Refrigeration & Air Conditioning Technology, 8e - 8
Section 1 Theory of Heat
want to remain competitive, they must obtain the necessary
training with regard to green building and LEED certification.
An alternative to LEED certification is the Green Globes®
program, which is offered by the Green Building Initiative.
The Green Globes program operates on a 1,000-point scale
and certifications range from one to four Green Globes, with
four Green Globes being their highest possible rating. Both the
LEED and Green Globes programs are nationally accepted.
HISToRy of HoME aND
Human beings' first exposure to fire was probably when
lightning or another natural occurrence, such as a volcanic
eruption, ignited forests or grasslands. After overcoming the
fear of fire, early humans found that placing a controlled fire
in a cave or other shelter could create a more comfortable
living environment. Fire was often carried from one place to
another. Smoke was always a problem, however, and methods needed to be developed for venting it outside. Native
Americans, for example, learned in later years to vent smoke
through holes at the peak of their tepees, and some of these
vents were constructed with a vane that could be adjusted to
prevent downdrafts. The fireplaces common in Europe and
North America were vented through chimneys.
Early stoves were found to be more efficient than fireplaces.
These early stoves were constructed of a type of firebrick, ceramic
materials, or iron. In the mid-eighteenth century, a jacket for the
stove and a duct system were developed. The stove could then be
located at the lowest place in a structure, and the heated air in
the jacket around the stove would rise through a duct system and
grates into the living area. This was the beginning of the development of circulating warm-air heating systems.
Boilers that heated water were also developed, and this
water was circulated through pipes in duct systems. The water
heated the air around the pipes, and the heated air passed
into the rooms to be heated. Radiators were then developed. The heated water circulated by convection through the
pipes to the radiators, and heat was passed into the room by
radiation. These early systems were forerunners of modern
hydronic heating systems.
Steam heat became a popular heating option at the
beginning of the nineteenth century and coal was the fuel of
choice for boilers. Coal was desirable because it burned hot
and lasted a long time. But coal was not inexpensive and the
coal dust that was ever-present resulted in health, primarily
breathing, problems for many people. In the late 1920s, the
oil burner was invented and was a very attractive alternative to coal. Oil was less expensive and cleaner than coal and
nobody had to keep feeding coal to keep the fire burning.
Oil remained popular, and inexpensive, until the Arab oil
embargo of 1973 and the Iranian Revolution in 1979. Oil
prices spiked and people had to wait in lines, sometimes for
hours, to get their ration of fuel for their cars. As a result,
many people switched to natural gas, comprised primarily
of methane. Natural gas boilers began to replace the old oil
boilers, just as oil had replaced coal.
After the price shocks of the 1970s, oil prices stayed low
for most of the 1980s and 1990s, with occasional moderate
peaks. Oil prices then rose steadily from the period between
September 11, 2001 and 2009, and continue to fluctuate today.
Today, commercial and residential heating needs are being
met in a number of ways that include traditional hot water
and steam, but new, more efficient technologies are becoming
more attractive. These include radiant heating, radiant cooling, and geothermal heat pump systems.
The HVAC/R industry is rapidly changing due to advancements in technology being spurred on by the need for increased
energy efficiencies. The career opportunities available in
HVAC/R for those who have acquired formal technical training coupled with field experience are unlimited. Schools that
provide excellent technical training in the field are becoming
easier to identify through HVAC/R program accreditation.
As new equipment becomes more technically challenging
and the existing workforce continues to age, the employment
positions available will continue to outnumber applicants for
the foreseeable future. This shortfall in available, competent
HVAC/R service technicians is being addressed through the
cooperative efforts of educational institutions, labor unions,
employers, and manufacturers. Many organizations offer
apprenticeship opportunities that can lead to high-income
positions. Manufacturers are also teaming up with select educational institutions across North America to help develop
the next generation of HVAC/R technicians.
Many newer buildings are constructed so tightly that the
quality of the air must be controlled by specialized equipment.
The conditions of the air must also be carefully controlled in
areas that perform manufacturing processes. Heating and airconditioning systems control the temperature, humidity, and
total air quality in residential, commercial, industrial, and other
types of buildings. Refrigeration systems are used to store and
transport food, medicine, and other perishable items. Refrigeration and air-conditioning technicians design, sell, install, or
maintain these systems. Many contractors and service companies specialize in commercial refrigeration. The installation and
service technicians employed by these companies install and
service refrigeration equipment in supermarkets, restaurants,
hotels/motels, flower shops, and many other types of retail and
wholesale commercial businesses.
Other contractors and service companies may specialize in
air-conditioning. Many specialize in residential-only or commercial-only installation and service; others may install and service both residential and commercial equipment up to a specific
size. Air-conditioning may include cooling, heating, humidifying,