U.S. patent application number 14/119344 was filed with the patent office on 2014-04-17 for outdoor unit of refrigeration system.
This patent application is currently assigned to DAIKIN INDUSTRIES, LTD.. The applicant listed for this patent is Hirokazu Fujino, Kazuhiro Furusho, Ikuhiro Iwata, Tetsuya Okamoto, Guozhong Yang, Shun Yoshioka. Invention is credited to Hirokazu Fujino, Kazuhiro Furusho, Ikuhiro Iwata, Tetsuya Okamoto, Guozhong Yang, Shun Yoshioka.
Application Number | 20140102131 14/119344 |
Document ID | / |
Family ID | 47423735 |
Filed Date | 2014-04-17 |
United States Patent
Application |
20140102131 |
Kind Code |
A1 |
Okamoto; Tetsuya ; et
al. |
April 17, 2014 |
OUTDOOR UNIT OF REFRIGERATION SYSTEM
Abstract
In an outdoor unit, first through third intermediate heat
exchangers and an outdoor heat exchanger are disposed to stand
along an air inlet of an outdoor casing, and the outdoor heat
exchanger is located above the first through third intermediate
heat exchangers.
Inventors: |
Okamoto; Tetsuya; (Osaka,
JP) ; Furusho; Kazuhiro; (Osaka, JP) ; Yang;
Guozhong; (Osaka, JP) ; Iwata; Ikuhiro;
(Osaka, JP) ; Fujino; Hirokazu; (Osaka, JP)
; Yoshioka; Shun; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Okamoto; Tetsuya
Furusho; Kazuhiro
Yang; Guozhong
Iwata; Ikuhiro
Fujino; Hirokazu
Yoshioka; Shun |
Osaka
Osaka
Osaka
Osaka
Osaka
Osaka |
|
JP
JP
JP
JP
JP
JP |
|
|
Assignee: |
DAIKIN INDUSTRIES, LTD.
Osaka-shi, Osaka
JP
|
Family ID: |
47423735 |
Appl. No.: |
14/119344 |
Filed: |
June 28, 2012 |
PCT Filed: |
June 28, 2012 |
PCT NO: |
PCT/JP2012/004185 |
371 Date: |
November 21, 2013 |
Current U.S.
Class: |
62/510 |
Current CPC
Class: |
F24F 1/16 20130101; F25B
13/00 20130101; F25B 2313/0233 20130101; F25B 2400/072 20130101;
F25B 2400/13 20130101; F24F 1/50 20130101; F25B 2313/0253 20130101;
F25B 2313/027 20130101; F25B 1/10 20130101 |
Class at
Publication: |
62/510 |
International
Class: |
F25B 1/10 20060101
F25B001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2011 |
JP |
2011-146263 |
Claims
1. An outdoor unit of a refrigeration system, the outdoor unit
comprising: a multistage compressor including a plurality of
serially connected compression mechanisms in which refrigerant
discharged from a low-stage one of the compression mechanisms is
sucked and compressed in a high-stage one of the compression
mechanisms; an intermediate heat exchanger located between adjacent
two of the compression mechanisms and configured to cause
refrigerant flowing from the low-stage compression mechanism to the
high-stage compression mechanism to exchange heat with outdoor air
to be cooled; an outdoor heat exchanger configured to cause
refrigerant discharged from the highest-stage compression mechanism
to exchange heat with outdoor air; and a casing having a side
surface in which an air suction port is provided and an upper
surface in which an air outlet is provided, and housing the
compression mechanisms, the intermediate heat exchanger, and the
outdoor heat exchanger, wherein the intermediate heat exchanger and
the outdoor heat exchanger are disposed to stand along the suction
port of the casing, and the outdoor heat exchanger is located above
all the intermediate heat exchanger.
2. The outdoor unit of claim 1, wherein the multistage compressor
includes three or more compression mechanisms, the intermediate
heat exchanger comprises a plurality of intermediate heat
exchangers, and the highest-stage intermediate heat exchanger is
located above the other intermediate heat exchangers and below the
outdoor heat exchanger.
3. The outdoor unit of claim 2, wherein the intermediate heat
exchangers are stacked from the bottom in the order of increasing
pressure of inflow refrigerant.
4. The outdoor unit of claim 1, wherein the intermediate heat
exchanger includes a plurality of flat tubes which are arranged in
an up and down direction with their side surfaces facing one
another and each of which includes a plurality of fluid passage
extending in a tube length direction, and also includes a plurality
of fins dividing space between adjacent ones of the flat tubes into
a plurality of air passages in which air flows.
5. The outdoor unit of claim 4, wherein the outdoor heat exchangers
includes a plurality of flat tubes which are arranged in the up and
down direction with their side surfaces facing one another, and
each of which includes a plurality of fluid passage extending in a
tube length direction, and also includes a plurality of fins
dividing space between adjacent ones of the flat tubes into a
plurality of air passages in which air flows.
Description
TECHNICAL FIELD
Background Art
[0001] The present invention relates to outdoor units of
refrigeration systems, and particularly to a refrigeration system
that performs a refrigeration cycle of a multistage compression
type.
[0002] An air conditioner that performs a two-stage compression
refrigeration cycle by using carbon dioxide as refrigerant as
described in Patent Document 1 is known as a refrigeration system
that performs a multistage compression refrigeration cycle by using
refrigerant that becomes active in a supercritical region. In this
air conditioner, refrigerant discharged from a compression element
at a previous stage is cooled in an intercooler to be sucked into a
compression element at a subsequent stage, so that the temperature
of refrigerant discharged from the subsequent-stage compression
element is reduced and, thereby, a loss in heat dissipation in an
outdoor heat exchanger is reduced.
[0003] In an air conditioner described in Patent Document 1, as
illustrated in FIG. 20, an intercooler (a) and a heat-source-side
heat exchanger (b) are housed in a heat source unit (c). The
intercooler (a) and the heat-source-side heat exchanger (b) are
disposed on a side surface of the heat source unit (c). The
intercooler (a) is located above the heat-source-side heat
exchanger (b). A heat-source-side fan is provided above the
intercooler (a).
CITATION LIST
Patent Document
[0004] [Patent Document 1] Japanese Unexamined Patent Publication
No. 2009-150641
SUMMARY OF THE INVENTION
Technical Problem
[0005] In the heat source unit (c) of Patent Document 1 configured
to draw in air from the side and blow the air upward, i.e., of a
so-called upward blowing type, the airflow velocity is higher in a
higher position than in a lower position as illustrated in FIG. 21,
and thus, the intercooler (a) located at a higher position has a
high heat exchange efficiency. Thus, the heat source unit (c) can
be reduced in size by placing the intercooler (a) at an upper
position.
[0006] Since the pressure of refrigerant flowing in the intercooler
(a) is lower than that of refrigerant flowing in the
heat-source-side heat exchanger (b), the density of refrigerant
flowing in the intercooler (a) is lower than that of refrigerant
flowing in the heat-source-side heat exchanger (b). Thus, as long
as the mass flow rates of refrigerant flowing in the intercooler
(a) and the heat-source-side heat exchanger (b) are approximately
the same, the volume flow rate of refrigerant flowing in the
intercooler (a) is higher than that of refrigerant flowing in the
heat-source-side heat exchanger (b). Even when the number of
refrigerant paths is approximately identical in the intercooler (a)
and the heat-source-side heat exchanger (b), the flow velocity of
refrigerant flowing in the intercooler (a) is higher than that of
refrigerant flowing in the heat-source-side heat exchanger (b), and
thus, the pressure loss of refrigerant in the intercooler (a) is
larger than that in the heat-source-side heat exchanger (b).
[0007] As described above, size reduction of the intercooler (a) to
reduce the number of refrigerant paths has a problem of a large
pressure loss of refrigerant in the intercooler (a). On the other
hand, an increase in size of the intercooler (a) for the purpose of
reducing an increase of the pressure loss of refrigerant also has a
problem of an increase in size of the heat source unit (c).
[0008] It is therefore an object of the present invention to reduce
an increase in size of a heat source unit with a reduced degree of
increase in pressure loss of refrigerant in an intercooler.
Solution to the Problem
[0009] According to the present invention, in an outdoor unit of a
refrigeration system, an outdoor heat exchanger (44, 162) is
located above an intermediate heat exchanger (41, 42, 43, 161).
[0010] An outdoor unit of a refrigeration system in a first aspect
of the present invention includes: a multistage compressor (20,
150) including a plurality of serially connected compression
mechanisms (21-24, 151, 152) in which refrigerant discharged from a
low-stage one (21, 22, 23, 151) of the compression mechanisms is
sucked and compressed in a high-stage one (22, 23, 24, 152) of the
compression mechanisms; an intermediate heat exchanger (41, 42, 43,
161) located between adjacent two of the compression mechanisms
(21, 22, 23, 24, 151, 152) and configured to cause refrigerant
flowing from the low-stage compression mechanism (21, 22, 23, 151)
to the high-stage compression mechanism (22, 23, 24, 152) to
exchange heat with outdoor air to be cooled; an outdoor heat
exchanger (44, 162) configured to cause refrigerant discharged from
the highest-stage compression mechanism (24, 152) to exchange heat
with outdoor air; and a casing (121, 163) having a side surface in
which an air suction port (123, 164) is provided and an upper
surface in which an air outlet (124, 165) is provided, and housing
the compression mechanisms (21-24, 151, 152), the intermediate heat
exchanger (41, 42, 43, 161), and the outdoor heat exchanger (44,
162). In this outdoor unit, the intermediate heat exchanger (41,
42, 43, 161) and the outdoor heat exchanger (44, 162) are disposed
to stand along the suction port (123, 164) of the casing (121,
163), and the outdoor heat exchanger (44, 162) is located above the
intermediate heat exchanger (41, 42, 43, 161).
[0011] In the first aspect, in the multistage compressor (20, 150),
refrigerant discharged from the low-stage compression mechanism
(21, 22, 23, 151) is sucked and compressed in the high-stage
compression mechanism (22, 23, 24, 152). The intermediate heat
exchanger (41, 42, 43, 161) is located between adjacent two (21,
22, 23, 24, 151, 152) of the compression mechanisms (21-24, 151,
152) and configured to cause refrigerant flowing from the low-stage
compression mechanism (21, 22, 23, 151) to the high-stage
compression mechanism (22, 23, 24, 152) to exchange heat with
outdoor air to be cooled. The outdoor heat exchanger (44, 162)
causes refrigerant discharged from the highest-stage compression
mechanism (24, 152) to exchange heat with outdoor air.
[0012] The casing (121, 163) has the side surface in which the air
suction port (123, 164) is provided and the upper surface in which
the air outlet (124, 165) is provided, and houses the compression
mechanisms (21-24, 151, 152), the intermediate heat exchanger (41,
42, 43, 161), and the outdoor heat exchanger (44, 162). In the
casing (121, 163), the outdoor heat exchanger (44, 162) and the
intermediate heat exchanger (41, 42, 43, 161) are disposed to stand
along the suction port (123, 164), and the outdoor heat exchanger
(44, 162) is located above the intermediate heat exchanger (41, 42,
43, 161).
[0013] The air taken in the casing (121, 163) from the suction port
(123, 164) is subjected to heat exchange in the intermediate heat
exchanger (41, 42, 43, 161) and the outdoor heat exchanger (44,
162), flows to upper space in the casing (121, 163), and is blown
out through the air outlet (124, 165).
[0014] Here, the outdoor unit of this aspect is of a so-called
upward blow type in which air is sucked from the suction port (123,
164) in the side surface and is blown upward from the air outlet
(124, 165). Thus, the airflow velocity is higher in an upper
portion of the suction port (123, 164) than in a lower portion of
the suction port (123, 164). The pressure of refrigerant flowing in
the intermediate heat exchanger (41, 42, 43, 161) is lower than
that of refrigerant flowing in the outdoor heat exchanger (44,
162), and thus, the density of refrigerant in the intermediate heat
exchanger (41, 42, 43, 161) is lower than that of refrigerant in
the outdoor heat exchanger (44, 162). In view of this, when the
mass flow rate of refrigerant flowing in the intermediate heat
exchanger (41, 42, 43, 161) is substantially equal to that of
refrigerant flowing in the outdoor heat exchanger (44, 162), the
volume flow rate of refrigerant in the intermediate heat exchanger
(41, 42, 43, 161) is higher than that of refrigerant in the outdoor
heat exchanger (44, 162). Even when the number of refrigerant paths
in the intermediate heat exchanger (41, 42, 43, 161) is equal to
that in the outdoor heat exchanger (44, 162), the flow velocity of
refrigerant flowing in the intermediate heat exchanger (41, 42, 43,
161) is higher than that of refrigerant flowing in the outdoor heat
exchanger (44, 162), and thus, a pressure loss of refrigerant in
the intermediate heat exchanger (41, 42, 43, 162) is larger than
that of refrigerant in the outdoor heat exchanger (44, 162).
[0015] The outdoor heat exchanger (44, 162) located in an upper
portion of the casing (121, 163) where the airflow velocity is
high, has a high heat exchange efficiency, and can be reduced in
size. On the other hand, the intermediate heat exchanger (41, 42,
43, 161) located in a lower portion of the casing (121, 163) where
the airflow velocity is low, has a low heat exchange efficiency.
Thus, to increase the amount of heat exchange, the intermediate
heat exchanger (41, 42, 43, 161) needs to be larger than that in a
case where this exchanger is located in an upper portion.
[0016] For this reason, the size of the outdoor unit does not
increase even when the size of the outdoor heat exchanger (44, 162)
and the intermediate heat exchanger (41, 42, 43, 161)
increases.
[0017] An increase in size of the intermediate heat exchanger (41,
42, 43, 161) increases the number of refrigerant paths in the
intermediate heat exchanger (41, 42, 43, 161). Thus, in the
intermediate heat exchanger (41, 42, 43, 161), the flow velocity of
refrigerant in each refrigerant path decreases, resulting in a
decrease in pressure loss of refrigerant passing through the
refrigerant path. The flow velocity of refrigerant flowing in the
intermediate heat exchanger (41, 42, 43, 161) is originally high,
and thus, a decrease in flow velocity due to an increase in the
number of refrigerant paths relatively greatly reduces the pressure
loss.
[0018] On the other hand, size reduction of the outdoor heat
exchanger (44, 162) reduces the number of refrigerant paths in the
outdoor heat exchanger (44, 162). The reduction of the number of
refrigerant paths increases the flow velocity of refrigerant in
each refrigerant path to increase the pressure loss of refrigerant
passing through the refrigerant path.
[0019] However, since the flow velocity of refrigerant flowing in
the outdoor heat exchanger (44, 162) is originally low, a certain
degree of increase in flow velocity due to the reduction of the
number of refrigerant paths relatively slightly increases the
pressure loss arising from the increase in flow velocity.
[0020] Thus, by disposing the outdoor heat exchanger (44, 162)
above the intermediate heat exchanger (41, 42, 43, 161), the
pressure loss of refrigerant in the intermediate heat exchanger
(41, 42, 43, 161) can be reduced with a reduced degree of increase
in size of the outdoor unit.
[0021] In a second aspect, in the outdoor unit of the first aspect,
the multistage compressor (20) includes three or more compression
mechanisms (21-24), the intermediate heat exchanger includes a
plurality of intermediate heat exchangers (41, 42, 43), and the
highest-stage intermediate heat exchanger (43) is located above the
other intermediate heat exchangers (41, 42) and below the outdoor
heat exchanger (44).
[0022] In the second aspect, the multistage compressor (20)
includes the three or more compression mechanisms (21-24), and
refrigerant discharged from the low-stage compression mechanism
(21, 22, 23) is sucked and compressed in the high-stage compression
mechanism (22, 23, 24). Thus, the intermediate heat exchanger
includes the plurality of intermediate heat exchangers (41, 42,
43), where the highest-stage intermediate heat exchanger (43) is
located above the other intermediate heat exchangers (41, 42) and
is located below the outdoor heat exchanger (44).
[0023] The pressure of refrigerant flowing in the highest-stage
intermediate heat exchanger (43) is higher than those of
refrigerant flowing in the other intermediate heat exchangers (41,
42), and thus, the densities of refrigerant in the other
intermediate heat exchangers (41, 42) are lower than that of
refrigerant in the highest-stage intermediate heat exchanger (43).
In view of this, when the mass flow rates of refrigerant flowing in
the other intermediate heat exchangers (41, 42) are is
substantially equal to that of refrigerant flowing in the
highest-stage intermediate heat exchanger (43), the volume flow
rates of refrigerant in the other intermediate heat exchangers (41,
42) are higher than that of refrigerant in the highest-stage
intermediate heat exchanger (43). Even when the number of
refrigerant paths in each of the other intermediate heat exchangers
(41, 42) is equal to that in the highest-stage intermediate heat
exchanger (43), the flow velocities of refrigerant flowing in the
other intermediate heat exchangers (41, 42) are higher than that of
refrigerant flowing in the highest-stage intermediate heat
exchanger (43), and thus, pressure losses of refrigerant in the
other intermediate heat exchangers (41, 42) are larger than that in
the highest-stage intermediate heat exchanger (43).
[0024] The high-stage intermediate heat exchanger (43) located in
an upper portion of the casing (121) where the airflow velocity is
high, has a high heat exchange efficiency, and can be reduced in
size. On the other hand, the other intermediate heat exchangers
(41, 42) located in a lower portion of the casing (121) where the
airflow velocity is low, have low heat exchange efficiencies. Thus,
to increase the amount of heat exchange, the other intermediate
heat exchangers (41, 42) need to be larger than those in a case
where these exchangers are located in an upper portion.
[0025] For this reason, the size of the outdoor unit does not
increase even when the size of the high-stage intermediate heat
exchanger (43) and the other intermediate heat exchangers (41, 42)
increases.
[0026] An increase in size of the other intermediate heat
exchangers (41, 42) increases the number of refrigerant paths in
the other intermediate heat exchangers (41, 42). Thus, in the other
intermediate heat exchangers (41, 42), the flow velocity of
refrigerant in each refrigerant path decreases, resulting in a
decrease in pressure loss of refrigerant passing through the
refrigerant path. The flow velocity of refrigerant flowing in the
other intermediate heat exchangers (41, 42) is originally high, and
thus, a decrease in flow velocity due to an increase in the number
of refrigerant paths relatively greatly reduces the pressure
loss.
[0027] On the other hand, size reduction of the high-stage
intermediate heat exchanger (43) reduces the number of refrigerant
paths in the high-stage intermediate heat exchanger (43). The
reduction of the number of refrigerant paths increases the flow
velocity of refrigerant in each refrigerant path to increase the
pressure loss of refrigerant passing through the refrigerant
path.
[0028] However, since the flow velocity of refrigerant flowing in
the high-stage intermediate heat exchanger (43) is originally low,
a certain degree of increase in flow velocity due to the reduction
of the number of refrigerant paths relatively slightly increases
the pressure loss arising from the increase in flow velocity.
[0029] Thus, by disposing the high-stage intermediate heat
exchanger (43) above the other intermediate heat exchangers (41,
42), the pressure loss of refrigerant in the other intermediate
heat exchangers (41, 42) can be reduced with a reduced degree of
increase in size of the outdoor unit.
[0030] In a third aspect, in the outdoor unit of the second aspect,
the intermediate heat exchangers (41, 42, 43) are stacked from the
bottom in the order of increasing pressure of inflow
refrigerant.
[0031] In the third aspect, the intermediate heat exchangers (41,
42, 43) are stacked from the bottom in the order of increasing
pressure of inflow refrigerant.
[0032] The refrigerant density in the intermediate heat exchanger
(42) where inflow refrigerant has a high pressure is higher than
that in the intermediate heat exchanger (41) where inflow
refrigerant has a low pressure. Thus, when the mass flow rate of
refrigerant flowing in the low-pressure intermediate heat exchanger
(41) is substantially equal to that of refrigerant flowing in the
high-pressure intermediate heat exchanger (42), the volume flow
rate of refrigerant in the low-pressure intermediate heat exchanger
(42) is higher than that of refrigerant in the high-pressure
intermediate heat exchanger (42). Even when the number of
refrigerant paths in the low-pressure intermediate heat exchanger
(41) is equal to that in the high-pressure intermediate heat
exchanger (42), the flow velocity of refrigerant flowing in the
low-pressure intermediate heat exchanger (41) is higher than that
of refrigerant flowing in the high-pressure intermediate heat
exchanger (42), and thus, a pressure loss of refrigerant in the
low-pressure intermediate heat exchanger (41) is larger than that
of refrigerant in the high-pressure intermediate heat exchanger
(42).
[0033] The high-pressure intermediate heat exchanger (42) located
in an upper portion of the casing (121) where the airflow velocity
is high, has a high heat exchange efficiency, and can be reduced in
size. On the other hand, the low-pressure intermediate heat
exchanger (41) located in a lower portion of the casing (121) where
the airflow velocity is low, has a low heat exchange efficiency.
Thus, to increase the amount of heat exchange, the low-pressure
intermediate heat exchanger (41) needs to be larger than that in a
case where this exchanger is located in an upper portion.
[0034] For this reason, the size of the outdoor unit does not
increase even when the size of the high-pressure intermediate heat
exchanger (42) and the low-pressure intermediate heat exchanger
(41) increases.
[0035] An increase in size of the low-pressure intermediate heat
exchanger (41) increases the number of refrigerant paths in the
low-pressure intermediate heat exchanger (41). Thus, in the
low-pressure intermediate heat exchanger (41), the flow velocity of
refrigerant in each refrigerant path decreases, resulting in a
decrease in pressure loss of refrigerant passing through the
refrigerant path. The flow velocity of refrigerant flowing in the
low-pressure intermediate heat exchanger (41) is originally high,
and thus, a decrease in flow velocity due to an increase in the
number of refrigerant paths relatively greatly reduces the pressure
loss.
[0036] On the other hand, size reduction of the high-pressure
intermediate heat exchanger (42) reduces the number of refrigerant
paths in the high-pressure intermediate heat exchanger (42). The
reduction of the number of refrigerant paths increases the flow
velocity of refrigerant in each refrigerant path to increase the
pressure loss of refrigerant passing through the refrigerant
path.
[0037] However, since the flow velocity of refrigerant flowing in
the high-pressure intermediate heat exchanger (42) is originally
low, a certain degree of increase in flow velocity due to the
reduction of the number of refrigerant paths relatively slightly
increases the pressure loss arising from the increase in flow
velocity.
[0038] Thus, by disposing the high-pressure intermediate heat
exchanger (42) above the low-pressure intermediate heat exchanger
(41), the pressure loss of refrigerant in the low-pressure
intermediate heat exchanger (41) can be reduced with a reduced
degree of increase in size of the outdoor unit.
[0039] In a fourth aspect, in the outdoor unit of one of the first
through third aspects, the intermediate heat exchanger (41, 42, 43,
161) includes a plurality of flat tubes (231) which are arranged in
an up and down direction with their side surfaces facing one
another and each of which includes a plurality of fluid passage
(232) extending in a tube length direction, and also includes a
plurality of fins (235, 235) dividing space between adjacent ones
of the flat tubes (231) into a plurality of air passages in which
air flows.
[0040] In the fourth aspect, the plurality of flat tubes (231) and
the plurality of fins (235, 235) are provided. The fins (235, 235)
are disposed between the flat tubes (231) arranged in the up and
down direction. In the intermediate heat exchanger (41, 42, 43,
161), air passes between the flat tubes (231) arranged in the up
and down direction, and exchanges heat with fluid flowing in the
fluid passages (232) in the flat tubes (231).
[0041] The intermediate heat exchanger (41, 42, 43, 161) has a
small stack loss (resistance of ventilation), and thus, has a high
velocity of air flowing therein. In addition, the flat tubes (231)
increase the heat transfer area of refrigerant, and thus, the heat
exchange efficiency of refrigerant increases. Accordingly, the
coefficient of performance (COP) of the refrigeration system can be
enhanced. Since the flat tubes (231) have pipe diameters smaller
than those of conventional heat exchanger tubes, the flow velocity
in the tubes increases. Thus, refrigerant passing through the fluid
passage (232) has a large pressure loss.
[0042] However, in the intermediate heat exchanger (41, 42, 43,
161) located in the lower portion of the casing (121, 163) where
the airflow velocity is low has a low heat exchange efficiency.
Thus, to increase the amount of heat exchange, the intermediate
heat exchanger (41, 42, 43, 161) is larger than that in a case
where the exchanger is located in an upper portion. The larger
intermediate heat exchanger (41, 42, 43, 161) includes a larger
number of the refrigerant paths (232), and thus, the flow velocity
of refrigerant in the refrigerant paths (232) of the intermediate
heat exchanger (41, 42, 43, 161) decreases, thereby reducing the
pressure loss of refrigerant occurring when refrigerant passes
through the refrigerant paths (232).
[0043] Consequently, reduction in diameter of the pipe diameter of
the flat tubes (231) relatively reduces the degree of increase in
pressure loss of refrigerant.
[0044] In a fifth aspect, in the outdoor unit of the fourth aspect,
the outdoor heat exchangers (44, 162) includes a plurality of flat
tubes (231) which are arranged in the up and down direction with
their side surfaces facing one another, and each of which includes
a plurality of fluid passage (232) extending in a tube length
direction, and also includes a plurality of fins (235, 235)
dividing space between adjacent ones of the flat tubes (231) into a
plurality of air passages in which air flows.
[0045] In the fifth aspect, the plurality of flat tubes (231) and
the plurality of fins (235, 235) are provided. The fins (235, 235)
are disposed between the flat tubes (231) arranged in the up and
down direction. In the outdoor heat exchanger (44, 162), air passes
between the flat tubes (231) arranged in the up and down direction,
and exchanges heat with fluid flowing in the fluid passages (232)
in the flat tubes (231).
[0046] The outdoor heat exchanger (44, 162) has a small stack loss,
and thus, has a high velocity of air flowing therein. In addition,
the flat tubes (231) increase the heat transfer area of
refrigerant, and thus, the heat exchange efficiency of refrigerant
increases. Accordingly, the coefficient of performance (COP) of the
refrigeration system is enhanced. Since the flat tubes (231) have
pipe diameters smaller than those of conventional heat exchanger
tubes, the flow velocity in the tubes increases. Thus, refrigerant
passing through the fluid passages (232) has a large pressure
loss.
[0047] However, since the flow velocity of refrigerant flowing in
the outdoor heat exchangers (44, 162) is originally low, a certain
degree of increase in flow velocity due to a decrease in the
diameters of pipes relatively slightly increases the pressure loss
arising from the increase in flow velocity.
Advantages of the Invention
[0048] In the first aspect, since the outdoor heat exchanger (44,
162) is located in the upper portion of the casing (121, 163) where
the airflow velocity is high, the heat exchange efficiency of the
outdoor heat exchanger (44, 162) can be increased. In addition,
since the outdoor heat exchanger (44, 162) having a low flow
velocity of refrigerant is located in the upper portion of the
casing (121, 163) where the airflow velocity is high, the size of
the outdoor heat exchanger (44, 162) can be reduced without an
increase in pressure loss of refrigerant.
[0049] On the other hand, the intermediate heat exchanger (41, 42,
43, 161) is located in the lower portion of the casing (121, 163)
where the airflow velocity is low to increase the number of
refrigerant paths, thereby ensuring prevention of an increase in
pressure loss of refrigerant in the intermediate heat exchanger
(41, 42, 43, and 161).
[0050] In the above-described configuration, the outdoor heat
exchanger (44, 162) where a pressure loss of refrigerant does not
easily increase is located in the upper portion for size reduction,
thereby reducing a pressure loss of refrigerant in the intermediate
heat exchanger (41, 42, 43, 161) with reduced size increase in the
outdoor unit.
[0051] In the second aspect, since the highest-stage intermediate
heat exchanger (43) is located in the upper portion of the casing
(121) where the airflow velocity is high, the heat exchange
efficiency of the highest-stage intermediate heat exchanger (43)
can be increased. In addition, since the highest-stage intermediate
heat exchanger (43) having a low flow velocity of refrigerant is
located in the upper portion of the casing (121) where the airflow
velocity is high, the size of the highest-stage intermediate heat
exchanger (43) can be reduced without an increase in pressure loss
of refrigerant.
[0052] On the other hand, the other heat exchangers (41, 42) having
large flow velocities of refrigerant are located in the lower
portion of the casing (121) where the airflow velocity is low to
increase the number of paths for refrigerant, thereby ensuring
prevention of an increase in pressure loss of refrigerant in the
other intermediate heat exchangers (41, 42).
[0053] In the above-described configuration, the highest-stage
intermediate heat exchanger (43) where a pressure loss of
refrigerant does not easily increase is located in the upper
portion for size reduction, thereby reducing a pressure loss of
refrigerant in the other intermediate heat exchangers (41, 42) with
reduced size increase in the outdoor unit.
[0054] In the third aspect, since the high-pressure intermediate
heat exchanger (42) is located in the upper portion of the casing
(121) where the airflow velocity is high, the heat exchange
efficiency of the high-pressure intermediate heat exchanger (42)
can be increased. In addition, since the high-pressure intermediate
heat exchanger (42) having a low flow velocity of refrigerant is
located in the upper portion of the casing (121) where the airflow
velocity is high, the size of the high-pressure intermediate heat
exchanger (42) can be reduced without an increase in pressure loss
of refrigerant.
[0055] On the other hand, the low-pressure intermediate heat
exchanger (41) having a large flow velocity of refrigerant is
located in the lower portion of the casing (121) where the airflow
velocity is low to increase the number of paths for refrigerant,
thereby ensuring prevention of an increase in pressure loss of
refrigerant in the low-pressure intermediate heat exchanger
(41).
[0056] In the above-described configuration, the high-pressure
intermediate heat exchanger (42) where a pressure loss of
refrigerant does not easily increase is located in the upper
portion for size reduction, thereby reducing a pressure loss of
refrigerant in the low-pressure intermediate heat exchanger (41)
with reduced size increase in the outdoor unit.
[0057] In the fourth aspect, the plurality of flat tubes (231), in
which the plurality of fluid passages (232) are provided, and the
plurality of fins (235, 235) are provided, thereby reducing a stack
loss. Thus, the flow velocity of air flowing in the air passages
increases. In addition, the flat tubes (231) increase the heat
transfer area of refrigerant, and thus, heat exchange efficiency of
refrigerant can be increased. Accordingly, the coefficient of
performance (COP) of the refrigeration system can be enhanced.
[0058] In the fifth aspect, the plurality of flat tubes (231), in
which the plurality of fluid passages (232) are provided, and the
plurality of fins (235, 235) are provided, thereby reducing a stack
loss. Thus, the flow velocity of air flowing in the air passages
increases. In addition, the flat tubes (231) increase the heat
transfer area of refrigerant, and thus, heat exchange efficiency of
refrigerant can be increased. Accordingly, the coefficient of
performance (COP) of the refrigeration system can be enhanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] FIG. 1 is a piping system diagram illustrating cooling
operation of a refrigerant circuit according to a first
embodiment.
[0060] FIG. 2 is a mollier chart of the refrigerant circuit of the
first embodiment.
[0061] FIG. 3 illustrates an outdoor unit according to the first
embodiment.
[0062] FIG. 4 is a top view schematically illustrating the outdoor
unit of the first embodiment.
[0063] FIG. 5 is a cross-sectional view taken along line V-V in
FIG. 4.
[0064] FIG. 6 illustrates an airflow velocity distribution in an
outdoor casing according to the first embodiment.
[0065] FIG. 7 is a piping system diagram illustrating heating
operation of the refrigerant circuit of the first embodiment.
[0066] FIG. 8 is a piping system diagram illustrating cooling
operation of a refrigerant circuit according to a second
embodiment.
[0067] FIG. 9 is a mollier chart of the refrigerant circuit of the
second embodiment.
[0068] FIG. 10 is a piping system diagram illustrating cooling
operation of a refrigerant circuit according to a third
embodiment.
[0069] FIG. 11 is a mollier chart of the refrigerant circuit of the
third embodiment.
[0070] FIG. 12 illustrates an outdoor unit according to the third
embodiment.
[0071] FIG. 13 is a piping system diagram illustrating heating
operation of the refrigerant circuit of the third embodiment.
[0072] FIG. 14 schematically illustrates an outdoor unit according
to a variation of the third embodiment.
[0073] FIG. 15 is an enlarged view of flat tubes and fins of a heat
exchanger according to the variation of the third embodiment.
[0074] FIG. 16 schematically illustrates an outdoor unit according
to another embodiment.
[0075] FIG. 17 is an enlarged view of flat tubes and fins of a heat
exchanger according to the another embodiment.
[0076] FIGS. 18A and 18B schematically illustrate a configuration
of an outdoor unit according to a reference example, where FIG. 18A
illustrates an example layout of an outdoor heat exchange unit, and
FIG. 18B illustrates an airflow velocity distribution of the
outdoor heat exchange unit.
[0077] FIG. 19 is a cross-sectional view illustrating an outdoor
heat exchange unit according to the reference example.
[0078] FIG. 20 illustrates an outdoor unit according to a
conventional example.
[0079] FIGS. 21A and 21B schematically illustrate a configuration
of the outdoor unit of the conventional example, where FIG. 21A
illustrates an example layout of an outdoor heat exchange unit, and
FIG. 21B illustrates an airflow velocity distribution of the
outdoor heat exchange unit.
DESCRIPTION OF EMBODIMENTS
[0080] Embodiments of the present invention will be described in
detail with reference to the drawings.
First Embodiment
Refrigerant Circuit of Air Conditioner
[0081] As illustrated in FIG. 1, an air conditioner (1) according
to the first embodiment will be described. The air conditioner (1)
includes a refrigerant circuit (10) in which a flow of refrigerant
is allowed to be changed reversibly, and is switchable between
cooling operation and heating operation. The air conditioner (1)
includes an outdoor unit (3) located outdoors and an indoor unit
(2) located indoors. The refrigerant circuit (10) of the air
conditioner (1) is obtained by connecting an outdoor circuit (11)
of the outdoor unit (3) and an indoor circuit (12) of the indoor
unit (2) to each other through a gas-side communication pipe (13)
and a liquid-side communication pipe (14). The refrigerant circuit
(10) is filled with carbon dioxide (hereinafter referred to as
refrigerant), and configured to perform a multistage compression
supercritical refrigeration cycle by circulating refrigerant in the
refrigerant circuit (10).
[0082] <Outdoor Circuit>
[0083] As illustrated in FIG. 1, the outdoor circuit (11) is
connected to a four-stage compressor (20), an outdoor heat exchange
unit (40), first through fourth four-way valves (93, 94, 95, 96),
first through third subcooling heat exchangers (100, 101, 102),
first through fifth expansion valves (80-84), an expander (87), and
a gas-liquid separator (88). The outdoor heat exchange unit (40)
includes first through third intermediate heat exchangers (41, 42,
43) and an outdoor heat exchanger (44).
[0084] The outdoor heat exchanger (44) in this embodiment
corresponds to an outdoor heat exchanger of the present invention,
and the first through third intermediate heat exchangers (41, 42,
43) are intermediate heat exchangers of the present invention. The
first and second intermediate heat exchangers (41, 42) are other
intermediate heat exchangers of the present invention, and the
third intermediate heat exchanger (43) is a highest-stage
intermediate heat exchanger of the present invention.
[0085] The outdoor circuit (11) is also connected to four oil
separators (89, 90, 91, 92), a distributor (18), a capillary tube
(15), a bridge circuit (17), and check valves (CV1-CV13).
[0086] In the first embodiment, the refrigerant circuit (10) is
switched between cooling operation and heating operation by
switching the first through fourth four-way valves (93, 94, 95,
96).
[0087] The four-stage compressor (20) includes first through fourth
compressors (21, 22, 23, 24) and corresponds to a multistage
compressor of the present invention. The first through fourth
compressors (21, 22, 23, 24) are connected to first through fourth
discharge pipes (25, 26, 27, 28) at discharge sides thereof, while
being connected to first through fourth suction pipes (29, 30, 31,
32) at suction sides thereof. Each of the compressors (21, 22, 23,
24) compresses a gas refrigerant sucked through an associated one
of the suction pipes (29, 30, 31, 32) to a predetermined pressure,
and discharges this refrigerant from an associated one of the
discharge pipes (25, 26, 27, 28).
[0088] The first four-way valve (93) has its first port connected
to the first discharge pipe (25) of the first compressor (21), its
second port connected to an end of a junction pipe (67), its third
port connected to an end of the first intermediate heat exchanger
(41), and its fourth port connected to the second suction pipe (30)
of the second compressor (22). The first four-way valve (93) is
switched between a first state (a state indicated by a continuous
line in FIG. 1) in which the first port communicates with the third
port and the second port communicates with the fourth port and a
second state (a state indicated by a broken line in FIG. 1) in
which the first port communicates with the fourth port and the
second port communicates with the third port.
[0089] The second four-way valve (94) has its first port connected
to the second discharge pipe (26) of the second compressor (22),
its second port connected to a midpoint of the junction pipe (67),
its third port connected to an end of the second intermediate heat
exchanger (42), and its fourth port connected to the third suction
pipe (31) of the third compressor (23). The second four-way valve
(94) is switched between a first state (a state indicated by a
continuous line in FIG. 1) in which the first port communicates
with the third port and the second port communicates with the
fourth port and a second state (a state indicated by a broken line
in FIG. 1) in which the first port communicates with the fourth
port and the second port communicates with the third port.
[0090] The third four-way valve (95) has its first port connected
to the third discharge pipe (27) of the third compressor (23), its
second port connected to a midpoint of the junction pipe (67), and
its third port connected to an end of the third intermediate heat
exchanger (43), and its fourth port connected to the fourth suction
pipe (32) of the fourth compressor (24). The third four-way valve
(95) is switched between a first state (a state indicated by a
continuous line in FIG. 1) in which the first port communicates
with the third port and the second port communicates with the
fourth port and a second state (a state indicated by a broken line
in FIG. 1) in which the first port communicates with the fourth
port and the second port communicates with the third port.
[0091] The fourth four-way valve (96) has its first port connected
to the fourth discharge pipe (28) of the fourth compressor (24),
its second port connected to an end of the connection pipe (66),
its third port connected to an end of the outdoor heat exchanger
(44), and its fourth port connected to the gas-side communication
pipe (13). The fourth four-way valve (96) is switched between a
first state (a state indicated by a continuous line in FIG. 1) in
which the first port communicates with the third port and the
second port communicates with the fourth port and a second state (a
state indicated by a broken line in FIG. 1) in which the first port
communicates with the fourth port and the second port communicates
with the third port.
[0092] The check valves (CV1, CV2, CV3) are connected to midpoints
of the second through fourth suction pipes (30, 31, 32). Each of
the check valves (CV1, CV2, CV3) allows refrigerant to flow from
the first through third four-way valves (93, 94, 95) to the
four-stage compressor (20), and prevents refrigerant from flowing
in a reverse direction.
[0093] Oil separators (89, 90, 91, 92) are connected to midpoints
of the first through fourth discharge pipes (25, 26, 27, 28),
respectively. The oil separators (89, 90, 91, 92) are used to
separate lubricating oil contained in refrigerant flowing in the
discharge pipes (25, 26, 27, 28) from refrigerant. The oil
separators (89, 90, 91, 92) are connected to oil outflow pipes (16,
16, 16, 16) through which lubricating oil separated in the oil
separators (89, 90, 91, 92) flows to the outside of the oil
separators (89, 90, 91, 92).
[0094] Specifically, the oil outflow pipe (16) of the first oil
separator (89) for the first discharge pipe (25) is connected to
the second suction pipe (30). The oil outflow pipe (16) of the
second oil separator (90) for the second discharge pipe (26) is
connected to the third suction pipe (31). The oil outflow pipe (16)
of the third oil separator (91) for the third discharge pipe (27)
is connected to the fourth suction pipe (32). The oil outflow pipe
(16) of the fourth oil separator (92) for the fourth discharge pipe
(28) is connected to the first suction pipe (29). The capillary
tube (15) is connected to the midpoint of each of the oil outflow
pipes (16, 16, 16, 16).
[0095] The first through third intermediate heat exchangers (41,
42, 43) and the outdoor heat exchanger (44) are configured as
fin-and-tube heat exchangers. An outdoor fan (122) is disposed near
each of the heat exchangers (41, 42, 43, 44) so that heat exchange
is performed between outdoor air from the outdoor fan (122) and
refrigerant flowing in the heat exchanger tubes (52) of each of the
heat exchangers (41, 42, 43, 44). The configurations of the heat
exchangers (41, 42, 43, 44) will be described in detail.
[0096] An end of the first intermediate heat exchanger (41) is
connected to the third port of the first four-way valve (93), an
end of the second intermediate heat exchanger (42) is connected to
the third port of the second four-way valve (94), an end of the
third intermediate heat exchanger (43) is connected to the third
port of the third four-way valve (95), and an end of the outdoor
heat exchanger (44) is connected to the third port of the fourth
four-way valve (96). On the other hand, the other ends of the first
through third intermediate heat exchangers (41, 42, 43) are
connected to the first through third refrigerant pipes (70, 71,
72), respectively, and the other end of the outdoor heat exchanger
(44) is connected to an end of the fourth refrigerant pipe
(73).
[0097] The other end of the fourth refrigerant pipe (73) branches
off into two parts, one of which is connected to the bridge circuit
(17) and the other of which is connected to a fourth outflow port
(P4) of the distributor (18). The check valve (CV7) and the
capillary tube (15) are located between the branch point of the
fourth refrigerant pipe (73) and the fourth outflow port (P4) of
the distributor. The check valve (CV7) allows refrigerant to flow
from the distributor (18) to the branch point of the fourth
refrigerant pipe (73), and prevents refrigerant from flowing in a
reverse direction.
[0098] The other end of the third refrigerant pipe (72) branches
off into two parts, one of which is connected to a midpoint
(between the check valve (CV3) and the fourth compressor (24)) of
the fourth suction pipe (32), and the other of which is connected
to a third outflow port (P3) of the distributor (18). The check
valve (CV6) and the capillary tube (15) are located between the
branch point of the third refrigerant pipe (72) and the third
outflow port (P3) of the distributor (18). The check valve (CV6)
allows refrigerant to flow from the distributor (18) to the branch
point of the third refrigerant pipe (72), and prevents refrigerant
from flowing in a reverse direction. The check valve (CV10) is
located between the branch point of the third refrigerant pipe (72)
and the connection point of the fourth suction pipe (32). The check
valve (CV10) allows refrigerant to flow from the branch point of
the third refrigerant pipe (72) to the connection point of the
fourth suction pipe (32), and prevents refrigerant from flowing in
a reverse direction.
[0099] The other end of the second refrigerant pipe (71) branches
off into two parts, one of which is connected to a midpoint
(between the check valve (CV2) and the third compressor (23)) of
the third suction pipe (31), and the other of which is connected to
a second outflow port (P2) of the distributor (18). The check valve
(CV5) and the capillary tube (15) are located between the branch
point of the second refrigerant pipe (71) and the second outflow
port (P2) of the distributor (18). The check valve (CV5) allows
refrigerant to flow from the distributor (18) to the branch point
of the second refrigerant pipe (71), and prevents refrigerant from
flowing in a reverse direction. The check valve (CV9) is located
between the branch point of the second refrigerant pipe (71) and
the connection point of the third suction pipe (31). The check
valve (CV9) allows refrigerant to flow from the branch point of the
second refrigerant pipe (71) to the connection point of the third
suction pipe (31), and prevents refrigerant from flowing in a
reverse direction.
[0100] The other end of the first refrigerant pipe (70) branches
off into two parts, one of which is connected to a midpoint
(between the check valve (CV1) and the second compressor (22)) of
the second suction pipe (30), and the other of which is connected
to a first outflow port (P1) of the distributor (18). The check
valve (CV4) and the capillary tube (15) are located between the
branch point of the first refrigerant pipe (70) and the first
outflow port (P1) of the distributor (18). The check valve (CV4)
allows refrigerant to flow from the distributor (18) to the branch
point of the first refrigerant pipe (70), and prevents refrigerant
from flowing in a reverse direction. The check valve (CV8) is
located between the branch point of the first refrigerant pipe (70)
and the connection point of the second suction pipe (30). The check
valve (CV8) allows refrigerant to flow from the branch point of the
first refrigerant pipe (70) to the connection point of the second
suction pipe (30), and prevents refrigerant from flowing in a
reverse direction.
[0101] The bridge circuit (17) is a circuit in which the check
valves (CV11, CV12, CV13) and a fifth expansion valve (84) are
bridged. In the bridge circuit (17), a connection end located
between an inflow end of the check valve (CV13) and the other end
of the fifth expansion valve (84) is connected to the first outflow
pipe (61), and a connection end located between an outflow end of
the check valve (CV13) and an inflow end of the check valve (CV12)
is connected to the liquid-side communication pipe (14). A
refrigerant pipe connecting the liquid-side communication pipe (14)
to the first indoor heat exchanger (110) includes a first indoor
expansion valve (85) having a variable opening degree. A
refrigerant pipe connecting the liquid-side communication pipe (14)
to the second indoor heat exchanger (111) includes a second indoor
expansion valve (86) having a variable opening degree. A connection
end located between an outflow end of the check valve (CV 12) and
an outflow end of the check valve (CV11) is connected to the inflow
pipe (60). An end of the fifth expansion valve (84) is connected to
the distributor (18), and the inflow end of the check valve (CV11)
is connected to the fourth refrigerant pipe (73).
[0102] On the inflow pipe (60), the first subcooling heat exchanger
(100), the second subcooling heat exchanger (101), expander (87),
the gas-liquid separator (88), and the third subcooling heat
exchanger (102) are disposed in this order.
[0103] The first subcooling heat exchanger (100) includes a
high-pressure channel (100a) and a low-pressure channel (100b). In
the first subcooling heat exchanger (100), heat exchange is
performed between refrigerant flowing in the high-pressure channel
(100a) and refrigerant flowing in the low-pressure channel (100b)
to subcool refrigerant flowing in the high-pressure channel
(100a).
[0104] An inflow end of the high-pressure channel (100a) is
connected to the inflow pipe (60), and an inflow end of the
low-pressure channel (100b) is connected to a first branch pipe
(62) serving as a passage for subcooling. The first branch pipe
(62) includes a second expansion valve (81) for subcooling. The
second expansion valve (81) is an electronic expansion valve having
an adjustable opening degree. An outflow end of the low-pressure
channel (100b) is connected to an end of the injection pipe
(106).
[0105] An end of the injection pipe (106) is connected to the
low-pressure channel (100b) of the first subcooling heat exchanger
(100) and the other end of the injection pipe (106) is connected to
the second refrigerant pipe (71). Specifically, the other end of
the injection pipe (106) is connected to an outflow end of the
check valve (CV9) in the second refrigerant pipe (71).
[0106] The second subcooling heat exchanger (101) includes a
high-pressure channel (101a) and a low-pressure channel (101b). In
the second subcooling heat exchanger (101), heat exchange is
performed between refrigerant flowing high-pressure channel (101a)
and refrigerant flowing in the low-pressure channel (101b) to
subcool refrigerant flowing in the high-pressure channel
(101a).
[0107] An inflow end of the high-pressure channel (101a) is
connected to the inflow pipe (60). An inflow end of the
low-pressure channel (101b) is connected to the other end of the
connection pipe (66), and an outflow end of the low-pressure
channel (101b) is connected to the first suction pipe (29).
[0108] An end of the connection pipe (66) is connected to the
second port of the fourth four-way valve (96), and the other end of
the connection pipe (66) is connected to an inflow end of the
low-pressure channel (101b) of the second subcooling heat exchanger
(101). The other end of the junction pipe (67) is connected to a
midpoint of the connection pipe (66).
[0109] An end of the junction pipe (67) is connected to the second
port of the first four-way valve (93), and the other end of the
junction pipe (67) is connected to a midpoint of the connection
pipe (66). A pipe communicating with the second port of the second
four-way valve (94) and the second port of the third four-way valve
(95) is connected to a midpoint of the junction pipe (67).
[0110] The expander (87) includes an expander casing having a
vertically elongated cylindrical shape, and is located between the
second subcooling heat exchanger (101) and the gas-liquid separator
(88) on the inflow pipe (60). In the expander casing, an expansion
mechanism for generating power by expanding refrigerant is
provided. The expander (87) constitutes a so-called rotary
positive-displacement fluid machine. The expander (87) expands
inflow refrigerant and sends the expanded refrigerant back to the
inflow pipe (60).
[0111] The inflow pipe (60) includes a bypass pipe (64) that
bypasses the expander (87). An end of the bypass pipe (64) is
connected to an inflow end of the expander (87), and the other end
of the bypass pipe (64) is connected to an outflow end of the
expander (87) to bypass the expander (87). The bypass pipe (64)
includes a first expansion valve (80). The first expansion valve
(80) is an electronic expansion valve having an adjustable opening
degree.
[0112] The gas-liquid separator (88) is an hermetic container
having a vertically elongated cylindrical shape. The gas-liquid
separator (88) is connected to the inflow pipe (60), the first
outflow pipe (61), and the second outflow pipe (65). The inflow
pipe (60) is open in an upper portion of the inner space of the
gas-liquid separator (88). The first outflow pipe (61) is open in a
lower portion of the inner space of the gas-liquid separator (88).
The second outflow pipe (65) is open in an upper portion of the
inner space of the gas-liquid separator (88). In the gas-liquid
separator (88), refrigerant from the inflow pipe (60) is separated
into a saturated liquid and a saturated gas, where the saturated
liquid flows out of the first outflow pipe (61) and the saturated
gas flows out of the second outflow pipe (65).
[0113] An end of the second outflow pipe (65) is connected to the
gas-liquid separator (88), and the other end of the second outflow
pipe (65) is connected to a midpoint of the return pipe (68). The
second outflow pipe (65) includes a fourth expansion valve (83).
The fourth expansion valve (83) is an electronic expansion valve
having an adjustable opening degree.
[0114] The third subcooling heat exchanger (102) is connected to a
midpoint of the first outflow pipe (61). The third subcooling heat
exchanger (102) includes a high-pressure channel (102a) and a
low-pressure channel (102b). In the third subcooling heat exchanger
(102), heat exchange is performed between refrigerant flowing in
the high-pressure channel (102a) and refrigerant flowing in the
low-pressure channel (102b) to subcool refrigerant flowing in the
high-pressure channel (102a).
[0115] An inflow end of the high-pressure channel (102a) is
connected to an outflow end of the gas-liquid separator (88), and
an outflow end of the high-pressure channel (102a) is connected to
the bridge circuit (17). An inflow end of the low-pressure channel
(102b) is connected to a second branch pipe (63) serving as a
passage for subcooling, and an outflow end of the low-pressure
channel (102b) is connected to the other end of the return pipe
(68).
[0116] An end of the second branch pipe (63) is connected to a
point of the first outflow pipe (61) between the gas-liquid
separator (88) and the third subcooling heat exchanger (102), and
the other end of the second branch pipe (63) is connected to an
inflow end of the low-pressure channel (102b) of the third
subcooling heat exchanger (102). The second branch pipe (63)
includes a third expansion valve (82). The third expansion valve
(82) is an electronic expansion valve having an adjustable opening
degree.
[0117] One end of the return pipe (68) is connected to the other
end of the connection pipe (66), and the other end of the return
pipe (68) is connected to an outflow end of the low-pressure
channel (102b) of the third subcooling heat exchanger (102). The
second outflow pipe (65) is connected to a point of the return pipe
(68) between the one end and the other end.
[0118] <Indoor Circuit>
[0119] In the indoor circuit (12), a pair of the first indoor
expansion valve (85) and the first indoor heat exchanger (110) and
a pair of the second indoor expansion valve (86) and the second
indoor heat exchanger (111) are disposed in this order from a
liquid side to a gas side, and are connected in parallel. Each of
the indoor expansion valves (85, 86) is an electronic expansion
valve having an adjustable opening degree. Each of the indoor heat
exchangers (110, 111) is a cross-fin type fin-and-tube heat
exchanger. Although not shown, indoor fans for sending indoor air
to the indoor heat exchangers (110, 111) are provided near the
indoor heat exchangers (110, 111). In each of the indoor heat
exchangers (110, 111), heat exchange is performed between
refrigerant and the indoor air.
[0120] <Configuration of Outdoor Unit>
[0121] As illustrated in FIGS. 3-5, the outdoor unit (3) includes
an outdoor casing (121) that is a casing of the present invention.
The outdoor casing (121) is in the shape of a vertically elongated
rectangular box, and has an air inlet (123) in a lower portion of
the front surface and an air outlet (124) in an upper surface
thereof. The air inlet (123) is a suction port of the present
invention. In the outdoor casing (121), the outdoor heat exchanger
(44), the first intermediate heat exchanger (41), the second
intermediate heat exchanger (42), and the third intermediate heat
exchanger (43) constituting the outdoor heat exchange unit (40),
and the outdoor fan (122) are placed. Each of the heat exchangers
(41, 42, 43, 44) has an approximately U shape in plan view, and
stands along the air inlet (123).
[0122] The outdoor fan (122) is a fan for sending air taken in the
outdoor casing (121) to the heat exchangers (41, 42, 43, 44), and
is a so-called sirocco fan. The outdoor fan (122) is located above
the heat exchangers (41, 42, 43, 44) in the outdoor casing (121).
The outdoor fan (122) causes air sucked through the air inlet (123)
to pass through the heat exchangers (41, 42, 43, 44) and then to
flow to the outside through the air outlet (124).
[0123] As illustrated in FIG. 5, in the outdoor casing (121), the
first intermediate heat exchanger (41), the second intermediate
heat exchanger (42), the third intermediate heat exchanger (43),
and the outdoor heat exchanger (44) are stacked in this order from
the bottom to the top. The first intermediate heat exchanger (41)
and the second intermediate heat exchanger (42) may be replaced
with each other in the up and down direction.
[0124] The first intermediate heat exchanger (41) is a so-called
cross-fin type fin-and-tube heat exchanger. The first intermediate
heat exchanger (41) includes a plurality of heat exchanger tube
groups (50) each including a plurality of heat exchanger tubes (52)
and a plurality of U-shaped tubes, and also includes heat
transmission fins (51).
[0125] As the heat exchanger tube groups (50), seven heat exchanger
tube groups (50) are aligned in the up and down direction. In each
of the heat exchanger tube groups (50), a plurality of (six in FIG.
5) heat exchanger tubes (52) are arranged such that three rows of
heat exchanger tubes (52) each along an airflow direction are
arranged side by side and each of the three rows includes two heat
exchanger tubes (52) aligned in the up and down direction. In
addition, a first bank of tubes (53) is disposed at the left in
FIG. 5 (i.e., the windward side), a second bank of tubes (54) is
disposed at the middle in FIG. 5, and a third bank of tubes (55) is
disposed at the right in FIG. 5 (i.e., the leeward side). That is,
in each of the heat exchanger tube groups (50), the heat exchanger
tubes (52) are disposed in two stages in each row.
[0126] In each of the heat exchanger tube groups (50), among the
heat exchanger tubes (52), ends of the heat exchanger tubes (52) at
one side except an end (a first end) of the upper-stage heat
exchanger tubes (52) of the first bank of tubes (53) and an end (a
second end) of the lower-stage heat exchanger tubes (52) of the
third bank of tubes (55) are connected together with the U-shaped
tubes, thereby forming one refrigerant path whose one end is the
first end and the other end is the second end. The first end of the
first bank of tubes (53) of each of the heat exchanger tube groups
(50) is connected to the first refrigerant pipe (70) of the
refrigerant circuit (10) via headers. The second end of the third
bank of tubes (55) of each of the heat exchanger tube groups (50)
communicates with the third port of the first four-way valve
(93).
[0127] As illustrated in FIG. 5, each of the heat transmission fins
(51) is in the shape of an approximately rectangular thin plate.
The heat transmission fins (51) are arranged at predetermined
intervals along the direction in which the heat exchanger tube
groups (50) extend. Each of the heat transmission fins (51) has
three rows of through holes through which the heat exchanger tubes
(52) penetrate. In this manner, the heat transmission fins (51) are
disposed around the heat exchanger tubes (52), and thereby, the
heat transfer area increases so that heat transmission is
promoted.
[0128] The second intermediate heat exchanger (42) is a so-called
cross-fin type fin-and-tube heat exchanger. The second intermediate
heat exchanger (42) includes a plurality of heat exchanger tube
groups (50) each including a plurality of heat exchanger tubes (52)
and a plurality of U-shaped tubes, and also includes heat
transmission fins (51).
[0129] As the heat exchanger tube groups (50), seven heat exchanger
tube groups (50) are aligned in the up and down direction. In each
of the heat exchanger tube groups (50), a plurality of (six in FIG.
5) heat exchanger tubes (52) are arranged such that three rows of
heat exchanger tubes (52) each along an airflow direction are
arranged side by side and each of the three rows includes two heat
exchanger tubes (52) aligned in the up and down direction. In
addition, a first bank of tubes (53) is disposed at the left in
FIG. 5 (i.e., the windward side), a second bank of tubes (54) is
disposed at the middle in FIG. 5, and a third bank of tubes (55) is
disposed at the right in FIG. 5 (i.e., the leeward side). That is,
in each of the heat exchanger tube groups (50), the heat exchanger
tubes (52) are disposed in two stages in each row.
[0130] In each of the heat exchanger tube groups (50), among the
heat exchanger tubes (52), ends of the heat exchanger tubes (52) at
one side except an end (a first end) of the upper-stage heat
exchanger tubes (52) of the first bank of tubes (53) and an end (a
second end) of the lower-stage heat exchanger tubes (52) of the
third bank of tubes (55) are connected together with the U-shaped
tubes, thereby forming one refrigerant path whose one end is the
first end and the other end is the second end. The first end of the
first bank of tubes (53) of each of the heat exchanger tube groups
(50) is connected to the second refrigerant pipe (71) of the
refrigerant circuit (10) via headers. The second end of the third
bank of tubes (55) of each of the heat exchanger tube groups (50)
communicates with the third port of the second four-way valve
(94).
[0131] As illustrated in FIG. 5, each of the heat transmission fins
(51) is in the shape of an approximately rectangular thin plate.
The heat transmission fins (51) are arranged at predetermined
intervals along the direction in which the heat exchanger tube
groups (50) extend. Each of the heat transmission fins (51) has
three rows of through holes through which the heat exchanger tubes
(52) penetrate. In this manner, the heat transmission fins (51) are
disposed around the heat exchanger tubes (52), and thereby, the
heat transfer area increases so that heat transmission is
promoted.
[0132] The third intermediate heat exchanger (43) is a so-called
cross-fin type fin-and-tube heat exchanger. The third intermediate
heat exchanger (43) includes a plurality of heat exchanger tube
groups (50) each including a plurality of heat exchanger tubes (52)
and a plurality of U-shaped tubes, and also includes heat
transmission fins (51).
[0133] As the heat exchanger tube groups (50), six heat exchanger
tube groups (50) are aligned in the up and down direction. In each
of the heat exchanger tube groups (50), a plurality of (six in FIG.
5) heat exchanger tubes (52) are arranged such that three rows of
heat exchanger tubes (52) each along an airflow direction are
arranged side by side and each of the three rows includes two heat
exchanger tubes (52) aligned in the up and down direction. In
addition, a first bank of tubes (53) is disposed at the left in
FIG. 5 (i.e., the windward side), a second bank of tubes (54) is
disposed at the middle in FIG. 5, and a third bank of tubes (55) is
disposed at the right in FIG. 5 (i.e., the leeward side). That is,
in each of the heat exchanger tube groups (50), the heat exchanger
tubes (52) are disposed in two stages in each row.
[0134] In each of the heat exchanger tube groups (50), among the
heat exchanger tubes (52), ends of the heat exchanger tubes (52) at
one side except an end (a first end) of the upper-stage heat
exchanger tubes (52) of the first bank of tubes (53) and an end (a
second end) of the lower-stage heat exchanger tubes (52) of the
third bank of tubes (55) are connected together with the U-shaped
tubes, thereby forming one refrigerant path whose one end is the
first end and the other end is the second end. The first end of the
first bank of tubes (53) of each of the heat exchanger tube groups
(50) is connected to the third refrigerant pipe (72) of the
refrigerant circuit (10) via headers. The second end of the third
bank of tubes (55) of each of the heat exchanger tube groups (50)
communicates with the third port of the third four-way valve
(95).
[0135] As illustrated in FIG. 5, each of the heat transmission fins
(51) is in the shape of an approximately rectangular thin plate.
The heat transmission fins (51) are arranged at predetermined
intervals along the direction in which the heat exchanger tube
groups (50) extend. Each of the heat transmission fins (51) has
three rows of through holes through which the heat exchanger tubes
(52) penetrate. In this manner, the heat transmission fins (51) are
disposed around the heat exchanger tubes (52), and thereby, the
heat transfer area increases so that heat transmission is
promoted.
[0136] The outdoor heat exchanger (44) is a so-called cross-fin
type fin-and-tube heat exchanger. The outdoor heat exchanger (44)
includes a plurality of heat exchanger tube groups (50) each
including a plurality of heat exchanger tubes (52) and a plurality
of U-shaped tubes, and also includes heat transmission fins
(51).
[0137] As the heat exchanger tube groups (50), eight heat exchanger
tube groups (50) are aligned in the up and down direction. In each
of the heat exchanger tube groups (50), a plurality of (six in FIG.
5) heat exchanger tubes (52) are arranged such that three rows of
heat exchanger tubes (52) each along an airflow direction are
arranged side by side and each of the three rows includes two heat
exchanger tubes (52) aligned in the up and down direction. In
addition, a first bank of tubes (53) is disposed at the left in
FIG. 5 (i.e., the windward side), a second bank of tubes (54) is
disposed at the middle in FIG. 5, and a third bank of tubes (55) is
disposed at the right in FIG. 5 (i.e., the leeward side). That is,
in each of the heat exchanger tube groups (50), the heat exchanger
tubes (52) are disposed in two stages in each row.
[0138] In each of the heat exchanger tube groups (50), among the
heat exchanger tubes (52), ends of the heat exchanger tubes (52) at
one side except an end (a first end) of the upper-stage heat
exchanger tubes (52) of the first bank of tubes (53) and an end (a
second end) of the lower-stage heat exchanger tubes (52) of the
third bank of tubes (55) are connected together with the U-shaped
tubes, thereby forming one refrigerant path whose one end is the
first end and the other end is the second end. The first end of the
first bank of tubes (53) of each of the heat exchanger tube groups
(50) is connected to the fourth refrigerant pipe (74) of the
refrigerant circuit (10) via headers. The second end of the third
bank of tubes (55) of each of the heat exchanger tube groups (50)
communicates with the third port of the fourth four-way valve
(96).
[0139] As illustrated in FIG. 5, each of the heat transmission fins
(51) is in the shape of an approximately rectangular thin plate.
The heat transmission fins (51) are arranged at predetermined
intervals along the direction in which the heat exchanger tube
groups (50) extend. Each of the heat transmission fins (51) has
three rows of through holes through which the heat exchanger tubes
(52) penetrate. In this manner, the heat transmission fins (51) are
disposed around the heat exchanger tubes (52), and thereby, the
heat transfer area increases so that heat transmission is
promoted.
[0140] --Operation--
[0141] Operation of the air conditioner (1) will now be described.
In the air conditioner (1), switching is performed among the first
through fourth four-way valves (93, 94, 95, 96) to switch operation
of the refrigerant circuit (10) between cooling operation and
heating operation. Reference numerals 1-26 in FIGS. 1 and 2
represent pressure states of refrigerant.
[0142] --Cooling Operation--
[0143] Cooling operation of the air conditioner (1) will be
described with reference to FIGS. 1 and 2. In FIG. 1, a refrigerant
flow in this cooling operation is represented by arrows of
continuous line. In the cooling operation, the outdoor heat
exchanger (44) operates as a heat dissipator, and the indoor heat
exchangers (110, 111) operate as evaporators, thereby performing a
four-stage compression supercritical refrigeration cycle. The first
through third intermediate heat exchangers (41, 42, 43) operate as
coolers that cool high-pressure refrigerant discharged from the
compressors (21, 22, 23).
[0144] In the cooling operation, all the four-way valves (93, 94,
95, 96) are set in the first states, and the four-stage compressor
(20) is driven. When the four-stage compressor (20) is driven,
refrigerant is compressed in the compressors (21, 22, 23, 24).
Refrigerant compressed in the first compressor (21) is discharged
to the first discharge pipe (25) (see "2" in FIGS. 1 and 2). In
this state, the first oil separator (89) of the first discharge
pipe (25) separates lubricating oil from gas refrigerant flowing in
the first discharge pipe (25). The separated lubricating oil is
sent from the oil outflow pipe (16) to the second suction pipe
(30). Refrigerant flowing in the first discharge pipe (25) passes
through the first four-way valve (93) and flows into the first
intermediate heat exchanger (41). In the first intermediate heat
exchanger (41), refrigerant dissipates heat to the outdoor air to
be cooled. Refrigerant cooled in the first intermediate heat
exchanger (41) flows into the first refrigerant pipe (70).
Refrigerant flowing in the first refrigerant pipe (70) passes
through the check valve (CV8), flows into the second suction pipe
(30), and is sucked into the second compressor (22) (see "3" in
FIGS. 1 and 2).
[0145] Refrigerant compressed in the second compressor (22) is
discharged to the second discharge pipe (26) (see "4" in FIGS. 1
and 2). In this state, the second oil separator (90) of the second
discharge pipe (26) separates lubricating oil from gas refrigerant
flowing in the second discharge pipe (26). The separated
lubricating oil is sent from the oil outflow pipe (16) to the
second suction pipe (30). Refrigerant flowing in the second
discharge pipe (26) passes through the second four-way valve (94)
and flows into the second intermediate heat exchanger (42). In the
second intermediate heat exchanger (42), refrigerant dissipates
heat to the outdoor air to be cooled. Refrigerant cooled in the
second intermediate heat exchanger (42) flows into the second
refrigerant pipe (71) (see "5" in FIGS. 1 and 2). Refrigerant
flowing in the second refrigerant pipe (71) passes through the
check valve (CV9), merges with refrigerant flowing in the injection
pipe (106), flows into the third suction pipe (31), and is sucked
into the third compressor (23) (see "6" in FIGS. 1 and 2).
[0146] Refrigerant compressed in the third compressor (23) is
discharged to the third discharge pipe (27) (see "7" in FIGS. 1 and
2). In this state, the third oil separator (91) of the third
discharge pipe (27) separates lubricating oil from gas refrigerant
flowing in the third discharge pipe (27). The separated lubricating
oil is sent from the oil outflow pipe (16) to the fourth suction
pipe (32). Refrigerant flowing in the third discharge pipe (27)
passes through the third four-way valve (95) and flows into the
third intermediate heat exchanger (43). In the third intermediate
heat exchanger (43), refrigerant dissipates heat to the outdoor air
to be cooled. Refrigerant cooled in the third intermediate heat
exchanger (43) flows into the third refrigerant pipe (72).
Refrigerant flowing in the third refrigerant pipe (72) passes
through the check valve (CV10), flows into the fourth suction pipe
(32), and is sucked into the fourth compressor (24) (see "8" in
FIGS. 1 and 2).
[0147] Refrigerant compressed in the fourth compressor (24) is
discharged to the fourth discharge pipe (28) (see "9" in FIGS. 1
and 2). The compression and cooling operations described above are
alternately performed in order to make compression strokes of the
four-stage compressor (20) approach those of isothermal compression
to reduce compression power necessary for the four-stage compressor
(20). At this time, the fourth oil separator (92) of the fourth
discharge pipe (28) separates lubricating oil from gas refrigerant
flowing in the fourth discharge pipe (28). The separated
lubricating oil is sent from the oil outflow pipe (16) to the first
suction pipe (29). Refrigerant flowing in the fourth discharge pipe
(28) passes through the fourth four-way valve (96) and flows into
the outdoor heat exchanger (44). In the outdoor heat exchanger
(44), refrigerant dissipates heat to the outdoor air to be cooled.
Refrigerant cooled in the outdoor heat exchanger (44) flows into
the fourth refrigerant pipe (73). Refrigerant flowing in the fourth
refrigerant pipe (73) passes through the check valve (CV11) and
flows into the inflow pipe (60).
[0148] Part of refrigerant flowing in the inflow pipe (60) flows
into the first branch pipe (62). The pressure of refrigerant
flowing in the first branch pipe (62) (see "10" in FIGS. 1 and 2)
is reduced in the second expansion valve (81). Refrigerant whose
pressure has been reduced in the second expansion valve (81) (see
"11" in FIGS. 1 and 2) flows into the low-pressure channel (100b)
of the first subcooling heat exchanger (100). On the other hand,
the other part of refrigerant flowing in the inflow pipe (60) flows
into the high-pressure channel (100a) of the first subcooling heat
exchanger (100) (see "10" in FIGS. 1 and 2). In the first
subcooling heat exchanger (100), heat exchange is performed between
refrigerant flowing in the high-pressure channel (100a) and
refrigerant flowing in the low-pressure channel (100b) to subcool
refrigerant flowing in the high-pressure channel (100a).
[0149] Refrigerant that has flown out of the high-pressure channel
(100a) of the first subcooling heat exchanger (100) flows in the
inflow pipe (60) again (see "13" in FIGS. 1 and 2), and flows into
the high-pressure channel (101a) of the second subcooling heat
exchanger (101). On the other hand, refrigerant that has flown out
of the low-pressure channel (100b) of the first subcooling heat
exchanger (100) (see "12" in FIGS. 1 and 2) flows into the
injection pipe (106). Refrigerant flowing in the injection pipe
(106) flows into the second refrigerant pipe (71) and merges with
refrigerant flowing in the second refrigerant pipe (71) (see "6" in
FIGS. 1 and 2). That is, refrigerant that has flown into the
injection pipe (106) is injected toward a suction side of the third
compressor (23).
[0150] In the second subcooling heat exchanger (101), heat exchange
is performed between refrigerant flowing in the high-pressure
channel (101a) and refrigerant flowing in the low-pressure channel
(101b) to subcool refrigerant flowing in the high-pressure channel
(101a).
[0151] Refrigerant that has flown out of the high-pressure channel
(101a) of the second subcooling heat exchanger (101) flows in the
inflow pipe (60) again (see "14" in FIGS. 1 and 2), and part of
this refrigerant flows into the expander (87). The expander (87)
expands the inflow refrigerant (see "14" to "16" in FIGS. 1 and 2),
and sends the expanded refrigerant back to the inflow pipe (60). On
the other hand, the other part of refrigerant that has flown out of
the high-pressure channel (101a) of the second subcooling heat
exchanger (101) branches off into the bypass pipe (64). Refrigerant
flowing in the bypass pipe (64) is subjected to pressure reduction
in the first expansion valve (80) (see "15" in FIGS. 1 and 2) and
returns back to the inflow pipe (60). Refrigerant that has flown
out of the expander (87) and refrigerant that has flown out of the
bypass pipe (64) merge together in the inflow pipe (60) (see "17"
in FIGS. 1 and 2) and flow into the gas-liquid separator (88). The
gas-liquid separator (88) separates the inflow refrigerant into gas
refrigerant (see "22" in FIGS. 1 and 2) and liquid refrigerant (see
"18" in FIGS. 1 and 2).
[0152] The liquid refrigerant (see "18" in FIGS. 1 and 2) that has
flown out of the gas-liquid separator (88) flows in the first
outflow pipe (61), and part of this refrigerant flows into the
second branch pipe (63). The pressure of refrigerant flowing in the
second branch pipe (63) is reduced in the third expansion valve
(82). Refrigerant whose pressure has been reduced in the third
expansion valve (82) (see "19" in FIGS. 1 and 2) flows into the
low-pressure channel (102b) of the third subcooling heat exchanger
(102). On the other hand, the other part of refrigerant flowing in
the outflow pipe (61) flows into the high-pressure channel (102a)
of the third subcooling heat exchanger (102).
[0153] In the third subcooling heat exchanger (102), heat exchange
is performed between refrigerant flowing in the high-pressure
channel (102a) and refrigerant flowing in the low-pressure channel
(102b) to subcool liquid refrigerant flowing in the high-pressure
channel (102a).
[0154] The liquid refrigerant that has flown out of the
high-pressure channel (102a) of the third subcooling heat exchanger
(102) (see "20" in FIGS. 1 and 2) flows in the first outflow pipe
(61) again, passes through the check valve (CV13) of the bridge
circuit (17), and flows into the liquid-side communication pipe
(14). On the other hand, refrigerant that has flown out of the
low-pressure channel (102b) of the third subcooling heat exchanger
(102) flows in the return pipe (68). Refrigerant flowing in the
return pipe (68) (see "24" in FIGS. 1 and 2) merges with gas
refrigerant that has flown out of the second outflow pipe (65) (see
"23" in FIGS. 1 and 2) at a midpoint thereof, and continues to
flow. Refrigerant that has flown out of the return pipe (68) merges
with refrigerant that has flown out of the connection pipe (66).
The merged refrigerant (see "26" in FIGS. 1 and 2) flows into the
low-pressure channel (101b) of the second subcooling heat exchanger
(101).
[0155] Part of liquid refrigerant flowing in the liquid-side
communication pipe (14) branches off, and is subjected to pressure
reduction in the first indoor expansion valve (85). The
pressure-reduced refrigerant (see "21a" in FIGS. 1 and 2) flows
into the first indoor heat exchanger (110). In the first indoor
heat exchanger (110), liquid refrigerant absorbs heat from indoor
air and evaporates. The evaporated gas refrigerant (see "25a" in
FIGS. 1 and 2) flows into the gas-side communication pipe (13).
[0156] The pressure of the other part of the liquid refrigerant
flowing in the liquid-side communication pipe (14) is reduced in
the second indoor expansion valve (86). The pressure-reduced
refrigerant (see "21b" in FIGS. 1 and 2) flows into the second
indoor heat exchanger (111). In the second indoor heat exchanger
(111), liquid refrigerant absorbs heat from indoor air and
evaporates. The evaporated gas refrigerant (see "25b" in FIGS. 1
and 2) flows into the gas-side communication pipe (13).
[0157] In the gas-side communication pipe (13), refrigerant that
has flown out of the first indoor heat exchanger (110) and
refrigerant that has flown out of the second indoor heat exchanger
(111) merge together. Refrigerant flowing in the gas-side
communication pipe (13) passes through the fourth four-way valve
(96) and flows into the connection pipe (66). Part of refrigerant
flowing in the connection pipe (66) branches off from the junction
pipe (67) into parts flowing into the first through third four-way
valves (92, 93, 94).
[0158] Refrigerant that has passed through the second port of the
first four-way valve (93) flows into the second suction pipe (30).
Refrigerant flowing in the second suction pipe (30) passes through
the check valve (CV1) and merges with refrigerant flowing in the
first refrigerant pipe (70) to be sucked into the second compressor
(22). Refrigerant that has passed through the second port of the
second four-way valve (94) flows into the third suction pipe (31).
Refrigerant flowing in the third suction pipe (31) passes through
the check valve (CV2) and merges with refrigerant flowing in the
second refrigerant pipe (71) to be sucked into the third compressor
(23). Refrigerant that has passed through the second port of the
third four-way valve (95) flows into the fourth suction pipe (32).
Refrigerant flowing in the fourth suction pipe (32) passes through
the check valve (CV3) and merges with refrigerant flowing in the
third refrigerant pipe (72) to be sucked into the fourth compressor
(24).
[0159] The other part of refrigerant flowing in the connection pipe
(66) merges with refrigerant flowing in the return pipe (68). The
merged refrigerant (see "26" in FIGS. 1 and 2) passes through the
low-pressure channel (101b) of the second subcooling heat exchanger
(101) and flows into the first suction pipe (29). Refrigerant
flowing in the first suction pipe (29) (see "1" in FIGS. 1 and 2)
is compressed in the first compressor (21) of the four-stage
compressor (20) again.
[0160] --Heating Operation--
[0161] Heating operation of the air conditioner (1) will now be
described with reference to FIG. 7. In FIG. 7, a refrigerant flow
in this heating operation is represented by arrows of broken line.
In the heating operation, the indoor heat exchangers (110, 111)
operate as heat dissipators, and the first through third
intermediate heat exchangers (41, 42, 43) and the outdoor heat
exchanger (44) operate as evaporators, thereby performing a
four-stage compression supercritical refrigeration cycle.
[0162] In the heating operation, all the four-way valves (93, 94,
95, 96) are set in the second states, and the four-stage compressor
(20) is driven. When the four-stage compressor (20) is driven,
refrigerant is compressed in the compressors (21, 22, 23, 24).
Refrigerant compressed in the first compressor (21) is discharged
to the first discharge pipe (25). Refrigerant flowing in the first
discharge pipe (25) passes through the first four-way valve (93)
and is sucked into the second compressor (22). Refrigerant further
compressed in the second compressor (22) passes through the second
four-way valve (94) and is sucked into the third compressor (23).
Refrigerant further compressed in the third compressor (23) passes
through the third four-way valve (95) and is sucked into the fourth
compressor (24). Refrigerant is further compressed in the fourth
compressor (24). In this manner, unlike the cooling operation,
four-stage compression is performed without cooling in the heating
operation. In this heating operation, the temperature of
refrigerant discharged from the four-stage compressor (20) does not
decrease, unlike the case of performing four-stage compression with
cooling. As a result, the heating operation shows a larger heating
capacity than that in the case of four-stage compression with
cooling.
[0163] Refrigerant discharged from the fourth compressor (24)
passes through the fourth four-way valve (96) and is sent to the
first and second indoor heat exchangers (110, 111). In the first
and second indoor heat exchangers (110, 111), refrigerant
dissipates heat to the indoor air to be cooled. Refrigerant cooled
in the indoor heat exchangers (110, 111) is subjected to pressure
reduction in the first and second indoor expansion valves (85, 86)
and then sent to the bridge circuit (17). This refrigerant passes
through the check valve (CV12) and flows into the inflow pipe
(60).
[0164] Part of refrigerant flowing in the inflow pipe (60) flows
into the first branch pipe (62). The pressure of refrigerant
flowing in the first branch pipe (62) is reduced in the second
expansion valve (81). Refrigerant whose pressure has been reduced
in the second expansion valve (81) flows into the low-pressure
channel (100b) of the first subcooling heat exchanger (100). On the
other hand, the other part of refrigerant flowing in the inflow
pipe (60) flows into the high-pressure channel (100a) of the first
subcooling heat exchanger (100). In the first subcooling heat
exchanger (100), heat exchange is performed between refrigerant
flowing in the high-pressure channel (100a) and refrigerant flowing
in the low-pressure channel (100b) to subcool refrigerant flowing
in the high-pressure channel (100a).
[0165] Refrigerant that has flown out of the high-pressure channel
(100a) of the first subcooling heat exchanger (100) flows in the
first outflow pipe (61) again, and flows into the high-pressure
channel (101a) of the second subcooling heat exchanger (101). On
the other hand, refrigerant that has flown out of the low-pressure
channel (100b) of the first subcooling heat exchanger (100) flows
into the injection pipe (106). Refrigerant flowing in the injection
pipe (106) flows into the second refrigerant pipe (71) and merges
with refrigerant in the second refrigerant pipe (71). That is,
refrigerant that has flown into the injection pipe (106) is
injected toward a suction side of the third compressor (23).
[0166] In the second subcooling heat exchanger (101), heat exchange
is performed between refrigerant flowing in the high-pressure
channel (101a) and refrigerant flowing in the low-pressure channel
(101b) to subcool refrigerant flowing in the high-pressure channel
(101a).
[0167] Refrigerant that has flown out of the high-pressure channel
(101a) of the second subcooling heat exchanger (101) flows in the
first outflow pipe (61) again, and part of this refrigerant flows
into the expander (87). The expander (87) expands the inflow
refrigerant, and sends the expanded refrigerant back to the inflow
pipe (60). On the other hand, the other part of refrigerant that
has flown out of the high-pressure channel (101a) of the second
subcooling heat exchanger (101) branches off into the bypass pipe
(64). Refrigerant flowing in the bypass pipe (64) is subjected to
pressure reduction in the first expansion valve (80) and returns
back to the inflow pipe (60). Refrigerant that has flown out of the
expander (87) and refrigerant that has flown out of the bypass pipe
(64) merge together in the inflow pipe (60) and flow into the
gas-liquid separator (88). The gas-liquid separator (88) separates
the inflow refrigerant into gas refrigerant and liquid
refrigerant.
[0168] The liquid refrigerant that has flown out of the gas-liquid
separator (88) flows in the first outflow pipe (61), and part of
this refrigerant flows into the second branch pipe (63). The
pressure of refrigerant flowing in the second branch pipe (63) is
reduced in the third expansion valve (82). Refrigerant whose
pressure has been reduced in the third expansion valve (82) flows
into the low-pressure channel (102b) of the third subcooling heat
exchanger (102). On the other hand, the other part of refrigerant
flowing in the inflow pipe (60) flows into the high-pressure
channel (102a) of the third subcooling heat exchanger (102).
[0169] In the third subcooling heat exchanger (102), heat exchange
is performed between refrigerant flowing in the high-pressure
channel (102a) and refrigerant flowing in the low-pressure channel
(102b) to subcool liquid refrigerant flowing in the high-pressure
channel (102a)
[0170] The liquid refrigerant that has flown out of the
high-pressure channel (102a) of the third subcooling heat exchanger
(102) flows in the first outflow pipe (61) again, is subjected to
pressure reduction in the fifth expansion valve (84) of the bridge
circuit (17), and then is sent to the distributor (18). Refrigerant
distributed in the distributor (18) passes through the capillary
tube (15) and the check valves (CV4, CV5, CV6, CV7) to flow into
the first through third intermediate heat exchangers (41, 42, 43)
and the outdoor heat exchanger (44). In the first through third
intermediate heat exchangers (41, 42, 43) and the outdoor heat
exchanger (44), liquid refrigerant absorbs heat from the outdoor
air and evaporates. Refrigerant that has flown out of the first
intermediate heat exchanger (41) passes through the first four-way
valve (93) and flows into the junction pipe (67). Refrigerant that
has flown out of the second intermediate heat exchanger (42) passes
through the second four-way valve (94) and flows into the junction
pipe (67). Refrigerant that has flown out of the third intermediate
heat exchanger (43) passes through the third four-way valve (95)
and flows into the junction pipe (67). Refrigerant that has flown
out of the first through third intermediate heat exchangers (41,
42, 43) passes through the junction pipe (67) and flows into the
connection pipe (66).
[0171] Refrigerant that has flown out of the outdoor heat exchanger
(44) passes through the fourth four-way valve (96), flows into the
connection pipe (66), and merges with refrigerant that has flown
out of the first through third intermediate heat exchangers (41,
42, 43). The merged refrigerant flows in the connection pipe (66)
and merges with refrigerant flowing in the return pipe (68). The
merged refrigerant flows into the first suction pipe (29).
Refrigerant flowing in the first suction pipe (29) is compressed in
the first compressor (21) of the four-stage compressor (20)
again.
[0172] --Outdoor Unit--
[0173] The outdoor unit will now be described. As illustrated in
FIG. 3, air taken into the outdoor casing (121) from the air inlet
(123) is subjected to heat exchange in the first through third
intermediate heat exchangers (41, 42, 43) and the outdoor heat
exchanger (44), flows to upper space in the outdoor casing (121),
and is blown out through the air outlet (124).
[0174] As illustrated in FIG. 6, the outdoor unit (3) is of a
so-called upward blow type in which air is sucked through the air
inlet (123) in the side surface and is blown upward from the air
outlet (124). Thus, the airflow velocity is higher in an upper
portion of the air inlet (123) than in a lower portion of the air
inlet (123). As illustrated in FIG. 2, the pressure of refrigerant
flowing in the first through third intermediate heat exchangers
(41, 42, 43) is lower than that of refrigerant flowing in the
outdoor heat exchanger (44), and thus, the densities of refrigerant
flowing in the first through third intermediate heat exchangers
(41, 42, 43) are lower than that of refrigerant flowing in the
outdoor heat exchanger (44). In view of this, when the mass flow
rates of refrigerant flowing in the first through third
intermediate heat exchangers (41, 42, 43) are substantially equal
to that of refrigerant flowing in the outdoor heat exchanger (44),
the volume flow rates of refrigerant in the first through third
intermediate heat exchangers (41, 42, 43) are higher than that of
refrigerant in the outdoor heat exchanger (44). Even when the
number of refrigerant paths in each of the first through third
intermediate heat exchangers (41, 42, 43) is equal to that in the
outdoor heat exchanger (44), the flow velocities of refrigerant
flowing in the first through third intermediate heat exchangers
(41, 42, 43) are higher than that of refrigerant flowing in the
outdoor heat exchanger (44), and thus, pressure losses of
refrigerant in the first through third intermediate heat exchangers
(41, 42, 43) are larger than that in the outdoor heat exchanger
(44).
[0175] The outdoor heat exchanger (44) located in an upper portion
of the outdoor casing (121) where the airflow velocity is high, has
a high heat exchange efficiency, and can be reduced in size. On the
other hand, the first through third intermediate heat exchangers
(41, 42, 43) located in a lower portion of the outdoor casing (121)
where the airflow velocity is low, have low heat exchange
efficiencies. Thus, to increase the amount of heat exchange, the
first through third intermediate heat exchangers (41, 42, 43) need
to be larger than those in a case where these exchangers are
located in an upper portion.
[0176] For this reason, the size of the outdoor heat exchange unit
(40) does not increase even when the size of the outdoor heat
exchanger (44) and the first through third intermediate heat
exchangers (41, 42, 43) increases.
[0177] An increase in size of the first through third intermediate
heat exchangers (41, 42, 43) increases the number of refrigerant
paths in each of the first through third intermediate heat
exchangers (41, 42, 43). Thus, in the first through third
intermediate heat exchangers (41, 42, 43), the flow velocity of
refrigerant in each refrigerant path decreases, resulting in a
decrease in pressure loss of refrigerant passing through the
refrigerant path. The flow velocities of refrigerant flowing in the
first through third intermediate heat exchangers (41, 42, 43) are
originally high, and thus, a decrease in flow velocity due to an
increase in the number of refrigerant paths relatively greatly
reduces the pressure loss.
[0178] On the other hand, size reduction of the outdoor heat
exchanger (44) reduces the number of refrigerant paths in the
outdoor heat exchanger (44). The reduction of the number of
refrigerant paths increases the flow velocity of refrigerant in
each refrigerant path to increase the pressure loss of refrigerant
passing through the refrigerant path.
[0179] However, since the flow velocity of refrigerant flowing in
the outdoor heat exchanger (44) is originally low, a certain degree
of increase in flow velocity due to the reduction of the number of
refrigerant paths relatively slightly increases the pressure loss
arising from the increase in flow velocity.
[0180] Thus, by disposing the outdoor heat exchanger (44) above the
first through third intermediate heat exchangers (41, 42, 43), the
pressure losses of refrigerant in the first through third
intermediate heat exchangers (41, 42, 43) can be reduced with a
reduced degree of increase in size of the outdoor heat exchange
unit (40).
[0181] Since the pressure of refrigerant flowing in the third
intermediate heat exchanger (43) is higher than that of refrigerant
flowing in the first and second intermediate heat exchangers (41,
42) as illustrated in FIG. 2, the densities of refrigerant flowing
in the first and second intermediate heat exchangers (41, 42) are
lower than that of refrigerant flowing in the third intermediate
heat exchanger (43). Thus, when the mass flow rates of refrigerant
flowing in the first and second intermediate heat exchangers (41,
42) are substantially equal to that of refrigerant flowing in the
third intermediate heat exchanger (43), the volume flow rates of
refrigerant in the first and second intermediate heat exchangers
(41, 42) are higher than that of refrigerant in the third
intermediate heat exchanger (43). Even when the numbers of
refrigerant paths in the first and second intermediate heat
exchangers (41, 42) are substantially equal to that in the third
intermediate heat exchanger (43), the pressure losses of
refrigerant in the first and second intermediate heat exchangers
(41, 42) are larger than that of refrigerant in the third
intermediate heat exchanger (43) because the refrigerant flow
velocities in the first and second intermediate heat exchangers
(41, 42) are higher than that in the third intermediate heat
exchanger (43).
[0182] Since the third intermediate heat exchanger (43) located in
an upper portion of the outdoor casing (121) where the airflow
velocity is high has a high heat exchange efficiency, the size of
the third intermediate heat exchanger (43) can be reduced. On the
other hand, the first and second intermediate heat exchangers (41,
42) located in a lower portion of the outdoor casing (121) where
the airflow velocity is low, have low heat exchange efficiencies.
Thus, to increase the amount of heat exchange, the first and second
intermediate heat exchangers (41, 42, 43) need to be larger than
those in a case where these exchangers are located in an upper
portion.
[0183] For this reason, the size of the outdoor heat exchange unit
(40) does not increase even when the size of the third intermediate
heat exchanger (43) and the first and second intermediate heat
exchangers (41, 42) increases.
[0184] An increase in size of the first and second intermediate
heat exchangers (41, 42) increases the numbers of refrigerant paths
in the first and second intermediate heat exchangers (41, 42).
Thus, in the first and second intermediate heat exchangers (41,
42), the flow velocity of refrigerant in each refrigerant path
decreases, resulting in a decrease in pressure loss of refrigerant
passing through the refrigerant path. The flow velocities of
refrigerant flowing in the first and second intermediate heat
exchangers (41, 42) are originally high, and thus, a decrease in
flow velocity due to an increase in the number of refrigerant paths
relatively greatly reduces the pressure loss.
[0185] On the other hand, size reduction of the third intermediate
heat exchanger (43) reduces the number of refrigerant paths in the
third intermediate heat exchanger (43). The reduction of the number
of refrigerant paths increases the flow velocity of refrigerant in
each refrigerant path to increase the pressure loss of refrigerant
passing through the refrigerant paths.
[0186] However, since the flow velocity of refrigerant flowing in
the third intermediate heat exchanger (43) is originally low, a
certain degree of increase in flow velocity due to the reduction of
the number of refrigerant paths relatively slightly increases the
pressure loss arising from the increase in flow velocity.
[0187] Thus, by disposing the third intermediate heat exchanger
(43) above the first and second intermediate heat exchangers (41,
42), the pressure losses of refrigerant in the first and second
intermediate heat exchangers (41, 42) can be reduced with a reduced
degree of increase in size of the outdoor heat exchange unit
(40).
[0188] As illustrated in FIG. 2, the refrigerant density in the
second intermediate heat exchanger (42) where inflow refrigerant
has a high pressure is higher than that in the first intermediate
heat exchanger (41) where inflow refrigerant has a low pressure.
Thus, when the mass flow rate of refrigerant flowing in the first
intermediate heat exchanger (41) is substantially equal to that of
refrigerant flowing in the second intermediate heat exchanger (42),
the volume flow rate of refrigerant in the first intermediate heat
exchanger (41) is higher than that of refrigerant in the second
intermediate heat exchanger (42). Even when the number of
refrigerant paths in the first intermediate heat exchanger (41) is
substantially equal to that in the second intermediate heat
exchanger (42), the pressure loss of refrigerant in the first
intermediate heat exchanger (41) is larger than that of refrigerant
in the second intermediate heat exchanger (42) because the
refrigerant flow velocity in the first intermediate heat exchanger
(41) is higher than that in the second intermediate heat exchanger
(42). The first intermediate heat exchanger (41) is located in a
lower portion of the outdoor casing (121) where the airflow
velocity is low does not have a high heat exchange efficiency, and
thus, does not decrease in size. Since the number of refrigerant
paths in the first intermediate heat exchanger (41) does not
decrease, the pressure loss of refrigerant does not increase. For
the foregoing reasons, an increase in pressure loss of refrigerant
in the first intermediate heat exchanger (41) can be reduced.
Advantages of First Embodiment
[0189] In the first embodiment, since the outdoor heat exchanger
(44) is located in an upper portion of the outdoor casing (121)
where the airflow velocity is high, the heat exchange efficiency of
the outdoor heat exchanger (44) can be increased. In addition,
since the outdoor heat exchanger (44) having a low flow velocity of
refrigerant is located in an upper portion of the outdoor casing
(121) where the airflow velocity is high, the size of the outdoor
heat exchanger (44) can be reduced without an increase in pressure
loss of refrigerant.
[0190] On the other hand, the first through third intermediate heat
exchangers (41, 42, 43) are located in a lower portion of the
outdoor casing (121) where the airflow velocity is low to increase
the number of refrigerant paths, thereby ensuring prevention of an
increase in pressure loss of refrigerant in the first through third
intermediate heat exchangers (41, 42, 43).
[0191] In the above-described configuration, the outdoor heat
exchangers (44, 162) where a pressure loss of refrigerant does not
easily increase is located in upper portions for size reduction,
thereby reducing pressure losses of refrigerant in the first
through third intermediate heat exchangers (41, 42, 43) with
reduced size increase in the outdoor heat exchange unit (40).
[0192] In addition, since the third intermediate heat exchanger
(43) is located in an upper portion of the outdoor casing (121)
where the airflow velocity is high, the heat exchange efficiency of
the third intermediate heat exchanger (43) can be increased.
Further, since the third intermediate heat exchanger (43) having a
low flow velocity of refrigerant is located in an upper portion of
the outdoor casing (121) where the airflow velocity is high, the
size of the third intermediate heat exchanger (43) can be reduced
without an increase in pressure loss of refrigerant.
[0193] On the other hand, the first and second intermediate heat
exchangers (41, 42) having high flow velocities of refrigerant are
located in a lower portion of the outdoor casing (121) where the
airflow velocity is low to increase the number of refrigerant
paths, thereby ensuring prevention of an increase in pressure loss
of refrigerant in the first and second intermediate heat exchangers
(41, 42).
[0194] In the above-described configuration, the third intermediate
heat exchanger (43) where a pressure loss of refrigerant does not
easily increase is located in the upper portion for size reduction,
thereby reducing a pressure loss of refrigerant in the other
intermediate heat exchangers (41, 42) with reduced size increase in
the outdoor heat exchange unit (40).
[0195] In addition, the first intermediate heat exchanger (41)
having a high flow velocity of refrigerant is located in a lower
portion of the outdoor casing (121) where the airflow velocity is
low to increase the number of refrigerant paths, thereby ensuring
prevention of an increase in pressure loss of refrigerant in the
first intermediate heat exchanger (41). This configuration can
reduce an increase in the pressure loss of refrigerant in the first
intermediate heat exchanger (41).
Second Embodiment
[0196] A second embodiment according to the present invention will
now be described. As illustrated in FIG. 8, the air conditioner (1)
according to this second embodiment has a configuration of a
refrigerant circuit different from that of the air conditioner (1)
of the first embodiment. In the second embodiment, only part of the
configuration different from that of the first embodiment is
described, and like reference characters are used to designate
identical or equivalent elements.
[0197] Specifically, the refrigerant circuit (10) of the second
embodiment includes three subcooling heat exchangers: a first-a
subcooling heat exchanger (103), a first-b subcooling heat
exchanger (104), and a first-c subcooling heat exchanger (105).
[0198] --Circuit Configuration--
[0199] The first-a subcooling heat exchanger (103) includes a
high-pressure channel (103a) and a low-pressure channel (103b). In
the first-a subcooling heat exchanger (103), heat exchange is
performed between the high-pressure channel (103a) and the
low-pressure channel (103b) to subcool refrigerant flowing in the
high-pressure channel (103a).
[0200] An inflow end of the high-pressure channel (103a) is
connected to an inflow pipe (60), and an inflow end of the
low-pressure channel (103b) is connected to a first-a branch pipe
(62a) serving as a passage for subcooling. The first-a branch pipe
(62a) includes a second-a expansion valve (81a) for subcooling. The
second-a expansion valve (81a) is an electronic expansion valve
having an adjustable opening degree. An outflow end of the
low-pressure channel (103b) is connected to an end of a first
injection pipe (107).
[0201] An end of the first injection pipe (107) is connected to the
low-pressure channel (103b) of the first-a subcooling heat
exchanger (103), and the other end of the first injection pipe
(107) is connected to a third refrigerant pipe (72). The other end
of the first injection pipe (107) is connected to an outflow end of
a check valve (CV10) in the third refrigerant pipe (72). The
first-a subcooling heat exchanger (103) and the second-a expansion
valve (81a) constitute a so-called economizer circuit.
[0202] The first-b subcooling heat exchanger (104) includes a
high-pressure channel (104a) and a low-pressure channel (104b). In
the first-b subcooling heat exchanger (104), heat exchange is
performed between refrigerant flowing in the high-pressure channel
(104a) and refrigerant flowing in the low-pressure channel (104b)
to subcool refrigerant flowing in the high-pressure channel
(104a).
[0203] An inflow end of the high-pressure channel (104a) is
connected to the inflow pipe (60), and an inflow end of the
low-pressure channel (104b) is connected to a first-b branch pipe
(62b) serving as a passage for subcooling. The first-b branch pipe
(62b) includes a second-b expansion valve (81b) for subcooling. The
second-b expansion valve (81b) is an electronic expansion valve
having an adjustable opening degree. An outflow end of the
low-pressure channel (104b) is connected to an end of a second
injection pipe (108).
[0204] An end of the second injection pipe (108) is connected to
the low-pressure channel (104b) of the first-b subcooling heat
exchanger (104), and the other end of the second injection pipe
(108) is connected to the second refrigerant pipe (71). The other
end of the second injection pipe (108) is connected to an outflow
end of a check valve (CV9) in the second refrigerant pipe (71). The
first-b subcooling heat exchanger (104) and the second-b expansion
valve (81b) constitute a so-called economizer circuit.
[0205] The first-c subcooling heat exchanger (105) includes a
high-pressure channel (105a) and a low-pressure channel (105b). In
the first-c subcooling heat exchanger (105), heat exchange is
performed between refrigerant flowing in the high-pressure channel
(105a) and refrigerant flowing in the low-pressure channel (105b)
to subcool refrigerant flowing in the high-pressure channel
(105a).
[0206] An inflow end of the high-pressure channel (105a) is
connected to the inflow pipe (60), and an inflow end of the
low-pressure channel (105b) is connected to a first-c branch pipe
(62c) serving as a passage for subcooling. The first-c branch pipe
(62c) includes a second-c expansion valve (81c) for subcooling. The
second-c expansion valve (81c) is an electronic expansion valve
having an adjustable opening degree. An outflow end of the
low-pressure channel (105b) is connected to an end of a third
injection pipe (109).
[0207] An end of the third injection pipe (109) is connected to the
low-pressure channel (105b) of the first-c subcooling heat
exchanger (105), and the other end of the third injection pipe
(109) is connected to the first refrigerant pipe (70). The other
end of the third injection pipe (109) is connected to an outflow
end of a check valve (CV8) in the first refrigerant pipe (70). The
first-c subcooling heat exchanger (105) and the second-c expansion
valve (81c) constitute a so-called economizer circuit.
[0208] --Circuit Operation--
[0209] Operations of the subcooling heat exchangers (103, 104, 105)
and the expansion valves (81a, 81b, 81c) will now be described with
reference to FIGS. 8 and 9. Description of part of operations also
described in the first embodiment will not be repeated.
[0210] Refrigerant compressed in a fourth compressor (24) of a
four-stage compressor (20) is discharged to a fourth discharge pipe
(28). Compression and cooling operations are alternately performed
in the four-stage compressor (20) and first through third
intermediate heat exchangers (41, 42, 43) in order to make
compression strokes of the four-stage compressor (20) approach
those of isothermal compression to reduce compression power
necessary for the four-stage compressor (20).
[0211] Refrigerant flowing in the fourth discharge pipe (28) passes
through a fourth four-way valve (96) and flows into an outdoor heat
exchanger (44). In the outdoor heat exchanger (44), refrigerant
dissipates heat to the outdoor air to be cooled. Refrigerant cooled
in the outdoor heat exchanger (44) flows into a fourth refrigerant
pipe (73). Refrigerant flowing in the fourth refrigerant pipe (73)
passes through a check valve (CV11) and flows into the inflow pipe
(60).
[0212] Part of refrigerant flowing in the inflow pipe (60) flows
into the first-a branch pipe (62a). The pressure of refrigerant
flowing in the first-a branch pipe (62a) (see "27" in FIGS. 8 and
9) is reduced in the second-a expansion valve (81a). Refrigerant
whose pressure has been reduced in the second-a expansion valve
(81a) (see "28" in FIGS. 8 and 9) flows into the low-pressure
channel (103b) of the first-a subcooling heat exchanger (103). On
the other hand, the other part of refrigerant flowing in the inflow
pipe (60) flows into the high-pressure channel (103a) of the
first-a subcooling heat exchanger (103) (see "27" in FIGS. 8 and
9). In the first-a subcooling heat exchanger (103), heat exchange
is performed between refrigerant flowing in the high-pressure
channel (103a) and refrigerant flowing in the low-pressure channel
(103b) to subcool refrigerant flowing in the high-pressure channel
(103a).
[0213] Refrigerant that has flown out of the high-pressure channel
(103a) of the first-a subcooling heat exchanger (103) flows in the
inflow pipe (60) again (see "31" in FIGS. 8 and 9), and flows into
the high-pressure channel (104a) of the first-b subcooling heat
exchanger (104). On the other hand, refrigerant that has flown out
of the low-pressure channel (103b) of the first-a subcooling heat
exchanger (103) (see "29" in FIGS. 8 and 9) flows into the first
injection pipe (107). Refrigerant flowing in the first injection
pipe (107) flows into the third refrigerant pipe (72) and merges
with refrigerant (see "30" in FIGS. 8 and 9) in the third
refrigerant pipe (72) to be merged refrigerant (see "8" in FIGS. 8
and 9). That is, refrigerant that has flown into the first
injection pipe (107) is injected toward a suction side of a fourth
compressor (24).
[0214] Then, part of refrigerant that has flown out of the first-a
subcooling heat exchanger (103) and is flowing in the inflow pipe
(60) flows into the first-b branch pipe (62b). The pressure of
refrigerant flowing in the first-b branch pipe (62b) (see "31" in
FIGS. 8 and 9) is reduced in the second-b expansion valve (81b).
Refrigerant whose pressure has been reduced in the second-b
expansion valve (81b) (see "32" in FIGS. 8 and 9) flows into the
low-pressure channel (104b) of the first-b subcooling heat
exchanger (104). On the other hand, the other part of refrigerant
flowing in the inflow pipe (60) flows into the high-pressure
channel (104a) of the first-b subcooling heat exchanger (104) (see
"31" in FIGS. 8 and 9). In the first-b subcooling heat exchanger
(104), heat exchange is performed between refrigerant flowing in
the high-pressure channel (104a) and refrigerant flowing in the
low-pressure channel (104b) to subcool refrigerant flowing in the
high-pressure channel (104a).
[0215] Refrigerant that has flown out of the high-pressure channel
(104a) of the first-b subcooling heat exchanger (104) flows in the
inflow pipe (60) again (see "34" in FIGS. 8 and 9) and flows into
the high-pressure channel (105a) of the first-c subcooling heat
exchanger (105). On the other hand, refrigerant that has flown out
of the low-pressure channel (104b) of the first-b subcooling heat
exchanger (104) (see "33" in FIGS. 8 and 9) flows into the second
injection pipe (108). Refrigerant flowing in the second injection
pipe (108) flows into the second refrigerant pipe (71), and merges
with refrigerant (see "5" in FIGS. 8 and 9) in the second
refrigerant pipe (71) to be merged refrigerant (see "6" in FIGS. 8
and 9). That is, refrigerant that has flown into the second
injection pipe (108) is injected toward a suction side of a third
compressor (23).
[0216] Part of refrigerant that has flown out of the first-b
subcooling heat exchanger (104) and is flowing in the inflow pipe
(60) flows into the first-c branch pipe (62c). The pressure of
refrigerant flowing in the first-c branch pipe (62c) (see "34" in
FIGS. 8 and 9) is reduced in the second-c expansion valve (81c).
Refrigerant whose pressure has been reduced in the second-c
expansion valve (81c) (see "35" in FIGS. 8 and 9) flows into the
low-pressure channel (105b) of the first-c subcooling heat
exchanger (105). On the other hand, the other part of refrigerant
flowing in the inflow pipe (60) flows into the high-pressure
channel (105a) of the first-c subcooling heat exchanger (105) (see
"34" in FIGS. 8 and 9). In the first-c subcooling heat exchanger
(105), heat exchange is performed between refrigerant flowing in
the high-pressure channel (105a) and refrigerant flowing in the
low-pressure channel (105b) to subcool refrigerant flowing in the
high-pressure channel (105a).
[0217] Refrigerant that has flown out of the high-pressure channel
(105a) of the first-c subcooling heat exchanger (105) flows in the
inflow pipe (60) again (see "38" in FIGS. 8 and 9), and flows into
the high-pressure channel (101a) of the second subcooling heat
exchanger (101). On the other hand, refrigerant that has flown out
of the low-pressure channel (105b) of the first-c subcooling heat
exchanger (105) (see "36" in FIGS. 8 and 9) flows into the first
injection pipe (107). Refrigerant flowing in the first injection
pipe (107) flows into the first refrigerant pipe (70) and merges
with refrigerant (see "37" in FIGS. 8 and 9) flowing in the first
refrigerant pipe (70) to be merged refrigerant (see "3" in FIGS. 8
and 9). That is, refrigerant that has flown into the third
injection pipe (109) is injected toward a suction side of a second
compressor (22). The other configurations, operations, and
advantages are similar to those of the first embodiment.
Third Embodiment
[0218] A third embodiment according to the present invention will
now be described. As illustrated in FIG. 10, an air conditioner
(140) according to the third embodiment has a configuration of a
refrigerant circuit different from that of the air conditioner (1)
of the first embodiment. In the third embodiment, only part of the
configuration different from that of the first embodiment is
described.
[0219] Specifically, the air conditioner (140) of the third
embodiment will now be described. The air conditioner (140)
includes a refrigerant circuit (143) in which a flow of refrigerant
is allowed to be changed reversibly, and is switchable between
cooling operation and heating operation. The air conditioner (140)
includes an outdoor unit (142) located outdoors and an indoor unit
(141) located indoors. The refrigerant circuit (143) of the air
conditioner (140) is obtained by connecting an outdoor circuit
(144) of the outdoor unit (142) and an indoor circuit (145) of the
indoor unit (141) to each other through a gas-side communication
pipe (146) and a liquid-side communication pipe (147). The
refrigerant circuit (143) is filled with carbon dioxide
(hereinafter referred to as refrigerant), and configured to perform
a multistage compression supercritical refrigeration cycle by
circulating refrigerant in the refrigerant circuit (143).
[0220] <Outdoor Circuit>
[0221] As illustrated in FIG. 10, the outdoor circuit (144) is
connected to a two-stage compressor (150), an outdoor heat exchange
unit (160), first and second four-way valves (175, 176), first and
second subcooling heat exchangers (191, 192), first through fifth
expansion valves (201-205), an expander (193), and a gas-liquid
separator (194). The outdoor heat exchange unit (160) includes an
intermediate heat exchanger (161) and an outdoor heat exchanger
(162).
[0222] The outdoor circuit (144) is also connected to two oil
separators (174, 174), a distributor (173), a capillary tube (170),
a bridge circuit (172), and check valves (CV1-CV7).
[0223] In the third embodiment, the refrigerant circuit (143) is
switched between cooling operation and heating operation by
switching the first and second four-way valves (175, 176).
[0224] The two-stage compressor (150) includes first and second
compressors (151, 152) and is a multistage compressor of the
present invention. The first and second compressors (151, 152) are
connected to first and second discharge pipes (153, 154) at
discharge sides thereof, while being connected to first and second
suction pipes (155, 156) at suction sides thereof. Each of the
compressors (151, 152) compresses low-pressure gas refrigerant
sucked through an associated one of the suction pipes (155, 156) to
be high-pressure gas refrigerant, which is then discharged from the
discharge pipe (153, 154).
[0225] The first four-way valve (175) has its first port connected
to the first discharge pipe (153) of the first compressor (151),
its second port connected to an end of the junction pipe (187), its
third port connected to an end of the intermediate heat exchanger
(161), and its fourth port connected to the second suction pipe
(156) of the second compressor (152). The first four-way valve
(175) is swithced between a first state (a state indicated by a
continuous line in FIG. 10) in which the first port communicates
with the third port and the second port communicates with the
fourth port and a second state (a state indicated by a broken line
in FIG. 10) in which the first port communicates with the fourth
port and the second port communicates with the third port.
[0226] The second four-way valve (176) has its first port connected
to the second discharge pipe (154) of the second compressor (152),
its second port connected to an end of the connection pipe (186),
its third port connected to an end of outdoor heat exchanger (162),
and its fourth port connected to the gas-side communication pipe
(146). The first four-way valve (175) is switched between a first
state (a state indicated by a continuous line in FIG. 10) in which
the first port communicates with the third port and the second port
communicates with the fourth port and a second state (a state
indicated by a broken line in FIG. 10) in which the first port
communicates with the fourth port and the second port communicates
with the third port.
[0227] The check valve (CV1) is connected to a midpoint of the
second suction pipe (156). The check valve (CV1) allows refrigerant
to flow from the first four-way valve (175) to the two-stage
compressor (150), and prevents refrigerant from flowing in a
reverse direction.
[0228] The oil separators (174, 174) are connected to midpoints of
the first and second discharge pipes (153, 154), respectively. The
oil separators (174, 174) separate lubricating oil contained in
high-pressure gas refrigerant flowing in the discharge pipes (153,
154) from the high-pressure gas refrigerant. The oil separators
(174, 174) are connected to oil outflow pipe (171, 171) through
which lubricating oil separated in the oil separators (174, 174)
flows to the outside of the oil separators (174, 174).
[0229] Specifically, the oil outflow pipe (171) of the oil
separator (174) for the first discharge pipe (153) is connected to
the second suction pipe (156). The oil outflow pipe (171) of the
oil separator (174) for the second discharge pipe (154) is
connected to the first suction pipe (155). The capillary tubes
(170, 170) are connected to midpoints of the oil outflow pipes
(171, 171), respectively.
[0230] The intermediate heat exchanger (161) and the outdoor heat
exchanger (162) are configured as fin-and-tube heat exchangers. The
intermediate heat exchanger (161) in this embodiment corresponds to
an intermediate heat exchanger of the present invention, and the
outdoor heat exchanger (162) in this embodiment corresponds to an
outdoor heat exchanger of the present invention. An outdoor fan
(122) is disposed near each of the heat exchangers (161, 162) so
that heat exchange is performed between outdoor air from the
outdoor fan (122) and refrigerant flowing in heat exchanger tubes
of the heat exchangers (161, 162).
[0231] An end of the intermediate heat exchanger (161) is connected
to the third port of the first four-way valve (175), and an end of
the outdoor heat exchanger (162) is connected to the third port of
the second four-way valve (176). On the other hand, the other end
of the intermediate heat exchanger (161) is connected to the first
refrigerant pipe (181), and the other end of the outdoor heat
exchanger (162) is connected to the second refrigerant pipe
(182).
[0232] The other end of the second refrigerant pipe (182) branches
off into two parts, one of which is connected to the bridge circuit
(172) and the other of which is connected to a second outflow port
(P2) of the distributor (173). The check valve (CV3) and the
capillary tube (170) are located between the branch point of the
second refrigerant pipe (182) and the second outflow port (P2) of
the distributer (173). The check valve (CV3) allows refrigerant to
flow from the distributor (173) to the branch point of the second
refrigerant pipe (182), and prevents refrigerant from flowing in a
reverse direction.
[0233] The other end of the first refrigerant pipe (181) branches
off into two parts, one of which is connected to a midpoint
(between the check valve (CV1) and the second compressor (152)) of
the second suction pipe (156) and the other of which is connected
to a first outflow port (P1) of the distributor (173). The check
valve (CV2) and the capillary tube (170) are located between the
branch point of the first refrigerant pipe (181) and the first
outflow port (P1) of the distributor (173). The check valve (CV2)
allows refrigerant to flow from the distributor (173) to the branch
point of the first refrigerant pipe (181), and prevents refrigerant
from flowing in a reverse direction. The check valve (CV4) is
located between the branch point of the first refrigerant pipe
(181) and the connection point of the second suction pipe (156).
The check valve (CV4) allows refrigerant to flow from the branch
point of the first refrigerant pipe (181) to the connection point
of the second suction pipe (156), and prevents refrigerant from
flowing in a reverse direction.
[0234] The bridge circuit (172) is a circuit in which the check
valves (CV5, CV6, CV7) and a fifth expansion valve (205) are
bridged. In the bridge circuit (172), a connection end between an
inflow end of the check valve (CV7) and the other end of the fifth
expansion valve (205) is connected to the first outflow pipe (180),
and a connection end located between outflow end of the check valve
(CV7) and an inflow end of the check valve (CV6) is connected to
the liquid-side communication pipe (147). A refrigerant pipe
connecting the liquid-side communication pipe (147) and the first
indoor heat exchanger (211) includes a first indoor expansion valve
(206) having a variable opening degree. A refrigerant pipe
connecting the liquid-side communication pipe (147) and the second
indoor heat exchanger (212) includes a second indoor expansion
valve (207) having a variable opening degree. A connection end
located between an outflow end of the check valve (CV6) and an
outflow end of the check valve (CV5) is connected to the inflow
pipe (179). An end of the fifth expansion valve (205) is connected
to the distributor (173), and an inflow end of the check valve
(CV5) is connected to the second refrigerant pipe (182).
[0235] On the inflow pipe (179), the first subcooling heat
exchanger (191), the expander (193), the gas-liquid separator
(194), and the second subcooling heat exchanger (192) are disposed
in this order.
[0236] The first subcooling heat exchanger (191) includes a
high-pressure channel (191a) and a low-pressure channel (191b). In
the first subcooling heat exchanger (191), heat exchange is
performed between refrigerant flowing in the high-pressure channel
(191a) and refrigerant flowing in the low-pressure channel (191b)
to subcool refrigerant flowing in the high-pressure channel
(191a).
[0237] An inflow end of the high-pressure channel (191a) is
connected to the inflow pipe (179), and an inflow end of the
low-pressure channel (191b) is connected to the first branch pipe
(177) serving as a passage for subcooling. The first branch pipe
(177) includes a second expansion valve (202) for subcooling. The
second expansion valve (202) is an electronic expansion valve
having an adjustable opening degree. An outflow end of the
low-pressure channel (191b) is connected to an end of the injection
pipe (188).
[0238] An end of the injection pipe (188) is connected to the
low-pressure channel (191b) of the first subcooling heat exchanger
(191), and the other end of the injection pipe (188) is connected
to the first refrigerant pipe (181). The other end of the injection
pipe (188) is connected to an outflow end of the check valve (CV4)
in the first refrigerant pipe (181).
[0239] The expander (193) includes an expander casing having a
vertically elongated cylindrical shape, and is located between the
first subcooling heat exchanger (191) and the gas-liquid separator
(194) on the inflow pipe (179). In the expander casing, an
expansion mechanism for generating power by expanding refrigerant
is provided. The expander (193) constitutes a so-called rotary
positive-displacement fluid machine. The expander (193) expands the
inflow refrigerant and sends the expanded refrigerant back to the
inflow pipe (179).
[0240] The inflow pipe (179) includes a bypass pipe (183) that
bypasses the expander (193). An end of the bypass pipe (183) is
connected to an inflow end of the expander (193), and the other end
of the bypass pipe (183) is connected to an outflow end of the
expander (193) to bypass the expander (193). The bypass pipe (183)
includes a first expansion valve (201). The first expansion valve
(201) is an electronic expansion valve having an adjustable opening
degree.
[0241] The gas-liquid separator (194) is an hermetic container
having a vertically elongated cylindrical shape. The gas-liquid
separator (194) is connected to the inflow pipe (179), the first
outflow pipe (180), and the second outflow pipe (184). The inflow
pipe (179) is open in an upper portion of the inner space of the
gas-liquid separator (194). The first outflow pipe (180) is open in
a lower portion of the inner space of the gas-liquid separator
(194). The second outflow pipe (184) is open in an upper portion of
the inner space of the gas-liquid separator (194). In the
gas-liquid separator (194), refrigerant from the inflow pipe (179)
is separated into a saturated liquid and a saturated gas, where the
saturated liquid flows out of the first outflow pipe (180) and the
saturated gas flows out of the second outflow pipe (184).
[0242] An end of the second outflow pipe (184) is connected to the
gas-liquid separator (194), and the other end of the second outflow
pipe (184) is connected to a midpoint of the second branch pipe
(178). The second outflow pipe (184) includes a fourth expansion
valve (204). The fourth expansion valve (204) is an electronic
expansion valve having an adjustable opening degree.
[0243] The second subcooling heat exchanger (192) is connected to a
midpoint of the first outflow pipe (180). The second subcooling
heat exchanger (192) includes a high-pressure channel (192a) and a
low-pressure channel (192b). In the second subcooling heat
exchanger (192), heat exchange is performed between refrigerant
flowing in the high-pressure channel (192a) and refrigerant flowing
in the low-pressure channel (192b) to subcool refrigerant flowing
in the high-pressure channel (192a).
[0244] An inflow end of the high-pressure channel (192a) is
connected to an outflow end of the gas-liquid separator (194), and
an outflow end of the high-pressure channel (192a) is connected to
the bridge circuit (172). An inflow end of the low-pressure channel
(192b) is connected to the second branch pipe (178) serving as a
passage for subcooling, and an outflow end of the low-pressure
channel (192b) is connected to the other end of the return pipe
(185).
[0245] One end of the second branch pipe (178) is connected to a
midpoint of the first outflow pipe (180) between the gas-liquid
separator (194) and the second subcooling heat exchanger (192), and
the other end of the second branch pipe (178) is connected to an
inflow end of the low-pressure channel (192b) of the second
subcooling heat exchanger (192), where the second outflow pipe
(184) is connected between the one end and the other end. The
second branch pipe (178) includes a third expansion valve (203).
The third expansion valve (203) is an electronic expansion valve
having an adjustable opening degree.
[0246] An end of the return pipe (185) is connected to the other
end of the connection pipe (186), and the other end of the return
pipe (185) is connected to an outflow end of the low-pressure
channel (192b) of the second subcooling heat exchanger (192).
[0247] An end of the connection pipe (186) is connected to the
second port of the second four-way valve (176), and the other end
of the connection pipe (186) is connected to an end of the return
pipe (185) and the other end of the first suction pipe (155), where
the other end of the junction pipe (187) is connected to a midpoint
of the connection pipe (186) between the second port and the
connection point connecting the end of the return pipe (185) and
the other end of the first suction pipe (155).
[0248] An end of the junction pipe (187) is connected to the second
port of the first four-way valve (175), and the other end of the
junction pipe (187) is connected to a midpoint of the connection
pipe (186).
[0249] <Indoor Circuit>
[0250] In the indoor circuit (145), a pair of the first indoor
expansion valve (206) and the first indoor heat exchanger (211) and
a pair of the second indoor expansion valve (207) and the second
indoor heat exchanger (212) are disposed in this order from a
liquid side to a gas side, and are connected in parallel. Each of
the indoor expansion valves (206, 207) is an electronic expansion
valve having an adjustable opening degree. Each of the indoor heat
exchangers (211, 212) is a cross-fin type fin-and-tube heat
exchanger. Although not shown, indoor fans for sending indoor air
to the indoor heat exchangers (211, 212) are provided near the
indoor heat exchangers (211, 212). In each of the indoor heat
exchangers (211, 212), heat exchange is performed between
refrigerant and the indoor air.
[0251] <Configuration of Outdoor Unit>
[0252] As illustrated in FIG. 12, the outdoor unit (142) includes
an outdoor casing (163). The outdoor casing (163) is in the shape
of a vertically elongated rectangular box, and has an air inlet
(164) in a lower portion of the front surface and an air outlet
(165) in an upper surface thereof. In the outdoor casing (163), the
outdoor heat exchange unit (160) and the outdoor fan (166) are
placed.
[0253] The outdoor fan (166) is a fan for sending air taken in the
outdoor casing (163) to the heat exchangers (161, 162), and is a
so-called sirocco fan. The outdoor fan (166) is located above the
heat exchangers (161, 162) in the outdoor casing (163). The outdoor
fan (166) causes air sucked through the air inlet (164) to pass
through the heat exchangers (161, 162) and then to flow to the
outside through the air outlet (165).
[0254] As illustrated in FIG. 12, in the outdoor casing (163), the
outdoor heat exchange unit (160) is oriented such that the
intermediate heat exchanger (161) and the outdoor heat exchanger
(162) are stacked this order from the bottom. That is, the outdoor
heat exchanger (162) is located above the intermediate heat
exchanger (161).
[0255] Each of the heat exchangers (161, 162) is a so-called
cross-fin type fin-and-tube heat exchanger. Each of the heat
exchangers (161, 162) includes a plurality of heat exchanger tube
groups each including a plurality of heat exchanger tubes and a
plurality of U-shaped tubes, and also includes a heat transmission
fin.
[0256] The heat exchanger tube groups are aligned in the up and
down direction. In each of the heat exchanger tube groups, a
plurality of heat exchanger tubes are arranged such that three rows
of heat exchanger tubes each along an airflow direction are
arranged side by side and each of the three rows includes two heat
exchanger tubes aligned in the up and down direction. In addition,
a first bank of tubes is disposed at the windward side, a second
bank of tubes is disposed at the middle, and a third bank of tubes
is disposed at the leeward side. That is, in each of the heat
exchanger tube groups, the heat exchanger tubes are disposed in two
stages in each row.
[0257] --Operation--
[0258] Operation of the air conditioner (140) will now be
described. In the air conditioner (140), the refrigerant circuit
(143) is switched between cooling operation and heating operation
by switching the first and second four-way valves (175, 176).
Reference numerals 1-18 in FIGS. 10 and 11 represent pressure
states of refrigerant.
[0259] --Cooling Operation--
[0260] Cooling operation of the air conditioner (140) will be
described with reference to FIG. 10. In FIG. 10, a refrigerant flow
in this cooling operation is represented by arrows of continuous
line. In the cooling operation, the outdoor heat exchanger (162)
operates as a heat dissipator, and the indoor heat exchangers (211,
212) operate as evaporators, thereby performing a two-stage
compression supercritical refrigeration cycle. The intermediate
heat exchanger (161) operates as a cooler that cools high-pressure
refrigerant discharged from the first compressor (151).
[0261] In the cooling operation, all the four-way valves (175, 176)
are set in the first states, and the two-stage compressor (150) is
driven. When the two-stage compressor (150) is driven, refrigerant
is compressed in the compressors (161, 162). Refrigerant compressed
in the first compressor (151) is discharged to the first discharge
pipe (153) (see "2" in FIGS. 10 and 11). In this state, the oil
separator (174) of the first discharge pipe (153) separates
lubricating oil from gas refrigerant flowing in the first discharge
pipe (153). The separated lubricating oil is sent from the oil
outflow pipe (171) to the second suction pipe (156). Refrigerant
flowing in the first discharge pipe (153) passes through the first
four-way valve (175) and flows into the intermediate heat exchanger
(161). In the intermediate heat exchanger (161), refrigerant
dissipates heat to the outdoor air to be cooled. Refrigerant cooled
in the intermediate heat exchanger (161) flows into the first
refrigerant pipe (181). Refrigerant flowing in the first
refrigerant pipe (181) (see "3" in FIGS. 10 and 11) passes through
the check valve (CV4) and merges with refrigerant flowing in the
injection pipe (188). The merged refrigerant flows into the second
suction pipe (156) and is sucked into the second compressor (152)
(see "4" in FIGS. 10 and 11).
[0262] Refrigerant compressed in the second compressor (152) (see
"5" in FIGS. 10 and 11) is discharged into the second discharge
pipe (154). The compression and cooling operations described above
are alternately performed in order to make compression strokes of
the two-stage compressor (150) approach those of isothermal
compression to reduce compression power necessary for the two-stage
compressor (150). At this time, the oil separator (174) of the
second discharge pipe (154) separates lubricating oil from gas
refrigerant flowing in the second discharge pipe (154). The
separated lubricating oil is sent from the oil outflow pipe (171)
to the first suction pipe (155). Refrigerant flowing in the second
discharge pipe (154) passes through the second four-way valve (176)
and flows into the outdoor heat exchanger (162). In the outdoor
heat exchanger (162), refrigerant dissipates heat to the outdoor
air to be cooled. Refrigerant cooled in the outdoor heat exchanger
(162) flows into the second refrigerant pipe (182). Refrigerant
flowing in the second refrigerant pipe (182) passes through the
check valve (CV5) and flows into the inflow pipe (179).
[0263] Part of refrigerant flowing in the inflow pipe (179) (see
"6" in FIGS. 10 and 11) flows into the first branch pipe (177). The
pressure of refrigerant flowing in the first branch pipe (177) is
reduced in the second expansion valve (202). Refrigerant whose
pressure has been reduced in the second expansion valve (202) (see
"7" in FIGS. 10 and 11) flows into the low-pressure channel (191b)
of the first subcooling heat exchanger (191). On the other hand,
the other part of refrigerant flowing in the inflow pipe (179)
flows into the high-pressure channel (191a) of the first subcooling
heat exchanger (191) (see "6" in FIGS. 10 and 11). In the first
subcooling heat exchanger (191), heat exchange is performed between
refrigerant flowing in the high-pressure channel (191a) and
refrigerant flowing in the low-pressure channel (191b) to subcool
refrigerant flowing in the high-pressure channel (191a).
[0264] Refrigerant that has flown out of the high-pressure channel
(191a) of the first subcooling heat exchanger (191) flows in the
inflow pipe (179) again, and refrigerant that has flown out of the
low-pressure channel (100b) of the first subcooling heat exchanger
(191) flows into the injection pipe (188). Refrigerant flowing in
the injection pipe (188) (see "8" in FIGS. 10 and 11) flows into
the first refrigerant pipe (181) and merges with refrigerant in the
first refrigerant pipe (181) (see "4" in FIGS. 10 and 11). That is,
refrigerant that has flown into the injection pipe (188) is
injected toward a suction side of the second compressor (152).
[0265] Refrigerant that has flown out of the high-pressure channel
(191a) of the first subcooling heat exchanger (191) flows in the
inflow pipe (179) again (see "9" in FIGS. 1 and 2), and part of
this refrigerant flows into the expander (193). The expander (193)
expands the inflow refrigerant (see "9" to "11" in FIGS. 10 and
11), and sends the expanded refrigerant back to the inflow pipe
(179). On the other hand, the other part of refrigerant that has
flown out of the high-pressure channel (191a) of the first
subcooling heat exchanger (191) branches off into the bypass pipe
(183). Refrigerant flowing in the bypass pipe (183) is subjected to
pressure reduction in the first expansion valve (201) (see "9" to
"10" in FIGS. 10 and 11) and returns back to the inflow pipe (179).
Refrigerant that has flown out of the expander (193) and
refrigerant that has flown out of the bypass pipe (183) merge
together in the inflow pipe (179) (see "12" in FIGS. 10 and 11) and
flow into the gas-liquid separator (194). The gas-liquid separator
(194) separates the inflow refrigerant into gas refrigerant (see
"15" in FIGS. 10 and 11) and liquid refrigerant (see "13" in FIGS.
10 and 11).
[0266] The liquid refrigerant (see "13" in FIGS. 10 and 11) that
has flown out of the gas-liquid separator (194) flows in the inflow
pipe (179), and part of this refrigerant flows into the second
branch pipe (178). On the other hand, the other part of refrigerant
flowing in the inflow pipe (179) flows into the high-pressure
channel (192a) of the second subcooling heat exchanger (192).
[0267] Refrigerant (see "15" in FIGS. 10 and 11) that has flown out
of the gas-liquid separator (194) flows in the second outflow pipe
(184), is subjected to pressure reduction in the fourth expansion
valve (204) (see "18" in FIGS. 10 and 11), and flows into the
second branch pipe (178). The pressure of refrigerant flowing in
the second branch pipe (178) is reduced in the third expansion
valve (203). The pressure-reduced refrigerant (see "17" in FIGS. 10
and 11) in the third expansion valve (203) merges with refrigerant
flowing in the second outflow pipe (184).
[0268] The merged refrigerant flows into the low-pressure channel
(192b) of the second subcooling heat exchanger (192). In the second
subcooling heat exchanger (192), heat exchange is performed between
refrigerant flowing in the high-pressure channel (192a) and
refrigerant flowing in the low-pressure channel (192b) to subcool
the liquid refrigerant flowing in the high-pressure channel
(192a).
[0269] The liquid refrigerant that has flown out of the
high-pressure channel (192a) of the second subcooling heat
exchanger (192) (see "14" in FIGS. 10 and 11) flows in the first
outflow pipe (180) again, passes through the check valve (CV7) of
the bridge circuit (172), and flows into the liquid-side
communication pipe (147). On the other hand, refrigerant that has
flown out of the low-pressure channel (192b) of the second
subcooling heat exchanger (192) flows in the return pipe (185).
Refrigerant that has flown out of the return pipe (185) merges with
refrigerant that has flown out of the connection pipe (186). The
merged refrigerant flows into a suction side of the first
compressor (151).
[0270] Part of liquid refrigerant flowing in the liquid-side
communication pipe (147) branches off, and is subjected to pressure
reduction in the first indoor expansion valve (206). The
pressure-reduced refrigerant (see "16a" in FIGS. 10 and 11) flows
into the first indoor heat exchanger (211). In the first indoor
heat exchanger (211), liquid refrigerant absorbs heat from indoor
air and evaporates. The evaporated gas refrigerant flows into the
gas-side communication pipe (146).
[0271] The pressure of the other part of liquid refrigerant flowing
in the liquid-side communication pipe (147) is reduced in the
second indoor expansion valve (207). The pressure-reduced
refrigerant (see "16b" in FIGS. 10 and 11) flows into the second
indoor heat exchanger (212). In the second indoor heat exchanger
(212), liquid refrigerant absorbs heat from indoor air and
evaporates. The evaporated gas refrigerant flows into the gas-side
communication pipe (146).
[0272] In the gas-side communication pipe (146), refrigerant that
has flown out of the first indoor heat exchanger (211) and
refrigerant that has flown out of the second indoor heat exchanger
(212) merge together. Refrigerant flowing in the gas-side
communication pipe (146) passes through the second four-way valve
(176) and flows into the connection pipe (186). Refrigerant flowing
in the connection pipe (186) merges with refrigerant flowing in the
return pipe (185) and is sucked into the first suction pipe (155).
Refrigerant flowing in the first suction pipe (155) (see "1" in
FIGS. 10 and 11) is compressed in the first compressor (151) of the
two-stage compressor (150) again.
[0273] --Heating Operation--
[0274] Heating operation of the air conditioner (140) will now be
described with reference to FIG. 13. In FIG. 13, a refrigerant flow
in this heating operation is represented by arrows of broken line.
In the heating operation, the indoor heat exchangers (211, 212)
operate as heat dissipators, and the intermediate heat exchanger
(161) and the outdoor heat exchanger (162) operate as evaporators,
thereby performing a two-stage compression supercritical
refrigeration cycle.
[0275] In the heating operation, all the four-way valves (175, 176)
are set in the second states, and the two-stage compressor (150) is
driven. When the two-stage compressor (150) is driven, refrigerant
is compressed in the compressors (151, 152). Refrigerant compressed
in the first compressor (151) is discharged to the first discharge
pipe (153). The oil separator (174) of the first discharge pipe
(153) separates lubricating oil from gas refrigerant flowing in the
first discharge pipe (153). The separated lubricating oil is sent
from the oil outflow pipe (171) to the second suction pipe (156).
Refrigerant flowing in the first discharge pipe (153) passes
through the first four-way valve (175) and is sucked into the
second compressor (152). Refrigerant is further compressed in the
second compressor (152). In this manner, unlike the cooling
operation, two-stage compression is performed without cooling in
the heating operation. In this heating operation, the temperature
of refrigerant discharged from the two-stage compressor (150) does
not decrease, unlike the case of performing two-stage compression
with cooling. As a result, the heating operation shows a larger
heating capacity than that in the case of two-stage compression
with cooling.
[0276] Refrigerant discharged from the second compressor (152)
passes through the second four-way valve (176) and is sent to the
first and second indoor heat exchangers (211, 212). In the first
and second indoor heat exchangers (211, 212), refrigerant
dissipates heat to the indoor air to be cooled. Refrigerant cooled
in the indoor heat exchangers (211, 212) is subjected to pressure
reduction in the first and second indoor expansion valves (206,
207) and then sent to the bridge circuit (172). This refrigerant
passes through the check valve (CV6) and flows into the inflow pipe
(179).
[0277] Part of refrigerant flowing in the inflow pipe (179) flows
into the first branch pipe (177). The pressure of refrigerant
flowing in the first branch pipe (177) is reduced in the second
expansion valve (202). Refrigerant whose pressure has been reduced
in the second expansion valve (202) flows into the low-pressure
channel (191b) of the first subcooling heat exchanger (191). On the
other hand, the other part of refrigerant flowing in the inflow
pipe (179) flows into the high-pressure channel (191a) of the first
subcooling heat exchanger (191). In the first subcooling heat
exchanger (191), heat exchange is performed between refrigerant
flowing in the high-pressure channel (191a) and refrigerant flowing
in the low-pressure channel (191b) to subcool refrigerant flowing
in the high-pressure channel (191a).
[0278] Refrigerant that has flown out of the high-pressure channel
(191a) of the first subcooling heat exchanger (191) flows in the
inflow pipe (179) again, and refrigerant that has flown out of the
low-pressure channel (191b) of the first subcooling heat exchanger
(191) flows into the injection pipe (188). Refrigerant flowing in
the injection pipe (188) flows into the first refrigerant pipe
(181) and merges with refrigerant in the first refrigerant pipe
(181). That is, refrigerant that has flown into the injection pipe
(188) is injected toward a suction side of the second compressor
(152).
[0279] Refrigerant that has flown out of the high-pressure channel
(191a) of the first subcooling heat exchanger (191) flows in the
inflow pipe (179) again, and part of refrigerant flows into the
expander (193). The expander (193) expands the inflow refrigerant,
and sends the expanded refrigerant back to the inflow pipe (179).
On the other hand, the other part of refrigerant that has flown out
of the high-pressure channel (191a) of the first subcooling heat
exchanger (191) branches off into the bypass pipe (183).
Refrigerant flowing in the bypass pipe (183) is subjected to
pressure reduction in the first expansion valve (201) and returns
back to the inflow pipe (179). Refrigerant that has flown out of
the expander (193) and refrigerant that has flown out of the bypass
pipe (183) merge together in the inflow pipe (179) and flow into
the gas-liquid separator (194). The gas-liquid separator (194)
separates the inflow refrigerant into gas refrigerant and liquid
refrigerant.
[0280] The liquid refrigerant that has flown out of the gas-liquid
separator (194) flows in the first outflow pipe (180), and part of
this refrigerant flows into the second branch pipe (178). On the
other hand, the other part of refrigerant flowing in the inflow
pipe (179) flows into the high-pressure channel (192a) of the
second subcooling heat exchanger (192).
[0281] Gas refrigerant that has flown out of the gas-liquid
separator (194) flows in the second outflow pipe (184), is
subjected to pressure reduction in the fourth expansion valve
(204), and flows into the second branch pipe (178). The pressure of
refrigerant flowing in the second branch pipe (178) is reduced in
the third expansion valve (203). Refrigerant whose pressure has
been reduced in the third expansion valve (203) merges with
refrigerant in the second outflow pipe (184).
[0282] The merged refrigerant flows into the low-pressure channel
(192b) of the second subcooling heat exchanger (192). In the second
subcooling heat exchanger (192), heat exchange is performed between
refrigerant flowing in the high-pressure channel (192a) and
refrigerant flowing in the low-pressure channel (192b) to subcool
the liquid refrigerant flowing in the high-pressure channel
(192a).
[0283] The liquid refrigerant that has flown out of the
high-pressure channel (192a) of the second subcooling heat
exchanger (192) flows in the first outflow pipe (180) again, is
subjected to pressure reduction in the fifth expansion valve (205)
of the bridge circuit (172), and then is sent to the distributor
(173). Refrigerant distributed in the distributor (173) passes
through the capillary tube (170) and the check valves (CV2, CV3)
and flows into the intermediate heat exchanger (161) and the
outdoor heat exchanger (162). In the intermediate heat exchanger
(161) the outdoor heat exchanger (162), liquid refrigerant absorbs
heat from the outdoor air and evaporates. Refrigerant that has
flown out of the intermediate heat exchanger (161) passes through
the first four-way valve (175), flows into the junction pipe (187),
and then flows into the connection pipe (186).
[0284] Refrigerant that has flown out of the outdoor heat exchanger
(162) passes through the second four-way valve (176), flows into
the connection pipe (186), and merges with refrigerant that has
flown out of the intermediate heat exchanger (161). The merged
refrigerant flows in the connection pipe (186) and merges with
refrigerant flowing in the return pipe (185). The merged
refrigerant flows into the first suction pipe (155). Refrigerant
flowing in the first suction pipe (155) is compressed again in the
first compressor (151) of the two-stage compressor (150).
[0285] --Outdoor Unit--
[0286] As illustrated in FIG. 12, air taken into the outdoor casing
(163) from the air inlet (164) is subjected to heat exchange in the
intermediate heat exchanger (161) and the outdoor heat exchanger
(162), flows to upper space in the outdoor casing (163), and is
blown out through the air outlet (124).
[0287] The outdoor unit (3) is a so-called upward blow type in
which air is sucked through the air inlet (164) in the side surface
and is blown upward from the air outlet (124). Thus, the airflow
velocity is higher in an upper portion of the air inlet (164) than
in a lower portion of the air inlet (164). As illustrated in FIG.
11, the pressure of refrigerant flowing in the intermediate heat
exchanger (161) is lower than that of refrigerant flowing in the
outdoor heat exchanger (162), and thus, the density of refrigerant
flowing in the intermediate heat exchanger (161) is lower than that
of refrigerant flowing in the outdoor heat exchanger (162). In view
of this, when the mass flow rate of refrigerant flowing in the
intermediate heat exchanger (161) is substantially equal to that of
refrigerant flowing in the outdoor heat exchanger (162), the volume
flow rate of refrigerant in the intermediate heat exchanger (161)
is higher than that of refrigerant flowing in the outdoor heat
exchanger (162). Even when the number of refrigerant paths in the
intermediate heat exchanger (161) is equal to that in the outdoor
heat exchanger (162), the flow velocity of refrigerant flowing in
the intermediate heat exchanger (161) is higher than that of
refrigerant flowing in the outdoor heat exchanger (162), and thus,
a pressure loss of refrigerant in the intermediate heat exchanger
(161) is larger than that in the outdoor heat exchanger (162).
[0288] The outdoor heat exchanger (162) located in an upper portion
of the outdoor casing (163) where the airflow velocity is high, has
a high heat exchange efficiency, and can be reduced in size. On the
other hand, the intermediate heat exchanger (161) located in a
lower portion of the outdoor casing (163) where the airflow
velocity is low, has a low heat exchange efficiency. Thus, to
increase the amount of heat exchange, the intermediate heat
exchanger (161) needs to be larger than that in a case where this
exchanger is located in an upper portion.
[0289] For this reason, the size of the outdoor heat exchange unit
(160) does not increase even when the size of the outdoor heat
exchanger (162) and the intermediate heat exchanger (161)
increases.
[0290] An increase in size of the intermediate heat exchanger (161)
increases the number of refrigerant paths in the intermediate heat
exchanger (161). Thus, in the intermediate heat exchanger (161),
the flow velocity of refrigerant in each refrigerant path
decreases, resulting in a decrease in pressure loss of refrigerant
passing through the refrigerant path. The flow velocity of
refrigerant flowing in the intermediate heat exchanger (161) is
originally high, and thus, a decrease in flow velocity due to an
increase in the number of refrigerant paths relatively greatly
reduces the pressure loss.
[0291] On the other hand, size reduction of the outdoor heat
exchanger (162) reduces the number of refrigerant paths in the
outdoor heat exchanger (162). The reduction of the number of
refrigerant paths increases the flow velocity of refrigerant in
each refrigerant path to increase the pressure loss of refrigerant
passing through the refrigerant path.
[0292] However, since the flow velocity of refrigerant flowing in
the outdoor heat exchanger (162) is originally low, a certain
degree of increase in flow velocity due to the reduction of the
number of refrigerant paths relatively slightly increases the
pressure loss arising from the increase in flow velocity.
[0293] Thus, by disposing the outdoor heat exchanger (162) above
the intermediate heat exchanger (161), the pressure loss of
refrigerant in the intermediate heat exchanger (161) can be reduced
with a reduced degree of increase in size of the outdoor heat
exchange unit (160).
Advantages of Third Embodiment
[0294] In the third embodiment, since the outdoor heat exchanger
(162) is located in an upper portion of the outdoor casing (163)
where the airflow velocity is high, the heat exchange efficiency of
the outdoor heat exchanger (162) can be increased. In addition,
since the outdoor heat exchanger (162) having a low flow velocity
of refrigerant is located in an upper portion of the outdoor casing
(163) where the airflow velocity is high, the size of the outdoor
heat exchanger (162) can be reduced without an increase in pressure
loss of refrigerant.
[0295] On the other hand, the intermediate heat exchanger (161) is
located in a lower portion of the outdoor casing (163) where the
airflow velocity is low to increase the number of refrigerant
paths, thereby ensuring prevention of an increase in pressure loss
of refrigerant in the intermediate heat exchanger (161).
[0296] In the above-described configuration, the outdoor heat
exchanger (162) where a pressure loss of refrigerant does not
easily increase is located in the upper portion for size reduction,
thereby reducing a pressure loss of refrigerant in the intermediate
heat exchanger (161) with reduced size increase in the outdoor heat
exchange unit (160). The other configurations, operations, and
advantages are similar to those of the first and second
embodiments.
Variation of Third Embodiment
[0297] A variation of the third embodiment of the present invention
will now be described with reference to the drawings. An air
conditioner according to this variation is different in
configuration of heat exchangers from that of the air conditioner
(140) of the third embodiment. In this variation, only part of the
configuration different from that of the third embodiment is
described.
[0298] Specifically, as illustrated in FIGS. 14 and 15, the outdoor
unit (142) includes the outdoor casing (163). The outdoor casing
(163) is in the shape of a vertically elongated rectangular box,
and has the air inlet (164) in a lower portion of the front surface
and the air the air outlet (165) in an upper surface thereof. In
the outdoor casing (163), the outdoor heat exchange unit (160) and
the outdoor fan (166) are placed. The outdoor heat exchange unit
(160) includes the outdoor heat exchanger (162) and the
intermediate heat exchanger (161).
[0299] The outdoor fan (166) is a fan for sending air taken in the
outdoor casing (163) to the heat exchangers (161, 162), and is a
so-called sirocco fan. The outdoor fan (166) is located above the
heat exchangers (161, 162) in the outdoor casing (163). The outdoor
fan (166) causes air sucked through the air inlet (164) to pass
through the heat exchangers (161, 162) and then to flow to the
outside through the air outlet (165).
[0300] As illustrated in FIG. 14, in the outdoor casing (163), the
intermediate heat exchanger (161) and the outdoor heat exchanger
(162) are stacked this order from the bottom.
[0301] --Configuration of Heat Exchanger--
[0302] As illustrated in FIGS. 14 and 15, each of the heat
exchangers (161, 162) of this variation includes a first header
concentrated pipe (240), a second header concentrated pipe (250), a
large number of flat tubes (231), and a large number of fins (235).
The first header concentrated pipe (240), the second header
concentrated pipe (250), the flat tubes (231), and the fins (235)
are made of an aluminium alloy, and brazed to one another.
[0303] The first header concentrated pipe (240) and the second
header concentrated pipe (250) are hollow slender tubes. In each of
the heat exchangers (161, 162), the first header concentrated pipe
(240) stands at an end of the flat tubes (231) and the second
header concentrated pipe (250) stands at the other end of the flat
tubes (231). That is, each of the first header concentrated pipe
(240) and the second header concentrated pipe (250) extends in the
up and down direction such that the axis thereof extends
vertically.
[0304] The first header concentrated pipe (240) has its upper and
lower ends closed, and has its lower end connected to a first
connection pipe (240b). The first connection pipe (240b)
communicates with a liquid side of the refrigerant circuit (143).
That is, the first header concentrated pipe (240) constitutes a
liquid-side header in which liquid-containing refrigerant (liquid
single-phase refrigerant or gas-liquid two-phase refrigerant)
flows. The second header concentrated pipe (250) has its upper and
lower ends closed, and a second connection pipe (250b) is connected
to an upper portion of the second header concentrated pipe (250).
The second connection pipe (250b) is connected to a gas side of the
refrigerant circuit (143). That is, the second header concentrated
pipe (250) constitutes a gas-side header in which a gas refrigerant
flows.
[0305] Each of the heat exchangers (161, 162) of this variation
includes a plurality of flat tubes (231). Each of the flat tubes
(231) is a heat exchanger tube whose shape in cross section
perpendicular to the axis thereof is a flat ellipse or a rectangle.
In each of the heat exchangers (161, 162), the flat tubes (231)
extend in the transverse direction with flat side surfaces thereof
facing one another. The flat tubes (231) are arranged side by side
at predetermined intervals in the up and down direction. An end of
each of the flat tubes (231) is placed in the first header
concentrated pipe (240), and the other end thereof is placed in the
second header concentrated pipe (250).
[0306] As illustrated in FIG. 15, each of the flat tubes (231)
includes a plurality of refrigerant paths (232). The refrigerant
paths (232) are passages extending in the direction in which the
flat tubes (231) extend. In each of the flat tubes (231), the
refrigerant paths (232) are arranged in a row along a transverse
direction perpendicular to the direction in which the flat tubes
(231) extend. Each of the refrigerant paths (232) of the flat tubes
(231) has its one end communicate with the inner space of the first
header concentrated pipe (240) and the other end communicate with
the inner space of the second header concentrated pipe (250). The
refrigerant paths (232) constitute fluid passages of the present
invention.
[0307] Each of the fins (235) is a corrugated fin that bends up and
down and is located between ones of the flat tubes (231) that are
adjacent to each other in the up and down direction. Each of the
fins (235) includes a plurality of heat transmission parts (236)
arranged in the direction in which the flat tubes (231) extend.
Each of the heat transmission parts (236) has a plate shape
extending from one of the adjacent flat tubes (231) to the other.
The heat transmission parts (236) includes a plurality of louvers
(237) that bend out from the heat transmission parts (236). The
louvers (237) extend in the up and down direction to be
substantially in parallel with front edges (i.e., windward ends) of
the heat transmission parts (236). In the heat transmission parts
(236), the louvers (237) are arranged side by side from the
windward side to the leeward side.
[0308] The leeward ends of the heat transmission parts (236) are
joined to the projecting plate parts (238) further projecting
leeward. Each of the projecting plate parts (238) is in the shape
of a trapezoidal plate protruding from the heat transmission parts
(236) in the up and down direction. In each of the heat exchangers
(161, 162), adjacent ones of the projecting plate parts (238, 238)
in the up and down direction overlap each other in the thickness
direction, and are substantially in contact with each other.
[0309] The number of each of the flat tubes (231) and the fins
(235, 235) are two or more. The fins (235, 235) are disposed
between the flat tubes (231) arranged in the up and down direction.
In the intermediate heat exchangers (41, 42, 43, 161), air passes
between the flat tubes (231) arranged in the up and down direction,
and exchanges heat with fluid flowing in the fluid passages (232)
in the flat tubes (231).
[0310] The intermediate heat exchanger (161) has a small stack loss
(resistance of ventilation), and thus, has a high velocity of air
flowing therein. In addition, the flat tubes (231) increase the
heat transfer area of refrigerant, and thus, the heat exchange
efficiency of refrigerant increases. Accordingly, the coefficient
of performance (COP) of the refrigeration system is enhanced. Since
the flat tubes (231) have pipe diameters smaller than those of
conventional heat exchanger tubes, the flow velocity in the tubes
increases. Thus, refrigerant passing through the refrigerant paths
(232) has a large pressure loss.
[0311] However, in the intermediate heat exchanger (161) located in
the lower portion of the outdoor casing (163) where the airflow
velocity is low has a low heat exchange efficiency. Thus, to
increase the amount of heat exchange, the intermediate heat
exchanger (161) needs to be larger than that in a case where this
exchanger is located in an upper portion. The larger intermediate
heat exchanger (161) includes a larger number of the refrigerant
paths (232), and thus, the flow velocity of refrigerant in the
refrigerant paths (232) of the intermediate heat exchanger (161)
decreases, thereby reducing the pressure loss of refrigerant
occurring when refrigerant passes through the refrigerant paths
(232). Consequently, reduction in pipe diameter of the flat tubes
(231) relatively reduces the degree of increase in pressure loss of
refrigerant.
[0312] The outdoor heat exchanger (162) has a small stack loss, and
thus, has a high velocity of air flowing therein. In addition, the
flat tubes (231) increase the heat transfer area of refrigerant,
and thus, the heat exchange efficiency of refrigerant increases.
Accordingly, the coefficient of performance (COP) of the
refrigeration system is enhanced. Since the flat tubes (231) have
pipe diameters smaller than those of conventional heat exchanger
tubes, the flow velocity in the tubes increases. Thus, refrigerant
passing through the refrigerant paths (232) has a large pressure
loss.
[0313] However, since the flow velocity of refrigerant flowing in
the outdoor heat exchanger (162) is originally low, even when the
flow velocity increases to some degree due to a reduction in pipe
diameter of the flat tubes (231), the amount of increase in
pressure loss due to this increase is relatively small.
[0314] In this variation, since the intermediate heat exchanger
(161) and the outdoor heat exchanger (162) include the flat tubes
(231) each including the refrigerant paths (232) and the fins (235,
235), the stack loss (resistance of ventilation) can be reduced. As
a result, the velocity of air flowing in the air passages
increases. In addition, the flat tubes (231) increase the heat
transfer area of refrigerant, the heat exchange efficiency of
refrigerant increases. As a result, the coefficient of performance
(COP) of the air conditioner can be enhanced. The other
configurations, operations, and advantages are similar to those of
the third embodiment.
Reference Example
[0315] Reference example will now be described. As illustrated in
FIGS. 18 and 19, in this reference example, the airflow velocity
distribution in the indoor unit is uniform in the up and down
direction.
[0316] An outdoor heat exchange unit (40) of this reference example
is configured such that an outdoor heat exchanger (44), a first
intermediate heat exchanger (41), a second intermediate heat
exchanger (42), and a third intermediate heat exchanger (43) are
stacked in this order from the bottom. The first intermediate heat
exchanger (41) and the second intermediate heat exchanger (42) may
be replaced with each other in the up and down direction.
[0317] The heat exchanger size increases in the order of the
outdoor heat exchanger (44), the third intermediate heat exchanger
(43), the first intermediate heat exchanger (41), and the second
intermediate heat exchanger (42).
[0318] The heat exchangers (41, 42, 43, 44) are so-called cross-fin
type fin-and-tube heat exchangers. Each of the heat exchangers (41,
42, 43, 44) includes a plurality of heat exchanger tube groups (50)
each including a plurality of heat exchanger tubes (52) and a
plurality of U-shaped tubes, and also includes heat transmission
fins (51).
[0319] The heat exchanger tube groups (50) are aligned in the up
and down direction. In each of the heat exchanger tube groups (50),
a plurality of heat exchanger tubes (52) are arranged such that
three rows of heat exchanger tubes (52) each along an airflow
direction are arranged side by side and each of the three rows
includes two heat exchanger tubes (52) aligned in the up and down
direction. In addition, a first bank of tubes (53) is disposed at
the left in FIG. 19 (i.e., the windward side), a second bank of
tubes (54) is disposed at the middle in FIG. 19, and a third bank
of tubes (55) is disposed at the right in FIG. 19 (i.e., the
leeward side). That is, in each of the heat exchanger tube groups
(50), the heat exchanger tubes (52) are disposed in two stages in
each row.
Other Embodiments
[0320] The present invention may have the following configurations
with respect to the first and second embodiments.
[0321] In the first and second embodiments, the four-stage
compressor (20) is used. However, the present invention is not
limited to this configuration, and two two-stage compressors may be
provided.
[0322] In the first through fourth embodiments, the two-stage
compression supercritical refrigeration cycle and the four-stage
compression supercritical refrigeration cycle are used. However,
the present invention is not limited to this, and is applicable to
a supercritical refrigeration cycle of a three-stage compressor or
a refrigeration cycle of another type of multistage compressor, for
example.
[0323] In the first and second embodiments, the heat exchanger is
the fin-and-tube heat exchanger. However, the present invention is
not limited to this type.
[0324] Specifically, as illustrated in 16, the outdoor unit (3) may
include the outdoor casing (121). The outdoor casing (121) is in
the shape of a vertically rectangular box, and has an air inlet
(123) in a lower portion of the front surface and an air outlet
(124) in an upper surface thereof. The outdoor heat exchange unit
(40) and the outdoor fan (122) are placed in the outdoor casing
(121). The outdoor heat exchange unit (40) includes the outdoor
heat exchanger (44), the first intermediate heat exchanger (41),
the second intermediate heat exchanger (42), and the third
intermediate heat exchanger (43).
[0325] As illustrated in FIG. 16, in the outdoor casing (121), the
first intermediate heat exchanger (41), the second intermediate
heat exchanger (42), the third intermediate heat exchanger (43),
and the outdoor heat exchanger (162) are stacked in this order from
the bottom. That is, the outdoor heat exchanger (162) is located
above the first through third intermediate heat exchangers (41, 42,
43). In this configuration, the first intermediate heat exchanger
(41) and the second intermediate heat exchanger (42) may be
replaced with each other in the up and down direction.
[0326] --Configuration of Heat Exchanger--
[0327] As illustrated in FIGS. 16 and 17, each of the heat
exchangers (41, 42, 43, 44) of this embodiment includes a first
header concentrated pipe (240), a second header concentrated pipe
(250), a large number of flat tubes (231), and a large number of
fins (235). The first header concentrated pipe (240), the second
header concentrated pipe (250), the flat tubes (231), and the fins
(235) are made of an aluminium alloy, and brazed to one
another.
[0328] The first header concentrated pipe (240) and the second
header concentrated pipe (250) are hollow slender tubes. In each of
the heat exchangers (41, 42, 43, 44), the first header concentrated
pipe (240) stands at an end of the flat tubes (231) and the second
header concentrated pipe (250) stands at the other end of the flat
tubes (231). That is, each of the first header concentrated pipe
(240) and the second header concentrated pipe (250) extends in the
up and down direction such that the axis thereof extends
vertically.
[0329] The first header concentrated pipe (240) has its upper and
lower ends closed, and its lower end connected to a first
connection pipe (240b). The first connection pipe (240b)
communicates with a liquid side of the refrigerant circuit (10).
That is, the first header concentrated pipe (240) constitutes a
liquid-side header in which liquid-containing refrigerant (liquid
single-phase refrigerant or gas-liquid two-phase refrigerant)
flows. The second header concentrated pipe (250) has its upper and
lower ends closed, and a second connection pipe (250b) is connected
to an upper portion of the second header concentrated pipe (250).
The second connection pipe (250b) is connected to a gas side of the
refrigerant circuit (10). That is, the second header concentrated
pipe (250) constitutes a gas-side header in which a gas refrigerant
flows.
[0330] Each of the heat exchangers (41, 42, 43, 44) of this
embodiment includes a plurality of flat tubes (231). Each of the
flat tubes (231) is a heat exchanger tube whose shape in cross
section perpendicular to the axis thereof is a flat ellipse or a
rectangle. In each of the heat exchangers (41, 42, 43, 44), the
flat tubes (231) extend in the transverse direction with flat side
surfaces thereof facing one another. The flat tubes (231) are
arranged side by side at predetermined intervals in the up and down
direction. An end of each of the flat tubes (231) is placed in the
first header concentrated pipe (240), and the other end thereof is
placed in the second header concentrated pipe (250).
[0331] As illustrated in FIG. 17, each of the flat tubes (231)
includes a plurality of refrigerant paths (232). The refrigerant
paths (232) are fluid passages of the present invention extending
in the direction in which the flat tubes (231) extend. In each of
the flat tubes (231), the refrigerant paths (232) are arranged in a
row along a transverse direction perpendicular to the direction in
which the flat tubes (231) extend. Each of the refrigerant paths
(232) of the flat tubes (231) has its one end communicate with the
inner space of the first header concentrated pipe (240) and the
other end communicate with the inner space of the second header
concentrated pipe (250).
[0332] Each of the fins (235) is a corrugated fin that bends up and
down and is located between ones of the flat tubes (231) that are
adjacent to each other in the up and down direction. Each of the
fins (235) includes a plurality of heat transmission parts (236)
arranged in the direction in which the flat tubes (231) extend.
Each of the heat transmission parts (236) has a plate shape
extending from one of the adjacent flat tubes (231) to the other.
The heat transmission parts (236) includes a plurality of louvers
(237) that bend out from the heat transmission parts (236). The
louvers (237) extend in the up and down direction to be
substantially in parallel with front edges (i.e., windward ends) of
the heat transmission parts (236). In the heat transmission parts
(236), the louvers (237) are arranged side by side from the
windward side to the leeward side.
[0333] The leeward ends of the heat transmission parts (236) are
joined to the projecting plate parts (238) further projecting
leeward. Each of the projecting plate parts (238) is in the shape
of a trapezoidal plate protruding from the heat transmission parts
(236) in the up and down direction. In each of the heat exchangers
(41, 42, 43, 44), adjacent ones of the projecting plate parts (238,
238) in the up and down direction overlap each other in the
thickness direction, and are substantially in contact with each
other. The other configurations, operations, and advantages are
similar to those of the variation of the third embodiment.
[0334] 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
[0335] As described above, the present invention is useful for a
refrigeration system that performs a multistage compression
refrigeration cycle.
DESCRIPTION OF REFERENCE CHARACTERS
[0336] 21 first compressor [0337] 22 second compressor [0338] 23
third compressor [0339] 24 fourth compressor [0340] 41 first
intermediate heat exchanger [0341] 42 second intermediate heat
exchanger [0342] 43 third intermediate heat exchanger [0343] 44
outdoor heat exchanger [0344] 121 outdoor casing [0345] 123 air
inlet [0346] 151 first compressor [0347] 152 second compressor
[0348] 161 outdoor heat exchanger [0349] 162 intermediate heat
exchanger [0350] 163 outdoor casing [0351] 164 air inlet [0352] 231
flat tube [0353] 232 refrigerant path [0354] 235 fin
* * * * *