U.S. patent application number 11/207720 was filed with the patent office on 2005-12-15 for refrigeration cycle.
This patent application is currently assigned to SANDEN CORPORATION. Invention is credited to Komatsu, Syunji, Yamamoto, Kiyokazu.
Application Number | 20050274140 11/207720 |
Document ID | / |
Family ID | 33508324 |
Filed Date | 2005-12-15 |
United States Patent
Application |
20050274140 |
Kind Code |
A1 |
Komatsu, Syunji ; et
al. |
December 15, 2005 |
Refrigeration cycle
Abstract
It is an object of the invention to provide a refrigeration
cycle which uses HFC-152a as refrigerant, and can be operated
stably without hunting of the superheat degree. A charge amount of
refrigerant is increased, and refrigerant at an inlet of an
expansion device is placed in a state where the subcool degree is
ensured to be at least 5 degrees such that the subcool degree does
not become equal to zero by variation in pressure. This suppresses
fluctuation in the superheat degree of refrigerant at an outlet of
an evaporator to thereby stabilize the system. In this state, to
enhance the efficiency of a compressor, the superheat degree can be
increased by decreasing the set value of the expansion device.
Inventors: |
Komatsu, Syunji; (Gunma,
JP) ; Yamamoto, Kiyokazu; (Gunma, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
SANDEN CORPORATION
Isesaki-shi
JP
|
Family ID: |
33508324 |
Appl. No.: |
11/207720 |
Filed: |
August 22, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11207720 |
Aug 22, 2005 |
|
|
|
PCT/JP04/02329 |
Feb 26, 2004 |
|
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|
Current U.S.
Class: |
62/498 ; 62/114;
62/222 |
Current CPC
Class: |
F25B 2400/16 20130101;
F25B 9/002 20130101; F25B 40/02 20130101; F25B 1/00 20130101; F25B
2500/15 20130101; F25B 2341/0683 20130101 |
Class at
Publication: |
062/498 ;
062/222; 062/114 |
International
Class: |
F25B 001/00; F25B
041/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 2, 2003 |
JP |
2003-156609 |
Claims
What is claimed is:
1. A refrigeration cycle comprising a compressor, a condenser, an
expansion device, and an evaporator, and using HFC-152a as
refrigerant circulating therethrough, wherein the refrigerant at an
inlet of the expansion device is necessarily placed in a state
where a predetermined degree of subcool is ensured, whereby
fluctuation in a degree of superheat of the refrigerant at an
outlet of the evaporator is suppressed, for stabilization.
2. The refrigeration cycle according to claim 1, wherein the degree
of subcool is ensured to be at least 5 degrees.
3. The refrigeration cycle according to claim 1, wherein a charge
amount of the refrigerant is adjusted to ensure the degree of
subcool.
4. The refrigeration cycle according to claim 1, wherein the
condenser is replaced by a subcool condenser to thereby ensure the
degree of superheat.
5. The refrigeration cycle according to claim 1, wherein the
expansion device is replaced by a thermostatic expansion valve, and
a set value of the thermostatic expansion valve is adjusted to
provide the degree of subcool.
Description
[0001] This application is a continuing application, filed under 35
U.S.C. .sctn.111(a), of International Application
PCT/JP2004/002329, filed Feb. 26, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a refrigeration cycle, and more
particularly to a refrigeration cycle using HFC-152a as
refrigerant.
[0004] 2. Description of the Related Art
[0005] A refrigeration cycle for an automotive air conditioning
system, for example, comprises a compressor that is driven by an
engine as a drive source, a condenser that condenses refrigerant
compressed by the compressor, a receiver that separates the
condensed refrigerant into a gas and a liquid, an expansion device
that throttles and expands the liquid refrigerant obtained by
gas/liquid separation, and an evaporator that evaporates the
expanded refrigerant to return the same to the compressor.
[0006] In the refrigeration cycle configured as above, to enhance
the efficiency of the compressor, it is a common practice to
provide control such that refrigerant at the outlet of the
evaporator has a predetermined degree of superheat. Further, in a
refrigeration cycle that carries out control of the degree of
superheat, refrigerant at the inlet of the expansion device is
controlled such that the refrigerant has no degree of subcool. In
this case, it is also known to further cool refrigerant delivered
from the receiver such that the refrigerant presents a degree of
subcool so as to improve efficiency of the compressor (see e.g.
Japanese Unexamined Patent Publication (Kokai) No. H06-2970
(Paragraph numbers [0006] and [0007], and FIG. 4).
[0007] In the conventional refrigeration system, in general, a CFC
substitute called HFC-134a is generally used as refrigerant.
[0008] FIG. 8 is a diagram showing characteristics of a
refrigeration cycle using HFC-134a as refrigerant.
[0009] In FIG. 8, there are shown temporal changes in the subcool
degree SC, the superheat degree SH, and the flow rate Gf of
HFC-134a as refrigerant. As is apparent from FIG. 8, in the case of
HFC-134a being used as refrigerant, the ranges of fluctuation in
the superheat degree SH and the flow rate Gf are small even when
the subcool degree SC assumes a small value of approximately 1, and
therefore the hunting of the superheat degree SH is small, which
means that the system is substantially stable.
[0010] However, when HFC-134a is used as refrigerant for the
refrigeration cycle, it has a significant influence on the global
warming, and hence alternatives to HFC-134a have been studied. One
of the alternatives being studied is refrigerant called HFC-152a,
whose influence on the global warming is approximately one tenth of
the influence of HFC-134a.
[0011] FIG. 9 is a diagram showing characteristics of a
refrigeration cycle using HFC-152a as refrigerant.
[0012] FIG. 9 shows a case in which HFC-152a is used as
refrigerant, the charge amount of which is set to 500 g, and an
expansion valve, whose set value is set to 0.177 MPa, is used as
the expansion device. In this case, it is known that the superheat
degree SH and the subcool degree SC are stable at approximately 2
degrees and approximately 1 degree, respectively, and the hunting
tends to be small in a region where the superheat degree SH is
small. However, when the superheat degree SH is as small as
approximately 2 degrees, the efficiency of the compressor is
degraded, and hence, it is preferable that the superheat degree SH
is increased to approximately 10 degrees.
[0013] However, when HFC-152a is used as refrigerant, if the set
value of the expansion valve is decreased so as to increase the
superheat degree SH, as shown in FIG. 9, the superheat degree SH is
increased, but the range of fluctuation in the superheat degree SH
is also increased to cause the hunting, which makes the system
unstable.
SUMMARY OF THE INVENTION
[0014] The present invention has been made in view of the above
points, and an object thereof is to provide a refrigeration cycle
which can be operated stably without hunting of a superheat degree
SH.
[0015] To solve the above problem, the present invention provides a
refrigeration cycle comprising a compressor, a condenser, an
expansion device, and an evaporator, and using HFC-152a as
refrigerant circulating therethrough, wherein the refrigerant at an
inlet of the expansion device is necessarily placed in a state
where a predetermined degree of subcool is ensured, whereby
fluctuation in a degree of superheat of the refrigerant at an
outlet of the evaporator is suppressed, for stabilization.
[0016] The above and other objects, features and advantages of the
present invention will become apparent from the following
description when taken in conjunction with the accompanying
drawings which illustrate preferred embodiments of the present
invention by way of example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a diagram showing characteristics of a
refrigeration cycle using HFC-152a as refrigerant.
[0018] FIG. 2 a diagram showing a flow rate characteristic of
HFC-152a as refrigerant.
[0019] FIG. 3 is a diagram showing part of a Mollier chart.
[0020] FIG. 4 is a diagram showing a method of improving the degree
of superheat.
[0021] FIG. 5 is a system diagram showing a refrigeration cycle
using a receiver.
[0022] FIG. 6 is a system diagram showing a refrigeration cycle
using a subcool condenser.
[0023] FIG. 7 is a system diagram showing a refrigeration cycle
using an accumulator.
[0024] FIG. 8 is a diagram showing characteristics of a
refrigeration cycle using HFC-134a as refrigerant.
[0025] FIG. 9 is a diagram showing characteristics of a
refrigeration cycle using HFC-152a as refrigerant.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Hereinafter, an embodiment of the present invention will be
described in detail by taking a case where it is applied to a
refrigeration cycle for an automotive air conditioning system, as
an example.
[0027] FIG. 1 is a diagram showing characteristics of a
refrigeration cycle using HFC-152a as refrigerant; FIG. 2 is a
diagram showing a flow rate characteristic of HFC-152a as
refrigerant; and FIG. 3 is a diagram showing part of a Mollier
chart.
[0028] First, FIG. 1 shows temporal changes in the subcool degree
SC, the superheat degree SH, and the flow rate Gf, of HFC-152a as
refrigerant, obtained when an expansion valve which is set to 0.186
MPa as a set point is employed as an expansion device.
[0029] It is understood from FIG. 1 that when the charge amount of
the refrigerant is set to 500 g, the superheat degree SH is not
less than 3 degrees, but the range of fluctuation in the superheat
degree SH is large, causing hunting thereof. It is also understood
that to prevent the hunting of the superheat degree SH, if the
charge amount of the refrigerant is increased to 600 g, and further
to 650 g to impart a subcool degree SC to the refrigerant, the
superheat degree SH largely fluctuates to make the system unstable
in a region where the subcool degree SC is only approximately 1 or
2 degrees, whereas in a region where the subcool degree SC is not
less than 5 degrees, the fluctuation in the superheat degree SH is
small, and the system becomes stabile. Therefore, in the
refrigeration cycle using HFC-152a as refrigerant, it is absolutely
essential that refrigerant at the inlet of the expansion valve is
placed in a subcooled state, and if the subcool degree SC is
ensured to be at least 5 degrees, it is possible to prevent hunting
of the superheat degree SH whereby the system is made stable.
[0030] It is presumed that the above tendency is due to the fact
that HFC-152a has a more readily vaporizable property than that of
HFC-134a. The flow rate characteristic of HFC-152a shown in FIG. 2
indicates changes in the flow rate of refrigerant with respect to
the valve lift of the expansion valve. From this, it is understood
that the flow rate of refrigerant does not largely change even when
the subcool degree SC is reduced from 5 degrees to zero. However,
when the refrigerant has even a slight degree of dryness, air
bubbles come to be mixed in the refrigerant flowing into the
expansion valve. This makes it difficult for the refrigerant to
flow smoothly, resulting in a sudden decrease in the flow rate of
the refrigerant.
[0031] Further, as is apparent from FIG. 1, it is preferable that
the subcool degree SC is not less than 5 degrees. The reason for
this will be explained with reference to FIG. 3. In FIG. 3, a
broken line indicates a saturation liquid line of the conventional
HFC-134a, and a solid line indicates a saturation liquid line of
HFC-152a. As shown in FIG. 3, the slopes of the saturation liquid
lines of HFC-134a and HFC-152a are different from each other, and
the saturation liquid line of HFC-152a has a gentler slope.
Therefore, even if HFC-134a and HFC-152a have the same subcool
degree SC of 5 degrees, HFC-152a enters a gas/liquid phase by a
smaller change in pressure. In the examples illustrated in FIG. 3,
although HFC-134a does not enter the gas/liquid phase without a
change in pressure of approximately 0.18 MPa, HFC-152a enters the
gas/liquid phase when the pressure undergoes a change of
approximately 0.13 MPa. Accordingly, it is necessary to positively
place refrigerant flowing into the expansion valve in a subcooled
state when the subcool degree SC is not less than 5 degrees, to
thereby prevent the refrigerant from easily entering the gas/liquid
phase even when the pressure of refrigerant undergoes a certain
amount of change. As is apparent from the above, in the
refrigeration cycle using HFC-152a as refrigerant, if the subcool
degree SC is not imparted to the refrigerant, the refrigerant
easily enters the gas/liquid phase even by a slight change in
pressure, and once the refrigerant has entered the gas/liquid
phase, the flow rate thereof sharply drops. Therefore, it is
necessary to impart the subcool degree SC to the refrigerant
sufficiently compared with a refrigeration cycle using HFC-134a as
refrigerant. This is why in the refrigeration cycle using HFC-152a
as refrigerant, the refrigerant at the inlet of the expansion valve
is required to be always placed in the subcooled state, and
moreover, in order to cause the system to perform stable operation
irrespective of variations in pressure, the subcool degree SC is
required to be not less than 5 degrees.
[0032] As described above, in the refrigeration cycle using
HFC-152a as refrigerant, the subcool degree SC is necessarily
required to be not less than 5 degrees. This subcool degree SC
makes it possible to suppress fluctuation in the superheat degree
SH, which makes the system stable. However, under the conditions
shown in FIG. 1, although the superheat degree SH is stable without
hunting, only 2 degrees of the superheat degree SH is obtained. To
enhance the efficiency of the compressor, it is preferable that the
superheat degree SH is equal to approximately 10 degrees.
[0033] FIG. 4 is a diagram showing a method of improving the degree
of superheat.
[0034] As shown in FIG. 4, the superheat degree SH is improved by
progressively decreasing the set value of the expansion valve. From
the illustrated example, it is understood that if the charge amount
of the refrigerant is set to 650 g, and the set value of the
expansion valve is decreased from 0.186 MPa to 0.167 MPa, and
further to 0.147 MPa, the superheat degree SH increases, and
moreover that the superheat degree SH is stable without hunting
even, when it increases.
[0035] This is because by decreasing the set value of the expansion
valve, the flow rate of refrigerant passing through the expansion
valve is reduced to relatively increase the capability of an
evaporator. If the refrigerant is further heated after being
completely evaporated by the evaporator, it is possible to place
the refrigerant at the outlet of the evaporator in a sufficiently
superheated state. Of course, the reduction of the flow rate of
refrigerant entering the expansion valve relatively increases the
capability of the condenser, so that as the superheat degree SH
increases, the subcool degree SC as well increases.
[0036] Next, a description will be given of a refrigeration cycle
which uses HFC-152a as refrigerant, and causes the subcool degree
SC of HFC-152a to be not less than 5 degrees, for
stabilization.
[0037] FIG. 5 is a system diagram showing a refrigeration cycle
using a receiver.
[0038] This refrigeration cycle comprises a compressor 1, a
condenser 2, the receiver 3, a thermostatic expansion valve 4, and
an evaporator 5, and configured such that the refrigerant of
HFC-152a circulates therethrough. The compressor 1 is driven by an
engine as a drive source, for compressing the refrigerant. The
refrigerant compressed by the compressor 1 to high-temperature,
high-pressure refrigerant is condensed by the condenser 2 to be
changed into high-temperature, high-pressure liquid refrigerant.
The liquid refrigerant is separated into a gas and a liquid by the
receiver 3, and the liquid refrigerant obtained by gas/liquid
separation is throttled and expanded by the thermostatic expansion
valve 4, for being changed into atomized low-temperature,
low-pressure refrigerant. The refrigerant having flown out from the
thermostatic expansion valve 4 is evaporated to be gasified by the
evaporator 5. The gasified refrigerant is caused to pass through a
portion of the thermostatic expansion valve 4 for sensing the
temperature and the pressure of the refrigerant, and returned to
the compressor 1. At this time, the thermostatic expansion valve 4
senses the temperature and the pressure of refrigerant at the
outlet of the evaporator 5, and controls the flow rate of
refrigerant to be delivered to the evaporator 5 such that the
refrigerant at the outlet of the evaporator 5 maintains a
predetermined superheat degree SH.
[0039] In the above refrigeration cycle, by overcharging the
refrigerant, the subcool degree SC at the inlet of the thermostatic
expansion valve 4 is ensured. Further, the subcool degree SC can be
also ensured by increasing the cooling capacity of the condenser 2
e.g. by increasing the number of fans provided thereon.
Furthermore, it is more effective in ensuring the subcool degree
SC, to reduce pressure loss in piping from the receiver 3 to the
thermostatic expansion valve 4 e.g. by integrally forming the
receiver 3 and the thermostatic expansion valve 4 with each other,
or by thickening and shortening the piping between the receiver 3
and the thermostatic expansion valve 4.
[0040] FIG. 6 is a system diagram showing a refrigeration cycle
using a subcool condenser.
[0041] This refrigeration cycle comprises the compressor 1, a
subcool condenser 6, the thermostatic expansion valve 4, and the
evaporator 5, and is configured such that the refrigerant of
HFC-152a circulates therethrough. The subcool condenser 6, which is
provided with the function of a receiver, cools refrigerant
delivered from the compressor 1 for complete liquefaction, and
further cools the liquefied refrigerant for delivery to the
thermostatic expansion valve 4. Therefore, the refrigerant
delivered from the subcool condenser 6 already has a predetermined
subcool degree SC imparted thereto, so that it is possible to
positively ensure the subcool degree SC by the subcool condenser
6.
[0042] FIG. 7 is a system diagram showing a refrigeration cycle
using an accumulator.
[0043] This refrigeration cycle comprises the compressor 1, the
condenser 2, an orifice tube 7, the evaporator 5, and an
accumulator 8, and is configured such that the refrigerant of
HFC-152a circulates therethrough. In this refrigeration cycle as
well, the refrigerant is overcharged, whereby it is possible to
suppress the hunting of the superheat degree SH of refrigerant at
the outlet of the evaporator 5.
[0044] It should be noted that in the refrigeration cycle which
uses HFC-152a as refrigerant having a smaller slope of the
saturation liquid line than that of the saturation liquid line of
HFC-134a, to prevent the refrigerant from entering the gas/liquid
phase easily by a slight change in pressure, it is required to
always place the refrigerant at the inlet of the expansion device
in the subcooled state, and hence as a matter of course, the
present invention can be applied to refrigeration cycles which use
a refrigerant having a similar tendency to HFC-152a in the slope of
a saturation liquid line thereof, thereby suppressing fluctuation
in the superheat degree SH of refrigerant, which makes it possible
to stabilize the system.
[0045] As described above, the refrigeration cycle according to the
present invention is configured such that refrigerant at the inlet
of the expansion device is always placed in the subcooled state,
and that the subcool degree SC is ensured to be at least 5 degrees
so as to prevent the subcool degree SC from becoming equal to zero
by variation in pressure. In the refrigeration cycle using the
conventional refrigerant, the system is stable since no hunting of
the superheat degree SH is caused irrespective of whether or not
the refrigerant has the subcool degree SC, whereas in the
refrigeration cycle using HFC-152a as refrigerant, the hunting of
the superheat degree SH is liable to occur in the state where the
refrigerant has no subcool degree SC, and hence by causing the
refrigerant to be always cooled such that it has the subcool degree
SC, it is possible to suppress the hunting of the superheat degree
SH, thereby making it possible to stabilize the system.
[0046] The foregoing is considered as illustrative only of the
principles of the present invention. Further, since numerous
modifications and changes will readily occur to those skilled in
the art, it is not desired to limit the invention to the exact
construction and applications shown and described, and accordingly,
all suitable modifications and equivalents may be regarded as
falling within the scope of the invention in the appended claims
and their equivalents.
* * * * *