Technical Field of the Invention
[0001] The present invention relates to a refrigeration cycle, and specifically relates
to a refrigeration cycle which can be efficiently operated when a specific new-type
refrigerant is used.
Background Art of the Invention
[0002] A refrigeration cycle used in an automotive air conditioning system, etc., has basic
configuration which is shown in Fig. 1, for example. In Fig. 1, refrigeration cycle
1 has compressor 2 for compressing refrigerant, condenser 3 for condensing compressed
refrigerant, expansion valve 4 as a pressure reduction and expansion means for reducing
in pressure and expanding condensed refrigerant, and evaporator 5 for evaporating
pressure-reduced and expanded refrigerant, where the refrigerant is circulated in
refrigeration cycle 1 as changing its state. It is known to be effective for improving
the refrigeration performance that such refrigeration cycle 1 is operated while the
refrigerant at the outlet side of evaporator 5 is kept in a condition superheated
with respect to its saturation curve.
[0003] For example, where sample 11 of operating condition of refrigeration cycle 1 is shown
in the Mollier diagram (enthalpy/pressure curve) of Fig. 2, it is known that the refrigeration
performance and the Coefficient Of Performance (COP) of refrigeration cycle 1 can
be sometimes improved by giving degree of superheat 14 with respect to saturation
curve 13 to refrigerant at the outlet side of evaporator before compression process
12 using compressor 2. In the Mollier diagram of Fig. 2, symbol 15 implies an isentrope
and symbol 16 implies an isotemperature line.
[0004] Characteristics as shown in Fig. 2 may be basically expressed as general characteristics
of a refrigeration cycle which is operated as keeping the refrigerant in a superheat
condition at the outlet side of the evaporator, regardless of the type of refrigerant.
However, the concrete characteristics having a concrete numeric value may depend greatly
on the type of refrigerant.
[0005] R134a is a refrigerant which is typical at present, however, research and development
to find a new-type refrigerant are being performed in order to improve Global Warming
Potential (GWP), as disclosed in non-patent document 1. R1234yf has been announced
recently as a new refrigerant aiming at such an improvement, and it is becoming possible
that it is examined and studied for applying to refrigeration cycle used for an automotive
air conditioning system, etc.
Prior art documents
Non-patent documents
Summary of the Invention
Problems to be solved by the Invention
[0007] At present when R134a is used as refrigerant, the refrigerant condition is generally
controlled around 5 superheat degrees at the outlet side of the evaporator, and the
operation, regardless of high load and low load, is performed in a condition around
5 degrees superheat. Such a condition of 5 degrees superheat has been configured for
the following reasons. (1) The condition of 5 superheat degrees is regarded as being
close to the requisite minimum to achieve a target refrigeration gasification state
at the outlet side of the evaporator. (2) If the condition is set as substantially
higher than 5 degrees superheat, the temperature of refrigerant discharged from the
evaporator might exceed a certain level as causing deterioration of refrigerant oil
contained in the refrigerant.
[0008] However, because specific enthalpy difference of R1234yf in an operating zone is
less than that of R134a, refrigerant flow rate for an operation using R1234yf has
to be increased to achieve a refrigeration performance same as that for an operation
using R134a as a conventional refrigerant. In order to achieve the same refrigeration
performance in refrigeration cycle 1 with basic configuration as shown in Fig. 1,
the refrigerant flow rate has to be increased by increasing the rotational speed of
compressor 2, however, it may cause an increase of the power consumption of compressor
2, and consequently refrigeration coefficient of performance may be reduced, so that
the operating condition becomes undesirable on efficiency.
[0009] According to the above-described new knowledge, an object of the present invention
is to provide a refrigeration cycle which can be operated with a high efficiency even
if the refrigerant has been replaced with R1234yf as new-type refrigerant.
Means for solving the Problems
[0010] To achieve the above-described object, a refrigeration cycle according to the present
invention is a refrigeration cycle comprising a compressor for compressing refrigerant,
a condenser for condensing compressed refrigerant, a pressure reduction and expansion
means for reducing in pressure and expanding condensed refrigerant, and an evaporator
for evaporating pressure-reduced and expanded refrigerant,
characterized in that R1234yf is used as refrigerant for the refrigeration cycle, and the refrigeration
cycle is operated so that the refrigerant at an exit side of the evaporator is controlled
in a superheated condition, and the superheated condition is controlled in a range
of 5 to 16 degrees of superheat.
[0011] In other words, it is
characterized in that conventional operating condition around 5 superheat degrees in a case using R134a
as refrigerant so as to keep the refrigerant superheated at the exit side of the evaporator
has been changed to an operating condition between 5 and 16 superheat degrees, when
the refrigerant has been replaced with R1234yf as a new-type refrigerant so as to
keep the refrigerant superheated at the exit side of the evaporator. As shown in Fig.
3, the use of R1234yf as refrigerant can improve the coefficient of performance (COP)
more greatly than the use of R134a as refrigerant, even when the refrigerant superheat
degree increases as well at the exit side of the evaporator. Further, when the R134a
is used the condition has actually to be maintained around 5 superheat degrees in
case that temperature of discharged refrigerant might increase to deteriorate the
refrigerant oil in the refrigerant, and on the other hand, when R1234yf is used the
operating condition can be controlled in a range of 5 - 16 superheat degrees as keeping
the same level of the discharged refrigerant temperature as operated around 5 superheat
degrees. Therefore, coefficient of performance (COP) can be improved by increasing
superheat degree, as properly preventing from excessive rise of the discharged refrigerant
temperature, so that operation with high-efficiency and deterioration prevention of
the refrigerant oil can be desirably achieved.
[0012] The refrigeration cycle according to the present invention may be operated at 5 -16
superheat degrees of refrigerant at the exit side of the evaporator, and more preferably,
is operated at in a range of 10 - 16 superheat degrees thereof as keeping the superheat
degree as high as possible, in order to achieve the deterioration prevention of the
refrigerant oil by suppressing the discharged refrigerant temperature rise. Namely,
if attention is focused on the discharged refrigerant temperature shown in Fig. 4,
the above-described operating condition of 10 superheat degrees is comparable with
the operating condition around 5 superheat degrees under low load in R134a case, and
the above-described operating condition of 16 superheat degrees is comparable with
the operating condition around 5 superheat degrees under high load in R134a case.
Therefore, the operating condition of 10 - 16 superheat degrees keeps the discharged
refrigerant temperature at the same level to any load condition in R134a case, so
that the lower limit for operating condition of superheat degree can be kept as high
as possible. The operating condition range of superheat degree with lower limit of
10 degrees does not overlap the conventional condition range around 5 superheat degrees
in R134a case at all.
[0013] In addition, the refrigeration cycle according to the present invention, whose basic
configuration is shown in Fig. 1, preferably has means for elevating the degree of
superheat of the refrigerant at the exit side of the evaporator, as compared with
a case where R134a is used as refrigerant. In other words, the means for elevating
the superheat degree may be provided in order to meet the operating condition of superheat
degree higher than around 5 superheat degrees for the R134a case. For such a means
for elevating the degree of superheat, conventionally known means and mechanisms can
be applied. For example, a liquid/gas heat exchanger, such as an internal heat exchanger
which exchange heat between high-pressure side of the condenser outlet and low-pressure
side of the evaporator outlet, can be provided. As well, the evaporation tube inside
the evaporator may be extended, a so-called sensible heat exchanger may be provided,
or the set value of the pressure-reduction/expansion means such as expansion valve
may be altered.
[0014] Such a refrigeration cycle according to the present invention is basically applicable
to any refrigeration cycle which aims to use the new-type refrigerant R1234yf, and
is specifically suitable to a refrigeration cycle used in an automotive air conditioning
system which is required to achieve efficient operation and to be highly durable for
a long term by preventing the refrigerant oil from deterioration.
Effect according to the Invention
[0015] The refrigeration cycle according to the present invention makes it possible that
when the refrigerant is replaced to the new-type refrigerant R1234yf, the improvement
of coefficient of performance (COP) can be greatly achieved and the discharged refrigerant
temperature can be properly kept from rising as preventing from the deterioration
of the refrigerant oil in refrigerant, so that refrigeration cycle can be operated
efficiently as a whole.
Brief explanation of the drawings
[0016]
[Fig. 1] Fig. 1 is a schematic framework showing a basic equipment layout of a refrigeration
cycle as an object of the present invention.
[Fig. 2] Fig. 2 is a Mollier diagram showing a sample of the operating condition of
the refrigeration cycle accompanying superheat degree of refrigerant at the exit side
of the evaporator.
[Fig. 3] Fig. 3 is a relationship diagram between superheat degree of refrigerant
at the exit side of the evaporator and the increase rate of coefficient of performance
(COP).
[Fig. 4] Fig. 4 is a relationship diagram between superheat degree of refrigerant
at the exit side of the evaporator and temperature of discharged refrigerant.
Embodiments for carrying out the Invention
[0017] Hereinafter, the present invention will be explained as referring to figures as well
as embodiments of the present invention.
The basic configuration of equipments provided in a refrigeration cycle of the present
invention can be the one as shown in Fig. 1. As described above, in Fig. 1 refrigeration
cycle 1 has compressor 2 for compressing refrigerant, condenser 3 for condensing compressed
refrigerant, expansion valve 4 as a pressure-reduction/expansion means for reducing
in pressure and expanding condensed refrigerant, and evaporator 5 for evaporating
refrigerant which is pressure-reduced and expanded, which is operated as keeping refrigerant
superheated at the exit side of evaporator 5 in refrigeration cycle 1 so as to improve
refrigeration performance. The Mollier diagram in Fig. 2 shows a basic cycle where
the refrigerant changes in state as the superheat degree is given.
[0018] Fig. 3 shows a relationship between superheat degree of refrigerant at the exit side
of the evaporator and the increase rate of coefficient of performance (COP), where
a case using refrigerant R134a is compared to a case using refrigerant R1234yf, in
a certain condition (refrigerant condensation temperature = 52.6 degrees Celsius;
refrigerant evaporation temperature = 10 degrees Celsius; subcool degree in front
of expansion valve = 6.1 deg) of a certain refrigeration cycle. Fig. 3 shows that
the COP increase rate rises in both R134a case and R1234yf case when increasing the
superheat degree of refrigerant at the exit side of the evaporator, and that the increase
rate of the R1234yf case is relatively higher. Therefore in the R1234yf case, the
more superior coefficient of performance (COP) can be obtained by keeping high superheat
degree of refrigerant at the exit side of the evaporator.
[0019] Fig. 4 shows a relationship between superheat degree of refrigerant at the exit side
of the evaporator and temperature of discharged refrigerant, for a high-pressure (high-load)
condition (Condensation temperature = 79.4 degrees Celsius), a medium-pressure (medium-load)
condition (Condensation temperature = 58.0 degrees Celsius), and a low-pressure (low-load)
condition (Condensation temperature = 43.0 degrees Celsius). The conventional set
value of superheat degree in the R134a case has been around 5 deg regardless of loads,
as described above. As shown in Fig. 4, a desirable range in the R1234yf case can
be defined by the superheat degree of refrigerant at the exit side of the evaporator
in the intersection where the line of discharged refrigerant temperature value in
the R134a case of each condition intersects the characteristic line of the R1234yf,
in order to keep the discharged refrigerant temperature at the same level between
the R1234yf case and the R134a case, as suppressing the discharged refrigerant temperature
increase. In other words, superheat of 5 deg in a low-pressure (low-load) condition
in the R134a case is comparable with superheat of 10 deg in a low-pressure (low-load)
condition in the R1234yf case, and superheat of 5 deg in a high-pressure (high-load)
condition in the R134a case is comparable with superheat of 16 deg in a high-pressure
(high-load) condition in the R1234yf case. Therefore, Fig. 4 shows that 5 deg as a
conventional set value of superheat degree to suppress the discharged refrigerant
temperature in the R134a case is comparable with 10 deg - 16 deg as a setting range
of superheat degree in the R1234yf case, where the deterioration of refrigerant oil
derived from the discharged refrigerant temperature increase can be suppressed in
operation to the same level as conventional. If the lower limit value of this range
is set to 5 deg which is the same as conventional, the increase of discharged refrigerant
temperature can be suppressed more securely, so that the deterioration of refrigerant
oil can be prevented more surely.
[0020] The characteristics comparison between R134a and R1234yf in Fig. 3 and Fig. 4 and
the proper setting of superheat degree of refrigerant at the exit side of the evaporator
in operation shows that the present invention makes it possible that, in a case using
R1234yf, coefficient of performance (COP) is improved by high superheat degree and
simultaneously the discharged refrigerant temperature is properly prevented from excessive
increase, so that both high-efficiency operation and deterioration prevention of refrigerant
oil can be achieved.
Industrial Applications of the Invention
[0021] The refrigeration cycle according to the present invention is applicable to any refrigeration
cycle, and specifically, is suitable as a refrigeration cycle used in an automotive
air conditioning system.
Explanation of symbols
[0022]
- 1:
- refrigeration cycle
- 2:
- compressor
- 3:
- condenser
- 4:
- expansion valve as pressure-reduction/expansion means
- 5:
- evaporator
- 11:
- sample of operating condition of refrigeration cycle
- 12:
- compression process
- 13:
- saturation curve
- 14:
- superheat degree
- 15:
- isentrope
- 16:
- isotemperature line
1. A refrigeration cycle comprising a compressor for compressing refrigerant, a condenser
for condensing compressed refrigerant, a pressure reduction and expansion means for
reducing in pressure and expanding condensed refrigerant, and an evaporator for evaporating
pressure-reduced and expanded refrigerant, characterized in that R1234yf is used as refrigerant for said refrigeration cycle, and said refrigeration
cycle is operated so that said refrigerant at an exit side of said evaporator is controlled
in a superheated condition, and said superheated condition is controlled in a range
of 5 to 16 degrees of superheat.
2. The refrigeration cycle according to claim 1, wherein said refrigeration cycle is
operated at said superheated condition in a range of 10 to 16 degrees of superheat
of said refrigerant at said exit side of said evaporator.
3. The refrigeration cycle according to claim 1, wherein said refrigeration cycle comprises
means for elevating said degree of superheat of said refrigerant at said exit side
of said evaporator, as compared with a case where R134a is used as refrigerant for
said refrigeration cycle.
4. The refrigeration cycle according to claim 1, wherein said refrigeration cycle is
used in an air conditioning system for vehicles.