Learning Objectives: Understand the principles of air conditioning and the operation
of basic air-conditioning systems. Recognize the characteristics and procedures
required to install, operate, and maintain air-conditioning systems
Air conditioning is the simultaneous control of
temperature, humidity, air movement, and the quality
of air in a conditioned space or building. The intended
use of the conditioned space is the determining factor
for maintaining the temperature, humidity, air
movement, and quality of air. Air conditioning is able
to provide widely varying atmospheric conditions
ranging from conditions necessary for drying
telephone cables to that necessary for cotton spinning.
Air conditioning can maintain any atmospheric
condition regardless of variations in outdoor weather.
This chapter explains the following subjects as they
pertain to air conditioning: principles of air
conditioning, heat pumps, chilled-water systems,
periodic maintenance, cooling towers, troubleshooting,
automotive air conditioning, and ductwork.
PRINCIPLES OF AIR CONDITIONING
Learning Objective: Understand the basic principles
of temperature, humidity, and air motion in relation to
Air conditioning is the process of conditioning the
air in a space to maintain a predetermined temperature-
humidity relationship to meet comfort or technical
requirements. This warming and cooling of the air is
usually referred to as winter and summer air
Here, you are introduced to the operating principles
of air-conditioning systems, the environmental factors
controlled by air conditioning, and their effects on
health and comfort. Refrigerative air conditioners and
general procedures pertaining to the installation,
operation, and maintenance of these systems are
examined. Also, the operation and maintenance of the
controls used with these systems are explained.
Temperature, humidity, and air motion are
interrelated in their effects on health and comfort. The
term given to the net effects of these factors is effective
temperature. This effective temperature cannot be
measured with a single instrument; therefore, a
psychrometric chart aids in calculating the effective
temperature when given sufficient known conditions
relating to air temperatures and velocity.
Research has shown that most persons are
comfortable in air where the effective temperature lies
within a narrow range. The range of effective
temperatures within which most people feel
comfortable is called the COMFORT ZONE. Since
winter and summer weather conditions are markedly
different, the summer zone varies from the winter
zone. The specific effective temperature within the
zone at which most people feel comfortable is called
the COMFORT LINE (fig. 7-1).
Air at a high temperature and saturated with
moisture makes us feel uncomfortable. However, with
the same temperature and the air fairly dry, we may
feel quite comfortable. Dry air, as it passes over the
surface of the skin, evaporates the moisture sooner
than damp air and, consequently, produces greater
cooling effect. However, air may be so dry that it
causes us discomfort. Air that is too dry causes the
surface of the skin to become dry and irritates the
membranes of the respiratory tract.
HUMIDITY is the amount of water vapor in a
given volume of air. RELATIVE HUMIDITY is the
amount of water vapor in a given amount of air in
comparison with the amount of water vapor the air
would hold at a temperature if it were saturated.
Relative humidity may be remembered as a fraction or
percentage of water vapor in the air; that is, DOES
HOLD divided by CAN HOLD.