Hudson 1955 Rambler, Техническое и сервисное руководство

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ALL SEASON AIR CONDITIONING SYSTEM 3
which denotes the quantity of heat present in the
substance.
Cold is the absence of heat or the lack of heat.
Then heat being energy cannot be destroyed and cold
is the lack of heat, consequently, a thing or place
is cold to the extent that heat has been removed
from it. Heat always moves from a warm object or
place to a colder object or place. Refrigeration
is a process developed to remove heat from objects
or places.
The control of temperature in air conditioning
is accomplished by transferring heat from a place
where it is not wanted to a place where it makes
no difference.
Lowering the temperature inside the car by
modified refrigeration to a comfort zone, namely
15 to 20 degrees below that of the outside
temperature is done in the case of passenger car
air conditioning. The outside ambient temperature
may be high, humid or dry, and uncomfortable in
respect to comfort. Ambient temperature is the
surrounding temperature around a place or object.
Humidity Control
The ambient air may be humid or dry. The air within
an enclosure such as the car will be correspond-
ingly affected as a certain amount of fresh air is
used in the air conditioning cycle. All atmo-
spheric air, unless specially treated, contains a
certain amount of moisture in the form of water
vapor. The amount of water vapor present varies
from day to day depending upon the weather
conditions.
A high relative humidity of the air is one
factor that is predominant in personal discomfort.
Humidity is the amount of moisture in the air in
the form of gaseous vapor. Relative humidity is
the ratio of the weight of water vapor present in
a given sample of air at a given temperature to
the weight of water vapor which would be present
in the same sample, if the air were saturated at
the same temperature and pressure. It should be
noted that air at any fixed temperature can only
hold a definite known quantity of water. At higher
temperatures, air is capable of holding more
moisture than at lower temperatures. Hence, if the
temperature of saturated air is lowered, the
excess water vapor will condense.
In air conditioning or refrigerating the air,
the air is dehumidified by lowering the moisture
content of the air. This is possible by lowering
the temperature of the air below the dew point and
consequently condensing some of the moisture out
of the air. The water vapor condenses on the cold
evaporator core and the liquid is drained off.
This is a basic principle in the control of
humidity in air conditioning.
To reduce the relative humidity completely in
an air conditioning system is not desirable.
Relative humidity does have a significant effect
on comfort within a fairly wide temperature range.
The normal "comfort zone" for people has been found
to exist within a temperature range of 67º to 91º
and the relative humidity range of 30 per cent to
70 per cent. Combinations of temperatures and
relative humidities outside of this range produce
various types of discomfort.
Control of Distribution and Cleanliness
The control of distribution, motion, and cleanli-
ness is carried on at the same time. Approximately
30 per cent fresh air is introduced into this
particular system. At the point of introduction,
the air is cleaned of dust and foreign material in
passing through the filter provided for this
purpose. The blower in the system will recirculate
the air in the car through the cooling unit,
consequently, the air temperature is being con-
stantly lowered. The air is being freshened by the
addition of the fresh air being introduced into
the car. The entrance of fresh air added to the
volume already present will serve to mildly
pressurize the car interior. Air will then leak
outward carrying with it smoke, odors, and carbon
dioxide. Pressurizing the car prevents entrance of
hot dusty air. The air being circulated is returned
and carried over the evaporator and cooled in a
continuous cycle, thus again cooling the air. It
must be remembered, to effectively air condition
the car, all windows should be closed and remain
closed during the time the air conditioner is being
used.
To accomplish the foregoing controls in air
conditioning, a mechanical means must be employed.
Mechanical refrigeration or mechanical air condi-
tioning is the system used.
Means of Producing Refrigeration
A substance or body is said to be refrigerated when
heat is removed from the substance or body faster
than it can gain heat. Whenever this condition
exists, the temperature of the substance is
lowered or reduced.
Refrigeration may be produced by several
methods. The vapor compression system is employed
in the "All Season Air Conditioning System". In
the compression system, a suitable liquid is
evaporated in the cooling unit at a low pressure
and then compressed to a high pressure in the
mechanical compressor and then condensed to a
liquid again in a condenser completing the
refrigeration cycle.
This method utilizes the
"Latent Heat" or hidden heat of vaporization to
produce the desired refrigerating effect.
"Latent heat of evaporation" is defined as the
quantity of heat necessary to evaporate or convert
one pound of liquid to vapor without a change of
temperature of the liquid.
Thus, the latent heat of evaporation for water
is 970 B.T.U., since it takes 970 B.T.U. to
evaporate one pound of water at 212°F. and
atmospheric pressure to steam at the same temper-
ature and pressure.
The latent heat of evaporation of different
substances differ considerably from each other.