Refrigerants
For every refrigerant there is a specific boiling, or vaporization, temperature
associated with each pressure, so that it is only necessary to control the pressure in the
evaporator to obtain a desired temperature. A similar pressure-temperature relationship
holds in the condenser.
Halocarbon Refrigerants
NUMERICAL
DESIGNATION
CHEMICAL NAME
CHEMICAL FORMULA
11
12
13
22
40
113
114
Trichloromonofluoromethane
Dichlorosifluoromethane
Monochlorotrifluoromethane
Monochlorodifluoromethane
Methyl Chloride
Trichlorotrifluoromethane
Dichlorotetrafluoroethane
Chloropentafluoroethane
Chlorodifluoroethane
R-22/115 (48.8/51.2)
CCl3F
CCl2F2
CClF3
CHClF2
CH3Cl
CCl2FCClF2
CClF2CClF2
C2F5Cl
C2H3ClF2
CHCIF2 /C2F5Cl
115
142b
502
Table 15.2 Some inorganic refrigerants
NUMERICAL
DESIGNATION
702
704
717
718
720
728
729
CHEMICAL NAME
CHEMICAL FORMULA
Hydrogen
Helium
Ammonia
Water
Neon
Nitrogen
Air
732
740
744
744A
764
Oxygen
Argon
Carbon Dioxide
Nitrous Oxide
Sulfur Dioxide
H2
He
NH3
H2O
Ne
N2
78.082% N2 ·20.945% O2 · .93
4% Ar
O2
Ar
CO2
N2O
SO2
Table 15.3 Hydrocarbon refrigerants
NUMERICAL
DESIGNATION
CHEMICAL NAME
CHEMICAL FORMULA
170
290
600
600a
Ethane
Propane
n-butane
Isobutane
C2H6
C3H3
C4H10
(CH3)3CH
Basic choice of refrigerants
REFRIGERANT
PRINCIPAL APPLICATION
Air
-
The major use of air as a refrigerant is in
aircraft,where the light weight of an air system
compensates for its low COP.
Ammonia
-
Large industrial low-temperature installations are the
applications where ammonia is most frequently used.
Many new ammonia systems come into operation
each year.
Carbon Dioxide
-
This refrigerant is sometimes used for direct-contact
freezing of food. Its high condensing pressure usually
limits its application to the low-temperature side of a
cascade system where a different refrigerant operates
in the high-temperature section.
Refrigerant 11
-
Along with the refrigerant 113, this refrigerant is
popular for centrifugal compressor systems.
Refrigerant 12
-
This refrigerant is used primarily with reciprocating
compressors for service in domestic refrigeration
appliances and in automotive air conditioners.
Refrigerant 22
-
Because a smaller and lower-cost compressor can be
used with refrigerant 22 than with refrigerant 12, this
refrigerant has taken over many air-onditioning
applications from refrigerant 12.
Refrigerant 502
-
This is one of the newer refrigerants,with some of the
advantages of refrigerant 22 but with the further
advantage of better behavior with oil and lower
compressor discharge temperatures than refrigerant
22.
Global Warming
Global Warming is increase in the average temperature of the atmosphere,
oceans, and landmasses of Earth. The planet has warmed (and cooled) many times during
the 4.65 billion years of its history. At present Earth appears to be facing a rapid
warming, which most scientists believe results, at least in part, from human activities.
The chief cause of this warming is thought to be the burning of fossil fuels, such as coal,
oil, and natural gas, which releases into the atmosphere carbon dioxide and other
substances known as greenhouse gases. As the atmosphere becomes richer in these gases,
it becomes a better insulator, retaining more of the heat provided to the planet by the Sun.
Since the early 20th century, Earth's mean surface temperature has increased
by about 0.8 °C (1.4 °F), with about two-thirds of the increase occurring since 1980.
Scientists predict further warming of 1.4 to 5.8 Celsius degrees (2.5 to 10.4 Fahrenheit
degrees) by the year 2100. This temperature rise is expected to melt polar ice caps and
glaciers as well as warm the oceans, all of which will expand ocean volume and raise sea
level by an estimated 9 to 100 cm (4 to 40 in), flooding some coastal regions and even
entire islands. Some regions in warmer climates will receive more rainfall than before,
but soils will dry out faster between storms. This soil desiccation may damage food
crops, disrupting food supplies in some parts of the world. Plant and animal species will
shift their ranges toward the poles or to higher elevations seeking cooler temperatures and
species that cannot do so may become extinct. The potential consequences of global
warming are so great that many of the world's leading scientists have called for
international cooperation and immediate action to counteract the problem.
Ozone Layer Depletion
The Earth’s atmosphere is made up of different layers. The layer closest to the
surface is called the troposphere which extends from the Earth’s surface up to about 10
kilometers. The ozone layer is located above the troposphere in the stratosphere (10 km
to about 50 km high). Stratospheric ozone is Earth’s natural protection for all life forms,
shielding our planet from harmful ultraviolet-B (UV-B) radiation. UV-B radiation is
harmful to humans, animals, and plant life. The ozone layer is being destroyed by certain
industrial chemicals including ozone depleting refrigerants, halons, and methyl bromide,
a deadly pesticide used on crops.
For over 50 years, chlorofluorocarbons (CFCs) were thought of as miracle
substances. They are stable, nonflammable, low in toxicity, and inexpensive to produce.
Over time, CFCs found uses as refrigerants, solvents, foam blowing agents, and in other
smaller applications. Other chlorine-containing compounds include methyl chloroform, a
solvent, andcarbon tetrachloride, an industrial chemical. Halons, extremely effective fire
extinguishing agents, and methyl bromide, an effective produce and soil fumigant,
contain bromine. All of these compounds have atmospheric lifetimes long enough to
allow them to be transported by winds into the stratosphere. Because they release
chlorine or bromine when they break down, they damage the protective ozone layer. The
discussion of the ozone depletion process below focuses on CFCs, but the basic concepts
apply to all of the ozone-depleting substances (ODS).
In the early 1970s, researchers began to investigate the effects of various chemicals on
the ozone layer, particularly CFCs, which contain chlorine. They also examined the
potential impacts of other chlorine sources. Chlorine from swimming pools, industrial
plants, sea salt, and volcanoes does not reach the stratosphere. Chlorine compounds from
these sources readily combine with water and repeated measurements show that they rain
out of the troposphere very quickly. In contrast, CFCs are very stable and do not dissolve
in rain. Thus, there are no natural processes that remove the CFCs from the lower
atmosphere. Over time, winds drive the CFCs into the stratosphere.
The CFCs are so stable that only exposure to strong UV radiation breaks them down.
When that happens, the CFC molecule releases atomic chlorine. One chlorine atom can
destroy over 100,000 ozone molecules. The net effect is to destroy ozone faster than it is
naturally created. To return to the analogy comparing ozone levels to a stream's depth,
CFCs act as a siphon, removing water faster than normal and reducing the depth of the
stream.
Large fires and certain types of marine life produce one stable form of chlorine that does
reach the stratosphere. However, numerous experiments have shown that CFCs and other
widely-used chemicals produce roughly 84% of the chlorine in the stratosphere, while
natural sources contribute only 16%.
Large volcanic eruptions can have an indirect effect on ozone levels. Although Mt.
Pinatubo's 1991 eruption did not increase stratospheric chlorine concentrations, it did
producelarge amounts of tiny particles called aerosols (different from consumer products
also known as aerosols). These aerosols increase chlorine's effectiveness at destroying
ozone. The aerosols only increased depletion because of the presence of CFC - based
chlorine. In effect, the aerosols increased the efficiency of the CFC siphon, lowering
ozone levels even more than would have otherwise occurred. Unlike long-term ozone
depletion, however, this effect is short-lived. The aerosols from Mt. Pinatubo have
disappeared, but satellite, ground-based, and balloon data still show ozone depletion
occurring closer to the historic trend.
One example of ozone depletion is the annual ozone "hole" over Antarcticathat has
occurred during the Antarctic Spring since the early 1980s. Rather than being a literal
hole through the layer, the ozone hole is a large area of the stratosphere with extremely
low amounts of ozone. Ozone levels fall by over 60% during the worst years.
In addition, research has shown that ozone depletion occurs over the latitudes that include
North America, Europe, Asia, and much of Africa, Australia, and South America. Over
the U.S., ozone levels have fallen 5-10%, depending on the season. Thus, ozone depletion
is a global issue and not just a problem at the South Pole.
Reductions in ozone levels will lead to higher levels of UVB reaching the Earth's surface.
The sun's output of UVB does not change; rather, less ozone means less protection, and
hence more UVB reaches the Earth. Studies have shown that in the Antarctic, the amount
of UVB measured at the surface can double during the annual ozone hole. Another study
confirmed the relationship between reduced ozone and increased UVB levels in Canada
during the past several years.
Laboratory and epidemiological studies demonstrate that UVB causes nonmelanoma skin
cancer and plays a major role in malignant melanoma development. In addition, UVB has
been linked to cataracts. All sunlight contains some UVB, even with normal ozone levels.
It is always important to limit exposure to the sun. However, ozone depletion will
increase the amount of UVB, which will then increase the risk of health effects.
Furthermore, UVB harms some crops, plastics and other materials, and certain types of
marine life.
Colder Temperatures Increase Ozone Damage
Ozone depletion damage gets much worse when the stratosphere is very cold.
This has been the case the past two years, causing extensive ozone depletion. This past
winter, ozone depletion reached the most severe levels ever recorded over the Northern
Hemisphere. Western United States ozone levels also continue to drop 3-4 percent per
decade. Even if all of our efforts to stop harmful emissions are successful, the ozone layer
is not expected to begin recovery until around 2020 at the earliest.
Global Warming Can Increase Ozone Depletion
Scientist's are concerned that continued global warming will accelerate ozone
destruction and increase stratospheric ozone depletion. Ozone depletion gets worse when
the stratosphere (where the ozone layer is), becomes colder. Because global warming
traps heat in the troposphere, less heat reaches the stratosphere which will make it colder.
Greenhouse gases act like a blanket for the troposphere and make the stratosphere
colder. In other words, global warming can make ozone depletion much worse right when
it is supposed to begin its recovery during the next century.
Effects of Ozone Depletion and Global Warming
(UV-B) radiation causes skin cancer, cataracts and immune suppression in both
animals and humans, (Learn More). UV-B also damages plants including hardwood
forests, and phytoplankton (algae is a type of phytoplankton which is the building block
of the oceanic food chain).
Skin Cancer Is Increasing
•
•
•
•
There has been an 1,800 percent rise in malignant melanoma since 1930.
One American dies of skin cancer every hour.
One in five Americans develops skin cancer.
People get 80 percent of their lifetime sun exposure by age 18.
Ozone Depletion Potentials
Compound
Ashrae Number
ODP
1.0
1.0
1.8
CFC
R-11
R-12
R-113
HCFC
R-22
R-123
R-124
R-141B
R-142B
0.05
0.02
0.02
0.7
0.06
HFC
R-125
R-134a
R-152a
0
0
0
Compound
Ashrae Number
CFC
R-11
R-12
Possible replacement
Refrigerants
R-123 or R-22
R-134a or R-600a
HCFC
R-22
R-123
R-134a
HFC
R-134a
R-413a
Replacements Refrigerants