U.S. patent application number 12/085677 was filed with the patent office on 2009-11-19 for refrigeration system.
Invention is credited to Shuuji Fujimoto, Takahiro Yamaguchi, Atsushi Yoshimi.
Application Number | 20090282849 12/085677 |
Document ID | / |
Family ID | 38092216 |
Filed Date | 2009-11-19 |
United States Patent
Application |
20090282849 |
Kind Code |
A1 |
Fujimoto; Shuuji ; et
al. |
November 19, 2009 |
Refrigeration System
Abstract
A refrigeration system (10) includes: a refrigerant circuit (15)
including a low-pressure stage compressor (21) variable in
displacement and a high-pressure stage compressor (31) variable in
displacement and operating in a two-stage compression refrigeration
cycle; and a controller (100) for controlling the operation of the
refrigeration system (10). The controller (100) includes a first
control section (101) and a second control section (102). The first
control section (101) controls the operating capacity of the
low-pressure stage compressor (21) to adapt to the load of the
refrigeration capacity. The second control section (102) controls
the operating capacity of the high-pressure stage compressor (31)
so that the ratio between a first pressure ratio, which is the
ratio of the discharge pressure of the low-pressure stage
compressor (21) to the suction pressure thereof, and a second
pressure ratio, which is the ratio of the discharge pressure of the
high-pressure stage compressor (31) to the suction pressure
thereof, is 1:1.
Inventors: |
Fujimoto; Shuuji; (Osaka,
JP) ; Yoshimi; Atsushi; (Osaka, JP) ;
Yamaguchi; Takahiro; (Osaka, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
38092216 |
Appl. No.: |
12/085677 |
Filed: |
November 29, 2006 |
PCT Filed: |
November 29, 2006 |
PCT NO: |
PCT/JP2006/323786 |
371 Date: |
May 29, 2008 |
Current U.S.
Class: |
62/228.5 ;
62/510 |
Current CPC
Class: |
F25B 2313/02731
20130101; F25B 2700/1931 20130101; F25B 13/00 20130101; F25B
2700/2109 20130101; F25B 2500/26 20130101; F25B 49/025 20130101;
F25B 2700/2106 20130101; F25B 2313/0315 20130101; F25B 2313/0314
20130101; F25B 2313/02741 20130101; F25B 2600/021 20130101; F25B
2700/21152 20130101; F25B 2700/2104 20130101; F25B 1/10 20130101;
Y02B 30/70 20130101; F25B 2700/1933 20130101; Y02B 30/741 20130101;
F25B 2313/006 20130101; F25B 2400/23 20130101 |
Class at
Publication: |
62/228.5 ;
62/510 |
International
Class: |
F25B 1/10 20060101
F25B001/10; F25B 49/02 20060101 F25B049/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2005 |
JP |
2005-345643 |
Claims
1. A refrigeration system that includes a refrigerant circuit (15)
including a first compression mechanism (21, 31) variable in
displacement and a second compression mechanism (31, 21) variable
in displacement and operates in a two-stage compression
refrigeration cycle, the refrigeration system further including: a
first control means (101) for increasing and decreasing the
operating capacity of the first compression mechanism (21, 31) to
adapt to the load of the refrigeration capacity; and a second
control means (102) for increasing and decreasing the operating
capacity of the second compression mechanism (31, 21) so that the
intermediate pressure in the two-stage compression refrigeration
cycle has a predetermined value.
2. The refrigeration system of claim 1, wherein the second control
means (102) controls the operating capacity of the second
compression mechanism (31, 21) so that the ratio between a first
pressure ratio, which is the ratio of the discharge pressure of the
first compression mechanism (21, 31) to the suction pressure
thereof, and a second pressure ratio, which is the ratio of the
discharge pressure of the second compression mechanism (31, 21) to
the suction pressure thereof, is 1:1.
3. The refrigeration system of claim 1, further including a third
control means (103) that, at startup, controls the operating
capacity of the second compression mechanism (31, 21) instead of
the second control means (102) so that the second compression
mechanism (31, 21) has a predetermined target operating capacity
derived based on the operating capacity of the first compression
mechanism (21, 31).
4. The refrigeration system of claim 1, wherein during a heating
operation, the first compression mechanism (21, 31) comprises a
low-pressure stage compression mechanism (21) and the second
compression mechanism (31, 21) comprises a high-pressure stage
compression mechanism (31), and wherein during the heating
operation, the first control means (101) controls the operating
capacity of the low-pressure stage compression mechanism (21) so
that the discharge pressure of the high-pressure stage compression
mechanism (31) has a predetermined target value while the second
control means (102) controls the operating capacity of the
high-pressure stage compression mechanism (31) so that the
intermediate pressure has a predetermined value.
5. The refrigeration system of claim 1, wherein during a cooling
operation, the first compression mechanism (21, 31) comprises a
high-pressure stage compression mechanism and the second
compression mechanism (31, 21) comprises a low-pressure stage
compression mechanism, and wherein during the cooling operation,
the first control means (101) controls the operating capacity of
the high-pressure stage compression mechanism (31) so that the
discharge pressure of the low-pressure stage compression mechanism
(21) has a predetermined target value while the second control
means (102) controls the operating capacity of the low-pressure
stage compression mechanism (21) so that the intermediate pressure
has a predetermined value.
6. The refrigeration system of claim 1, wherein the first
compression mechanism (21, 31) and the second compression mechanism
(31, 21) are inverter-controlled.
Description
TECHNICAL FIELD
[0001] This invention relates to refrigeration systems including a
refrigerant circuit including two compression mechanisms and
operating in a two-stage compression refrigeration cycle, and
particularly relates to control on the operating capacities of the
compression mechanisms.
BACKGROUND ART
[0002] Refrigeration systems are conventionally known that include
two compression mechanisms to operate in a two-stage compression
refrigeration cycle for refrigerant (see, for example, Patent
Document 1).
[0003] The refrigeration system disclosed in Patent Document 1 is
an air conditioning system and includes an outdoor unit, an indoor
unit and a power-up unit for use in increasing the power by
performing a two-stage compression mainly during a heating
operation. The outdoor unit includes an outdoor expansion valve, an
outdoor heat exchanger and a low-pressure stage compressor serving
as a main compression mechanism. The indoor unit includes an indoor
heat exchanger and an indoor expansion valve. The power-up unit
includes a high-pressure stage compressor serving as an auxiliary
compression mechanism, a gas expansion valve provided in a gas
line, a liquid expansion valve provided in a liquid line, and an
intermediate cooler.
[0004] During a heating operation, refrigerant discharged from the
high-pressure stage compressor in the power-up unit exchanges heat
with room air at the indoor heat exchanger to condense or liquefy
and thereby heat the room air. The liquid refrigerant obtained by
condensation is reduced to an intermediate pressure by the liquid
expansion valve and then flows into the intermediate cooler to cool
refrigerant flowing from the low-pressure stage compressor towards
the high-pressure stage compressor. Thereafter, the refrigerant is
reduced in pressure by the outdoor expansion valve and then
evaporates in the outdoor heat exchanger. Then, the evaporated
refrigerant is sucked into the low-pressure stage compressor. The
refrigerant compressed by the low-pressure stage compressor is
pumped into the power-up unit, flows through the gas expansion
valve, is then cooled in the intermediate cooler by liquid
refrigerant coming from the indoor heat exchanger and then flows
into the high-pressure stage compressor. The air conditioning
system increases the heating power by performing a two-stage
compression in the above manner.
Patent Document 1: Published Japanese Patent Application No.
2001-56156
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0005] In the refrigeration system disclosed in Patent Document 1,
however, no consideration is given to how to individually control
the operating capacities of the two compression mechanisms
compressing refrigerant in two stages during operation in a
two-stage compression refrigeration cycle. Therefore, it is hard to
say that the known refrigeration system actually controls the
compression appropriately according to the operating
conditions.
[0006] The present invention has been made in view of the foregoing
point and, therefore, an object thereof is that the refrigeration
system including a refrigerant circuit operating in a two-stage
compression refrigeration cycle performs an operation appropriate
to the operating conditions by individually controlling the
operating capacities of the compression mechanisms.
Means to Solve the Problem
[0007] A first aspect of the invention is a refrigeration system
that includes a refrigerant circuit (15) including a first
compression mechanism (21, 31) variable in displacement and a
second compression mechanism (31, 21) variable in displacement,
operates in a two-stage compression refrigeration cycle, and
further includes: a first control means (101) for increasing and
decreasing the operating capacity of the first compression
mechanism (21, 31) to adapt to the load of the refrigeration
capacity; and a second control means (102) for increasing and
decreasing the operating capacity of the second compression
mechanism (31, 21) so that the intermediate pressure in the
two-stage compression refrigeration cycle has a predetermined
value.
[0008] In the first aspect of the invention, since the first
control means (101) controls the operating capacity of the first
compression mechanism (21, 31), the refrigeration system performs
an operation with power appropriate to the load of the
refrigeration capacity. Furthermore, in this aspect of the
invention, since the second control means (102) controls the
operating capacity of the second compression mechanism (31, 21),
this provides an appropriate control on the intermediate pressure.
By individually controlling the compression mechanisms (21, 31) in
the above manners, the refrigeration system performs an operation
appropriate to the operating conditions.
[0009] A second aspect of the invention is the refrigeration system
according to the first aspect of the invention, wherein the second
control means (102) controls the operating capacity of the second
compression mechanism (31, 21) so that the ratio between a first
pressure ratio, which is the ratio of the discharge pressure of the
first compression mechanism (21, 31) to the suction pressure
thereof, and a second pressure ratio, which is the ratio of the
discharge pressure of the second compression mechanism (31, 21) to
the suction pressure thereof, is 1:1.
[0010] In the second aspect of the invention, since the second
control means (102) controls the second compression mechanism so
that the ratio between the first and second pressure ratios is 1:1,
the COP is enhanced. Specifically, if the pressure ratio between
the compression mechanisms (21, 31) increases, the COP decreases.
Therefore, the ratio of the high pressure (PH) to the low pressure
(PL) in the two-stage compression refrigeration cycle is divided
equally between the two compression mechanisms (21, 31), thereby
maximizing the COP. Furthermore, in the second aspect of the
invention, the predetermined value of the intermediate pressure in
the first aspect of the invention is the geometric mean
{(PLPH).sup.1/2} of the low pressure (PL) and the high pressure
(PH) in the two-stage compression refrigeration cycle.
[0011] A third aspect of the invention is the refrigeration system
according to the first aspect of the invention, wherein the
refrigeration system further includes a third control means (103)
that, at startup, controls the operating capacity of the second
compression mechanism (31, 21) instead of the second control means
(102) so that the second compression mechanism (31, 21) has a
predetermined target operating capacity derived based on the
operating capacity of the first compression mechanism (21, 31).
[0012] In the third aspect of the invention, at startup, the third
control means (103) controls the operating capacity of the second
compression mechanism (31, 21) so that the second compression
mechanism (31, 21) has a predetermined target operating capacity
derived from the operating capacity of the first compression
mechanism (21, 31), thereby promptly providing an operation adapted
to the load of the refrigeration capacity at startup. The
predetermined target operating capacity is, for example, n times
(for example, n=1.3) as large as the operating capacity of the
first compression mechanism (21, 31). Specifically, the second
control means (102) may make a feedback control of controlling the
operating capacity of the second compression mechanism (31, 21)
after the control of the first control means (101) on the operating
capacity of the first compression mechanism (21, 31). If in this
case the second control means (102) controls the operating capacity
of the second compression mechanism (31, 21) at startup, a delay
due to the feedback control may occur to deteriorate the operating
power. To cope with this, at startup, the third control means (103)
controls the second compression mechanism (31, 21) to enhance the
rising characteristic of the operating power at startup.
[0013] A fourth aspect of the invention is the refrigeration system
according to the first aspect of the invention, wherein during a
heating operation, the first compression mechanism (21, 31)
comprises a low-pressure stage compression mechanism (21) and the
second compression mechanism (31, 21) comprises a high-pressure
stage compression mechanism (31). Furthermore, during the heating
operation, the first control means (101) controls the operating
capacity of the low-pressure stage compression mechanism (21) so
that the discharge pressure of the high-pressure stage compression
mechanism (31) has a predetermined target value while the second
control means (102) controls the operating capacity of the
high-pressure stage compression mechanism (31) so that the
intermediate pressure has a predetermined value.
[0014] In the fourth aspect of the invention, during the heating
operation, the first control means (101) controls the operating
capacity of the low-pressure stage compression mechanism (21) so
that the discharge pressure of the high-pressure stage compression
mechanism (31) becomes a pressure corresponding to a target
condensation pressure.
[0015] There is the case where an option unit (30) including the
high-pressure stage compression mechanism (31) is connected to a
refrigeration system including the low-pressure stage compression
mechanism (21) and operating in a single-stage compression
refrigeration cycle to provide a refrigeration system operating in
a two-stage compression refrigeration cycle. In the single-stage
compression refrigeration cycle using no option unit (30), the
operating capacity of the low-pressure stage compression mechanism
(21) is controlled to provide an operating power control according
to the heating load that is the load of the refrigeration capacity.
Also in the two-stage compression refrigeration cycle, the
operating power control based on the control on the operating
capacity of the low-pressure stage compression mechanism (21) in
the single-stage compression refrigeration cycle is applied as it
is. In other words, in each of the single-stage and two-stage
compression refrigeration cycles, the first control means (101)
controls the operating capacity of the low-pressure stage
compression mechanism (21) to provide an operation adapted to the
heating load.
[0016] A fifth aspect of the invention is the refrigeration system
according to the first aspect of the invention, wherein during a
cooling operation, the first compression mechanism (21, 31)
comprises a high-pressure stage compression mechanism and the
second compression mechanism (31, 21) comprises a low-pressure
stage compression mechanism. Furthermore, during the cooling
operation, the first control means (101) controls the operating
capacity of the high-pressure stage compression mechanism (31) so
that the suction pressure of the low-pressure stage compression
mechanism (21) has a predetermined target value while the second
control means (102) controls the operating capacity of the
low-pressure stage compression mechanism (21) so that the
intermediate pressure has a predetermined value.
[0017] In the fifth aspect of the invention, during the cooling
operation, the first control means (101) controls the operating
capacity of the high-pressure stage compression mechanism (31) so
that the suction pressure of the low-pressure stage compression
mechanism (21) becomes a pressure corresponding to a target
evaporation pressure.
[0018] There is the case where an option unit (30) including the
low-pressure stage compression mechanism (21) is connected to a
refrigeration system including the high-pressure stage compression
mechanism (31) and operating in a single-stage compression
refrigeration cycle to provide a refrigeration system operating in
a two-stage compression refrigeration cycle. In the single-stage
compression refrigeration cycle using no option unit (30), the
operating capacity of the high-pressure stage compression mechanism
(31) is controlled to provide an operating power control according
to the cooling load that is the load of the refrigeration capacity.
Also in the two-stage compression refrigeration cycle, the
operating power control based on the control on the operating
capacity of the high-pressure stage compression mechanism (31) in
the single-stage compression refrigeration cycle is applied as it
is. In other words, in each of the single-stage and two-stage
compression refrigeration cycles, the first control means (101)
controls the operating capacity of the high-pressure stage
compression mechanism (31) to provide an operation adapted to the
cooling load.
[0019] A sixth aspect of the invention is the refrigeration system
according to the first aspect of the invention, wherein the first
compression mechanism (21, 31) and the second compression mechanism
(31, 21) are inverter-controlled.
[0020] In the sixth aspect of the invention, the capacities of the
first compression mechanism (21, 31) and second compression
mechanism (31, 21) are easily controlled.
EFFECTS OF THE INVENTION
[0021] According to the first aspect of the invention, since the
first control means (101) and the second control means (102)
individually control their respective compression mechanisms (21,
31), the refrigeration system can perform an operation appropriate
to the operating conditions.
[0022] According to the second aspect of the invention, since the
second control means (102) controls the second compression
mechanism so that the ratio between the first and second pressure
ratios is 1:1, this provides the highest COP.
[0023] According to the third aspect of the invention, since at
startup the third control means (103) controls the operating
capacity of the second compression mechanism (31, 21) so that the
second compression mechanism (31, 21) has a predetermined target
operating capacity derived from the operating capacity of the first
compression mechanism (21, 31), an operation adapted to the load of
the refrigeration capacity can be promptly carried out. In this
case, the predetermined target operating capacity is, for example,
n times (for example, n=1.3) as large as the operating capacity of
the first compression mechanism (21, 31). Thus, even with a system
configuration in which the first control means (101) first controls
the operating capacity of the first compression mechanism (21, 31)
and the second control means (102) then makes a feedback control of
controlling the operating capacity of the second compression
mechanism (31, 21) based on the operating capacity of the first
compression mechanism (21, 31), the rising characteristic of the
operating power at startup can be enhanced.
[0024] According to the fourth aspect of the invention, since
during the heating operation the first control means (101) controls
the operating capacity of the low-pressure stage compression
mechanism (21) so that the discharge pressure of the high-pressure
stage compression mechanism (31) has a predetermined target value,
the operating capacity of the low-pressure stage compression
mechanism (21) can be controlled so that the discharge pressure of
the high-pressure stage compression mechanism (31) has a pressure
value corresponding to a condensation pressure for a target
condensation temperature, thereby adapting the operation to the
heating load that is the load of the refrigeration capacity.
[0025] Furthermore, there is the case where an option unit (30)
including the high-pressure stage compression mechanism (31) is
connected to a refrigeration system including the low-pressure
stage compression mechanism (21) and operating in a single-stage
compression refrigeration cycle to provide a refrigeration system
operating in a two-stage compression refrigeration cycle. In the
single-stage compression refrigeration cycle using no option unit
(30), the operating capacity of the low-pressure stage compression
mechanism (21) is controlled to provide an operating power control
according to the heating load that is the load of the refrigeration
capacity. Also in the two-stage compression refrigeration cycle,
the operating power control based on the control on the operating
capacity of the low-pressure stage compression mechanism (21) in
the single-stage compression refrigeration cycle is applied as it
is. In other words, in each of the single-stage and two-stage
compression refrigeration cycles, the first control means (101)
controls the operating capacity of the low-pressure stage
compression mechanism (21) to provide an operation adapted to the
heating load. Therefore, the configuration of the control means can
be simplified.
[0026] According to the fifth aspect of the invention, since during
the cooling operation the first control means (101) controls the
operating capacity of the high-pressure stage compression mechanism
(31) so that the suction pressure of the low-pressure stage
compression mechanism (21) has a predetermined target value, the
operating capacity of the high-pressure stage compression mechanism
(31) can be controlled so that the suction pressure of the
low-pressure stage compression mechanism (21) has a pressure value
corresponding to an evaporation pressure for a target evaporation
temperature, thereby adapting the operation to the cooling load
that is the load of the refrigeration capacity.
[0027] Furthermore, there is the case where an option unit (30)
including the low-pressure stage compression mechanism (21) is
connected to a refrigeration system including the high-pressure
stage compression mechanism (31) and operating in a single-stage
compression refrigeration cycle to provide a refrigeration system
operating in a two-stage compression refrigeration cycle. In the
single-stage compression refrigeration cycle using no option unit
(30), the operating capacity of the high-pressure stage compression
mechanism (31) is controlled to provide an operating power control
according to the cooling load that is the load of the refrigeration
capacity. Also in the two-stage compression refrigeration cycle,
the operating power control based on the control on the operating
capacity of the high-pressure stage compression mechanism (31) in
the single-stage compression refrigeration cycle is applied as it
is. In other words, in each of the single-stage and two-stage
compression refrigeration cycles, the first control means (101)
controls the operating capacity of the high-pressure stage
compression mechanism (31) to provide an operation adapted to the
cooling load. Therefore, the configuration of the control means can
be simplified.
[0028] According to the sixth aspect of the invention, since the
first compression mechanism (21, 31) and the second compression
mechanism (31, 21) are inverter-controlled, the capacities of the
first compression mechanism (21, 31) and second compression
mechanism (31, 21) can be easily controlled.
BRIEF DESCRIPTION OF DRAWINGS
[0029] FIG. 1 is a piping diagram showing a refrigerant circuit of
an air conditioning system according to Embodiment 1.
[0030] FIG. 2 is a piping diagram showing a refrigerant flow in the
air conditioning system according to Embodiment 1 during a cooling
operation.
[0031] FIG. 3 is a piping diagram showing a refrigerant flow in the
air conditioning system according to Embodiment 1 during a heating
operation in a single-stage compression refrigeration cycle.
[0032] FIG. 4 is a piping diagram showing a refrigerant flow in the
air conditioning system according to Embodiment 1 during a heating
operation in a two-stage compression refrigeration cycle.
[0033] FIG. 5 is flow charts showing controls on the operating
frequencies of a low-pressure stage compressor and a high-pressure
stage compressor in the air conditioning system according to
Embodiment 1.
[0034] FIG. 6 is a piping diagram showing a refrigerant circuit of
a refrigeration system according to Embodiment 2.
[0035] FIG. 7 is a piping diagram showing a refrigerant flow in the
refrigeration system according to Embodiment 2 during a cooling
operation in a single-stage compression refrigeration cycle.
[0036] FIG. 8 is a piping diagram showing a refrigerant flow in the
refrigeration system according to Embodiment 2 during a cooling
operation in a two-stage compression refrigeration cycle.
[0037] FIG. 9 is flow charts showing controls on the operating
frequencies of a low-pressure stage compressor and a high-pressure
stage compressor in the refrigeration system according to
Embodiment 2.
LIST OF REFERENCE NUMERALS
[0038] 10 air conditioning system (refrigeration system) [0039] 15
refrigerant circuit [0040] 21 low-pressure stage compressor (first
compression mechanism, second compression mechanism) [0041] 31
high-pressure stage compressor (first compression mechanism, second
compression mechanism) [0042] 101 first control section (first
control means) [0043] 102 second control section (second control
means) [0044] 103 third control section (third control means)
[0045] 120 refrigeration system
BEST MODE FOR CARRYING OUT THE INVENTION
[0046] Embodiments of the present invention will be described below
in detail with reference to the drawings.
Embodiment 1 of the Invention
[0047] Embodiment 1 of the present invention is, as shown in FIG.
1, a heat pump air conditioning system (10) capable of a cooling
operation and a heating operation. The air conditioning system (10)
includes an outdoor unit (20) placed outdoors, an option unit (30)
constituting an expansion unit, an indoor unit (40) placed in a
room, and a controller (100) for controlling the operation of the
air conditioning system (10). The outdoor unit (20) is connected
via a first connection pipe (11) and a second connection pipe (12)
to the option unit (30). The indoor unit (40) is connected via a
third connection pipe (13) and a fourth connection pipe (14) to the
option unit (30). Thus, in the air conditioning system (10), a
refrigerant circuit (15) operating in a vapor compression
refrigeration cycle by circulating refrigerant therethrough is
constituted.
[0048] The option unit (30) constitutes a power-up unit for an
existing separate-type air conditioning system. Specifically, in
the existing air conditioning system, a refrigerant circuit
including the outdoor unit (20) and the indoor unit (40) performs
cooling and heating operations in a single-stage compression
refrigeration cycle. When the option unit (30) is additionally
connected between the outdoor unit (20) and the indoor unit (40),
the refrigerant circuit can perform a heating operation in a
two-stage compression refrigeration cycle.
[0049] <Outdoor Unit>
[0050] The outdoor unit (20) includes a low-pressure stage
compressor (21), an outdoor heat exchanger (22), an outdoor
expansion valve (25) and a four-way selector valve (23).
[0051] The low-pressure stage compressor (21) is a scroll
compressor and is configured to be supplied with power through an
inverter to change its operating frequency and specifically to
change the rotational speed of the compressor motor by changing the
output frequency of the inverter. In other words, the low-pressure
stage compressor (21) is constituted as a first compression
mechanism variable in displacement by controlling the inverter.
[0052] The outdoor heat exchanger (22) is constituted by a
cross-fin-and-tube heat exchanger. Disposed close to the outdoor
heat exchanger (22) is an outdoor fan (24). The outdoor fan (24)
delivers outdoor air to the outdoor heat exchanger (22). The
outdoor expansion valve (25) is composed of an electronic expansion
valve controllable in opening.
[0053] The four-way selector valve (23) has first to fourth ports.
The first port of the four-way selector valve (23) is connected to
a discharge pipe (21a) of the low-pressure stage compressor (21)
and the second port thereof is connected to a suction pipe (21b) of
the low-pressure stage compressor (21). Furthermore, the third port
of the four-way selector valve (23) is connected via the outdoor
heat exchanger (22) and the outdoor expansion valve (25) to one end
of the second connection pipe (12) and the fourth port thereof is
connected to one end of the first connection pipe (11). The
four-way selector valve (23) is configured to be switchable between
a first position (the position shown in the solid lines in FIG. 1)
in which the first port is communicated with the fourth port and
the second port is communicated with the third port and a second
position (the position shown in the broken lines in FIG. 1) in
which the first port is communicated with the third port and the
second port is communicated with the fourth port.
[0054] The discharge pipe (21a) of the low-pressure stage
compressor (21) is provided with a low-pressure stage oil separator
(26). The low-pressure stage oil separator (26) is connected to one
end of a first oil return pipe (27). The other end of the first oil
return pipe (27) is connected to the suction pipe (21b) of the
low-pressure stage compressor (21). The first oil return pipe (27)
is provided with a first capillary tube (28). Thus, refrigerating
machine oil separated by the low-pressure stage oil separator (26)
is reduced in pressure during flow through the first oil return
pipe (27) and then returned to the low-pressure stage compressor
(21).
[0055] Furthermore, the outdoor unit (20) is provided with various
sensors. Specifically, the discharge pipe (21a) of the low-pressure
stage compressor (21) is provided with a discharge pressure sensor
(82) and a discharge temperature sensor (86) and the suction pipe
(21b) thereof is provided with a suction pressure sensor (83) and a
suction temperature sensor (87). The outdoor unit (20) is also
provided with an outdoor temperature sensor (18) and a refrigerant
temperature sensor (29) for the outdoor heat exchanger (22).
[0056] <Option Unit>
[0057] The option unit (30) includes a high-pressure stage
compressor (31), a three-way selector valve (32), a gas-liquid
separator (33) and an option side expansion valve (34).
[0058] The high-pressure stage compressor (31) is a scroll
compressor and is configured to be supplied with power through an
inverter to change its operating frequency and specifically to
change the rotational speed of the compressor motor by changing the
output frequency of the inverter. In other words, the high-pressure
stage compressor (31) is constituted as a second compression
mechanism variable in displacement by controlling the inverter.
[0059] The three-way selector valve (32) has first to third ports.
The first port of the three-way selector valve (32) is connected to
a discharge pipe (31a) of the high-pressure stage compressor (31).
One end of the third connection pipe (13) is connected halfway
along the discharge pipe (31a). The second port of the three-way
selector valve (32) is connected to a suction pipe (31b) of the
high-pressure stage compressor (31) and the third port thereof is
connected to the other end of the first connection pipe (11). The
three-way selector valve (32) is configured to be switchable
between a first position (the position shown in the solid line in
FIG. 1) in which the second port is communicated with the third
port and a second position (the position shown in the broken line
in FIG. 1) in which the first port is communicated with the third
port.
[0060] The gas-liquid separator (33) is for the purpose of
separating refrigerant in a gas-liquid two-phase state into liquid
refrigerant and gas refrigerant. Specifically, the gas-liquid
separator (33) is formed of a cylindrical hermetic vessel and
includes a liquid refrigerant reservoir formed in a lower part
thereof and a gas refrigerant reservoir formed above the liquid
refrigerant reservoir. The gas-liquid separator (33) is connected
to a liquid inflow pipe (33a) passing through the sidewall thereof
and opening into the gas refrigerant reservoir and a liquid outflow
pipe (33b) passing through the sidewall thereof and opening into
the liquid refrigerant reservoir. The gas-liquid separator (33) is
also connected to a gas outflow pipe (33c) passing through the top
thereof and opening into the gas refrigerant reservoir.
[0061] The inflow end of the liquid inflow pipe (33a) and the
outflow end of the liquid outflow pipe (33b) are connected halfway
along a main pipe (35) extending from one end of the fourth
connection pipe (14) to the other end of the second connection pipe
(12) in order from the fourth connection pipe (14). The liquid
inflow pipe (33a) is provided with the option side expansion valve
(34). The option side expansion valve (34) is composed of an
electronic expansion valve controllable in opening. The outflow end
of the gas outflow pipe (33c) is connected halfway along the
suction pipe (31b) of the high-pressure stage compressor (31).
[0062] The option unit (30) also includes a high-pressure stage oil
separator (36) disposed in the discharge pipe (31a) of the
high-pressure stage compressor (31). The high-pressure stage oil
separator (36) is connected to one end of a second oil return pipe
(37). The other end of the second oil return pipe (37) is connected
between the connecting part of the suction pipe (31b) of the
high-pressure stage compressor (31) with the gas outflow pipe (33c)
and the high-pressure stage compressor (31). The second oil return
pipe (37) is also connected to a second capillary tube (38). Thus,
refrigerating machine oil separated by the high-pressure stage oil
separator (36) is reduced in pressure during flow through the
second oil return pipe (37) and then returned to the high-pressure
stage compressor (31).
[0063] The option unit (30) also includes a solenoid valve for
selectively opening and closing the flow path and check valves for
restricting the refrigerant flow. Specifically, the main pipe (35)
has a solenoid valve (SV) disposed between the connecting part with
the liquid inflow pipe (33a) and the connecting part with the
liquid outflow pipe (33b). Furthermore, the liquid outflow pipe
(33b) is provided with a first check valve (CV-1) and the discharge
pipe (31a) of the high-pressure stage compressor (31) is provided
with a second check valve (CV-2). Each of the first and second
check valves (CV-1, CV-2) allows only a refrigerant flow in the
direction shown in the arrow in FIG. 1.
[0064] Furthermore, the option unit (30) is provided with various
sensors. Specifically, the discharge pipe (31a) of the
high-pressure stage compressor (31) is provided with a discharge
pressure sensor (80) and a discharge temperature sensor (84) and
the suction pipe (31b) thereof is provided with a suction pressure
sensor (81) and a suction temperature sensor (85). The liquid
outflow pipe (33b) of the gas-liquid separator (33) is provided
with a temperature sensor (88) and a pressure sensor (89).
[0065] <Indoor Unit>
[0066] The indoor unit (40) includes an indoor heat exchanger (41)
and an indoor expansion valve (42). The indoor heat exchanger (41)
is constituted by a cross-fin-and-tube heat exchanger. Disposed
close to the indoor heat exchanger (41) is an indoor fan (43). The
indoor fan (43) delivers room air to the indoor heat exchanger
(41). The indoor expansion valve (42) is composed of an electronic
expansion valve controllable in opening.
[0067] In the indoor unit (40), the other end of the third
connection pipe (13) is connected via the indoor heat exchanger
(41) and the indoor expansion valve (42) to the other end of the
fourth connection pipe (14).
[0068] The indoor unit (40) is also provided with a room
temperature sensor (44) and a refrigerant temperature sensor (45)
for the indoor heat exchanger (41).
[0069] <Controller>
[0070] The controller (100) is used for controlling the operational
behavior of the air conditioning system (10) by changing the
positions of the various valves disposed in the refrigerant circuit
(15) and controlling the openings thereof. The controller (100)
includes a first control section (101), a second control section
(102) and a third control section (103). The first control section
(101) inverter-controls the operating frequency of the low-pressure
stage compressor (21) to adapt to the load of the refrigeration
capacity and is constituted as a first control means. The second
control section (102) inverter-controls the operating frequency of
the high-pressure stage compressor (31) so that the intermediate
pressure in the two-stage compression refrigeration cycle has a
predetermined value, and is constituted as a second control means.
The third control section (103) inverter-controls, at startup,
instead of the second control section (102), the operating
frequency of the high-pressure stage compressor (31) so that the
high-pressure stage compressor (31) has a predetermined target
operating frequency derived based on the operating frequency of the
low-pressure stage compressor (21), and is constituted as a third
control means.
[0071] --Operational Behavior--
[0072] Next, a description is given of the operational behavior of
the air conditioning system (10) of this embodiment.
[0073] The air conditioning system (10) performs cooling and
heating operations in a single-stage compression refrigeration
cycle and a heating operation in a two-stage compression
refrigeration cycle.
[0074] <Cooling Operation>
[0075] In the cooling operation, as shown in FIG. 2, by the control
of the controller (100), the four-way selector valve (23) and the
three-way selector valve (32) are selected to their respective
second positions and the solenoid valve (SV) is selected to its
open position. Furthermore, the outdoor expansion valve (25) and
the option side expansion valve (34) are selected to fully open and
fully closed positions, respectively, and the opening of the indoor
expansion valve (42) is appropriately controlled according to the
operating conditions. Furthermore, in the cooling operation, the
low-pressure stage compressor (21) is driven while the
high-pressure stage compressor (31) is shut off. In other words,
the refrigerant circuit (15) during the cooling operation
compresses refrigerant only in the low-pressure stage compressor
(21) so that the suction and discharge pressures of the
low-pressure stage compressor (21) are low and high pressures,
respectively, in a single-stage compression refrigeration
cycle.
[0076] In the outdoor unit (20), high-pressure refrigerant
discharged from the low-pressure stage compressor (21) flows
through the outdoor heat exchanger (22) to release heat to outdoor
air and thereby condense or liquefy. The liquid refrigerant
obtained by condensation in the outdoor heat exchanger (22) flows
through the outdoor expansion valve (25) in fully open position,
then flows through the second connection pipe (21) and is then
pumped into the option unit (30).
[0077] In the option unit (30), the high-pressure liquid
refrigerant flows through the main pipe (35), then flows through
the fourth connection pipe (14) and is then pumped into the indoor
unit (40).
[0078] The refrigerant pumped in the indoor unit (40) is reduced in
pressure during passage through the indoor expansion valve (42) to
expand into low-pressure refrigerant. The low-pressure refrigerant
flows through the indoor heat exchanger (41) to take heat from room
air and thereby evaporate. As a result, the room air is cooled to
cool the room. The refrigerant having evaporated in the indoor heat
exchanger (41) is pumped through the third connection pipe (13)
into the option unit (30), then flows via the three-way selector
valve (32) into the first connection pipe (11) and is then pumped
into the outdoor unit (20). The low-pressure refrigerant pumped in
the outdoor unit (20) is sucked into the low-pressure stage
compressor (21) and then compressed therein into high-pressure
refrigerant.
[0079] <Control During Cooling Operation>
[0080] During the cooling operation, the first control section
(101) of the controller (100) inverter-controls the operating
frequency of the low-pressure stage compressor (21) to adapt to the
cooling load that is the load of the refrigeration capacity. In
other words, the first control section (101) controls the operating
frequency of the low-pressure stage compressor (21) so that the
evaporation temperature in the indoor heat exchanger (41) becomes a
set room temperature Te.degree. C. Specifically, the first control
section (101) controls the operating frequency of the low-pressure
stage compressor (21) so that the suction pressure of the
low-pressure stage compressor (21) has a pressure value appropriate
to the evaporation pressure corresponding to the set temperature
Te.degree. C.
[0081] To attain this, as shown in FIG. 5(a), the first control
section (101) first calculates, in a comparison circuit (150), the
temperature difference between the set temperature Te.degree. C.
and the actual room temperature measured by the room temperature
sensor (44). Thereafter, the first control section (101)
calculates, in a gain circuit (151), the operating frequency of the
low-pressure stage compressor (21) by multiplying the temperature
difference output from the comparison circuit (150) by a constant K
and then controls the low-pressure stage compressor (21).
[0082] Note that since the high-pressure stage compressor (31) is
shut off, the second control section (102) does not control it.
[0083] <Heating Operation in Single-Stage Compression
Refrigeration Cycle>
[0084] In the heating operation in a single-stage compression
refrigeration cycle, as shown in FIG. 3, by the control of the
controller (100), the four-way selector valve (23) is selected to
its first position, the three-way selector valve (32) is selected
to its second position and the solenoid valve (SV) is selected to
its open position. Furthermore, the option side expansion valve
(34) and the indoor expansion valve (42) are selected to fully
closed and fully open positions, respectively, and the opening of
the outdoor expansion valve (25) is appropriately controlled
according to the operating conditions. Furthermore, in this heating
operation, the low-pressure stage compressor (21) is driven while
the high-pressure stage compressor (31) is shut off. In other
words, the refrigerant circuit (15) during this heating operation
compresses refrigerant only in the low-pressure stage compressor
(21) so that the suction and discharge pressures of the
low-pressure stage compressor (21) are low and high pressures,
respectively, in the single-stage compression refrigeration
cycle.
[0085] In the outdoor unit (20), high-pressure refrigerant
discharged from the low-pressure stage compressor (21) flows via
the four-way selector valve (23) through the first connection pipe
(11) and is then pumped into the option unit (30).
[0086] The high-pressure refrigerant pumped in the option unit (30)
flows via the three-way selector valve (32) through the third
connection pipe (13) and is then pumped into the indoor unit
(40).
[0087] In the indoor unit (40), the high-pressure refrigerant flows
through the indoor heat exchanger (41) to release heat to room air
and thereby condense or liquefy. As a result, the room air is
heated to heat the room. The liquid refrigerant obtained by
condensation in the indoor heat exchanger (41) flows through the
indoor expansion valve (42) in fully open position, then flows
through the fourth connection pipe (14) and is then pumped into the
option unit (30).
[0088] The high-pressure liquid refrigerant pumped in the option
unit (30) flows through the main pipe (35), then flows through the
second connection pipe (12) and is then pumped into the outdoor
unit (20).
[0089] The refrigerant pumped in the outdoor unit (20) is reduced
in pressure during passage through the outdoor expansion valve (25)
to expand into low-pressure refrigerant. The low-pressure
refrigerant flows through the outdoor heat exchanger (22) to take
heat from outdoor air and thereby evaporate. The low-pressure
refrigerant having evaporated in the outdoor heat exchanger (22) is
sucked via the four-way selector valve (23) into the low-pressure
stage compressor (21) and then compressed therein into
high-pressure refrigerant.
[0090] <Control During Heating Operation in Single-Stage
Compression Refrigeration Cycle>
[0091] During the heating operation in a single-stage compression
refrigeration cycle, the first control section (101) of the
controller (100) inverter-controls the operating frequency of the
low-pressure stage compressor (21) to adapt to the heating load
that is the load of the refrigeration capacity. In other words, the
first control section (101) controls the operating frequency of the
low-pressure stage compressor (21) so that the condensation
temperature in the indoor heat exchanger (41) becomes a set room
temperature Tc.degree. C. Specifically, the first control section
(101) controls the operating frequency of the low-pressure stage
compressor (21) so that the discharge pressure of the low-pressure
stage compressor (21) has a pressure value appropriate to the
condensation pressure corresponding to the set temperature
Tc.degree. C.
[0092] To attain this, as shown in FIG. 5(a), the first control
section (101) first calculates, in the comparison circuit (150),
the temperature difference between the set temperature Tc.degree.
C. and the actual room temperature measured by the room temperature
sensor (44). Thereafter, the first control section (101)
calculates, in the gain circuit (151), the operating frequency of
the low-pressure stage compressor (21) by multiplying the
temperature difference output from the comparison circuit (150) by
a constant K and then controls the low-pressure stage compressor
(21).
[0093] Note that since the high-pressure stage compressor (31) is
shut off, the second control section (102) does not control it.
[0094] <Heating Operation in Two-Stage Compression Refrigeration
Cycle>
[0095] In the heating operation in a two-stage compression
refrigeration cycle, as shown in FIG. 4, by the control of the
controller (100), the four-way selector valve (23) and the
three-way selector valve (32) are selected to their respective
first positions and the solenoid valve (SV) is selected to its
closed position. Furthermore, the openings of the indoor expansion
valve (42), the option side expansion valve (34) and the outdoor
expansion valve (25) are appropriately controlled according to the
operating conditions. Furthermore, in this heating operation, the
low-pressure stage compressor (21) and the high-pressure stage
compressor (31) are both driven. In other words, the refrigerant
circuit (15) during this heating operation operates in a two-stage
compression refrigeration cycle in which refrigerant compressed by
the low-pressure stage compressor (21) is further compressed by the
high-pressure stage compressor (31) so that the suction and
discharge pressures of the low-pressure stage compressor (21) are
low and intermediate pressures, respectively, in the refrigeration
cycle and that the discharge pressure of the high-pressure stage
compressor (31) is a high pressure in the refrigeration cycle.
[0096] In the option unit (30), the high-pressure refrigerant
discharged from the high-pressure stage compressor (31) flows
through the third connection pipe (13) and is then pumped into the
indoor unit (40).
[0097] In the indoor unit (40), the high-pressure refrigerant
releases heat to room air during passage through the indoor heat
exchanger (41) to condense or liquefy. As a result, the room air is
heated to heat the room.
[0098] The liquid refrigerant obtained by condensation in the
indoor heat exchanger (41) flows through the indoor expansion valve
(42), then flows through the fourth connection pipe (14), is then
pumped into the option unit (30), then flows through the main pipe
(35), then flows through the option side expansion valve (34), and
then flows into the liquid inflow pipe (33a). The liquid
refrigerant is stepwise reduced in pressure by the indoor expansion
valve (42) and the option side expansion valve (34) to expand into
intermediate-pressure, gas-liquid two-phase refrigerant and then
flows into the gas-liquid separator (33).
[0099] In the gas-liquid separator (33), the intermediate-pressure
refrigerant in a gas-liquid two-phase state is separated into gas
refrigerant and liquid refrigerant. The separated gas refrigerant
in a saturated state flows through the gas outflow pipe (33c) and
is then sent to the suction pipe (31b) of the high-pressure stage
compressor (31). On the other hand, the separated liquid
refrigerant flows out through the liquid outflow pipe (33b), then
flows through the second connection pipe (12) and is then pumped
into the outdoor unit (20).
[0100] The intermediate-pressure liquid refrigerant pumped in the
outdoor unit (20) is reduced in pressure during passage through the
outdoor expansion valve (25) to expand into low-pressure
refrigerant, and the low-pressure refrigerant takes heat from
outdoor air during passage through the outdoor heat exchanger (22)
to evaporate. The low-pressure refrigerant having evaporated in the
outdoor heat exchanger (22) is sucked via the four-way selector
valve (23) into the low-pressure stage compressor (21). In the
low-pressure stage compressor (21), the low-pressure refrigerant is
compressed into intermediate-pressure refrigerant. The
intermediate-pressure refrigerant flows via the four-way selector
valve (23) into the first connection pipe (11) and is then pumped
into the option unit (30).
[0101] In the option unit (30), the intermediate-pressure
refrigerant discharged from the low-pressure stage compressor (21)
flows via the three-way selector valve (32) through the suction
pipe (31b) of the high-pressure stage compressor (31). Refrigerant
is supplied through the gas outflow pipe (33c) to the
intermediate-pressure refrigerant flowing through the suction pipe
(31c) and the refrigerant mixture is sucked into the high-pressure
stage compressor (31). In the high-pressure stage compressor (31),
the intermediate-pressure refrigerant is compressed into
high-pressure refrigerant.
[0102] As described so far, during the heating operation in a
two-stage compression refrigeration cycle, intermediate-pressure
refrigerant in a gas-liquid two-phase state is separated into gas
refrigerant and liquid refrigerant by the gas-liquid separator (33)
and the separated gas refrigerant is returned to the high-pressure
stage compressor (31), thereby sending only liquid refrigerant to
the outdoor heat exchanger (22). This reduces the pressure loss in
the pipes for liquid running from the gas-liquid separator (33) to
the outdoor heat exchanger (22) and prevents the occurrence of a
so-called flash phenomenon in which part of liquid refrigerant
evaporates and remains in the pipes.
[0103] <Control During Heating Operation in Two-Stage
Compression Refrigeration Cycle>
[0104] During the heating operation in a two-stage compression
refrigeration cycle, the first control section (101) of the
controller (100) controls the low-pressure stage compressor (21)
and the second control section (102) and third control section
(103) thereof inverter-control the high-pressure stage compressor
(31).
[0105] First, as shown in FIG. 5(a), the first control section
(101) controls the operating frequency of the low-pressure stage
compressor (21) to adapt to the heating load that is the load of
the refrigeration capacity. In other words, the first control
section (101) controls the operating frequency of the low-pressure
stage compressor (21) so that the condensation temperature in the
indoor heat exchanger (41) becomes a set room temperature
Tc.degree. C. Specifically, the first control section (101)
controls the operating frequency of the low-pressure stage
compressor (21) so that the discharge pressure of the high-pressure
stage compressor (31) has a pressure value appropriate to the
condensation pressure corresponding to the set temperature
Tc.degree. C.
[0106] To attain this, as shown in FIG. 5(a), the first control
section (101) first calculates, in the comparison circuit (150),
the temperature difference between the set temperature Tc.degree.
C. and the actual room temperature measured by the room temperature
sensor (44). Thereafter, the first control section (101)
calculates, in the gain circuit (151), the operating frequency of
the low-pressure stage compressor (21) by multiplying the
temperature difference output from the comparison circuit (150) by
a constant K and then controls the low-pressure stage compressor
(21).
[0107] On the other hand, the second control section (102) controls
the high-pressure stage compressor (31) so that the intermediate
pressure (PM) between the low-pressure stage compressor (21) and
the high-pressure stage compressor (31) has a predetermined value.
In this embodiment, the predetermined value of the intermediate
pressure is the intermediate pressure value at which the ratio
between the first pressure ratio (PM/PL), i.e., the ratio of the
discharge pressure (PM) of the low-pressure stage compressor (21)
to the suction pressure (PL) thereof, and the second pressure ratio
(PH/PM), i.e., the ratio of the discharge pressure (PH) of the
high-pressure stage compressor (31) to the suction pressure (PM)
thereof, is 1:1. In other words, the intermediate pressure value is
the geometric mean {(PLPH).sup.1/2} of the suction pressure (PL) of
the low-pressure stage compressor (21) and the discharge pressure
(PH) of the high-pressure stage compressor (31).
[0108] Specifically, as shown in FIG. 5(b), the second control
section (102) calculates the first pressure ratio (PM/PL) of the
low-pressure stage compressor (21) in a first dividing circuit
(152) and calculates the second pressure ratio (PH/PM) of the
high-pressure stage compressor (31) in a second dividing circuit
(153). Then, the second control section (102) calculates the
pressure difference {(PM/PL)-(PH/PM)} between the first pressure
ratio (PM/PL) and the second pressure ratio (PH/PM) in a comparison
circuit (154) and derives a gain K from the pressure difference in
a gain circuit (155). Then, the second control section (102)
derives, in a derivation circuit (156), a target operating
frequency of the high-pressure stage compressor (31) by multiplying
the current operating frequency of the high-pressure stage
compressor (31) by the gain K and controls the high-pressure stage
compressor (31) so that it is driven at the target operating
frequency.
[0109] In this embodiment, a value measured by the suction pressure
sensor (83) is used as the suction pressure (PL) of the
low-pressure stage compressor (21), a value measured by the
discharge pressure sensor (82) is used as the discharge pressure
(PM) of the low-pressure stage compressor (21), a value measured by
the suction pressure sensor (81) is used as the suction pressure
(PM) of the high-pressure stage compressor (31) and a value
measured by the discharge pressure sensor (80) is used as the
discharge pressure (PH) of the high-pressure stage compressor (31).
However, other values may be used as these pressures. Specifically,
a value measured by the pressure sensor (89) of the liquid outflow
pipe (33b) of the gas-liquid separator (33) or a saturated pressure
corresponding to a value measured by the temperature sensor (88) of
the liquid outflow pipe (33b) may be used as the discharge pressure
(PM) of the low-pressure stage compressor (21) and the suction
pressure (PM) of the high-pressure stage compressor (31) both of
which are the intermediate pressure (PM). Furthermore, for the sake
of simplicity, the condensation pressure according to the
condensation temperature in the indoor heat exchanger (41) and the
evaporation pressure according to the evaporation temperature in
the outdoor heat exchanger (22) may be used as the discharge
pressure (PH) of the high-pressure stage compressor (31) and the
suction pressure (PL) of the low-pressure stage compressor (21),
respectively.
[0110] Then, by repeating the above controls of the first control
section (101) and second control section (102), the operating
frequencies of the high-pressure stage compressor (31) and
low-pressure stage compressor (21) become operating frequencies
appropriate to the heating load and providing the highest COP.
[0111] At startup of the heating operation in the two-stage
compression refrigeration cycle, the third control section (103)
controls, instead of the second control section (102), the
operating frequency of the high-pressure stage compressor (31).
Specifically, the third control section (103) controls the
high-pressure stage compressor (31) so that its operating frequency
is n times (for example, n=1.3) as high as that of the low-pressure
stage compressor (21). The reason for this is as follows: In order
to bring the intermediate pressure to the predetermined value, the
second control section (102) makes a feedback control of changing
the operating frequency of the high-pressure stage compressor (31)
following the change in the operating frequency of the low-pressure
stage compressor (21) controlled by the first control section
(101). If, at startup, the second control section (102) controls
the high-pressure stage compressor (31), a delay due to the
feedback control occurs so that it takes a long time to reach a
predetermined operating power. This problem must be prevented.
[0112] --Effects of Embodiment 1--
[0113] According to this embodiment, since during the heating
operation in the two-stage compression refrigeration cycle the
first control section (101) controls the operating frequency of the
low-pressure stage compressor (21) to adapt to the heating load
that is the load of the refrigeration capacity and the second
control section (102) controls the operating frequency of the
high-pressure stage compressor (31) so that the ratio between the
first pressure ratio (PM/PL) of the low-pressure stage compressor
(21) and the second pressure ratio (PH/PM) of the high-pressure
stage compressor (31) is 1:1, the air conditioning system (10) can
perform an operation appropriate to the heating load and can
enhance the COP. Therefore, the air conditioning system (10) can
perform an operation appropriate to the operating conditions.
[0114] Furthermore, according to this embodiment, the first control
section (101) provides an operating power control according to the
refrigeration load not only by controlling the operating frequency
of the low-pressure stage compressor (21) during operation in the
single-stage compression refrigeration cycle with the existing
outdoor unit (20) and indoor unit (40) connected to each other, but
also by controlling the operating frequency of the low-pressure
stage compressor (21) through the application of the above
operating power control during operation in the two-stage
compression refrigeration cycle with the existing units connected
to the option unit (30). This simplifies the configuration of the
control means.
[0115] Furthermore, since at startup the third control section
(103) controls, instead of the second control section (102), the
operating frequency of the high-pressure stage compressor (31),
this prevents a delay in control on the high-pressure stage
compressor (31) from being caused by feedback control of the second
control section (102) at startup and thereby promptly provides an
operation adapted to the heating load.
Embodiment 2 of the Invention
[0116] Embodiment 2 of the present invention is, as shown in FIG.
6, a refrigeration system (120) for cooling the interior of a
cooling room. The refrigeration system (120) includes an outdoor
unit (20) placed outdoors, an option unit (30) constituting an
expansion unit, an indoor unit (40) placed in a cooling room, and a
controller (100) for controlling the operation of the refrigeration
system (120). The outdoor unit (20) is connected via a first
connection pipe (11) and a second connection pipe (12) to the
option unit (30). The indoor unit (40) is connected via a third
connection pipe (13) and a fourth connection pipe (14) to the
option unit (30). Thus, in the refrigeration system (120), a
refrigerant circuit (15) operating in a vapor compression
refrigeration cycle by circulating refrigerant therethrough is
constituted.
[0117] The option unit (30) constitutes a power-up unit for an
existing separate-type refrigeration system. Specifically, in the
existing refrigeration system, a refrigerant circuit including the
outdoor unit (20) and the indoor unit (40) performs a cooling
operation in a single-stage compression refrigeration cycle for
chilling materials in the cooling room. When the option unit (30)
is additionally connected between the outdoor unit (20) and the
indoor unit (40), the refrigerant circuit can perform a cooling
operation in a two-stage compression refrigeration cycle for
freezing materials in the cooling room.
[0118] <Outdoor Unit>
[0119] The outdoor unit (20) includes a high-pressure stage
compressor (31) and an outdoor heat exchanger (22).
[0120] The high-pressure stage compressor (31) is a scroll
compressor and is configured to be supplied with power through an
inverter to change its operating frequency and specifically to
change the rotational speed of the compressor motor by changing the
output frequency of the inverter. In other words, the high-pressure
stage compressor (31) is constituted as a first compression
mechanism variable in displacement by controlling the inverter.
[0121] The outdoor heat exchanger (22) is constituted by a
cross-fin-and-tube heat exchanger. Disposed close to the outdoor
heat exchanger (22) is an outdoor fan (24). The outdoor fan (24)
delivers outdoor air to the outdoor heat exchanger (22).
[0122] A suction pipe (31b) of the high-pressure stage compressor
(31) is connected to one end of the second connection pipe (12) and
a discharge pipe (31a) thereof is connected via the outdoor heat
exchanger (22) to one end of the first connection pipe (11).
[0123] The discharge pipe (31a) of the high-pressure stage
compressor (31) is provided with a high-pressure stage oil
separator (36). The high-pressure stage oil separator (36) is
connected to one end of a second oil return pipe (37). The other
end of the second oil return pipe (37) is connected to the suction
pipe (31b) of the high-pressure stage compressor (31). The second
oil return pipe (37) is also connected to a second capillary tube
(38). Thus, refrigerating machine oil separated by the
high-pressure stage oil separator (36) is reduced in pressure
during flow through the second oil return pipe (37) and then
returned to the high-pressure stage compressor (31).
[0124] Furthermore, the outdoor unit (20) is provided with various
sensors. Specifically, the discharge pipe (31a) of the
high-pressure stage compressor (31) is provided with a discharge
pressure sensor (80) and a discharge temperature sensor (84) and
the suction pipe (31b) thereof is provided with a suction pressure
sensor (81) and a suction temperature sensor (85). The outdoor unit
(20) is also provided with an outdoor temperature sensor (18) and a
refrigerant temperature sensor (29) for the outdoor heat exchanger
(22).
[0125] <Option Unit>
[0126] The option unit (30) includes a low-pressure stage
compressor (21), a gas-liquid separator (33), an option side
expansion valve (34), a first three-way selector valve (70) and a
second three-way selector valve (71).
[0127] The low-pressure stage compressor (21) is a scroll
compressor and is configured to be supplied with power through an
inverter to change its operating frequency and specifically to
change the rotational speed of the compressor motor by changing the
output frequency of the inverter. In other words, the low-pressure
stage compressor (21) is constituted as a second compression
mechanism variable in displacement by controlling the inverter.
[0128] The gas-liquid separator (33) is formed of a cylindrical
hermetic vessel and includes a liquid refrigerant reservoir as a
liquid layer formed in a lower part thereof and a gas refrigerant
reservoir formed above the liquid refrigerant reservoir. The
gas-liquid separator (33) is connected to a liquid inflow pipe
(33a) passing through the sidewall thereof and opening into the gas
refrigerant reservoir and a liquid outflow pipe (33b) passing
through the bottom thereof and opening into the liquid refrigerant
reservoir. The gas-liquid separator (33) is also connected to a gas
outflow pipe (33c) passing through the top thereof and opening into
the gas refrigerant reservoir.
[0129] The first three-way selector valve (70) has first to third
ports. The first port of the first three-way selector valve (70) is
connected to an outflow end of the liquid outflow pipe (33b) of the
gas-liquid separator (33), the second port thereof is connected to
an inflow end of the liquid inflow pipe (33a) of the gas-liquid
separator (33) and the third port thereof is connected to the other
end of the first liquid-side connection pipe (11). The first
three-way selector valve (70) is configured to be switchable
between a first position (the position shown in the solid line in
FIG. 6) in which the second port is communicated with the third
port and a second position (the position shown in the broken line
in FIG. 6) in which the first port is communicated with the third
port.
[0130] The second three-way selector valve (71) has first to third
ports. The first port of the second three-way selector valve (71)
is connected through a connecting pipe (47) to one end of the third
connection pipe (13), the second port thereof is connected to a
discharge pipe (21a) of the low-pressure stage compressor (21) and
the third port thereof is connected to the other end of the second
connection pipe (12). The second three-way selector valve (71) is
configured to be switchable between a first position (the position
shown in the solid line in FIG. 6) in which the second and third
ports are communicated with each other and a second position (the
position shown in the broken line in FIG. 6) in which the first and
third ports are communicated with each other.
[0131] One end of the fourth connection pipe (14) is connected
halfway along the liquid outflow pipe (33b). The option side
expansion valve (34) is provided halfway along the liquid inflow
pipe (33a). The option side expansion valve (34) is composed of an
electronic expansion valve controllable in opening. The outflow end
of the gas outflow pipe (33c) is connected halfway along the
discharge pipe (21a) of the low-pressure stage compressor (21).
[0132] The discharge pipe (21a) of the low-pressure stage
compressor (21) is provided with a low-pressure stage oil separator
(26). The low-pressure stage oil separator (26) is connected to one
end of a first oil return pipe (27). The other end of the first oil
return pipe (27) is connected to a suction pipe (21b) of the
low-pressure stage compressor (21). The first oil return pipe (27)
is provided with a first capillary tube (28). Thus, refrigerating
machine oil separated by the low-pressure stage oil separator (26)
is reduced in pressure during flow through the first oil return
pipe (27) and then returned to the low-pressure stage compressor
(21).
[0133] Furthermore, the option unit (30) is provided with various
sensors. Specifically, the discharge pipe (21a) of the low-pressure
stage compressor (21) is provided with a discharge pressure sensor
(82) and a discharge temperature sensor (86) and the suction pipe
(21b) thereof is provided with a suction pressure sensor (83) and a
suction temperature sensor (87). The liquid outflow pipe (33b) of
the gas-liquid separator (33) is provided with a temperature sensor
(88) and a pressure sensor (89).
[0134] <Indoor Unit>
[0135] The indoor unit (40) includes an indoor heat exchanger (41)
and an indoor expansion valve (42). The indoor heat exchanger (41)
is constituted by a cross-fin-and-tube heat exchanger. Disposed
close to the indoor heat exchanger (41) is an indoor fan (43). The
indoor fan (43) delivers room air to the indoor heat exchanger
(41). The indoor expansion valve (42) is composed of an electronic
expansion valve controllable in opening.
[0136] In the indoor unit (40), the other end of the third
connection pipe (13) is connected via the indoor heat exchanger
(41) and the indoor expansion valve (42) to the other end of the
fourth connection pipe (14).
[0137] The indoor unit (40) is also provided with a cooling room
temperature sensor (44) and a refrigerant temperature sensor (45)
for the indoor heat exchanger (41).
[0138] <Controller>
[0139] The controller (100) is used for controlling the operational
behavior of the refrigeration system (120) by changing the
positions of the various valves disposed in the refrigerant circuit
(15) and controlling the openings thereof. The controller (100)
includes a first control section (101), a second control section
(102) and a third control section (103). The first control section
(101) inverter-controls the operating frequency of the
high-pressure stage compressor (31) to adapt to the load of the
refrigeration capacity and is constituted as a first control means.
The second control section (102) inverter-controls the operating
frequency of the low-pressure stage compressor (21) so that the
intermediate pressure in the two-stage compression has a
predetermined value, and is constituted as a second control means.
The third control section (103) is constituted as a third control
means that, at startup, controls the operating frequency of the
low-pressure stage compressor (21) instead of the second control
section (102) so that the low-pressure stage compressor (21) has a
predetermined target operating frequency derived based on the
operating frequency of the high-pressure stage compressor (31).
[0140] --Operational Behavior--
[0141] Next, a description is given of the operational behavior of
the refrigeration system (120) of this embodiment.
[0142] The refrigeration system (120) performs a cooling operation
in a single-stage compression refrigeration cycle for chilling
materials in the cooling room and a cooling operation in a
two-stage compression refrigeration cycle for freezing materials in
the cooling room.
[0143] <Cooling Operation in Single-Stage Compression
Refrigeration Cycle>
[0144] In the cooling operation in a single-stage compression
refrigeration cycle, as shown in FIG. 7, by the control of the
controller (100), the first three-way selector valve (70) and the
second three-way selector valve (71) in the option unit (30) are
selected to their respective second positions. Furthermore, the
opening of the indoor expansion valve (42) is appropriately
controlled according to the operating conditions. Furthermore, in
this cooling operation, the high-pressure stage compressor (31) is
driven while the low-pressure stage compressor (21) is shut off. In
other words, the refrigerant circuit (15) during the cooling
operation compresses refrigerant only in the high-pressure stage
compressor (31) so that the suction and discharge pressures of the
high-pressure stage compressor (31) are low and high pressures,
respectively, in a single-stage compression refrigeration
cycle.
[0145] In the outdoor unit (20), the high-pressure refrigerant
discharged from the high-pressure stage compressor (31) is sent to
the outdoor heat exchanger (22) and releases heat therein to
outdoor air and thereby condenses or liquefies. The high-pressure
liquid refrigerant obtained by condensation in the outdoor heat
exchanger (22) flows through the first connection pipe (11) and is
then pumped into the option unit (30).
[0146] In the option unit (30), the high-pressure refrigerant flows
via the first three-way selector valve (70) through the liquid
outflow pipe (33b), then flows through the fourth connection pipe
(14) and is then pumped into the indoor unit (40).
[0147] The high-pressure refrigerant pumped in the indoor unit (40)
is reduced in pressure during passage through the indoor expansion
valve (42) to expand into low-pressure refrigerant. The
low-pressure refrigerant flows through the indoor heat exchanger
(41) to take heat from room air and thereby evaporate. As a result,
the air in the cooling room is cooled. The refrigerant having
evaporated in the indoor heat exchanger (41) is pumped through the
third connection pipe (13) into the option unit (30).
[0148] The low-pressure refrigerant pumped in the option unit (30)
flows through the connecting pipe (47), then flows via the second
three-way selector valve (71) through the second connection pipe
(12) and is then pumped into the outdoor unit (20). The
low-pressure refrigerant pumped in the outdoor unit (20) is sucked
into the high-pressure stage compressor (31) and then compressed
therein into high-pressure refrigerant.
[0149] <Control During Cooling Operation in Single-Stage
Compression Refrigeration Cycle>
[0150] During the cooling operation in a single-stage compression
refrigeration cycle, the first control section (101) of the
controller (100) inverter-controls the operating frequency of the
high-pressure stage compressor (31) to adapt to the cooling load
that is the load of the refrigeration capacity. In other words, the
first control section (101) controls the operating frequency of the
high-pressure stage compressor (31) so that the evaporation
temperature in the indoor heat exchanger (41) becomes a set cooling
room temperature Te.degree. C. Specifically, the first control
section (101) controls the operating frequency of the high-pressure
stage compressor (31) so that the suction pressure of the
high-pressure stage compressor (31) has a pressure value
appropriate to the evaporation pressure corresponding to the set
temperature Te.degree. C.
[0151] To attain this, as shown in FIG. 9(a), the first control
section (101) first calculates, in a comparison circuit (160), the
temperature difference between the set temperature Te.degree. C.
and the actual cooling room temperature measured by the room
temperature sensor (44). Thereafter, the first control section
(101) calculates, in a gain circuit (161), the operating frequency
of the high-pressure stage compressor (31) by multiplying the
temperature difference output from the comparison circuit (160) by
a constant K and then controls the high-pressure stage compressor
(31).
[0152] Note that since the low-pressure stage compressor (21) is
shut off, the second control section (102) does not control it.
[0153] <Cooling Operation in Two-Stage Compression Refrigeration
Cycle>
[0154] In the cooling operation in a two-stage compression
refrigeration cycle, as shown in FIG. 8, by the control of the
controller (100), the first three-way selector valve (70) and the
second three-way selector valve (71) in the option unit (30) are
selected to their respective first positions. Furthermore, the
opening of the indoor expansion valve (42) is appropriately
controlled according to the operating conditions. Furthermore, in
this cooling operation, the low-pressure stage compressor (21) and
the high-pressure stage compressor (31) are both driven. In other
words, the refrigerant circuit (15) during this cooling operation
operates in a two-stage compression refrigeration cycle in which
refrigerant compressed by the low-pressure stage compressor (21) is
further compressed by the high-pressure stage compressor (31) so
that the suction and discharge pressures of the low-pressure stage
compressor (21) are low and intermediate pressures, respectively,
in the refrigeration cycle and that the discharge pressure of the
high-pressure stage compressor (31) is a high pressure in the
refrigeration cycle.
[0155] In the outdoor unit (20), the high-pressure refrigerant
discharged from the high-pressure stage compressor (31) is sent to
the outdoor heat exchanger (22) and releases heat therein to
outdoor air and thereby condenses or liquefies. The high-pressure
liquid refrigerant obtained by condensation in the outdoor heat
exchanger (22) flows through the first connection pipe (11) and is
then pumped into the option unit (30).
[0156] In the option unit (30), the high-pressure liquid
refrigerant flows via the first three-way selector valve (70)
through the liquid inflow pipe (33a). The high-pressure liquid
refrigerant is reduced in pressure during passage through the
option side expansion valve (34) to expand into
intermediate-pressure, gas-liquid two-phase refrigerant and then
flows into the gas-liquid separator (33). In the gas-liquid
separator (33), the intermediate-pressure refrigerant in a
gas-liquid two-phase state is separated into gas refrigerant and
liquid refrigerant. The separated gas refrigerant in a saturated
state flows through the gas outflow pipe (33c) and is then sent to
the discharge pipe (21a) of the low-pressure stage compressor (21).
On the other hand, the separated liquid refrigerant flows out
through the liquid outflow pipe (33b), then flows through the
fourth connection pipe (14) and is then pumped into the indoor unit
(40).
[0157] In the indoor unit (40), the intermediate-pressure liquid
refrigerant is reduced in pressure during passage through the
indoor expansion valve (42) to expand into low-pressure
refrigerant. The low-pressure refrigerant takes heat from room air
during passage through the indoor heat exchanger (41) to evaporate.
As a result, the air in the cooling room is cooled. The evaporated
low-pressure refrigerant flows through the third connection pipe
(13) and is then pumped into the option unit (30).
[0158] In the option unit (30), the low-pressure refrigerant flows
through the third connection pipe (13) and then through the suction
pipe (21b) of the low-pressure stage compressor (21), is then
sucked into the low-pressure stage compressor (21) and then
compressed therein into intermediate-pressure refrigerant. While
the intermediate-pressure refrigerant flows through the discharge
pipe (21a) of the low-pressure stage compressor (21), saturated gas
refrigerant is supplied through the gas outflow pipe (33c) to the
intermediate-pressure refrigerant. Then, the refrigerant mixture
flows via the second three-way selector valve (71) through the
second connection pipe (12) and is then pumped into the outdoor
unit (20).
[0159] The intermediate-pressure refrigerant pumped in the outdoor
unit (20) is sucked through the suction pipe (31b) of the
high-pressure stage compressor (31) into the high-pressure stage
compressor (31) and then compressed therein into high-pressure
refrigerant.
[0160] <Control During Cooling Operation in Two-Stage
Compression Refrigeration Cycle>
[0161] During the cooling operation in a two-stage compression
refrigeration cycle, the first control section (101) of the
controller (100) inverter-controls the operating frequency of the
high-pressure stage compressor (31) to adapt to the cooling load
that is the load of the refrigeration capacity. In other words, the
first control section (101) controls the operating frequency of the
high-pressure stage compressor (31) so that the evaporation
temperature in the indoor heat exchanger (41) becomes a set cooling
room temperature Te.degree. C. Specifically, the first control
section (101) controls the operating frequency of the high-pressure
stage compressor (31) so that the suction pressure of the
low-pressure stage compressor (21) has a pressure value appropriate
to the evaporation pressure corresponding to the set temperature
Te.degree. C.
[0162] To attain this, as shown in FIG. 9(a), the first control
section (101) first calculates, in the comparison circuit (160),
the temperature difference between the set temperature Te.degree.
C. and the actual cooling room temperature measured by the room
temperature sensor (44). Thereafter, the first control section
(101) calculates, in the gain circuit (161), the operating
frequency of the high-pressure stage compressor (31) by multiplying
the temperature difference output from the comparison circuit (160)
by a constant K and then controls the high-pressure stage
compressor (31).
[0163] On the other hand, the second control section (102) controls
the low-pressure stage compressor (21) so that the intermediate
pressure in the two-stage compression refrigeration cycle has a
predetermined value. In this embodiment, the predetermined value of
the intermediate pressure is the intermediate pressure value (PM)
at which the ratio between the second pressure ratio (PM/PL) of the
low-pressure stage compressor (21) and the first pressure ratio
(PH/PM) of the high-pressure stage compressor (31) is 1:1. In other
words, the intermediate pressure value (PM) is the geometric mean
{(PLPH).sup.1/2} of the suction pressure (PL) of the low-pressure
stage compressor (21) and the discharge pressure (PH) of the
high-pressure stage compressor (31).
[0164] Specifically, as shown in FIG. 9(b), the second control
section (102) calculates the first pressure ratio (PH/PM) of the
high-pressure stage compressor (31) in a first dividing circuit
(162) and then calculates the second pressure ratio (M/PL) of the
low-pressure stage compressor (21) in a second dividing circuit
(163). Then, the second control section (102) calculates the
pressure difference {(PH/PM)-(PM/PL)} between the first pressure
ratio (PH/PM) and the second pressure ratio (PM/PL) in a comparison
circuit (164) and derives a gain K from the pressure difference in
a gain circuit (165). Then, the second control section (102)
derives, in a derivation circuit (166), a target operating
frequency of the low-pressure stage compressor (21) by multiplying
the current operating frequency of the low-pressure stage
compressor (21) by the gain K and controls the low-pressure stage
compressor (21) so that it is driven at the target operating
frequency.
[0165] Then, by repeating the above controls of the first control
section (101) and second control section (102), the operating
frequencies of the high-pressure stage compressor (31) and
low-pressure stage compressor (21) become operating frequencies
appropriate to the refrigeration load and providing the highest
COP.
[0166] At startup of the cooling operation in the two-stage
compression refrigeration cycle, the third control section (103)
controls, instead of the second control section (102), the
operating frequency of the low-pressure stage compressor (21).
Specifically, the third control section (103) controls the
low-pressure stage compressor (21) so that its operating frequency
is n times (for example, n=1.3) as high as that of the
high-pressure stage compressor (31). The reason for this is as
follows: In order to bring the intermediate pressure to the
predetermined value, the second control section (102) makes a
feedback control of changing the operating frequency of the
low-pressure stage compressor (21) following the change in the
operating frequency of the high-pressure stage compressor (31)
controlled by the first control section (101). If, at startup, the
second control section (102) controls the low-pressure stage
compressor (21), a delay due to the feedback control occurs so that
it takes a long time to reach a predetermined operating power. This
problem must be prevented.
[0167] --Effects of Embodiment 2--
[0168] According to this embodiment, since during the cooling
operation in the two-stage compression refrigeration cycle the
first control section (101) controls the operating frequency of the
high-pressure stage compressor (31) to adapt to the load of the
refrigeration capacity and the second control section (102)
controls the operating frequency of the low-pressure stage
compressor (21) so that the ratio between the first pressure ratio
(PH/PM) of the high-pressure stage compressor (31) and the second
pressure ratio (PM/PL) of the low-pressure stage compressor (21) is
1:1, the refrigeration system (120) can perform an operation
appropriate to the load of the refrigeration capacity and can
enhance the COP. Therefore, the refrigeration system (120) can
perform an operation appropriate to the operating conditions.
[0169] Furthermore, according to this embodiment, the first control
section (101) provides an operating power control according to the
refrigeration load not only by controlling the operating frequency
of the high-pressure stage compressor (31) during operation in the
single-stage compression refrigeration cycle with the existing
outdoor unit (20) and indoor unit (40) connected to each other, but
also by controlling the operating frequency of the high-pressure
stage compressor (31) through the application of the above
operating power control during operation in the two-stage
compression refrigeration cycle with the existing units connected
to the option unit (30). This simplifies the configuration of the
control means.
[0170] Furthermore, since at startup the third control section
(103) controls, instead of the second control section (102), the
operating frequency of the low-pressure stage compressor (21), this
prevents a delay in control on the low-pressure stage compressor
(21) from being caused by feedback control of the second control
section (102) at startup and thereby promptly provides an operation
adapted to the refrigeration load.
[0171] The rests of the configuration and operational behavior and
the other effects are the same as in Embodiment 1.
Other Embodiments
[0172] The above embodiments may have the following
configurations.
[0173] Although in the above embodiments the refrigerant circuit
(15) is formed by connecting an option unit (30) between the
outdoor unit (20) and the indoor unit (40), the option unit (30)
and the outdoor unit (20) may not necessarily be separate units but
may be formed as an integrated outdoor unit.
[0174] The configuration of the refrigerant circuit (15) in each
embodiment is not particularly limited. For example, each
compression mechanism may not necessarily be composed of a single
compressor but may be composed of a plurality of parallel-connected
compressors. Furthermore, a solenoid valve may be disposed instead
of the option side expansion valve (34) in Embodiment 1 and, during
a heating operation in a two-stage compression refrigeration cycle,
the refrigerant may be reduced to an intermediate pressure only by
the outdoor expansion valve (42) with the solenoid valve fully
opened.
[0175] The refrigeration system according to the present invention
may be applied to a chilling unit. In this case, for example, a
plate heat exchanger for cooling and heating water is provided
instead of the indoor heat exchanger in each embodiment.
[0176] The above embodiments are merely preferred embodiments in
nature and are not intended to limit the scope, applications and
use of the invention.
INDUSTRIAL APPLICABILITY
[0177] As can be seen from the above description, the present
invention is useful for control on the operating capacities of two
compression mechanisms in a refrigeration system including a
refrigerant circuit that includes the two compression mechanisms
and operates in a two-stage compression refrigeration cycle.
* * * * *