U.S. patent application number 13/056535 was filed with the patent office on 2011-07-21 for refrigerating apparatus.
Invention is credited to Azuma Kondou, Satoru Sakae, Masaaki Takegami, Ryuuji Takeuchi.
Application Number | 20110174005 13/056535 |
Document ID | / |
Family ID | 41610108 |
Filed Date | 2011-07-21 |
United States Patent
Application |
20110174005 |
Kind Code |
A1 |
Takegami; Masaaki ; et
al. |
July 21, 2011 |
REFRIGERATING APPARATUS
Abstract
A refrigerating apparatus having a plurality of compressors
includes an injection circuit (40) which includes a first injection
pipe (37) branched from a first refrigerant pipe (32) of a
refrigerant circuit (10) and branch injection pipes (37a, 37b, 37c)
branched from the first injection pipe (37), a subcooling
pressure-reducing valve (29) provided to the first injection pipe
(37), and flow rate adjusting valves (30a, 30b, 30c) provided to
the branch injection pipes (37a, 37b, 37c), respectively, thereby
providing an appropriate refrigerant injection to each of the
compressors.
Inventors: |
Takegami; Masaaki; (Osaka,
JP) ; Sakae; Satoru; (Osaka, JP) ; Takeuchi;
Ryuuji; (Osaka, JP) ; Kondou; Azuma; (Osaka,
JP) |
Family ID: |
41610108 |
Appl. No.: |
13/056535 |
Filed: |
July 2, 2009 |
PCT Filed: |
July 2, 2009 |
PCT NO: |
PCT/JP2009/003070 |
371 Date: |
January 28, 2011 |
Current U.S.
Class: |
62/228.1 ;
62/470; 62/510 |
Current CPC
Class: |
F25B 2313/0233 20130101;
F25B 2400/0751 20130101; F25B 2600/2509 20130101; Y02B 30/70
20130101; F25B 31/004 20130101; F25B 2313/02741 20130101; Y02B
30/741 20130101; F25B 1/10 20130101; F25B 49/025 20130101; F25B
2600/021 20130101; F25B 2400/13 20130101; F25B 13/00 20130101; F25B
2700/21152 20130101 |
Class at
Publication: |
62/228.1 ;
62/510; 62/470 |
International
Class: |
F25B 49/02 20060101
F25B049/02; F25B 1/10 20060101 F25B001/10; F25B 43/02 20060101
F25B043/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2008 |
JP |
2008-198113 |
Feb 27, 2009 |
JP |
2009-046660 |
Claims
1. A refrigerating apparatus comprising: a refrigerant circuit (10)
which has a plurality of compressors (21a, 21b, 21c) and which
performs a vapor compression refrigeration cycle; an injection
circuit (40) which has a main pipe (37) branched from a high
pressure line (33) of the refrigerant circuit (10) and branch pipes
(37a, 37b, 37c) branched from the main pipe (37), and in which the
branch pipes (37a, 37b, 37c) are connected to intermediate ports
(5, 6, 7) of the compressors (21a, 21b, 21c), respectively; and a
pressure-reducing mechanism (29) provided to the main pipe (37) of
the injection circuit (40), wherein at least one of the plurality
of compressors (21a, 21b, 21c) is a variable displacement
compressor (21a), and a flow rate adjusting mechanism (30a, 30b,
30c) is provided at least to the branch pipe (37a, 37b, 37c) of the
variable displacement compressor (21a).
2. The refrigerating apparatus of claim 1, wherein the flow rate
adjusting mechanism (30a, 30b, 30c) is provided to each of the
branch pipes (37a, 37b, 37c) of the injection circuit (40).
3. The refrigerating apparatus of claim 1, comprising a subcooling
heat exchanger (28) having a reduced-pressure side flow path (28b)
through which a refrigerant decompressed by the pressure-reducing
mechanism (29) flows and a high pressure side flow path (28a)
through which a high pressure refrigerant of the refrigerant
circuit (10) flows, wherein the reduced-pressure side flow path
(28b) is connected to the main pipe (37) of the injection circuit
(40), and the high pressure side flow path (28a) is connected to
the high pressure line (33) of the refrigerant circuit (10).
4. The refrigerating apparatus of claim 1, comprising: oil
separators (38a, 38b, 38c) respectively provided to discharge pipes
(22a, 22b, 22c) of the compressors (21a, 21b, 21c), for separating
a refrigerating machine oil from a discharge refrigerant discharged
from the compressors (21a, 21b, 21c); oil discharge pipes (39a,
39b, 39c) connected to the oil separators (38a, 38b, 38c); and an
oil return circuit (39) of which one end side is connected to the
oil discharge pipes (39a, 39b, 39c) and of which the other end side
is connected to a branch pipe branched from the injection circuit
(40), for returning the refrigerating machine oil from the oil
discharge pipes (39a, 39b, 39c) to the compressors (21a, 21b,
21c).
5. The refrigerating apparatus of claim 1, wherein the flow rate
adjusting mechanism (30a, 30b, 30c) is a flow rate adjusting valve
whose degree of opening is variable.
6. The refrigerating apparatus of claim 1, wherein the flow rate
adjusting mechanism (30a, 30b, 30c) is an on/off valve.
7. The refrigerating apparatus of claim 1, wherein the plurality of
compressors (21a, 21b, 21c) include a variable displacement
compressor (21a) and a fixed displacement compressor (21b, 21c),
and the flow rate adjusting mechanism (30a) provided to the branch
pipe (37a) connected to the intermediate port (5) of the variable
displacement compressor (21a) is a flow rate adjusting valve whose
degree of opening is variable, and the flow rate adjusting
mechanism (30b, 30c) provided to the branch pipe (37b, 37c)
connected to the intermediate port (6, 7) of the fixed displacement
compressor (21b, 21c) is an on/off valve.
8. The refrigerating apparatus of claim 1, comprising a discharge
refrigerant temperature detection mechanism (61) for detecting a
temperature of a discharge refrigerant discharged from the
compressors (21a, 21b, 21c), and a control mechanism (9) for
adjusting a degree of opening of each of the flow rate adjusting
mechanisms (30a, 30b, 30c) such that a value detected by the
discharge refrigerant temperature detection mechanism (61) falls
within a predetermined temperature range.
9. The refrigerating apparatus of claim 3, comprising a discharge
condition detection mechanism (61, 66) for detecting at least one
of a discharge temperature and a discharge superheat of each of the
compressors (21a, 21b, 21c), a discharge condition setting
mechanism (76) for setting a discharge target value Tm, Tgshm for
the at least one of the discharge temperature and the discharge
superheat of each of the compressors (21a, 21b, 21c), an
intermediate superheat detection mechanism (75) for detecting a
superheat of an intermediate-pressure refrigerant having passed
through the reduced-pressure side flow path (28b) of the subcooling
heat exchanger (28), an intermediate superheat setting mechanism
(77) for setting an intermediate superheat target value Tgshm for
the superheat of the intermediate-pressure refrigerant having
passed through the reduced-pressure side flow path (28b) of the
subcooling heat exchanger (28), a first discharge target control
section (56a) for changing a degree of opening of the
pressure-reducing mechanism (29) such that a maximum detection
value Ttd, which is a maximum value among values Td detected by the
discharge condition detection mechanisms (61, 66) for the
respective compressors (21a, 21b, 21c), becomes the discharge
target value Tm, Tgshm, an intermediate superheat control section
(60) for changing the degree of opening of the pressure-reducing
mechanism (29) such that a value Tgsh detected by the intermediate
superheat detection mechanism (75) becomes the intermediate
superheat target value Tgshm, and a first control section (16) for
exerting control, if a refrigerant condition value of the
refrigerant in the refrigerant circuit (10) is in a predetermined
range, by selecting the first discharge target control section
(56a) or the intermediate superheat control section (60) based on
the refrigerant condition value.
10. The refrigerating apparatus of claim 9, wherein the first
control section (16) is configured to exert control by selecting
the first discharge target control section (56a) if the maximum
detection value Ttd of the discharge condition detection mechanism
(61, 66) is larger than the discharge target value Tm.
11. The refrigerating apparatus of claim 9, wherein the first
control section (16) is configured to exert control by selecting
the intermediate superheat control section (60) if the maximum
detection value Ttd of the discharge condition detection mechanism
(61, 66) is equal to or smaller than the discharge target value
Tm.
12. The refrigerating apparatus of claim 9, wherein the first
control section (16) is configured to exert control by selecting
the intermediate superheat control section (60) if the maximum
detection value Ttd of the discharge condition detection mechanism
(61, 66) continues to decrease during a predetermined time t1.
13. The refrigerating apparatus of claim 9, comprising a first
superheat avoidance control section (78a) for having the degree of
opening of the pressure-reducing mechanism (29) greater than the
present degree of opening of the pressure-reducing mechanism (29),
a first wet avoidance control section (79a) for having the degree
of opening of the pressure-reducing mechanism (29) smaller than the
present degree of opening of the pressure-reducing mechanism (29),
and an avoidance control section (58) for exerting control, if the
refrigerant condition value of the refrigerant in the refrigerant
circuit (10) exceeds the predetermined range, by selecting the
first superheat avoidance control section (78a) or the first wet
avoidance control section (79a) until the refrigerant condition
value is in the predetermined range.
14. The refrigerating apparatus of claim 13, wherein the avoidance
control section (58) is configured to exert control by selecting
the first superheat avoidance control section (78a) in at least one
of the cases where the value Td detected by the discharge condition
detection mechanism (61, 66) is even larger than an upper threshold
value Tdmax set larger than the discharge target value Tm, and
where the value Tgsh detected by the intermediate superheat
detection mechanism (75) is even larger than an upper threshold
value Tgshmax set larger than the intermediate superheat target
value Tgshm.
15. The refrigerating apparatus of claim 13, wherein the avoidance
control section (58) is configured to exert control by selecting
the first wet avoidance control section (79a) in at least one of
the cases where the value Td detected by the discharge condition
detection mechanism (61, 66) is even smaller than a lower threshold
value Tdmin set smaller than the discharge target value Tm, and
where the value Tgsh detected by the intermediate superheat
detection mechanism (75) is even smaller than a lower threshold
value Tgshmin set smaller than the intermediate superheat target
value Tgshm.
16. The refrigerating apparatus of claim 9, comprising a second
control section (17) for changing a degree of opening of the flow
rate adjusting mechanism (30a, 30b, 30c) such that the values Td
detected by the discharge condition detection mechanisms (61, 66)
for the respective compressors (21a, 21b, 21c) are approximate to
each other.
17. The refrigerating apparatus of claim 3, wherein the plurality
of compressors (21a, 21b, 21c) include a first compressor (21a,
21b) and a second compressor (21c), a low pressure line of the
refrigerant circuit (10) includes a first low pressure line (102)
for connecting between a suction side of the first compressor (21a,
21b) and a cooling heat exchanger (53b, 81) which is provided in
the refrigerant circuit (10) and which provides cooling for a
storage room, and a second low pressure line (101) for connecting
between a suction side of the second compressor (21c) and an
air-conditioning heat exchanger (53a) which is provided in the
refrigerant circuit (10) and which provides air conditioning for an
indoor space, the refrigerating apparatus includes low-level
pressure detection mechanisms (120, 121) for detecting a pressure
of a low pressure refrigerant flowing in each of the first and
second low pressure lines (102, 101), an intermediate pressure
detection mechanism (71) for detecting a pressure of an
intermediate-pressure refrigerant having been decompressed by the
pressure-reducing mechanism (29), an intermediate superheat
detection mechanism (75) for detecting a superheat of the
intermediate-pressure refrigerant having passed through the
reduced-pressure side flow path (28b) of the subcooling heat
exchanger (28), and an intermediate superheat setting mechanism
(77) for setting an intermediate superheat target value Tgshm for
the superheat of the intermediate-pressure refrigerant having
passed through the reduced-pressure side flow path (28b) of the
subcooling heat exchanger (28), and the refrigerating apparatus
includes an intermediate pressure control section (59) for changing
a degree of opening of the pressure-reducing mechanism (29) such
that a value MP detected by the intermediate pressure detection
mechanism (71) becomes larger than values LP of the low pressure
lines (102, 101) detected by the low-level pressure detection
mechanisms (120, 121), an intermediate superheat control section
(60) for changing the degree of opening of the pressure-reducing
mechanism (29) such that a value Tgsh detected by the intermediate
superheat detection mechanism (75) becomes the intermediate
superheat target value Tgshm, and a third control section (18) for
exerting control by selecting the intermediate pressure control
section (59) or the intermediate superheat control section (60),
based on an operating condition of the plurality of compressors
(21a, 21b, 21c).
18. The refrigerating apparatus of claim 17, wherein the third
control section (18) is configured to exert control by selecting
the intermediate pressure control section (59) if the first
compressor (21a, 21b) and the second compressor (21c) are activated
together.
19. The refrigerating apparatus of claim 17, wherein the third
control section (18) is configured to exert control by selecting
the intermediate superheat control section (60) if one of the first
compressor (21a, 21b) and the second compressor (21c) is
actuated.
20. The refrigerating apparatus of claim 17, comprising a discharge
condition detection mechanism (61, 66) for detecting at least one
of a discharge temperature and a discharge superheat of each of the
compressors (21a, 21b, 21c), and a discharge condition setting
mechanism (76) for setting a discharge target value Tm for the at
least one of the discharge temperature and the discharge superheat
of each of the compressors (21a, 21b, 21c), a second discharge
target control section (56b) for changing a degree of opening ,of
the flow rate adjusting mechanism (30a, 30b, 30c) such that a value
Td detected by the discharge condition detection mechanism (61, 66)
becomes the discharge target value Tm, a second superheat avoidance
control section (78b) for having the degree of opening of the flow
rate adjusting mechanism (30a, 30b, 30c) greater than the present
degree of opening of the flow rate adjusting mechanism (30a, 30b,
30c), a second wet avoidance control section (79b) for having the
degree of opening of the flow rate adjusting mechanism (30a, 30b,
30c) smaller than the present degree of opening of the flow rate
adjusting mechanism (30a, 30b, 30c), a fourth control section (19)
for exerting control by selecting the second discharge target
control section (56b) if a refrigerant condition value of the
refrigerant in the refrigerant circuit (10) is in a predetermined
range, and selecting the second superheat avoidance control section
(78b) or the second wet avoidance control section (79b) if the
refrigerant condition value exceeds the predetermined range.
21. The refrigerating apparatus of claim 20, wherein the fourth
control section (19) is configured to exert control by selecting
the second superheat avoidance control section (78b) in at least
one of the cases where the value Td detected by the discharge
condition detection mechanism (61, 66) is even larger than an upper
threshold value Tdmax set larger than the discharge target value
Tm, or where the value Tgsh detected by the intermediate superheat
detection mechanism (75) is even larger than an upper threshold
value Tgshmax set larger than the intermediate superheat target
value Tgshm.
22. The refrigerating apparatus of claim 20, wherein the fourth
control section (19) is configured to exert control by selecting
the second wet avoidance control section (79b) in at least one of
the cases where the value Td detected by the discharge condition
detection mechanism (61, 66) is even smaller than a lower threshold
value Tdmin set smaller than the discharge target value Tm, or
where the value Tgsh detected by the intermediate superheat
detection mechanism (75) is even smaller than a lower threshold
value Tgshmin set smaller than the intermediate superheat target
value Tgshm.
23. The refrigerating apparatus of claim 20, wherein the fourth
control section (19) is configured to exert control by selecting
the second discharge target control section (56b) if the value Td
detected by the discharge condition detection mechanism (61, 66) is
equal to or larger than a lower threshold value Tdmin set smaller
than the discharge target value Tm, and equal to or smaller than an
upper threshold value Tdmax set larger than the discharge target
value Tm.
Description
TECHNICAL FIELD
[0001] The present invention relates to refrigerating apparatuses
having a plurality of compressors and performing a vapor
compression refrigeration cycle, especially relates to
refrigerating apparatuses which include an injection circuit for
injecting a refrigerant into each compressor.
BACKGROUND ART
[0002] Refrigerating apparatuses having a refrigerant circuit which
includes a plurality of compressors and which performs a vapor
compression refrigeration cycle have been known. The refrigerating
apparatuses of this type include, as shown in Patent Document 1,
refrigerating apparatuses which have an injection circuit for
injecting a refrigerant separated from a main pipe of the
refrigerant circuit to each compressor.
[0003] One end of the injection circuit is connected to a branch
pipe branched from a high pressure line of the refrigerant circuit,
and the other end is branched into multiple lines each of which is
connected to an intermediate port that is open to a compression
chamber in the state of intermediate pressure in each compressor. A
pressure-reducing valve for reducing the pressure of the
refrigerant is provided to the branch pipe.
[0004] According to this structure, the refrigerants discharged
from the compressors are collected together, and then flow into an
outdoor heat exchanger. The discharged refrigerant is condensed in
the outdoor heat exchanger, and thereafter, part of the discharged
refrigerant flows into the branch pipe branched from the
refrigerant circuit. The refrigerant is decompressed to a
predetermined pressure by the pressure-reducing valve provided to
the branch pipe. The flow of the refrigerant decompressed by the
pressure-reducing valve is divided into the intermediate ports of
the respective compressors, and is then injected into the
compression chambers of the respective compressors through the
intermediate ports.
[0005] Here, the above-described refrigerating apparatuses have a
temperature sensor for detecting the temperature of a discharge
pipe of each of the compressors. The degree of opening of the
pressure-reducing valve is adjusted based on the amount of change
in temperature of the discharge pipe per unit time that is detected
by the temperature sensor, thereby making it possible to maintain
the temperature of the refrigerant discharged from each compressor
within a predetermined temperature range.
Citation List
Patent Document
[0006] Patent Document 1: Japanese Patent Publication No.
2008-076017
SUMMARY OF THE INVENTION
Technical Problem
[0007] However, depending on the configuration of the refrigerant
circuit, the temperature of the refrigerant discharged from each
compressor sometimes does not likely fall within the predetermined
temperature range even if the conventional injection circuit is
used.
[0008] The above phenomenon occurs, for example, in the case where
at least one of the plurality of compressors of the refrigerant
circuit is a variable displacement compressor, and the others are
fixed displacement compressors. Now, suppose that in such a
refrigerant circuit, the refrigerant in the injection circuit is
being injected to each compressor, while the variable displacement
compressor is operated at predetermined operation capacity, and the
fixed displacement compressors are operated at fixed operation
capacity. Here, the temperature of the refrigerant discharged from
each compressor is in a predetermined temperature range due to the
injection.
[0009] From this state, the operational frequency is decreased in
order to reduce the operation capacity of the variable displacement
compressor. As a result, a period of change in capacity of the
compression chamber of this compressor is increased, and therefore,
a period of time in which the compression chamber is in the state
of intermediate pressure is increased as well. Consequently, a
period of time in which the intermediate port is open to the
compression chamber in the state of intermediate pressure is
increased as well. Because the time in which the intermediate port
is open is increased, more refrigerant in the injection circuit is
likely to flow into the variable displacement compressor.
[0010] As a result, in the above injection circuit, the refrigerant
decompressed by the pressure-reducing valve flows more into the
variable displacement compressor, than into the fixed displacement
compressors, and the temperature of the refrigerant discharged from
the variable displacement compressor may be lower than the
temperature of the refrigerant discharged from the fixed
displacement compressors. If this happens, the temperature of the
refrigerant discharged from each compressor does not likely fall
within the predetermined temperature range.
[0011] Another example is the case where the plurality of
compressors in the refrigerant circuit are configured to include a
first compressor and a second compressor whose suction pressures
are different from each other. In this case, the refrigerant
circuit is provided with a first evaporator corresponding to the
first compressor, and a second evaporator corresponding to the
second compressor, and is configured such that the refrigerants
flowing in the first evaporator and the second evaporator are
evaporated at temperatures different from each other.
[0012] If the suction pressure differs between the first compressor
and the second compressor as described above, the intermediate
pressure in the compression chambers differs as well. Thus, the
refrigerant decompressed by the pressure-reducing valve tends to be
suctioned more into the compressor having a lower pressure in the
compression chamber in the state of intermediate pressure, than
into the compressor having a higher pressure in the compression
chamber in the state of intermediate pressure. As a result, the
temperature of the refrigerant discharged from the compressor
having a lower intermediate pressure may become lower than the
temperature of the refrigerant discharged from the compressor
having a higher intermediate pressure. If this happens, the
temperature of the refrigerant discharged from each compressor does
not likely fall within the predetermined temperature range.
[0013] As described above, in the above injection circuit, the
amount of refrigerant decompressed by the pressure-reducing valve
and flowing into the compressors may be unbalanced between the
compressors, depending on the configuration or operating condition
of the refrigerant circuit.
[0014] The present invention was made in view of the above
problems, and it is an objective of the invention to provide an
appropriate refrigerant injection for each compressor in a
refrigerating apparatus having a plurality of compressors.
Solution to the Problem
[0015] The first aspect of the present invention is intended for a
refrigerating apparatus including: a refrigerant circuit (10) which
has a plurality of compressors (21a, 21b, 21c) and which performs a
vapor compression refrigeration cycle; an injection circuit (40)
which has a main pipe (37) branched from a high pressure line (33)
of the refrigerant circuit (10) and branch pipes (37a, 37b, 37c)
branched from the main pipe (37), and in which the branch pipes
(37a, 37b, 37c) are connected to intermediate ports (5, 6, 7) of
the compressors (21a, 21b, 21c), respectively; and a
pressure-reducing mechanism (29) provided to the main pipe (37) of
the injection circuit (40).
[0016] In the refrigerant circuit (10), at least one of the
plurality of compressors (21a, 21b, 21c) is a variable displacement
compressor (21a), and a flow rate adjusting mechanism (30a, 30b,
30c) is provided at least to the branch pipe (37a, 37b, 37c) of the
variable displacement compressor (21a). Here, the intermediate
ports (5, 6, 7) are provided to the compressors (21a, 21b, 21c) so
as to be open to the compression chambers in the state of
intermediate pressure.
[0017] According to the first aspect of the present invention, part
of the high pressure refrigerant flowing in the high pressure line
(high pressure pipe) (33) of the refrigerant circuit (10) is
separated to flow into the main pipe (37). The high pressure
refrigerant having flowed into the main pipe (37) is decompressed
by the pressure-reducing mechanism (29), and is then separated to
flow into the branch pipes (37a, 37b, 37c). The flow rate of the
refrigerant having flowed into the branch pipes (37a, 37b, 37c) is
adjusted by the flow rate adjusting mechanisms (30a, 30b, 30c), and
then the refrigerant passes through the intermediate ports (5, 6,
7) to be injected to the compression chambers.
[0018] Thus, in such a case as described above in which at least
one of the plurality of compressors (21a, 21b, 21c) is a variable
displacement compressor (21a) and the other compressors are fixed
displacement compressors (21b, 21c), if the operation capacity of
the variable displacement compressor (21a) is reduced, the degree
of opening of the flow rate adjusting mechanism (30a) which
corresponds to the variable displacement compressor (21a) is
reduced, thereby making it possible to prevent the refrigerant from
being injected into the variable displacement compressor (21a) in a
large amount.
[0019] Further, if the suction pressure of the variable
displacement compressor (21a) of the plurality of compressors (21a,
21b, 21c) becomes lower than the suction pressures of the other
compressors (21b, 21c), the degree of opening of the flow rate
adjusting mechanism (30a) which corresponds to the variable
displacement compressor (21a) is reduced, thereby making it
possible to prevent the refrigerant from being injected into the
variable displacement compressor (21a) in a large amount.
[0020] The second aspect of the present invention is that in the
first aspect of the present invention, the flow rate adjusting
mechanism (30a, 30b, 30c) is provided to each of the branch pipes
(37a, 37b, 37c) of the injection circuit (40).
[0021] According to the second aspect of the present invention, the
flow rate adjusting mechanism (30a, 30b, 30c) is provided to all of
the branch pipes (37a, 37b, 37c). Thus, for example, if the suction
pressure of the compressor (21a) of the plurality of compressors
(21a, 21b, 21c) becomes lower than the suction pressures of the
other compressors (21b, 21c), the degree of opening of the flow
rate adjusting mechanism (30a) which corresponds to the compressor
(21a) having the lower suction pressure is reduced, thereby making
it possible to prevent the refrigerant from being injected in a
large amount into the compressor (21a) having the lower suction
pressure.
[0022] The third aspect of the present invention includes, in the
first or second aspect of the present invention, a subcooling heat
exchanger (28) having a reduced-pressure side flow path (28b)
through which a refrigerant decompressed by the pressure-reducing
mechanism (29) flows and a high pressure side flow path (28a)
through which a high pressure refrigerant of the refrigerant
circuit (10) flows, wherein the reduced-pressure side flow path
(28b) is connected to the main pipe (37) of the injection circuit
(40), and the high pressure side flow path (28a) is connected to
the high pressure line (33) of the refrigerant circuit (10).
[0023] According to the third aspect of the present invention, the
refrigerant decompressed by the pressure-reducing mechanism (29)
can be injected into the compression chambers (21a, 21b, 21c) after
being heat exchanged with the high pressure refrigerant flowing in
the refrigerant circuit (10) by the subcooling heat exchanger
(28).
[0024] The fourth aspect of the present invention includes, in any
one of the first to third aspects of the present invention, oil
separators (38a, 38b, 38c) respectively provided to discharge pipes
(22a, 22b, 22c) of the compressors (21a, 21b, 21c), for separating
a refrigerating machine oil from a discharge refrigerant discharged
from the compressors (21a, 21b, 21c); oil discharge pipes (39a,
39b, 39c) connected to the oil separators (38a, 38b, 38c); and an
oil return circuit (39) of which one end side is connected to the
oil discharge pipes (39a, 39b, 39c) and of which the other end side
is connected to a branch pipe branched from the injection circuit
(40), for returning the refrigerating machine oil from the oil
discharge pipes (39a, 39b, 39c) to the compressors (21a, 21b,
21c).
[0025] According to the fourth aspect of the present invention, the
refrigerating machine oil separated from the discharge refrigerant
by the oil separators (38a, 38b, 38c) can be returned, through the
injection circuit (40), to the compression chambers of the
compressors (21a, 21b, 21c) in the state of intermediate
pressure.
[0026] The fifth aspect of the present invention is that, in any
one of the first to fourth aspects of the present invention, the
flow rate adjusting mechanism (30a, 30b, 30c) is a flow rate
adjusting valve whose degree of opening is variable.
[0027] According to the fifth aspect of the present invention, the
flow rate adjusting mechanism (30a, 30b, 30c) is a flow rate
adjusting valve. Thus, the degree of opening of the valve can be
freely changed from a fully opened state to a fully closed
state.
[0028] The sixth aspect of the present invention is that, in any
one of the first to fifth aspects of the present invention, the
flow rate adjusting mechanism (30a, 30b, 30c) is an on/off valve.
Here, reducing the degree of opening of the flow rate adjusting
mechanism (30a, 30b, 30c) means closing the on/off valve.
Increasing the degree of opening means opening the on/off
valve.
[0029] According to the sixth aspect of the present invention, the
flow rate adjusting mechanism (30a, 30b, 30c) is an on/off valve.
Thus, the structure of the flow rate adjusting mechanism (30a, 30b,
30c) can be simplified, and therefore the cost can be reduced,
compared to the case in which the flow rate adjusting mechanism
(30a, 30b, 30c) is a flow rate adjusting valve, for example.
[0030] The seventh aspect of the present invention is that, in any
one of the first to sixth aspects of the present invention, the
plurality of compressors (21a, 21b, 21c) include a variable
displacement compressor (21a) and a fixed displacement compressor
(21b, 21c), and the flow rate adjusting mechanism (30a) provided to
the branch pipe (37a) connected to the intermediate port (5) of the
variable displacement compressor (21a) is a flow rate adjusting
valve whose degree of opening is variable, and the flow rate
adjusting mechanism (30b, 30c) provided to the branch pipe (37b,
37c) connected to the intermediate port (6, 7) of the fixed
displacement compressor (21b, 21c) is an on/off valve.
[0031] According to the seventh aspect of the present invention, an
injection amount of the variable displacement compressor (21a) can
be adjusted by the flow rate adjusting valve, and an injection
amount of the fixed displacement compressor (21b, 21c) can be
adjusted by the on/off valve.
[0032] The eighth aspect of the present invention includes, in any
one of the first to seventh aspects of the present invention, a
discharge refrigerant temperature detection mechanism (61) for
detecting a temperature of a discharge refrigerant discharged from
the compressors (21a, 21b, 21c), and a control mechanism (9) for
adjusting a degree of opening of each of the flow rate adjusting
mechanisms (30a, 30b, 30c) such that a value detected by the
discharge refrigerant temperature detection mechanism (61) falls
within a predetermined temperature range.
[0033] According to the eighth aspect of the present invention, if
a refrigerant discharged from any of the plurality of compressors
(21a, 21b, 21c) has a temperature higher than a predetermined
temperature range, the degree of opening of the flow rate adjusting
mechanism (30a, 30b, 30c) which corresponds to that compressor
(21a, 21b, 21c) is increased, thereby making it possible to
increase the injection amount of the compressor (21a, 21b, 21c). As
a result, it is possible to reduce the temperature of the discharge
refrigerant to a temperature within the predetermined temperature
range.
[0034] Further, if a refrigerant discharged from any of the
compressors (21a, 21b, 21c) has a temperature lower than the
predetermined temperature range, the degree of opening of the flow
rate adjusting mechanism (30a, 30b, 30c) which corresponds to that
compressor (21a, 21b, 21c) is reduced, thereby making it possible
to reduce the injection amount of the compressor (21a, 21b, 21c).
As a result, it is possible to increase the temperature of the
discharge refrigerant to a temperature within the predetermined
temperature range.
[0035] The ninth aspect of the present invention includes, in any
one of the third to seventh aspects of the present invention, a
discharge condition detection mechanism (61, 66) for detecting at
least one of a discharge temperature and a discharge superheat of
each of the compressors (21a, 21b, 21c), a discharge condition
setting mechanism (76) for setting a discharge target value Tm for
the at least one of the discharge temperature and the discharge
superheat of each of the compressors (21a, 21b, 21c), an
intermediate superheat detection mechanism (75) for detecting a
superheat of an intermediate-pressure refrigerant having passed
through the reduced-pressure side flow path (28b) of the subcooling
heat exchanger (28), an intermediate superheat setting mechanism
(77) for setting an intermediate superheat target value Tgshm for
the superheat of the intermediate-pressure refrigerant having
passed through the reduced-pressure side flow path (28b) of the
subcooling heat exchanger (28), a first discharge target control
section (56a) for changing a degree of opening of the
pressure-reducing mechanism (29) such that a maximum detection
value Ttd, which is a maximum value among values Td detected by the
discharge condition detection mechanisms (61, 66) for the
respective compressors (21a, 21b, 21c), becomes the discharge
target value Tm, Tdshm, an intermediate superheat control section
(60) for changing the degree of opening of the pressure-reducing
mechanism (29) such that a value Tgsh detected by the intermediate
superheat detection mechanism (75) becomes the intermediate
superheat target value Tgshm, and a first control section (16) for
exerting control, if a refrigerant condition value of the
refrigerant in the refrigerant circuit (10) is in a predetermined
range, by selecting the first discharge target control section
(56a) or the intermediate superheat control section (60) based on
the refrigerant condition value.
[0036] Here, the discharge condition setting mechanism (76) sets,
as the discharge target value Tm, an appropriate value which does
not cause the compressors (21a, 21b, 21c) to perform a relatively
excessive superheat operation or wet operation. Further, the
intermediate superheat setting mechanism (77) sets, as the
intermediate superheat target value Tgshm, an appropriate value
which does not cause the intermediate-pressure refrigerant having
passed through the reduced-pressure side flow path (28b) of the
subcooling heat exchanger (28) to be in a relatively excessive
superheat condition or wet condition. The predetermined range of
the refrigerant condition value is set within a range which does
not make the compressors (21a, 21b, 21c) perform an abnormal
operation.
[0037] According to the ninth aspect of the present invention, the
first discharge target control section (56a) or the intermediate
superheat control section (60) is selected by the first control
section (16) if the refrigerant condition value of the refrigerant
circuit (10) is in the predetermined range, that is, if the
compressors (21a, 21b, 21c) are not operating abnormally. If the
first discharge target control section (56a) is selected, the
degree of opening of the pressure-reducing mechanism (29) is
changed such that a discharge temperature or a discharge superheat
of each of the compressors (21a, 21b, 21c) can be maintained
constant at a target value. If the intermediate superheat control
section (60) is selected, the degree of opening of the
pressure-reducing mechanism (29) is changed such that a superheat
of the intermediate-pressure refrigerant in the reduced-pressure
side flow path (28b) of the subcooling heat exchanger (28) can be
maintained constant at a target value.
[0038] The tenth aspect of the present invention is that, in the
ninth aspect of the present invention, the first control section
(16) is configured to exert control by selecting the first
discharge target control section (56a) if the maximum detection
value Ttd of the discharge condition detection mechanism (61, 66)
is larger than the discharge target value Tm.
[0039] According to the tenth aspect of the present invention, if
the maximum detection value Ttd of the discharge condition
detection mechanism (61, 66) is larger than the discharge target
value Tm, that is, if one of the plurality of compressors (21a,
21b, 21c) is in an excessive superheat operation, the degree of
opening of the pressure-reducing mechanism (29) is changed by the
first discharge target control section (56a). As a result, the
discharge temperature or the discharge superheat of the compressors
(21a, 21b, 21c) can be maintained at an appropriate value.
[0040] The eleventh aspect of the present invention is that, in the
ninth or tenth aspect of the present invention, the first control
section (16) is configured to exert control by selecting the
intermediate superheat control section (60) if the maximum
detection value Ttd of the discharge condition detection mechanism
(61, 66) is equal to or smaller than the discharge target value
Tm.
[0041] According to the eleventh aspect of the present invention,
if the maximum detection value Ttd of the discharge condition
detection mechanism (61, 66) is equal to or smaller than the
discharge target value Tm, that is, if all of the compressors (21a,
21b, 21c) are not performing a relatively excessive superheat
operation, the degree of opening of the pressure-reducing mechanism
(29) is changed by the intermediate superheat control section (60).
As a result, the superheat of the intermediate-pressure refrigerant
in the reduced-pressure side flow path (28b) of the subcooling heat
exchanger (28) can be maintained at an appropriate value.
[0042] The twelfth aspect of the present invention is that, in any
one of the ninth to eleventh aspects of the present invention, the
first control section (16) is configured to exert control by
selecting the intermediate superheat control section (60) if the
maximum detection value Ttd of the discharge condition detection
mechanism (61, 66) continues to decrease during a predetermined
time t1.
[0043] According to the twelfth aspect of the present invention, if
the maximum detection value Ttd of the discharge condition
detection mechanism (61, 66) continues to decrease during a
predetermined time t1, that is, for example, if one of the
plurality of compressors (21a, 21b, 21c) is performing a relatively
excessive superheat operation and the excessive superheat operation
is changing to a wet operation, the degree of opening of the
pressure-reducing mechanism (29) is changed by the intermediate
superheat control section (60) regardless of the operating
condition of the one of the compressors (21a, 21b, 21c). As a
result, it is possible to start the operation of the intermediate
superheat control section earlier.
[0044] The thirteenth aspect of the present invention includes, in
any one of the ninth to the twelfth aspects of the present
invention, a first superheat avoidance control section (78a) for
having the degree of opening of the pressure-reducing mechanism
(29) greater than the present degree of opening of the
pressure-reducing mechanism (29), a first wet avoidance control
section (79a) for having the degree of opening of the
pressure-reducing mechanism (29) smaller than the present degree of
opening of the pressure-reducing mechanism (29), and an avoidance
control section (58) for exerting control, if the refrigerant
condition value of the refrigerant in the refrigerant circuit (10)
exceeds the predetermined range, by selecting the first superheat
avoidance control section (78a) or the first wet avoidance control
section (79a) until the refrigerant condition value is in the
predetermined range.
[0045] According to the thirteenth aspect of the present invention,
if the refrigerant condition value exceeds a predetermined range,
that is, if the compressors (21a, 21b, 21c) are operating
abnormally, the pressure-reducing mechanism (29) is controlled by
the avoidance control section (58) until the refrigerant condition
value is in the predetermined range. As a result, it is possible to
prevent the refrigerating apparatus from continuously performing an
abnormal operation. Thus, if the refrigerant condition value of the
refrigerant circuit (10) is in the predetermined range, the
pressure-reducing mechanism (29) is controlled by the first control
section (16). If the refrigerant condition value exceeds the
predetermined range, the pressure-reducing mechanism (29) is
controlled by the avoidance control section (58).
[0046] The fourteenth aspect of the present invention is that, in
the thirteenth aspect of the present invention, the avoidance
control section (58) is configured to exert control by selecting
the first superheat avoidance control section (78a) in at least one
of the cases where the value Td detected by the discharge condition
detection mechanism (61, 66) is even larger than an upper threshold
value Tdmax set larger than the discharge target value Tm, and
where the value Tgsh detected by the intermediate superheat
detection mechanism (75) is even larger than an upper threshold
value Tgshmax set larger than the intermediate superheat target
value Tgshm.
[0047] Here, at least one of the value Td detected by the discharge
condition detection mechanism (61, 66) and the value Tgsh detected
by the intermediate superheat detection mechanism (75) is used as a
refrigerant condition value of the refrigerant circuit (10).
Further, an upper threshold value Tdmax, Tgshmax set even larger
than the target value Tm corresponding to the detected value Td,
Tgsh is used as a maximum value of the refrigerant condition value
within a predetermined range.
[0048] According to the fourteenth aspect of the present invention,
the degree of opening of the pressure-reducing mechanism (29) is
forced to increase by being adjusted by the first superheat
avoidance control section (78a), if the compressors (21a, 21b, 21c)
start to perform an abnormal superheat operation when the discharge
temperature or the discharge superheat as the refrigerant condition
value increases too much and the detected value Td, Tgsh exceeds
the upper threshold value Tdmax, Tgshmax.
[0049] The fifteenth aspect of the present invention is that, in
the thirteen or fourteenth aspect of the present invention, the
avoidance control section (58) is configured to exert control by
selecting the first wet avoidance control section (79a) in at least
one of the cases where the value Td detected by the discharge
condition detection mechanism (61, 66) is even smaller than a lower
threshold value Tdmin set smaller than the discharge target value
Tm, and where the value Tgsh detected by the intermediate superheat
detection mechanism (75) is even smaller than a lower threshold
value Tgshmin set smaller than the intermediate superheat target
value Tgshm.
[0050] Here, similar to the fourteenth aspect of the present
invention, at least one of the value Td detected by the discharge
condition detection mechanism (61, 66) and the value Tgsh detected
by the intermediate superheat detection mechanism (75) is used as a
refrigerant condition value of the refrigerant circuit (10).
Further, a lower threshold value Tdmin, Tgshmin set even smaller
than the target value Tdm, Tgshm corresponding to the detected
value Td, Tgsh is used as a minimum value of the refrigerant
condition value within a predetermined range.
[0051] According to the fifteenth aspect of the present invention,
the degree of opening of the pressure-reducing mechanism (29) is
forced to decrease by being adjusted by the first wet avoidance
control section (79a), if the compressors (21a, 21b, 21c) start to
perform an abnormal wet operation when the discharge temperature or
the discharge superheat as the refrigerant condition value
decreases too much and the detected value Td, Tgsh becomes lower
than the lower threshold value Tdmin, Tgshmin.
[0052] The sixteenth aspect of the present invention includes, in
any one of the ninth to fifteenth aspects of the present invention,
a second control section (17) for changing a degree of opening of
the flow rate adjusting mechanism (30a, 30b, 30c) such that the
values Td detected by the discharge condition detection mechanisms
(61, 66) for the respective compressors (21a, 21b, 21c) are
approximate to each other.
[0053] According to the sixteenth aspect of the present invention,
the discharge temperatures or the discharge superheats of the
compressors (21a, 21b, 21c) can be approximate to one another.
[0054] The seventeenth aspect of the present invention is that, in
any one of the third to seventh aspects of the present invention,
the plurality of compressors (21a, 21b, 21c) include a first
compressor (21a, 21b) and a second compressor (21c), a low pressure
line of the refrigerant circuit (10) includes a first low pressure
line (102) for connecting between a suction side of the first
compressor (21a, 21b) and a cooling heat exchanger (53b, 81) which
is provided in the refrigerant circuit (10) and which provides
cooling for a storage room, and a second low pressure line (101)
for connecting between a suction side of the second compressor
(21c) and an air-conditioning heat exchanger (53a) which is
provided in the refrigerant circuit (10) and which provides air
conditioning for an indoor space; the refrigerating apparatus
includes low-level pressure detection mechanisms (120, 121) for
detecting a pressure of a low pressure refrigerant flowing in each
of the first and second low pressure lines (102, 101), an
intermediate pressure detection mechanism (71) for detecting a
pressure of an intermediate-pressure refrigerant having been
decompressed by the pressure-reducing mechanism (29), an
intermediate superheat detection mechanism (75) for detecting a
superheat of the intermediate-pressure refrigerant having passed
through the reduced-pressure side flow path (28b) of the subcooling
heat exchanger (28), and an intermediate superheat setting
mechanism (77) for setting an intermediate superheat target value
Tgshm for the superheat of the intermediate-pressure refrigerant
having passed through the reduced-pressure side flow path (28b) of
the subcooling heat exchanger (28); and the refrigerating apparatus
includes an inteiinediate pressure control section (59) for
changing a degree of opening of the pressure-reducing mechanism
(29) such that a value MP detected by the intermediate pressure
detection mechanism (71) becomes larger than values LP of the low
pressure lines (102, 101) detected by the low-level pressure
detection mechanisms (120, 121), an intermediate superheat control
section (60) for changing the degree of opening of the
pressure-reducing mechanism (29) such that a value Tgsh detected by
the intermediate superheat detection mechanism (75) becomes the
intermediate superheat target value Tgshm, and a third control
section (18) for exerting control by selecting the intermediate
pressure control section (59) or the intermediate superheat control
section (60), based on an operating condition of the plurality of
compressors (21a, 21b, 21c).
[0055] In general, the evaporation temperature of the cooling heat
exchanger (53b, 81) is lower than the evaporation temperature of
the air-conditioning heat exchanger (53a). Thus, the pressure of
the low pressure refrigerant flowing in the first low pressure line
(102) is lower than the pressure of the low pressure refrigerant
flowing in the second low pressure line (101).
[0056] Further, similar to the eighth aspect of the present
invention, the intermediate superheat setting mechanism (77) sets,
as the intermediate superheat target value Tgshm, an appropriate
value which does not cause the intermediate-pressure refrigerant
having passed through the reduced-pressure side flow path (28b) of
the subcooling heat exchanger (28) to be in a relatively excessive
superheat condition or wet condition.
[0057] According to the seventeenth aspect of the present
invention, the intermediate pressure control section (59) or the
intermediate superheat control section (60) is selected based on
the operating condition of the compressors (21a, 21b, 21c). If the
intermediate pressure control section (59) is selected, the
pressure of the injection circuit (40) is controlled to always be a
pressure higher than the pressures of the first and second low
pressure lines (102, 101). If the intermediate superheat control
section (60) is selected, the superheat of the
inteHnediate-pressure refrigerant of the reduced-pressure side flow
path (28b) of the subcooling heat exchanger (28) is controlled to
be constant at a target value.
[0058] The eighteenth aspect of the present invention is that, in
the seventeenth aspect of the present invention, the third control
section (18) is configured to exert control by selecting the
intermediate pressure control section (59) if the first compressor
(21a, 21b) and the second compressor (21c) are activated
together.
[0059] Here, if the first compressor (21a, 21b) and the second
compressor (21c) are activated together, the pressure of the low
pressure refrigerant flowing in the first low pressure line (102)
is lower than the pressure of the low pressure refrigerant flowing
in the second low pressure line (101). Also, the suction pressure
of the first compressor (21a, 21b) is lower than the suction
pressure of the second compressor (21c). Thus, the pressure at the
intermediate port of the first compressor (21a, 21b) is also lower
than the pressure at the intermediate port of the second compressor
(21c).
[0060] Accordingly, the low pressure refrigerant suctioned into the
second compressor (21c) through the second low pressure line (101)
may flow out through the intermediate port (7) of the second
compressor (21c) in the middle of the compression process in the
second compressor (21c), and may flow back to the intermediate port
(5, 6) of the first compressor (21a, 21b) via the injection circuit
(40).
[0061] According to the eighteenth aspect of the present invention,
if the first compressor (21a, 21b) and the second compressor (21c)
are activated together, the degree of opening of the
pressure-reducing mechanism (29) is changed by the intermediate
pressure control section (59), thereby controlling the pressure of
the injection circuit (40) to always be a pressure higher than the
pressure of the first and second low pressure lines. Thus, the
backflow of the refrigerant from the second compressor (21c) to the
first compressor (21a, 21b) as described above can be avoided.
[0062] The nineteenth aspect of the present invention is that in
the seventeenth or eighteenth aspect of the present invention, the
third control section (18) is configured to exert control by
selecting the intermediate superheat control section (60) if one of
the first compressor (21a, 21b) and the second compressor (21c) is
actuated.
[0063] Here, if one of the first compressor (21a, 21b) and the
second compressor (21c) is activated, the backflow of the
refrigerant from the second compressor (21c) to the first
compressor (21a, 21b) as described above does not occur.
[0064] According to the nineteenth aspect of the present invention,
it is not necessary to consider the backflow of the refrigerant
from the second compressor (21c) to the first compressor (21a, 21b)
if one of the first compressor (21a, 21b) and the second compressor
(21c) is activated, and therefore, the degree of opening of the
pressure-reducing mechanism (29) is adjusted by the intermediate
superheat control section (60). As a result, the superheat of the
intermediate-pressure refrigerant of the reduced-pressure side flow
path (28b) of the subcooling heat exchanger (28) can be maintained
at an appropriate value.
[0065] The twentieth aspect of the present invention includes, in
any one of the seventeenth to nineteenth aspects of the present
invention, a discharge condition detection mechanism (61, 66) for
detecting at least one of a discharge temperature and a discharge
superheat of each of the compressors (21a, 21b, 21c), and a
discharge condition setting mechanism (76) for setting a discharge
target value Tm for the at least one of the discharge temperature
and the discharge superheat of each of the compressors (21a, 21b,
21c); a second discharge target control section (56b) for changing
a degree of opening of the flow rate adjusting mechanism (30a, 30b,
30c) such that a value Td detected by the discharge condition
detection mechanism (61, 66) becomes the discharge target value Tm;
a second superheat avoidance control section (78b) for having the
degree of opening of the flow rate adjusting mechanism (30a, 30b,
30c) greater than the present degree of opening of the flow rate
adjusting mechanism (30a, 30b, 30c); a second wet avoidance control
section (79b) for having the degree of opening of the flow rate
adjusting mechanism (30a, 30b, 30c) smaller than the present degree
of opening of the flow rate adjusting mechanism (30a, 30b, 30c);
and a fourth control section (19) for exerting control by selecting
the second discharge target control section (56b) if a refrigerant
condition value of the refrigerant in the refrigerant circuit (10)
is in a predetermined range, and selecting the second superheat
avoidance control section (78b) or the second wet avoidance control
section (79b) if the refrigerant condition value exceeds the
predetermined range.
[0066] Here, the discharge condition setting mechanism (76) sets,
as the discharge target value Tm, an appropriate value which does
not cause the compressors (21a, 21b, 21c) to perform a relatively
excessive superheat operation or wet operation.
[0067] According to the twentieth aspect of the present invention,
one of the three control sections (i.e., the second discharge
target control section (56b), the second superheat avoidance
control section (78b), and the second wet avoidance control section
(79b)) is selected based on the refrigerant condition value of the
refrigerant circuit (10).
[0068] If the second discharge target control section (56b) is
selected, the discharge temperature or the discharge superheat of
each of the compressors (21a, 21b, 21c) is controlled to be
constant at a target value. If the second superheat avoidance
control section (78b) is selected, the degree of opening of the
flow rate adjusting mechanism (30a, 30b, 30c) is controlled to be
greater than the present degree of opening thereof. If the second
wet avoidance control section (79b) is selected, the degree of
opening of the flow rate adjusting mechanism (30a, 30b, 30c) is
controlled to be smaller than the present degree of opening
thereof.
[0069] The twenty-first aspect of the present invention is that, in
the twentieth aspect of the present invention, the fourth control
section (19) is configured to exert control by selecting the second
superheat avoidance control section (78b) in at least one of the
cases where the value Td detected by the discharge condition
detection mechanism (61, 66) is even larger than an upper threshold
value Tdmax set larger than the discharge target value Tm, or where
the value Tgsh detected by the intermediate superheat detection
mechanism (75) is even larger than an upper threshold value Tgshmax
set larger than the intermediate superheat target value Tgshm.
[0070] Here, at least one of the value Td detected by the discharge
condition detection mechanism (61, 66) and the value Tgsh detected
by the intermediate superheat detection mechanism (75) is used as a
refrigerant condition value of the refrigerant circuit (10).
Further, an upper threshold value Tdmax, Tgshmax set even larger
than the target value Tm corresponding to the detected value Td,
Tgsh is used as a maximum value of the refrigerant condition value
within a predetermined range.
[0071] According to the twenty-first aspect of the present
invention, if any of the compressors (21a, 21b, 21c) starts to
perform an abnormal superheat operation when a discharge
temperature or a discharge superheat as the refrigerant condition
value increases too much and the detected value Td or the detected
value Tgsh exceeds the upper threshold value
[0072] Tdmax or Tgshmax, the degree of opening of the flow rate
adjusting valve (30a, 30b, 30c) corresponding to the compressor
(21a, 21b, 21c) that performs the abnormal superheat operation is
forced to increase by being adjusted by the second superheat
avoidance control section (78b).
[0073] The twenty-second aspect of the present invention is that,
in the twentieth or twenty-first aspect of the present invention,
the fourth control section (19) is configured to exert control by
selecting the second wet avoidance control section (79b) in at
least one of the cases where the value Td detected by the discharge
condition detection mechanism (61, 66) is even smaller than a lower
threshold value Tdmin set smaller than the discharge target value
Tm, or where the value Tgsh detected by the intermediate superheat
detection mechanism (75) is even smaller than a lower threshold
value Tgshmin set smaller than the intermediate superheat target
value Tgshm.
[0074] Here, a lower threshold value Tdmin, Tgshmin set even
smaller than the target value Tm corresponding to the detected
value Td, Tgsh is used as a minimum value of the refrigerant
condition value within a predetermined range.
[0075] According to the twenty-second aspect of the present
invention, if any of the compressors (21a, 21b, 21c) starts to
perform an abnormal wet operation when a discharge temperature or a
discharge superheat as the refrigerant condition value decreases
too much and the detected value Td or the detected value Tgsh
becomes lower than the lower threshold value Tdmin or Tgshmin, the
degree of opening of the flow rate adjusting valve (30a, 30b, 30c)
corresponding to the compressor (21a, 21b, 21c) that performs the
abnormal wet operation is forced to decrease by being adjusted by
the second wet avoidance control section (79b).
[0076] The twenty-third aspect of the present invention is that, in
any one of the twentieth to the twenty-second aspects of the
present invention, the fourth control section (19) is configured to
exert control by selecting the second discharge target control
section (56b) if the value Td detected by the discharge condition
detection mechanism (61, 66) is equal to or larger than a lower
threshold value Tdmin set smaller than the discharge target value
Tm, and equal to or smaller than an upper threshold value Tdmax set
larger than the discharge target value Tm.
[0077] According to the twenty-third aspect of the present
invention, the degree of opening of the flow rate adjusting valve
(30a, 30b, 30c) corresponding to the compressor (21a, 21b, 21c) of
which the discharge temperature or the discharge superheat as the
refrigerant condition value is in a predetermined range, is changed
by the second discharge target control section (56b).
Advantages of the Invention
[0078] According to the present invention, the flow rate of the
refrigerant flowing in each of the branch pipes (37a, 37b, 37c)
after being decompressed by the pressure-reducing mechanism (29)
can be adjusted for each of the compressors (21a, 21b, 21c) by the
flow rate adjusting mechanism (30a, 30b, 30c). As a result, an
appropriate injection into the compressor (21a, 21b, 21c) can be
performed.
[0079] According to the second aspect of the present invention, the
flow rate adjusting mechanism (30a, 30b, 30c) is provided to all of
the branch pipes (37a, 37b, 37c). Therefore, it is possible to
adjust the degree of opening of the flow rate adjusting mechanism
(30a, 30b, 30c) selected according to the operating condition of
the refrigerating apparatus. As a result, an appropriate injection
into the compressor (21a, 21b, 21c) corresponding to the selected
flow rate adjusting mechanism (30a, 30b, 30c) can be performed.
[0080] According to the third aspect of the present invention, it
is possible to increase the degree of subcooling of the high
pressure refrigerant, while injection to the compressors (21a, 21b,
21c) is being performed. Thus, the injection to the plurality of
compressors (21a, 21b, 21c) can be achieved, while improving the
COP of the refrigerating apparatus (1) more than in the case where
the subcooling heat exchanger (28) is not provided.
[0081] According to the fourth aspect of the present invention, it
is possible to return the refrigerating machine oil to the
compressors (21a, 21b, 21c), while the refrigerant is being
injected to the compressors (21a, 21b, 21c) via the injection
circuit (40).
[0082] According to the fifth aspect of the present invention, the
flow rate adjusting mechanism (30a, 30b, 30c) is a flow rate
adjusting valve. Thus, the degree of opening of the valve can be
freely changed from a fully opened state to a fully closed state.
As a result, the amount of the refrigerant passing through the
valve can be adjusted with accuracy. Thus, a more appropriate
injection to the compressors (21a, 21b, 21c) can be achieved.
[0083] According to the sixth aspect of the present invention, the
flow rate adjusting mechanism (30a, 30b, 30c) is an on/off valve.
Thus, the structure of the flow rate adjusting mechanism (30a, 30b,
30c) can be simplified, compared to the case in which the flow rate
adjusting mechanism (30a, 30b, 30c) is a flow rate adjusting valve
whose degree of opening is variable. Accordingly, the injection
amount of each of the compressors (21a, 21b, 21c) can be adjusted
with less cost.
[0084] According to the seventh aspect of the present invention,
the amount of refrigerant suctioned into the variable displacement
compressor (21a) through the intermediate port (5) is changed due
to change in operation capacity of the variable displacement
compressor (21a), as described above. Thus, it is possible to
accurately adjust the injection amount to the variable displacement
compressor (21a) by the flow rate adjusting valve. On the other
hand, the amount of refrigerant suctioned into the fixed
displacement compressor (21b, 21c) through the intermediate port
(6, 7) is not likely to be changed, compared to the amount of
refrigerant suctioned into the variable displacement compressor
(21a), because the operation capacity of the fixed displacement
compressor (21b, 21c) is not changed. Thus, it is not necessary to
accurately adjust the injection amount for the fixed displacement
compressor (21b, 21c) by the flow rate adjusting valve.
Accordingly, an on/off valve having a simpler structure than the
flow rate adjusting valve can be used, thereby making it possible
to decrease the cost of the refrigerating apparatus.
[0085] According to the eighth aspect of the present invention, the
temperature of the discharge refrigerant discharged from each of
the compressors (21a, 21b, 21c) can be maintained in a
predetermined temperature range, by adjusting the injection amount
for each of the compressors (21a, 21b, 21c) according to the
temperature of the discharge refrigerant discharged from the
plurality of compressors (21a, 21b, 21c) using the control
mechanism (9). As a result, a more appropriate injection to the
compressors (21a, 21b, 21c) can be achieved.
[0086] According to the ninth aspect of the present invention, the
first control section (16) can control the pressure-reducing
mechanism (29) to maintain the discharge temperature or the
discharge superheat of each of the compressors (21a, 21b, 21c)
constant at a target value, or can control the pressure-reducing
mechanism (29) to maintain the superheat of the
intermediate-pressure refrigerant of the reduced-pressure side flow
path (28b) of the subcooling heat exchanger (28) constant at a
target value. A more appropriate injection to the compressors (21a,
21b, 21c) can be achieved by exerting these two types of control
depending on the situation.
[0087] According to the tenth aspect of the present invention, if
one of the plurality of compressors (21a, 21b, 21c) is in a
relatively excessive superheat operation, the degree of opening of
the pressure-reducing mechanism (29) is changed by the first
discharge target control section (56a). As a result, the discharge
temperature or the discharge superheat of the compressor (21a, 21b,
21c) can be maintained at an appropriate value, and no compressors
(21a, 21b, 21c) performs a relatively excessive superheat
operation. It is thus possible to perform an appropriate injection
to the compressors (21a, 21b, 21c).
[0088] According to the eleventh aspect of the present invention,
if all of the compressors (21a, 21b, 21c) are not in the relatively
excessive superheat operation, the degree of opening of the
pressure-reducing mechanism (29) is changed by the intermediate
superheat control section (60). As a result, the superheat of the
intermediate-pressure refrigerant of the reduced-pressure side flow
path (28b) of the subcooling heat exchanger (28) can be maintained
at an appropriate value.
[0089] For example, if one of the plurality of compressors (21a,
21b, 21c) is in the relatively excessive superheat operation, the
first discharge target control section (56a) according to the ninth
aspect of the present invention exerts control to prevent the
situation where all of the compressors (21a, 21b, 21c) are in the
relatively excessive superheat operation, and thereafter, the
degree of opening of the pressure-reducing mechanism (29) is
changed by the intermediate superheat control section (60)
according to the tenth aspect of the present invention. As a
result, the superheat of the intermediate-pressure refrigerant can
be maintained at an appropriate value.
[0090] According to the twelfth aspect of the present invention,
if, for example, one of the plurality of compressors (21a, 21b,
21c) is performing a relatively excessive superheat operation and
the excessive superheat operation is changing to a wet operation,
the degree of opening of the pressure-reducing mechanism (29) is
changed by the intermediate superheat control section (60)
regardless of the operating condition of the one of the compressors
(21a, 21b, 21c). As a result, it is possible to start the operation
of the intermediate superheat control section earlier. Thus, the
superheat of the intermediate-pressure refrigerant of the
reduced-pressure side flow path (28b) of the subcooling heat
exchanger (28) can be maintained at an appropriate value
earlier.
[0091] According to the thirteenth aspect of the present invention,
if the refrigerant condition value exceeds the predetermined range
and the compressor (21a, 21b, 21c) is in an abnormal operation, the
pressure-reducing mechanism (29) is controlled by the avoidance
control section (58) until the refrigerant condition value is in
the predetermined range. As a result, it is possible to achieve a
more appropriate injection to the compressors (21a, 21b, 21c),
while preventing the refrigerating apparatus from continuously
operating abnormally.
[0092] According to the fourteenth aspect of the present invention,
if the discharge temperature or the discharge superheat of the
compressor (21a, 21b, 21c) increases too much and the compressor
(21a, 21b, 21c) falls in an abnormal superheat operation, the
degree of opening of the pressure-reducing mechanism (29) is forced
to increase by being adjusted by the first superheat avoidance
control section (78a). As a result, the amount of the
intermediate-pressure refrigerant flowing through the intermediate
ports (5, 6, 7) of the compressors (21a, 21b, 21c) increases,
thereby making it possible to prevent the compressors (21a, 21b,
21c) from continuously performing the abnormal superheat
operation.
[0093] According to the fifteenth aspect of the present invention,
if the discharge temperature or the discharge superheat of the
compressor (21a, 21b, 21c) decreases too much and the compressor
(21a, 21b, 21c) falls in an abnormal wet operation, the degree of
opening of the pressure-reducing mechanism (29) is forced to
decrease by being adjusted by the first wet avoidance control
section (79a). As a result, the amount of the intermediate-pressure
refrigerant flowing through the intermediate ports (5, 6, 7) of the
compressors (21a, 21b, 21c) is reduced, thereby making it possible
to prevent the compressor (21a, 21b, 21c) from continuously
performing the abnormal wet operation.
[0094] According to the sixteenth aspect of the present invention,
the discharge temperatures or the discharge superheats of the
compressors (21a, 21b, 21c) can be approximate to one another by
the second control section (17). As a result, the discharge
temperatures or the discharge superheats of the plurality of
compressors (21a, 21b, 21c) become approximately the same
temperatures. Therefore, operation control over the refrigerating
apparatus becomes easier, compared to the case where the discharge
temperature or the discharge superheat is different between the
compressors (21a, 21b, 21c).
[0095] According to the seventeenth aspect of the present
invention, the third control section (18) can control the pressure
of the injection circuit (40) to always be higher than the
pressures of the first and second low pressure lines (102, 101), or
can control the superheat of the intermediate-pressure refrigerant
of the reduced-pressure side flow path (28b) of the subcooling heat
exchanger (28) to be maintained constant at a target value. A more
appropriate injection to the compressors (21a, 21b, 21c) can be
achieved by exerting these two types of control depending on the
situation.
[0096] According to the eighteenth aspect of the present invention,
if both of the first compressor (21a, 21b) and the second
compressor (21c) are activated together, the degree of opening of
the pressure-reducing mechanism (29) is changed by the intermediate
pressure control section (59), thereby making it possible to always
maintain the pressure (intermediate pressure) of the injection
circuit (40) higher than the pressure (low-level pressure) of the
first and second low pressure lines. Thus, the injection to the
compressors (21a, 21b, 21c) can be performed while avoiding the
backflow of the refrigerant from the second compressor (21c)to the
first compressor (21a, 21b) as described above.
[0097] According to the nineteenth aspect of the present invention,
if one of the first compressor (21a, 21b) and the second compressor
(21c) is activated, no backflow of refrigerant from the second
compressor (21c) to the first compressor (21a, 21b) as described
above occurs. Thus, the degree of opening of the pressure-reducing
mechanism (29) is changed by the intermediate superheat control
section (60), not by the intermediate pressure control section
(59), thereby making it possible to achieve the injection to the
compressors (21a, 21b, 21c) while maintaining the superheat of the
intermediate-pressure refrigerant of the reduced-pressure side flow
path (28b) of the subcooling heat exchanger (28) at an appropriate
value.
[0098] According to the twentieth aspect of the present invention,
the fourth control section (19) can control the discharge
temperature or the discharge superheat of each of the compressors
(21a, 21b, 21c) to be maintained constant at a target value, can
control the degree of opening of the flow rate adjusting mechanism
(30a, 30b, 30c) to be larger than the present degree of opening, or
can control the degree of opening of the flow rate adjusting
mechanism (30a, 30b, 30c) to be smaller than the present degree of
opening. A more appropriate injection to the compressors (21a, 21b,
21c) can be achieved by exerting these three types of control
depending on the situation.
[0099] According to the twenty-first aspect of the present
invention, if the discharge temperature or the discharge superheat
of the compressor (21a, 21b, 21c) increases too much and the
compressor (21a, 21b, 21c) starts to perform an abnormal superheat
operation, the degree of opening of the flow rate adjusting valve
(30a, 30b, 30c) which corresponds to the compressor (21a, 21b, 21c)
performing the abnormal superheat operation is forced to increase
by the second superheat avoidance control section (78b). As a
result, the amount of the intermediate-pressure refrigerant flowing
through the intermediate port (5, 6, 7) of the compressor (21a,
21b, 21c) increases, thereby making it possible to prevent the
abnormal superheat operation.
[0100] According to the twenty-second aspect of the present
invention, if the discharge temperature or the discharge superheat
of the compressor (21a, 21b, 21c) decreases too much and the
compressor (21a, 21b, 21c) starts to perform an abnormal wet
operation, the degree of opening of the flow rate adjusting valve
(30a, 30b, 30c) which corresponds to the compressor (21a, 21b, 21c)
performing the abnormal wet operation is forced to decrease by the
second wet avoidance control section (79b). As a result, the amount
of the intermediate-pressure refrigerant flowing through the
intermediate port (5, 6, 7) of the compressor (21a, 21b, 21c) is
reduced, thereby making it possible to prevent the abnormal wet
operation.
[0101] According to the twenty-third aspect of the present
invention, if the discharge temperature or the discharge superheat
of the compressor (21a, 21b, 21c) is in a predetermined range, the
degree of opening of the flow rate adjusting valve (30a, 30b, 30c)
corresponding to the compressor (21a, 21b, 21c) whose discharge
temperature or the discharge superheat is in the predetermined
range is changed by the second discharge target control section
(56b). As a result, the amount of the intermediate-pressure
refrigerant flowing through the intermediate port (5, 6, 7) of the
compressor (21a, 21b, 21c) becomes an appropriate amount, thereby
making it possible to maintain the discharge temperature or the
discharge superheat of the compressor (21a, 21b, 21c) at an
appropriate value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0102] FIG. 1 is a circuit diagram of a refrigerant circuit of a
refrigerating apparatus according to Embodiment 1.
[0103] FIG. 2 is a circuit diagram of a refrigerant circuit of a
refrigerating apparatus according to Embodiment 2.
[0104] FIG. 3 is a circuit diagram of a refrigerant circuit of a
refrigerating apparatus according to another embodiment.
[0105] FIG. 4 is a circuit diagram of a refrigerant circuit of a
refrigerating apparatus according to a variation of Embodiment
1.
[0106] FIG. 5 is a control flow diagram of a first control
section.
[0107] FIG. 6 is a control flow diagram of a first wet avoidance
control section in an avoidance control section.
[0108] FIG. 7 is a control flow diagram of a first superheat
avoidance control section in the avoidance control section.
[0109] FIG. 8 is a control flow diagram of a second control
section.
[0110] FIG. 9 is a circuit diagram of a refrigerant circuit of a
refrigerating apparatus according to a variation of Embodiment
2.
[0111] FIG. 10 is a control flow diagram of a third control
section.
[0112] FIG. 11 is a control flow diagram of a fourth control
section.
DESCRIPTION OF EMBODIMENTS
[0113] Embodiments of the present invention will be described in
detail hereinafter based on the drawings.
Embodiment 1 of the Invention
[0114] Embodiment 1 of the present invention will be described.
[0115] A refrigerating apparatus (1) of the present embodiment is
for cooling a plurality of cold storage rooms. As shown in FIG. 1,
the refrigerating apparatus (1) includes an external unit (2), a
plurality of internal units (3), and a controller (9). The external
unit (2) is placed outside, and each of the internal units (3) is
placed in each of the cold storage rooms. Further, the external
unit (2) includes an external circuit (20), and each of the
internal units (3) includes an internal circuit (50). A refrigerant
circuit (10) of this refrigerating apparatus (1) is configured such
that the plurality of internal circuits (50) are connected in
parallel to the external circuit (20), for performing a vapor
compression refrigeration cycle.
[0116] Specifically, the external circuit (20) and the internal
circuits (50) are connected to each other by a first communicating
pipe (14) and a second communicating pipe (15). One end of the
first communicating pipe (14) is connected to a first stop valve
(11) provided to one end portion of the external circuit (20), and
the other end of the first communicating pipe (14) is branched and
connected to one end of each of the internal circuits (50).
Further, one end of the second communicating pipe (15) is connected
to a second stop valve (12) provided to the other end portion of
the external circuit (20), and the other end of the second
communicating pipe (15) is branched and connected to the other end
of each of the internal circuits (50).
[0117] <External Unit>
[0118] The external circuit (20) of the external unit (2) includes
first to third, three compressors (21a, 21b, 21c), a four-way
switching valve (24), an external heat exchanger (25), a receiver
(27), a subcooling heat exchanger (28), a subcooling
pressure-reducing valve (a pressure-reducing mechanism) (29), and
an outdoor expansion valve (31).
[0119] All the compressors (21a, 21b, 21c) are hermetically
enclosed, high pressure dome type scroll compressors. Each of the
compressors (21a, 21b, 21c) is provided with a compressor mechanism
having a compression chamber which includes an intermediate port
(5, 6, 7) that is open to the compression chamber in the state of
intermediate pressure, and with an electric motor which drives the
compressor mechanism.
[0120] An inverter capable of freely changing the number of
revolutions of the electric motor of the first compressor (21a)
within a predetermined range is connected to the electric motor of
the first compressor (21a). This inverter adjusts the number of
revolutions of the electric motor, thereby making it possible to
increase and decrease the operation capacity of the first
compressor (21a). Further, no inverter is provided to the electric
motors of the second and third compressors (21b, 21c), and the
number of revolutions of these electric motors is fixed. Thus, the
operation capacity of the second and third compressors (21b, 21c)
is constant.
[0121] Discharge pipes (discharge piping) (22a, 22b, 22c) are
connected to the discharge sides of the compressors (21a, 21b,
21c), respectively. Each of the discharge pipes (22a, 22b, 22c) is
provided with a check valve (CV). The discharge pipes (22a, 22b,
22c) are connected to the first port of the four-way switching
valve (24) via a discharge collection pipe (22). The check valve
(CV) is located in a direction which only allows the refrigerant
flowing from the compressors (21a, 21b, 21c) toward the discharge
collection pipe (22).
[0122] Further, oil separators (38a, 38b, 38c) are provided to the
upstream sides of the check valves (CV) of the discharge pipes
(22a, 22b, 22c), respectively. Each of the oil separators (38a,
38b, 38c) is for separating a refrigerating machine oil from the
high pressure refrigerant in the compressors (21a, 21b, 21c). Oil
discharge pipes (39a, 39b, 39c) to which the refrigerating machine
oil is discharged are connected to the oil separators (38a, 38b,
38c), respectively. These three oil discharge pipes (39a, 39b, 39c)
are combined together at one end of an oil discharge collection
pipe (39d). The other end of the oil discharge collection pipe
(39d) is connected to a portion of a second injection pipe (38)
described later, at which portion a vent pipe (48) is connected to
the second injection pipe (38). Each of the oil discharge pipes
(39a, 39b, 39c) is provided with a check valve (CV) and a capillary
tube (CP) sequentially from the oil separator (38b, 38c).
[0123] These three oil discharge pipes (39a, 39b, 39c) and the oil
discharge collection pipe (39d) form an oil return circuit (39).
Further, the check valves (CV) provided to the oil discharge pipes
(39a, 39b, 39c) are located in a direction which only allows the
refrigeratin.sub.g machine oil flowing toward the oil discharge
collection pipe (39d).
[0124] Suction pipes (23a, 23b, 23c) are connected to the suction
sides of the compressors (21a, 21b, 21c), respectively. These
suction pipes (23a, 23b, 23c) are connected to the second port of
the four-way switching valve (24) via a suction collection pipe
(23).
[0125] One end of the external heat exchanger (25) is connected to
the third port of the four-way switching valve (24), and the second
stop valve (12) is connected to the fourth port of the four-way
switching valve (24). The four-way switching valve (24) is capable
of switching between a first state (the state as shown in solid
line in FIG. 1) in which the first port and the third port
communicate with each other and in which the second port and the
fourth port communicate with each other, and a second state (the
state as shown in broken line in FIG. 1) in which the first port
and the fourth port communicate with each other and in which the
second port and the third port communicate with each other.
[0126] The other end of the external heat exchanger (25) is
connected to the roof of the receiver (27) via a first refrigerant
pipe (32). The external heat exchanger (25) is a cross-fin type,
fin and tube heat exchanger. An outdoor fan (26) is provided near
the external heat exchanger (25). The external heat exchanger (25)
is configured to exchange heat between an outdoor air transferred
by the outdoor fan (26) and the refrigerant flowing in the external
heat exchanger (25). A check valve (CV) is provided to the first
refrigerant pipe (32), and the check valve (CV) is located in a
direction which only allows the refrigerant flowing from the
external heat exchanger (25) to the receiver (27).
[0127] The subcooling heat exchanger (28) includes a high pressure
side flow path (28a) and a reduced-pressure side flow path (28b),
and is configured to exchange heat between the refrigerant flowing
in the high pressure side flow path (28a) and the refrigerant
flowing in the reduced-pressure side flow path (28b).
[0128] The inflow end of the high pressure side flow path (28a) is
connected to the bottom of the receiver (27). The outflow end of
the high pressure side flow path (28a) is connected to the first
stop valve (11) via a second refrigerant pipe (a high pressure
line) (33). The second refrigerant pipe (33) is provided with a
check valve (CV), and the check valve (CV) is located in a
direction which only allows the refrigerant flowing from the
subcooling heat exchanger (28) toward the first stop valve (11). On
the other hand, the inflow end and the outflow end of the
reduced-pressure side flow path (28b) are connected to the
injection circuit (40) according to the present invention.
[0129] The injection circuit (40) is for injecting the refrigerant
to each of the compressors (21a, 21b, 21c), and includes a first
injection pipe (a main pipe) (37), a second injection pipe (38),
and first, second and third branch injection pipes (branch pipes)
(37a, 37b, 37c).
[0130] The first injection pipe (37) is branched from the second
refrigerant pipe (33) at the upstream side of the check valve (CV),
and is connected to the inflow end of the reduced-pressure side
flow path (28b). Further, the first injection pipe (37) is provided
with a subcooling pressure-reducing valve (a pressure-reducing
mechanism) (29). The subcooling pressure-reducing valve (29) is an
electronic expansion valve whose degree of opening is variable.
[0131] The outflow end of the reduced-pressure side flow path (28b)
is connected to one end of the second injection pipe (38). The
other end of the second injection pipe (38) is branched into the
first, second and third branch injection pipes (37a, 37b, 37c). The
first, second and third branch injection pipes (37a, 37b, 37c) are
connected to the intermediate ports (5, 6, 7) of the compressors
(21a, 21b, 21c), respectively.
[0132] First, second and third flow rate adjusting valves (flow
rate adjusting mechanisms) (30a, 30b, 30c) are provided to the
first, second and third branch injection pipes (37a, 37b, 37c),
respectively. The first, second and third flow rate adjusting
valves (30a, 30b, 30c) are electronic expansion valves whose degree
of opening is variable.
[0133] The receiver (27) is positioned at a location between the
external heat exchanger (25) and the subcooling heat exchanger (28)
as described above, and is configured to be capable of temporarily
storing the high pressure refrigerant condensed in the external
heat exchanger (25) when the four-way switching valve (24) is in
the first state. Further, one end of the vent pipe (48) having a
solenoid valve (SV) is connected to the roof of the receiver (27).
The other end of the vent pipe (48) is connected to a portion of
the second injection pipe (38). The vent pipe (48) allows a gas
refrigerant to flow from the receiver (27) to the second injection
pipe (38) by opening the solenoid valve (SV).
[0134] One end of the third refrigerant pipe (35) is connected to a
portion of the second refrigerant pipe (33) between the check valve
(CV) and the first stop valve (11). The other end of the third
refrigerant pipe (35) is connected to the first refrigerant pipe
(32) at the downstream side of the check valve (CV). A check valve
(CV) is provided to the third refrigerant pipe (35), and this check
valve (CV) is located in a direction which only allows the
refrigerant flowing from the first stop valve (11) toward the first
refrigerant pipe (32).
[0135] Further, the first refrigerant pipe (32) and the second
refrigerant pipe (33) are connected to each other by a fourth
refrigerant pipe (36) which bypasses the receiver (27) and the
subcooling heat exchanger (28). One end of the fourth refrigerant
pipe (36) is connected to the first refrigerant pipe (32) at the
upstream side of the check valve (CV). The other end of the fourth
refrigerant pipe (36) is connected to a portion of the second
refrigerant pipe (33) that is on the upstream side of the
connecting portion at which the first injection pipe (37) is
connected to the second refrigerant pipe (33). The outdoor
expansion valve (31) is provided to the fourth refrigerant pipe
(36). The outdoor expansion valve (31) is an electronic expansion
valve whose degree of opening is adjustable.
[0136] The external circuit (20) includes a various kinds of
sensors and pressure switches. Specifically, each of the discharge
pipes (22a, 22b, 22c) is provided with a discharge pipe temperature
sensor (a discharge refrigerant temperature detection mechanism)
(61) and a high-level pressure switch (62). The discharge pipe
temperature sensor (61) is for detecting the temperature of each of
the discharge pipes (22a, 22b, 22c). The high-level pressure switch
(62) is for detecting the discharge pressure, and in the case of
abnormally high pressure, for immediately stopping the
refrigerating apparatus (1). The suction collection pipe (23) is
provided with a suction pipe temperature sensor (63) for detecting
the temperature of the suction collection pipe (23).
[0137] A discharge pressure sensor (64) for detecting the discharge
pressure of the compressors (21a, 21b, 21c) is provided at a
location where the discharge pipes (22a, 22b, 22c) are collected
together (i.e., the inflow end of the discharge collection pipe
(22)). A suction pressure sensor (65) for detecting the suction
pressure of the compressors (21a, 21b, 21c) is provided at a
location where the suction pipes (23a, 23b, 23c) are collected
together. An outdoor air temperature sensor (67) for detecting an
outdoor air temperature is provided near the outdoor fan (26).
[0138] Further, a first liquid temperature sensor (68) is provided
to the second refrigerant pipe (33). A second liquid temperature
sensor (69) is provided to the first injection pipe (37) at the
downstream side of the subcooling pressure-reducing valve (29).
Each of the liquid temperature sensors (68, 69) is for detecting
the temperature of the liquid refrigerant.
[0139] <Internal Unit>
[0140] The above two internal units (3) have the same
configuration. Each internal unit (3) includes an internal circuit
(50). The internal circuit (50) sequentially includes, from its one
end to the other end, a pipe for heating (51), an internal
expansion valve (52), and an internal heat exchanger (53).
[0141] The pipe for heating (51) is attached to a drain pan (55)
located under the internal heat exchanger (53). The drain pan (55)
is for collecting condensed water dropping from the internal heat
exchanger (53). The pipe for heating (51) is attached to the drain
pan (55)to melt ice blocks made of frozen condensed water, by
utilizing heat of the high pressure refrigerant flowing in the pipe
for heating (51).
[0142] The internal expansion valve (52) is an electronic expansion
valve whose degree of opening is adjustable.
[0143] The internal heat exchanger (53) is a cross-fm type, fin and
tube heat exchanger. An internal fan (54) is located near the
internal heat exchanger (53). Further, the internal heat exchanger
(53) is configured such that a refrigerant exchanges heat between
the air in the storage room transferred by the internal fan (54)
and the refrigerant flowing in the internal heat exchanger
(53).
[0144] Further, the internal circuit (50) is provided with three
temperature sensors. Specifically, an evaporation temperature
sensor (72) for detecting the evaporation temperature of the
refrigerant is provided to the heat exchanger pipe of the internal
heat exchanger (53). A refrigerant temperature sensor (73) for
detecting the temperature of the gas refrigerant is provided near
the gas-side end of the internal circuit (50). An internal
temperature sensor (74) for detecting the temperature in the
storage room is provided near the internal fan (54).
[0145] <Controller>
[0146] Values detected by the sensors (61-69, 71-74) and the
high-level pressure switch (62) are input to the controller
(control mechanism) (9). Based on these detected values, the
controller (9) controls the driving of the compressors (21a, 21b,
21c) and the fans (26, 54), switches between the various types of
valves (24, 29, 31, 52, SV), adjusts the degree of opening of the
valves, and adjusts the operating frequency of the inverter,
thereby controlling the operation of the refrigerating apparatus
(1).
[0147] For example, the controller (9) adjusts the degree of
opening of the first, second and third flow rate adjusting valves
(30a, 30b, 30c) based on the respective discharge pipe temperature
sensors (61). Specifically, the degree of opening of each of the
flow rate adjusting valves (30a, 30b, 30c) is adjusted so that the
temperature detected by the discharge pipe temperature sensor (61)
falls within a predetermined temperature range. If a refrigerant
discharged from any of the compressors (21a, 21b, 21c) has a
temperature higher than the predetermined temperature range, the
degree of opening of the flow rate adjusting valve (30a, 30b, 30c)
which corresponds to that compressor (21a, 21b, 21c) is increased,
thereby increasing the injection amount of the compressor (21a,
21b, 21c). As a result, it is possible to reduce the temperature of
the discharge refrigerant to a temperature within the predetermined
temperature range.
[0148] Further, if a refrigerant discharged from any of the
compressors (21a, 2 lb, 21c) has a temperature lower than the
predetermined temperature range, the degree of opening of the flow
rate adjusting valve (30a, 30b, 30c) which corresponds to that
compressor (21a, 21b, 21c) is reduced, thereby reducing the
injection amount of the compressor (21a, 21b, 21c). As a result, it
is possible to increase the temperature of the discharge
refrigerant to a temperature within the predetermined temperature
range.
[0149] Here, the first compressor is configured such that its
operating frequency can be changed by an inverter. Thus, the
temperature of the discharge refrigerant tends to be lower than the
predetermined temperature range. This is because, as described
above, if the operating frequency of the first compressor (21a) is
reduced, the time in which the intermediate port (5) is open is
extended, and therefore, the intermediate-pressure refrigerant of
the injection circuit (40) is suctioned more into the first
compressor (21a) by the amount corresponding to the extended
time.
[0150] Thus, in the case where the operation capacity of the first
compressor (21a) is reduced, the temperature of the discharge
refrigerant is reduced, and according to this change in
temperature, the degree of opening of the first flow rate adjusting
valve (30a) is reduced. In this way, the refrigerant is prevented
from being injected into the first compressor (21a) in a large
amount.
[0151] --Operational Behavior--
[0152] An operational behavior of the refrigerating apparatus (1)
will be described below. The refrigerating apparatus (1) is
configured to exert control by selecting a cooling operation for
maintaining the interior of the cold storage room at a
predetermined temperature (e.g., 5.degree. C.).
[0153] In this cooling operation, each of the internal units (3)
cools the interior of the storage room by driving at least one of
the three compressors (21a, 21b, 21c). Here, the situation in which
all of the three compressors (21a, 21b, 21c) are driven will be
described. Further, in this cooling operation, the four-way
switching valve (24) is set in the first state. The degree of
opening of the subcooling pressure-reducing valve (29) and the
degree of opening of the internal expansion valve (52) are
appropriately adjusted, and the outdoor expansion valve (31) is
fully closed. Each of the solenoid valves (SV) is opened or closed
according to the operating condition.
[0154] In the cooling operation, the refrigerant flows in the
refrigerant circuit (10) in a direction of arrow shown in solid
line in FIG. 1 when the first, second, and third compressors (21a,
21b, 21c) are driven. Here, the external heat exchanger (25) serves
as a condenser, and each of the internal heat exchangers (53)
serves as an evaporator, thereby performing a vapor compression
refrigeration cycle in the refrigerant circuit (10).
[0155] Specifically, the high-pressure gas refrigerant compressed
in the first, second, and third compressors (21a, 21b, 21c) is
discharged through the discharge pipes (22a, 22b, 22c). The
high-pressure gas refrigerant discharged through the discharge
pipes (22a, 22b, 22c) flows into the respective oil separators
(38a, 38b, 38c). The oil separators (38a, 38b, 38c) separate a
refrigerating machine oil from the high pressure refrigerant. The
separated refrigerating machine oil is temporarily stored in the
respective oil separators (38a, 38b, 386), and then flows into the
second injection pipe (38) through the oil discharge pipes (39a,
39b, 39c) and the oil discharge collection pipe (39d). The flow of
the refrigerating machine oil having flowed into the second
injection pipe (38) is divided to pass through the branch injection
pipes (37a, 37b, 37c), and is then suctioned into the compressors
(21a, 21b, 21c) through the intermediate ports (5, 6, 7).
[0156] On the other hand, the high pressure refrigerant from which
the refrigerating machine oil has been separated flows out the oil
separators (38a, 38b, 38c), and is collected together in the
discharge collection pipe (22). The high pressure refrigerant
collected together in the discharge collection pipe (22) flows into
the external heat exchanger (25) through the four-way switching
valve (24). In the external heat exchanger (25), the high pressure
refrigerant exchanges heat with the outdoor air, and is condensed.
The condensed refrigerant sequentially passes through the first
refrigerant pipe (32), the receiver (27), and the high pressure
side flow path (28a) of the subcooling heat exchanger (28), and
then flows into the second refrigerant pipe (33). Part of the
refrigerant having flowed into the second refrigerant pipe (33)
flows into the first injection pipe (37), and the rest of the
refrigerant flows into the first communicating pipe (14) through
the first stop valve (11).
[0157] The high pressure refrigerant having flowed into the first
injection pipe (37) is decompressed to a predetermined pressure by
the subcooling pressure-reducing valve (29) until the refrigerant
becomes an intermediate-pressure refrigerant, and thereafter, the
intermediate-pressure refrigerant flows into the reduced-pressure
side flow path (28b) of the subcooling heat exchanger (28). In the
subcooling heat exchanger (28), the intermediate-pressure
refrigerant and the high pressure refrigerant flowing in the high
pressure side flow path (28a) exchange heat with each other. As a
result, the high pressure refrigerant is cooled, and the degree of
subcooling increases, whereas the intermediate-pressure refrigerant
is heated to become a gas refrigerant. After flowing out the
subcooling heat exchanger (28), the flow of the gas refrigerant is
divided into the first, second and third branch injection pipes
(37a, 37b, 37c) through the second injection pipe (38).
[0158] A flow rate of the intermediate-pressure refrigerant having
flowed into the branch injection pipes (37a, 37b, 37c) is adjusted
by the flow rate adjusting valves (30a, 30b, 30c), respectively,
and then, the refrigerant is injected into the compression chamber
in the state of intermediate pressure in each of the compressors
(21a, 21b, 21c). Here, the controller (9) adjusts the degree of
opening of each of the flow rate adjusting valves (30a, 30b, 30c)
so that the temperature detected by the discharge pipe temperature
sensor (61) is in the predetermined temperature range.
[0159] On the other hand, the flow of the high pressure refrigerant
having flowed into the first communicating pipe (14) is divided
into the internal circuits (50). The high pressure refrigerant
having flowed into the internal circuits (50) flows through the
pipe for heating (51). Here, at the drain pan (55), the ice blocks
made of frozen condensed water is melted by the refrigerant flowing
in the pipe for heating (51). Thus, the high pressure refrigerant
flowing in the pipe for heating (51) is further subcooled. The high
pressure refrigerant having flowed out the pipe for heating (51) is
decompressed by the internal expansion valve (52) to become a low
pressure refrigerant, and thereafter flows into the internal heat
exchanger (53).
[0160] In the internal heat exchanger (53), the low pressure
refrigerant exchanges heat with the air in the storage room, and
evaporates. The air in the storage room is cooled as a result. The
refrigerant evaporated in the internal heat exchanger (53) flows
into the external circuit (20) again through the second
communicating pipe (15). The low pressure refrigerant having flowed
into the external circuit (20) flows into the suction collection
pipe (23) through the four-way switching valve (24), and suctioned
into the compressors (21a, 21b, 21c) from the suction pipes (23a,
23b, 23c), respectively. The low pressure refrigerant suctioned
into the compressors (21a, 21b, 21c) is compressed to a
predetermined pressure, together with the intermediate-pressure
refrigerant having flowed from the intermediate ports (5, 6, 7),
until the refrigerant becomes a high pressure refrigerant. The high
pressure refrigerant is discharged again from the compressors (21a,
21b, 21c). The refrigerant circulates as described above, thereby
performing a cooling operation for maintaining the interior of the
cold storage room at a predetermined temperature.
[0161] Further, if the four-way switching valve (24) is switched
from the first state to the second state, the refrigerant
circulates in an opposite direction. As a result, the external heat
exchanger (25) serves as an evaporator, and the internal heat
exchanger (53) severs as a condenser, which means that a reverse
cycle defrost operation can also be performed.
[0162] --Effects of Embodiment 1--
[0163] According to the present Embodiment 1, the flow rate of the
refrigerant flowing in each of the branch injection pipes (37a,
37b, 37c) after being decompressed by the subcooling
pressure-reducing valve (29) can be adjusted for each of the
compressors (21a, 21b, 21c) by the flow rate adjusting valves (30a,
30b, 30c). Thus, an appropriate injection to the compressors (21a,
21b, 21c) can be performed.
[0164] Further, according to the present Embodiment 1, the control
mechanism (9) adjusts the injection amount of each of the plurality
of compressors (21a, 21b, 21c) according to the temperature of the
refrigerant discharged from the compressors (21a, 21b, 21c),
thereby making it possible to control the temperature of the
refrigerant discharged from the compressors (21a, 21b, 21c) within
a predetermined temperature range. As a result, an appropriate
injection to the compressors (21a, 21b, 21c) can be performed with
reliability.
[0165] Further, according to the present Embodiment 1, owing to the
provision of the subcooling heat exchanger (28), the refrigerant
decompressed by the subcooling pressure-reducing valve (29) can be
injected into the compression chambers (4a, 4b, 4c), after being
heat exchanged with the high pressure refrigerant flowing in the
refrigerant circuit (10). Thus, the refrigerant can be injected
into the plurality of compressors (21a, 21b, 21c), while improving
the COP of the refrigerating apparatus (1) more than in the case
where the subcooling heat exchanger (28) is not provided.
--Variation of Embodiment 1--
[0166] FIG. 4 shows a refrigerant circuit according to a variation
of Embodiment 1. The configuration of the controller which controls
the operation of the refrigerating apparatus (1) differs between
Embodiment 1 and the variation. Further, the second injection pipe
(38) of Variation 1 is provided with an intermediate refrigerant
temperature sensor (70) for measuring a temperature of the
intermediate-pressure refrigerant having passed through the
reduced-pressure side flow path (28b) of the subcooling heat
exchanger (28), and with an intermediate-pressure pressure sensor
(71) for measuring a pressure of the intermediate-pressure
refrigerant.
[0167] The controller (4) according to this variation of Embodiment
1 includes a first control section (16), an avoidance control
section (58), and a second control section (17). The degree of
opening of the subcooling pressure-reducing valve (29) is adjusted
by the first control section (16) and the avoidance control section
(58). The degree of opening of the flow rate adjusting mechanism
(30a, 30b, 30c) is adjusted by the second control section (17).
[0168] Further, a discharge pipe temperature sensor (61) and a
discharge pressure sensor (64) as the discharge condition detection
mechanisms, and an intermediate refrigerant temperature sensor (70)
and an intermediate-pressure pressure sensor (71) as the
intermediate superheat detection mechanisms, are electrically
connected to the controller (4). Also, the controller (4) includes
a discharge condition setting section (a discharge condition
setting mechanism) (76) and an intermediate superheat setting
section (an intermediate superheat setting mechanism) (77). The
discharge condition setting section (76) is for setting a target
value Tm for the discharge temperatures of the compressors (21a,
21b, 21c). The intermediate superheat setting section (77) is for
setting a target value Tgshm for the degree of superheat of the
intermediate-pressure refrigerant flowing in the injection circuit
(40).
[0169] Next, a control operation of the first control section (16),
the avoidance control section (58), and the second control section
(17) will be described with reference to FIG. 5 to FIG. 8 showing
the control flow diagram.
[0170] <First Control Section>
[0171] The first control section (16) includes a first discharge
target control section (56a) and intermediate superheat control
section (60). The first control section (16) is for exerting
control by selecting the first discharge target control section
(56a) or the intermediate superheat control section (60), based on
the discharge temperatures of the compressors (21a, 21b, 21c) and
the degree of superheat of the intermediate-pressure refrigerant in
the injection circuit (40).
[0172] Specifically, first, in step ST1, a maximum value among the
values Td1-Td3 detected by the discharge pipe temperature sensors
(61) is determined, i.e., the determined value is set as a maximum
value Ttd of the discharge pipe temperature sensors (61) as shown
in FIG. 5.
[0173] Then, in step ST2, whether or not any one of the first,
second, and third conditions is met is determined. Here, the first
condition is that the maximum value Ttd set in step ST1 is equal to
or smaller than the target value Tm set by the discharge condition
setting section (76) of the controller (4). The second condition is
that the maximum value Ttd in step ST1 is larger than the target
value Tm, and that the maximum value Ttd continues to decrease
during a time t1.
[0174] The third condition is the situation in which the maximum
value Ttd in step ST1 is larger than a value obtained by adding a
predetermined value Tdx to the target value Tm of the discharge
condition setting section (76), and in which the maximum value Ttd
is smaller than an upper threshold value Tdmax that is set larger
than the target value Tm, wherein the state in which a value Tgsh
detected by the intermediate superheat detection section (75) is
smaller than a predetermined intermediate superheat value Tgshs
continues for a time t2 or longer. The upper threshold value Tdmax
is set to such a value that causes the compressors (21a, 21b, 21c)
to perform an abnormal superheat operation when the maximum value
Ttd in step ST1 exceeds the threshold value Tdmax.
[0175] If any one of the first, second, and third conditions is met
in step ST2, the process moves to step ST3. In step ST3, an amount
dpls of change in a value of degree of opening of the subcooling
pressure-reducing valve (29) is determined based on a difference
between the value Tgsh of the intermediate refrigerant superheat
that is detected based on the intermediate refrigerant temperature
sensor (70) and the intermediate-pressure pressure sensor (71), and
the target value Tgshm of the intermediate superheat setting
section (77). The smaller the difference is, the smaller the amount
dpls of change becomes. Next, in step ST5, a value obtained by
adding the amount dpls of change determined in step ST3 to a value
EV2pls of degree of opening of the present subcooling
pressure-reducing valve (29) is set as a new value EV2pls of degree
of opening. The degree of opening of the subcooling
pressure-reducing valve (29) is changed to this new value EV2pls of
degree of opening.
[0176] The processes in step ST3 and step ST5 correspond to the
control operation of the intermediate superheat control section
(60). Due to this operation, the superheat of the
intermediate-pressure refrigerant having flowed out the subcooling
heat exchanger (28) can be maintained constant at the target value
of the intermediate superheat setting section (77).
[0177] On the other hand, if all of the first, second, and third
conditions are not met in step ST2, the process moves to step ST4.
In step ST4, an amount dpls of change in a value of degree of
opening of the subcooling pressure-reducing valve (29) is
determined based on a difference between the maximum value Ttd in
step ST1 and the target value Tm of the discharge condition setting
section (76). The smaller the difference is, the smaller the amount
dpls of change becomes. Next, in step ST5, a value obtained by
adding the amount dpls of change determined in step ST4 to the
value EV2pls of degree of opening of the present subcooling
pressure-reducing valve (29) is set as a new value EV2pls of degree
of opening. The degree of opening of the subcooling
pressure-reducing valve (29) is changed to this new value EV2pls of
degree of opening.
[0178] The processes in step ST4 and step ST5 correspond to the
control operation of the first discharge target control section
(56a). Due to this operation, the discharge temperatures of the
compressors (21a, 21b, 21c) can be maintained constant at the
target value of the discharge condition setting section (76).
[0179] As described above, in the case where the operations of the
compressors (21a, 21b, 21c) tend to be a superheating operation,
the discharge temperature control is performed by the first
discharge target control section (56a). In the case where the
operations of the compressors (21a, 21b, 21c) do not tend to be a
superheating operation, an intermediate superheat control is
performed by the inteimediate superheat control section (60).
[0180] After the completion of step ST5, the process returns to
step ST1, in which the maximum value Ttd determined by the
discharge pipe temperature sensor (61) is determined again. These
processes in steps ST1 to ST5 are repeated. Since two types of
control are implemented depending on the situation, a more
appropriate injection to the compressors (21a, 21b, 21c) can be
performed, compared to the case where the discharge temperature
control is implemented all the time as in Embodiment 1.
[0181] <Avoidance Control Section>
[0182] The avoidance control section (58) includes a first
superheat avoidance control section (78a) and a first wet avoidance
control section (79a). The avoidance control section (58) is for
preventing the compressors (21a, 21b, 21c) from continuously
performing an abnormal operation, such as an abnormal superheat
operation or an abnormal wet operation, which is caused, for
example, by change in load of the refrigerating apparatus (1), when
compressors (21a, 21b, 21c) start to perform such an abnormal
operation. Further, the first superheat avoidance control section
(78a) performs a control operation for avoiding an abnormal
superheat operation of the compressors (21a, 21b, 21c). The first
wet avoidance control section (79a) performs a control operation
for avoiding an abnormal wet operation of the compressors (21a,
21b, 21c).
[0183] The control operation of the first wet avoidance control
section (79a) will be described first, and then, the control
operation of the first superheat avoidance control section (78a)
will be described.
[0184] First, as shown in FIG. 6, the first wet avoidance control
section (79a) determines whether or not fourth and fifth conditions
are met in step ST6. Here, the fourth condition is the following
situation which continues for a time t3 or longer and in which a
value Tgsh detected by the intermediate refrigerant temperature
sensor (70) and the intermediate-pressure pressure sensor (71) as
an intermediate refrigerant superheat is even smaller than a lower
threshold value Tgshmin set smaller than the intermediate superheat
target value Tgshm of the intermediate superheat setting section
(77). The lower threshold value Tgshmin is set to such a value that
causes the compressors (21a, 21b, 21c) to perform an abnormal wet
operation when the detected value Tgsh as the intermediate
refrigerant superheat becomes lower than the threshold value
Tgshmin.
[0185] The fifth condition is that at least one of values
Tdsh1-Tdsh3 detected by the discharge pipe temperature sensor (61)
and the discharge pressure sensor (64) as a discharge superheat is
even smaller than a lower threshold value Tdshmin set smaller than
a discharge superheat target value Tdshm of the discharge condition
setting section (76). Whether or not the compressors (21a, 21b,
21c) are performing an abnormal wet operation is determined based
on the fourth and fifth conditions.
[0186] The determination process in step ST6 is repeated until both
of the fourth and fifth conditions are met. When both of the fourth
and fifth conditions are met, the compressors are considered as
performing an abnormal wet operation, and the process moves to step
ST7.
[0187] In step ST7, an amount dpls of change in a value of degree
of opening of the subcooling pressure-reducing valve (29) is
determined based on a value EV2pls of degree of opening of the
present subcooling pressure-reducing valve (29). Here, if the
present value EV2pls of degree of opening is large, the amount dpls
of change is also large. If the present value EV2pls of degree of
opening is small, the amount dpls of change is also small.
[0188] Next, in step ST8, a value obtained by subtracting the
amount dpls of change determined in step ST7 from the value EV2pls
of degree of opening of the present subcooling pressure-reducing
valve (29), is set as a new value EV2pls of degree of opening. As a
result, the degree of opening of the subcooling pressure-reducing
valve (29) decreases.
[0189] After the completion of step ST8, the process returns to
step ST6, and whether both of the fourth and fifth conditions are
met is determined again in step ST6. The processes in steps ST6 to
ST8 are repeated.
[0190] As described above, the degree of opening of the subcooling
pressure-reducing valve (29) is decreased, if the compressors (21a,
21b, 21c) start to perform an abnormal wet operation when the
discharge temperature or the discharge superheat of each of the
compressors (21a, 21b, 21c) decreases too much due to such as
change in load of the refrigerating apparatus (1). As a result, the
amount of the intermediate-pressure refrigerant flowing into the
compressors (21a, 21b, 21c) through the intermediate ports (5, 6,
7) of the compressors (21a, 21b, 21c) is reduced, and it is
possible to prevent the compressors from continuously performing
the abnormal wet operation.
[0191] In step ST9, the first superheat avoidance control section
(78a) first determines a maximum value among the values Td1-Td3
detected by the discharge pipe temperature sensors (61), i.e., the
determined value is set as a maximum value Ttd of the discharge
pipe temperature sensors (61) as shown in FIG. 7.
[0192] Next, in step ST10, whether or not at least one of the sixth
and seventh conditions is met is determined. Here, the sixth
condition is that at least one of predicted discharge temperatures
of all the compressors (21a, 21b, 21c) is larger than an upper
threshold value Tpmax of the predicted discharge temperature. The
upper threshold value Tpmax is set to such a value that causes the
compressors (21a, 21b, 21c) to perform an abnormal superheat
operation when the predicted discharge temperature Tp exceeds the
threshold value Tpmax.
[0193] Here, the predicted discharge temperatures of the
compressors (21a, 21b, 21c) are determined by a
predicted-discharge-temperature calculation section (80) provided
in the controller (4). This predicted-discharge-temperature
calculation section (80) is configured to calculate the predicted
discharge temperatures of the compressors (21a, 21b, 21c), based on
the discharge pressure, the suction pressure, and the suction
temperature of the compressors (21a, 21b, 21c), assuming that the
compression operation of the compressors (21a, 21b, 21c) is a
polytropic compression operation.
[0194] Further, the seventh condition is that the maximum value Ttd
set in step ST7 is even larger than an upper threshold value Tdmax
set larger than the target value Tm of the discharge condition
setting section (76). The upper threshold value Tdmax is set to
such a value that causes the compressors (21a, 21b, 21c) to perform
an abnormal superheat operation when the maximum value Ttd in step
ST7 exceeds the threshold value Tdmax. Whether or not the
compressors (21a, 21b, 21c) are performing an abnormal superheat
operation is determined based on the sixth and seventh
conditions.
[0195] The processes in step ST9 and step ST10 are repeated until
at least one of the sixth and seventh conditions is met. When at
least one of the sixth and seventh conditions is met, the
compressors (21a, 21b, 21c) are considered as performing an
abnormal superheat operation, and the process moves to step
ST11.
[0196] In step ST11, a first amount dplsl of change in a value of
degree of opening of the subcooling pressure-reducing valve (29) is
determined based on a difference between the maximum value Ttd in
step ST9 and the upper threshold value Tdmax. The smaller the
difference is, the smaller the amount dpls1 of change becomes.
Next, in step ST12, a second amount dpls2 of change in a value of
degree of opening of the subcooling pressure-reducing valve (29) is
determined based on a difference between a value Tp determined by
the predicted-discharge-temperature calculation section (80) and
the upper threshold value Tpmax. The smaller the difference is, the
smaller the amount dpls2 of change becomes. Here, if all of the
compressors (21a, 21b, 21c) are actuated, the second amount dpls2
of change of the subcooling pressure-reducing valve (29) is
determined based on a difference between a maximum value of the
values Tp for the compressors (21a, 21b, 21c) which are determined
by the predicted-discharge-temperature calculation section (80) and
the upper threshold value Tpmax. The smaller the difference is, the
smaller the amount dpls2 of change becomes.
[0197] Next, in step ST13, a maximum value among the first amount
dpls1 of change determined in step ST11 and the second amount dpls2
of change determined in step ST12 is set as an amount dpls of
change in a value of degree of opening of the subcooling
pressure-reducing valve (29). Here, even if the amount dpls of
change is larger than 15, the amount is limited to 15. The minimum
value of degree of opening of the subcooling pressure-reducing
valve (29) is zero (a fully closed state), and the maximum value
thereof is 480 (a fully opened state).
[0198] Next, in step ST14, a value obtained by adding the amount
dpls of change set in step ST13 to the value EV2pls of degree of
opening of the present subcooling pressure-reducing valve (29) is
set as a new value EV2pls of degree of opening. The degree of
opening of the subcooling pressure-reducing valve (29) is changed
to this new value EV2pls of degree of opening.
[0199] After the completion of step ST14, the process returns to
step ST9. In step ST9, the maximum value Ttd of each of the
discharge pipe temperature sensors (61) is determined again. The
processes in steps ST9 to ST14 are repeated.
[0200] As described above, the degree of opening of the subcooling
pressure-reducing valve (29) is increased, if the compressors (21a,
21b, 21c) start to perform an abnormal superheat operation when the
discharge temperature or the discharge superheat of each of the
compressors (21a, 21b, 21c) increases too much due to such as
change in load of the refrigerating apparatus (1). As a result, the
amount of the intermediate-pressure refrigerant flowing into the
compressors (21a, 21b, 21c) through the intermediate ports (5, 6,
7) of the compressors (21a, 21b, 21c) is increased, and it is
possible to prevent the compressors from continuously performing
the abnormal superheat operation.
[0201] <Second Control Section>
[0202] The second control section (17) is for making the discharge
temperatures of the compressors (21a, 21b, 21c) approximate to each
other. In the present variation, the first compressor (21a) is a
variable displacement compressor, and the second and third
compressors (21b, 21c) are fixed displacement compressors. Thus,
the discharge temperatures of the second and third compressors
(21b, 21c) may be considered approximately equal to each other.
Therefore, in the second control section (17), the discharge
temperature of the first compressor (21a) is controlled so as to be
approximate to the discharge temperatures of the second and third
compressors (21b, 21c), by adjusting the degree of opening of the
first flow rate adjusting valve (30a) which corresponds to the
first compressor (21a).
[0203] Specifically, first, in step ST15, the determination process
in step ST15 is repeated until an absolute value of the difference
between the value Tdl detected by the discharge pipe temperature
sensor (61) of the first compressor (21a) and the maximum value
among the values Td2, Td3 detected by the discharge pipe
temperature sensors (61) of the second and third compressors (21b,
21c) becomes equal to or larger than a predetermined value T1, as
shown in FIG. 8. When the absolute value becomes the predetermined
value T1 or larger than the predetermined value T1, the process
moves to step ST16 as it is considered that the difference between
the discharge temperature of the first compressor (21a) and the
discharge temperatures of the second and third compressors (21b,
21c) is large.
[0204] In step ST16, an amount dpls of change in a value of degree
of opening of the first flow rate adjusting valve (30a) is
determined based on a difference between the value Td1 detected by
the discharge pipe temperature sensor (61) of the first compressor
(21a) and the maximum value among the values Td2, Td3 detected by
the discharge pipe temperature sensors (61) of the second and third
compressors (21b, 21c). The smaller the difference is, the smaller
the amount dpls of change becomes.
[0205] Next, in step ST17, whether or not the degree of opening of
the present first flow rate adjusting valve (30a) is larger than a
predetermined value b of degree of opening is determined. If the
value of degree of opening of the first flow rate adjusting valve
(30a) is larger than the predetermined value b of degree of
opening, the process moves to step ST18. Otherwise, the process
moves to step ST19.
[0206] In step ST18, if the amount dpls of change determined in
step ST16 is smaller than -0.08 times the predetermined value b of
degree of opening, the amount dpls of change is corrected to the
-0.08 times the predetermined value b of degree of opening. If the
amount dpls of change determined in step ST16 is larger than 0.08
times the predetermined value b of degree of opening, the amount
dpls of change is corrected to 0.08 times the predetermined value b
of degree of opening. That is, if the degree of opening of the
first flow rate adjusting valve (30a) is large, the degree of
opening of the first flow rate adjusting valve (30a) is changed in
a relatively great amount. Here, the figure 0.08 is an example
figure, and the figure can be set to any figure as long as the
figure regulates the value of degree of opening of the first flow
rate adjusting valve (30a).
[0207] In step ST19, if the amount dpls of change determined in
step ST16 is smaller than -0.04 times the predetermined value b of
degree of opening, the amount dpls of change is corrected to -0.04
times the predetermined value b of degree of opening. If the amount
dpls of change determined in step ST16 is larger than 0.04 times
the predetermined value b of degree of opening, the amount dpls of
change is corrected to 0.04 times the predetermined value b of
degree of opening. That is, if the degree of opening of the first
flow rate adjusting valve (30a) is small, the degree of opening of
the first flow rate adjusting valve (30a) is changed in a
relatively small amount. Here, the figure 0.04 is an example
figure, and the figure can be set to any figure as long as the
figure regulates the value of degree of opening of the first flow
rate adjusting valve (30a).
[0208] Next, in step ST20, a value obtained by adding the amount
dpls of change corrected as necessary in step ST18 or step ST19 to
the value EV3pls of degree of opening of the present first flow
rate adjusting valve (30a), is set as a new value EV3pls of degree
of opening. The degree of opening of the first flow rate adjusting
valve (30a) is changed to this new value EV3pls of degree of
opening.
[0209] After the completion of step ST20, the process returns to
step ST15. In step ST15, it is determined again whether or not the
absolute value of the difference between the value Td1 detected by
the discharge pipe temperature sensor (61) of the first compressor
(21a) and the maximum value among the values Td2, Td3 detected by
the discharge pipe temperature sensors (61) of the second and third
compressors (21b, 21c) is equal to or larger than the predetermined
value T1. The first flow rate adjusting valve (30a) is adjusted by
repeating the processes in steps ST15 to ST20, thereby
approximating the discharge temperature of the first compressor
(21a) to the discharge temperatures of the second and third
compressors (21b, 21c).
[0210] Accordingly, owing to the controller (4), it is possible to
perform an appropriate injection to each of the compressors (21a,
21b, 21c), and also possible to make the discharge temperatures of
the compressors (21a, 21b, 21c) uniform.
Embodiment 2
[0211] A refrigerating apparatus (91) of Embodiment 2 is placed for
such as convenience stores, and provides cooling for a refrigerator
and a freezer, and simultaneously provides indoor air
conditioning.
[0212] As shown in FIG. 2, the refrigerating apparatus (91)
includes an external unit (92), an air-conditioning unit (93), a
cooling unit (94), a refrigeration unit (95), and a controller
(9).
[0213] The external unit (92) is provided with an external circuit
(96). The air-conditioning unit (93) is provided with an
air-conditioning circuit (97). The cooling unit (94) is provided
with a cooling circuit (98). The refrigeration unit (95) is
provided with a refrigeration circuit (99). According to the
present embodiment, the air-conditioning circuit (97) forms a first
utilization system, and the cooling circuit (98) and the
refrigeration circuit (99) form a second utilization system.
[0214] In this refrigerating apparatus (91), a plurality of
utilization-side circuits (97, 98, 99) are connected in parallel to
the external circuit (96), thereby forming a refrigerant circuit
which performs a vapor compression refrigeration cycle. The
external circuit (96) is connected to the utilization-side circuits
(97, 98, 99) by a fluid-side communicating pipe (100), a first
gas-side communicating pipe (101), and a second gas-side
communicating pipe (102). One end of the fluid-side communicating
pipe (100) is connected to a fluid-side stop valve (103) of the
external circuit (96). The other end of the fluid-side
communicating pipe (100) is branched into three paths to be
connected to the air-conditioning circuit (97), the cooling circuit
(98), and the refrigeration circuit (99). One end of the first
gas-side communicating pipe (101) is connected to a first gas-side
stop valve (105) of the external circuit (96), and the other end of
the first gas-side communicating pipe (101) is connected to the
air-conditioning circuit (97). One end of the second gas-side
communicating pipe (102) is connected to a second gas-side stop
valve (104) of the external circuit (96). The other end of the
second gas-side communicating pipe (102) is branched into two paths
to be connected to the cooling circuit (98) and the refrigeration
circuit (99).
[0215] Each of the units will be described in detail hereinafter.
The same reference characters are given to the same portions as
those in Embodiment 1, and explanation of the portions is
simplified. The explanations of the air-conditioning unit (93) and
the cooling unit (94) are omitted since the configurations thereof
are similar to the configuration of the internal unit (3) in
Embodiment 1.
[0216] <External Unit>
[0217] The external circuit (96) of the external unit (2) includes
first to third, three compressors (21a, 21b, 21c), a first four-way
switching valve (24), an external heat exchanger (25), a receiver
(27), a subcooling heat exchanger (28), a subcooling
pressure-reducing valve (a pressure-reducing mechanism) (29), and
an outdoor expansion valve (31). Further, in Embodiment 2, second
and third four-way switching valves (42, 43) are provided.
[0218] The first to third, three compressors (21a, 21b, 21c)
include a compressor for the first utilization system and a
compressor for the second utilization system. Specifically, the
first compressor (21a) is used, in principle, exclusively for the
second utilization system for cooling and refrigeration, and the
third compressor (21c) is used, in principle, exclusively for the
first utilization system for air conditioning. On the other hand,
the second compressor (21b) is switched between use for the first
utilization system and use for the second utilization system, and
forms one of a compressor for the first utilization system and a
compressor for the second utilization system.
[0219] One end sides of the first, second, and third suction pipes
(23a, 23b, 23c) are connected to the suction sides of the first,
second, and third compressors (21a, 21b, 21c), respectively. The
other end side of the first suction pipe (23a) is branched into two
paths, one of which is connected to the second gas-side stop valve
(104), and the other of which is connected to the third four-way
switching valve (43). The other end side of the second suction pipe
(23b) is connected to the third four-way switching valve (43). The
other end side of the third suction pipe (23c) is branched into two
paths, one of which is connected to the third four-way switching
valve (43), and the other of which is connected to the second
four-way switching valve (42).
[0220] Here, the first suction pipe (23a) is provided with a first
suction pressure sensor (120). The third suction pipe (23c) is
provided with a second suction pressure sensor (121). The first
suction pressure sensor (120) detects a low-level pressure of the
refrigeration side. The second suction pressure sensor (121)
detects a low-level pressure of the air-conditioning side.
[0221] Each of the first to third, three four-way switching valves
(24, 42, 43) includes first to fourth, four ports. In the first
four-way switching valve (24), the first port is connected to the
discharge collection pipe (22); the second port is connected to the
fourth port of the second four-way switching valve (42); the third
port is connected to one end side of the external heat exchanger
(25); and the fourth port is connected to the first gas-side stop
valve (105). In the second four-way switching valve (42), the first
port is connected to the discharge collection pipe (22); the second
port is connected to the third suction pipe (23c); and the third
port is closed.
[0222] Both of the first four-way switching valve (24) and the
second four-way switching valve (42) are capable of switching
between a first state (the state as shown in solid line in FIG. 1)
in which the first port and the third port communicate with each
other and in which the second port and the fourth port communicate
with each other, and a second state (the state as shown in broken
line in FIG. 1) in which the first port and the fourth port
communicate with each other and in which the second port and the
third port communicate with each other.
[0223] In the third four-way switching valve (43), the first port
is connected to the third refrigerant pipe (35); the second port is
connected to the second suction pipe (23b); the third port is
connected to the third suction pipe (23c); and the fourth port is
connected to the first suction pipe (23a). Further, check valves
are provided at a location between the first suction pipe (23a) and
the third four-way switching valve (43), and a location between the
third suction pipe (23c) and the third four-way switching valve
(43). Here, in the third four-way switching valve (43), the
discharge pressures of the compressors (31, 32, 33) are always
applied to the first port, whereas the suction pressures of the
second compressor (21b), the third compressor (21c) and the first
compressor (21a) are always applied to the second port, the third
port, and the fourth port, respectively.
[0224] The third four-way switching valve (43) is capable of
switching between a first state (the state as shown in solid line
in FIG. 1) in which the first port and the third port communicate
with each other and in which the second port and the fourth port
communicate with each other, and a second state (the state as shown
in broken line in FIG. 1) in which the first port and the fourth
port communicate with each other and in which the second port and
the third port communicate with each other.
[0225] <Refrigeration Unit>
[0226] One end (the fluid-side end) of the refrigeration circuit
(99) of the refrigeration unit (95) is connected to the branched
portion of the fluid-side communicating pipe (100), and the other
end (the gas-side end) is connected to the branched portion of the
second gas-side communicating pipe (102). The refrigeration circuit
(99) includes, sequentially from the fluid-side end, a
refrigeration expansion valve (82), a refrigeration heat exchanger
(81), and a booster compressor (84). The refrigeration heat
exchanger (81) is a cross-fin type, fin and tube heat exchanger. A
refrigeration fan (83) is provided near the refrigeration heat
exchanger (81). The refrigeration heat exchanger (81) exchanges
heat between the refrigerant and the air in the storage room
transferred by the refrigeration fan (83).
[0227] In the refrigeration circuit (99), an outlet refrigerant
temperature sensor (111) is provided at the outlet side of the
refrigeration heat exchanger (81). The refrigeration expansion
valve (82) is a temperature sensitive valve whose degree of opening
is adjusted according to the temperature detected by the outlet
refrigerant temperature sensor (111). A solenoid valve (SV) capable
of being opened or closed is provided near the upstream side of the
refrigeration expansion valve (82). Further, an internal
temperature sensor (112) for detecting a temperature of the air in
the freezer is provided near the refrigeration heat exchanger
(81).
[0228] The booster compressor (84) is a high pressure dome type
scroll compressor, and forms a variable displacement compressor. A
discharge pipe (85) of the booster compressor (84) is connected to
the second gas-side communicating pipe (102), and a suction pipe
(86) of the booster compressor (84) is connected to the
refrigeration heat exchanger (81). The discharge pipe (85) is
provided with, sequentially from the booster compressor (84) side,
a high-level pressure switch (113), an oil separator (87), and a
check valve (CV). The suction pipe (86) is provided with a suction
pressure sensor (114) for detecting a suction pressure of the
booster compressor (84). An oil return pipe (88) for returning the
refrigerating machine oil separated from the refrigerant to the
suction side (the suction pipe (86)) of the booster compressor
(84), is connected to the oil separator (87). A capillary tube (CP)
is provided to this oil return pipe (88).
[0229] Further, the refrigeration circuit (99) includes a bypass
pipe (89) which connects between the suction pipe (86) and the
discharge pipe (85). The bypass pipe (89) is provided with a check
valve (CV). The bypass pipe (89) is configured to allow the
refrigerant flowing in the suction pipe (86) to bypass the booster
compressor (84) and flow into the discharge pipe (85) in the event
of such as a breakdown of the booster compressor (84).
[0230] Further, in the refrigerating apparatus (91) of the present
embodiment, the temperature at which the refrigerant evaporates
differs between the air-conditioning circuit (97), the cooling
circuit (98), and the refrigeration circuit (99). That is, the
pressure at which the refrigerant evaporates differs between the
air-conditioning circuit (97), the cooling circuit (98), and the
refrigeration circuit (99).
[0231] Accordingly, the suction pressures of the compressors (21a,
21b, 21c) which are connected to the first utilization system or
the second utilization system differ from one another. In such a
case, the intermediate-pressure refrigerant in the injection
circuit (40) tends to be suctioned into a compressor whose
compression chamber in the state of intermediate pressure has a
lower pressure. As a result, the temperature of the discharge
refrigerant discharged from the compressor decreases. According to
this change in temperature, the degree of opening of each of the
flow rate adjusting valves (30a, 30b, 30c) is reduced. In this way,
the refrigerant is prevented from being injected into the
compressors (21a, 21b, 21c) in a large amount.
[0232] --Operational Behavior--
[0233] Next, an operational behavior of the refrigerating apparatus
(91) will be described. The refrigerating apparatus (91) is capable
of switching between a cooling operation in which the indoor space
is cooled by the air-conditioning unit (93) while the cooling unit
(94) cools the refrigerator and the refrigeration unit (95) cools
the freezer, and a heating operation in which the indoor space is
heated by the air-conditioning unit (93) while the cooling unit
(94) cools the refrigerator and the refrigeration unit (95) cools
the freezer. The cooling operation will be described below.
[0234] The cooling operation is capable of switching between a
first mode in which the second compressor (21b) is used for the
second utilization system for cooling and freezing, and a second
mode in which the second compressor (21b) is used for the first
utilization system for air conditioning.
[0235] As shown in FIG. 2, all the four-way switching valves (24,
42, 43) are set in the first state in the cooling operation of the
first mode. The outdoor expansion valve (36) is set in the fully
closed state. Further, the degree of opening of each of the indoor
space expansion valve (52a), the cooling expansion valve (52b), and
the refrigeration expansion valve (82) is appropriately adjusted.
Further, each of the fans (26, 54, 83), the three compressors (21a,
21b, 21c), and the booster compressor (84) are in the operating
condition.
[0236] The high-pressure gas refrigerant compressed in the first,
second, and third compressors (21a, 21b, 21c) is discharged through
the discharge pipes (22a, 22b, 22c), respectively. The
high-pressure gas refrigerant discharged through the discharge
pipes (22a, 22b, 22c) flows into the respective oil separators
(38a, 38b, 38c). The oil separators (38a, 38b, 38c) separate a
refrigerating machine oil from the high pressure refrigerant. The
separated refrigerating machine oil is temporarily stored in the
respective oil separators (38a, 38b, 38c), and then flows into the
second injection pipe (38) through the oil discharge pipes (39a,
39b, 39c) and the oil discharge collection pipe (39d). The flow of
the refrigerating machine oil having flowed into the second
injection pipe (38) is divided to pass through the branch injection
pipes (37a, 37b, 37c), and is then suctioned into the compressors
(21a, 21b, 21c) through the intermediate ports (5, 6, 7).
[0237] On the other hand, the high pressure refrigerant from which
the refrigerating machine oil has been separated flows out the oil
separators (38a, 38b, 38c), and is collected together in the
discharge collection pipe (22). The high pressure refrigerant
collected together in the discharge collection pipe (22) flows into
the external heat exchanger (25) through the first and second
four-way switching valves (24, 42). In the external heat exchanger
(25), the high pressure refrigerant exchanges heat with the outdoor
air, and is condensed. The condensed refrigerant sequentially
passes through the first refrigerant pipe (32), the receiver (27),
and the high pressure side flow path (28a) of the subcooling heat
exchanger (28), and then flows into the second refrigerant pipe
(33). Part of the refrigerant having flowed into the second
refrigerant pipe (33) flows into the first injection pipe (37), and
the rest of the refrigerant flows into the fluid-side communicating
pipe (100) through the first stop valve (11).
[0238] The high pressure refrigerant having flowed into the first
injection pipe (37) is decompressed to a predetermined pressure by
the subcooling pressure-reducing valve (29) until the refrigerant
becomes an intermediate-pressure refrigerant, and thereafter, the
intermediate-pressure refrigerant flows into the reduced-pressure
side flow path (28b) of the subcooling heat exchanger (28). In the
subcooling heat exchanger (28), the intermediate-pressure
refrigerant and the high pressure refrigerant flowing in the high
pressure side flow path (28a) exchange heat with each other. As a
result, the high pressure refrigerant is cooled, and the degree of
subcooling increases, whereas the intermediate-pressure refrigerant
is heated to become a gas refrigerant. After flowing out the
subcooling heat exchanger (28), the flow of the gas refrigerant is
divided into the first, second and third branch injection pipes
(37a, 37b, 37c) through the second injection pipe (38).
[0239] A flow rate of the intermediate-pressure refrigerant having
flowed into the branch injection pipes (37a, 37b, 37c) is adjusted
by the flow rate adjusting valves (30a, 30b, 30c), respectively,
and then, the refrigerant is injected into the compression chamber
in the state of intermediate pressure in each of the compressors
(21a, 21b, 21c). Here, the controller (9) adjusts the degree of
opening of each of the flow rate adjusting valves (30a, 30b, 30c)
so that the temperature detected by the discharge pipe temperature
sensor (61) is in the predetermined temperature range.
[0240] On the other hand, the flow of the liquid refrigerant having
flowed into the fluid-side communicating pipe (100) is divided into
the air-conditioning circuit (97), the cooling circuit (98), and
the refrigeration circuit (99).
[0241] The high pressure refrigerant having flowed into the
air-conditioning circuit (97) is decompressed by the indoor space
expansion valve (52), and then flows into the indoor space heat
exchanger (53). In the indoor space heat exchanger (53), the
refrigerant absorbs heat from the indoor air, and evaporates. As a
result, the indoor air is cooled, thereby providing cooling for the
inside of the store. The refrigerant evaporated in the indoor space
heat exchanger (53) is suctioned into the third compressor (21c)
through the third suction pipe (23c), after sequentially passing
through the first gas-side communicating pipe (101), the first
four-way switching valve (24), and the second four-way switching
valve (42).
[0242] The refrigerant having flowed into the cooling circuit (98)
passes through the pipe for heating (51). Here, at refrigerant
drain pan (55), the ice blocks made of frozen condensed water is
melted by the refrigerant flowing in the pipe for heating (51).
Thus, the high pressure refrigerant flowing in the pipe for heating
(51) is further subcooled. The high pressure refrigerant having
flowed out the pipe for heating (51) is decompressed by the cooling
expansion valve (52), and thereafter, flows into a cooling heat
exchanger (81). In the cooling heat exchanger (81), the refrigerant
absorbs heat from the air in the refrigerator, and evaporates. As a
result, the inside of the refrigerator is cooled. According to the
cooling unit (94), the temperature in the refrigerator is
maintained at 5.degree. C., for example. The refrigerant evaporated
in the cooling heat exchanger (81) flows into the second gas-side
communicating pipe (102).
[0243] The refrigerant having flowed into the refrigeration circuit
(99) is decompressed by the refrigeration expansion valve (82), and
then flows into the refrigeration heat exchanger (81). In the
refrigeration heat exchanger (81), the refrigerant absorbs heat
from the air in the freezer, and evaporates. As a result, the
inside of the freezer is cooled. According to the refrigeration
unit (95), the temperature in the freezer is maintained at
-10.degree. C., for example. The refrigerant evaporated in the
refrigeration heat exchanger (81) is compressed by the booster
compressor (84), and thereafter, flows into the second gas-side
communicating pipe (102) to be merged with the refrigerant flowing
from the cooling circuit (98). The refrigerant merged together
flows into the first suction pipe (106), and part of the
refrigerant is suctioned into the first compressor (21a), and the
rest of the refrigerant is suctioned into the second compressor
(21b) through the second suction pipe (107), after passing through
a third connection pipe (49c) and the third four-way switching
valve (43).
[0244] The cooling operation of the second mode is the same as the
cooling operation of the first mode, only except that the third
four-way switching valve (43) is switched to the second state.
[0245] In the cooling operation of this mode, the refrigerant
evaporated in the indoor space heat exchanger (53) flows into the
third suction pipe (23c) through the first gas-side communicating
pipe (101), sequentially passing through the first four-way
switching valve (24) and the second four-way switching valve (42).
Part of the refrigerant having flowed into the third suction pipe
(23c) is suctioned into the third compressor (21c), and the rest of
the refrigerant is suctioned into the second compressor (21b)
through the second suction pipe (23b) after passing through the
third four-way switching valve (43).
[0246] Further, it is possible to perform a heating operation by
switching only the first four-way switching valve (24) to the
second state, from the state of the above cooling operation. In
this case, if the outdoor expansion valve (31) is fully closed, the
operation will be a first heating operation. If the degree of the
opening of the outdoor expansion valve (31) is adjusted as
necessary without fully closing the outdoor expansion valve (31),
the operation will be a second heating operation.
[0247] Further, if the first four-way switching valve (24) and the
second four-way switching valve (42) are switched to the second
state, and the degree of opening of the outdoor expansion valve
(31) is adjusted as necessary without fully closing the outdoor
expansion valve (31), then the operation will be a third heating
operation.
[0248] Here, in the first heating operation, the air-conditioning
heat exchanger (53a) provided in the air-conditioning circuit (97)
serves as a condenser. The refrigeration heat exchanger (81) and
the cooling heat exchanger (53b) which is provided in the cooling
circuit (98) serve as evaporators. In the second heating operation,
the air-conditioning heat exchanger (53a) serves as a condenser.
The external heat exchanger (25), the cooling heat exchanger (53b),
and the refrigeration heat exchanger (81) serve as evaporators. In
the third heating operation, the air-conditioning heat exchanger
(53a) and the external heat exchanger (25) serve as condensers. The
refrigeration heat exchanger (81) and the cooling heat exchanger
(53b) serve as evaporators.
[0249] --Effects of Embodiment 2--
[0250] According to the present Embodiment 2, the plurality of
compressors (21a, 21b, 21c) are compressors whose suction pressures
are different from one another. Even in such a case, the flow rate
of the refrigerant flowing in each of the branch injection pipes
(37a, 37b, 37c) after being decompressed by the subcooling
pressure-reducing valve (29) can be adjusted for each of the
compressors (21a, 21b, 21c) by the flow rate adjusting valves (30a,
30b, 30c). Thus, an appropriate injection to the compressors (21a,
21b, 21c) can be performed.
[0251] Further, according to the present Embodiment 2, the
refrigerating machine oil can be returned to the compressors (21a,
21b, 21c), while the refrigerant is being injected to the
compressors (21a, 21b, 21c) through the injection circuit (40).
Because the injection circuit (40) as well can be used as a circuit
for returning the refrigerating machine oil, it is not necessary to
separately provide a dedicated oil return circuit. Thus, the cost
of the refrigerating apparatus can be reduced.
[0252] --Variation of Embodiment 2--
[0253] FIG. 9 shows a refrigerant circuit according to a variation
of Embodiment 2. The configuration of the controller which controls
the operation of the refrigerating apparatus (1) differs between
Embodiment 2 and the variation. Further, the second injection pipe
(38) of Variation 2 is provided with an intermediate refrigerant
temperature sensor (70) for measuring a temperature of the
intermediate-pressure refrigerant having passed through the
reduced-pressure side flow path (28b) of the subcooling heat
exchanger (28), and with an intermediate-pressure pressure sensor
(71) for measuring a pressure of the intermediate-pressure
refrigerant.
[0254] The controller (8) according to this variation of Embodiment
2 includes a third control section (18) and a fourth control
section (19). The degree of opening of the subcooling
pressure-reducing valve (29) is adjusted by the third control
section (18). The degree of opening of the flow rate adjusting
mechanism (30a, 30b, 30c) is adjusted by the fourth control section
(19).
[0255] Further, first and second suction pressure sensors (120,
121) as the low-level pressure detection mechanisms, an
intermediate-pressure pressure sensor (71) as the intermediate
pressure detection mechanisms, an intermediate refrigerant
temperature senor (70) and an intermediate-pressure pressure sensor
(71) as the intermediate superheat detection mechanisms, and a
discharge pipe temperature sensor (61) and a discharge pressure
sensor (64) as the discharge condition detection mechanisms, are
electrically connected to the controller (8). Also, the controller
(8) includes a discharge condition setting section (a discharge
condition setting mechanism) (76) and an intermediate superheat
setting section (an intermediate superheat setting mechanism)
(77).
[0256] The discharge condition setting section (76) is for setting
a target value Tm for the discharge temperatures of the compressors
(21a, 21b, 21c). The intermediate superheat setting section (77) is
for setting a target value Tgshm for the degree of superheat of the
intermediate-pressure refrigerant flowing in the injection circuit
(40).
[0257] Next, a control operation of the third control section (18)
and the fourth control section (19) will be described with
reference to FIG. 10 and FIG. 11 showing the control flow
diagram.
[0258] <Third Control Section>
[0259] The third control section (18) includes the intermediate
pressure control section (59) and the intermediate superheat
control section (60). The third control section (18) is for
exerting control by selecting the intermediate pressure control
section (59) or the intermediate superheat control section (60),
based on the operating condition of the compressors (21a, 21b,
21c).
[0260] Specifically, first, in step ST21, it is determined whether
or not the compressors (21a, 21b) connected to the first low
pressure line (102), and the compressor (21c) connected to the
second low pressure line (101), as shown in FIG. 10, are
activated.
[0261] In step ST21, if the compressors (21a, 21b) connected to the
first low pressure line (102), and the compressor (21c) connected
to the second low pressure line (101) are activated together, the
process moves to step ST22. In step ST22, an amount dpls of change
in a value of degree of opening of the subcooling pressure-reducing
valve (29) is determined based on a difference between a minimum
value of the values LP1, LP2 detected by the first and second
suction pressure sensors (120, 121) and a value MP detected by the
intermediate-pressure pressure sensor (71). The smaller the
difference is, the smaller the amount dpls of change becomes. If
the amount dpls of change is a negative value, the amount dpls of
change is set zero.
[0262] Next, in step ST24, a value obtained by adding the amount
dpls of change determined in step ST21 to a value EV2pls of degree
of opening of the present subcooling pressure-reducing valve (29)
is set as a new value EV2pls of degree of opening. The degree of
opening of the subcooling pressure-reducing valve (29) is changed
to this new value EV2pls of degree of opening.
[0263] The processes in step ST22 and step ST24 correspond to the
control operation of the intermediate pressure control section
(59). Due to this operation, it is possible to make the pressure
(intermediate pressure) of the injection circuit (40) higher than
the pressures (low-level pressures) of the first and second low
pressure lines all the time.
[0264] On the other hand, in step ST21, if the compressors (21a,
21b) connected to the first low pressure line (102), or the
compressor (21c) connected to the second low pressure line (101) is
activated, the process moves to step ST23. In step ST23, an amount
dpls of change in a value of degree of opening of the subcooling
pressure-reducing valve (29) is determined based on a difference
between a value Tgsh of an intermediate refrigerant superheat
detected by the intermediate refrigerant temperature sensor (70)
and the intermediate-pressure pressure sensor (71), and a target
value Tgshm of the intermediate superheat setting section (77). The
smaller the difference is, the smaller the amount dpls of change
becomes.
[0265] Next, in step ST24, a value obtained by adding the amount
dpls of change determined in step ST23 to the value EV2pls of
degree of opening of the present subcooling pressure-reducing valve
(29) is set as a new value EV2pls of degree of opening. The degree
of opening of the subcooling pressure-reducing valve (29) is
changed to this new value EV2pls of degree of opening.
[0266] The processes in step ST23 and step ST24 correspond to the
control operation of the intermediate superheat control section
(60). Due to this operation, the superheat of the
intermediate-pressure refrigerant having flowed out the subcooling
heat exchanger (28) can be maintained constant at the target value
of the intermediate superheat setting section (77).
[0267] As described above, if the compressors (21a, 21b) connected
to the first low pressure line (102), and the compressor (21c)
connected to the second low pressure line (101) are activated
together; the intermediate pressure control is performed by the
intermediate pressure control section (59). If the compressors
(21a, 21b) connected to the first low pressure line (102), or the
compressor (21c) connected to the second low pressure line (101) is
activated, the intermediate superheat control is performed by the
intermediate superheat control section (60). Thus, as described
above, the refrigerant does not flow back from the intermediate
port of the compressor (21c) connected to the second low pressure
line (101) to the intermediate ports of the compressors (21a, 21b)
connected to the first low pressure line (102).
[0268] Further, because the backflow of the refrigerant does not
occur as described above in the case where the compressors (21a,
21b) connected to the first low pressure line (102), or the
compressor (21c) connected to the second low pressure line (101) is
activated, the refrigerant can be injected to each of the
compressors (21a, 21b, 21c), while maintaining the superheat of the
intermediate-pressure refrigerant in the reduced-pressure side flow
path (28b) of the subcooling heat exchanger (28) at an appropriate
value.
[0269] After the completion of step ST24, the process returns to
step ST21, in which it is determined again whether or not the
compressors (21a, 21b) connected to the first low pressure line
(102), and the compressor (21c) connected to second low pressure
line (101) are activated together. The processes in steps ST21 to
ST24 are repeated. Since these two types of control are implemented
depending on the situation, a more appropriate injection to the
compressors (21a, 21b, 21c) can be performed, compared to the case
where the discharge temperature control is implemented all the time
as in Embodiment 2.
[0270] <Fourth Control Section>
[0271] The fourth control section (19) includes a second discharge
target control section (56b), a second superheat avoidance control
section (78b), and a second wet avoidance control section (79b).
The fourth control section (19) is for exerting control by
selecting any one of the second discharge target control section
(56b), the second superheat avoidance control section (78b), and
the second wet avoidance control section (79b), based on the
discharge temperatures and the discharge superheats of the
compressors (21a, 21b, 21c) and based on the superheat of the
intermediate-pressure refrigerant in the injection circuit (40).
The control operation of the fourth control section (19) is
performed for each of the first, second and third flow rate
adjusting valves (30a, 30b, 30c). However, only the control of the
first flow rate adjusting valve (30a) will be described below.
[0272] Specifically, first, in step ST25, whether or not at least
one of the eighth condition and the ninth condition is met is
determined as shown in FIG. 11. Here, the eighth condition is a
condition in which a value Tdsh1 detected as a discharge superheat
by the discharge pipe temperature sensor (61) and the discharge
pressure sensor (64) is smaller than a predetermined discharge
superheat Tdshs; in which a value Td1 detected by the discharge
pipe temperature sensor (61) is even smaller than a lower threshold
value Tdmin set smaller than the discharge temperature target value
Td of the discharge condition setting section (76); and in which a
value Tgsh detected as an intermediate refrigerant superheat by the
intermediate refrigerant temperature sensor (70) and the
intermediate-pressure pressure sensor (71) is smaller than an
intermediate superheat target value Tgshm of the intermediate
superheat setting section (77).
[0273] The eighth condition is for determining whether or not the
first compressor (21a) performs an abnormal wet operation. Here,
the predetermined discharge superheat Tdshs is set within a range
that does not cause the first compressor (21a) to perform an
abnormal wet operation. Further, the lower threshold value Tdmin is
set to such a value that causes the first compressor (21a) to
perform an abnormal wet operation when the value Td1 detected by
the discharge pipe temperature sensor (61) becomes lower than the
threshold value Tdmin.
[0274] The ninth condition is that the value Td1 detected by the
discharge pipe temperature sensor (61) is even larger than an upper
threshold value Tdmax set larger than the discharge temperature
target value Tm of the discharge condition setting section
(76).
[0275] The ninth condition is for determining whether or not the
first compressor (21a) performs an abnormal superheat operation.
Here, the upper threshold value Tdmax is set to such a value that
causes the first compressor (21a) to perform an abnormal superheat
operation when the value Td1 detected by the discharge pipe
temperature sensor (61) exceeds the threshold value Tdmax.
[0276] If at least one of the eighth and ninth conditions is met in
step ST25, it is determined that the first compressor (21a)
performs an abnormal wet operation or an abnormal wet operation,
and the process moves to step ST26.
[0277] In step ST26, whether or not the ninth condition is met is
determined. If the ninth condition is met, the process moves to
step ST28. In step ST28, an amount dpls of change in a value of
degree of opening of the first flow rate adjusting valve (30a) is
determined based on a value EV3pls of degree of opening of the
present first flow rate adjusting valve (30a). Here, if the present
value EV3pls of degree of opening is large, the amount dpls of
change is also large. If the present value EV2pls of degree of
opening is small, the amount dpls of change is also small. Next, in
step ST30, a value obtained by adding the amount dpls of change
determined in step ST28 to the value EV3pls of degree of opening of
the present first flow rate adjusting valve (30a) is set as a new
value EV3pls of degree of opening. As a result, the degree of
opening of the subcooling pressure-reducing valve (29)
increases.
[0278] The processes in step ST28 and step ST30 correspond to the
control operation of the second superheat avoidance control section
(78b). Due to this operation, the amount of the
intermediate-pressure refrigerant flowing into the first compressor
(21a) through the intermediate port (5) is increased, and it is
possible to prevent the compressors from continuously performing
the abnormal superheat operating.
[0279] On the other hand, if the ninth condition is not met in step
ST26, the process moves to step ST29. In step ST29, an amount dpls
of change in a value of degree of opening of the first flow rate
adjusting valve (30a) is determined based on a value EV3pls of
degree of opening of the present first flow rate adjusting valve
(30a). Here, if the present value EV3pls of degree of opening is
large, the amount dpls of change is also large. If the present
value EV2pls of degree of opening is small, the amount dpls of
change is also small. Next, in step ST30, a value obtained by
subtracting the amount dpls of change determined in step ST29 from
the value EV3pls of degree of opening of the present first flow
rate adjusting valve (30a), is set as a new value EV3pls of degree
of opening. As a result, the degree of opening of the subcooling
pressure-reducing valve (29) decreases.
[0280] The processes in step ST29 and step ST30 correspond to the
control operation of the second wet avoidance control section
(79b). Due to this operation, the amount of intermediate-pressure
refrigerant flowing into the first compressor (21a) through the
intermediate port (5) is reduced, and it is possible to prevent the
compressors from continuously performing an abnormal humidity
operating.
[0281] On the other hand, if both of the eighth and ninth
conditions are not met in step ST25, it is determined that the
first compressor (21a) is not performing an abnormal wet operation
or an abnormal wet operation, and the process moves to step
ST27.
[0282] In step ST27, an amount dpls of change in a value of degree
of opening of the first flow rate adjusting valve (30a) is
determined based on a difference between a value Td1 detected by
the discharge pipe temperature sensor (61) and a discharge
temperature target value Tm of the discharge condition setting
section (76). The smaller the difference is, the smaller the amount
dpls of change becomes. Next, in step ST30, a value obtained by
adding the amount dpls of change determined in step ST29 to the
value EV3pls of degree of opening of the present first flow rate
adjusting valve (30a), is set to a new value EV3pls of degree of
opening. The degree of opening of the first flow rate adjusting
valve (30a) is changed to this new value EV2pls of degree of
opening.
[0283] The processes in step ST27 and step ST30 correspond to the
control operation of the second discharge target control section
(56b). Due to this operation, the discharge temperature of the
first compressor (21a) can be maintained constant at the target
value of the discharge condition setting section (76).
[0284] After the completion of step ST30, the process returns to
step ST25, in which the determination process in step ST25 is
performed again. The processes in steps ST25 to ST30 are repeated.
Since these three types of control are implemented depending on the
situation, a more appropriate injection to the compressors (21a,
21b, 21c) can be performed, compared to the case where the
discharge temperature control is implemented all the time as in
Embodiment 1.
Other Embodiments
[0285] The following structures may also be used in the above
embodiments.
[0286] In the above embodiments, all of the flow rate adjusting
mechanisms (30a, 30b, 30c) for adjusting the injection amount of
each of the compressors (21a, 21b, 21c) are motor-operated valves.
However, the structure is not limited to this, but the flow rate
adjusting mechanisms (30a, 30b, 30c) may be solenoid valves capable
of being opened or closed. In this case, the injection amount may
be adjusted by using the time in which the solenoid valves are held
open. That is, to increase the injection amount, the time in which
the solenoid valves are held open is extended. On the contrary, to
reduce the injection amount, the time in which the solenoid valves
are held open is shortened.
[0287] Further, as shown in FIG. 3, the injection amount of the
variable displacement first compressor (21a) may be adjusted by a
motor-operated valve, and the injection amount of the second and
third fixed displacement compressors (21b, 21c) may be adjusted by
solenoid valves. In this case, the injection amount of the first
compressor (21a) can be accurately adjusted by the motor-operated
valve, according to change in operation capacity of the first
compressor (21a).
[0288] On the other hand, it is not necessary to accurately adjust
the injection amount of the second and third compressors (21b, 21c)
because the operation capacity of the second and third compressors
(21b, 21c) is fixed. Thus, the cost of the refrigerating apparatus
can be reduced by using the solenoid valves having a structure
simpler than the structure of the motor-operated valve.
[0289] In the case where a motor-operated valve and an on/off valve
are used as flow rate adjusting mechanisms of the injection circuit
as described above, these valves may have different CV values
(coefficient of flow value) from each other. For example, if the CV
value of the motor-operated valve in the fully-opened state is set
larger than the CV value of the on/off valve, it is possible to
make the first compressor (21a) have an injection amount larger
than the injection amount of the second and third compressors (21b,
21c) when the motor-operated valve is fully open and the solenoid
valves are open.
[0290] In the above embodiments, the flow rate adjusting mechanisms
(30a, 30b, 30c) are provided to all of the branch pipes (37a, 37b,
37c) in the injection circuit (40). However, the structure is not
limited to this, but the flow rate adjusting mechanism (30a, 30b,
30c) may be provided only to the branch pipe (37a) of the variable
displacement compressor.
[0291] The foregoing embodiments are merely preferred examples in
nature, and are not intended to limit the scope, applications, and
use of the invention.
INDUSTRIAL APPLICABILITY
[0292] As described above, the present invention is useful for a
refrigerating apparatus having a plurality of compressors and
performing a vapor compression refrigeration cycle.
Description of Reference Characters
[0293] 1 refrigerating apparatus
[0294] 5, 6, 7 intermediate port
[0295] 9 controller (control mechanism)
[0296] 10 refrigerant circuit
[0297] 21a first compressor (compressor)
[0298] 21b second compressor (compressor)
[0299] 21c third compressor (compressor)
[0300] 28 subcooling heat exchanger
[0301] 29 subcooling pressure-reducing valve (pressure-reducing
mechanism)
[0302] 30a first flow rate adjusting valve (flow rate adjusting
mechanism)
[0303] 30b second flow rate adjusting valve (flow rate adjusting
mechanism)
[0304] 30c third flow rate adjusting valve (flow rate adjusting
mechanism)
[0305] 32 first refrigerant pipe (high pressure line)
[0306] 37 first injection pipe (main pipe)
[0307] 38 second injection pipe
[0308] 37a first branch injection pipe (branch pipe)
[0309] 37b second branch injection pipe (branch pipe)
[0310] 37c third branch injection pipe (branch pipe)
[0311] 40 injection circuit
* * * * *