13A1. Air-conditioning. Air-conditioning is
a field of engineering dealing with the design,
construction, and operation of equipment used
in establishing and maintaining desirable in
door air conditions. These conditions vary
according to the special requirements of the
installation, which may be in a theater, factory, store, submarine, or any other enclosure
occupied by human beings.
In the modern engineering practice of air
conditioning, two phases are involved:
1. Actual conditioning of air, that is, the
alteration under control of its temperature,
humidity, purity, and oxygen content.
2. Ventilation, or replacement of stale air
in an enclosure by conditioned air.
These two aspects of air-conditioning are
discussed separately in detail.
13A2. Need for air. Human beings are air
breathing animals. As such, man's lungs
work unceasingly, awake or asleep. No one
can hold his breath longer than a minute or
two. The mechanism of the body demands
that air, regardless of whether it is fresh or
stale, be pumped in and out of the lungs continuously. The muscles that do the pumping
operate automatically and no effort of will
can stop them for longer than a couple of
minutes at most. As a result, every person
inhales and exhales a large number of cubic
feet of air per day.
13A3. Purposes of air-conditioning. Apart
from this merely mechanical reaction, considerations of health, efficiency, and morale
require that the air should be fit to breathe.
This necessitates, among other things, the removal of fumes from a ship's galley, engine
room, battery room, and water closets. Stale
air must then be replaced by fresh air. More
over, the body gives off excess heat and moisture by means of the air that is breathed and
the air in contact with the surface of the
body. It becomes obvious, therefore, that
proper air-conditioning within the enclosed
quarters of a ship is important, and that during the long dives of a submarine it is of even
greater importance.
Air-conditioning is also needed for the
protection of equipment, especially electrical
apparatus. The large amount of moisture in
the air given off daily from the bodies of the
crew, from cooking, batteries, and bilges,
would condense on any cool surface if it
were not removed by air-conditioning. This
moisture, is extracted from the air by the air
conditioning equipment, and is run into a
tank. It is not suitable for drinking, cooking,
or bathing, but is suitable for the washing of
clothes.
B. AIR AS AFFECTED BY HUMAN PRESENCE
13B1. Oxygen content of the air. What we
call air is not a single substance, but is a
physical mixture of various gases. About 1/5
of ordinary outdoor air is oxygen; a little less
than 4/5 is the inert gas nitrogen; about 0.03
percent is carbon dioxide; and the balance,
less than 1 percent, is composed of the gases
argon, helium, krypton, neon, xenon, and
hydrogen. These are the components of dry
air. Usually some water vapor is present also,
varying greatly from day to day according to
the weather.
It is oxygen, of course, that is used by the
body. Measurements have shown that for each
lungful of air breathed in by a person, only
4 percent of the oxygen in it is absorbed by
the blood. It is therefore, evident that the
air in a room can be circulated and breathed
for a considerable period without ill effects.
13B2. Odors. Odors are always present,
though the human sense of smell is not a
keen one and usually is not aware of them.
Almost everything gives off an odor, machinery, clothing, leather, books, food, the human
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body, even when clean and newly bathed,
flowers, and perfume. The odor in an enclosed space is a combination of all such
odors and is carried by the air. However, it is
well known that even if an odor is noticed on
entering a room, a person rapidly becomes
unaware of it because the sense of smell is
easily fatigued.
13B3. The heat and moisture contributed by
human presence. An adult, when engaged in
light work, as in a submarine, gives off on an
average of about 500 Btu per hour. In comparison, a 25-watt electric light bulb gives off
85 Btu per hour; a 60-watt bulb, 205 Btu per
hour; and a 200-watt bulb, 682 Btu per hour.
The heat from a bulb can be felt by the hand
at a distance of several inches, because the
heat-giving surface is concentrated in a small
area. The heat from a human body cannot be
felt because the surface of the body is large,
measuring about 29 square feet for the aver
age adult male. The body also gives off considerable moisture, but the amount varies
greatly according to the activity.
Under normal conditions a person takes in
somewhat more than 3 pounds of water per
day, in beverages and food. Since the body
is maintained at an average condition of
equilibrium, this means that he gives off the
same quantity per day, and much of this is
evaporated directly into the air. If his activity or the air temperature is such as to cause
a greater loss of water through perspiration,
he feels thirsty and drinks more to maintain
the balance. In a small enclosure, or room,
the rise in temperature and moisture of the
air caused by the presence of a number of
people is considerable.
