Page 162 - Boiler_Operators_Handbook,_Second_Edition

Refrigeration & AC 147

tions one portion boils off at a slightly lower temperature sic refrigeration cycle has four stages. Once a couple of
than the other, creating bubbles of the lower temperature differences are cleared up you should have no trouble
refrigerant then that vapor is superheated a few degrees understanding what’s going on. The four basic stages
until the other portion reaches its saturation temperature. are evaporation, compression, condensation, and throt-
The span between the dew point and the bubble point is tling.
referred to as “temperature glide.” Handling of binary re-
frigerants requires special procedures, so once again, it’s
important to read that instruction manual. There are also
ternary blends, three refrigerants blended together. Some
blends are azeotropic, they have no temperature glide
and act just like a single refrigerant.
R-728 is actually liquid nitrogen it’s expendable
and one of the only refrigerants that can be vented legal-
ly. R-13 is carbon dioxide, can be vented, but is normally
contained because simply venting a refrigerant gets ex-
pensive and now it’s considered a pollutant as a “green-
house gas.”
Venting of refrigerants other than nitrogen and car-
bon dioxide is illegal and perpetrators can be subjected to
a fine of up to $27,500.00. That’s one of the many things
you should learn about handling refrigerants when you
take a course in that activity to obtain your certification
as a technician for handling refrigerants to comply with
Section 608 of the Federal Clean Air Act of 1990. That Figure 5-2. Basic Refrigeration Cycle
class will teach you about stratospheric ozone depletion,
the Clean Air Act, refrigerants and oils, and recovering Evaporation
refrigerants. Then you will have to take an examination Evaporation, as the title implies, is converting a
and pass it before receiving your certification. I suggest liquid to a gas, just like making steam in a boiler. The re-
you take the course and get certified if you’re working in frigerant absorbs heat by evaporating and that’s how the
a refrigeration plant so you are qualified to handle refrig- evaporator removes heat from another substance to cool
erants and understand fully what to do in that process. it. The principal difference is the refrigerant is exposed
You may feel you’re contented with simply operating to pressures in the evaporator where the saturation tem-
the equipment but your employer may choose to employ perature of the refrigerant is lower than the substance to
someone else that has that certification. be cooled. Heat flows from the substance to be cooled
Oil for refrigeration equipment is special because through the tubing or casing of the evaporator into the
it has to work in an environment where it’s surround- refrigerant causing the refrigerant to boil. Despite some
ed with refrigerant. The lubricating oils for refrigerants descriptions you may have heard a refrigeration system
can be specific to a particular refrigerant or to a group doesn’t push heat, it always flows in one direction, from
of them and extreme care is required in handling them. a higher temperature to a lower temperature. By reduc-
Almost all refrigerant oils are hygroscopic, they suck ing the evaporator pressure the boiling temperature of
up water, and since water isn’t desirable in a refriger- the refrigerant is lowered until it’s colder than the sub-
ant system it’s important that those oils are handled and stance to be cooled.
stored in sealed containers so they can’t soak up water Why do I use the word substance? It’s a catch-all
from the air. word to replace what I would have to say, which is—a
gas, a liquid, a liquid that upon removal of heat becomes
a solid, a solid, or another refrigerant. That’s because
THE REFRIGERATION CYCLE refrigeration is not only associated with changing the
temperature of a substance, it can also change the state,
I covered steam cycles near the beginning of this from gas to liquid and liquid to solid. We cool air and
book and hope to show that the refrigeration cycle isn’t dehumidify it, cool water and freeze it, and that’s only
significantly different. As shown in Figure 5-2, the ba- the simple ones.