124
Modern Refrigeration and Air Conditioning
Although it is illegal to manufacture HVACR
systems with phased-out refrigerants, it is not illegal
to service existing units that have these refrigerants.
Remaining stockpiles of CFC refrigerants such as
R-12 are still available today. However, the purchase
of these refrigerants is restricted to EPA-certified
technicians, who may still acquire large cans (over
20 lb) of R-12 and other CFC refrigerants. Technicians
who have completed the EPA Motor Vehicle
Certification may purchase small cans (under 20 lb)
of R-12.
As the stock of available CFC refrigerants is
exhausted, the cost will continue to increase. Phased-
out CFC refrigerants typically cost much more
than the price prior to phaseout. For economic rea-
sons, it is often more practical—and better for the
environment—to replace a phased-out refrigerant
in a system with an approved refrigerant, refer to
Figure 6-15.
6.5.2 Criteria for New Refrigerants
As scientists learn more about global warming
and the ozone layer, they have shifted their focus
to reducing a refrigerant’s length of decay and global
warming potential. Although there is not a man-
datory phaseout, even R-134a is beginning to be
replaced in automotive air conditioning applications
by R-1234yf, which has an ODP of zero and a GWP
of four. Besides having an ODP of zero and a low
GWP, a new refrigerant should have the following
properties:
• It must follow the standards set forth by the EPA
for recyclability and reclamation.
• It should be nonexplosive.
• It should be noncorrosive.
• It should make leaks easy to detect and locate.
• It should have a low boiling point.
• It should be a stable gas.
• It should permit machine or compressor parts
moving in the fluid to be easily lubricated.
• It should have a high latent heat per pound (be
able to absorb or expel a lot of heat during phase
change) to produce a good cooling effect per
pound of vapor pumped.
• It should have as little pressure difference as possible
between evaporating pressure and condensing
pressure. This increases pumping efficiency.
• It should be compatible with common materials
used in HVACR systems, such as copper ACR
tubing.
While the environmental impact of refrigerants is
of great concern, newer refrigerants still must be safe
for technicians to work with—stable and nonexplosive.
New refrigerants must also be effective at removing
heat from a conditioned space—high latent heat and
low boiling point, refer to Figure 6-15.
6.5.3 Commonly Used New Refrigerants
The following refrigerants are the ones most
commonly used in the manufacture of new HVACR
equipment:
• R-134a—automotive air conditioning and transport
refrigeration.
• R-404A—medium- and low-temperature
refrigeration.
• R-410A—air conditioning.
6.6 Inorganic Refrigerants
There is a diversity of refrigerant applications
beyond just comfort cooling and refrigeration. A num-
ber of industrial processes use refrigerants that do not
fall under the category of halogenated, organic refrig-
erants as CFCs, HCFCs, and HFCs do. Instead, many
industrial processes use inorganic refrigerants, which
are classified in the 700 series. The most common of
these inorganic refrigerants are explained in the sec-
tions that follow.
6.6.1 R-717 Ammonia
R-717 is commonly used in industrial systems. It is
a chemical compound of nitrogen and hydrogen (NH
3
).
Under standard conditions, it is a colorless gas with a
boiling point of –28°F (–33°C). The low boiling point
makes it possible to have refrigeration at temperatures
below zero without using pressures below atmospheric
in the evaporator. Ammonia’s latent heat is 565 Btu/lb
(1310 kJ/kg) at 5°F (–15°C). See Figure 6-16. Thus, large
refrigerating effects are possible with relatively small-
sized machinery.
R-717 is flammable at 150,000 to 270,000 ppm.
Ammonia has a strong effect on the respiratory system,
and only very small quantities of it can be breathed
safely. Because of its pronounced and distinguishable
odor, R-717 is easily detected in the air. At 3 to 5 ppm,
ammonia can be identified by smell. At 15 ppm, the
odor is quite irritating. At 30 ppm, a service technician
will need a respirator. Exposure for five minutes to
50 ppm is the maximum allowed by the Occupational
Safety and Health Administration (OSHA). Ammonia
poses a fatal hazard at 5000 ppm.