?

For years, the refrigerant in more than

90 percent of air-conditioners (and in refrig-

erators, which operate using the same princi-

ple) was Freon. Freon, however, is a chloro-

fluorocarbon (CFC). CFCs are the chemicals

that have been dissolving holes in our ozone

layer, so they’ve been almost entirely banned.

New air-conditioners use various alternative

refrigerants such as DuPont’s HFC-134a

(a hydrofluorocarbon), R-12 or R-22 (also

hydrofluorocarbons), or OZ Technology’s

HC-12a (an organic, environmentally com-

patible hydrocarbon compound).

Air-Conditioner Types

For boats, just two types of air-conditioning

are commonly available: direct expansion and

Air-Conditioning

and Heating

CHAPTER 15 With Notes on Refrigeration